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    INTERNATIONAL PROGRAMME ON CHEMICAL SAFETY

    CONCISE INTERNATIONAL CHEMICAL ASSESSMENT DOCUMENT NO. 25




    CHLORAL HYDRATE




    INTER-ORGANIZATION PROGRAMME FOR THE SOUND MANAGEMENT OF CHEMICALS
    A cooperative agreement among UNEP, ILO, FAO, WHO, UNIDO, UNITAR and
    OECD


    This report contains the collective views of an international group of
    experts and does not necessarily represent the decisions or the stated
    policy of the United Nations Environment Programme, the International
    Labour Organization, or the World Health Organization.


    First draft prepared by Dr R. Benson, Region VIII, Environmental
    Protection Agency, Denver, CO, USA



    Published under the joint sponsorship of the United Nations
    Environment Programme, the International Labour Organization, and the
    World Health Organization, and produced within the framework of the
    Inter-Organization Programme for the Sound Management of Chemicals.


    World Health Organization
    Geneva, 2000

         The International Programme on Chemical Safety (IPCS),
    established in 1980, is a joint venture of the United Nations
    Environment Programme (UNEP), the International Labour Organization
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    sound management of chemicals in relation to human health and the
    environment.

    WHO Library Cataloguing-in-Publication Data

    Chloral hydrate.

         (Concise international chemical assessment document ; 25)

         1.Chloral hydrate - toxicity  2.Risk assessment
         3.Environmental exposure 
         I.International Programme on Chemical Safety  II.Series

         ISBN 92 4 153025 1            (NLM Classification: QV 85)
         ISSN 1020-6167

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    TABLE OF CONTENTS

         FOREWORD

    1. EXECUTIVE SUMMARY

    2. IDENTITY AND PHYSICAL/CHEMICAL PROPERTIES

    3. ANALYTICAL METHODS

    4. SOURCES OF HUMAN AND ENVIRONMENTAL EXPOSURE

    5. ENVIRONMENTAL TRANSPORT, DISTRIBUTION, AND TRANSFORMATION

    6. ENVIRONMENTAL LEVELS AND HUMAN EXPOSURE

         6.1. Environmental levels

         6.2. Human exposure

    7. COMPARATIVE KINETICS AND METABOLISM IN LABORATORY ANIMALS AND HUMANS
 
    8. EFFECTS ON LABORATORY MAMMALS AND IN VITRO TEST SYSTEMS

         8.1. Single exposure

              8.1.1. Oral

              8.1.2. Inhalation

         8.2. Irritation and sensitization

         8.3. Short-term exposure

         8.4. Long-term exposure

              8.4.1. Subchronic exposure

              8.4.2. Chronic exposure and carcinogenicity

         8.5. Genotoxicity and related end-points

              8.5.1. Genotoxicity

              8.5.2. Cell proliferation

              8.5.3. Oncogene activation

              8.5.4. Free radicals and DNA adduct formation

              8.5.5. Cell communication

              8.5.6. Peroxisome proliferation

         8.6. Reproductive and developmental toxicity

         8.7. Immunological and neurological effects

    9. EFFECTS ON HUMANS

    10. EFFECTS ON OTHER ORGANISMS IN THE LABORATORY AND FIELD

    11. EFFECTS EVALUATION

         11.1. Evaluation of health effects

              11.1.1. Hazard identification and dose-response assessment

              11.1.2. Criteria for setting tolerable intakes or guidance values for chloral hydrate

              11.1.3. Sample risk characterization

         11.2. Evaluation of environmental effects

    12. PREVIOUS EVALUATIONS BY INTERNATIONAL BODIES

         REFERENCES

         APPENDIX 1 -- TOXICOKINETICS

         APPENDIX 2 -- CALCULATION OF BENCHMARK DOSE FOR TUMOUR INCIDENCE

         APPENDIX 3 -- SOURCE DOCUMENT

         APPENDIX 4 -- CICAD PEER REVIEW

         APPENDIX 5 -- CICAD FINAL REVIEW BOARD

         APPENDIX 6 -- INTERNATIONAL CHEMICAL SAFETY CARD

         RÉSUMÉ D'ORIENTATION

         RESUMEN DE ORIENTACI²N
    

    FOREWORD

         Concise International Chemical Assessment Documents (CICADs) are
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         Risks to human health and the environment will vary considerably
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    considered as representing all possible exposure situations, but are
    provided as guidance only. The reader is referred to EHC 1701 for
    advice on the derivation of health-based tolerable intakes and
    guidance values.

                  

    1 International Programme on Chemical Safety (1994)
       Assessing human health risks of chemicals: deriviation of guidance
       values for health-based exposure limits. Geneva, World Health
      Organization (Environmental Health Criteria 170).

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    the scientific literature to the date shown in the executive summary.
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    Procedures

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    FIGURE 1

    1.  EXECUTIVE SUMMARY

         This CICAD on chloral hydrate was prepared by the US
    Environmental Protection Agency (EPA) and is based on the US EPA's
     Toxicological review on chloral hydrate (US EPA, 2000). Scientific
    literature identified as of March 1999 was included. Information on
    the nature of the review processes and the availability of the source
    document is presented in Appendix 3. Information on the peer review of
    this CICAD is presented in Appendix 4. This CICAD was approved as an
    international assessment at a meeting of the Final Review Board, held
    in Sydney, Australia, on 21-24 November 1999. Participants at the
    Final Review Board meeting are listed in Appendix 5. The International
    Chemical Safety Card (ICSC 0234) for chloral hydrate, produced by the
    International Programme on Chemical Safety, has been reproduced in
    Appendix 6 (IPCS, 1993).

         Chloral hydrate (CAS No. 302-17-0) is synthesized by the
    chlorination of ethanol. It is used in human and veterinary medicine
    as a sedative and hypnotic drug. The anhydrous chemical, chloral 
    (CAS No. 75-87-6), is used as an intermediate in the synthesis of 
    DDT, methoxychlor, naled, trichlorfon, dichlorvos, and 
    trichloroacetic acid.

         The major route of exposure of the general public is from
    drinking-water, as chloral hydrate is formed when drinking-water is
    disinfected with chlorine. A typical concentration of chloral hydrate
    in a public water supply in the USA is 5 µg/litre. Since chloral
    hydrate is a metabolite of trichloroethylene and tetrachloroethylene,
    people will be exposed to chloral hydrate if they are exposed to these
    chemicals. The public will be exposed to the metabolites of chloral
    hydrate, trichloroacetic acid and dichloroacetic acid, as these
    chemicals are also formed when drinking-water is disinfected with
    chlorine. In its use as a sedative for people, the usual clinical dose
    is 250 mg, 3 times a day (equivalent to 10.7 mg/kg body weight per
    day). The metabolite trichloroethanol is responsible for the
    pharmacological effect. No quantitative information is available from
    occupational exposure.

         Chloral hydrate is irritating to the skin and mucous membranes
    and often causes gastric distress, nausea, and vomiting at the
    recommended clinical dose. An acute overdose produces (in order of
    progression) ataxia, lethargy, deep coma, respiratory depression,
    hypotension, and cardiac arrhythmia. There is some evidence of hepatic
    injury in people surviving near-lethal, acute overdoses, but no
    convincing evidence that hepatic injury results from the recommended
    clinical dose. Several studies of the clinical use of chloral hydrate
    show a low incidence of minor side-effects. Despite its long use in
    human medicine, there is no published information on toxicity in
    controlled studies in humans following extended exposure.

         Chloral hydrate is completely absorbed and rapidly metabolized
    following oral administration. The major metabolites are
    trichloroethanol and its glucuronide and trichloroacetic acid. Some
    data suggest that a small amount of dichloroacetic acid may be formed.
    In humans, the half-life of trichloroethanol and its glucuronide is
    about 8 h; the half-life of trichloroacetic acid is about 4 days. Some
    data suggest that the half-life of trichloroethanol is increased
    several-fold in pre-term and full-term infants compared with toddlers
    and adults. The major route of excretion of the metabolites of chloral
    hydrate is elimination in the urine. Chloral hydrate and its
    metabolites have been found in milk from women treated with chloral
    hydrate. The concentration of these chemicals, however, is too low to
    cause a pharmacological effect in the nursing infant.

         Acute administration of chloral hydrate to mice causes loss of
    coordination (ataxia) at about the same exposure as in humans for the
    same effect. A 90-day study in mice shows no evidence of behavioural
    changes or other neurotoxicity. Chronic studies in rats and mice show
    no evidence of behavioural changes and no evidence of
    histopathological changes in nervous tissue. A slight decrement in
    humoral immunity was observed following exposure of mice for 90 days.
    Chloral hydrate has been tested for developmental effects in rats and
    mice. No structural abnormalities were observed. In a
    neurodevelopmental study in mice, there was a slight effect in passive
    avoidance learning. Although chloral hydrate has not been tested in a
    two-generation reproduction study, the data on reproductive
    performance and on effects on sperm and oocytes do not suggest that
    reproductive toxicity is likely to be a critical effect. In addition,
    no histopathological effects are observed in reproductive organs of
    rodents in subchronic or chronic studies. All of the studies in
    laboratory animals show non-cancer health effects at an exposure far
    in excess of the exposure that is effective for sedation in humans.

         There are no carcinogenicity data from humans. Two bioassays in
    rats show no increase in tumours at any site. Three separate bioassays
    in male mice show an increased incidence of liver tumours. The most
    definitive of these studies shows an increased incidence and
    multiplicity of liver tumours at each of three exposures. These data
    provide suggestive evidence of carcinogenicity in male mice but are
    not considered appropriate for conducting a human health risk
    assessment with a linear response at low exposure.1

                  

    1 In a National Toxicology Program carcinogenicity bioassay in mice
      that became available after the Final Review Board meeting, males 
      had an increased incidence of hepatic tumours, and females had a 
      low increased incidence of pituitary adenomas that was of borderline
      statistical significance.

         There is an extensive database on genetic toxicity. A variety of
    results show that chloral hydrate is a weak gene mutagen and
    clastogen. Chloral hydrate induces aneuploidy in a wide variety of
    cell types. These latter effects are thought to arise by disruption of
    the spindle apparatus. High concentrations of chloral hydrate are
    required to cause observable effects. Although these data suggest that
    genotoxicity may play a role in the toxicity of chloral hydrate, the
    data indicate that these effects require concentrations that are
    unlikely to occur under physiological conditions at the exposures
    typically encountered in the environment. Some likely candidates for
    the induction of liver tumours in male mice include the formation of
    DNA adducts caused by free radicals generated by the metabolism of
    chloral hydrate by cytochrome P450 2E1 (CYP2E1) and through
    cytotoxicity leading to compensatory hyperplasia.

         The tolerable intake for non-cancer health effects of 0.1 mg/kg
    body weight per day was estimated from the
    lowest-observed-adverse-effect level (LOAEL) for sedation in humans of
    10.7 mg/kg body weight per day using a total uncertainty factor of
    100.

         Only limited data are available on environmental effects.
    Methanotrophs can convert chloral hydrate to trichloroethanol and
    trichloroacetic acid. Chloral hydrate also undergoes abiotic
    degradation under some conditions. Limited data are available on the
    inhibition of growth of bacteria, algae, and protozoa and
    developmental effects in sea urchins. Insufficient data are available
    with which to assess the risk to the environment from chloral hydrate.
    

    2.  IDENTITY AND PHYSICAL/CHEMICAL PROPERTIES

         Chloral hydrate (CAS No. 302-17-0) is synthesized by the
    chlorination of ethanol. The structural formula is given in section 7.
    The CAS name is 2,2,2-trichloro-1,1-ethanediol. Synonyms include
    chloral monohydrate, trichloroacetaldehyde hydrate,
    trichloroacetaldehyde monohydrate, and
    1,1,1-trichloro-2,2-dihydroxyethane. The relative molecular mass is
    165.42; the solubility in water is 8.3 g/ml; the octanol/water
    partition coefficient (log  Kow) is 0.99; and the vapour pressure
    is 2 kPa at 25°C. The chemical and physical properties of chloral
    hydrate are summarized in the International Chemical Safety Card
    included in this document (Appendix 6).

         Chloral (CAS No. 75-87-6) is the anhydrous form of the chemical.
    The conversion from chloral to chloral hydrate occurs spontaneously
    when chloral is placed in aqueous media.
    

    3.  ANALYTICAL METHODS

         A method for the determination of trace amounts of chloral
    hydrate in environmental samples is available. Carbonyl compounds are
    converted to their 2,4-dinitrophenylhydrazone derivatives, separated
    with high-performance liquid chromatography, and detected by
    ultraviolet absorbance (Fung & Grosjean, 1981). The lowest
    quantifiable limit for a variety of carbonyls ranges from 1 to 6 ng.

         Chloral hydrate and its metabolites (trichloroethanol,
    trichloroethanol glucuronide, and trichloroacetic acid) can be
    determined in rat liver homogenates using headspace gas chromatography
    and electron capture detection (Koppen & Dalgaard, 1988). The
    detection limits are 0.06 µg/ml for trichloroethanol and
    trichloroethanol glucuronide and 0.02 µg/ml for chloral hydrate and
    trichloroacetic acid. A comparable method for the determination of
    these chemicals in blood and urine is also available (Breimer et al.,
    1974). The detection limits are 0.5 µg/ml for chloral hydrate and
    trichloroethanol and 0.1 µg/ml for trichloroacetic acid.

         Chloral hydrate and its metabolites can be measured in biological
    samples after conversion to the methyl esters and separation and
    detection with gas chromatography/mass spectrometry (Yan et al.,
    1999). The range for measurement is between 0.12 and 7.83 µmol/litre
    (equivalent to about 20-1290 µg/litre).

         A method for determining trichloroethanol in plasma for use in a
    clinical laboratory with liquid chromatography has also been developed
    (Gupta, 1990). The method is useful for determining trichloroethanol
    in plasma in the pharmacologically active range (up to 12 mg/litre)
    and in the acutely toxic range (about 100 mg/litre). The method takes
    about 2 h to complete.

         A spectrophotometric method for the determination of chloral
    hydrate in commercial drug products is based on the reaction of
    quinaldine ethyl iodide with chloral hydrate to produce a stable blue
    cyanine dye with an absorption maximum at about 605 nm 
    (Helrich, 1990).
    

    4.  SOURCES OF HUMAN AND ENVIRONMENTAL EXPOSURE

         Chloral hydrate is not known to occur as a natural product. The
    major route of human exposure to chloral hydrate is from
    drinking-water. Chloral hydrate and its metabolites, trichloroacetic
    acid and dichloroacetic acid, are formed as by-products when water is
    disinfected with chlorine. The carbon is derived from natural organic
    matter (humic and fulvic substances) in the source water. The amount
    of chloral hydrate formed depends on the concentration of humic and
    fulvic substances and the conditions of chlorination. Additional
    chloral hydrate can be formed if water containing chlorine is mixed
    with food containing humic and fulvic acids (Wu et al., 1998). Chloral
    hydrate is also a metabolite of trichloroethylene and
    tetrachloroethylene. Humans will be exposed to chloral hydrate if they
    are exposed to these chemicals. Chloral hydrate has been widely used
    as a sedative and hypnotic drug in adult and pediatric medicine.
    Chloral is used as an intermediate in the synthesis of the
    insecticides DDT, methoxychlor, naled, trichlorfon, and dichlorvos and
    the herbicide trichloroacetic acid (IARC, 1995).

