INTERNATIONAL PROGRAMME ON CHEMICAL SAFETY
ENVIRONMENTAL HEALTH CRITERIA 62
1,2-DICHLOROETHANE
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the International Labour Organisation,
and the World Health Organization
World Health Orgnization
Geneva, 1987
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CONTENTS
ENVIRONMENTAL HEALTH CRITERIA FOR 1,2-DICHLOROETHANE
1. SUMMARY AND CONCLUSIONS
2. IDENTITY, PHYSICAL AND CHEMICAL PROPERTIES, ANALYTICAL METHODS
2.1. Identity
2.2. Physical and chemical properties
2.3. Analytical methods
3. SOURCES IN THE ENVIRONMENT, ENVIRONMENTAL TRANSPORT AND DISTRIBUTION
3.1. Natural occurrence
3.2. Man-made sources
3.2.1. Production, disposal of waste, and uses
3.2.1.1 Production levels
3.2.1.2 Production processes
3.2.1.3 Disposal of wastes
3.2.1.4 Uses
3.3. Transport and fate in the environment
4. ENVIRONMENTAL LEVELS AND HUMAN EXPOSURE
4.1. Environmental levels
4.1.1. Water
4.1.2. Air
4.1.3. Food
4.1.4. Industrial wastes
4.2. General population exposure
4.3. Occupational exposure
5. KINETICS AND METABOLISM
5.1. Absorption
5.2. Distribution
5.3. Metabolism
5.4. Excretion and elimination
6. EFFECTS ON ORGANISMS IN THE ENVIRONMENT
6.1. Aquatic organisms
6.1.1. Acute toxicity
6.1.2. Short-term exposures
6.1.3. Long-term exposure
6.1.4. Bioconcentration
6.2. Microorganisms
6.3. Terrestrial toxicity
6.3.1. Birds
6.3.2. Plants
7. EFFECTS ON ANIMALS
7.1. Single exposures
7.1.1. Inhalation and oral exposure
7.1.2. Skin and eye irritation
7.2. Short-term exposures
7.2.1. Inhalation exposure
7.2.2. Oral exposure
7.3. Long-term exposure
7.3.1. Inhalation exposure
7.3.2. Oral exposure
7.4. Carcinogenicity
7.4.1. Inhalation exposure
7.4.2. Oral exposure
7.4.3. Dermal exposure
7.5. Mutagenicity and related end-points
7.5.1. Mutations
7.5.1.1 Bacteria
7.5.1.2 Fungi
7.5.1.3 Insects
7.5.1.4 Mammals/mammalian
7.5.2. Chromosome damage/DNA damage
7.5.3. Cell transformation
7.6. Reproduction and teratogenicity
7.6.1. Inhalation exposure
7.6.2. Oral exposure
7.7. Immunotoxicity
8. EFFECTS ON MAN
8.1. Accidental exposures
8.1.1. Inhalation exposure
8.1.2. Oral exposure
8.1.3. Acute effects on eyes and skin
8.2. Occupational exposure
9. EVALUATION OF HUMAN HEALTH RISKS AND EFFECTS ON THE ENVIRONMENT
9.1. Evaluation of human health risks
9.2. Evaluation of effects on the environment
9.2.1. Air
9.2.2. Water
9.2.3. Soil
10. RECOMMENDATIONS FOR FURTHER STUDIES
11. PREVIOUS EVALUATIONS BY INTERNATIONAL BODIES
REFERENCES
WHO TASK GROUP ON 1,2-DICHLOROETHANE
Members
Dr B. Gilbert, CODETEC, University City, Campinas, Brazil
Professor P. Grasso, Robens Institute, University of Surrey,
Guildford, Surrey, United Kingdom
Mr M. Greenberg, Environmental and Criteria Assessment Office,
US Environmental Protection Agency MD-52, Research Triangle
Park, North Carolina, USA (Rapporteur)
Professor M. Ikeda, Department of Environmental Health, Tohoku
University School of Medicine, Sendai, Japan (Chairman)
Dr N.N. Litvinov, A.N. Sysin Institute of General and Community
Hygiene, USSR Academy of Medical Science, Moscow, USSR
(Vice-Chairman)
Dr G.B. Maru, Carcinogenesis Division, Cancer Research Insti-
tute, Tata Memorial Center, Parel, Bombay, India
Professor M. Noweir, Occupational Health Research Centre, High
Institute of Public Health, University of Alexandria,
Alexandria, Egypt
Dr E. Rauckman, Carcinogenesis and Toxicologica Evaluation
Branch, National Institute of Environmental Health Sciences,
National Toxicology Program, Research Triangle Park, North
Carolina, USA
Professor D.J. Reed, Environmental Health Sciences Center,
Oregon State University, Corvallis, Oregon, USA
Dr E. Rosskamp, Institute for Water, Soil and Air Hygiene of
the Federal Ministry of Health, Berlin (West)
Dr S. Susten, Document Development Branch, Division of Standards
Development and Technology Transfer, National Institute for
Occupational Safety and Health, Cincinnati, Ohio, USA
Secretariat
Professor F. Valic, Andrija Stampar School of Public Health,
University of Zagreb, Zagreb, Yugoslavia (Secretary)a
Dr T. Ng, Office of Occupational Health, World Health Organ-
ization, Geneva, Switzerland
Ms F. Ouane, International Register of Potentially Toxic
Chemicals, United Nations Environment Programme, Geneva,
Switzerland
Dr T. Vermeire, National Institute of Public Health and
Environmental Hygiene, Bilthoven, Netherlands (Temporary
Adviser)
Mr J. Wilbourn, Unit of Carcinogen Identification and
Evaluation, International Agency for Research on Cancer,
Lyons, France
a IPCS Consultant.
NOTE TO READERS OF THE CRITERIA DOCUMENTS
Every effort has been made to present information in the
criteria documents as accurately as possible without unduly
delaying their publication. In the interest of all users of the
environmental health criteria documents, readers are kindly
requested to communicate any errors that may have occurred to
the Manager of the International Programme on Chemical Safety,
World Health Organization, Geneva, Switzerland, in order that
they may be included in corrigenda, which will appear in
subsequent volumes.
* * *
A detailed data profile and a legal file can be obtained
from the International Register of Potentially Toxic Chemicals,
Palais des Nations, 1211 Geneva 10, Switzerland (Telephone no.
988400 - 985850).
ENVIRONMENTAL HEALTH CRITERIA FOR 1,2-DICHLOROETHANE
A WHO Task Group on Environmental Health Criteria for
1,2-Dichloroethane met in Geneva from 25 to 30 August, 1986.
Professor F. Valic opened the meeting on behalf of the Director-
General. The Task Group reviewed and revised the draft criteria
document and made an evaluation of the health risks of exposure
to 1,2-dichloroethane.
The drafts of this document were prepared by DR T. VERMEIRE
of the National Institute of Public Health and Environmental
Hygiene, Bilthoven, the Netherlands.
The efforts of all who helped in the preparation and
finalization of the document are gratefully acknowledged.
* * *
Partial financial support for the publication of this
criteria document was kindly provided by the United States
Department of Health and Human Services, through a contract from
the National Institute of Environmental Health Sciences,
Research Triangle Park, North Carolina, USA - a WHO
Collaborating Centre for Environmental Health Effects. The
United Kingdom Department of Health and Social Security
generously supported the costs of printing.
1. SUMMARY AND CONCLUSIONS
1,2-Dichloroethane (DCE) is a colourless, flammable, and
volatile liquid that decomposes slowly in the presence of air,
moisture, and light; its vapour decomposes in flame and on hot
surfaces yielding hydrogen chloride, phosgene, and other
chlorine-containing compounds.
Sensitive analytical methods have been developed for the
determination of 1,2-dichloroethane using gas chromatography.
Detection limits are in the range of 0.02 - 1.2 µg/m3 air,
0.001 - 10 µg/litre water, 25 µg/litre blood, and 44 - 100
µg/kg food or tissue. Methods used for air analysis
include direct ultraviolet or infrared spectroscopy and direct
reading colorimetry tubes.
World production of 1,2-dichloroethane in 1981 was estimated
to be about 23 000 kilotonnes. In 1983, the chemical was ranked
as the 15th highest volume chemical produced in the USA. It is
principally used in the synthesis of vinyl chloride. Human
exposure mainly occurs at, and in the vicinity of, production
facilities, through skin contact and inhalation. Almost 60% of
the total emission (about 0.2% of production) is estimated to be
lost to the air, water, and soil from these industries; nearly
one-third of this loss is estimated to occur via disposal of
heavy ends in vinyl chloride production (EDC tars). Human
exposure to the vapour as a result of dispersive uses of 1,2-
dichloroethane can occur when it is used in gasoline or as a
solvent or seed fumigant. Losses via dispersive uses account
for about 40% of the total emission. Emissions also occur from
contaminated water and from waste-disposal sites.
Average concentrations found in the vicinity of production
facilities have been below 40 µg/m3. In the air of cities,
average concentrations of between 0.3 and 6.5 µg/m3, with a
reported maximum of 30 µg/m3, have been measured. Only two old
reports on small groups of occupationally-exposed men are
available, indicating exposure levels of 40 - 800 mg/m3.
In air, 1,2-dichloroethane is degraded by sunlight fairly
rapidly yielding mainly carbon oxides and hydrogen chloride.
This prevents accumulation in the atmosphere.
Emissions of 1,2-dichloroethane entering water may amount to
about 0.1% of production volume; in addition, some of the
emissions from EDC tars will also contaminate water. However,
average levels in drinking-water are generally below 1
µg/litre. The main removal process from water is
evaporation, since chemical degradation, biodegradation, and
bioconcentration are unlikely to occur.
LC50 values for fish exposed for 1 - 4 days ranged between
85 and 550 mg/litre water, with bioaccumulation unlikely. A no-
observed-adverse-effect level of 11 mg/litre was found for
Daphnia magna, following long-term exposure. 1,2-Dichloro-
ethane does not pose a signficant hazard for the aquatic
environment, except in cases of accident or inappropriate
disposal.
1,2-Dichloroethane is readily absorbed via the dermal, oral,
or inhalation routes.
After oral administration, blood levels peak earlier with
low than with high doses, and are 5 times higher with oral
exposure to doses of the order of 150 mg/kg body weight than
with similar inhalation exposure. After inhalation, a
disproportionate increase in blood level occurs with increasing
dose. At an exposure level of 3200 mg/m3, a steady blood level
is achieved after 2 - 3 h. After oral dosing, 1,2-dichloro-
ethane showed a preference for adipose tissue and liver.
Following inhalation, accumulation was mainly observed in
adipose tissue, but not in the liver. At higher levels of
exposure, relatively more 1,2-dichloroethane accumulated.
1,2-Dichloroethane was found in fetal tissues and in the
placenta, when pregnant rats were exposed by inhalation to the
compound at 1000 mg/m3 for 3 days.
When administered orally, parenterally, or by inhalation to
rats and mice, it is extensively biotransformed to urinary
metabolites (55 - 90%). Relatively more is metabolized at lower
doses. Metabolism may occur via two known pathways: one via
cytochrome P-450-mediated oxidation and the other via
glutathione conjugation. The former pathway involves the
formation of 2-chloroacetaldehyde and 2-chloroethanol. Although
this pathway appears to be important in vitro in producing
intermediates capable of interacting with DNA, it does not
appear to be important in vivo. Reactive intermediates are
formed when 1,2-dichloroethane is metabolized via glutathione
conj ugation. The identity of these intermediates has not been
confirmed, though some evidence suggests the formation of S-(2-
chloroethyl) glutathione and its alkylating episulfonium ion,
which, by reaction with DNA, yield an indicated adduct, S-[2-
(N7-guanyl)-ethyl] glutathione.
