752. Dichloroethane, 1,2- (WHO Food Additives Series 30)

1,2-DICHLOROETHANE

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

1. EXPLANATION

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. BIOLOGICAL DATA

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.,
1980).

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.,
1983).

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.,
1988).

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.,
1985).

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.,
1990).

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

2.2.2.1 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.,
1976).

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.,
1990).

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

2.2.3.1 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).

2.2.3.2 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

2.2.4.1 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
F_1a litters. Two weeks postweaning of the F_1a litters the F₀
adults were rerandomized to produce the F_1b litters. The F₀
females were rested for two weeks, following weaning of the F_1b
pups, and randomly remated (F_1c mating) for dominant lethal and
teratology testing. At weaning the F_1b 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
F_2a litters. Two weeks postweaning of the F_2a pups the F_1b
adults were randomly remated (F_2b 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 F_1b 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 F_1a, F_1b, and F_2a 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 F_1c and F_2b 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 F_1c and F_2b 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).

2.2.4.2 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).

2.2.2.5 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
1.2-dichloroethane

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 Positive^2,6
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
1.2-dichloroethane

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
mutation

Table 1. cont'd

Test system Test object Concentration of Results Reference
1.2-dichloroethane

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
1.2-dichloroethane

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

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
test

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
1.2-dichloroethane

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

Intrasanguineous E. coli K12 0-200 mg/kg bw Negative King et al., 1979
host mediated (343/113) intraperitoneal
assay¹⁸

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

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

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
1.2-dichloroethane

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
Negative¹⁹

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.,
1987).

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,
1985).

[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.,
1985).

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-hydroxyethyl)-N-acetyl-DL-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.,
1988).

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.,
1987).

3. COMMENTS

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.

4. EVALUATION

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)