         Chlorate hydrate could be released to the environment from
    wastewater treatment facilities, from the manufacture of
    pharmaceutical-grade chloral hydrate, and from the waste stream during
    the manufacture of insecticides and herbicides that use chloral as an
    intermediate.

         In the USA, production of chloral hydrate/chloral was estimated
    at 590 tonnes in 1975, and imports were estimated at 47 tonnes in 
    1986 (HSDB, 1999). Production of chloral hydrate/chloral by Member 
    States of the European Union was estimated at 2500 tonnes in 1984 
    (IARC, 1995).
    

    5.  ENVIRONMENTAL TRANSPORT, DISTRIBUTION, AND TRANSFORMATION

         Newman & Wackett (1991) reported the transformation of chloral
    hydrate to trichloroethanol and trichloroacetic acid by methanotrophic
    bacteria. These investigators also reported the abiotic breakdown of
    chloral hydrate to chloroform and formic acid. No detectable breakdown
    occurred at pH 7.0 and 30°C for 24 h. At pH 9.0 and 60°C, the
    half-time for breakdown was 16 min.
    

    6.  ENVIRONMENTAL LEVELS AND HUMAN EXPOSURE

    6.1  Environmental levels

         No information is available.

    6.2  Human exposure

         The major route of exposure to chloral hydrate is from
    chlorinated drinking-water. A typical concentration of chloral hydrate
    in a public water supply in the USA is 5 µg/litre (US EPA, 1994). More
    than 200 million people in the USA are routinely exposed to chloral
    hydrate from this route. Assuming water consumption of 2 litres per
    day and a body weight of 70 kg, the exposure is 0.14 µg/kg body weight
    per day. Additional exposure could result from inhalation of aerolized
    water during showering. As these water droplets are typically not
    small enough to penetrate deep in the lung, they are deposited in the
    upper airways. Thus, the water droplets are an additional source of
    oral exposure to chloral hydrate. Some chloral hydrate from water used
    for showering/bathing would also be absorbed through the skin.
    Quantitative data on these additional sources of exposure are not
    available.

         Simpson & Hayes (1998) reported the occurrence of chloral hydrate
    in the drinking-water of seven cities in Australia. The reported range
    was 0.2-19 µg/litre.

         When chloral hydrate is used in clinical medicine, the
    recommended dose for an adult as a sedative is 250 mg, 3 times a day
    (equivalent to 10.7 mg/kg body weight per day); the recommended dose
    as a hypnotic drug is 500-1000 mg (equivalent to 7.1-14.3 mg/kg body
    weight) (Goodman & Gilman, 1985). The recommended dose for a child
    undergoing a medical or dental procedure is 50-100 mg/kg body weight
    (Badalaty et al., 1990; Fox et al., 1990). A child is typically given
    a higher dose than an adult because a deeper level of sedation is
    desired to obtain better cooperation from the child during the medical
    or dental procedure. There is no evidence that a child is less
    sensitive than an adult to the sedative effects of chloral hydrate.

         No quantitative information is available from occupational
    exposure.
    

    7.  COMPARATIVE KINETICS AND METABOLISM IN LABORATORY ANIMALS
        AND HUMANS

         Chloral hydrate is completely absorbed following oral
    administration; no information is available on dermal absorption.
    Qualitatively similar metabolism occurs in mice, rats, dogs, Japanese
    medaka  (Oryzias latipes), and humans (Marshall & Owens, 1954; Owens
    & Marshall, 1955; Breimer, 1977; Gosselin et al., 1981; Goodman &
    Gilman, 1985; Hobara et al., 1986, 1987a,b, 1988a,b; Reimche et al.,
    1989; Gorecki et al., 1990; Hindmarsh et al., 1991; Mayers et al.,
    1991; Abbas et al., 1996; Lipscomb et al., 1996, 1998; Abbas & Fisher,
    1997; Henderson et al., 1997; Stenner et al., 1997, 1998; 
    Beland et al., 1998; Elfarra et al., 1998; Fisher et al., 1998; 
    Merdink et al., 1998, 1999; Greenberg et al., 1999). The metabolic 
    pathway is shown in Figure 1.

         Chloral hydrate is rapidly metabolized in both hepatic and
    extrahepatic tissues to trichloroethanol and trichloroacetic acid. The
    alcohol dehydrogenase responsible for reducing it to trichloroethanol
    is located in both liver and erythrocytes. A portion of the
    trichloroethanol produced is conjugated with glucuronic acid. The
    majority of the trichloroethanol glucuronide is excreted in the urine.
    A portion of the trichloroethanol glucuronide is secreted into the
    bile and is subject to enterohepatic circulation. Oxidation of chloral
    hydrate to trichloracetic acid occurs primarily in the liver and
    kidney via an aldehyde dehydrogenase using nicotinamide adenine
    dinucleotide (NAD) as a cofactor. The major route of excretion of the
    metabolites of chloral hydrate is elimination in the urine. Chloral
    hydrate and its metabolites have been found in milk from women treated
    with chloral hydrate (Bernstine et al., 1954). The concentration of
    these chemicals, however, is too low to cause a pharmacological effect
    in the nursing infant (HSDB, 1999).

         In mice and rats, 8% of the administered dose of chloral hydrate
    is directly eliminated in urine, 15% is converted to trichloroacetic
    acid (including the contribution from enterohepatic circulation), and
    77% is converted to trichloroethanol (Beland et al., 1998). In humans,
    92% of the administered dose of chloral hydrate is converted to
    trichloroethanol, and 8% is converted directly to trichloroacetic
    acid; additional trichloroacetic acid is formed during enterohepatic
    circulation of trichloroethanol, such that 35% of the initial dose of
    chloral hydrate is converted to trichloroacetic acid (Allen & Fisher,
    1993).

    FIGURE 2

         Although earlier reports claimed the detection of substantial
    quantities of dichloroacetic acid in blood in studies with rodents
    (Abbas et al., 1996), data show that the dichloroacetic acid is most
    likely formed by an acid-catalysed dechlorination of trichloroacetic
    acid in the presence of reduced haemoglobin (Ketcha et al., 1996).
    Recent experimental data and pharmacokinetic model simulations in
    rodents suggest that dichloroacetic acid occurs only as a short-lived
    metabolite in the liver and is rapidly converted to two-carbon,
    non-chlorinated metabolites and carbon dioxide, with the chlorine
    atoms entering the chloride pool (Merdink et al., 1998). Using a
    different extraction procedure less likely to induce the artefactual
    formation of dichloroacetic acid, Henderson et al. (1997) showed the
    presence of dichloroacetic acid in children treated with chloral
    hydrate in a clinic.

         Breimer (1977) administered an aqueous solution of chloral
    hydrate to five human volunteers. Each volunteer received a single
    oral dose of 15 mg/kg body weight. Chloral hydrate could not be
    detected in the plasma even at the first sampling time of 10 min. 
    A method with a limit of detection of 0.5 mg/litre was used.
    Trichloroethanol and trichloroethanol glucuronide reached peak
    concentrations 20-60 min after administration of chloral hydrate. The
    maximum concentration of trichloroethanol in the plasma was about 
    5 mg/litre. The average half-lives of trichloroethanol and
    trichloroethanol glucuronide were 8 h (range 7-9.5 h) and 6.7 h (range
    6-8 h), respectively. The half-life of trichloroacetic acid was about
    4 days. Zimmermann et al. (1998) administered a single dose of 250 mg
    chloral hydrate in drinking-water to 18 healthy male volunteers 
    (20-28 years of age). Chloral hydrate, trichloroethanol, and 
    trichloroacetic acid were measured in plasma. Chloral hydrate could be 
    detected 8-60 min after dosing in only some of the plasma samples. 
    The measured concentration of chloral hydrate was not reported, but 
    the limit of detection was stated as 0.1 mg/litre. The maximum plasma 
    concentration of trichloroethanol of 3 mg/litre was achieved 0.67 h 
    after dosing, and the maximum plasma concentration of trichloroacetic 
    acid of 8 mg/litre was achieved 32 h after dosing. The terminal 
    half-life was 9.3-10.2 h for trichloroethanol and 89-94 h for 
    trichloroacetic acid.

         Two toxicokinetic models are available for chloral hydrate in
    rats and mice (Abbas et al., 1996; Beland et al., 1998). Beland et al.
    (1998) treated rats and mice with chloral hydrate by gavage with 1 or
    12 doses using 50 or 200 mg/kg body weight per dose. The maximum
    levels of chloral hydrate, trichloroethanol, and trichloroethanol
    glucuronide in the plasma were observed at the initial sampling time
    of 0.25 h. The half-life of chloral hydrate in the plasma was
    approximately 3 min. The half-lives of trichloroethanol and
    trichloroethanol glucuronide in the plasma were approximately 5 and 
    7 min, respectively. Trichloroacetic acid was the major metabolite 

    found in the plasma, with the maximum level being reached 1-6 h after
    dosing. The half-life of trichloroacetic acid in the plasma was
    approximately 8-11 h. Comparable values were obtained for rats.

         Estimates of the concentrations of trichloroacetic acid and
    trichloroethanol at steady state under various exposure conditions are
    in Appendix 1.

         Several studies have investigated the age dependence of the
    metabolism of chloral hydrate (Reimche et al., 1989; Gorecki et al.,
    1990; Hindmarsh et al., 1991; Mayers et al., 1991). These studies were
    conducted in critically ill patients in neonatal and paediatric
    intensive care units and may not be representative of a population of
    healthy infants. The half-lives for trichloroethanol and its
    glucuronide were increased several-fold in pre-term and full-term
    infants compared with toddlers and adults. The half-lives for
    trichloroethanol in toddlers and adults were similar. These
    age-related differences likely are the result of the immaturity of
    hepatic metabolism, particularly glucuronidation, and decreased
    glomerular filtration.

         Kaplan et al. (1967) investigated the effect of ethanol
    consumption on the metabolism of chloral hydrate in adults. Subjects
    ingested doses of ethanol (880 mg/kg body weight), chloral hydrate
    (9-14 mg/kg body weight), or both. In subjects consuming both ethanol
    and chloral hydrate, blood trichloroethanol levels rose more rapidly
    and reached higher values than in subjects consuming chloral hydrate
    only. Ethanol promotes the formation of trichloroethanol because the
    oxidation of ethanol provides NADH used for the reduction of chloral
    hydrate (Watanabe et al., 1998).
    

    8.  EFFECTS ON LABORATORY MAMMALS AND IN VITRO TEST SYSTEMS

    8.1  Single exposure

    8.1.1  Oral

         Sanders et al. (1982) studied the acute toxicity of chloral
    hydrate in CD-1 mice. Groups of eight male and eight female mice were
    given chloral hydrate by gavage in distilled water at 300, 600, 900,
    1200, 1500, or 1800 mg/kg body weight. No deaths occurred at 900 mg/kg
    body weight or below in either sex. The calculated LD50 for females
    was 1265 mg/kg body weight and for males was 1442 mg/kg body weight.
    Effects were seen within 10 min of dosing. The mice became sedated at
    300 mg/kg body weight. At 600 and 900 mg/kg body weight, the animals
    became lethargic and exhibited loss of righting reflex. Respiration
    was markedly inhibited at 1200, 1500, and 1800 mg/kg body weight.
    Inhibition of respiration appeared to be the immediate cause of death.
    Most deaths occurred within 4 h at 1800 mg/kg body weight. At 1200 and
    1500 mg/kg body weight, some deaths occurred after 4 h, with all
    deaths occurring within 24 h.

         Goldenthal (1971) reported an oral LD50 in rats of 480 mg/kg
    body weight.

    8.1.2  Inhalation

         Odum et al. (1992) exposed four female CD-1 mice to chloral for
    6 h at a concentration of 100 ppm (603 mg/m3). This exposure induced
    deep anaesthesia. The mice recovered normally after the exposure
    stopped. The effects in the lung included vacuolization of clara
    cells, alveolar necrosis, desquamination of the epithelium, and
    alveolar oedema. The lung to body weight ratio increased 1.5-fold,
    most likely due to the alveolar oedema.

    8.2  Irritation and sensitization

         There are no studies of irritation or sensitization in laboratory
    animals.

    8.3  Short-term exposure

         Sanders et al. (1982) studied the short-term toxicity of chloral
    hydrate in mice. Groups of male CD-1 mice were given chloral hydrate
    by gavage in distilled water at 14.4 or 144 mg/kg body weight per day
    for 14 days. No significant effect on body weight was observed. No
    changes in internal organs were noted from a gross examination. Groups
    of 11-12 mice were evaluated for several toxicological parameters. No
    significant effects on haematological or serum biochemical parameters
    were noted. There was a statistically significant  (P < 0.05)
    increase in liver weight (17%) and a decrease in spleen weight (27%)

    at the high exposure. The no-observed-adverse-effect level (NOAEL) in
    this study is 14.4 mg/kg body weight per day; the LOAEL is 144 mg/kg
    body weight per day. The increase in liver weight, but not the
    decrease in spleen weight, was confirmed in a subsequent 90-day study
    by the same researchers.

    8.4  Long-term exposure

    8.4.1  Subchronic exposure

         Sanders et al. (1982) administered chloral hydrate in
    drinking-water to CD-1 mice at 70 or 700 mg/litre (equivalent to 16 or
    160 mg/kg body weight per day) for 90 days. In males, hepatomegaly (an
    increase in weight of 20% and 34% at the low and high exposure,
    respectively) and microsome proliferation (no increase in total
    microsomal protein, increase in cytochrome b5 of 26% and 40%,
    increase in aminopyrine  N-demethylase of 28% and 20%, and increase
    in aniline hydroxylase of 24% and 30% at the low and high exposures,
    respectively, when reported as mg of protein per mg of total liver
    protein) were observed. There were no biologically significant changes
    in serum enzymes. Hepatomegaly was not seen in females, but there were
    changes in hepatic microsomal parameters (increase in total microsomal
    protein of 10%, increase in aniline hydroxylase of 23%, and decrease
    in cytochrome b5 of 12% when reported as mg of protein per mg of
    total liver protein), but only at the high exposure. No other
    significant toxicological changes were observed. Based on hepatomegaly
    and changes in microsomal parameters in males at the high exposure,
    this study identifies a LOAEL of 160 mg/kg body weight per day and a
    NOAEL of 16 mg/kg body weight per day.