Excretion of 1,2-dichloroethane or its metabolites from
rodents is rapid. At least 89% of the body burden was excreted
via the lungs or urine within 24 h in intraperitoneally-injected
mice and within 48 h in orally-dosed mice.
The oral LD50 was found to be 413 - 489 mg/kg body weight in
the mouse, 680 - 850 mg/kg body weight in the rat, and 2500
mg/kg body weight in the dog. The 6-h LC50 was estimated to be
1060 mg/m3 in the mouse and 5100 - 6660 mg/m3 in the rat.
Deaths occurred within a narrow range of concentrations.
In an exposure-response inhalation study on rats, no adverse
effects were observed in a 7-h exposure to 1200 mg/m3. At the
next higher exposure level (2400 mg/m3), depression of the
central nervous system (CNS) was observed, and some of the rats
died after 7 h. As the exposure levels increased, depression of
the CNS became more severe, and deaths occurred after
progressively shorter exposure periods. At the highest
concentration (81 000 mg/m3), rats became comatose and some died
within 0.3 h. Liver and kidney damage was found in most of the
animals that died.
After single oral doses of 615 - 770 mg/kg body weight,
liver damage was observed histologically in rats. Myocardial
oedema and damage to coronary vessels were observed.
In 3 short-term inhalation studies, various species were
exposed to concentrations of between 405 and 3900 mg 1,2-
dichloroethane/m3 air, 6 or 7 h per day, for 5 days/week. Mice
and rats appeared to be more sensitive than guinea-pigs,
rabbits, monkeys, dogs, and cats. The overall no-observed-
adverse-effect level for exposure periods ranging from 4 to 9
monhts in the rat was about 400 mg/m3. Signs of intoxication,
including central nervous system depression and death, were
observed in all species exposed to the higher concentrations of
between 1620 and 3900 mg/m3. For rats, liver damage, mainly
consisting of fatty changes, was observed after exposure to 1540
mg/m3 for up to 12 weeks, 1620 mg/m3 for up to 8 weeks, and 1900
mg/m3 for up to 1 week. In rats, guinea-pigs, and mice, an
increased mortality rate was observed at concentrations of 730
mg/m3 or more. In rabbits, there was an increase in the
mortality rate from 1540 mg/m3 and, in monkeys, from 1620 mg/m3.
Dogs and cats only showed increased mortality at 3900 mg/m3.
Repeated oral administration of 1,2-dichloroethane at a dose
of 300 mg/kg body weight was lethal for rats after 5 doses and
produced necrosis and fatty changes in the liver. No effects
were observed when the chemical was given orally to rats at 10
mg/kg body weight daily for 90 days or at 150 mg/kg, 5 times per
week, for 2 weeks.
1,2-Dichloroethane is weakly mutagenic in Salmonella
typhimurium TA 1535, both in the absence of, and in the presence
of, a microsomal activation system. However, in the presence of
cytosolic glutathione-S-transferase, a stronger positive
response was obtained. Negative results were obtained with
strains TA 1537, TA 1538, and TA 98. Mutagenicity occurs in
fungi, Drosophila, and mammalian cells in vitro. In two human
cell lines exposed to 1,2-dichloroethane, the incidence of gene
mutations was found to increase with increasing levels of
glutathione-S-transferase. Micronuclei or dominant lethals were
not induced, and a weak mutagenic effect was reported in a spot
test on mice. DNA damage has been observed in bacteria,
mammalian cells in vitro, and in mammals in vivo. 1,2-
Dichloroethane did not induce cell transformation in one of two
assays, and enhanced virus-induced cell transformation in the
other.
1,2-Dichloroethane is carcinogenic in B6C3F1 mice and
Osborne-Mendel rats following administration of doses of 50 -
300 mg/kg body weight, given by gavage, in oil. In male rats,
squamous cell carcinomas of the forestomach, subcutaneous
fibromas, and haemangiosarcomas in several organs (mainly the
spleen) were produced following gavage; in female rats, mammary
gland fibromas and mammary adenocarcinomas were increased. In
mice, increased incidences of hepatocellular carcinomas in males
and mammary gland adenocarcinomas in females, and lung adenomas
in both sexes were observed. No increase in tumour incidence
was reported in inhalation studies on Swiss mice and Sprague
Dawley rats exposed to concentrations of up to 607 mg/m3.
A prolongation of the estrus cycle, an increase in embryonal
mortality, pre-implantation losses, and haematomas were found
when female rats were exposed to 15 mg/m3, 4 h per day, 6
days/week, for 4 months prior to mating and during pregnancy.
While the fetal toxicity of 1,2-dichloroethane was not confirmed
at higher exposure levels, severe toxic effects on rats were
observed and all implantation sites resorbed. No fetal
abnormalities were observed in the rabbit. Oral adminstration
to male and female rats of up to 35 mg 1,2-dichloroethane/kg
body weight per day, via the food, for up to 2 years, did not
affect reproduction. No effects on fertility or gestation
index, and no teratological effects were observed in a 2-
generation study on mice treated with 5 - 50 mg 1,2-
dichloroethane/kg body weight per day, via drinking-water, for
up to 25 weeks.
1,2-Dichloroethane may cause severe corneal damage in
animals, but no gross skin reactions occurred in a 12-h occluded
patch test on guinea-pigs. Corneal opacity was observed in
dogs, following subcutaneous injection.
In man, immersion of the hands for 4 h at intermittent
intervals caused severe dermatitis. Conjunctivitis has been
reported from exposure to vapour, and corneal opacity from
accidental ingestion.
Two early reports describe human effects from occupational
exposure, and a number of fatal case histories through
accidental oral ingestion. Complaints referrable to the CNS,
liver, and gastrointestinal tract were reported in workers
occupationally exposed to concentrations of 1,2-dichloroethane
of 250 - 800 mg/m3. Similar complaints were reported less
frequently by workers exposed to concentrations of 40 - 150
mg/m3. Liver and bile-duct disorders, neurotic conditions,
autonomous dystonia, neuromyalgia, and hyperthyroidism have been
reported in workers exposed to 5 - 150 mg 1,2-dichlorethane/m3.
Accidental ingestion of 10 - 250 g 1,2-dichloroethane
resulted in death in all instances. Haemorrhage at various
sites, depression of the CNS, liver and kidney damage, and
pulmonary oedema occurred.
Making an overall evaluation, in the absence of human data,
and taking into account that: (a) 1,2-dichloroethane produces a
reactive intermediate that alkylates DNA, (b) it is positive in
a number of mutagenicity tests in vitro, though weakly so, and
(c) both rare and common tumours are produced in rats and mice,
it would be prudent to consider 1,2-dichloroethane as a possible
human carcinogen. Thus, it should be regarded, for practical
purposes, as if it presented a carcinogenic risk for man. In
evaluating reproduction hazards and teratogenicity, it is
necessary to rely on the limited data available from laboratory
investigations since there are no human data. The weight of
evidence does not suggest that exposure to prevailing
environmental levels poses a reproductive or teratogenic
hazard.
Degradation processes are rapid enough to prevent accumu-
lation of 1,2-dichloroethane in the atmosphere. Except in the
case of accidents or inappropriate disposal, 1,2-dichloroethane
does not present a significant hazard for the aquatic
environment. Available data are not sufficient to evaluate its
effects on soil.
Further studies are needed on: (a) DNA alkylation (adduct
identification); (b) sub-chronic toxicity by various routes of
exposure; (c) assessment of the extent to which EDC tars
contribute to contamination of groundwater by 1,2-dichloro-
ethane; and (d) dose-response on sensitive, commercially
important fish species (particularly studies relevant to EDC tar
spills).
2. IDENTITY, PHYSICAL AND CHEMICAL PROPERTIES, ANALYTICAL METHODS
2.1 Identity
Structural formula: H H
| |
Cl--C---C--Cl
| |
H H
Molecular formula: C2H4Cl2
Abbreviation: EDC
Synonyms: alpha,beta-dichloroethane, 1,2-bi-
chloroethane, ethane dichloride,
ethylene chloride, ethylene dichlor-
ide, 1,2-ethylene dichloride, sym-
(metric)-dichlorethane
Common trade names: Borer-Sol, Brocide, Destruxol
Dichlor-emulsion, Dichlor-mulsion,
Dutch Liquid, Dutch Oil, ENT 1656,
Gaze Olefiant
CAS registry number: 107-06-2
Conversion factor: 1 ppm = 4.05 mg/m3 air at 25 °C and
101.3 kPa (760 mmHg)
2.2 Physical and Chemical Properties
1,2-Dichloroethane is a flammable compound that burns with a
smoky flame. When dry, 1,2-dichloroethane is stable at ordinary
temperatures. In the presence of air, moisture, and light, the
liquid decomposes slowly, yielding hydrogen chloride and other
corrosive products. Vapour-air mixtures are readily ignited.
In a flame, or at a hot surface, 1,2-dichloroethane decomposes,
yielding hydrogen chloride, phosgene, and other chlorine-
containing compounds. Some physical characteristics of 1,2-
dichloroethane are given in Table 1.
2.3 Analytical Methods
A summary of relevant methods of sampling and analysis is
presented in Table 2.
Table 1. Some physical characteristics of 1,2-dichloroethane
-------------------------------------------------------------
Physical state liquid
Colour colourless
Taste sweet
Odour chloroform-like
Odour threshold 25 - 450 mg/m3, for perception;
162 - 750 mg/m3 for recognitiona
Relative molecular mass 98.96
Melting point -35 °C
Boiling point 83 °C
Water solubility 8.69 g/litre, 20 °C
log n-Octanol/water 1.48
partition coefficient
Relative density 1.23, 20 °C
Relative vapour density 3.42
Vapour pressure 8.53 kPa (64 mmHg), 20 °C
Flash point 13 °C (closed cup)
Flammable limits 0.25 - 0.64 g/litre, 6 to 16 vol %
-------------------------------------------------------------
a From: May (1966), Hellmann & Small (1974),
and Kleinschmidt (1983).
Table 2. Sampling, preparation, analysis
---------------------------------------------------------------------------------------------------------
Medium Sampling method Analytical method Detection Sample Comments Reference
limit size
---------------------------------------------------------------------------------------------------------
air manual sampling colorimetry, not specific Saltzman
pump direct reading (1972)
indicating tube
air continuous monit- UV-photodetection approximately not specific, contin- Nelson &
oring with or 4 mg/m3 uous monitoring por- Shapiro
without built-in table halide meter (1971)
aspirator
air continuous monitoring infra-red spectro- subject to interfer- Baretta
and breath analysis scopy ence by similar com- et al.
pounds (1969)
air sampling on charcoal desorption by car- 0.013 ug 3 - 40 NIOSH
bon disulfide, gas per sample litre (1977)
chromatography with
flame ionization
detection
air sampling on charcoal thermal desorption; 1.2 ug/m3 10 litre Parkes
or Chromosorb gas chromatography et al.
with flame ioniza- (1976)
tion detection
air gas chromatography 0.02 ug/m3 20 ml direct injection Grimsrud &
with mass spectro- Rasmussen
metric detection (1975)
air sampling on Tenax thermal desorption; 0.032 ug/m3 Krost et
polymeric beads gas chromatography al. (1982)
with mass spectro-
metric detection
---------------------------------------------------------------------------------------------------------
Table 2 (contd).
