First draft prepared by
    Dr J.C. Larsen
    Institute of Toxicology
    National Food Agency of Denmark
    Soborg, Denmark


         1,2-Dichloroethane was evaluated for an acceptable daily intake
    at the fourteenth meeting of the Committee (Annex 1, reference 22).
    The Committee was of the opinion that the use of 1,2-dichloroethane
    as an extraction solvent should be restricted to that determined by
    observing good manufacturing practice, which was expected to result
    in minimal residues unlikely to have any toxicological effect. A
    toxicological monograph was prepared (Annex 1, reference 23).
    1,2-Dichloroethane was again evaluated at the twenty-third meeting
    of the Committee (Annex 1, reference 50). Based on new bioassays
    indicating that it is carcinogenic in the rat and mouse, the
    Committee considered that it was not suitable for use as a food
    additive. No toxicological monograph was prepared.

         An Environmental Health Criteria Document on 1,2-dichloroethane
    has been published by WHO under the International Programme on
    Chemical Safety (IPCS) (WHO, 1987). Guidelines for the evaluation of
    solvents used in food processing have been published by WHO under
    the IPCS (Annex 1, reference 76).

         1,2-Dichloroethane has been reviewed by the International
    Agency for Research on Cancer (IARC, 1979).

         At its thirty-fifth meeting (Annex 1, reference 88) the
    Committee during its deliberations on specifications for spice
    oleoresins considered solvent residues and expressed the opinion
    that the use of 1,2-dichloroethane as an extraction solvent should
    be discouraged because of toxicological concerns. Because this and
    other solvents had not been recently evaluated and new data had
    become available, the Committee concluded that an overall review of
    solvents used in food processing would be appropriate. The Committee
    further stressed that levels of residues resulting from the use of
    any solvent should be both toxicologically insignificant and the
    minimum technically achievable.

         Since the last review additional data on 1,2-dichloroethane
    have become available and are summarized and are discussed in the
    following monograph addendum.


    2.1  Biochemical aspects

    2.1.1  Absorption, distribution, and excretion

         After oral exposure of Sprague-Dawley rats to 25, 50, or 150 mg
    of 1,2-dichloroethane/kg bw in corn oil, peak levels of the parent
    compound in adipose tissue at 45-60 min exceeded those in blood by
    4-8 times. Peak levels in the liver, after 10 min, exceeded those in
    blood by 1-2 times. The half-lives in the blood increased from 25
    min in the rats given 25 mg/kg bw to 57 min at 150 mg/kg bw. The
    concentrations in blood, and especially in adipose tissue and liver,
    were lower than expected at the two higher doses indicating
    saturation of the tissues and of gastrointestinal absorption at
    higher doses (Spreafico  et al., 1980).

         [14C]-1,2-Dichloroethane was extensively metabolized after
    administration to groups of four male Osborne-Mendel rats by gavage
    (150 mg/kg bw in corn oil) or by inhalation (100 ppm, 6 h). No
    significant differences were observed in the route of excretion of
    non-volatile metabolites after 48 h. In each case approximately 85%
    of the total metabolites appeared in the urine, while 7-8, 4, and 2%
    were found in the exhaled carbon monoxide, carcass, and faeces,
    respectively. The major urinary metabolites were thiodiacetic acid
    and thiodiacetic acid sulfoxide. After 48 h remaining radioactivity
    was distributed rather evenly among liver, kidney, lung, spleen,
    forestomach, and stomach. Most radioactivity appeared to be bound
    irreversibly to macromolecules, mainly proteins, as judged by
    studies conducted 4-6 h after administration by either route,
    whereas the amounts bound to DNA were low, although DNA alkylation
    after gavage was five times higher than after inhalation. Based on
    modelling of the pharmacokinetic data, it appeared that the
    elimination of 1,2-dichloroethane may become saturated when high
    blood levels are produced, and this is more likely to occur after
    gavage than after inhalation (Reitz  et al., 1982).

         When given by gavage at a dose of 100 mg/kg bw to groups of
    five male Wistar rats, 1,2-dichloroethane was more easily absorbed
    from the gastro-intestinal tract when administered in aqueous
    solution than in corn oil. Serial blood samples collected over a
    five-hour period showed that the peak concentration of
    1,2-dichloroethane was about five times higher following oral
    administration in water than when given in corn oil. Furthermore,
    the time taken to reach peak level was approximately three times
    longer when the compound was administered in corn oil as compared to
    water (Withey  et al., 1983).

         1,2-Dichloroethane in corn oil was given by gavage to groups of
    4 male B6C3F1 mice and Osborne-Mendel rats (4-6 weeks old) 5
    days/week at dose levels of 37.5 and 150 mg/kg bw/day (mice) or 25
    and 100 mg/kg bw/day (rats). After 4 weeks the animals were dosed
    with 1,2-[14C]-dichloroethane and placed in metabolism cages for
    48 h. The metabolic disposition was very similar in the two species.
    The majority of the radioactivity was recovered from the urine as
    metabolites (81.9 (mouse) and 69.5 (rat)% of the dose). In the mouse
    25.9% (18.2% as carbon dioxide) and in the rat 19.7% (11.5% as
    carbon dioxide) was found in the exhaled air. An additional 2.4%
    (mouse) and 7.1% (rat) of the dose was recovered from the carcass
    after 48 h. Hepatic protein binding (nanomole equivalents bound to
    1 mg of liver protein) was 0.14 at the low-dose level and 0.52 at
    the high-dose level in the mouse and 0.18 and 1.07 in the rat. The
    urinary metabolite patterns of the compound examined by HPLC
    appeared to be similar in both species (Mitoma  et al., 1985).

         Bile collected from isolated perfused livers from male Wistar
    rats was highly mutagenic towards  Salmonella typhimurium TA1535
    15-30 min after the addition of 1,2-dichloroethane to the perfusion
    medium. No mutagenic activity was detected when 2-chloroethanol was
    tested. When groups of 5 male CBA mice were given intraperitoneal
    injections of 80 mg of 1,2-dichloroethane/kg bw the pooled bile
    collected after 30 and 60 min also showed mutagenicity in
     Salmonella typhimurium TA1535 (Rannug & Beije, 1979).

         Groups of five female Sprague-Dawley rats, on the 17th day of
    pregnancy, were exposed for five hours to 0, 153, 305, 552, 1039,
    1509, or 1999 ppm of 1,2-dichloroethane. Immediately following
    exposure, the concentrations of 1,2-dichloroethane were determined
    in each fetus and in the maternal blood. Fetal weights and fetal
    concentrations were related to their position on the two horns of
    the uterus. A linear decrease was observed in fetal concentration of
    1,2-dichloroethane with the location of the fetus from the ovarian
    to the cervical end of the uterine horns. This relationship was
    consistent across doses. Good linear relationships were observed
    between the mean fetal concentrations and the maternal blood
    concentrations with exposure level (Withey & Karpinski, 1985).

         Two groups of six weanling male Sprague-Dawley rats were
    exposed in glass chambers to 0 or 150 ppm of 1,2-dichloroethane (7 h
    per day, 5 days per week) for 35 days. A third group of six rats was
    treated similarly with 1,2-dichloroethane, but in addition given a
    diet containing 0.15% of disulfiram for 55 days, 10 of these prior
    to the beginning of the experiment. A fourth group of rats was
    treated with disulfiram only. At the end of the treatment period
    (day 36) the rats were given an intraperitoneal dose of 150 mg of
    [U-1,2-14C]-dichloroethane/kg bw and transferred to metabolism
    cages for collection of urine and faeces. Three rats from each group

    were sacrificed after 4 and 24 h. The distribution and presence of
    metabolites of 1,2-dichloroethane and their binding to an
    acid-insoluble extract of the tissues, as well as purified protein
    and DNA, were evaluated. Dietary disulfiram was found to modulate
    the distribution, excretion, and macromolecular binding of
    1,2-dichloroethane and/or its metabolites at 4 and 24 h following
    intraperitoneal administration. The distribution of radioactivity in
    the lung, liver, spleen, kidney, testis, blood, heart, and fat as
    well as the urinary excretion of labelled metabolites was not
    affected by subchronic inhalation exposure to non-radiolabelled
    1,2-dichloroethane. However, disulfiram pretreatment increased the
    fat deposition of 1,2-dichloroethane and decreased the urinary
    excretion of its metabolites. Disulfiram also increased the binding
    of 1,2-dichloroethane metabolites to DNA and decreased the binding
    to protein in the liver, kidneys, spleen, and testes. However, prior
    exposure to 1,2-dichloroethane alone increased the binding of its
    metabolites to DNA in the kidneys only (Igwe  et al., 1986c).

         Seven female C57BL mice were injected intravenously with
    0.73 mg of 14C-labelled 1,2-dichloroethane/kg bw and killed after
    1 or 5 min, 1, 4, or 24 h, or after 4 days. As shown by whole-body
    autoradiography with heated and organic solvent-extracted tissue
    sections a selective localization of non-volatile and bound
    metabolites occurred in the nasal olfactory mucosa and the
    tracheobronchial epithelium. Low levels of metabolites were also
    present in the epithelia of the upper alimentary tract, vagina and
    eyelid, and in the liver and kidney. A decreased mucosal and
    epithelial binding was observed after pre-treatment with metyrapone,
    indicating that the binding might be due to an oxidative metabolism
    of 1,2-dichloroethane.  In vitro experiments with 1000 g
    supernatants from various tissues showed that the nasal mucosa has a
    marked ability to activate 1,2-dichloroethane into products that
    become irreversibly bound to the tissue (Brittebo  et al., 1989).

    2.1.2  Biotransformation

         14C-Labelled 1,2-dichloroethane was given by intraperitoneal
    injections to female albino mice at doses of 50, 100, 140, and
    170 mg/kg bw. Mice were placed in metabolism cages for 3 days. Ten
    to 42% of the 1,2-dichloromethane was expired unchanged and 12-15%
    as carbon dioxide. Fifty one to 73% was found in the urine, 0.6-1.3%
    in the faeces, and 0-0.6% remained in the body. The following
    metabolites were identified in the urine: chloroacetic acid,
    S-carboxymethylcysteine, and thiodiacetic acid. Traces of
    2-chloroethanol and S,S'-ethylene-bis-cysteine were also found in
    the urine (Yllner, 1971).