         Daniel et al. (1992b) exposed male and female Sprague-Dawley rats
    (10 per sex per dose) for 90 days to chloral hydrate in drinking-water
    at a concentration of 300, 600, 1200, or 2400 mg/litre (equivalent to
    an exposure of 24, 48, 96, or 168 mg/kg body weight per day in males
    and 33, 72, 132, or 288 mg/kg body weight per day in females). The
    tissues of animals from the high-exposure group and liver sections
    from all treated males were examined histopathologically. No mortality
    occurred in any groups prior to sacrifice. Organ weights, including
    liver weight, and clinical chemistry values in treated animals were
    only sporadically or inconsistently different from control animal
    values. Focal hepatocellular necrosis was observed in 2 of 10 males in
    each of the groups exposed to 96 and 168 mg/kg body weight per day.
    The necrotic lesion was minimal at 96 mg/kg body weight per day and
    was significantly more severe at 168 mg/kg body weight per day.
    Necrotic lesions were not reported in any treated females or in any
    control animals. While serum enzymes were generally increased in
    treated animals, dramatic increases were reported in males in the 
    168 mg/kg body weight per day group; mean aspartate aminotransferase,
    alanine aminotransferase, and lactate dehydrogenase levels in this
    group were elevated 89%, 54%, and 127% above the corresponding control
    values, respectively.

    8.4.2  Chronic exposure and carcinogenicity

         Rijhsinghani et al. (1986) evaluated carcinogenic effects in male
    mice (C57BL × C3HF1). Groups of 15-day-old mice received chloral
    hydrate by gavage in distilled water at 0, 5, or 10 mg/kg body weight
    (26, 15, and 14 mice per group, respectively). Animals were sacrificed
    when moribund or at week 78, at week 88, or between weeks 89 and 92.
    Livers were examined histopathologically using light and electron
    microscopy. In mice sacrificed 48-92 weeks after treatment, the
    incidence of hepatic nodules (adenomas or trabecular carcinomas) was
    3/9 and 6/8 for animals from the 5 and 10 mg/kg body weight per day
    dose groups, respectively, compared with 2/19 in controls. The
    increase in tumours was statistically significant  (P < 0.05) only
    in the 10 mg/kg body weight group.1

         Daniel et al. (1992a) exposed 40 male B6C3F1 mice for 104 weeks
    to drinking-water containing chloral hydrate at 1 g/litre (equivalent
    to 166 mg/kg body weight per day). Untreated control animals (23 in
    one group and 10 in a second group) received distilled water. Interim
    sacrifices were conducted at 30 and 60 weeks of exposure (five animals
    per group at each sacrifice interval). Complete necropsy and
    microscopic examination were performed. There were no significant
    treatment-related effects on survival or body weight. There were no
    changes in spleen, kidney, or testis weights or histopathological
    changes in any tissue except the liver. The toxicity in the liver was
    characterized by increased absolute liver weight and liver to body
    weight ratio at all three sacrifice intervals. At week 104, liver
    weight was 37% higher than in controls, and liver to body weight ratio
    was 42% higher than in controls. Hepatocellular necrosis was noted in
    10/24 (42%) treated animals; other pathological changes of mild
    severity reported in the livers of treated animals included
    cytoplasmic vacuolization, cytomegaly, and cytoplasmic alteration. The
    prevalence of liver tumours at terminal sacrifice was statistically
    significantly  (P < 0.05) increased over controls, with
    hepatocellular carcinomas in 11/24 and hepatocellular adenomas in 
    7/24 animals; for carcinomas and adenomas combined, the prevalence was
    17/24. In control animals, carcinomas, adenomas, and carcinomas and
    adenomas (combined) occurred in 2/20, 1/20, and 3/20, respectively. 
    At the 60-week sacrifice, there were 2/5 treated animals with
    hepatocellular carcinomas, compared with 0/5 controls. No carcinomas,
    adenomas, or hyperplastic nodules were reported in animals sacrificed
    at week 30.

                  

    1 After the Final Review Board meeting, a National Toxicology
      Program carcinogenicity bioassay became available. In this study, an
      up to 5 times higher single dose of chloral hydrate than that used 
      in the Rijhsinghani et al. (1986) study administered to male or 
      female B6C3F1 mice failed to induce tumours in any organ
     (NTP, 2000a).

         George et al. (2000) conducted a chronic bioassay for
    carcinogenicity in male B6C3F1 mice. Mice were administered chloral
    hydrate in drinking-water for 104 weeks. Mice (72 in each group) had a
    mean exposure of 0, 13.5, 65, or 146.6 mg/kg body weight per day.
    There was no change in water consumption, survival, behaviour, body
    weight, or organ weights at any exposure. There was no evidence of
    hepatocellular necrosis at any exposure and only minimal changes in
    the levels of serum enzymes. This study identifies a NOAEL for
    non-cancer effects in mice of 146.6 mg/kg body weight per day (the
    highest exposure tested). There was no increase in the prevalence of
    neoplasia at sites other than the liver. Although the background
    response in this study is higher than normal for this strain of mice,
    the mice showed an increase in proliferative lesions in the liver
    (hyperplasia, adenoma, carcinoma, and combined adenoma and carcinoma)
    at all exposures. These data are summarized in Table 1. The calculated
    effective dose for a 10% tumour incidence (ED10) is 1.98 mg/kg body
    weight per day, and its 95% lower confidence limit (LED10) is
    1.09 mg/kg body weight per day (see Appendix 2).

         Leuschner & Beuscher (1998) conducted a chronic bioassay for
    carcinogenicity in Sprague-Dawley rats. Chloral hydrate was
    administered in drinking-water for 124 weeks (males) and 128 weeks
    (females). The rats (50 males and 50 females in each group) had an
    exposure of 15, 45, or 135 mg/kg body weight per day. There was no
    effect on survival, appearance, behaviour, body weight, food and water
    consumption, or organ weights. There was no evidence of an increased
    incidence of tumours in any organ. Histopathological examination
    revealed an increased incidence of hepatocellular hypertrophy at the
    highest exposure in males only (11% in controls versus 28% at the
    highest exposure;  P < 0.01). This finding, graded as minimal to
    slight in severity, was characterized by a diffuse liver cell
    enlargement with slightly eosinophilic cytoplasm and was considered by
    the authors as a first sign of toxicity. The type, incidence, and
    severity of other non-neoplastic lesions were not increased in treated
    animals compared with controls. Based on the evidence of minimal
    toxicity in the liver, which is of doubtful biological significance,
    this study establishes a NOAEL of 45 mg/kg body weight per day and a
    LOAEL of 135 mg/kg body weight per day.

         George et al. (2000) conducted a chronic bioassay for
    carcinogenicity in male F344 rats. Rats were administered chloral
    hydrate in drinking-water for 104 weeks. Rats (78 in each group) had a
    mean daily exposure of 0, 7.4, 37.4, or 162.6 mg/kg body weight per
    day. There was no change in water consumption, survival, behaviour,
    body weight, or organ weights at any exposure. There was no indication
    of liver toxicity at any exposure as shown by the lack of liver
    necrosis, lack of hyperplasia, no increase in mitotic index, and only

    minimal changes in the levels of serum enzymes. There was no increase
    at any exposure in the prevalence or multiplicity of hepatocellular
    neoplasia or neoplasia at any other site. This study identifies a
    NOAEL of 162.6 mg/kg body weight per day (the highest exposure
    tested).1

         Two of the metabolites of chloral hydrate, trichloroacetic acid
    and dichloroacetic acid, have been shown to cause liver tumours in
    rodents. For example, trichloroacetic acid in drinking-water induced
    liver tumours in male and female mice when the exposure exceeded 200
    mg/kg body weight per day (Herren-Freund et al., 1987; Bull et al.,
    1990; Pereira, 1996). There was no evidence of increased
    carcinogenicity, however, when male rats were exposed to
    trichloroacetic acid at 360 mg/kg body weight per day (DeAngelo et
    al., 1997). Dichloroacetic acid in drinking-water induced liver
    tumours in male and female mice when the exposure exceeded 160 mg/kg
    body weight per day (Herren-Freund et al., 1987; Bull et al., 1990;
    DeAngelo et al., 1991; Daniel et al., 1992a; Ferreira-Gonzalez et al.,
    1995; Pereira, 1996). Dichloroacetic acid also induced liver tumours
    in male rats when the exposure exceeded 40 mg/kg body weight per day
    (Richmond et al., 1995; DeAngelo et al., 1996).

         A number of studies have shown that trichloroethylene is toxic to
    the mouse lung bronchiolar epithelium, causing a highly specific
    lesion to the clara cells of mice. Short-term exposure causes
    vacuolization of the clara cells; long-term exposure causes pulmonary
    adenomas and adenocarcinomas (Odum et al., 1992; Green et al., 1997).
    These effects are thought to be due to the accumulation of chloral
    within the clara cells. Trichloroethylene is efficiently metabolized
    to chloral, but the major pathway from chloral to trichloroethanol and
    its glucuronide is blocked, leading to an accumulation of chloral and
    the observed toxicity.

                  

    1 After the Final Review Board meeting, a National Toxicology
      Program carcinogenicity assay became available. In this study,
      lifetime gavage administration of chloral hydrate at similar dose
      levels induced hepatocellular tumours in male B6C3F1 mice and a low
      frequency of pituitary hyperplasia and adenomas in females that was 
      of borderline statistical significance (NTP, 2000b).



        Table 1: Prevalence and multiplicity of hepatocellular proliferative lesions in mice at 104 weeks.a
                                                                                                                      

    Treatment group     Number examinedc    Hyperplasia       Adenoma               Carcinoma         Adenoma 
    (mg/kg body                                                                                       + carcinoma
    weight per day)b
                                                                                                                      

    0                   42                  7.1d              21.4d                 54.8d             64.3d
                                            0.07 ± 0.04e      0.21 ± 0.06e          0.74 ± 0.12e      0.95 ± 0.12e

    13.5                46                  32.6f             43.5f                 54.3              78.6f
                                            0.41 ± 0.10f      0.65 ± 0.12f          0.72 ± 0.11       1.37 ± 0.16f

    65                  39                  33.3f             51.3f                 59.0              79.5f
                                            0.38 ± 0.09f      0.95 ± 0.18f          1.03 ± 0.19       1.97 ± 0.23f

    146.6               32                  37.5f             50.0f                 84.4f             90.6f
                                            0.41 ± 0.10f      0.72 ± 0.15f          1.31 ± 0.17f      2.03 ± 0.25f
                                                                                                                      

    a From George et al. (2000).
    b Time-weighted mean daily dose.
    c Animals surviving longer than 78 weeks.
    d Prevalence (percentage of animals with at least one lesion).
    e Multiplicity (number of lesions per animal ± SEM).
    f Statistically different from the control value, P < 0.05.
    


    8.5  Genotoxicity and related end-points

    8.5.1  Genotoxicity

         There is an extensive database on the genotoxicity of chloral
    hydrate and its metabolites. A complete summary of these results is
    provided in US EPA (2000).

         Chloral hydrate did not induce mutation in most strains of
     Salmonella typhimurium, but did in some studies with  S. typhimurium
    TA100 and in a single study with  S. typhimurium TA104. The latter
    response was inhibited by free-radical scavengers alpha-tocopherol and
    menadione (Ni et al., 1994).

         Chloral hydrate did not induce mitotic crossing-over in
     Aspergillus nidulans in the absence of metabolic activation. Chloral
    hydrate caused weak induction of meiotic recombination in the presence
    of metabolic activation and gene conversion in the absence of
    metabolic activation in  Saccharomyces cerevisiae. It did not induce
    reverse mutation in  S. cerevisiae. Chloral hydrate clearly induced
    aneuploidy in various fungi in the absence of metabolic activation.

         Chloral hydrate induced somatic and germ cell mutations in
     Drosophila melanogaster.

         Chloral hydrate did not produce DNA-protein cross-links in rat
    liver nuclei, DNA single-strand breaks/alkaline-labile sites in
    primary hepatocytes  in vitro, or DNA repair in  Escherichia coli.
    One study showed induction of single-strand breaks in liver DNA of
    both rats and mice treated  in vivo; another study in both species
    using higher concentrations of chloral hydrate found no such effect.

         Chloral hydrate was weakly mutagenic, but did not induce
    micronuclei in mouse lymphoma cells  in vitro. Chloral hydrate
    increased the frequency of micronuclei in Chinese hamster cell lines.
    Although a single study suggested that chloral hydrate induces
    chromosomal aberrations in Chinese hamster CHED cells  in vitro, the
    micronuclei produced probably contained whole chromosomes and not
    chromosome fragments, as the micronuclei could all be labelled with
    antikinetochore antibodies.

         In kangaroo rat kidney epithelial cells, chloral hydrate
    inhibited spindle elongation and broke down mitotic microtubuli,
    although it did not inhibit pole-to-pole movement of chromosomes. It
    produced multipolar spindles, chromosomal dislocation from the mitotic
    spindle, and a total lack of mitotic spindles in Chinese hamster
    DON:Wg.3h cells.

         Chloral hydrate weakly induced sister chromatid exchange in
    cultures of human lymphocytes. It induced micronuclei, aneuploidy,
    C-mitosis, and polyploidy in human lymphocytes  in vitro. Micronuclei
    were induced in studies with human whole blood cultures but not in one
    study with isolated lymphocytes. The differences seen in the
    micronucleus test have been attributed to differences between whole
    blood and purified lymphocyte cultures (Vian et al., 1995), but this
    hypothesis has not been tested.

         Chloral hydrate increased the frequency of chromosomal
    aberrations in mouse bone marrow, spermatogonia, and primary and
    secondary spermatocytes, but not in oocytes, after  in vivo
    treatment. Chloral hydrate induced chromosomal aberrations in mouse
    bone marrow erythrocytes after treatment  in vivo. In one of these
    studies, the use of antikinetochore antibodies suggested induction of
    micronuclei containing both whole chromosomes and fragments. Chloral
    hydrate induced micronuclei in the spermatids of mice treated  in vivo
    in some studies. Chloral hydrate induced aneuploidy in the bone
    marrow of mice treated  in vivo. It increased the rate of aneuploidy
    in mouse secondary spermatocytes. It did not produce polyploidy in
    bone marrow, oocytes, or gonosomal or autosomal univalents in primary
    spermatocytes of mice treated  in vivo. Chloral hydrate, however,
    induced polyploidy and meiotic delay when a synchronized population of
    mouse oocytes was exposed  in vitro prior to the resumption of
    maturation.

         Trichloroethanol, a reduction product of chloral hydrate, did not
    induce lambda prophage in  E. coli or mutation in  S. typhimurium
    TA100. Trichloroethanol caused spindle aberrations when mouse oocytes
    were treated  in vitro.

         Trichloroacetic acid did not induce lambda prophage in  E. coli
    and was not mutagenic to  S. typhimurium in the presence or absence
    of metabolic activation. Trichloroacetic acid was weakly positive in
    the mouse lymphoma assay with metabolic activation. Trichloroacetic
    acid also did not induce chromosomal damage in human lymphocytes or
    micronuclei in bone marrow  in vitro. It is unclear whether
    trichloroacetic acid can induce chromosomal damage  in vivo, because
    some studies have been positive and others negative.