---------------------------------------------------------------------------------------------------------
water stripping by helium thermal desorption; 0.001 ug/litre Sauer
adsorption on Tenax gas chromatography (1981)
with flame ioniza-
tion detection or
mass spectrometric
detection
water stripping by helium thermal desorption; 0.1 - 0.4 5 ml Symons
or nitrogen, sorption gas chromatography ug/litre et al.
on Tenax or Chromo- with microcoulo- (1975)
sorb metric detection
water gas chromatography 0.5 ug/litre 0.1 ml direct injection, di- Fujii
with mass spectro- glycerol precolumn (1977)
metric detection
water gas chromatography 10 ug/litre 1 litre headspace analysis Piet
with electron cap- et al.
ture detection (1978)
blood, gas chromatography 25 ug/litre 1 ml headspace analysis of Zuccato
tissue with flame ioniza- blood, blood, acidified blood and et al.
tion detection 50 ug/kg 0.5 g tissue homogenate (1980)
tissue (wet tissue
weight)
food extraction by gas chromatography 100 ug/kg 5 - analysis of fumigant Heuser &
acetone-water (5:1 with ß-ionization 10 g residues Scudamore
by volume) detection (1969)
food, stripping by nitrogen elution by pentane, 44 ug/kg 10 g also suitable for air Bauer
tissue, sorption on XAD-2 gas chromatography solid solid, analysis (elution by (1981)
water with electron cap- (wet weight), 2 litre pentane-ether, detec-
ture detection 0.2 ug/litre tion limit 2.9 ug/m3
water for a 0.3 m3 sample)
---------------------------------------------------------------------------------------------------------
3. SOURCES IN THE ENVIRONMENT, ENVIRONMENTAL TRANSPORT AND DISTRIBUTION
3.1 Natural Occurrence
There are no reports of 1,2-dichloroethane occurring as a
natural product.
3.2 Man-Made Sources
3.2.1 Production, disposal of waste, and uses
3.2.1.1 Production levels
In 1983, 1,2-dichloroethane was ranked as the 15th highest
volume chemical produced in the USA (Webber, 1984). World
production in 1981 was estimated to be 23 130 kilotonnes (Gold,
1980). In the countries of the European Community, the
production capacity was estimated to be 9446 kilotonnes in 1982
(DeQuinze et al., 1984), an increase over the estimated 5290
kilotonnes capacity reported for 1977 (Atri, 1984). In the USA,
production increased from 4750 kilotonnes in 1977 (Drury &
Hammons, 1979) to 5740 kilotonnes in 1983 (Webber, 1984). In
Japan, a total production of 1800 kilotonnes was reported in
1976 (IARC, 1979).
3.2.1.2 Production processes
Two processes are used, which are very often combined into
one so-called "balanced process". The first is the vapour or
liquid phase reaction of chlorine with ethene in the presence of
a catalyst, usually 1,2-dibromoethane or metal chlorides. The
second is the reaction of ethene with oxygen and hydrogen
chloride in the presence of the catalyst, copper (II) chloride
(Drury & Hammons, 1979).
Most commercial 1,2-dichloroethane is 97 - 99% pure and
contains approximately 0.1% by weight of alkylamines to inhibit
decomposition. Impure 1,2-dichloroethane may contain poly-
chlorinated ethanes, and the uninhibited product may also
contain chlorine and/or hydrogen chloride (Drury & Hammons,
1979; IARC, 1979).
The above production processes and the production of end-
products, mainly vinyl chloride, are important sources of
emission of 1,2-dichloroethane into the environment. In 1979,
in the USA, almost 60% of the total emission of 12 kilotonnes
was lost by these industries to the air, water, and soil and
about 40% via dispersive uses as a solvent (Seufert et al.,
1980). In the USA, in 1977, approximately 35% of the emissions
of 1,2-dichloroethane associated with the production of the
compound itself and end-products were estimated to occur via
disposal of heavy ends, the so-called EDC tars, a mixture of
low- and high-boiling chlorinated hydrocarbons (Gold, 1980).
3.2.1.3 Disposal of wastes
Large amounts of western European tars used to be dumped in
the North Sea, but incineration at sea seems to be the present
practice (Jensen et al., 1975). In the USA, disposal of EDC
tars is usually by burial in a landfill or incineration (Drury &
Hammons, 1979; Gold, 1980).
3.2.1.4 Uses
The major industrial use of the compound is in the synthesis
of vinyl chloride (approximately 90% of the total production in
Japan and approximately 85% of total production in the USA)
(IARC, 1979). Other chemicals produced from 1,2-dichloroethane
are 1,1,1-trichloroethane, ethyleneamines, vinylidene chloride,
trichloroethylene, and tetrachloroethylene. In 1977, 2 - 4% of
the total production of 1,2-dichloroethane in the USA was used
for the synthesis of each of these chemicals. Another 2% was
used in the USA as a lead scavenger in gasoline. This
application will decline in importance with the world-wide
conversion to unleaded fuel. A small fraction of the total
production, approximately 0.1% in the USA in 1977, was used for
solvent and fumigant applications (Gold, 1980). When used as a
fumigant, 1,2-dichloroethane is usually mixed with carbon
tetrachloride to reduce the fire hazard, and small portions of
other fumigants may be added (WHO, 1972).
3.3 Transport and Fate in the Environment
Out of the total production of 1,2-dichloroethane in the USA
in 1979, approximately 0.2% was estimated to be lost to the
atmosphere, 40% of this during dispersive use as a solvent or
fumigant (Seufert et al., 1980). Evaporation from disposal
sites also occurs. In 1977, losses to the atmosphere were
estimated to be higher (1% of total production). Minimal
estimates for emissions entering water and for emissions via
EDC tars in 1977 were 0.1 and 0.5% of total production,
respectively (Gold, 1980).
Evaporation appears to be the major pathway by which 1,2-
dichloroethane is lost from water. In a controlled outdoor
experiment, the half-life for the disappearance from running
river water was found to be 1.4 h (Scherb, 1978). This agrees
well with laboratory findings (Dilling et al., 1975). Loss by
chemical reaction with water is insignificant (Radding et al.,
1977).
In the troposphere, rain-out and adsorption on atmospheric
aerosols are unlikely because of the high vapour pressure and
the low solubility of the compound (Cupitt, 1980). The major
part of the 1,2-dichloroethane is removed from the atmosphere
via oxidation by hydroxyl radicals. On the basis of experi-
mentally-derived rate constants, and hydroxyl radical concen-
trations of 4.8 x 106 and 1.0 x 106 radicals/ml, respectively,
half-lives for this reaction have been calculated of 10 days
(Radding et al., 1977) and 36 days (Howard & Evenson, 1976). A
lifetime of 53 days was predicted, which would preclude
accumulation in the troposphere and transport to the strato-
sphere (Howard & Evenson, 1976). The reported degradation
products are formyl chloride, hydrogen chloride, carbon dioxide,
carbon monoxide, and monochloroacetyl chloride (Pearson &
McConnell, 1975; Spence & Hanst, 1978). Since 1,2-dichloro-
ethane absorbs light within the solar spectral region, photo-
lytic transformation is possible (Cupitt, 1980). However, the
extent of this reaction has not been verified experimentally.
Slow biodegradation of 1,2-dichloroethane was observed in
fresh water, seeded by settled domestic waste water. Non-
acclimated cultures caused a biological demand of 16% of the
theoretical oxygen demand for the compound in 10 days (Price et
al., 1974). 1,2-Dichloroethane was biodegraded in aqueous media
by acclimated aerobic mixed cultures from soil or sewage samples
(Stucki et al., 1981; Tabak et al., 1981). An aerobic bacterium
G10, a Pseudomonas strain, that was able to use 1,2-dichloro-
ethane as a sole source of carbon and energy for growth, was
isolated from samples containing a mixture of activated sludge
and soil samples (Janssen et al., 1984). In addition, slow
anaerobic biodegradation, mainly to carbon dioxide, was observed
in an aqueous medium with a mixed methanogenic culture, grown on
waste activated sludge with sodium acetate as a primary
substrate (Bouwer & McCarty, 1983).
In soil, 1,2-dichloroethane adsorbs aselectively to
bentonite clay and peat moss, but not to dolomitic limestone and
silica (Dilling et al., 1975).
4. ENVIRONMENTAL LEVELS AND HUMAN EXPOSURE
4.1 Environmental Levels
4.1.1 Water
Concentrations of 1,2-dichloroethane measured at different
locations are summarized in Table 3. It will be noted that
Symons et al. (1975) observed more positive samples in finished
water than in untreated water. This suggests treatment-related
contamination during water chlorination.
4.1.2 Air
Concentrations of 1,2-dichloroethane measured in air at
various locations are summarized in Table 4.
4.1.3 Food
Reports on 1,2-dichloroethane in food are scarce. Bauer
(1981) found that levels were generally low in the Federal
Republic of Germany. Milk products with added fruits contained
an average of 0.8 µg/kg. In Canada, 15 out of 34 samples of
spice oleoresins contained between 2 and 34 mg of 1,2-
dichloroethane, used as an extractant, per kg (Page & Kennedy,
1975).
In residue studies, various amounts of 1,2-dichloroethane
were found to remain in fumigated grain, depending on the type
of grain and fumigation mixture, exposure conditions, and the
extent of subsequent ventilation (Berck, 1965, 1974). Wheat was
found to contain the highest residue levels, varying from 16 to
213 mg/kg, following common fumigation practices. Processing
reduces residue levels; for example, 1 - 10 mg/kg were recovered
in ground wheat flour; less than 2 mg/kg was present in bread
(Lynn & Vorhes, 1957; Wit et al., 1969). In the United Kingdom,
1 out of 281 samples of wheat contained 1,2-dichloroethane at a
level of 290 mg/kg; in the remaining samples, the concentration
was below the detection limit of 4.0 mg/kg (Bailey et al.,
1982). 1,2-Dichloroethane at a level of 51 mg/kg in fumigated
soybeans was completely extracted by hexane, during the
production of oil by solvent extraction (Storey et al., 1972).
4.1.4 Industrial wastes
EDC tar originating from vinyl chloride production in 1974
(400 000 tonnes on a global basis) contained up to 35% 1,2-
dichloroethane together with other components, seven of which
have been identified.
Table 3. Environmental levels in water
--------------------------------------------------------------------------------------
Type of water Location Detection Levels observeda Reference
limit (ug/litre)
(ug/litre)
--------------------------------------------------------------------------------------
Sea water Gulf of Mexico, open 0.001 nd Sauer (1981)
ocean;
near Mississippi mouth 0.05 - 0.21
Osaka Bay 0.69 (average) Okamoto &
Tatsukawa (1981)
River water Germany, Federal Rep- 1.0 1.0 (average) Bauer (1978)
ublic of; 3 rivers nd - 4.0
USA; 14 industrial 1.0 5.6 (average in Ewing et al.
river basins 25% of samples) (1977)
nd - 90
Untreated USA; 80 drinking-water 0.2 - 0.4 nd (86%) Symons et al.
water stations 3.0 (maximum) (1975)
Netherlands; 232 ground- 0.5 nd (229 stations) Zoeteman
water stations 0.8 - 1.7 et al. (1979)
(3 stations)
Drinking-water USA; 80 stations 0.2 - 0.4 nd (68%) Symons et
6.0 (maximum) al. (1975)
Japan; 5 locations 0.5 nd (4 locations) Fujii (1977)
0.9 (1 location)
Germany, Federal Rep- 1.0 nd Bauer (1981)
ublic of; 100 cities
--------------------------------------------------------------------------------------
a nd = not detected.
4.2 General Population Exposure
Daily intake from urban air in the USA has been estimated to
be between 8 and 140 µg per day (Singh et al., 1983). In the
Netherlands, the figure is 26.5 µg per day (Guicherit &
Schulting, 1985).
