CHLOROFORM BIOLOGICAL DATA BIOCHEMICAL ASPECTS 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). TOXICOLOGICAL STUDIES 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 >500-<768 Rat Sprague-Dawley M 1 970 F 2 440 Short-term toxicity Rat 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). Dogs 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. Monkey 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). Comments 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. EVALUATION This substance is unsuitable as a food additive. REFERENCES 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, 141-148 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)