         Dichloroacetic acid did not induce differential toxicity in DNA
    repair-deficient strains of  S. typhimurium but did induce lambda
    prophage in  E. coli. Dichloroacetic acid gave equivocal results for
    gene mutation in  S. typhimurium TA100 and TA98. Dichloroacetic acid
    was weakly mutagenic in the  in vitro mouse lymphoma assay and
    induced chromosomal aberrations but not micronuclei or aneuploidy in
    that test system. Dichloroacetic acid induced micronuclei in mouse
    polychromatic erythrocytes  in vivo and mutations at the  lacI locus
    in the transgenic B6C3F1 mouse (the Big Blue Mouse)  in vivo at an
    exposure that induces liver tumours in male mice. It is unclear
    whether dichloroacetic acid can induce primary DNA damage, as some
    assays are positive and others negative.

    8.5.2  Cell proliferation

         Rijhsinghani et al. (1986) evaluated the acute effects of chloral
    hydrate on liver cell proliferation in 15-day-old male mice (C57BL ×
    C3HF1). Mice were given 0, 5, or 10 mg chloral hydrate/kg body
    weight by gavage in distilled water (9, 10, and 6 mice per group,
    respectively) and sacrificed after 24 h. Cell proliferation was
    evaluated by calculating the mitotic index (number of mitoses per 100
    nuclei) from liver sections. The mitotic index in liver cells was
    significantly increased (0.9235) in mice receiving 5 mg/kg body weight
    when compared with the control value (0.3382), and elevated (0.7433)
    (although not statistically significantly) in mice receiving 10 mg/kg
    body weight. Hepatic necrosis was not observed in mice from either
    treatment group at autopsy.

         As part of the chronic bioassay for carcinogenicity, George et
    al. (2000) evaluated hepatocyte proliferation in male F344 rats and
    male B6C3F1 mice. Exposures are given in section 8.4.2. Five days
    prior to sacrifice at 13, 26, 52, or 72 weeks in rats and 26, 52, or
    78 weeks in mice, animals were given bromodeoxyuridine. Labelled
    nuclei were identified by chromogen pigment over the nuclei, and the
    labelling index was calculated. Outside of the areas with tumours in
    the liver of mice, there was no significant evidence of increased
    hepatocyte proliferation in rats or mice.

    8.5.3  Oncogene activation

         Velazquez (1994) investigated the induction of H- ras
    proto-oncogene mutations in mice. DNA from normal liver and tumour
    tissue was obtained from male B6C3F1 mice administered 1 g chloral
    hydrate/litre (166 mg/kg body weight per day) in drinking-water for
    2 years. H- ras mutations were present in one out of seven (14%)
    tumours. The spectrum of mutations was the same as that of spontaneous
    liver tumours. Based on these data, it is unlikely that H- ras
    activation is a mechanism of carcinogenicity relevant to chloral
    hydrate.

    8.5.4  Free radicals and DNA adduct formation

         Ni et al. (1994, 1995, 1996) studied the metabolism of chloral
    hydrate in an  in vitro system using microsomes from male B6C3F1
    mice. The metabolism of chloral hydrate generated free radicals as
    detected by electron spin resonance spectroscopy and caused endogenous
    lipid peroxidation, resulting in the production of malondialdehyde,
    formaldehyde, and acetaldehyde, all of which are known to produce
    liver tumours in rodents. Trichloroacetic acid and trichloroethanol
    also produced free radicals and induced lipid peroxidation when tested
    in this system. The authors speculated that the free radicals were
    Cl3CCO2Ê. and/or Cl3CÊ. Incubation of chloral hydrate,

    trichloroethanol, or trichloroacetic acid in the presence of
    microsomes and calf thymus DNA resulted in the formation of a
    malondialdehyde-modified DNA adduct. This research group further
    showed that chloral hydrate induced an increase in mutations at the
     hprt and  tk loci in transgenic human lymphoblastoid cells
    containing CYP2E1. In contrast, when the parental cell line lacking
    CYP2E1 was treated with the same concentration of chloral hydrate, no
    mutations were found at either locus. These data implicate CYP2E1 as
    the primary cytochrome subfamily involved in the metabolism of chloral
    hydrate to reactive intermediates. 

    8.5.5  Cell communication

         The effects of 1-, 4-, 6-, 24-, 48-, and 168-h exposures to
    chloral hydrate (0, 1, 5, or 10 mmol/litre) on gap junction
    intercellular communication in Clone 9 cell cultures (normal rat
    hepatocytes) were reported by Benane et al. (1996). No differences in
    intercellular communication were seen between the groups treated with
    1 mmol/litre at 1, 4, and 6 h of exposure and controls, as measured by
    a dye transfer protocol. There were significant differences between
    all other groups and the controls. The shortest exposure time and
    lowest exposure concentration that reduced dye transfer significantly
    were in the group treated with 1 mmol/litre for 24 h.

    8.5.6  Peroxisome proliferation

         As part of the chronic bioassay for carcinogenicity in mice,
    George et al. (2000) found no evidence of peroxisome proliferation
    using cyanide-insensitive palmitoyl CoA oxidase in the livers of male
    mice treated with chloral hydrate for 26 weeks.

    8.6  Reproductive and developmental toxicity

         Klinefelter et al. (1995) evaluated effects on sperm morphology
    and motility in F344 rats administered chloral hydrate in
    drinking-water for 52 weeks at levels of 0, 55, or 188 mg/kg body
    weight per day. The researchers examined cauda epididymal sperm motion
    parameters and testicular and epididymal histopathology. Chloral
    hydrate did not cause any visible systemic toxicity and had no effects
    on epididymal or testicular histopathology. However, the percentage of
    motile sperm was significantly decreased  (P < 0.01) from 68% in
    controls to 58% in rats exposed to 188 mg/kg body weight per day. The
    percentage of progressively motile sperm was also significantly
    decreased  (P < 0.01) from 63% in controls to 53% in this group. In
    addition, the frequency distribution of the average straight-line
    velocities of sperm at this exposure was significantly shifted
     (P < 0.01) to the lower ranges when compared with controls. In this
    study, the NOAEL is 55 mg/kg body weight per day; the LOAEL is 188
    mg/kg body weight per day.

         Kallman et al. (1984) exposed male and female CD-1 mice to
    chloral hydrate in drinking-water at 21.3 or 204.8 mg/kg body weight
    per day. Animals were exposed for 3 weeks prior to breeding. Exposure
    of females (5 per group) continued during gestation and until pups
    were weaned at 21 days of age. No gross malformations were noted, and
    no significant effects were observed in duration of gestation, number
    of pups delivered, pup weight, or number of stillborn pups. All pups
    (15 per group) showed the same rate of development and level of
    performance on several neurobehavioural tests, except that pups
    exposed to 204.8 mg/kg body weight per day when tested at 23 days of
    age showed impaired retention of passive avoidance learning on both
    the 1-h and 24-h retention tests  (P < 0.05). This study identified
    a NOAEL for neurodevelopmental toxicity of 21.3 mg/kg body weight per
    day and a LOAEL of 204.8 mg/kg body weight per day based on the
    impairment in passive avoidance learning. This study also identifies a
    NOAEL for reproductive and other developmental effects of 204.8 mg/kg
    body weight per day (the highest exposure tested).

         Johnson et al. (1998) tested the potential for chloral hydrate to
    cause developmental toxicity in Sprague-Dawley rats. Chloral hydrate
    was administered in drinking-water to 20 rats from gestational day 1
    to gestational day 22 at an average exposure of 151 mg/kg body weight
    per day. Control animals were given distilled water. There was no
    evidence of maternal toxicity, no change in the number of implantation
    or resorption sites, no change in the number of live or dead fetuses,
    no change in placental or fetal weight, no change in crown-rump
    length, and no increase in the incidence of morphological changes. A
    detailed examination found no evidence of cardiac anomalies. Based on
    this study, the NOAEL for developmental toxicity is 151 mg/kg body
    weight per day (the highest exposure tested).

         Johnson et al. (1998) also tested the potential for
    trichloroethanol and trichloroacetic acid to cause developmental
    toxicity in Sprague-Dawley rats. The protocol was identical to the
    study with chloral hydrate. Trichloroethanol was administered to 10
    rats at an average exposure of 153 mg/kg body weight per day. No
    evidence of developmental toxicity was found. In contrast, when
    trichloroacetic acid was administered to 11 rats at an average
    exposure of 291 mg/kg body weight per day, developmental toxicity was
    observed. The effects included statistically significant  (P < 0.05)
    increases in average resorptions, in average implantations, and in
    cardiac anomalies. Although the specific cardiac anomalies found were
    different, the results with trichloroacetic acid are generally
    consistent with those reported by Smith et al. (1989), who observed
    adverse developmental effects from trichloroacetic acid at an exposure
    of 330 mg/kg body weight per day and above.

         Saillenfait et al. (1995) tested the potential of chloral hydrate
    to cause developmental toxicity using a rat whole-embryo culture
    system. Embryos (20 per dose) from Sprague-Dawley rats were explanted
    on gestational day 10 and exposed to chloral hydrate at a
    concentration of 0, 0.5, 1, 1.5, 2, or 2.5 mmol/litre (equivalent to
    0, 83, 165, 248, 331, or 414 mg/litre) for 46 h. At 2.5 mmol/litre,
    all embryos died. No lethality was seen at lower exposures. Chloral
    hydrate caused concentration-dependent decreases in growth and
    differentiation and increases in the incidence of morphologically
    abnormal embryos. No effects were observed in any parameter at 
    0.5 mmol/litre. Decreases in crown-rump length, somite 
    (embryonic segment) number, and the protein or DNA content of embryos 
    were seen at 1 mmol/litre and above. At 1, 1.5, and 2 mmol chloral 
    hydrate/litre, respectively, 18%, 68%, and 100% of embryos were 
    malformed. Brain, eye, and ear malformations were the most prominent 
    effects at these concentrations. Abnormalities in the trunk and 
    pericardial dilation also occurred at 2 mmol/litre. In this  in vitro
    test system, chloral hydrate was a slightly more potent teratogen than 
    trichloroacetic acid or dichloroacetic acid.

         Although chloral hydrate did not cause meiotic delay in the
    oocytes of adult mice when administered at the time of resumption of
    maturation induced by hormones (Mailhes & Marchetti, 1994), it did
    cause adverse effects  in vitro when a synchronized population of
    oocytes was exposed prior to resumption of maturation
    (Eichenlaub-Ritter & Betzendahl, 1995; Eichenlaub-Ritter et al.,
    1996). In this test system, chloral hydrate induced lagging of
    chromosomes during telophase I, inhibited spindle elongation in
    anaphase B, and caused chromosome displacement from the spindle
    equator in metaphase I and II. Oocytes became irreversibly arrested in
    maturation when exposed to chloral hydrate prior to resumption of
    maturation or when chloral hydrate was present during the first or
    second 8 h of maturation. Spindle aberrations were observed when
    oocytes were treated with trichloroethanol (Eichenlaub-Ritter et al.,
    1996).

    8.7  Immunological and neurological effects

         Kauffmann et al. (1982) administered chloral hydrate by gavage in
    distilled water at 14.4 or 144 mg/kg body weight per day to groups of
    11-12 male CD-1 mice for 14 days. No effects on humoral or
    cell-mediated immunity were detected at either exposure.

         Kauffmann et al. (1982) administered chloral hydrate to male and
    female CD-1 mice in drinking-water at 70 or 700 mg/litre (equivalent
    to 16 or 160 mg/kg body weight per day) for 90 days. Humoral immunity
    was assessed by the number of splenic antibody-forming cells produced
    against sheep red blood cells (12 mice in the control group and 8 mice
    in the exposed groups) and haemagglutination titres (20-21 mice in the
    control group and 13-16 mice in the exposed groups).

    Cell-mediated immunity was assessed by delayed-type hypersensitivity
    to sheep red blood cells (17-20 mice in the control group and 
    15-16 mice in the exposed groups). Lymphocyte response was assessed 
    using a T-cell mitogen (Con A) and a B-cell mitogen (LPS) 
    (17-22 animals in the control group and 13-16 mice in the exposed 
    groups). In males, no effects were detected in either humoral or 
    cell-mediated immunity at either exposure. No effects on cell-mediated 
    immunity were noted in females at either exposure. In females, both 
    exposures resulted in a statistically significant decrease 
     (P < 0.05) in humoral immune function (36% and 40% at the 
    low and high exposures, respectively) when expressed as 
    antibody-forming cells per spleen. The decrease, however, was
    statistically significant only at the higher exposure when 
    expressed as antibody-forming cells per million spleen cells 
    (a 32% decrease). There was no effect on haemagglutination titres 
    or on spleen cell response to the B-cell mitogen at either exposure. 
    The decrease in antibody-forming cells per million spleen cells at 
    the higher exposure in female mice is regarded as an adverse 
    response in this study. Accordingly, the NOAEL for immunotoxicity is 
    16 mg/kg body weight per day; the LOAEL is 160 mg/kg body weight
    per day.

         Kallman et al. (1984) administered chloral hydrate by gavage in
    distilled water at 50, 100, 200, 300, or 400 mg/kg body weight to
    groups of 12 male CD-1 mice. All doses resulted in the rapid onset of
    ataxia, with an ED50 (maximal effect seen in 50% of animals) of
    84.2 mg/kg body weight at 5 min (the time of maximal effect). Animals
    recovered within 2-3 h. No delayed changes in muscular coordination
    were detectable when the mice were tested 24 h after treatment.

         Kallman et al. (1984) evaluated behavioural toxicity in groups of
    12 male CD-1 mice administered chloral hydrate by gavage in distilled
    water at 14.4 or 144 mg/kg body weight per day for 14 days. When
    measured 24-48 h after exposure was terminated, no significant effects
    on body weight, motor activity, physical appearance, behaviour,
    muscular coordination, or endurance were observed.

         Kallman et al. (1984) exposed groups of 12 male CD-1 mice to
    drinking-water containing chloral hydrate at a concentration of 70 or
    700 mg/litre (equivalent to 16 or 160 mg/kg body weight per day) for
    90 days. When measured 24 h after exposure was terminated, no
    treatment-related effects on mortality, body weight, physical
    appearance, behaviour, locomotor activity, learning in repetitive
    tests of coordination, response to painful stimuli, strength,
    endurance, or passive avoidance learning were observed. Both exposures
    resulted in a decrease of about 1°C in mean body temperature
     (P < 0.05). Because of the lack of increased effect with a 10-fold
    increase in exposure and because hypothermia as a side-effect of
    chloral hydrate or from an overdose of chloral hydrate has not been
    reported in humans, the decrease in body temperature is not considered
    an adverse effect. This study identifies a NOAEL for neurobehavioural
    toxicity of 160 mg/kg body weight per day (the highest exposure
    tested).

         A condensation product of tryptamine and chloral hydrate,
    1-trichloromethyl-1,2,3,4-tetrahydro-ß-carboline (TaClo), has been
    found in the blood of elderly patients administered chloral hydrate
    for 2-7 days (Bringmann et al., 1999). This metabolite initiated a
    slowly progressive neurodegeneration when administered to rats in a
    subchronic study (Gerlach et al., 1998). There is, however, no
    evidence of neurodegeneration in the chronic studies with chloral
    hydrate in rats and mice.
    