More specifically, people can be exposed via air at, or
near, sites of production and dispersive use, notably in anti-
knock agents in gasoline. At 12 locations near production
facilities in each of 3 areas in the USA, average air
concentrations gradually decreased from 61 µg/m3 to 2 µg/m3 at
distances of 1 km and 3 - 4 km, respectively. Thus, near
production facilities, approximately 12.5 million people in the
USA were estimated to be exposed to average annual concentra-
tions of up to 40 µg/m3 (Elfers, 1979; Kellam & Dusetzina,
1980).
The annual average population exposure to 1,2-dichloroethane
from gasoline, in the USA, has been estimated to remain below
0.12 µg/m3 (Kellam & Dusetzina, 1980).
4.3 Occupational Exposure
No data were available to the Task Group concerning exposure
levels in the 1,2-dichloroethane- and vinyl chloride-
synthesizing industries. Poisoning incidents following
inhalation or skin exposure have been reported frequently for
places of work where 1,2-dichloroethane is used as a solvent or
fumigant, but data concerning exposure levels are scarce
(Hadengue & Martin, 1953; Paparopoli & Cali, 1956; Suveev &
Babichenko, 1969).
1,2-Dichloroethane levels of up to 150 mg/m3 (Kozik, 1957)
and ranging from 40 to 800 mg/m3 (Cetnarowicz, 1959) were
detected in industrial plants using the chemical as a solvent.
Time-weighted averages of 0.1 and 1 mg/m3, respectively,
have been reported for 2 different jobs in an anti-knock agent
blending plant in the USA. The maximum exposure level measured
was 8.9 mg/m3 (Jacobs, 1980).
Table 4. Environmental levels in air
------------------------------------------------------------------------------
Type of site Location Detection Average Reference
limit levels
(ug/m3) observed
(ug/m3)
------------------------------------------------------------------------------
Marine Osaka Bay 8.4 Okamoto &
Tatsukawa (1981)
Pacific 0.168 Singh et al.
(1982)
Rural USA 0.02 nd Grimsrud &
Rasmussen (1975)
Japan 0.05 0.3 - 0.4a Environment Agency,
Japan (1983)
United Kingdom 0.08 Clark et al.
(1984a,b)
Netherlands 0.2 Guicherit &
Schulting (1985)
Urban United Kingdom 0.48 - 2.14a Tsani-Bazaca
et al. (1981)
USA; 10 cities 0.335 - 6.11 Singh et al.
30 (maximum) (1983)
United Kingdom 1.2 Clark et al.
(1984a,b)
Netherlands 1.2 Guicherit &
Schulting (1985)
Industrial area USA 0.02 nd Harkov et al.
(1984)
Heavily USA 5.3b Bozzelli &
industrialized 65 (maximum) Kebbekus (1982)
areas
Japan 0.05 0.09 - 3.5a Environment Agency,
Japan (1983)
Near gasoline USA 0.2b Tsani-Bazaca
station et al. (1982)
Gasoline station Sweden 0.01 4.0 Jonsson & Berg
(1980)
Table 4 (contd.)
------------------------------------------------------------------------------
Type of site Location Detection Average Reference
limit levels
(ug/m3) observed
(ug/m3)
------------------------------------------------------------------------------
Parking garage and Sweden 0.01 2.0 - 6.5 Jonsson & Berg
repair shop (1980)
Inside cars Sweden 0.01 0.4 - 1.2 Jonsson & Berg
(1980)
Exhaust gases United Kingdom 38 - 3250a Tsani-Bazaca
(cars) et al. (1981)
Airport vicinity USA nd Tsani-Bazaca
et al. (1982)
Motorway United Kingdom 0.08 Clark et al.
(1984a)
------------------------------------------------------------------------------
a Range of values (not average).
b Many sites with undetectable levels of 1,2-dichloroethane were not
considered in the average.
nd = not detected.
5. KINETICS AND METABOLISM
5.1 Absorption
1,2-Dichloroethane can be found in the blood of rodents,
almost immediately after dermal, oral, or inhalation exposure.
During a 12-h dermal exposure of guinea-pigs to undiluted
1,2-dichloroethane, blood concentrations of 1,2-dichloroethane
increased rapidly during the first half hour and then more
slowly, up to the end of exposure (Jakobson et al., 1982). In
mice, a dermal absorption rate of 47 µg/cm2 per min was
measured over the first 15 min following application of
undiluted 1,2-dichloroethane (Tsuruta, 1975).
Oral exposure of rats to 25 or 250 mg EDC/kg body weight in
corn oil produced peak blood levels within 9 and 90 min,
respectively. Blood levels appeared to increase linearly with
exposure from 13 mg/litre at 25 mg/kg up to levels of between 30
and 70 mg/litre at 150 and 250 mg/kg. Small quantities of
metabolites, but no detectable amounts of 1,2-dichloroethane,
were recovered in faeces (Sopikov & Gorshunova, 1979; Reitz et
al., 1982).
During inhalation at concentrations of up to 3200 mg/m3,
steady-state blood levels of the chemical in rats were reached
within 2 - 3 h. The blood levels increased disproportionally
with exposure from 1.4 mg/litre at 202 mg/m3 to 8.3 mg/litre at
607 mg/m3 and 56 mg/litre at 3200 mg/m3. These data suggest
saturation of the metabolic capacity at a blood level of
approximately 5 mg/litre. Peak blood levels of 1,2-dichloro-
ethane were almost 5 times higher following oral exposure to
150 mg/kg body weight than after inhalation exposure to
607 mg/m3, which appeared equivalent to 113 mg/kg body weight
(Sopikov & Gorshunova, 1979; Spreafico et al., 1980; Reitz et
al., 1982). These exposure concentrations were the high dose
levels for the NCI (1978) oral study and the Maltoni et al.
(1980) inhalation study.
5.2 Distribution
The distribution of 1,2-dichloroethane in tissue has mainly
been investigated during exposure of laboratory animals. How-
ever, one report, has been identified that gives an indication
of the relative distribution of 1,2-dichloroethane in human
tissues (Luznikov et al., 1985). As shown in Table 5, 1,2-
dichloroethane concentrations were measured in ten biological
compartments following acute oral poisoning. 2-Chloroacet-
aldehyde, a metabolite of 1,2-dichloroacetaldehyde, was not
detected. In addition to 1,2-dichloroethane, detectable
quantities of 2-chloroethanol and monochloroacetic acid were
reported. In this report, the omentum and stomach contained
similar high levels of 1,2-dichloroethane; liver and kidney
contents were comparable, but approximately 10 times less. The
detectable amounts of metabolites were too low to make
comparisons.
Table 5. Levels of 1,2-dichloroethane and its metabolites determined by
gas chromatography in cadaveric organs and tissues of 15 human beings
who died after acute oral poisoninga
-----------------------------------------------------------------------------
Tissues/ 1,2-dichloro- 2-chloro- 2-chloro- Monochloro-
organs ethane acetalde- ethanol acetic acid
hyde
(mg/kg) (mg/kg) (mg/kg) (mg/kg)
-----------------------------------------------------------------------------
Liver 5 - 100 nd nd nd
Kidney 5 - 80 nd 0.1 1.0
Myocardium 10 - 150 nd 0.12 - 1.1 2.3 - 3.8
Spleen 1 - 50 nd 0.1 1.0
Omentum 100 - 950 nd 0.1 1.0
Brain 10 - 100 nd 0.12 - 0.28 1.0 - 2.0
Stomach 100 - 1000 nd 0.14 - 0.56 1.0 - 2.0
Small 10 - 90 nd 0.13 - 0.21 0
intestine
Large 5 - 60 nd nd nd
intestine
Blood 10 - 150 nd nd nd
-----------------------------------------------------------------------------
a From: Luznikov et al. (1985).
nd = not detected.
Note: The analytical detection limit for 1,2-dichloroethane and all meta-
bolites except monochloroacetic acid was 100 g/litre or 100 g/kg
tissue; for monochloroacetic acid, the limit was 100 g/litre or 100
g/kg tissue.
After oral exposure of rats to 25, 50, or 150 mg 1,2-
dichloroethane/kg, in corn oil, peak levels of the parent
compound in adipose tissue at 45 - 60 min exceeded those in
blood by 3.9 - 8.3 times. Peak levels in the liver, 10 min
after exposure, exceeded those in blood by 1.3 - 2.2 times.
This accumulation was lower than expected at the 2 higher
exposure levels, indicating saturation of the tissues at higher
doses. During inhalation, steady-state levels in rat tissues
were reached within 2 - 3 h and increased 20- to 30-fold when
the exposure increased from 202 to 1012 mg/m3, suggesting a
saturable metabolic capacity (section 5.3). Levels in adipose
tissue, at steady-state, were 7 - 8 times higher than those in
blood, while levels in the liver were 20% below those in blood.
At comparable blood levels, the maximum concentration of 1,2-
dichloroethane after inhalation was lower in the liver and
higher in lung and adipose tissue than after oral exposure.
Levels in the spleen, brain, and kidney were similar to those in
the blood, irrespective of the route of administration
(Spreafico et al., 1980).
Forty-eight h after ingestion of 150 mg/kg body weight or
inhalation exposure to a concentration of 607 mg/m3, 3 - 4% of
the body burden of labelled 1,2-dichloroethane was recovered in
the carcass of rats. Most radioactivity was found in the liver
and kidneys. Residual radioactivity in selected tissues was 1 -
2 times higher after oral exposure than after inhalation.
Another difference between oral and inhalation exposure was the
higher residual activity in the forestomach, well after the oral
exposure. A similar distribution pattern emerged for macro-
molecular binding, as determined 4 h after oral ingestion or
directly after inhalation. At these times, oral exposure pro-
duced lower levels of total macromolecular binding, but higher
levels of DNA alkylation than inhalation exposure. The absolute
levels of DNA alkylation (2 - 14 µmol equivalents of 1,2-
dichloroethane per mol DNA at 1 mmol/kg body weight) were
considered low (Reitz et al., 1982).
In another study, rats and mice were compared with respect
to DNA binding in liver, kidney, stomach, and lung, 22 h after a
single intraperitoneal injection of 0.86 mg labelled 1,2-
dichloroethane/kg body weight in ethanol. Binding to lung DNA
was low compared with that in the other tissues. Binding to DNA
of mouse organs was always greater than that to DNA of rat
organs (Arfellini et al., 1984).
When pregnant rats inhaled 1,2-dichloroethane at a level of
1000 mg/m3, for 4 h per day, the compound was found to accumu-
late in the placental and fetal tissues over a period of 7 days
(Vosovaya, 1977). Withey & Karpinski (1985) also obtained
evidence that exposure of rats to 1,2-dichloroethane via
inhalation results in detectable levels in fetuses in a dose-
related manner.
Binding of 1,2-dichloroethane to protein, lipid, and DNA was
also observed in vitro (Guengerich et al., 1980).
5.3 Metabolism
Metabolism of 1,2-dichloroethane appears to have a signi-
ficant role in the manifestation of the toxic, carcinogenic, and
mutagenic effects of this chemical.
Biotransformation of 1,2-dichloroethane is extensive in the
mouse; ip doses of 50 and 170 mg/kg body weight were associated
with 88 and 55% conversion to metabolites, respectively (Yllner,
1971). The metabolites identified by Yllner (1971) are shown in
Table 6. Reitz et al. (1982) observed extensive metabolism of
1,2-dichloroethane in the rat, i.e., 70 and 91% transformation,
with oral (150 mg/kg) and inhalation (607 mg/m3; 6 h) exposures,
respectively, 85% of the metabolites appearing in the urine.
Biotransformation of 1,2-dichloroethane approaches saturation at
high blood levels.