         Groups of 4 male Sprague-Dawley rats were exposed by inhalation
    to 0, 153, 304 or 455 ppm of 1,2-dichloroethane (corresponding to 0,
    98, 194, or 291 mg/kg bw/day), 7 h/day, 5 days/week, for 30 exposure
    days. Urinary levels of thioethers, indicative of 1,2-dichloroethane
    metabolites, were determined during the study. The groups treated at
    different concentrations showed parallel excretion patterns
    throughout the exposure period. Steady state urinary thio-compound
    excretion occurred by day 22 (Igwe  et al., 1988).

         Liver cytosolic preparations from male Sprague-Dawley rats were
    able to metabolize 1,2-dichloroethane into ethylene. The production
    of ethylene was highly dependent on the presence of reduced
    glutathione (Livesey & Anders, 1979).

         When incubated with glutathione and liver cytosol from male
    Long-Evans rats, meso-1,2-dideutero-1,2-dichloroethane was converted
    exclusively to (Z)-1,2-dideuteroethylene, determined by gas
    chromatography. The stereo-chemical configuration of the
    1,2-dideuteroethylene was determined by Fourier-transform infrared
    spectroscopy. These results suggest that 1,2-dichloroethane
    metabolism to ethylene proceeds by a substitution-elimination
    mechanism, involving a nucleophilic attack of glutathione on the
    substrate resulting in S-(beta-chloroethyl)glutathione formation
    followed by a subsequent attack of a second thiol on the sulfur atom
    of the conjugate. This latter reaction yields glutathione disulfide,
    ethylene, and chlorine ion. This result is consistent with the
    formation of ethylene-S-glutathionylepisulfonium ion, a possible
    reactive species involved in 1,2-dichloroethane mutagenicity
    (Livesey  et al., 1982).

         1,2-Dichloroethane was metabolized by microsomal and cytosolic
    fractions from livers of phenobarbital-induced male Sprague-Dawley
    rats to nonvolatile products and to products irreversibly bound to
    protein and added DNA. Cytosolic metabolism was dependent on the
    presence of reduced glutathione. Microsomal metabolism to all three
    types of products occurred via mixed function oxidases; the
    formation of metabolites that bound to DNA was catalyzed by
    microsomal glutathione transferases. 2-Chloroacetaldehyde,
    S-(2-chloroethyl)-glutathione, and 1-chlorosoethane were suggested
    as major species involved in the irreversible binding. Only the
    cytosolic glutathione system produced metabolites that were
    mutagenic in  Salmonella typhimurium TA1535 (Guengerich  et al.,

         The activation of 1,2-dichloroethane to metabolites mutagenic
    in  Salmonella typhimurium TA1535 was enhanced by the
    postmitochondrial fraction from livers of male Sprague-Dawley rats
    but was non-microsomal and NADPH-independent. The activation was

    further enhanced by the addition of reduced glutathione, but not by
    L-cysteine, N-acetyl-L-cysteine or 2-mercaptoethanol. A synthetic
    conjugate, S-(2-chloroethyl)-L-cysteine gave a strong direct
    mutagenic effect (Rannug  et al., 1978).

         The stimulation of rat liver microsomal carbon
    monoxide-inhibitable NADPH oxidation by 1,2-dichloroethane was
    enhanced by induction with phenobarbital but not with
    beta-naphthoflavone. Incubation of 1,2-dichloroethane with hepatic
    microsomes from phenobarbital-treated rats, NADPH-generating system
    and EDTA resulted in the conversion to chloro-acetaldehyde and to a
    lesser extent to chloroacetic acid and probably 2-chloroethanol. In
    addition, reaction mixtures constituted as described above resulted
    in slight but significant losses (ca. 13%) of hepatic microsomal
    cytochrome P-450. The omission of 1,2-dichloroethane or the NADPH-
    generating system from incubation mixtures eliminated the above
    effects, and SKF-525A or carbon monoxide diminished or eliminated
    the effects (McCall  et al., 1983).

         The metabolic rate of 1,2-dichloroethane was measured  in vitro
    with the 10 000 g supernatant fraction of livers from male Wistar
    rats (n=5) that had consumed ethanol for 3 weeks in combination with
    various diets. Ethanol increased the metabolism of
    1,2-dichloroethane. A decrease in carbohydrate intake augmented the
    action of ethanol in a dose-related manner (Sato  et al., 1983).

         The effects of food deprivation, carbohydrate restriction and
    ethanol consumption on the metabolism of 1,2-dichloroethane in
    microsomal and cytosolic fractions of livers from male Wistar rats
    were compared with the effects of enzyme induction by phenobarbital
    (80 mg/kg bw per day for three days), polychlorinated biphenyl
    (a single dose of 500 mg/kg bw) and 3-methylcholanthrene (20 mg/kg
    bw per day for three days) on the metabolism of these compounds.
    None of these enzyme-inducing agents had any effect on the metabolic
    rate of 1,2-dichloroethane. In contrast, food deprivation,
    carbohydrate restriction and three-week ingestion of ethanol
    (2.0 g/day) each enhanced the metabolism with little or no increase
    in microsomal protein and cytochrome P-450 contents (Sato &
    Nakajima, 1985).

         Using isolated hepatocytes from male Wistar rats as a model
    system, and electron spin resonance spectroscopy coupled to the spin
    trapping technique as a detection technique, free radical production
    was only detectable under hypoxic conditions when 1,2-dichloroethane
    was added to the hepatocyte suspensions (Tomasi  et al., 1984).

         In contrast to the higher chlorinated ethanes
    1,2-dichloroethane did not undergo reductive metabolism during
    anaerobic incubations with liver microsomes from phenobarbital
    pretreated male Sprague-Dawley rats (Thompson  et al., 1984).

         1,2-Dichloroethane was converted to chloroacetaldehyde by
    hepatic nuclear cytochrome P-450 from phenobarbital pretreated male
    Long-Evans rats when incubated with the hepatic nuclei fraction and
    an NADPH-generating system plus EDTA. Carbon monoxide, an inhibitor
    of cytochrome P-450, diminished the production of
    chloroacetaldehyde. Although produced at a lower level the pathway
    for the formation of the metabolite by hepatic nuclear cytochrome
    P-450 was the same as for its production by hepatic microsomal
    cytochrome P-450. Nuclear cytochrome P-450 was degraded in the
    presence of 1,2-dichloroethane in an NADPH dependent process which
    was inhibited by carbon monoxide (Casciola & Ivanetich, 1984).

         Microsomal and cytosolic fractions isolated from liver, lung,
    kidneys, and stomach of phenobarbital pretreated Wistar rats or
    Balb/c mice were able to activate [U-14C]1,2-dichloroethane to
    forms able to bind covalently with DNA and protein  in vitro. Rat
    enzymes were generally more efficient than mouse enzymes in
    bioactivating 1,2-dichloroethane (Colacci  et al., 1985).

    2.1.3  Effects on enzymes and other biochemical parameters

         The effect of 1,2-dichloroethane and a series of other
    haloalkanes on hepatic triglyceride secretion was investigated in
    groups of 4 male Swiss-Webster mice given the test compound by
    gavage 2 h after an intravenous treatment with Triton WR 1339, which
    prevents the egress of triglycerides from serum. The dose which
    decreased triglyceride secretion 50% (ID50) was calculated to be
    400 mg/kg bw. It was demonstrated that a dose-related decrease in
    hepatic triglyceride secretion is a common effect produced by
    chlorinated alkanes. Using isolated hepatocytes from male
    Sprague-Dawley rats an ID50 of 14.9 mg/ml incubation medium was
    found and a positive correlation between chlorinated alkane potency
    and increasing solvent lipid solubility was observed. However, this
    order of potency did not correlate with  in vivo findings in which
    the less lipid soluble solvents were found to be the most potent
    (Selan & Evans, 1987).

         Groups of 8 male Sprague-Dawley rats were exposed to
    1,2-dichloroethane in inhalation chambers at concentrations of 0,
    618, 850, 1056, or 1304 ppm for 4 h or for 2 or 4 days (6 h daily).
    Serum enzyme activities were recorded as measures of liver damage.
    It appeared that a single exposure period induced more marked
    enhancement of serum activities than repeated exposures, and that
    glutaryl dehydrogenase and sorbitol dehydrogenase were more
    sensitive and more constant indices of hepatotoxicity than aspartate
    aminotransferase and alanine aminotransferase (Brondeau  et al.,

         Male Sprague-Dawley rats in groups of 6 were exposed by
    inhalation to 1,2-dichloroethane at 0, 153, 304, or 455 ppm (v/v),
    7 h/day for 5 days/week for 30 exposure days. Kidney, liver, spleen,
    and testes at exposure day 30 as well as progressive urine samples
    were examined for elemental content. Dose-related changes (r >
    0.8) in metal content were induced by 1,2-dichloroethane in the
    liver and in the spleen. In the liver P and Sr were increased, and
    decreases for Fe, Mg, and P were seen in the spleen (Hee  et al.,

         No differences were observed in the cytotoxicity (measured as
    cell survival) of 1,2-dichloroethane towards primary cultures of rat
    hepatocytes isolated from normal, partially hepatectomized, nor
    preneoplastic/neoplastic livers from male Fischer-344 rats.
    Preneoplastic/neoplastic lesions were induced by initiation with
    diethylnitrosamine and promoted with either 2 weeks of 0.02%
    2-acetylaminofluorene in the diet and a single gavage dose of carbon
    tetra-chloride, or with 500 ppm sodium phenobarbital in the drinking
    water for 24 weeks. Treatment with SKF-525A and diethyl maleate
    increased the cytotoxicity of 1,2-dichloroethane (Chang  et al.,

         When 1,2-dichloroethane was tested for cytotoxicity on cultured
    human epidermoid carcinoma cells and African green monkey kidney
    cells, ED50 were found to be 1500 µg/ml in the human cells and
    1000 µg/ml in the monkey cells (Mochida  et al., 1986).