    9.  EFFECTS ON HUMANS

         Chloral hydrate has been widely used as a sedative and hypnotic
    drug in humans. Trichloroethanol is responsible for the
    pharmacological activity (Marshall & Owens, 1954; Breimer, 1977;
    Goodman & Gilman, 1985). Exposure information is discussed in section
    6.2.

         Chloral hydrate is irritating to the skin and mucous membranes
    and often causes gastric distress, nausea, and vomiting at recommended
    doses. There are no reports of sensitization in humans. Overdoses
    produce (in order of progression) ataxia, lethargy, deep coma,
    respiratory depression, hypotension, and cardiac arrhythmias. The
    life-threatening effects are from severe respiratory depression,
    hypotension, and cardiac arrhythmias. For some representative case
    reports, see Marshall (1977), Anyebuno & Rosenfeld (1991), Ludwigs et
    al. (1996), and Sing et al. (1996). A potentially life-threatening
    oral dose for humans is approximately 10 g (143 mg/kg body weight),
    although death has been reported from as little as 4 g, and some
    individuals have survived ingesting 30 g or more. Extended use of
    chloral hydrate may result in development of tolerance to the
    pharmacological effect and physical dependence on or addiction to
    chloral hydrate.

         Shapiro et al. (1969) reviewed the medical records of 1618
    patients who had received chloral hydrate at 1 g (213 patients, 13%),
    0.5 g (1345 patients, 83%), or various other doses (60 patients, 4%).
    Adverse reactions were reported in 38 patients (2.3%). Of these
    patients, 4 received 1 g, 1 received 0.75 g, and 33 received 0.5 g.
    Reported adverse reactions included gastrointestinal symptoms in 10
    patients, central nervous system (CNS) depression in 20 patients, skin
    rash in 5 patients, prolonged prothrombin time in 1 patient, and
    bradycardia in 1 patient. In all patients, the side-effects
    disappeared when chloral hydrate therapy was stopped. There was no
    evidence of association between adverse side-effects and age, weight,
    or sex.

         Miller & Greenblatt (1979) reviewed the medical records of 5435
    hospital patients who received chloral hydrate at a dose of either 
    0.5 g (about 7-8 mg/kg body weight) or 1 g (about 14-16 mg/kg body
    weight). Adverse reactions were noted in 119 cases (2.2%). 
    CNS depression was most common (58 patients, or 1.1%), with minor
    sensitivity reactions, including rash, pruritus, fever, and
    eosinophilia, second most common (19 patients, or 0.35%). Other
    adverse reactions included gastrointestinal disturbances (0.28%) and
    CNS excitement (0.22%). Three individuals (0.05%) were judged to have
    life-threatening reactions involving CNS depression, asterixis
    (involuntary jerking movements), or hypotension. The data show that
    adverse reactions involving the CNS become more frequent with

    increasing dosage in patients older than 50 years, in patients who
    died during hospitalization, in patients who received concurrently
    benzodiazepine anti-anxiety drugs, and in patients with elevated
    levels of blood urea nitrogen.

         Greenberg et al. (1991) reported various side-effects experienced
    by children receiving chloral hydrate sedation in preparation for
    computer tomography (CT) procedures. In a "high-dose" group, composed
    of 295 children (average age 2.18 years) who received a single dose of
    80-100 mg/kg body weight and a maximum total dose of 2 g, adverse
    reactions occurred in 23 of the patients (7%) and included vomiting
    (14 patients), hyperactivity (5 patients), and respiratory symptoms,
    such as wheezing and secretion aspiration (4 patients). Cardiac
    monitoring did not reveal any abnormalities or arrhythmias in any of
    the children. A second "lower-dose" cohort of 111 children (average
    age 1.9 years) received 40-75 mg chloral hydrate/kg body weight. These
    patients received the lower dose because of existing liver or renal
    impairment, respiratory insufficiency, or CNS depression. There were
    no adverse side-effects or complications reported in this group.
    Children with severe liver or renal disease or affected by severe 
    CNS depression were not treated with chloral hydrate.

         Lambert et al. (1990) conducted a retrospective analysis of
    hospital medical records to investigate a possible link between
    chloral hydrate administration and direct hyperbilirubinaemia (DHB) in
    neonates following prolonged administration of chloral hydrate
    (25-50 mg/kg body weight for up to 20 days). Direct bilirubin is a
    measure of the free, unconjugated bilirubin in the serum. In the first
    study, the DHB was of unknown etiology in 10 of the 14 newborns with
    DHB; all 10 of these DHB patients had received chloral hydrate. In the
    second study, among 44 newborns who had received chloral hydrate, 
    10 patients who developed DHB had received a mean cumulative dose of 
    1035 mg/kg body weight. In contrast, 34 patients whose direct 
    bilirubin levels were within normal ranges received a mean cumulative 
    dose of 183 mg/kg body weight. The total bilirubin levels (free plus
    conjugated) were the same in both groups and within the normal range.

         Kaplan et al. (1967) investigated whether ethanol ingestion
    increased the effects of chloral hydrate. Five male volunteers
    weighing 70-107 kg consumed ethanol (880 mg/kg body weight), chloral
    hydrate (1 g, 9-14 mg/kg body weight), or both. Blood pressure and
    cardiac rate did not vary significantly among treatments. In the
    presence of ethanol, the concentration of trichloroethanol in the
    blood rose more rapidly and reached a higher value, but the rate of
    depletion was not significantly changed. The increase in the
    concentration of trichloroethanol was not sufficient to produce a
    marked enhancement of the hypnotic effect. The volunteers reported
    symptoms (drowsiness, dizziness, blurred vision) and their severity
    during the 6-h observation period. At all time points, the rank order
    of effects was ethanol plus chloral hydrate > ethanol > chloral
    hydrate.

         No long-term studies of chloral hydrate in humans were located.
    Chloral hydrate is addictive and is a controlled substance (Schedule
    IV) in the USA.
    

    10. EFFECTS ON OTHER ORGANISMS IN THE LABORATORY AND FIELD

         Some data are available from cell multiplication inhibition tests
    (toxic thresholds) in bacteria, algae, and protozoa. These data are
    summarized in Table 2.

         Schatten & Chakrabarti (1998) showed that chloral hydrate at 0.1%
    (only concentration tested) causes alteration of centrosomal material
    and abnormal microtubule configurations in California sea urchins
     (Strongylocentrotus purpuratus and  Lytechinus pictus). Chakrabarti
    et al. (1998) also showed that chloral hydrate at 4 mmol/litre (660
    mg/litre, only concentration tested) induced ciliary loss in the early
    embryo phase of  Lytechinus pictus. Exposure in this study was for 30
    h at the blastula stage (14 h after fertilization).

        Table 2: Effects of chloral hydrate on bacteria, algae, and protozoa.
                                                                                          

    Test system                   Effect                            Reference
                                                                                          

    Bacteria                      16-h EC3 at 1.6 mg/litre          Bringmann & Kuehn, 
    (Pseudomonas putida)                                            1980a

    Green alga                    7-day EC3 at 2.8 mg/litre         Bringmann & Kuehn, 
    (Scenedesmus                                                    1980a
    quadricaudata)

    Blue-green alga               8-day EC3 at 78 mg/litre          Bringmann & Kuehn, 
    (cyanobacterium)                                                1976
    (Microcystis
    aeruginosa)

    Protozoan                     72-h EC5 at 79 mg/litre           Bringmann & Kuehn, 
    (Enterosiphon sulcatum)                                         1980a

    Protozoan                     EC5 at 86 mg/litre                Bringmann & Kuehn, 
    (Uronema parduczi)                                              1980b
                                                                                          
        

    11. EFFECTS EVALUATION

    11.1 Evaluation of health effects

    11.1.1 Hazard identification and dose-response assessment

         Chloral hydrate has been extensively used as a sedative and
    hypnotic drug in human and veterinary medicine. The metabolite
    trichloroethanol is responsible for the pharmacological effect.
    Chloral hydrate is irritating to the skin and mucous membranes and
    often causes gastric distress, nausea, and vomiting at recommended
    doses. Acute overdoses produce (in order of progression) ataxia,
    lethargy, deep coma, respiratory depression, hypotension, and cardiac
    arrhythmias. There is some evidence of hepatic injury in people
    surviving near-lethal, acute overdoses, but no convincing evidence
    that hepatic injury results from the recommended clinical dose.
    Despite its long use in human medicine, there is no published
    information on toxicity in controlled studies in humans following
    extended exposure.

         Chloral hydrate is completely absorbed and rapidly metabolized
    following oral administration. The major metabolites are
    trichloroethanol and its glucuronide and trichloroacetic acid. Some
    data suggest that a small amount of dichloroacetic acid may be formed.
    In humans, the half-life of trichloroethanol and its glucuronide is
    about 8 h; the half-life of trichloroacetic acid is about 4 days. Some
    data suggest that the half-life of trichloroethanol is increased
    several-fold in pre-term and full-term infants compared with toddlers
    and adults. The major route of excretion of the metabolites of chloral
    hydrate is elimination in the urine. Chloral hydrate and its
    metabolites have been found in milk from women treated with chloral
    hydrate. The concentration of these chemicals, however, is too low to
    cause a pharmacological effect in the nursing infant.

         Acute administration of chloral hydrate to mice causes loss of
    coordination (ataxia) at about the same exposure as in humans for the
    same effect. A 90-day study in mice shows no evidence of behavioural
    changes or other neurotoxicity. Chronic studies in rats and mice show
    no evidence of behavioural changes and no evidence of
    histopathological changes in nervous tissue. These studies used an
    exposure approximately 15 times the recommended clinical dose in
    humans. There is some evidence of mild liver toxicity following
    chronic exposure in rats and mice. A slight decrement in humoral
    immunity was observed in female mice following exposure for 90 days.
    The antibody-forming cell response is considered an excellent
    indicator of the status of humoral immunity because of the complex
    cellular cooperation required to produce antibody and because the
    number of cells that produce antibody can be quantified. A depression
    in the number of these cells is considered an adverse response because
    the production of antibodies is important to the defence strategy of
    the organism. However, the quantitative relationship between the

    depression in antibody-forming cells in the spleen and the
    concentration of circulating antibody is unknown. In this study,
    because there was no depression in circulating antibodies measured by
    the haemagglutination titre, there might be no significant depression
    in the ability of the host to mount a protective antibody response.
    Chloral hydrate has been tested for developmental effects in rats and
    mice. No structural abnormalities were observed. A slight effect was
    observed in mice in passive avoidance learning when dams were exposed
    prior to breeding, during gestation, and during nursing and pups were
    tested at 23 days of age. Although chloral hydrate has not been tested
    in a two-generation reproduction study, the data on reproductive
    performance and on effects on sperm and oocytes do not suggest that
    reproductive toxicity is likely to be a critical effect. In addition,
    no histopathological effects are observed in reproductive organs of
    rodents in subchronic or chronic studies. Some  in vitro data,
    however, suggest that chloral hydrate administered to young female
    children might have a latent effect on fertility. All of the studies
    in laboratory animals show non-cancer health effects at an exposure
    far in excess of the exposure that is effective for sedation in
    humans. A complete summary of the exposure-response data is presented
    in Table 3.

         Simultaneous ingestion of ethanol and chloral hydrate increases
    the sedative effects and side-effects of chloral hydrate. The
    mechanism is the increase in the concentration of the
    pharmacologically active metabolite, trichloroethanol, in the presence
    of ethanol. Chronic users of ethanol are, therefore, somewhat more
    sensitive to the adverse effects of chloral hydrate.

         Because of the immaturity of hepatic metabolism, particularly the
    glucuronidation pathway, and decreased glomerular filtration in
    infants, the half-life of trichloroethanol is longer in pre-term and
    full-term infants. This group is therefore somewhat more sensitive to
    the adverse effects of chloral hydrate. Toddlers and adults are likely
    to show similar sensitivity to chloral hydrate.

         Although male laboratory rodents seem to be more sensitive than
    female laboratory rodents to hepatic effects, there is no evidence of
    a gender effect in humans with respect to the sedative effects or
    side-effects of chloral hydrate at the recommended clinical dose.

         There are no carcinogenicity data from humans. Two bioassays in
    rats show no increase in tumours at any site. These studies were
    limited, because only minimal toxicity was observed in the livers of
    the rats in these bioassays. In one study, only slight hypertrophy was
    observed at the highest exposure; in the other study, no effects were
    observed at the highest exposure. No data are available in female
    mice. There are three separate bioassays showing an increased
    incidence of liver tumours in male mice. One study, conducted in a
    very limited number of animals, showed an increase in tumours



        Table 3: Summary of non-neoplastic effects.
                                                                                                                              

    Species        Duration           End-point                    NOAEL            LOAEL          Reference
                                                                   (mg/kg body      (mg/kg body
                                                                   weight per       weight per
                                                                   day)             day)
                                                                                                                              

    Human          1 day, 3 doses     Sedation                     -                10.7           Goodman & Gilman, 1985

    Rat            90 days            Mild liver necrosis          96               168            Daniel et al., 1992b
                                      and increase in
                                      serum enzymes

    Rat            104 weeks          -                            162.6            -              George et al., 2000

    Rat            124 weeks          Liver hypertrophy            45               135            Leuschner & Beuscher, 1998

    Rat            52 weeks           Sperm motility               55               188            Klinefelter et al., 1995

    Rat            gestation          Development                  151              -              Johnson et al., 1998
                   days 1-22

    Mouse          14 days            Increased liver weight       14.4             144            Sanders et al., 1982

    Mouse          90 days            Increased liver weight       16               160            Sanders et al., 1982

    Mouse          104 weeks          Increased liver weight       -                166a           Daniel et al., 1992a
                                      and necrosis

    Mouse          104 weeks          -                            146.6b           -              George et al., 2000

    Mouse          3 weeks            Reproduction and             204.8            -              Kallman et al., 1984
                   pre-breeding       development
                   and during
                   gestation

    Mouse          Pre-breeding,      Passive avoidance            21.3             204.8          Kallman et al., 1984
                   gestation, and     learning in pups
                   nursing

    Table 3 (cont'd)
                                                                                                                              

    Species        Duration           End-point                    NOAEL            LOAEL          Reference
                                                                   (mg/kg body      (mg/kg body
                                                                   weight per       weight per
                                                                   day)             day)
                                                                                                                              
    Mouse          1 day              Ataxia                       -                50             Kallman et al., 1984

    Mouse          14 days            Neurobehaviour               144              -              Kallman et al., 1984

    Mouse          90 days            Neurobehaviour               160              -              Kallman et al., 1984

    Mouse          14 days            Immunotoxicity               144              -              Kauffmann et al., 1982

    Mouse          90 days            Humoral immunity             16               160            Kauffmann et al., 1982
                                                                                                                              

    a Tumours at 166 mg/kg body weight per day.

    b Hyperplasia and tumours at 13.5, 65, and 146.6 mg/kg body weight per day.
    


    following a single exposure. The second study tested only one exposure
    level but used an adequate number of animals. The third study shows an
    increase in incidence and multiplicity of liver tumours at each of
    three exposures. There are no data identifying a lesion that is a
    precursor to the tumours. The strain of mice used has a very high
    spontaneous incidence of liver tumours. Two of the metabolites of
    chloral hydrate, trichloroacetic acid and dichloroacetic acid, have
    been shown to cause liver tumours in rodents. Trichloroacetic acid
    causes liver tumours only in mice. Dichloroacetic acid causes tumours
    in both rats and mice.1

         Chloral hydrate has been extensively studied as a genotoxic
    agent. Chloral hydrate was positive in some bacterial mutation tests,
    indicating that it may be capable of inducing point mutations. It was
    also positive in the mouse lymphoma assay for mutations at the  tk
    locus. Chloral hydrate also induced somatic and germ cell mutations
    in  D. melanogaster. Some data also show chloral hydrate to be a very
    weak clastogen in mammalian cells.

