It is thought unlikely that chloroform undergoes fission to
    produce the trichloromethyl-free radical which is thought to account
    for the hepatotoxicity of CCL4. Studies have indicated that a large
    proportion of an oral dose of chloroform is eliminated unchanged via
    the expired air (up to 68% of the dose in humans) while studies with
    13C- and 14C-labelled chloroform in monkeys, rats and humans, have
    shown that between 18% and 80% of an oral dose could be recovered in
    the form of carbon dioxide from the expired air (Paul & Rubenstein,
    1963; Fry et al., 1972; Brown et al., 1974). There is also evidence to
    suggest that blood levels of chloroform in humans dosed with
    chloroform fall rapidly and no traces of the possible products of a
    homolytic C- Cl bond fission could be detected (i.e. CH2 Cl2 or
    C2H2Cl4) (Fry et al., 1972; Smith et al., 1973).


    Acute toxicity

         The oral LD50 values for chloroform in three strains of mice and
    in Sprague-Dawley rats were determined as below (Anonymous A):


    Species   Strain            Sex        LD50 (mg/kg)

    Mouse     Swiss             M          1 664
                                F          1 919
              CBA               M          > 500-<768
                                F          >768-<1 200
              C57BL                        >250-<500

    Rat       Sprague-Dawley    M          1 970
                                F          2 440

    Short-term toxicity


         Male and female rats of the Sprague-Dawley strain were given in a
    toothpaste base doses ranging from 15 to 410 mg/kg chloroform daily
    for 90 days. The no-untoward-effect level of this study was 
    30 mg/kg/day. At the highest level of treatment there was evidence of
    liver necrosis, splenic hyperplasia and congestion, pericarditis,
    vacuolation of the adrenal cortex and atrophy of the gonads
    (Anonymous B).

         Groups of BRL albino male and female rats were given by gavage in
    olive oil 30 mg chloroform/kg daily for six months with no untoward
    effects (Anonymous B).

         Groups of male and female Long-Evans rats were given up to 
    55 mg/kg chloroform/day for 12 months again without adverse effects
    (Anonymous B).


         There were no untoward effects in dogs exposed to 0.35 mg/kg
    chloroform daily for six months. However there were histological
    changes reported in the livers of the animals given 72 mg/kg
    chloroform for six months.


         Monkeys (Macaca inulatta) were given up to 27.5 mg
    chloroform/kg daily for 12 months. No adverse effects were reported
    (Anonymous B).

    Reproduction and teratology studies

         There have been a number of reproduction and teratology studies
    in both rats and rabbits given oral doses of chloroform as well as
    rats exposed to the solvent at concentrations of up to 300 ppm in air.
    The only effects seen in these studies were in the offspring of dams
    at the highest treatment levels where there was evidence of maternal
    toxicity. The effects were confined to reduced foetal weights. There
    was no evidence of skeletal or soft tissue abnormality attributable to
    treatment with chloroform (Anonymous A).

    Mutagenicity studies

         Bacterial studies utilizing S. typhimurium TA 1535 and TA 1538
    and E. coli K-12m with microsomal activation showed no evidence of
    mutagenic activity of chloroform (Anonymous A).

    Human data

         The serum transaminase levels, a serum alkaline phosphatase
    levels and blood urea nitrogen levels of a group of human volunteers
    using toothpaste containing 3.4% chloroform and a further group using
    the toothpaste and a mouth-rinse containing 0.425% chloroform.
    Assuming total absorption, the daily intake of chloroform would be
    68 mg for the former and 197 mg for the latter group. The exposure was
    carried out for up to five years with six-monthly measurements of the
    serum enzymes and blood urea nitrogen. There were no untoward effects
    detected in this study (De Salva et al., 1975).

    Long-term studies

         The increased incidence of kidney tumours found in ICI/CFLP male
    mice exposed to 60 mg/chloroform/kg/day for 90 weeks was thought to be
    a peculiarity in response - namely a sex-specific, species-specific
    and strain-specific phenomenon. This is borne out by the lack of
    similar findings in oral carcinogenicity studies in three other
    strains of mouse and in the rat at the same dose.

         More recently, a statistically significant number of liver and
    kidney tumours have been found in mice and rats exposed to higher dose
    levels. In the case of the mouse studies there was an increased
    incidence of liver tumours in both sexes at both dose levels in the
    111-week study. In the rat, males showed an increased incidence of
    kidney tumours at both dose levels in the 92-week study. Neither sex
    showed an increased incidence of hepatic tumours (Anonymous, 1975).


         There is a wealth of data relating to the exposure of animals and
    man to chloroform by several routes of administration. The data
    clearly demonstrate that chloroform is hepatotoxic and nephrotoxic to
    rodents at high levels of exposure although it is possible to obtain
    an overall no-effect level from these studies.

         There is now evidence of a carcinogenic effect on the part of
    chloroform in mice and one strain of rat. However this has been
    criticized because of the excessive levels of treatment employed and
    the question has been raised as to whether the neoplastic changes
    reported in this experiment are a response to initial toxic damage. A
    monograph was prepared.


         This substance is unsuitable as a food additive.


    Anonymous A (?) Acute toxicity studies, Unpublished report from
         Huntingdon Research Laboratories submitted by Beechams Ltd

    Anonymous B (?) Short-term toxicity studies, reproduction and
         teratology, US Cosmetic, Toiletry and Fragrance Association.
         Unpublished data

    Brown, D. M. et al. (1974) Metabolism of chloroform - I metabolism of
         [14C] chloroform by different species. Xenobiotica, 4, 151-163

    De Salva, S. et al. (1975) Long-term safety studies of a chloroform
         containing dentifrice and mouth-rinse in man, Fd. Cosmet.
         Toxicol., 13, 529-532

    Fry, B. J., Taylor, T. & Hathaway, D. E. (1972) Pulmonary elimination
         of chloroform and its metabolites in man, Arch. int. Pharmacol.
         Therap., 196, 98-111

    Paul, B. B. & Rubenstein, D. (1963) Metabolism of carbon tetrachloride
         and chloroform by the rat, J. Pharmacol. exp. Therap., 141,

    Smith, A. A. et al. (1973) Chloroform, halothane and regional
         anaesthesia, A comparative study, Anesth. Analg., 52, 1-11

    See Also:
       Toxicological Abbreviations
       Chloroform (EHC 163, 1994)
       Chloroform (HSG 87, 1994)
       Chloroform (ICSC)
       CHLOROFORM (JECFA Evaluation)
       Chloroform (PIM 121)
       Chloroform (CICADS 58, 2004)
       Chloroform  (IARC Summary & Evaluation, Supplement7, 1987)
       Chloroform  (IARC Summary & Evaluation, Volume 1, 1972)
       Chloroform  (IARC Summary & Evaluation, Volume 20, 1979)
       Chloroform  (IARC Summary & Evaluation, Volume 73, 1999)