         The pro-oxidant effects of 1,2-dichloroethane were assessed in
    cultured arterial endothelial and aortic smooth muscle cells.
    Exposure of the cells to 1,2-dichloroethane (6-40 µl/ml) alone did
    not increase the formation of thiobarbiturate-reactive products
    above background levels. However, in the presence of low levels of
    iron (3.1-25 µM Fe3+ chelated by ADP), 1,2-dichloroethane promoted
    lipid peroxidation up to 200% of control values (Tse  et al.,

    2.2  Toxicological studies

    2.2.1  Acute toxicity studies

         The available acute mortality data on 1,2-dichloroethane
    following oral and inhalation exposure have been summarized in WHO
    (1987). In the rat oral LD50 of 680 (corn oil) and 850 (vehicle
    not given) mg/kg bw have been reported. In the CD1 mouse oral
    LD50s of 489 (male) and 413 (female) mg/kg bw were reported.
    Exposure to a single high dose of 1,2-dichloroethane results in
    adverse effects on the central nervous system (depression), liver,
    kidneys, adrenals (haemorrhage), and lungs (oedema). The liver

    showed fatty changes and hepatocellular necrosis with haemorrhage,
    and the kidney damage consisted of haemorrhage and tubular necrosis.
    The injury to organs has been accompanied by increases in blood urea
    levels and levels of serum transaminase and increased lipid
    concentrations in the liver.

    2.2.2  Short-term toxicity studies  Rats

         Groups of 6 male rats were given diets containing approximately
    0, 20, or 40 mg of 1,2-dichloroethane/kg bw/day for 5 weeks, and
    100 mg/kg bw/day for 7 weeks. At the highest dose administered total
    fat and triglycerides were elevated in the liver (Alumot  et al.,

         The liver appeared to be the principal target organ following
    oral exposure. Rats, treated by gavage with 1,2-dichloroethane in
    corn oil for two weeks, 5 times per week, at doses of 150 mg/kg bw
    or less did not show any treatment-related abnormalities in organ or
    body weight, histology, clinical chemistry, or haematology. After 5
    doses of 300 mg/kg bw in 5 days, all 6 rats died, and their livers
    showed fatty degeneration with an increase in the triglyceride
    level. Rats were also exposed for 90 days, 5 times per week, to
    doses of 0, 10, 30, or 90 mg/kg bw. At the two highest dose levels a
    tendency towards decreased body weight gain was observed. At
    90 mg/kg bw/day rats of both sexes showed an increase in the
    relative weight of kidneys, while only the females at this dose
    level showed increased relative weights of liver and brain compared
    to controls. Histology and clinical chemistry were normal. Some
    haematological parameters were altered, but not in a dose-related
    manner (reviewed in WHO, 1987).

         Groups of 8 male Fischer 344 rats received 0, 350, or 700 mg of
    1,2-dichloroethane/kg bw by gavage in corn oil 5 days/week for two
    weeks. Histopathologic examination of forestomachs of rats killed
    24 h after the last dose indicated no significant difference in the
    incidence or severity of epithelial cell proliferation in the rat
    forestomach between the vehicle control group and the 2 groups given
    1,2-dichloroethane (Ghanayem  et al., 1986).

         Studies were conducted to compare the toxicity of
    1,2-dichloroethane in F344/N rats, Sprague-Dawley rats, and
    Osborne-Mendel rats. Ten rats/sex/group were exposed to
    1,2-dichloroethane (purity > 99%) in the drinking water at
    concentrations of 0, 500, 1000, 2000, 4000 and 8000 ppm for 13
    weeks. The highest concentration was limited by the maximum
    solubility of the compound in water. In addition, groups of 10 male
    F344/N rats were administered 0, 30, 60, 120, 240, or 480 mg of

    1,2-dichloroethane/kg bw in corn oil by gavage 5 days/week, and
    groups of 10 female F344/N rats were administered 0, 18, 37, 75,
    150, or 300 mg of 1,2-dichloroethane/kg bw in corn oil by gavage 5
    days/week to compare toxicity resulting from bolus administration
    with that of continuous exposure in drinking water. Additional
    groups of 10 male rats were exposed to 0, 2000, 4000, or 8000 ppm in
    drinking water, or administered 0, 120, 240, or 480 mg/kg bw by
    gavage. Serial blood samples were taken on days 3, 7, 14, and 45 and
    at the last kill for extensive haematology and blood biochemistry.
    Gavage doses of 1,2-dichloroethane were within the range of total
    daily doses (in mg/kg bw/day) resulting from exposure in drinking
    water. Autopsy was performed on all animals not used in biochemical
    studies and microscopic examinations were carried out on 30 tissues
    and organs. The liver, right kidney, brain, heart, thymus, lung and
    right testis were weighed. 1,2-Dichloroethane administered by gavage
    resulted in greater toxicity to F344/N rats than did administration
    of similar doses in drinking water. All males receiving 240 and
    480 mg/kg bw and 9/10 females receiving 300 mg/kg bw by gavage died
    before the end of the study. Necrosis of the cerebellum was observed
    in 3 males receiving 240 mg/kg bw/day and 3 females receiving
    300 mg/kg bw/day. Hyperplasia and inflammation of the forestomach
    mucosa were observed in 8 male and 3 female rats that died or were
    killed in moribund condition. Mean body weights of treated rats were
    not affected. Compound-related clinical signs included tremor,
    salivation, emaciation, abnormal postures, ruffled fur, and dyspnoea
    in males at 240 mg/kg bw/day and in females at 300 mg/kg bw/day. The
    absolute and relative kidney weights were increased in males at 60
    and 120 mg/kg bw/day and in females at 75 and 150 mg/kg bw/day. The
    absolute and relative liver weights were increased in males at
    120 mg/kg bw/day and in females at 18, 37, 75, and 150 mg/kg bw/day.
    The increased liver and kidney weights were not followed by
    histological evidence of toxicity, and no changes were observed in
    blood biochemistry nor haematology. 1,2-Dichloroethane caused less
    toxicity to F344/N, Sprague-Dawley and Osborne-Mendel rats at the
    drinking water concentrations used in these studies. Decreased mean
    body weights were seen at the two highest dose levels. Increased
    absolute kidney weights were observed in males at 1000 ppm or higher
    and in females at 500 ppm and higher concentrations. Increased
    relative liver weights were seen in some of the strains/sexes at
    1000 ppm or higher. The incidence of tubular regeneration was
    dose-related only in female F344/N rats and was observed in 9/10
    females at 8000 ppm, 3/10 at 4000 ppm, 2/10 at 2000 ppm, 1/10 at
    1000 ppm, 0/10 at 500 ppm and in 0/10 controls (Morgan  et al.,

         Groups of 2 male Sprague-Dawley rats were given 0 or 150 mg/kg
    bw/day 1,2-dichloroethane for either 5, 10, 20, or 30 days by
    intraperitoneal injections. Food consumption and body weights were
    measured, and at necropsy the weights of liver, kidney, lung,
    spleen, and testes were recorded. Food consumption and body weights

    were not affected. After 30 days the relative liver weight was
    increased, while the other organ weights were not affected. Groups
    of 12 male Sprague-Dawley rats were exposed to 1,2-dichloroethane in
    inhalation chambers at concentrations of 0, 153, 304, or 445 ppm
    1,2-dichloroethane 7 h a day for 30 days. Decreased body weights and
    increased relative liver weight were observed at 445 ppm.
    Histological examination of sections of the livers indicated
    midzonal necrosis, cytoplasmic swelling, and moderate bile duct
    proliferation. When the animals were fed 0.15% disulfiram in the
    diet simultaneously with the 1,2-dichloroethane treatment these
    effects were augmented, and in addition testicular atrophy was
    observed (Igwe  et al., 1986a).

         In the above-mentioned study where 1,2-dichloroethane was
    sub-chronically administered to male Sprague-Dawley rats by
    inhalation at three levels blood and liver samples were analyzed for
    a variety of biochemical parameters. At the highest level
    1,2-dichloroethane increased liver-to-body weight ratios and the
    serum activity of 5'-nucleotidase, but not the serum activity of
    sorbitol dehydrogenase nor alkaline phosphatase. 1,2-Dichloroethane
    caused an increase in the glutathione concentration and a
    non-concentration-dependent depression of cytochrome P450 in the
    liver. Simultaneously feeding of the animals with disulfiram caused
    a potentiation of the hepatotoxicity of 1,2-dichloroethane, possibly
    due to an inhibition of microsomal mixed-function oxidase-mediated
    metabolism of 1,2-dichloroethane and to a compensatory increase in
    metabolism to reactive metabolites generated by
    glutathione-S-transferase-mediated conjugation of 1,2-dichloroethane
    with reduced glutathione (Igwe  et al., 1986b).

    2.2.3  Long-term/carcinogenicity studies  Mice

         Groups of 50 male and 50 female 5 week-old B6C3F1 mice
    were administered technical-grade 1,2-dichloroethane (purity 98-99%)
    in corn oil by gavage on 5 consecutive days/week for 78 weeks.
    High-dose males received 150 mg/kg bw/day for 8 weeks and then
    200 mg/kg bw/day for 70 weeks followed by 13 weeks without
    treatment. High-dose females received 250 mg/kg bw/day for 8 weeks,
    400 mg/kg bw/day for 3 weeks and 300 mg/kg bw/day for 67 weeks,
    followed by 13 weeks without treatment. Low-dose males received
    75 mg/kg bw/day for 8 weeks and 100 mg/kg bw for 70 weeks, followed
    by 12 weeks without treatment. Low-dose females received 125 mg/kg
    bw/day for 8 weeks, 200 mg/kg bw/day for 3 weeks, and 150 mg/kg
    bw/day for 67 weeks, followed by 13 weeks without treatment. The
    time-weighted average doses were 195 and 299 mg/kg bw/day for
    high-dose males and females, respectively, and 97 and 149 mg/kg
    bw/day for low-dose males and females, respectively. A group of 20