Table 6. Non-volatile urinary metabolites of 1,2-dichloroethane in rodents
-----------------------------------------------------------------------------
Species Route Metabolite Fraction of Reference
total (%)
-----------------------------------------------------------------------------
mouse oral (conjugated) S-carboxy- 48 Yllner (1971)
(in methylcysteine
oil)
thiodiacetic acid 33
chloroacetic acid 16
S,S'-ethene-bis-cysteine 0.9
2-chloroethanol 0.3
rat inhal- thiodiacetic acid 67 - 68 Reitz et al.
ation (1982)
or
oral
(in thiodiacetic acid 26 - 29
oil) sulfoxide
oral S-(2-hydroxyethyl)mercap- Nachtomi et al.
(in turic acid (1966)
oil)
S-(2-hydroxyethyl)cysteine
2-chloroethanol Kokarovtseva &
Kiselyova (1978)
-----------------------------------------------------------------------------
1,2-Dichloroethane metabolism involves the formation of
sulfur-containing metabolites, which appear in the urine. Two
proposed pathways of metabolism of 1,2-dichloroethane are
depicted in Fig. 1; one pathway begins with cytochrome P-450-
mediated oxidation, and the other begins with glutathione
conjugation. There is a lack of evidence that doses of 1,2-
dichloroethane, either by gavage or inhalation, have any effects
on the distribution of its metabolites between these pathways.
Cytochrome P-450 enzymes catalyse an oxidative transformation of
1,2-dichloroethane to form reactive intermediates, which result
in the formation of 2-chloroacetaldehyde and 2-chloroethanol
(Guengerich et al., 1980) (Fig. 1). Johnson (1965, 1966, 1967)
has shown that 2-chloroacetaldehyde reacts both enzymatically
and non-enzymatically with glutathione (GSH).
Rannug et al. (1978) first reported that mutagenic compounds
could be formed by the reaction of GSH with 1,2-dihaloalkanes in
the presence of cytosolic glutathione-S-transferases. This
observation led workers to investigate in greater detail the
role of glutathione-S-transferases in the metabolism and bio-
activation of both dibromoethane (DBE) and 1,2-dichloroethane
(Rannug, 1980; Sundheimer et al., 1982; Ozawa & Guengerich,
1983; Inskeep & Guengerich, 1984). This pathway (Fig. 1)
involves the direct reaction of GSH with 1,2-dichloroethane to
form S-(2-chloroethyl) glutathione, which is a half mustard with
a half-life of 69 min at 20 °C (Schasteen & Reed, 1983) and less
than 15 min at 37 °C (Foureman & Reed, 1985). Non-enzymic
conversion of the half mustard to the corresponding episulfonium
ion gives a putative alkylating agent (episulfonium ion) that
has several fates (Fig. 1). Reaction can occur with water to
form S-(2-hydroxyethyl) glutathione or reaction with thiols such
as GSH to form ethene bis-glutathione or with DNA to form
adducts. With the exception of DNA adducts, the reaction pro-
ducts are considered non-toxic and undergo further metabolism.
These reactions and subsequent metabolism of the products can
account for all of the known sulfur-containing metabolites found
in the urine of 1,2-dichloroethane-treated animals.
Although much evidence has been reported that supports the
P-450 mediated metabolism of 1,2-dihaloethanes, this branch of
the pathway (Fig. 1) does not appear relevant to DNA adduct
formation by 1,2-dichloroethane (Koga et al., 1986). Guengerich
et al. (1980) proposed the possibility of chloroso oxidation
products of 1,2-dichloroethane in DNA adduct formation (Fig. 1).
However, they observed that the apparent stimulation of P-450-
directed DNA adduct formation by GSH was a result of incomplete
removal of GSH conjugates during analysis (Koga et al., 1986).
In addition, they concluded that 2H and 18O studies on the
formation of 2-haloethanols and 2-haloacetaldehydes from 1,2-
dihaloethanes are inconsistent with a major role of such a
mechanism for DNA damage (Guengerich et al., 1986; Koga et al.,
1986).
It should be pointed out that the P-450 directed pathway can
presumably form considerable quantities of 2-haloacetaldehydes,
which readily bind to protein and non-protein thiols, as shown
for vinyl bromide and vinyl chloride (Guengerich et al., 1981)
and dibromoethane (DBE) (van Bladeren et al., 1981).
Although some DNA damage can be produced via the P-450 path-
way under in vitro conditions (Hill et al., 1978; Banerjee et
al., 1980; Guengerich et al., 1980; Lin et al., 1985), several
lines of evidence suggest that the GSH conjugation pathway is
probably of greater significance than the P-450 pathway as the
major in vivo route for DNA damage (Guengerich et al., 1980;
Rannug, 1980; Sundheimer et al., 1982; Inskeep et al., 1986).
It has been possible to correlate the 1,2-dichloroethane-
induced mutation frequency of two human cell lines with the
difference in levels of glutathione-S-transferase activities.
AHH-1 cell line mutation frequency was 25 times that in the TK6
cell line in the presence of 1,2-dichloroethane. The difference
was attributed to the fact that the AHH-1 cell line possesses 5
times more glutathione-S-transferase activity than the TK6 cell
line (Crespi et al., 1985).
Male B6C3F1 mice, pretreated with piperonyl butoxide (PIB),
were examined for the extent of hepatic DNA damage produced 4 h
after 1,2-dichloroethane administration (Storer & Conolly,
1985). PIB is a P-450 inhibitor. Hepatic DNA damage, as
measured by the alkaline DNA unwinding assay for single-strand
breaks and alkali-labile lesions, was potentiated by PIB.
Treatment of mice with high doses of 2-chloroethanol failed to
produce DNA damage, as measured by this assay. Diethylmaleate,
a GSH depletor, potentiated the hepatotoxicity of 2-chloro-
ethanol but not DNA damage. Although the significance of this
observation is uncertain, it is not inconsistent with the
hypothesis that reduction of GSH levels is associated with a
reduction in DNA damage.
Recent evidence suggests that the putative episulfonium ion,
resulting from a non-enzymatic conversion of S-(2-chloroethyl)
glutathione, is a major intermediate in the formation of DNA
adducts in vivo from 1,2-dichloroethane exposures (Fig. 2)
(Inskeep et al., 1986). When rats were administered a single
dose of 14C-1,2-dichloroethane in vivo and the liver analysed 8
h later, 78% of the DNA adducts (0.25 nmol/mg DNA) could be
released by neutral thermal hydrolysis. A major adduct and
several minor adducts were present; the major adduct co-
chromatographed with S-[2-(N7-guanyl)ethyl] glutathione. DNA
adducts released from kidney preparations by neutral thermal
hydrolysis were represented by 5 different fractions containing
radioactivity after chromatography. The postulated adduct of
liver DNA after 14C-1,2-dichloroethane exposure, S-[2-(N7-
guanyl)ethyl] glutathione, appears to be chromatographically
identical to the major adduct in rats after exposure to DBE
(Koga et al., 1986). This DBE adduct, which has been isolated
and characterized by NMR and mass spectrometry, gives strong
support to an identical adduct being the principal DNA adduct
from exposure to 1,2-dihaloethanes. The formation of apurinic
sites, as this adduct cleaves from DNA, may be a key factor in
the mutagenic and carcinogenic effects of these compounds.
5.4 Excretion and Elimination
Excretion of 1,2-dichloroethane from rodents is rapid.
Approximately 89% or more of the body burden of the compound was
excreted within 24 h in ip-injected mice (Yllner, 1971), within
48 h in orally exposed mice (Mitoma et al., 1985), and within
48 h in rats exposed orally or via inhalation (Reitz et al.,
1982; Mitoma et al., 1985). In the 3 studies cited above,
excretion of 1,2-dichloroethane or its metabolites mainly
occurred in exhaled air via the lungs and in urine via the
kidneys. In both species, and at various exposure levels, 7 -
18% of the metabolized 1,2-dichloroethane was excreted as carbon
dioxide (CO2) and approximately 80 - 85% as non-volatile
metabolites (Table 6). The metabolism of 1,2-dichloroethane in
mice and rats is dose-dependent. For example, in mice, 11 and
45% of the body burdens of 1,2-dichloroethane, resulting from ip
exposure to 50 and 170 mg/kg body weight, respectively, were
excreted unchanged via the lungs within 72 h (Yllner, 1971). In
rats, 1.8, 11.5, and 29% of the body burdens were excreted
unchanged via the lungs within 48 h following: an inhalation
exposure at 607 mg/m3 for 6 h (equivalent to a dose of 113 mg/kg
body weight) (Reitz et al., 1982), an oral dose of 100 mg/kg
body weight (Mitoma et al., 1985), and an oral dose of 150 mg/kg
body weight (Reitz et al., 1982), respectively.
The rate of elimination from blood and tissues appears to
depend on the exposure level; the higher the exposure level, the
slower the elimination rate of 1,2-dichloroethane, after both
oral and inhalation exposure. Half-lives in the blood of rats,
exposed orally, increased from 25 min at 25 mg/kg body weight to
57 min at 150 mg/kg body weight. With inhalation exposure,
half-lives increased from 13 min at 202 mg/m3 to 22 min at 1012
mg/m3, after a 6-h inhalation exposure (Spreafico et al., 1980).
In addition, after oral exposure of rats to 150 mg/kg body
weight, an initial half-life of 90 min in blood decreased to
20 - 30 min, when blood levels fell below 5 - 10 mg/litre after
3 h (Reitz et al., 1982). Elimination of 1,2-dichloroethane
from blood, adipose tissue, lung, liver, brain, kidneys, and
spleen was comparable after oral exposures of up to 150 mg/kg
body weight. Elimination from the liver was reported to be
biphasic with a higher elimination rate just after reaching peak
levels of 1,2-dichloroethane. Elimination from other organs was
monophasic. Following inhalation, elimination was the slowest
in adipose tissue and the most rapid in the lung, up to an
exposure level of 1012 mg/m3 (Spreafico et al., 1980). Withey &
Collins (1980) also reported that the elimination of 1,2-
dichloroethane was dose-dependent. After iv administration of
from 3 to 15 mg/kg body weight to male Wistar rats, the authors
found that the elimination fitted a two-compartment model at a
low-dose level and a three-compartment model at high-dose
levels.
6. EFFECTS ON ORGANISMS IN THE ENVIRONMENT
6.1 Aquatic Organisms
6.1.1 Acute toxicity
The acute toxicity of 1,2-dichloroethane for aquatic
organisms is summarized in Table 7. The concentration of 1,2-
dichloroethane was measured in four of the studies cited (see
footnotea in Table 7); the concentrations reported in the
other studies were nominal. It should be noted that, in open
systems, the toxic effects observed must have occurred at
concentrations lower than the nominal ones reported in latter
studies, due to the anticipated evaporation of 1,2-dichloro-
ethane in the aquatic media.
The species most sensitive to 1,2-dichloroethane were
members of the class Crustacea. A no-observed-adverse-effect
level below 68 mg/litre was found for Daphnia magna (Le Blanc,
1980). The shrimp Crangon crangon showed a 96-h LC50 of
85 mg/litre in sea water, measured by the flow-through method
(Adema, 1976). When the brine shrimp Artemia salina was exposed
to 1,2-dichloroethane at levels ranging from 0.25 to
25 mg/litre, growth inhibition was noted 24 h after cyst wetting
(Kerster & Schaeffer, 1983).
EDC tar is much more toxic for marine species than 1,2-
dichloroethane, the heavy fractions of the tar being responsible
for the high toxicity observed (Jernelöv et al., 1972; Rosen-
berg, 1972; Jensen et al., 1975; Rosenberg et al., 1975).
6.1.2 Short-term exposures
When blue algae Mycrocystis aerigunosa and green algae
Scenedesmus quadricauda were exposed in closed containers to
1,2-dichloroethane at 105 and 710 mg/litre, respectively, for 8
days, cell multiplication started to be inhibited (Bringmann &
Kühn, 1978). Guppies (Poecilia reticulata) were exposed for 7
days in a static test, and an LC50 of 106 mg/litre was found.