         Chloral hydrate has been shown to induce aneuploidy in a variety
    of cells, including  S. cerevisiae,  A. nidulans, Chinese hamster
    embryonic fibroblasts, Chinese hamster primary cell lines LUC2 and
    DON:Wg3h, human peripheral blood lymphocytes, mouse spermatocytes, and
    mouse spermatids. Because there is a mixture of positive and negative
     in vivo data, with no reason to weigh some studies more than others,
    it is not clear whether chloral hydrate is capable of inducing genetic
    damage  in vivo. Additional  in vivo studies using standard
    protocols would help clarify the relevance of genetic damage to a
    human health risk assessment.

         The effects on aneuploidy are thought to arise via disruption of
    the mitotic spindle structure or function by inhibition of tubulin
    and/or microtubule-associated proteins; both substances are components
    of the spindle apparatus. Some data also suggest that chloral hydrate
    may act on the spindle apparatus through an increase in the
    concentration of intracellular free calcium.

                  

    1 In a National Toxicology Program carcinogenicity bioassay that
      became available after the Final Review Board meeting, a 
      carcinogenic effect was not observed after a single dose of chloral 
      hydrate; after lifetime exposure, males had an increased incidence 
      of hepatic tumours, and females had a low increased incidence of 
      pituitary adenomas that was of borderline statistical significance.

         Several other mechanisms may play a role in the induction of
    tumours in the liver of male mice. There is no convincing evidence
    that chloral hydrate causes direct damage to DNA.  In vitro studies
    with chloral hydrate, trichloroethanol, and trichloroacetic acid and
    mouse microsomes, however, show lipid peroxidation and the formation
    of covalently bound DNA adducts. These effects appear to be mediated
    by the formation of free radicals by CYP2E1. Another possibility is
    cytotoxicity leading to compensatory hyperplasia. A single treatment
    of mice with chloral hydrate caused an increase in the mitotic index
    in liver cells. The increased cell division is hypothesized to either
    provide additional opportunities for errors in DNA replication or
    allow initiated cells to progress to a tumour. Another potentially
    contributing mechanism of carcinogenesis is disruption of
    intercellular communication, which has been shown in one experiment to
    be influenced by chloral hydrate.

         The mechanism of chloral hydrate-induced carcinogenicity in male
    mice is unclear. Two mechanisms that appear ruled out are H- ras
    proto-oncogene activation and peroxisome proliferation.

         Although there is suggestive evidence of carcinogenicity in male
    mice, the weight of evidence is not sufficient to consider tumour
    induction as the critical effect.

    11.1.2 Criteria for setting tolerable intakes or guidance values for
           chloral hydrate

         The effect that occurs at the lowest exposure is mild sedation in
    humans. As this effect would not be intended or desirable in the
    general population outside of the clinical setting, this response is
    considered an adverse effect and is used to derive the tolerable
    intake.

         Acute gavage exposure in mice shows neurological effects (ataxia)
    at about the same exposure for the comparable effect in humans. A
    subchronic study in mice using sensitive tests for neurobehavioural
    changes found none. Chronic studies in rats and mice show no evidence
    of neurobehavioural changes and no evidence of histopathological
    changes in nervous tissue. As with other chlorinated chemicals, there
    is some evidence of carcinogenic effects in the liver of male mice
    following chronic exposure.

         Although the tolerable intake derived from the pharmacologically
    active dose in humans is an acute tolerable intake, keeping the
    exposure below this level will also be protective for any non-cancer
    health effect from chronic exposure. Therefore, it is appropriate to
    use the acute tolerable intake as the chronic tolerable intake as
    well.

          No data are available to determine a NOAEL in humans. The
    recommended clinical dose for sedation in adults is 250 mg, taken 3
    times a day (Goodman & Gilman, 1985). A low incidence of side-effects
    also occurs at this exposure. The LOAEL is 10.7 mg/kg body weight per
    day (assuming a 70-kg body weight). The pharmacokinetic information
    shows that chloral hydrate and the pharmacologically active
    metabolite, trichloroethanol, will not bioaccumulate.

         The tolerable intake (IPCS, 1994) of 0.1 mg/kg body weight per
    day was derived from the LOAEL of 10.7 mg/kg body weight per day using
    a total uncertainty factor of 100. An uncertainty factor of 10 was
    used to extrapolate from a LOAEL to a NOAEL, and an uncertainty factor
    of 10 was used for intraspecies variability. An uncertainty factor for
    chronic duration was not used. Chloral hydrate and the active
    metabolite, trichloroethanol, do not bioaccumulate. The half-life of
    chloral hydrate is a few minutes, and the half-life of
    trichloroethanol is a few hours. Therefore, an enhanced effect from
    continuous, daily exposure is not possible. Finally, there is
    information from clinical use that long-term exposure to chloral
    hydrate results in tolerance to the sedative effect. Developmental
    toxicity, including developmental neurotoxicity, and immunotoxicity
    are not critical effects. Although there is no two-generation
    reproduction study, an uncertainty factor for database limitations is
    not needed, as there is evidence from several studies that
    reproductive toxicity is not likely to be a critical effect.

         There are no inhalation studies adequate for setting a guidance
    value or tolerable intake.

         There are data in male mice showing that chloral hydrate causes
    tumours in the liver. It is not known whether this response is
    relevant for humans.

    11.1.3 Sample risk characterization

         The quantitative estimate of human risk for non-cancer effects is
    based on the recommended clinical dose for sedation in humans and the
    minor incidence of side-effects at this dose. The tolerable intake is
    0.1 mg/kg body weight per day. This is 1% of the recommended single
    dose for sedation in humans.

         Although there is suggestive evidence of formation of tumours in
    the liver of male mice and there are some data showing genotoxicity,
    the mode of action for the formation of tumours is not known. It is
    also not known whether this response is relevant for humans.     

         Millions of people are exposed to chloral hydrate on a daily
    basis because it is formed during the disinfection of drinking-water
    with chlorine. The typical concentration in a public water supply in

    the USA is 5 µg/litre. Assuming a water consumption of 2 litres
    per day and a body weight of 70 kg, the exposure is 0.14 µg/kg body
    weight per day. This exposure is approximately 700 times lower than
    the tolerable intake.

    11.2 Evaluation of environmental effects

         Insufficient data are available with which to assess the risk to
    the environment from chloral hydrate.
    

    12. PREVIOUS EVALUATIONS BY INTERNATIONAL BODIES

         IARC (1995) evaluated the carcinogenicity data for chloral
    hydrate. It was concluded that there is inadequate evidence in humans
    and limited evidence in experimental animals for the carcinogenicity
    of chloral hydrate. Chloral hydrate is therefore not classifiable as
    to its carcinogenicity to humans (Group 3).

         IPCS (2000) recently evaluated the toxicological data on water
    disinfectants and disinfectant by-products, including chloral hydrate.
    Considering the dose level of 16 mg/kg body weight per day in the
    90-day study in mice (Sanders et al., 1982; see section 8.4.1) as a
    LOAEL (rather than as a NOAEL, as was done in the present document)
    and using an uncertainty factor of 10 for intra- and interspecies
    extrapolation and another factor of 10 for the use of a LOAEL rather
    than a NOAEL, the Task Group calculated a tolerable daily intake (TDI)
    for chloral hydrate of 16 µg/kg body weight per day. (As the present
    document considered the increase in liver weight at 16 mg/kg body
    weight to be a NOAEL rather than a LOAEL, the tolerable intake derived
    from the studies among humans was lower, as discussed in section
    11.1.)
    

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    APPENDIX 1 -- TOXICOKINETICS

         This toxicokinetic analysis is used to estimate the steady-state
    concentrations of trichloroacetic acid (TCA) and trichloroethanol
    (TCEOH) in mice and humans using a one-compartment model, assuming
    that the absorption of chloral hydrate (CH) from the gastrointestinal
    tract and its metabolism in the blood are very rapid compared with the
    rate of elimination of TCA and TCEOH. This assumption is supported by
    the data of Beland et al. (1998) in mice and Breimer (1977) and
    Zimmermann et al. (1998) in humans.

         Beland et al. (1998) indicated that 15% of the dose of chloral
    hydrate is converted directly to TCA and 77% is converted to TCEOH. In
    humans, Allen & Fisher (1993) estimated that 8% of a dose of chloral
    hydrate is converted directly to TCA and 92% is converted to TCEOH.
    Additional TCA is formed from TCEOH. The total TCA formed in humans is
    approximately 35% of the dose of chloral hydrate.

    Estimation of TCA concentration in mice at steady state at the
    clinically recommended dose for humans:

    [TCA]ss-blood =  PKo/ VKel = 2.5 mg/litre

    [TCA]ss-liver = [TCA]ss-blood ×  PC = 3.0 mg/litre

    where:

    *     P is the proportion of CH converted to TCA = 0.15 
         (Beland et al., 1998)

    *     Ko is the dosing rate for CH = 10.7 mg/kg body weight per
         day, equivalent to 0.446 mg/kg body weight per hour

    *     V is the volume of distribution = 0.321 litre/kg 
         (Beland et al., 1998)

    *     Kel is the first-order elimination constant for TCA =
         0.0819/h (Beland et al., 1998)

    *     PC is the liver/blood partition coefficient = 1.18 (Abbas &
         Fisher, 1997)

    Estimation of TCA concentration in humans at steady state at the
    clinically recommended dose:

    [TCA]ss-blood =  PKo/ VKel = 55 mg/litre

    [TCA]ss-liver = [TCA]ss-blood ×  PC = 36 mg/litre

    where:

    *     P is the proportion of CH converted to TCA = 0.35 (Allen &
         Fisher, 1993)

    *     Ko is the dosing rate for CH = 10.7 mg/kg body weight per
         day, equivalent to 0.446 mg/kg body weight per hour

    *     V is the volume of distribution = 0.102 litre/kg (Allen &
         Fisher, 1993)

    *     Kel is the first-order elimination constant for TCA = 0.028/h
         (Allen & Fisher, 1993)

    *     PC is the liver/blood partition coefficient = 0.66 
         (Fisher et al., 1998)

    Estimation of TCA concentration in humans at steady state at the
    tolerable intake:

    [TCA]ss-blood =  PKo/ VKel = 1.8 mg/litre

    [TCA]ss-liver = [TCA]ss-blood ×  PC = 1.2 mg/litre

    where:

    *     P is the proportion of CH converted to TCA = 0.35 (Allen &
         Fisher, 1993)

    *     Ko is the dosing rate for CH = 0.1 mg/kg body weight per day,
         equivalent to 0.004 mg/kg body weight per hour

    *     V is the volume of distribution = 0.102 litre/kg (Allen &
         Fisher, 1993)

    *     Kel is the first-order elimination constant for TCA =
         0.0078/h (Allen & Fisher, 1993)

    *     PC is the liver/blood partition coefficient = 0.66 
         (Fisher et al., 1998)

    Estimation of TCEOH concentration in mice at steady state at 166 mg/kg
    body weight per day:

    [TCEOH]ss-blood =  PKo/ VKel = 0.6 mg/litre

    where:

    *     P is the proportion of CH converted to TCEOH = 0.77 
         (Beland et al., 1998)

    *     Ko is the dosing rate for CH = 166 mg/kg body weight per day,
         equivalent to 6.917 mg/kg body weight per hour

    *     V is the volume of distribution = 1 litre/kg (cited in 
         Beland et al., 1998)

    *     Kel is the first-order elimination constant for TCEOH =
         9.24/h (Beland et al., 1998)

         Chloral hydrate at 160 mg/kg body weight per day was the highest
    exposure used in the 90-day neurobehavioural study by Kallman et al.
    (1984); chloral hydrate at 166 mg/kg body weight per day was the
    highest exposure used in the 104-week bioassay of Daniel et al.
    (1992a). These exposures are a NOAEL for sedation in mice.

    Estimation of TCEOH concentration in humans at steady state at the
    clinically recommended dose:

    [TCEOH]ss-blood =  PKo/ VKel = 4.7 mg/litre

    where:

    *     P is the proportion of CH converted to TCEOH = 0.92 (Allen &
         Fisher, 1993)

    *     Ko is the dosing rate for CH = 10.7 mg/kg body weight per
         day, equivalent to 0.446 mg/kg body weight per hour

    *     V is the volume of distribution -- not available, assumed 
         1 litre/kg

    *     Kel is the first-order elimination constant for TCEOH =
         0.087/h (Breimer, 1977)

    Estimation of TCEOH concentration in humans at steady state at the
    tolerable intake:

    [TCEOH]ss-blood =  PKo/ VKel = 0.04 mg/litre

    where:

    *     P is the proportion of CH converted to TCEOH = 0.92 (Allen &
         Fisher, 1993)

    *     Ko is the dosing rate for CH = 0.1 mg/kg body weight per day,
         equivalent to 0.004 mg/kg body weight per hour

    *     V is the volume of distribution -- not available, assumed 
         1 litre/kg

    *     Kel is the first-order elimination constant for TCEOH =
         0.087/h (Breimer, 1977)
    

    APPENDIX 2 -- CALCULATION OF BENCHMARK DOSE FOR
    TUMOUR INCIDENCE

         The Benchmark Dose (ED) for tumour incidence was derived from the
    incidence of adenoma plus carcinoma as reported by George et al.
    (2000). The human equivalent dose was calculated using (body
    weight)3/4, assuming a human body weight of 70 kg and a mouse body
    weight of 0.035 kg. EPA Benchmark Dose Software was used to calculate
    the ED and its lower 95% confidence limit (LED) corresponding to a 10%
    increase in extra risk for tumour prevalence with the multistage
    model.

     Multistage Model, Version Number 1.1.0b

    The form of the probability function is:

    P[response] =

    (1 -  background ) ×  [1 -  (e -  beta 1 ×  dose 1 -  beta 2 ×  dose 2) ]

    The parameter betas are restricted to be positive.