    male and 20 female mice that received corn oil alone served as
    matched vehicle controls. Another group of 60 male and 60 female
    mice that received the same vehicle served as pooled vehicle
    controls. The animals were housed in the same room where several
    other hydrocarbons or other substances were tested. Of high-dose
    males, 50% survived at least 84 weeks, and 42% survived until the
    end of the study; 72% (36/50) of high-dose female mice died between
    weeks 60 and 80. In the low-dose groups, 52% (26/50) of males
    survived less than 74 weeks, and 68% (34/50) of females survived
    until the end of the study. In the vehicle control groups, 55%
    (11/20) of males and 80% (16/20) of females survived until the end
    of the study. Almost all organs, and many tissues containing visible
    lesions, were examined histologically. The numbers of animals with
    tumours and the total number of tumours were significantly greater
    in male and female mice at the high-dose level, and in female mice
    at the low dose level, than in controls. Increased incidences of the
    following neoplasms were observed: Mammary adenocarcinomas
    (high-dose: 7/48; low-dose: 9/50 versus 0/60 in controls), uterine
    adenocarcinomas (high-dose: 4/48; low-dose: 3/50 versus 1/60 in
    controls), endometrial stromal neoplasms of the uterus (high-dose:
    3/48; low-dose: 2/50 versus 0/60 in controls), and squamous-cell
    carcinomas of the forestomach of females (high-dose: 5/48; low-dose:
    2/50 versus 1/60 in controls); lung adenomas in males and females
    (males: high-dose: 15/47; low-dose: 1/46 versus 0/59 in controls;
    females: high-dose: 15/48; low-dose: 7/50 versus 2/60 in controls)
    and malignant histiocytic lymphomas (males: high-dose: 5/47;
    low-dose: 8/46 versus 0/59 in controls; females: high-dose: 2/48;
    low-dose: 10/50 versus 0/60 in controls); and hepatocellular
    carcinomas in male mice (high-dose: 12/47; low-dose: 6/46 versus
    4/59 in controls). A group of 20 male and 20 female untreated
    matched controls was included, but was not considered in the
    statistical analyses of tumour incidences (IARC, 1979; Ward, 1980).

         1,2-Dichloroethane was administered to groups of 70
    four-week-old male B6C3F1 mice at concentrations of 0, 835, or
    2500 mg/l in the drinking water using a two-stage
    (initiation/promotion) treatment protocol to study the effect on
    liver tumour incidence. Of the mice in each group, 35 were initiated
    by treatment with diethylnitrosamine (10 mg/l) in the drinking water
    for 4 weeks. The remaining 35 mice received deionized drinking
    water. Each group was subsequently treated with the two
    concentrations of 1,2-dichloroethane in drinking water for 52 weeks.
    An additional group received phenobarbital (500 mg/l) and served as
    the positive control for liver tumour promotion. Mice were sampled
    after 24 weeks (10 mice) and 52 weeks (25 mice). 1,2-Dichloroethane
    did not increase the number nor incidence of lung or liver tumours
    by itself. Phenobarbital promoted liver tumour formation (but not
    lung tumours) in the diethylnitrosamine-initiated mice.
    1,2-Dichloroethane did not affect the incidence nor number of liver
    or lung tumours in the diethylnitrosamine-initiated animals (Klaunig
     et al., 1986).

         In an inhalation experiment groups of 90 11-week-old Swiss mice
    of each sex were exposed to 5, 10, 50, or 250 ppm of
    1,2-dichloroethane (purity 99.82%; containing 1,1-dichloroethane
    0.02%; carbon tetrachloride 0.02%; trichloroethylene 0.02%;
    perchloroethylene 0.03%; benzene 0.09%) for 78 weeks, 7 h per day, 5
    days per week, and observed for their lifetimes. The highest
    exposure was reduced to 150 ppm after a few weeks because of high
    mortality. The control group consisted of 115 male mice and 134
    female mice. Percentage survivals of male and female mice, 52 weeks
    after initiation of the treatment, were 63% and 84% in the controls;
    47% and 93% at 5 ppm, 66% and 80% at 10 ppm, 51% and 81% at 50 ppm,
    and 43% and 64% at 150 ppm. The last mouse died about 100 weeks
    after initiation of treatment. No specific types of tumours or
    changes in the incidences of tumours were found (reviewed in Maltoni
     et al., 1980; WHO, 1987).  Rats

         Groups of 18 male and 18 female rats (strain not stated) were
    given feed fumigated with 1,2-dichloroethane for two years. The
    doses administered were estimated to be 0, 11-17, or 23-35 mg/kg
    bw/day. No adverse effects were recorded on feed consumption,
    growth, nor mortality. At termination of the study blood was
    obtained for serum biochemistry. No differences were seen in serum
    biochemical measurements between controls and treated animals. No
    histopathology was reported (Alumot  et al., 1976).

         1,2-Dichloroethane was examined in a rat liver foci assay for
    evidence of initiating and promoting potential. Groups of 10 young
    adult male Osborne-Mendel rats were given partial hepatectomies,
    followed 24 h later by a single intraperitoneal dose of either
    diethylnitrosamine (30 mg/kg bw) or 1,2-dichloroethane in corn oil
    at the maximum tolerated dose (100 mg/kg bw). One week later either
    a diet containing 0.05% (w/w) phenobarbital or daily oral gavage
    (5 days/week) of 1,2-dichloroethane (100 mg/kg bw) in corn oil for 7
    weeks was initiated, and animals were sacrificed one week later.
    Putative preneoplastic markers monitored were foci with increased
    gamma glutamyl-transpeptidase activity.

         1,2-Dichloroethane had no significant effect on either the
    initiation or the promotion protocol at the maximum tolerated dose
    (Milman  et al., 1988).

         Groups of 50 male and 50 female Osborne-Mendel rats, 9 weeks
    old, were administered technical-grade 1,2-dichloroethane (purity
    98-99%) in corn oil by gavage on 5 consecutive days/week for 78
    weeks. High and low doses were 100 and 50 mg/kg bw/day for 7 weeks,
    150 and 75 mg/kg bw/day for 10 weeks, and 100 and 50 mg/kg bw/day
    for 18 weeks, respectively, followed by cycles of one treatment-free
    week and 4 weeks under treatment (100 and 50 mg/kg bw/day) for 43

    weeks (34 weeks under treatment and 9 treatment-free weeks). The
    time-weighted average doses were 95 and 47 mg/kg bw/day for high-
    and low-dose animals, respectively. Groups of 20 male and 20 female
    rats received corn oil alone and were used as matched vehicle
    controls. Other groups of 60 male and 60 female rats received the
    same vehicle and were used as the pooled vehicle control group. The
    animals were housed in the same room as rats intubated with other
    halogenated hydrocarbons or carbon disulphide. The last high-dose
    male rat died during week 23 of the observation period following
    administration of the chemical, and the last high-dose female rat
    died during week 15 of the observation period. Low-dose rats were
    observed for 32 weeks after administration. Mortality was increased
    in the high-dose groups: 50% of males were dead by week 55% and 50%
    of females by week 57; by week 75, 84% of males and 80% of females
    were dead. In the low-dose group, 52% of the males survived over 82
    weeks, and 50% of the females survived over 85 weeks. All treated
    and control animals were examined histologically. The total number
    of tumours was significantly greater than that in controls only in
    female rats treated with the high dose; however, significant
    increases in the number of squamous-cell carcinomas of the
    forestomach in male rats (9/50 versus 0/60) and of mammary gland
    adenocarcinomas and fibroadenomas (24/50 versus 6/59) in female rats
    treated with the high dose were observed. An increase in the
    incidence of haemangiosarcomas in animals of both sexes was also
    noted, but it was statistically significant only in males (low-dose:
    11/50; high-dose: 7/50 versus 1/60 in control males). A group of 20
    male and 20 female untreated matched controls was included, but it
    was not considered in the statistical analyses of tumour incidences
    (IARC, 1979; Ward, 1980).

         In an inhalation experiment groups of 90 12-week-old
    Sprague-Dawley rats of each sex were exposed to 5, 10, 50, or 250
    ppm of 1,2-dichloroethane (purity 99.82%; containing
    1,1-dichloroethane 0.02%; carbon tetrachloride 0.02%;
    trichloroethylene 0.02%; perchloroethylene 0.03%; benzene 0.09%) for
    78 weeks, 7 hours per day, 5 days per week, and observed for their
    lifetimes. The highest exposure was reduced to 150 ppm after a few
    weeks because of high mortality. The control group consisted of 180
    male rats and 180 female rats. Percentage survivals of male and
    female rats, 52 weeks after initiation of the treatment were 67% and
    73% in the controls; 75% and 85% at 5 ppm, 70% and 81% at 10 ppm,
    70% and 84% at 50 ppm, and 67% and 79% at 150 ppm. Most rats had
    died by about 140 weeks after initiation of treatment. No specific
    types of tumours nor changes in the incidence of tumours were found,
    with the exception of an increased incidence (not dose-related) of
    fibromas and fibroadenomas of the mammary glands of female rats at
    5, 50, and 150 ppm. The average latency time for these tumours was

    83 weeks in control rats and rats exposed to 5 ppm, and 79 weeks in
    the rat exposed to the two highest levels. The authors ascribe the
    differences seen in the incidence of mammary tumours to the
    different survival rates in the groups (reviewed in Maltoni  et al.,
    1980; WHO, 1987).

         Groups of 50 male and 50 female Sprague-Dawley rats were
    exposed to 50 ppm 1,2-dichloroethane for 7 h/day, 5 days/week, for 2
    years by inhalation, and thereafter subjected to extensive gross and
    microscopic pathology. No changes were observed in food and water
    consumption, body weight gain, nor survival. At pathology the only
    effects reported were testicular lesions in males and a slight
    increase in the incidence of basophilic focal cellular changes in
    the pancreas of female rats. No significant increases in tumour
    incidences over controls were observed when the rats were exposed
    only to 1,2-dichloroethane.

         Additional rats were exposed by inhalation to 50 ppm
    1,2-dichloroethane with either 0.05% disulfiram in the diet or 5%
    ethanol in the drinking water. Histopathologic lesions related to
    the combination of inhaled 1,2-dichloroethane and dietary disulfiram
    were observed in the liver, mammary, and testicular tissues of rats.
    This combined exposure resulted in a significant increase in the
    incidence of intrahepatic bile duct cholangiomas in both male (9/49
    versus 0/50 in controls) and female rats (17/50 versus 0/50). Male
    rats exposed to 1,2-dichloroethane and disulfiram also had an
    increased incidence of subcutaneous fibromas (10/50 versus 2/50),
    neoplastic nodules (6/49 versus 0/50), and interstitial cell tumours
    in the testes (11/50 versus 2/50). The female rats similarly exposed
    also had a higher incidence of mammary adenocarcinomas (12/48 versus
    4/50). No significant increase in the number of any tumour type was
    observed in rats exposed to only 1,2-dichloroethane, disulfiram, or
    ethanol. Similarly, no significant increase in the number of tumours
    was observed in rats exposed to inhaled 1,2-dichloroethane and
    ethanol in water.