Solutions were renewed daily, but no water analysis data were
reported (Könemann, 1981). Finally, an early life stage flow-
through test was done. Fathead minnows (Pimephales promelas)
were exposed to concentrations of between 4 and 56 mg/litre
beginning from 2 to 5 days after spawning and continuing
throughout the subsequent embryonal, larval, and juvenile stages
up to 28 days after hatching. Water was analysed for 1,2-
dichloroethane. Body weight was reduced at 59 mg/litre. The
survival of juveniles, the percentage of normal larvae at hatch,
and the hatchability of embryos were not affected (Benoit et
al., 1982).
Table 7. Acute aquatic toxicity
---------------------------------------------------------------------------------------------------------
Organism Description t (°C) pH Dissolved Hardness Flow/b Parameter Concen- Reference
oxygen (mg CaCO3/ stat tration
(mg/litre) litre) open/ (mg/litre)
closed
---------------------------------------------------------------------------------------------------------
Fresh water
-----------
Bacteria Pseudomonas 25 7 stat 16-h MICc 135 Bringmann
putida closed & Kühn
(1980)
Protozoa Entosipon sulc- 25 7 stat 72-h MIC 943-1127 Bringmann
atum, Uronema closed & Kühn
parduczi, Chilo- (1981)
monas paramecium
Crustacea water flea 22 6.7-8.1 6.5-9.1 72 stat 24-h LC50 250 Le Blanc
(Daphnia magna) open no-observed- < 68 (1980)
adverse-
effect level
Crustacea water flea 20 8.0 > 2 - stat 24-h EC50 540a,d Bringmann
(Daphnia magna) open & Kühn
(1982)
Crustacea water flea 20 7.1-7.7 7.9-9.9 44.7 stat 48-h LC50 270a,d Richter
(Daphnia magna) closed 48-h EC50 160a,d et al.
20 7.0-7.5 4.1-8.4 44.7 stat 48-h LC50 320a,e (1983)
closed 48-h EC50 180a,e
Fish bluegill sunfish 21-23 6.5-7.9 32-48 stat 96-h LC50 430 Buccafusco
(Lepomis macro- closed et al.
chirus) (1981)
Fish bluegill sunfish 23 7.6-7.9 55 stat 96-h LC50 550 Dawson
(Lepomis macro- open et al.
chirus) (1977)
Fish fathead minnow 25 6.7-7.6 8.0 45.1 flow 96-h LC50 116a Walbridge
(Pimephales prom- open et al.
elas) (1983)
Table 7 (contd.)
---------------------------------------------------------------------------------------------------------
Sea water
---------
Alga Phaeodactylum stat EC50 340a Pearson &
tricornutum McConnell
(1975)f
Worm chaetopod 23 stat 96-h LC50 400 Rosenberg
(Ophryotrocha closed et al.
labronica) (1975)g
Crustacea shrimp 15 8.0 > 8.0 flow 96-h LC50 85a Adema
(Crangon crangon) open (1976)
Crustacea shrimp 16 stat 24-h LC50 170 Rosenberg
(Crangon crangon) open et al.
(1975)h
Mollusca barnacle nauplii stat 48-h LC50 186a Pearson &
(Elminius modestus) closed McConnell
(1975)
Fish dab flow 96-h LC50 115a Pearson &
(Limanda limanda) open McConnell
(1975)
Fish tidewater silver- 20 7.6-7.9 55 stat 96-h LC50 480 Dawson
sides (Menidia open et al.
beryllina) (1977)
Fish sheepshead minnow 25-31 stat 96-h LC50 130-230 Heitmüller
(Cyprinodon open no-observed- 130 et al.
variegatus) adverse- (1981)
effect level
Fish goby 15 8.0 > 8.0 flow 96-h LC50 185a Adema
(Gobius minutus) open (1976)
---------------------------------------------------------------------------------------------------------
a Water analysis for 1,2-dichloroethane was reported.
b Flow-through or static method; open or closed system.
c MIC = minimum inhibitory concentration for cell multipication. EC50 and LC50 = concentration,
causing an effect and death, respectively, in 50% of the population.
d Fleas unfed. Effect was complete immobilization.
e Fleas fed. Effect was complete immobilization.
f Effect was growth inhibition, measured by 4C uptake during photosynthesis.
g When the concentration was gradually built up during the first hour, the 96-h LC50 was
900 mg/litre, and the percentage of hatched eggs, laid within 15 days, was decreased by 90% at
400 mg/litre. The latter was not noted at 200 mg/litre.
h Concentration was gradually built up during the first hour.
6.1.3 Long-term exposure
No-observed-adverse-effect and effect concentrations were
determined on the basis of reproduction or length for Daphnia
magna in a 28-day test, in stoppered flasks. The test solution
was analysed by gas chromatography. The lowest observed adverse
effect concentrations were 21 mg/litre, on the basis of repro-
duction, and 72 mg/litre, on the basis of length. The no-
observed-adverse-effect concentrations were 11 mg/litre, on the
basis of reproduction and 42 mg/litre, on the basis of length
(Richter et al., 1983).
6.1.4 Bioconcentration
Bioconcentration of 1,2-dichloroethane in aquatic species is
unlikely in view of its physical and chemical properties. In a
tracer study, a bioconcentration factor of 2 was found for
bluegill sunfish (Lepomis macrochirus) in flowing water. The
half-life for the elimination of 1,2-dichloroethane from tissues
was 1 - 2 days (Barrows et al., 1980).
When tissues of several aquatic species, collected from near
the discharge zone of a wastewater treatment plant, were ana-
lysed for 1,2-dichloroethane, the concentration of the compound
was less than 0.5 µg/kg wet weight in all cases, while the
average effluent concentration was 41 µg/litre and the average
sediment concentration was less than 0.5 µg/kg dry weight
(Gossett et al., 1983).
6.2 Microorganisms
1,2-Dichloroethane at an influent concentration of
258 mg/litre did not affect the treatment efficiency of a bench-
scale activated sludge system. The compound itself was
virtually completely removed by stripping but not by biodegra-
dation (Stover & Kincannon, 1983). In a batch anaerobic
toxicity assay, 1,2-dichloroethane was slightly toxic to the
anaerobic digestion process from a concentration of
2.5 mg/litre, though acclimation was observed after several
days. A concentration of 20 mg/litre caused more severe
retardation, while acclimation was slow. In semi-continuous
assays, stress became evident at 1,2-dichloroethane concentra-
tions of between 5 and 7.5 mg/litre (Stuckey et al., 1980).
6.3 Terrestrial Organisms
6.3.1 Birds
The effects on reproduction were investigated in groups of
10 male and 20 female white leghorn chickens after 2 years of
oral exposure to 0, 250, or 500 mg 1,2-dichloroethane/kg feed
mash. From the fourth month of laying onwards, decreased egg
weight was observed at both dose levels, while at the higher
dose level, the number of eggs and the feed intake were also
reduced. 1,2-Dichloroethane did not affect serum composition
and growth, semen characteristics, or fertility of chickens
(Alumot et al., 1976b).
6.3.2 Plants
1,2-Dichloroethane is used as a seed fumigant, usually in
combination with compounds such as carbon tetrachloride, 1,2-
dibromomethane, or 2-chloroethanol. Such fumigants inhibited
the germination of seeds (Caswell & Clifford, 1958; Kamel,
1959), broke the dormancy period of potato tubers (Varga &
Ferenczy, 1956; Jolivet, 1968) and beech (Thorup, 1957), and
adversely affected the nodulation status and yield of groundnuts
treated with Rhizobium (Kulkarni et al., 1975). 1,2-Dichloro-
ethane vapour was both lethal and mutagenic for barley seeds at
3 mg/m3 during 24 h (Ehrenberg et al., 1974).
7. EFFECTS ON ANIMALS
7.1 Single Exposures
7.1.1 Inhalation and oral exposure
The available acute mortality data following inhalation and
oral exposure are summarized in Table 8.
Table 8. Acute mortality after inhalation or oral exposure to
1,2-dichloroethane
-----------------------------------------------------------------------------
Species/ Route Vehicle Parameter Result Reference
strain studied
-----------------------------------------------------------------------------
dog oral acacia LD50 2500 mg/kg Barsoum & Saad
gum (1934)
rat oral corn oil LD50 680 mg/kg McCollister et
al. (1956)
CD-1 oral water LD50 489 mg/kg Munson et al.
mouse (1982)
(male)
CD-1 oral water LD50 413 mg/kg Munson et al.
mouse (1982)
(female)
Wistar inhalation 6-h LC50 5100 mg/m3 Spencer et al.
rat (1951)
Sprague inhalation - 6-h LC50 6660 mg/m3 Bonnet et al.
Dawley (1980)
rat
OF1 inhalation 6-h LC50 1060 mg/m3 Gradiski et al.
mouse (1978)
(female)
rat oral LD50 850 mg/kg Larionov &
Kokarovtseva
(1976)
albino inhalation LC50(expo- 30 000 mg/m3 Nevrotsky et al.
rat sure period (1971)
unknown)
-----------------------------------------------------------------------------
Deaths occur within a narrow range of concentrations. In
rats, the difference between the 6-h LC10 and 6-h LC90 was
approximately 2800 mg/m3 (Bonnet et al., 1980). No deaths were
observed in rats after 6 h of exposure to 2000 mg/m3 (Spencer et
al., 1951). In mice, an extremely narrow range of about
500 mg/m3 was observed between the 6-h LC10 and the 6-h LC90
(Gradiski et al., 1978).
Exposure of rats to single high doses of 1,2-dichloroethane
resulted in adverse effects on the CNS, liver, kidneys,
adrenals, and lungs (Spencer et al., 1951). Groups of 10 - 52
Wistar rats were exposed to 81 000, 48 600, 12 100, 6100, 4000,
3200, 2400, or 1200 mg 1,2-dichloroethane/m3 for various lengths
of time. At the highest concentration (81 000 mg/m3), deaths
were observed in animals exposed for 0.3 h or longer. Deaths
were observed at all except the lowest of the other concentra-
tions with exposure periods of 0.4, 0.7, 3.0, 4.0, 7.0, and
7.0 h, respectively. No deaths were observed in rats exposed to
the lowest concentration for 7 h.
Severe depression of the central nervous system resulting in
coma was observed in rats exposed to the highest concentration.
At lower concentrations, this depressant action expressed itself
as various levels of "drunkeness". In this investigation,
Spencer et al. (1951) did not specify the sex of the rats.
In the same publication, the authors reported another study
in which groups of 4 - 6 female rats were exposed to 48 600,
12 100, 4000, 1200, or 800 mg/m3. "Adverse effects" (not
described by the authors) were observed at the 4 highest levels
in rats exposed for 0.2, 0.5, 3.0, and 5.5 h, respectively. No
adverse effects were observed in female rats exposed to the
lowest concentration, for 7 h.
Examination of internal organs in groups of rats killed,
either when moribund or 24 h after the last exposure, showed
that, after exposure to 1,2-dichloroethane levels of 2400 mg/m3
or more, the most severe damage occurred in the kidney and
consisted of haemorrhage and tubular necrosis. The liver showed
fatty changes and hepatocellular necrosis with haemorrhage, and
adrenal glands were haemorrhagic. Lung oedema was observed at
concentrations above 12 100 mg/m3. The injury to organs in this
study was accompanied by high blood-urea levels, a decrease in
serum-phosphatase activity, and increased lipid concentration in
the liver (Spencer et al., 1951).
