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).
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
Rat Sprague-Dawley M 1 970
F 2 440
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
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
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
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).
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).
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).
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.
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