         At the end of the 2-year period animals from each group were
    evaluated for 1,2-dichloroethane metabolism and DNA binding. The
    rats received 150 mg/kg bw doses of [1,2-U-14C]dichloroethane by
    gavage in corn oil. Blood levels of 1,2-dichloroethane at the end of
    a 7 h exposure period were significantly higher for rats exposed to
    both 1,2-dichloroethane and disulfiram than for rats exposed to
    1,2-dichloroethane alone. In addition, the elimination of a single
    oral dose of radiolabelled 1,2-dichloroethane was affected. The
    urinary excretion of 14C from control rats was 47 to 55% of the
    administered dose with 28 to 30% detected as unchanged compound in
    the breath. In disulfiram-treated rats, only 35 to 36% of the
    administered 14C was eliminated in the urine with 41 to 55% as
    unchanged compound in the breath. The urinary metabolite HPLC
    profile was qualitatively unchanged by long-term 1,2-dichloroethane,

    disulfiram, or ethanol treatment, either alone or in combination,
    and consisted primarily of thiodiglycolic acid, thiodiglycolic acid
    sulfoxide, and chloroacetic acid. As regards covalent binding of
    radioactivity to liver DNA relatively high amounts (36 to 44
    micromolar equivalents per mole of DNA) were measured in the
    unpretreated rats. However, no significant exposure-related
    differences were noted (Cheever  et al., 1990).

    2.2.4  Reproduction studies including special studies on
           teratogenicity and dominant lethal effects  Mice

         Groups of 10 male and 30 female ICR mice received 0, 0.03,
    0.09, or 0.29 mg of 1,2-dichloroethane in their drinking-water. The
    concentrations corres-ponded to 0, 5, 15, or 50 mg of
    1,2-dichloroethane/kg bw/day, respectively. After 35 days on the
    test solutions the F0 mice were randomly mated to produce the
    F1a litters. Two weeks postweaning of the F1a litters the F0
    adults were rerandomized to produce the F1b litters. The F0
    females were rested for two weeks, following weaning of the F1b
    pups, and randomly remated (F1c mating) for dominant lethal and
    teratology testing. At weaning the F1b litters were culled to 10
    males and 30 females per group and placed on the appropriate test
    solutions, and at 14 weeks of age were randomly mated to produce the
    F2a litters. Two weeks postweaning of the F2a pups the F1b
    adults were randomly remated (F2b mating) for dominant lethal and
    teratology screening. No effects were observed on body weights
    (recorded weekly), or fluid consumption (recorded twice-weekly), nor
    as mortality in the F0 or F1b adult mice. Adult reproductive
    performance measured as fertility and gestation indices were not
    affected by the treatment with the test compound. No effects were
    observed on litters from the F1a, F1b, and F2a matings as
    regards 21-day survival, litter size (recorded on days 0, 4, 7, 14,
    and 21), litter weights, nor viability and lactation indices. At
    necropsy of the pups on day 21 no adverse effects were observed.

         In the F1c and F2b matings, each treated male was co-housed
    with three 9-week old naive, nulliparous females for 7 days. Females
    were sacrificed after 14 days, and number of fetal implants, early
    and late resorptions, and viable fetuses were counted. No effects
    were observed on a number of reproductive indices as well as on the
    frequency of dominant lethal factors (Lane  et al., 1982).

         In the F1c and F2b matings the treated females were
    co-housed in groups of three with one 9-week old naive male for 7
    days. Females were sacrificed on day 18 of gestation, and the number
    of implants, resorptions, and viable and nonviable males and females

    were counted. Fetuses were weighed and examined for gross effects.
    All fetuses were then examined for visceral and skeletal
    malformations. No treatment-related teratogenic effects were
    observed (Lane  et al., 1982).  Rats

         In a review, negative results have been reported in a
    reproduction study using Sprague-Dawley rats, and in teratogenicity
    studies in rats and rabbits exposed to 1,2-dichloroethane by
    inhalation (WHO, 1987).

         Groups of 18 female rats (strain not stated) fed, for up to 2
    years, on diets containing 1,2-dichloroethane at concentrations
    corresponding to 0, 11-17, or 23-35 mg/kg bw/day were mated with
    similarly treated males up to 5 times during the study period. No
    compound-related effects were observed on reproductive performance
    (Alumot  et al., 1976).  Special studies on genotoxicity

         The genotoxic effects of 1,2-dichloroethane have been reviewed
    (Rannug, 1980). The results of genotoxicity studies are summarized
    in Table 1.

        Table 1. Results of genotoxicity assays on 1,2-dichloroethane

    Test system              Test object                   Concentration of              Results                Reference
    Ames test                S. typhimurium                10-25 µmol/plate                                     Brem et al., 1974
                             TA 1530                                                     Positive (weak)1
                             TA 1535                                                     Positive (weak)1
                             TA 1538                                                     Positive (weak)1

    Ames test                S. typhimurium                13 mg/plate                                          McCann et al., 1975
                             TA 100                                                      Positive (weak)1

    Ames test                S. typhimurium                5-45 µmol/plate                                      Rannug & Ramel, 1977
                             TA 1535                                                     Positive2

    Ames test                S. typhimurium                20-60 µmol/plate                                     Rannug et al., 1978
                             TA 1535                                                     Positive (weak)1
                             TA 1535                                                     Positive2,6
                             TA 1538                                                     Positive3

    Ames test                S. typhimurium                0-3.6 mg/plate                                       King et al., 1979
                             TA 98                                                       Negative4
                             TA 100                                                      Negative4
                             TA 1535                                                     Negative4
                             TA 1537                                                     Negative4
                             TA 1538                                                     Negative4

    Ames test                S. typhimurium                0-4 mg/plate                                         Guengerich et al., 1980
                             TA 1535                                                     Negative5
                             TA 1535                                                     Positive6

    Ames test                S. typhimurium                10-40 mM                                             van Bladeren et al., 1981
                             TA 100                                                      Positive6


    Table 1. cont'd

    Test system              Test object                   Concentration of              Results                Reference

    Ames test                S. typhimurium                0-100 µl/plate                                       Principe et al., 1981
                             TA 98                                                       Negative4
                             TA 100                                                      Negative4
                             TA 1535                                                     Positive (weak)2
                             TA 1537                                                     Negative4
                             TA 1538                                                     Negative4

    Ames test                S. typhimurium                31.8-231.8                                           Barber et al., 1981
                             TA 98                         µmol/plate7                   Negative4
                             TA 100                                                      Positive (weak)4
                             TA 1535                                                     Positive4
                             TA 1537                                                     Negative4
                             TA 1538                                                     Negative4

    Ames test                S. typhimurium                7.06 µmol/ml8                                        Reitz et al., 1982
                             TA 1535                                                     Negative9
                             TA 1535                                                     Positive10

    Ames test                S. typhimurium                Not given                                            Milman et al., 1988
                             TA 98                                                       Negative4
                             TA 100                                                      Positive4
                             TA 1535                                                     Positive4
                             TA 1597                                                     Negative4

    Forward                  Streptomyces                  0-100 µl/plate                Negative               Principe et al., 1981
    mutation                 coelicolor

    Forward                  Aspergillus nidulans          0-500 µl/plate                Negative               Principe et al., 1981


    Table 1. cont'd

    Test system              Test object                   Concentration of              Results                Reference

    Somatic                  Aspergillus nidulans,         1-2.5 ml/20 l                 Positive11             Crebelli et al., 1984
    segregation              diploid strain P1             chamber
                                                           0.1-0.4% (v/v)                Positive11             Crebelli et al., 1988

    Aneuploidy               Aspergillus nidulans,         0.2% (v/v)                    Positive               Crebelli et al., 1988
                             haploid strain 35

    Forward                  E. coli K12                   0-1 mg/ml                     Negative12             King et al., 1979
    mutation                 (343/113)

    HGPRT mutation           Chinese hamster               0-3 mM                        Positive               Tan & Hsie, 1981
    assay                    ovary cells (CHO)                                           (weak)2,13
                             in vitro                      0-50 mM                       Positive1

    HGPRT mutation           Chinese hamster               1-40 µg/cm3                   Positive2              Zamora et al., 1983
    assay                    ovary cells (CHO)             in glass bottle
                             in vitro

    Enhancement of           Syrian golden                 0.2-0.8 ml/                   Positive               Hatch et al., 1983
    viral14 cell             hamster embryo                chamber15
    transformation           cells in vitro

    Transformation           BALB/c-3T3 cells              5-50 µg/ml                    Negative               Tu et al., 1985
    assay                    in vitro

    Transformation           BALB/c-3T3 cells              Not given                     Negative               Milman et al., 1988
    assay                    in vitro


    Table 1. cont'd

    Test system              Test object                   Concentration of              Results                Reference

    Unscheduled DNA          Hepatocytes                   Not given                     Positive               Milman et al., 1988
    synthesis (UDS)          Primary culture
                             B6C3F1 mice                                                 Positive

    Unscheduled DNA          Human lymphocytes             Not given                     Positive               Perocco & Prodi, 1981
    synthesis (UDS)          in vitro

    Induction of             Human embryo                  1-50 mM                       Positive               Ferreri et al., 1983
    diphtheria-toxin-        epithelial-like
    resistant mutants        cells in vitro

    HGPRT mutation           Human lymphoblasts                                                                 Crespi et al., 1985
    assay                    in vitro
                             AHH-1                         100-1000 µg/ml                Positive16
                             TK6                           100-1000 µg/ml                Positive16

    Somatic mutation         D. melanogaster               5 mg/ml p.o.                  Positive               Nylander et al., 1978
    and recombination        larvae                        until pupation

    Sex-linked recessive     D. melanogaster               0-5 mg/ml p.o.                Positive               King et al., 1979
    lethal assay             male

    Sex-linked recessive     D. melanogaster               8-125 mg/m3 for               Positive               Kramers et al., 1991
    lethal assay             male                          96 h

    Somatic mutation         D. melanogaster               40-250 mg/m3,                 Positive               Kramers et al., 1991
    and recombination        larvae                        inhalation until
    test                                                   pupation

    Table 1. cont'd

    Test system              Test object                   Concentration of              Results                Reference

    Somatic mutation         D. melanogaster               50-1000 ppm p.o.              Positive17             Romert et al., 1990
    and recombination        larvae                        until pupation

    Intrasanguineous         E. coli K12                   0-200 mg/kg bw                Negative               King et al., 1979
    host mediated            (343/113)                     intraperitoneal

    Micronucleous            Male and female               0-400 mg/kg bw                Negative               King et al., 1979
    test                     NMRI mice,                    intraperitoneal

    Micronucleous            Male CBA mice,                100 mg/kg bw                  Negative               Jenssen & Ramel, 1980
    test                     polychromatic                 intraperitoneal

    Mouse spot test          C57BL/6J Han female           300 mg/kg bw                  Positive (weak)        Gocke et al., 1983
                             x T stock male mice

    Sister chromatid         Male Swiss mice,              0.5 mg/kg bw i.p.             Negative               Giri & Que Hee, 1988
    exchange (SCE)           bone marrow cells             1, 2, 4, 8, and               Positive
                                                           16 mg/kg bw i.p.