    Dependent variable = Incidence
    Independent variable = Dose

    Total number of observations = 4
    Total number of records with missing values = 0
    Total number of parameters in model = 3
    Total number of specified parameters = 0
    Degree of polynomial = 2

    Maximum number of iterations = 250
    Relative function convergence has been set to 2.220 45e-16
    Parameter convergence has been set to 1.490 12e-8

    Default initial parameter values
    Background = 0.698 863
    Beta(1) = 0.043 897
    Beta(2) = 0.000 400 241

    Parameter estimates

    Variable          Estimate                   Standard error 
                                                              
    Background        0.691 141                  0.073 072 3

    Beta(1)           0.053 218 1                0.084 548 3

    Beta(2)           0                          0.004 035 19
                                                              

    Asymptotic correlation matrix of parameter estimates
                                                               
                      Background             Beta(1)    Beta(2)
                                                               
    Background        1                      -0.6319    0.5007

    Beta(1)           -0.6319                1          -0.9507

    Beta(2)           0.5007                 -0.9507    1
                                                               

    Analysis of deviance table
                                                                      
    Model            Log(likelihood)   Deviance    DF     P-value
                                                                      
    Full model       -81.2046

    Fitted model     -81.922           1.434 7     2      0.230 999

    Reduced mode     -85.0504          6.256 83    2      0.043 787
                                                                      

        Goodness of fit analysis
                                                                                           
    Administered dose    Human equivalent      Estimated      Expected   Observed    Size 
    (mg/kg body weight   dose                  probability    
    per day)             (mg/kg body weight
                         per day)
                                                                                           
    0                    0                     0.6911         29.028     27          42

    13.5                 2.0000                0.7223         33.227     36          46

    65                   9.7                   0.8157         31.812     31          39

    146.6                21.9                  0.9037         28.919     29          32
                                                                                           
    Chi-square = 1.41; DF = 2;  P-value = 0.4949.
    
    Benchmark dose computation
                                   
    Specified effect     0.100 000
                                   
    Risk type            Extra risk

    Confidence level     0.950 000

    ED                   1.979 786

    LED                  1.090 1
                                   
    

    APPENDIX 3 -- SOURCE DOCUMENT

    US Environmental Protection Agency (2000):
     Toxicological review on chloral hydrate

         Copies of the document may be obtained from:

         EPA Risk Assessment Hotline
         513-569-7254 (phone)
         513-569-7159 (fax)
         rih.iris@epa.gov (e-mail address)
         www.epa.gov/iris (Website)

         This document was prepared by R. Benson, Region VIII, Denver, CO.

         The document and summary information on the Integrated Risk
    Information System (IRIS) have received peer review both by EPA
    scientists and by independent scientists external to EPA. Subsequent
    to external review and incorporation of comments, this assessment has
    undergone an Agency-wide review process whereby the IRIS Program
    Manager has achieved a consensus approval among the Office of Research
    and Development; Office of Air and Radiation; Office of Prevention,
    Pesticides, and Toxic Substances; Office of Solid Waste and Emergency
    Response; Office of Water; Office of Policy, Planning, and Evaluation;
    and the Regional Offices.

          Internal EPA reviewers:

         National Center for Environmental Assessment, Washington, DC
              J. Cogliano
              C. Siegel Scott
              V. Vu

         National Health and Environmental Effects Research Laboratory,
         Research Triangle Park, NC
              A. DeAngelo
              R. Luebke

         Office of Water, Washington, DC
              A. Bathija

          External peer reviewers:

         P.E. Brubaker, Private Consultant
         J.W. Fisher, Operational Toxicology Branch, Wright-Patterson 
            Air Force Base
         C.C. Willhite, Department of Toxic Substances Control, 
            State of California
    

    APPENDIX 4 -- CICAD PEER REVIEW

         The draft CICAD on chloral hydrate was sent for review to
    institutions and organizations identified by IPCS after contact with
    IPCS National Contact Points and Participating Institutions, as well
    as to identified experts. Comments were received from:

         Centre of Industrial Hygiene and Occupational Diseases, Czech
         Republic

         Department of Health, London, United Kingdom

         Federal Institute for Health Protection of Consumers and
         Veterinary Medicine, Berlin, Germany

         Fraunhofer Institute for Toxicology and Aerosol Research,
         Hannover, Germany

         GSF Forschungszentrum für Umwelt und Gesundheit, GmbH,
         Oberschleissheim, Germany

         Health and Safety Executive, Bootle, United Kingdom

         Institut de Recherche en Santé et en Sécurité du Travail du
         Québec, Montreal, Canada

         Institute of Occupational Medicine, Chinese Academy of Preventive
         Medicine, Beijing, People's Republic of China

         National Center for Environmental Assessment, US Environmental
         Protection Agency, Washington, DC, USA

         National Center for Toxicological Research, US Food and Drug
         Administration, Jefferson, AK, USA

         National Chemicals Inspectorate, Solna, Sweden

         National Industrial Chemicals Notification and Assessment Scheme
         (NICNAS), Sydney, Australia

         National Institute for Occupational Safety and Health,
         Cincinnati, OH, USA

         National Institute of Environmental Health Sciences, National
         Institutes of Health, Research Triangle Park, NC, USA

         University of Bielefeld, Bielefeld, Germany
    

    APPENDIX 5 -- CICAD FINAL REVIEW BOARD

    Sydney, Australia, 21-24 November 1999

    Members

    Dr R. Benson, Drinking Water Program, US Environmental Protection
    Agency, Region VIII, Denver, CO, USA

    Dr T. Berzins, National Chemicals Inspectorate (KEMI), Solna, Sweden

    Dr R.M. Bruce, National Center for Environmental Assessment, 
    US Environmental Protection Agency, Cincinnati, OH, USA

    Mr R. Cary, Health and Safety Executive, Merseyside, United Kingdom

    Dr R.S. Chhabra, National Institute of Environmental Health Sciences,
    National Institutes of Health, Research Triangle Park, NC, USA

    Dr S. Chou, Agency for Toxic Substances and Disease Registry, 
    Atlanta, GA, USA

    Dr S. Dobson, Institute of Terrestrial Ecology, Monks Wood,
    Cambridgeshire, United Kingdom

    Dr H. Gibb, National Center for Environmental Assessment, 
    US Environmental Protection Agency, Washington, DC, USA

    Dr R.F. Hertel, Federal Institute for Health Protection of Consumers
    and Veterinary Medicine, Berlin, Germany

    Dr J. Kielhorn, Fraunhofer Institute for Toxicology and Aerosol
    Research, Hannover, Germany

    Dr S. Kristensen, National Occupational Health and Safety Commission
    (Worksafe), Sydney, NSW, Australia

    Mr C. Lee-Steere, Environment Australia, Canberra, ACT, Australia

    Ms M. Meek, Environmental Health Directorate, Health Canada, Ottawa,
    Ontario, Canada

    Ms F. Rice, National Institute for Occupational Safety and Health,
    Cincinnati, OH, USA

    Dr J. Sekizawa, National Institute of Health Sciences, Tokyo, Japan

    Dr D. Willcocks, National Industrial Chemicals Notification and
    Assessment Scheme (NICNAS), Sydney, NSW, Australia  (Chairperson)

    Professor P. Yao, Institute of Occupational Medicine, Chinese Academy
    of Preventive Medicine, Beijing, People's Republic of China

    Observers

    Mr P. Howe, Institute of Terrestrial Ecology, Huntingdon,
    Cambridgeshire, United Kingdom

    Dr K. Ziegler-Skylakakis, GSF-Forschungszentrum für Umwelt und
    Gesundheit, GmbH, Oberschleissheim, Germany

    Secretariat

    Dr A. Aitio, International Programme on Chemical Safety, World Health
    Organization, Geneva, Switzerland

    Ms M. Godden, Health and Safety Executive, Bootle, Merseyside, United
    Kingdom

    Dr M. Younes, International Programme on Chemical Safety, World Health
    Organization, Geneva, Switzerland
    


        APPENDIX 6 -- INTERNATIONAL CHEMICAL SAFETY CARD
                                                                                                                

    CHLORAL HYDRATE                                                                   ICSC: 0234

                                                                                    October 1999

                                                                                                                
    CAS#             302-17-0           Trichloroacetaldehyde monohydrate
    RTECS#           FM8750000           2,2,2-Trichloro-1,1-ethanediol
    UN#              2811                  C2H3Cl3O2/Cl3CCH(OH)2
    EC#              605-014-00-6
                                              Molecular mass: 165.4
                                                                                                                
    TYPES OF HAZARD        ACUTE HAZARDS/             PREVENTION               FIRST AID / FIRE
    / EXPOSURE             SYMPTOMS                                            FIGHTING
                                                                                                                
    FIRE                   Not combustible.                                    In case of fire in the
                           Gives off irritating                                surroundings, all
                           or toxic fumes                                      extinguishing agents allowed.
                           (or gases) in a
                           fire.
                                                                                                                
    EXPLOSION                                                                  In case of fire: keep drums, 
                                                                               etc., cool by spraying with
                                                                               water.
                                                                                                                
    EXPOSURE                                          PREVENT DISPERSION
                                                      OF DUST!
                                                                                                                
    Inhalation             Confusion.                 Local exhaust            Fresh air, rest. Artificial
                           Drowsiness.                or breathing             respiration if indicated. Refer
                           Nausea.                    protection.              for medical attention.
                           Unconsciousness.
                                                                                                                
    Skin                   Redness.                   Protective gloves.       Rinse skin with plenty
                                                                               of water or shower.
                                                                                                                

                                                                                                                
    Eyes                   Redness.                   Safety spectacles or     First rinse with plenty
                                                      eye protection in        of water for several minutes
                                                      combination with         (remove contact lenses if
                                                      breathing protection     easily possible), then take
                                                      if powder.               to a doctor.
                                                                                                                
    Ingestion              Abdominal pain.            Do not eat, drink, or    Rinse mouth. Give a slurry of
                           Vomiting (further          smoke during work.       activated charcoal in water
                           see inhalation).           Wash hands before        to drink. Refer for medical
                                                      eating.                  attention.
                                                                                                                
    SPILLAGE DISPOSAL                                 PACKAGING & LABELLING
                                                                                                                

    Sweep spilled substance into containers;          Do not transport with food and feedstuffs.
    if appropriate, moisten first to prevent          EU Classification
    dusting. Carefully collect remainder, then        Symbol: T
    remove to safe place.                             R: 25-36/38
    (Extra personal protection: P3 filter             S: (1/2-)25-45
    respirator for toxic particles).                  UN Classification
                                                      UN Hazard Class: 6.1
                                                                                                                

    EMERGENCY RESPONSE                                STORAGE
                                                                                                                
    Transport Emergency Card: TEC (R)-61G12b          Separated from strong bases,
                                                      food and feedstuffs.





                                                                                                                

                                                                                                                
                                     IMPORTANT DATA
                                                                                                                

    PHYSICAL STATE; APPEARANCE:                       ROUTES OF EXPOSURE:
    TRANSPARENT, COLOURLESS CRYSTALS, WITH            The substance can be absorbed
    CHARACTERISTIC ODOUR.                             into the body by inhalation of
                                                      its aerosol and by ingestion.

    CHEMICAL DANGERS:                                 INHALATION RISK:
    The substance decomposes on heating               A harmful contamination of the air will be
    producing toxic and corrosive fumes including     reached rather slowly on evaporation of this
    hydrogen chloride. Reacts with strong bases       substance at 20°C.
    producing chloroform.                             
                                                      
    OCCUPATIONAL EXPOSURE LIMITS:                     EFFECTS OF LONG-TERM OR REPEATED EXPOSURE:
    TLV not established.                              The substance irritates the eyes, the skin
                                                      and the respiratory tract. The substance
                                                      may cause effects on the central nervous
                                                      system, cardiovascular system, liver and
                                                      kidneys, resulting in lowering of
                                                      consciousness, cardiac disorders and impaired
                                                      functions. Exposure at high levels may result
                                                      in unconsciousness.

                                                                                                                

                                   PHYSICAL PROPERTIES
                                                                                                                
    Boiling Point:         97°C
    Melting Point:         57-60°C
    Density:               1.9 g/cm3
    Solubility in water:   very good
    Octanol/water partition coefficient as log Pow: 0.99
                                                                                                                

                                                                                                                
                                  ENVIRONMENTAL DATA
                                                                                                                

    This substance may be hazardous to the environment; special attention should
    be given to water organisms.
                                                                                                                
                                          NOTES
                                                                                                                
    Use of alcoholic beverages enhances the harmful effect.
                                                                                                                
                                  ADDITIONAL INFORMATION
                                                                                                                















                                                                                                                
    LEGAL NOTICE        Neither the CEC nor the IPCS nor any person acting on
                        behalf of the CEC or the IPCS is responsible for the use
                        which might be made of this information.
                                                                                                                
    

    RÉSUMÉ D'ORIENTATION

         Le présent CICAD relatif à l'hydrate de chloral a été préparé par
    l'Environmental Protection Agency des États-Unis (EPA) sur la base
    d'un de ses documents intitulé  Toxicological review on chloral
     hydrate (US EPA, 2000). Les données qu'il contient proviennent d'un
    dépouillement de la littérature scientifique jusqu'en mars 1999. On
    trouvera à l'appendice 3 des renseignements sur la manière dont
    l'étude bibliographique a été effectuée et sur les sources de données
    disponibles. L'appendice 4 donne des indications sur les modalités
    d'examen du présent CICAD par des pairs. Ce CICAD a été approuvé en
    tant qu'évaluation internationale lors d'une réunion du Comité
    d'évaluation finale qui s'est tenue à Sydney (Australie) du 21 au 24
    novembre 1999. La liste des participants à cette réunion figure à
    l'appendice 5. La Fiche internationale sur la sécurité chimique (ICSC
    0234) de l'hydrate de chloral établie par le Programme international
    sur la sécurité chimique est reproduite à l'appendice 6 (IPCS, 1993).

         La synthèse de l'hydrate de chloral (No CAS 302-17-0) s'effectue
    par chloration de l'éthanol. On l'utilise en médécine humaine et
    vétérinaire comme sédatif et hypnotique. Le chloral, qui en est la
    forme anhydre (No CAS 75-87-6) est utilisé comme intermédiaire dans la
    synthèse du DDT, du méthoxychlore, du naled, du trichlorfon, du
    dichlorvos et de l'acide trichloracétique.

         La principale voie d'exposition de la population générale est
    l'eau de boisson, car il se forme de l'hydrate de chloral lors de la
    désinfection de l'eau par le chlore. Aux États-Unis, la concentration
    habituelle d'hydrate de chloral dans l'eau des réseaux publics de
    distribution est de 5 µg/litre. Comme ce composé est un métabolite du
    trichloréthylène et du tétrachloréthylène, la population se trouve
    exposée à l'hydrate de chloral si elle l'est à ces deux composés. Par
    ailleurs, il y a également exposition à deux métabolites de l'hydrate
    de chloral, les acides dichlor- et trichloracétique, du fait que ces
    deux composés se forment également dans l'eau de consommation lors de
    sa désinfection par le chlore. Lorsque l'hydrate de chloral est
    utilisé comme sédatif, la dose habituelle est de 250 mg trois fois par
    jour (soit l'équivalent de 10,7 mg/kg de poids corporel par jour).
    C'est un métabolite, le trichloréthanol, qui est responsable de
    l'effet pharmacologique. On ne dispose d'aucune donnée quantitative
    sur l'exposition professionnelle.