Depression of the central nervous system was noted during
exposure of rats to 1,2-dichloroethane concentrations exceeding
1200 mg/m3 (Bonnet et al., 1980). From an exposure level of
4000 mg/m3, for 4 h, rats showed altered behaviour. A narcotic
effect was observed at 9100 mg/m3 (Wolff et al., 1979).
Albino rats, given a single oral dose of 615 mg/kg body
weight, showed congested livers with cloudy swelling and fatty
degeneration. The myocardium showed oedema and haemorrhaging in
the walls of the coronary vessels, stasis, and thrombi in the
vessels. These changes were associated with an increased
activity of alanine- and aspartate aminotransferase in the serum
and decreased tissue levels of nicotinamide coenzymes (Natsyuk &
Chekman, 1975). A single administration of 861 mg/kg, by
gavage, was reported to partially uncouple oxidative phosphory-
lation measured in vitro in albino rat livers, 1, 3, or 6 days
after exposure (Natsyuk et al., 1974). In rat liver microsomes,
cytochrome P-450 levels were slightly decreased after an oral
dose of 625 mg/kg (Moody et al., 1981). After a single oral
dose of 1,2-dichloroethane in corn oil at 770 mg/kg body weight
in rats, dystrophy in the cytoplasm and hyperchromatosis in the
nuclei of hepatocytes were observed. A decrease in protein
synthesis and lysosomal enzyme activity was also reported. The
same changes took place in renal nephrons (Boikova & Kravtsova,
1982). A single dose of 850 mg/kg in albino rats resulted in a
decrease in RBC count, haematocrit, and other haematological
changes (Larionov & Kokarovtseva, 1976). Oral administration of
1,2-dichloroethane (615 mg/kg) to rabbits induced pronounced
morphological changes in the liver in about 24 h (Nazikhi &
Skrizhinsky, 1973). Effects on fibrinolytic activity in the
blood of rabbits administered 1,2-dichloroethane at 1476 mg/kg
have been reported by Kagramanov & Kazieva (1972). Electro-
cardiographic changes in albino rats associated with doses of 1,
1.5, and 2 mg/kg have been reported (Saitanov & Arsenieva,
1969).
7.1.2 Skin and eye irritation
When undiluted 1,2-dichloroethane was applied directly on
the clipped skin of guinea-pigs for up to 12 h in occluded patch
tests, no gross skin reactions were visible (Jakobson et al.,
1982). Microscopic changes appeared 4 h after application,
comprising karyopyknosis, perinuclear oedema, spongiosis, and
junctional separation (Kronevi et al., 1981). In similar tests
on rabbits, moderate erythema and oedema were observed, 24 h
after application. Microscopy on the third day revealed
necrosis and other lesions such as ulcerations and acanthosis.
The severity of the changes was not indicated (Duprat et al.,
1976).
Instillation of 0.1 ml of undiluted 1,2-dichloroethane into
the conjunctival sac of the eye of rabbits generated reversible,
mild irritation characterized by conjunctivitis and epithelial
abrasion. Epithelial keratitis, described as being "in a state
of repair", was observed microscopically, 7 days after
application (Duprat et al., 1976). Reversible clouding of the
cornea was observed in dogs within 10 h of subcutaneous
administration of undiluted 1,2-dichloroethane at 0.9/kg body
weight. The clouding continued up to 48 h, but the corneas
appeared clear after 5 days. The histological changes,
including necrosis of the corneal endothelium, partially denuded
Descemet's membrane, formation of excess basement membrane, and
swelling of the corneal stroma, were also observed in dogs,
cats, and rabbits after ocular injection of 1.8 mg 1,2-
dichloroethane (0.15 ml of a 1% solution) into the anterior
chamber (Kuwabara et al., 1968).
7.2 Short-Term Exposures
7.2.1 Inhalation exposure
The effects of repeated exposure to 1,2-dichloroethane have
been studied in mice, rats, guinea-pigs, rabbits, cats, dogs,
and monkeys (Heppel et al., 1946; Spencer et al., 1951; Hofmann
et al., 1971).
Heppel et al. (1946) exposed rats of the Wistar and Osborne-
Mendel strains to 1,2-dichloroethane concentrations of 420, 730,
1540, or 3900 mg/m3 in air, 7 h daily, 5 days/week, for several
weeks. The duration varied with each exposure level. No loss
of weight and no deaths occurred in rats of either strain
exposed to 420 mg/m3 for up to 4 months (74 exposures). Seven
out of 12 Wistar rats exposed to 730 mg/m3 died within 15 weeks
(after 1 - 73 exposures) and 8/12 similarly treated rats of the
Osborne-Mendel strain died after 1 - 6 exposures. Nine out of
16 rats (strain unspecified) died within 12 weeks after 2 - 60
exposures to 1540 mg/m3; 20/26 (strain unspecified) died within
3 weeks after 3 - 15 exposures to 3900 mg/m3. Guinea-pigs were
exposed to the same concentrations of 1,2-dichloroethane as the
rats. Several deaths, which occurred in the lowest exposure
group (420 mg/m3) and in controls, were attributed to an
intercurrent disease. At higher dose levels, mortality was
related to 1,2-dichloroethane exposure. Five out of 14 guinea-
pigs died after 5 - 115 exposures to 730 mg/m3 within 23 weeks.
Fourteen out of 20 guinea-pigs died after 8 - 65 exposures to
1,2-dichloroethane at 1540 mg/m3 within 13 weeks. All guinea-
pigs exposed to 3900 mg/m3 had died by the 4th day of the
study.
Rabbits were exposed to the three higher concentrations of
1,2-dichloroethane only. No deaths were observed when rabbits
were exposed to 730 mg/m3 for 25 weeks. All 5 rabbits exposed
to 1540 mg/m3 died, one after one exposure and the rest after
89 - 97 exposures within 19 weeks. Five out of 6 rabbits
exposed to 3900 mg/m3 died after 2 - 43 exposures within 9
weeks.
A group of 19 mice survived for 4 weeks when exposed to 420
mg/m3, but 18/20 mice died within 10 days by the end of 7
exposures to 730 mg/m3. In other species, a group of 6 female
dogs survived up to 35 weeks of exposure to 1540 mg/m3. Two out
of 6 dogs exposed to 3900 mg/m3 died after 30 and 43 exposures,
respectively. Two out of six cats exposed to 3900 mg/m3 died
after 43 exposures. Cats were not exposed to lower
concentrations. Two monkeys died after 2 and 32 exposures,
respectively, to 3900 mg/m3, but 2 others exposed to 730 mg/m3
survived for 25 weeks.
Kidney and liver damage, consisting of fatty changes and
necrosis in both organs, was found in animals that died from
exposure to the highest dose level (3900 mg/m3). In addition,
the rats showed pulmonary congestion and haemorrhage; one monkey
that died after 32 exposures and one dog showed a focal
myocarditis. Approximately half of the animals that died after
exposure to 1540 mg/m3 showed similar histological changes in
the liver and kidneys, but no such changes were observed in rats
that died from exposure to lower levels. Hepatic fatty changes
were observed in guinea-pigs exposed to 730 mg/m3. Histological
examinations were not carried out on mice.
Spencer et al. (1951) exposed rats, guinea-pigs, monkeys,
and rabbits to 1,2-dichloroethane at concentrations of 1620,
810, or 405 mg/m3, 7 h per day, 5 days/week, for various lengths
of time. In a group of 15 male and 15 female rats, exposed to
the highest level, no animals survived for more than 8 weeks,
and 60% mortality occurred in a second group exposed to the same
regime after 2 or 3 exposures. Mortality was also high in a
group of 8 male and 8 female guinea-pigs exposed to 1620 mg/m3.
All males had died by the second week and all females by
approximately the 5th week. Two male monkeys experienced rapid
and severe intoxication. Both were killed when moribund after
10 - 12 exposures. On the other hand, 2 male and 1 female
rabbits tolerated 33 weeks exposure with no evidence of adverse
effects. No mortality was observed when groups of 15 male and
15 female rats and 8 male and 8 female guinea-pigs were exposed
to 810 mg/m3 for about 30 weeks (151 exposures) or 36 weeks
(180 exposures), respectively. Similarly, no clinical effects
were observed in groups of 15 male and female rats, 8 male or
female guinea-pigs, 2 male and 1 female rabbits, and 1 male and
1 female monkey exposed for approximately 30 - 36 weeks to 405
mg/m3.
Histological examination was carried out on animals exposed
to the three dose levels. In both guinea-pigs and rats exposed
to the highest dose level, liver changes consisting of cloudy
swelling and fatty changes were observed. None of the other
organs were affected. Similar but less marked changes were
observed in the monkeys, while no adverse changes were found in
the rabbits. In rats exposed to 810 mg/m3, there were no
adverse changes in the liver or other organs, but reduced growth
and some fatty changes were found in the liver of guinea-pigs.
No adverse changes were found in animals exposed to the lowest
dose level (405 mg/m3).
Hofmann et al. (1971) exposed cats, rabbits, guinea-pigs,
and rats to 1,2-dichloroethane at 1980 mg/m3 or 405 mg/m3 for
6 h/day, 5 days/week, for up to 17 weeks. At the higher
concentration, rats became dyspnoeic and guinea-pigs apathetic.
Three out of 4 rabbits died after 10 - 17 exposures, and 9/10
guinea-pigs died after 4 - 14 exposures. Rats were more
sensitive, dying after only 1 - 5 exposures. All cats survived
30 exposures. Histologically, rats showed pulmonary hyperaemia
and oedema, fatty liver, and adrenal and myocardial necrosis.
Cats and rabbits exhibited a heart lesion and guinea-pigs, fatty
changes in the myocardium, liver, and adrenals and necrosis in
the myocardium and liver. At the lower concentration (405
mg/m3), rats, guinea-pigs, rabbits, and cats exposed for 17
weeks did not show any clinical or histological changes.
Of the species studied, mice and rats appear to be more
sensitive than other species to the adverse effects of 1,2-
dichloroethane. The no-observed-adverse-effect level for short-
term exposures (4 - 9 months) in rats studied in the 3
investigations is about 400 mg/m3.
Signs of central nervous system depression observed in the
above studies were apathy in guinea-pigs at 1980 mg/m3 (Hofmann
et al., 1971) and 3900 mg/m3 (Heppel et al., 1946), and coma in
dogs and monkeys at 3900 mg/m3 (Heppel et al., 1946). When rats
were exposed continuously for 3.5 months to 5 mg/m3, changes in
EEG were observed (Dmitrieva & Kuleshova, 1971). However, the
significance of these findings is not known.
7.2.2 Oral exposure
The liver appeared to be the principal target organ
following oral exposure. Rats, treated by gavage with 1,2-
dichloroethane in corn oil for 2 weeks, 5 times per week, at
doses of 150 mg/kg body weight or less did not show any
treatment-related abnormalities in organ or body weights,
histology, clinical chemistry, or haematology (Van Esch et al.,
1977; Reitz et al., 1982).
Rats were also exposed for 90 days, 5 times per week, to 0,
10, 30, or 90 mg/kg body weight (Van Esch et al., 1977). At the
2 highest exposure levels, a tendency to decreased weight gain
was observed. At 90 mg/kg, rats of both sexes showed an
increase in the relative weight of kidneys, but only the females
on this dose showed increased relative weights of liver and
brain compared with controls. Histology and clinical chemistry
were normal. Some haematological parameters were altered, but
not in a dose-related manner. In another study, after 5 doses
of 300 mg 1,2-dichloroethane/kg body weight in 5 days, all 6
rats died, and their livers showed fatty degeneration with an
increase in the triglycerides level (Van Esch et al., 1977).