    Alkaline DNA             B6C3F1 mice, liver            100-300 mg/kg bw p.o.         Positive               Storer & Conolly, 1983
    unwinding                in vivo/in vitro


    Table 1. cont'd

    Test system              Test object                   Concentration of              Results                Reference

    Alkaline DNA             B6C3F1 mice, liver            100-400 mg/kg bw p.o.         Positive               Storer et al., 1984
    unwinding                in vivo/in vitro              100-300 mg/kg bw
                                                           i.p.                          Positive
                                                           150-2000 ppm for 4 h

    Alkaline DNA             B6C3F1 mice, liver            200 mg/kg bw i.p.             Positive               Storer & Conolly, 1985
    unwinding                in vivo/in vitro              200 mg/kg bw i.p.             Positive20

    Alkaline DNA             BALB/c mice, liver            300 mg/kg bw i.p.             Positive               Taningher et al., 1991
    unwinding                in vivo/in vitro

    1    Without rat liver S-9 fraction
    2    With rat liver S-9 fraction
    3    With rat liver cytosol
    4    Both with and without rat liver S-9 fraction
    5    Rat liver microsomes. No effect of glutathione addition
    6    Rat liver cytosol. Enhanced effect by addition of glutathione
    7    Closed inert test system
    8    Preincubation test
    9    Rat liver microsomes
    10   Rat liver cytosol
    11   Increased frequency of haploid sectors and diploid non-disjunctional sectors
    12   Both with and without liver homogenate from male NMRI mice
    13   Toxicity
    14   SA7 adenovirus
    15   ml 1,2-dichloroethane added per 4.6 litre chamber
    16   Direct acting mutagenicity related to the level of glutathione-S-transferase activity in the cell lines
    17   Enhanced by pretreatment with 1000 ppm of phenobarbital, inhibited by pretreatment with glutathione inhibitor buthionine sulfoxime
    18   Female NMRI mice
    19   At higher doses 80-100% mortality
    20   Enhanced effect in animals pretreated with the microsomal oxidative metabolism inhibitor piperonyl butoxide

    2.2.6  Special studies on immune responses

         Groups of 32 male CD-1 mice were exposed to 3, 24, or 189 mg of
    1,2-dichloroethane (purity unknown)/kg bw/day via the drinking water
    for 90 days. In addition, groups of 10 male CD-1 mice were exposed,
    once/day, to 4.9 or 49 mg/kg bw by gavage in water solution. Control
    groups consisted of 48 mice in the 90-day study and 12 mice in the
    14-day study. No effects were found on organ weights nor
    haematological parameters, except for a 30% reduction in the
    leucocyte count after 14 days of exposure to 49 mg/kg bw/day. After
    the 90-day exposure, decreases in body weight and water consumption
    were observed. There was a tendency toward a reduction in
    immunoglobulin spleen antibody-forming cells and in the
    serum-antibody level after sheep erythrocyte immunization, while no
    effects were observed in the response to B-cell mitogen
    lipopolysaccharide S. After the 14-day exposure, 25% and 40%
    suppression of antibody-forming cells were measured at 4.9 and
    49 mg/kg bw, respectively. After the 90-day exposure, no effects
    were seen on cell-mediated immunity, assessed by measuring the
    delayed hypersensitivity response to the T-cell mitogen concanavalin
    A. After the 14-day exposure, a slight suppression of the delayed
    hypersensitivity response was found, which was not dose-dependent
    (Munson  et al., 1982; WHO, 1987).

         The effects of single or multiple inhalation exposures to
    1,2-dichoroethane on the pulmonary defence systems of mice and rats
    were evaluated. Groups of 28 female CD1 mice were subjected to
    single 3 h inhalation exposures to 0, 2.5, 5.0, or 10 ppm or
    multiple 3 h/day exposures for 5 days to 2.5 ppm of
    1,2-dichloroethane. Groups of male Sprague-Dawley rats (numbers not
    given) were given single exposures to 0, 100 or 200 ppm of
    1,2-dichloroethane for 3-5 h or 0, 10, 20, 50, or 100 ppm of
    1,2-dichloroethane 5 h/day, 5 days/week for 12 exposure days. A
    single exposure of mice to 10 ppm of 1,2-dichloroethane resulted in
    decreased pulmonary bactericidal activity to inhaled  Klebsiella
     pneumoniae and increased mortality from  Streptococcus
     zooepidemicus respiratory infection, while a single exposure to
    5 ppm caused increased mortality from streptococcal pneumonia,
    although bactericidal activity was not affected. Neither of these
    two parameters changed following single or five consecutive daily
    exposures to 2.5 ppm of 1,2-dichloroethane. Single exposures to 10
    or even 100 ppm did not affect mouse alveolar macrophage inhibition
    of the proliferation of a tumour target cell  in vitro nor
     in vitro phagocytosis of red blood cells. In rats, no effects were
    observed on pulmonary bactericidal activity, alveolar macrophage
     in vitro phagocytosis, cytostasis and cytolysis of tumour target
    cells, ectoenzymes, nor blastogenesis of mitogen-stimulated rat T-
    and B-lymphocytes from lung-associated, mesenteric, or popliteal
    lymph nodes following the exposures indicated (Sherwood  et al.,

    2.2.7  Special studies on behavioural effects

         The ability of 1,2-dichloroethane to produce conditioned taste
    aversion against saccharin, typically a preferred substance, was
    evaluated in the taste aversion paradigm to determine the threshold
    for producing the aversion effect. After six days with limited
    access to drinking water 6 groups of 7 male CD-1 mice received a
    conditioning trial with a 0.3% solution of sodium saccharin for
    30 min. Within 5 min after the termination of the 30 min limited
    access to saccharin the rats were dosed by gavage with 0, 10, 30,
    100, 300, or 450 mg of 1,2-dichloroethane/kg bw. Twenty-four hours
    after this conditioning trial the animals were exposed to a
    two-bottle choice test with the saccharin solution versus deionized
    water presented for 30 min. As during the conditioning trial, all
    animals were intubated with the test solutions within 5 min of
    removal of the two bottles. Comparisons were thus made between
    threshold determination for acute and repetitive conditioning
    trials. Within the 7 days, 6 animals in the group receiving 300 mg
    of 1,2-dichloroethane/kg bw/day and 7 animals in the 450 mg/kg
    bw/day group had died. The compound produced significant saccharin
    aversions at both 300 mg and 450 mg/kg bw following one pairing of
    the chemical exposure with saccharin ingestion. The ED50 value,
    calculated as the dose which reduced the proportion of saccharin
    intake to 50% of the total fluid consumption, was calculated as
    41.7 mg/kg bw. The repetitive conditioning trials did not seem to
    alter the threshold for producing aversions, but the test was
    hampered by high mortality at the two highest doses (Kallman
     et al., 1983).

    2.2.8  Special studies on macromolecular binding

         When incubated with liver microsomes from either male
    B6C3F1 mice or Osborne-Mendel rats [1,2-14C]-dichloroethane
    was activated to species bound to liver microsomal protein and added
    salmon sperm DNA. Binding was not obtained when the compound was
    incubated with microsomes from stomach tissue. The binding to liver
    proteins of mice was significantly higher than the corresponding
    binding in rats (Banerjee & Van Duuren, 1979).

         The interaction of 1,2-dichloroethane with rat and mouse
    nucleic acids was studied both  in vivo (liver, lung, kidney and
    stomach) and  in vitro (liver microsomal and/or cytosolic
    fractions).  In vivo, groups of two male Wistar rats and eight male
    Balb/c mice received intraperitoneal doses of 8.7 µmol
    14C-1,2-dichloroethane, DNA binding of radioactivity was examined
    after 22 h.  In vitro experiments were conducted with liver
    microsomes from 4 rats and 22 mice either pretreated or not
    pretreated with phenobarbital.  In vivo, liver and kidney DNA
    showed the highest labelling, whereas the binding to lung DNA was
    barely detectable. Mouse DNA labelling was higher than rat DNA

    labelling whatever the organ considered. RNA and protein labelling
    were higher than DNA labelling, with no particular pattern in terms
    of organ or species involvement.  In vitro, 1,2-dichloroethane was
    bioactivated by both liver microsomes and cytosolic fractions to
    reactive forms capable of binding to DNA and polynucleotides. UV
    irradiation did not photoactivate 1,2-dichloroethane. The  in vitro
    interaction with DNA mediated by enzymatic fractions was inducible
    by phenobarbital pretreatment (one order of magnitude, using rat
    microsomes).  In vitro bioactivation was mainly performed by
    microsomes. When microsomes plus cytosol were used, mouse enzymes
    were more efficient than rat enzymes in inducing a
    1,2-dichloroethane-DNA interaction, in agreement with the  in vivo
    pattern (Arfellini  et al., 1984).