         L'hydrate de chloral est irritant pour la peau et les muqueuses
    et il provoque souvent des troubles gastriques, des nausées et des
    vomissements lorsqu'on l'utilise à la dose recommandée dans la
    pratique clinique. Une surdose aiguë entraîne progressivement ataxie,
    léthargie, coma profond, dépression respiratoire, hypotension et
    arrythmie cardiaque. On a trouvé des signes de lésions hépatiques chez
    des sujets ayant échappé de peu à la mort par intoxication aiguë due
    une surdose, mais rien ne prouve par contre de façon convaincante qu'à
    la dose clinique recommandée, le composé entraîne des lésions

    hépatiques. Plusieurs études portant sur l'utilisation clinique de
    l'hydrate de chloral ont mis en évidence des effets secondaires
    mineurs et peu fréquents. Bien que ce produit soit utilisé depuis
    longtemps en médecine, aucune étude toxicologique contrôlée sur des
    sujets humains n'a été publiée.

         L'hydrate de chloral est intégralement absorbé et rapidement
    métabolisé après administration par la voie orale. Ses principaux
    métabolites sont le trichloréthanol et son glucuronide ainsi que
    l'acide trichloracétique. D'après certaines données, il pourrait se
    former également un peu d'acide dichloracétique. Chez l'Homme, la
    demi-vie du trichloréthanol et de son glucuronide est d'environ 8 h;
    celle de l'acide trichloracétique est à peu près égale à 4 jours. Un
    certain nombre de données incitent à penser que la demi-vie du
    trichloréthanol est plus de deux fois plus longue chez les prématurés
    et les nouveau-nés à terme que chez les enfants en bas âge et les
    adultes. La principale voie d'excrétion des métabolites de l'hydrate
    de chloral est la voie urinaire. On peut le retrouver, accompagné de
    ses métabolites, dans le lait de mères traitées par ce produit.
    Toutefois leur concentration est trop faible pour avoir des effets
    pharmacologiques chez les nourrissons alimentés au sein.

         Administré à des souris, le composé provoque une perte de
    coordination (ataxie) à une dose comparable à celle qui produit le
    même effet chez l'Homme. Une étude de 90 jours sur des souris n'a
    révélé aucun signe d'altération du comportement ni de neurotoxicité.
    Des études au long cours sur des rats et des souris n'ont pas non plus
    permis de constater d'anomalies comportementales ni de modifications
    histopathologiques touchant les tissus nerveux. Après exposition de
    souris pendant 90 jours, on a observé une légère diminution de
    l'immunité humorale. D'autres études n'ont mis en évidence aucun effet
    sur le développement des souris et des rats. Aucune anomalie
    structurale n'a été relevée. Une étude consacrée à l'action de
    l'hydrate de chloral sur le développement nerveux de la souris n'a mis
    en évidence qu'un léger effet sur l'apprentissage de l'évitement
    passif. Le composé n'a pas fait l'objet d'études de toxicité génésique
    sur deux générations, mais les données dont on dispose sur l'activité
    génésique des animaux et les effets sur les spermatozoïdes et les
    ovocytes ne permettent pas de penser que l'hydrate de chloral puisse
    avoir des effets majeurs sur la reproduction. Par ailleurs, les études
    chroniques et subchroniques effectuées sur des rongeurs n'ont pas mis
    en évidence d'effets histopathologiques au niveau de l'appareil
    reproducteur. Toutes les études effectuées sur des animaux de
    laboratoire mettent en évidence un certain nombre d'effets, mais à
    l'exclusion de tout effet cancérogène et à des doses qui sont très
    supérieures à celle qui provoque la sédation chez l'Homme.

         En ce qui concerne l'Homme, on ne possède aucune donnée de
    cancérogénicité. Deux tests biologiques effectués sur le rat ne
    révèlent aucune augmentation de la fréquence des tumeurs, quelle que
    soit la localisation. Par contre, dans trois autres tests distincts
    effectués sur des souris mâles, on constate une augmentation de
    l'incidence des tumeurs hépatiques. Celle de ces études dont le

    caractère est le plus définitif indique une augmentation de
    l'incidence et de la multiplicité des tumeurs pour chacune des trois
    doses utilisées. Ces données semblent indiquer que le produit est
    cancérogène chez la souris mâle mais on estime qu'elles ne permettent
    pas d'évaluer le risque pour l'Homme avec une réponse linéaire aux
    faibles doses.1

         Il existe une importante base de données sur les effets
    génotoxiques. Divers résultats indiquent que l'hydrate de chloral est
    faiblement mutagène et clastogène. Il provoque une aneuploïdie chez
    des cellules très diverses. On pense que cet effet est dû à
    destruction de l'appareil fusorial. Des concentrations élevées sont
    nécessaires pour que ces effets soient observables. Même si ces
    résultats donnent à penser que la toxicité de l'hydrate de chloral
    s'exerce notamment au niveau des gènes, ils montrent également que ces
    effets ne se produisent qu'à des concentrations qui ont peu de chances
    d'exister dans les conditions physiologiques, compte tenu de
    l'exposition habituelle à ce produit dans l'environnement. La
    formation des tumeurs hépatiques chez la souris mâle peut s'expliquer
    par la formation d'adduits de l'ADN avec des radicaux libres produits
    lors de la métabolisation de l'hydrate de chloral par les enzymes du
    cytochrome P450 2E1 (CYP 2E1) ou par une cytotoxicité conduisant à une
    hyperplasie compensatoire.

         La dose journalière tolérable pour les effets non cancérogènes a
    été estimée à 0,1 mg/kg pc à partir de la dose la plus faible
    produisant un effet sédatif observable chez l'Homme (LOAEL), dose qui
    est égale à 10,7 mg/kg par jour, avec un facteur d'incertitude de 100.

         On ne possède que des données limitées sur les effets
    environnementaux. Les méthanotrophes sont capables de transformer
    l'hydrate de chloral en trichloréthanol et en acide trichloracétique.
    Le composé subit également une dégradation abiotique dans certaines
    conditions. On dispose de données limitées sur l'inhibition de la
    croissance des bactéries, des algues et des protozoaires. Des
    résultats sont également disponibles concernant l'effet du composé sur
    le développement des oursins. On ne possède pas assez de données pour
    pouvoir évaluer le risque que l'hydrate de chloral représente pour
    l'environnement.

                  

    1 Un test biologique effectué dans le cadre du Programme national de
      toxicologie et dont les résultats n'ont été connus qu'après la 
      réunion du Comité d'évaluation finale, a montré que l'incidence des 
      tumeurs hépatiques était en augmentation chez les souris mâles et 
      que chez les femelles, il y avait une faible augmentation des 
      adénomes hypophysaires, augmentation dont la signification 
      statistique était limite.
    

    RESUMEN DE ORIENTACI²N

         Este CICAD sobre el hidrato de cloral, preparado por la Agencia
    para la Protección del Medio Ambiente (EPA), se basó en el
     Examen toxicológico sobre el hidrato de cloral de la EPA de los
    Estados Unidos (US EPA, 2000). Se incluyó la bibliografía científica
    localizada hasta marzo de 1999. La información relativa al carácter de
    los procesos de examen y a la disponibilidad del documento original
    figura en el apéndice 3. La información sobre el examen colegiado de
    este CICAD se presenta en el apéndice 4. Este CICAD se aprobó como
    evaluación internacional en una reunión de la Junta de Evaluación
    Final celebrada en Sydney, Australia, los días 21-24 de noviembre de
    1999. En el apéndice 5 figura la lista de participantes en esta
    reunión. La Ficha internacional de seguridad química (ICSC 0234) para
    el hidrato de cloral, preparada por el Programa Internacional de
    Seguridad de la Sustancias Químicas, se reproduce en el apéndice 6
    (IPCS, 1993).

         El hidrato de cloral (CAS No 302-17-0) se sintetiza mediante la
    cloración de etanol. Se utiliza en la medicina humana y veterinaria
    como sedante e hipnótico. El cloral (CAS No 75-87-6), producto
    químico anhidro, se utiliza como intermediario en la síntesis de DDT,
    metoxicloro, naled, triclorfon, diclorvos y ácido tricloroacético.

         La vía principal de exposición del público general es el agua de
    bebida, puesto que al desinfectar dicha agua con cloro se forma
    hidrato de cloral. La concentración normal de hidrato de cloral en el
    sistema público de abastecimiento de agua de los Estados Unidos es 5
    µg/litro. Debido a que el hidrato de cloral es un metabolito del
    tricloroetileno y el tetracloroetileno, el público estará expuesto al
    hidrato de cloral si lo está a estos productos químicos. La población
    está expuesta a los ácidos tricloroacético y dicloroacético,
    metabolitos del hidrato de cloral, porque también se forman cuando se
    desinfecta el agua de bebida con cloro. En su uso como sedante humano,
    la dosis clínica normal es de 250 mg tres veces al día (equivalente a
    10,7 mg/kg de peso corporal al día). El metabolito tricloroetanol es
    el responsable del efecto farmacológico. No se dispone de información
    cuantitativa relativa a la exposición ocupacional.

         El hidrato de cloral es irritante de la piel y las membranas
    mucosas y con frecuencia provoca trastornos gástricos, náuseas y
    vómitos con la dosis clínica recomendada. Una sobredosis aguda produce
    (en orden de progresión) ataxia, letargo, coma profundo, depresión
    respiratoria, hipotensión y arritmia cardíaca. Hay algunas pruebas de
    lesiones hepáticas en personas que sobreviven a sobredosis agudas casi
    letales, pero no hay pruebas convincentes de que se produzcan tales
    lesiones con la dosis clínica recomendada. En varios estudios sobre el
    uso clínico del hidrato de cloral se ha puesto de manifiesto una
    incidencia baja de efectos secundarios menores. A pesar de utilizarse
    desde hace mucho tiempo en la medicina humana, no hay información
    publicada sobre la toxicidad en estudios controlados realizados con
    personas después de una exposición prolongada.

         Tras la administración oral, el hidrato de cloral se absorbe
    completamente y se metaboliza con rapidez. Los principales metabolitos
    son el tricloroetanol y su glucurónido y el ácido tricloroacético.
    Algunos datos parecen indicar que se puede formar una pequeña cantidad
    de ácido dicloroacético. En el ser humano, la semivida del
    tricloroetanol y su glucurónido es de unas ocho horas; la semivida del
    ácido tricloroacético es de alrededor de cuatro días. Algunos datos
    indican que la semivida del tricloroetanol aumenta varias veces en los
    niños prematuros y los nacidos a término en comparación con los niños
    que empiezan a caminar y los adultos. La vía principal de excreción de
    los metabolitos del hidrato de cloral es la orina. Se han detectado
    hidrato de cloral y sus metabolitos en la leche de mujeres tratadas
    con este producto. Sin embargo, su concentración es demasiado baja
    para provocar un efecto farmacológico en los niños lactantes.

         La administración aguda de hidrato de cloral a ratones provoca la
    pérdida de la coordinación (ataxia) con una exposición prácticamente
    semejante a la de las personas para el mismo efecto. En un estudio de
    90 días en ratones no se obtuvieron pruebas de cambios de
    comportamiento u otros signos de neurotoxicidad. En estudios crónicos
    con ratas y ratones no se detectaron cambios de comportamiento ni
    cambios histopatológicos en el tejido nervioso. Tras la exposición de
    ratones durante 90 días al hidrato de cloral se observó una ligera
    disminución en la inmunidad humoral. Se han realizado pruebas con
    hidrato de cloral para estudiar sus efectos en el desarrollo de ratas
    y ratones. No se observaron anomalías estructurales. En un estudio del
    neurodesarrollo en ratones, se observó un ligero efecto en el
    aprendizaje de la evitación pasiva. Aunque no se ha realizado ningún
    estudio de reproducción de dos generaciones con hidrato de cloral, los
    datos sobre el rendimiento reproductivo y sobre sus efectos en el
    esperma y los oocitos no indican que haya probabilidad de que la
    toxicidad reproductiva sea un efecto crítico. Además, en estudios
    subcrónicos o crónicos no se observaron efectos histopatológicos en
    los órganos reproductores de roedores. En todos los estudios
    realizados con animales de laboratorio se detectaron efectos en la
    salud distintos del cáncer con una exposición muy superior a la eficaz
    para la sedación humana.

         No hay datos de carcinogenicidad en el ser humano. En dos
    biovaloraciones en ratas no se observó un aumento de tumores en
    ninguna parte. En tres biovaloraciones separadas en ratones machos se
    detectó un aumento de la incidencia de tumores hepáticos. El más
    definitivo de estos estudios demostró una mayor incidencia y
    multiplicidad de tumores hepáticos en cada una de las tres
    exposiciones. Estos datos parecen indicar la existencia de

    carcinogenicidad en ratones machos, pero no se consideran adecuados
    para realizar una evaluación del riesgo en la salud humana con una
    respuesta lineal para una exposición baja.1

         Hay una amplia base de datos sobre la toxicidad genética.
    Diversos resultados ponen de manifiesto que el hidrato de cloral tiene
    una actividad mutagénica de los genes y clastogénica débil. El hidrato
    de cloral induce aneuploidía en una gran variedad de tipos de células.
    Se considera que estos últimos efectos se deben a una perturbación del
    huso acromático. Se necesitan concentraciones altas de hidrato de
    cloral para provocar efectos observables. Aunque estos datos parecen
    indicar que la genotoxicidad puede desempeñar una función en la
    toxicidad del hidrato de cloral, también ponen de manifiesto que estos
    efectos requieren concentraciones que no es probable que se alcancen
    en condiciones fisiológicas con las exposiciones que se producen
    normalmente a partir del medio ambiente. Algunos mecanismos probables
    para la inducción de tumores hepáticos en ratones machos son la
    formación de aductos de ADN mediante radicales libres generados en el
    metabolismo del hidrato de cloral en el citocromo P450 2E1 (CYP2E1) y
    la citotoxicidad que da lugar a una hiperplasia compensatoria.

         Se estimó una ingesta tolerable para los efectos en la salud
    distintos del cáncer de 0,1 mg/kg de peso corporal al día a partir de
    la concentración más baja con efectos adversos observados (LOAEL) para
    la sedación en las personas de 10,7 mg/kg, utilizando un factor de
    incertidumbre total de 100.

         Sólo se dispone de datos limitados sobre los efectos en el medio
    ambiente. Los organismos metanotróficos pueden convertir el hidrato de
    cloral en tricloroetanol y ácido tricloroacético. El hidrato de cloral
    experimenta asimismo degradación abiótica en algunas condiciones. Hay
    datos limitados sobre la inhibición del crecimiento de bacterias,
    algas y protozoos y sobre los efectos en el desarrollo de los erizos
    de mar. No hay datos disponibles suficientes que permitan evaluar el
    riesgo para el medio ambiente derivado del hidrato de cloral.

                  

    1 En una biovaloración de la carcinogenicidad en ratones del
      Programa Nacional de Toxicología, disponible después de la reunión 
      de la Junta de Evaluación Final, los machos presentaban una mayor
      incidencia de tumores hepáticos y las hembras un pequeño aumento 
      de la incidencia de adenomas hipofisiarios, en el límite de la 
      significación estadística.
    


    See Also:
       Toxicological Abbreviations
       Chloral hydrate (ICSC)