         1,2-Dichloroethane was found to be metabolized by liver
    microsomes from phenobarbital-induced male Sprague-Dawley rats to
    1,N6-ethenoadenine-forming products. Cyclic AMP was used as a
    suitable adenine for the trapping reaction under the incubation
    conditions, and the fluorescent 1,N6-ethenoadenine was determined
    using HPLC. Based on studies using bromoacetaldehyde in the
    incubation mixture it was supposed that monohaloacetaldehydes are
    early oxidative metabolites of dihaloethanes accounting at least
    partly for their irreversible binding to DNA (Rinkus & Legator,

         [1,2-14C]-Dichloroethane was incubated under air for 3 h with
    polynucleotides and liver microsomal or cytosolic fractions (with
    added glutathione) from Sprague-Dawley rats.
    [1,2-14C]-Dichloroethane was metabolized by rat hepatic microsomes
    to products that irreversibly bound polynucleotides. The products of
    microsome-mediated binding were identified in HPLC eluates as
    1,N6-ethenoadenosine to polyadenylic acid, 3,N4-ethenocytidine
    to polycytidylic acid, and two cyclic derivatives to polyguanylic
    acid. No evidence was obtained for glutathione plus cytosol-mediated
    covalent binding to polynucleotides when [1,2-14C] dichloroethane
    was metabolized in the presence of a glutathione-cytosolic fraction
    and a polynucleotide. The products of the glutathione plus cytosol
    metabolism of [1,2-14C]-dichloroethane appeared to be glutathione
    metabolites rather than covalently bound adducts (Lin  et al.,

         The binding of 1,2-dichloroethane to nucleic acids and proteins
    of different murine organs was studied in  in vivo and  in vitro
    systems. 1,2-Dichloroethane was bound to DNA of liver, kidney, and
    lung to a similar extent.  In vitro activation of the chemical was
    mediated by microsomal P-450-dependent mixed function oxidases
    present in rat and mouse liver and, in smaller amount, in mouse
    lung. Activation by liver cytosolic glutathione-S-transferases also
    occurred (Prodi  et al., 1986).

         S-[2-(N7-Guanyl)ethyl]glutathione was found in liver and
    kidney DNA of male Sprague-Dawley rats 8 h after an intraperitoneal
    treatment with 150 mg of [1,2-14C]-dichloroethane/kg bw, but other
    adducts were also present. The  in vitro half-life of
    S-[2-(N7-guanyl)ethyl]glutathione in calf thymus DNA was 150 h;
    the half-life of the adduct in rat liver, kidney, stomach, and lung
    was between 70 and 100 h (Inskeep  et al., 1986).

         Male CBA mice were given [U-14C]-1,2-dichloroethane by
    intra-peritoneal injection. The doses given were 0.16, 0.23, or
    0.37 mmol/kg bw. After 22 h haemoglobin, DNA from livers, testes,
    spleens, kidneys, and lungs, and urinary purines were analyzed for
    alkylated products. The products found in haemoglobin and the
    pattern of alkylation suggested that chloroacetaldehyde and
    S-(2-chloroethyl)glutathione are important reactive metabolites
     in vivo. The alkyl purines, 7-(2-oxoethyl)guanine and
    7-[S-(2-cysteine)-ethyl]guanine, were found in DNA hydrolysates, as
    well as in the urine (Svensson & Osterman Golkar, 1986).

         Groups of two female F-344 rats (183-188 g) were exposed to
    [1,2-14C]-dichloroethane in a closed inhalation chamber to either
    a low, constant concentration (0.3 mg/l = 80 ppm for 4 h) or to a
    peak concentration (up to 18 mg/l = 4400 ppm) for a few minutes.
    After 12 h in the chamber, the doses metabolized under the two
    conditions were 34 mg/kg body weight and 140 mg/kg body weight,
    respectively. The levels of DNA adducts (not identified) in livers
    and lungs were determined as radioactivity covalently bound to DNA.
    In liver DNA 1.8 and 69 µmol adduct per mol DNA nucleotide/mmol
    1,2-dichloroethane per kg bw was found for constant low and peak
    1,2-dichloroethane exposure levels, respectively. In the lung the
    respective values were 0.9 and 31 (Baertsch  et al., 1991).

         The effect of 1,2-dichloroethane (29 mg/kg bw) on the
    incorporation of [3H]thymidine into DNA was evaluated in various
    tissues of mice. The compound was given intraperitoneally 24 h
    before sacrifice at a dose of 293 µmoles/kg bw. Two hours before the
    animals were killed, 0.5 µCi [3H]-thymidine/g bw was injected
    intraperitoneally. 1,2-Dichloroethane inhibited the [3H]thymidine
    incorporation in the forestomach and in the kidney, but not in the
    nasal mucosa, the thymus, nor the glandular stomach (Hellman &
    Brandt, 1986).

         DNA damage was measured by DNA alkylation in groups of three
    male Sprague-Dawley rats and of B6C3F1 mice induced with
    Aroclor 1254 exposed to 1.38 mg of [14C]-1,2-dichloroethane. The
    groups of animals were sacrificed after 0.25, 0.5, 1, 3, 5, 18, 24,
    48, and 72 h, and liver nuclear DNA was examined for covalently
    bound radioactivity. The alkylation of DNA in the mouse was found to
    be highest 15 min after the administration of 1,2-dichloroethane.
    DNA damage was then removed with time. Fifty per cent of damage was

    removed at 3 h, and 80% at 48 h following the administration of the
    compound. In the rat, alkylation of DNA was found to be
    comparatively slower, and significantly lower, and 50% was removed
    at 48 h and 75% at 72 h. Similar time-dependent DNA damage was seen
     in vitro when liver microsomes and nuclei were incubated with
    [14C]-1,2-dichloroethane. A significant inhibition of RNA
    synthesis was observed when transcription was carried out  in vitro
    using nuclei of treated rats. The inhibition in RNA synthesis
    persisted even when 50% of DNA damage was removed. Similarly,
    nuclear DNA synthesis  in vitro was also significantly inhibited
    during DNA damage. However, DNA synthesis recovered rapidly even
    though 50% of DNA damage persisted (Banerjee, 1988).

    2.2.9  Special studies on metabolites

         Groups of 8, 3, 3, and 10 male Long-Evans rats were given
    S-(2-chloroethyl)-DL-cysteine intraperitoneally at doses of 0, 50,
    75, and 100 mg/kg bw, respectively, and examined for nephrotoxicity
    after 36 h by blood and urine biochemistry and histopathological
    examination. Significant increases in blood urea nitrogen were seen
    at 75 and 100 mg/kg bw and in urine glucose concentrations at
    100 mg/kg bw. Histopathological examination of kidneys showed acute
    proximal tubular nephrosis and punctuate glomerular necrosis at
    100 mg/kg bw. No hepatic lesions were seen and serum
    glutamate-pyruvate transaminase activities were elevated only
    slightly. The extent of S-(2-chloroethyl)-DL-cysteine renal toxicity
    was dose- and time-dependent. Equimolar doses of analogs of
    S-(2-chloroethyl)-DL-cysteine, S-ethyl-L-cysteine,
    S-(2-hydroxy-ethyl)-DL-cysteine, or S-(3-chloropropyl)-DL-cysteine
    failed to produce nephrotoxicity. Rats given intraperitoneal
    injections of L-cysteine (100 mg/kg bw), S-ethyl-L-cysteine
    (100 mg/kg bw) or probenecid (60 mg/kg bw) 30 min before receiving
    S-(2-chloroethyl)-DL-cysteine had significant reductions in the
    S-(2-chloroethyl)-DL-cysteine-induced blood urea nitrogen and urine
    glucose elevations. The authors concluded that
    S-(2-chloroethyl)-DL-cysteine is a potent, selective nephrotoxin
    that may be responsible for the renal damage associated with
    1,2-dichloroethane. The authors speculated that the formation of an
    episulfonium ion may play an important role in
    S-(2-chloroethyl)-DL-cysteine-induced nephrotoxicity. The protection
    against renal damage provided by S-ethyl-L-cysteine or probenecid
    may involve competition with S-(2-chloroethyl)-DL-cysteine for
    cellular or transport binding sites (Elfarra  et al., 1985).

         The cysteine S conjugate of 1,2-dichloroethane,
    S-(2-chloroethyl)-DL-cysteine was incubated with isolated
    hepatocytes from male Long-Evans rats at concentrations of 1-10 nM.
    S-(2-chloroethyl)-DL-cysteine. Addition resulted in both a time- and
    concentration-dependent loss of cell viability as determined by

    trypan blue exclusion, release of lactic dehydrogenase, and
    succinate-stimulated oxygen consumption. Depletion of intracellular
    glutathione concentrations (greater than 70%) and inhibition of
    microsomal Ca2+ transport and Ca2+-ATPase activity preceded the
    loss of cell viability, and initiation of lipid peroxidation
    paralleled the loss of viability. The depletion of glutathione
    concentrations was partially attributable to a reaction between
    glutathione and the test compound to form
    S-[2-(DL-cysteinyl)ethyl]glutathione, which was identified by NMR
    and mass spectrometry. N-Acetyl-L-cysteine, vitamin E, and
    N,N'-diphenyl-p-phenylenediamine protected against the loss of cell
    viability. N,N'-Diphenyl-p-phenylenediamine inhibited lipid
    peroxidation but did not protect against cell death at 4 h,
    indicating that lipid peroxidation was not the cause of cell death.
    The analogues S-ethyl-L-cysteine, S-(3-chloropropyl)-DL-cysteine,
    and S-(2-hydroxyethyl)-L-cysteine, which cannot form an episulfonium
    ion, were not cytotoxic, thus demonstrating a role for an
    episulfonium ion in the cytotoxicity associated with exposure to
    S-(2-chloroethyl)-DL-cysteine and, possibly, 1,2-dichloroethane
    (Webb  et al., 1987).

         Treatment of male B6C3F1 mice with single,
    intraperitoneal doses of 2-chloroethanol as high as 1.2 mmol/kg body
    weight failed to produce any evidence of single-strand breaks and/or
    alkalilabile lesions in hepatic DNA. When diethyl maleate was used
    to deplete hepatic glutathione levels prior to administration of
    2-chloroethanol, the acute hepatotoxicity of 2-chloroethanol was
    potentiated but again there was no evidence of hepatic DNA damage.
    These results indicate that microsomal, oxidative metabolism of
    1,2-dichloroethane to 2-chloroethanol and/or 2-chloroacetaldehyde is
    not responsible for the hepatic DNA damage observed after
    1,2-dichloroethane administration (Storer & Conolly, 1985).

         S-(2-Chloroethyl)-L-cysteine in concentrations ranging from
    0.01-0.1 nM induced unscheduled DNA synthesis and micronucleus
    formation in Syrian hamster embryo fibroblasts (Vamvakas  et al.,

         Synthetic S-(2-chloroethyl)-L-cysteine,
    N-acetyl-S-(2-chloroethyl)-L-cysteine, and
    S-(2-hydroxyethyl)-L-cysteine were tested in  Salmonella typhimurium
    TA1535, the former two compounds at concentrations of 0.2, 0.4, and
    0.6 µmol/plate, the latter compound at 2, 4, 6, and 20 µmol/plate.
    The former two compounds were direct acting mutagens in  Salmonella,
    while the latter compound showed no mutagenicity (Rannug  et al.,
    1978; Rannug & Beije, 1979).

         S-[2-(N7-Guanyl)ethyl]glutathione was formed when
    deoxyguanosine was incubated with chemically synthesized
    S-(2-chloroethyl)glutathione. Evidence was also presented for the
    formation of S-[2-(N7-guanyl)ethyl]-L-cysteine in incubation
    mixtures containing deoxyguanosine and S-(2-chloroethyl)-L-cysteine,
    the corresponding cysteine conjugate (Foureman & Reed, 1987).

    2.3  Observations in humans

         The effects of acute oral exposure are similar to those found
    after inhalation, but are more pronounced. Oral doses of 20-50 ml of
    1,2-dichloroethane have been identified as being lethal. Several
    major syndromes can be identified including central nervous system
    depression, gastroenteritis, and disorders of the liver and kidneys.
    Frequently-observed cardiovascular insufficiency and haemorrhagic
    diathesis may be related to changes in oxygenation and effects on
    the liver. Symptoms of central nervous system depression commonly
    appear within 1 hour, frequently with cyanosis, nausea, vomiting,
    diarrhoea, epigastric and abdominal pains, and irritation of the
    mucous membranes. Irreversible brain damage has been reported, and
    brain damage has been found in several fatal cases. In some of the
    cases, an interval relatively free of symptoms followed ingestion.
    In the next phase, decreasing consciousness and circulatory and
    respiratory failure occurred, often leading to death some hours or
    days after exposure. Heart rhythm disturbances can lead to cardiac
    arrest. Autopsy reports have revealed damage to the mucosae of the
    gastrointestinal tract, liver, kidneys, lung, heart, and brain.
    Livers can be enlarged. Liver and kidney epithelium can show fatty
    degenerations and necrosis. Renal insufficiency has been reported to
    follow development of hepatic insufficiency and has been shown to
    progress to uraemic coma. Lung oedema is often found. Hyperaemia and
    haemorrhagic lesions are found in some organs. According to some
    authors, it appeared that the blood coagulation time was increased
    because of a decrease in blood clotting factors and thrombocytes.
    These effects appear secondary to liver cell necrosis complicated
    further by intravascular coagulation. Biochemically, liver damage is
    illustrated by increased serum levels of bilirubin, transaminases,
    and lactate dehydrogenase. Kidney damage is expressed by anuria or
    oliguria, and albumin, leucocytes, and epithelium cells in the
    urine. Together with the histopathology this points to acute
    necrosis of the kidney tubule, possibly as a result of the liver
    cell necrosis and the changes in circulation. Haematological changes
    include decreases in the erythrocyte count and haemoglobin content
    (WHO, 1987; Nouchi  et al., 1984).

         The Iowa Cancer Registry contains information on age-adjusted
    sex-specific cancer incidence rates for the years 1969-1981 for
    towns with a population of 1000-10 000 and a public water supply
    from a single stable ground source. These rates were related to
    levels of volatile organic compounds and metals found in the

    finished drinking-water of these towns in the spring of 1979.
    Results showed association between 1,2 dichloroethane and cancers of
    the colon and rectum. The effects were most clearly seen in males.
    These associations were independent of other water quality and
    treatment variables and were not explained by occupational or other
    socio-demographic features including smoking. Because of the low
    levels of the organics, the authors suggested that they are not
    causal factors, but rather indicators of possible anthropogenic
    contamination of other types (Isacson  et al., 1985).

         1,2-Dichloroethane inhibited glutathione S-transferase in human
    erythrocytes  in situ. The concentration needed to obtain 50%
    inhibition in the assay was approximately 10 mM (Ansari  et al.,


         1,2-Dichloroethane is readily absorbed from the
    gastrointestinal tract after oral ingestion and via the lungs after
    inhalation. Following gastrointestinal absorption, radiolabelled
    1,3-dichloroethane shows a preference for liver and adipose tissue
    but is readily metabolized and excreted as non-volatile metabolites
    in the urine and as volatile metabolites via exhalation. In a study
    in rats 70-85% of an oral dose appeared in the urine as metabolites
    within 48 h, 10-20% appeared in the exhaled air, partly as carbon
    dioxide, and small amounts were elimated via the faeces or remained
    in the carcass at 48 h irreversibly bound to macromolecules, mainly
    proteins. At high dose levels, the metabolism of 1,2-dichloroethane
    may become saturated. 1,2-Dichloroethane is more easily absorbed
    from the gastrointestinal tract when administered in aqueous rather
    than in oil solution.

         The compound is able to cross the placental barrier of pregnant
    rats. However, no reproductive or teratogenic effects have been
    observed in inhalation studies in rats and rabbits.

         Metabolism of 1,2-dichloroethane may occur via two pathways:
    one dependent on microsomal cytochrome P-450-mediated oxidation and
    the other on glutathione conjugation mediated by cytosolic
    glutathione S-transferases. The metabolism of 1,2-dichloroethane
     in vitro by microsomal mixed-function oxidases leads to the
    formation of 2-chloroacetaldehyde and 2-chloroethanol.
    2-Chloroacetaldehyde may react with cellular macro-molecules or
    undergo further metabolism to 2-chloroacetic acid, which is excreted
    in the urine either unchanged or as thioethers after conjugation
    with glutathione. Although the microsomal mixed-function oxidase
    pathway  in vitro produces intermediates that bind to
    macromolecules, this pathway does not appear to be the most
    important in producing metabolites that are mutagenic in  Salmonella
     typhimurium. In contrast, conjugation of 1,2-dichloroethane with
    glutathione is thought to lead to the formation of the mutagenic
    2-chloroethyl glutathione and of ethylene. Of these, the former
    binds irreversibly to protein, DNA, and RNA and forms glutathione
    conjugates, which are excreted in the urine as thioethers. When the
    microsomal metabolism of 1,2-dichloroethane is inhibited, the
    glutathione-dependent metabolism increases, resulting in increased
    toxicity and carcinogenicity.

         1,2-Dichloroethane is more toxic when given by a bolus gavage
    to rats than when given at corresponding doses in the
    drinking-water. In short-term studies in rats, the main target
    tissues were liver, kidney, central nervous system, and forestomach.
    The first three of these are also the sites affected in humans
    accidentally exposed to high concentrations of the compound. No
    effects were observed when 1,2-dichloroethane was given orally to
    rats at 10 mg/kg bw 5 times/week for 90 days.

         1,2-Dichloroethane has been shown to be carcinogenic in
    long-term studies in mice and rats following administration by
    gavage in corn oil of doses of 50-300 mg/kg bw 5 days/week. In
    female mice, the compound induced mammary and uterine
    adenocarcinomas and possibly squamous-cell carcinomas of the
    forestomach, while hepatocellular carcinomas were induced in male
    mice. Lung adenomas and malignant histiocytic lymphomas were induced
    in mice of both sexes. When tested by inhalation, 1,2-dichloroethane
    was not carcinogenic in mice.

         In the rat, 1,2-dichloroethane given by gavage in corn oil at
    time-weighted average doses of 47 and 95 mg/kg bw/day caused an
    increase in the total number of tumours in females only at the
    higher dose. In addition, an increased number of mammary-gland
    adenocarcinomas and fibroadenomas was seen in the females and of
    squamous-cell carcinomas of the forestomach in the males at the
    higher dose. An increase in the incidence of haemangiosarcomas seen
    in animals of either sex at both dose levels was statistically
    significant only for males. When tested in an inhalation experiment,
    1,2-dichloroethane exposures of 5-150 mg/litre for 78 weeks did not
    significantly increase the tumour incidence in rats.

         1,2-Dichloroethane was weakly mutagenic in  Salmonella
     typhimurium TA1535 and TA100. Mutagenicity was enchanced by the
    addition of glutathione, and seemed to depend on cytosolic
    glutathione S-transferases. Mutagenic effects also occur in fungi,
     Drosophila spp. and mammalian cells  in vitro. Neither
    micronuclei nor dominant lethals were induced by 1,2-dichloroethane
    in mice, but a weak mutagenic effect was reported in the mouse spot
    test. DNA damage, measured as unscheduled DNA synthesis in mammalian
    cells  in vitro and as alkaline DNA unwinding in an  in vivo/
     in vitro system, has been reported.


         The Committee concluded that this compound has shown
    genotoxicity in both  in vitro and  in vivo test systems and that
    it is carcinogenic in mice and rats when administered by the oral
    route. No ADI was therefore allocated. The Committee expressed the
    opinion that 1,2-dichloroethane should not be used in food.


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    See Also:
       Toxicological Abbreviations
       Dichloroethane, 1,2- (EHC 176, 1995, 2nd edition)
       Dichloroethane, 1,2- (EHC 62, 1987, 1st edition)
       Dichloroethane, 1,2- (FAO Nutrition Meetings Report Series 48a)
       Dichloroethane, 1,2-  (WHO Pesticide Residues Series 1)
       Dichloroethane, 1,2- (Pesticide residues in food: 1979 evaluations)
       Dichloroethane, 1,2- (CICADS 1, 1998)
       Dichloroethane, 1,2- (IARC Summary & Evaluation, Volume 71, 1999)