Total fat and triglycerides were elevated in the livers of
rats exposed to approximately 100 mg/kg body weight per day via
the feed, which was administered twice daily, for 7 weeks
(Alumot et al., 1976a).
No adverse effects related to liver and kidney function were
observed at the lowest dose (10 mg/kg).
7.3 Long-Term Exposure
7.3.1 Inhalation exposure
Clinical chemical investigations were performed on Sprague
Dawley rats exposed by inhalation to 1,2-dichloroethane at 0, 5,
40, 202, or 1012 mg/m3 for 7 h per day, 5 days/week (Spreafico
et al., 1980). The highest exposure level was reduced to 607
mg/m3 after a few weeks because of high mortality. Animals of
each sex were exposed, starting at 3 months of age, for 3, 6, or
18 months. In addition, animals starting at 14 months of age
were exposed for 12 months. Groups of 8 - 10 animals of each
sex were sacrificed at the specified time intervals and clinical
chemistry tests performed. Changes in SGOT, SGPT, and
c-glutamyl transpeptidase activities in the 12-month animals
were not observed in the 18-month animals. Likewise, increases
in serum-uric acid and blood urea-nitrogen levels in the 12-
month animals were not observed in the 18-month animals. In
addition, the 12-month animals, but not the 18-month animals,
displayed decreases in serum-cholesterol. On the basis of the
negative results obtained in the animals starting exposure at 3
months of age and sacrificed after 3, 6, or 18 months, the
authors suggested a lack of significant toxicity, in spite of
the biochemical changes found in the older 12-month animals.
Neurotoxic changes (conditioned reflexes) in albino rats
have been associated with a 1,2-dichloroethane exposure of 50
mg/m3, 4 h/day, for 6 months (Borissova, 1957, 1960).
7.3.2 Oral exposure
In a controlled feeding schedule for 2 years, three groups
of 18 locally-bred rats of each sex were provided with feed
fumigated with 1,2-dichloroethane. The doses of 1,2-
dichloroethane administered were estimated to be 0, 11 - 17, or
23 - 35 mg 1,2-dichloroethane/kg body weight per day. No
adverse effects were observed on growth, mortality rates, or
serum composition. The mean survival period was 18 months or
more (Alumot et al., 1976a).
7.4 Carcinogenicity
7.4.1 Inhalation exposure
Groups of 11-week-old Swiss mice and 12-week-old Sprague
Dawley rats, comprising 90 animals of each sex, were exposed to
20, 40, 202, and 1012 mg 1,2-dichloroethane/m3 air (5, 10, 50,
and 250 ppm) for 78 weeks, 7 h per day, 5 days per week, and
observed for a lifetime. Purity was reported to be greater than
99%. The highest exposure was reduced to 607 mg/m3 (150 ppm)
after a few weeks because of high mortality. Control groups
contained 115 male mice, 134 female mice, or 180 rats of each
sex. Percentage survival in male and female mice, 52 weeks
after the beginning of treatment, was, respectively, 63 and 84%
in the controls; 47 and 93% at 20 mg/m3; 66 and 80% at 40 mg/m3;
51 and 81% at 202 mg/m3; and 43 and 64% at 607 mg/m3. The last
mouse died about 100 weeks after initiation of treatment. In
male and female rats, survival at 52 weeks was, respectively, 67
and 73% in the controls; 75 and 85% at 20 mg/m3; 70 and 81% at
40 mg/m3; 70 and 84% at 202 mg/m3; and 67 and 79% at 607 mg/m3.
Most rats had died by about 140 weeks after the start of
treatment. No specific types of tumours or changes in the
incidence of tumours were found in either species, with the
exception of an increased incidence (not dose-related) of
fibromas and fibroadenomas of the mammary glands of female rats
at 20, 202, and 607 mg/m3. The average latency time for these
tumours was 83 weeks in control rats and in rats exposed at
20 mg/m3, and 79 weeks at the 2 highest exposures. The authors
ascribe the differences in the incidence of mammary tumours
between the groups to the different survival rates in the groups
(Maltoni et al., 1980).
7.4.2 Oral exposure
Groups of 50 Osborne-Mendel rats of each sex were exposed to
average doses of 1,2-dichloroethane (technical grade with
reported purity > 90%)a in corn oil of 47 or 95 mg/kg body
weight for 78 weeks (NCI, 1978). Treatment was usually given 5
times per week, and the animals were observed for another 15 -
32 weeks after the end of treatment. Control groups consisted
of 20 matched controls of each sex treated with corn oil and 60
pooled control-treated rats of each sex. Eleven minor
contaminants were detected in the test compound. The rats were
housed in the same room as rats intubated with other halogenated
hydrocarbons or carbon disulfide. Body weights were not
affected by the exposures. A dose-related increase was found in
mortality rate, which was 100%, 27 weeks after cessation of
exposure to 95 mg/kg body weight. As shown in Table 9, male
rats had a dose-related increased incidence of subcutaneous
fibromas, and forestomach squamous cell carcinomas were
observed. In treated females, the stomach showed hyperplastic
lesions. The incidence of haemangiosarcomas (in various organs,
mainly the spleen) was increased in a dose-related manner in
both sexes, but the increase was statistically significant in
males only. In females, an increase was found in the incidence
of adenocarcinomas of the mammary gland (NCI, 1978).
a Subsequent analysis indicated a purity of about 98 - 99%
(Hooper et al., 1980; Ward, 1980).
Table 9. Summary of main tumour types after oral administration of 1,2-dichoroethane to mice and ratsa
---------------------------------------------------------------------------------------------------------
Group Maximum Number of animals with:
number of Forestomach Subcutaneous Mammary Haemangiosarcomas
animals squamous cell fibromas adeno- (several organs)
examined carcinomas carcinomas
---------------------------------------------------------------------------------------------------------
Rat (male)
Pooled vehicle controls 59 0 0 0 0
Matched vehicle controls 19 0 0 1 0
Low dose 46 3 5 2 9
(P < 0.002)b (P = 0.003)b
High dose 47 9 6 0 7
(P < 0.04)c (P < 0.01)b (P < 0.02)b
Rat (female) Mammary gland
fibroma
Pooled vehicle controls 59 0 5 1 0
Matched vehicle controls 20 0 0 0 0
Low dose 50 0 14 1 4
(P < 0.01)b
High dose 50 0 8 18 4
(P < 0.001)b
---------------------------------------------------------------------------------------------------------
Group Maximum Number of animals with:
number of Hepatocellular Alveolar/ Forestomach Mammary gland
animals carcinomas bronchiolar squamous adenocarcinomas
examined adenomas cell carcinomas
---------------------------------------------------------------------------------------------------------
Mice (male)
Pooled vehicle controls 59 4 0 1 -
Matched vehicle controls 19 1 0 1 -
Low dose 46 6 1 1 -
High dose 47 12 15 2 -
(P < 0.01)b (P < 0.001)b (NS)
Mice (female)
Pooled vehicle controls 60 0 2 1 0
Matched vehicle controls 20 1 1 1 0
Low dose 50 0 7 2 9
(P = 0.001)b
High dose 48 1 15 5 7
(P < 0.001)b (NS) (P = 0.003)b
---------------------------------------------------------------------------------------------------------
a Adapted from: NCI (1978).
b Statistical analyses shown are in comparison with the pooled matched controls.
c Statistical analyses shown are in comparison with the matched vehicle controls.
In the same set of studies, B6C3F1 mice were exposed in a
similar fashion to average doses of 0, 97, or 195 mg technical
grade compound/kg body weight for males and 0, 149, or 299 mg/kg
body weight for females. They were housed in the same room
where several other hydrocarbons or other substances were
tested. After exposure, they were observed for another 12 - 13
weeks. In females, body weights were depressed at the highest
doses from week 15 onwards, while the survival rate decreased in
a dose-related manner. Mean survival exceeded 65 weeks in all
groups. Many treated mice suffered from bronchopneumonia. As
shown in Table 9, dose-related increased incidences of alveolar
or bronchiolar adenomas were found in both sexes. In males, a
dose-related increased incidence of hepatocellular carcinomas
was observed. Female mice showed slight, dose-related increases
in the incidence of squamous cell carcinomas of the forestomach,
but this was not statistically significant. In male mice,
hyperplastic changes were found at this site. The incidence of
adenocarcinomas of the mammary gland was significantly increased
in females at both doses (NCI, 1978).
7.4.3 Dermal exposure
Groups of 30 female Ha:ICR Swiss mice were treated with 42
or 126 mg 1,2-dichloroethane in acetone on the shaven dorsal
skin, 3 times per week for 440 - 594 days. In a third group,
each female received one application of 126 mg of the test
compound followed 2 weeks later by phorbol myristate acetate, a
promotor, in acetone 3 times per week for 428 - 576 days. There
were 3 control groups, a positive control, one for the promotor,
and one for no treatment. 1,2-Dichloroethane did not initiate
skin tumours. There was an elevated incidence of lung
papillomas at the highest dose compared with controls (Van
Duuren et al., 1979).
7.5 Mutagenicity and Related End-Points
7.5.1 Mutations
Information in this section is summarized in Table 10.
7.5.1.1 Bacteria
Several investigators have observed a weak or no effect of
1,2-dichloroethane in Salmonella typhimurium TA1535 or TA 100 in
spot tests or standard plate incorporation assays with or
without rat liver S9 fraction or pure microsomes (Brem et al.,
1974; McCann et al., 1975; King et al., 1979; Guengerich et al.,
1980; Principe et al., 1981). A weak mutagenic effect was
observed in 1,2-dichoroethane vapour-exposed S. typhimurium TA
1535 and TA 100, which did not increase further by the addition
of a metabolic activation system (Barber et al., 1981). However,
a stronger positive response was observed by others (Rannug et
al., 1978; Rannug & Beije, 1979; Principe et al., 1981) in TA
1535 in the presence of rat liver metabolic activation system.
It has been established that this effect has been caused by
cytosolic glutathione-S-transferases (Rannug et al., 1978; Guen-
gerich et al., 1980; Reitz et al., 1982), and similar results
have also been obtained in TA 100 (van Bladeren et al., 1981b).
In vitro Salmonella tests using the bile of mice or rats
exposed to 1,2-dichloroethane, probably containing active con-
jugates, have confirmed these results (Rannug & Beije, 1979).
No mutagenic effects were observed in forward mutation tests
with Escherichia coli (King et al., 1979).
Table 10. Tests for gene mutations/chromosome/DNA damage and cell transformation induced
by 1,2-dichloroethane
---------------------------------------------------------------------------------------------------------
Test description System description Activation Result Reference
Organism Strain/cell type system (S9)
---------------------------------------------------------------------------------------------------------
Gene mutations
reverse mutation bacteria S. typhimurium TA 1530 A + (weak) Brem et al. (1974)
TA 1535 A + (weak)
TA 1538 A + (weak)
reverse mutation bacteria S. typhimurium TA 100 A + (weak) McCann et al. (1975)
reverse mutation bacteria S. typhimurium TA 1535 P - King et al. (1979)
TA 100 P -
TA 1537 P -
TA 1538 P -
TA 98 P -
reverse mutation bacteria S. typhimurium TA 1535 P + Principe et al.
TA 1537 A or P - (1981)
TA 1538 A or P -
TA 98 A or P -
TA 100 A or P -
reverse mutation bacteria S. typhimurium TA 1535 Pa - Guengerich et al.
Pb + (1980)
reverse mutation bacteria S. typhimurium TA 1535 A or P + Barber et al.
TA 100 A or P ± (1981)
TA 1538 A or P -
TA 98 A or P -
---------------------------------------------------------------------------------------------------------
Table 10 (contd).
---------------------------------------------------------------------------------------------------------
Gene mutations (contd)
reverse mutation bacteria S. typhimurium TA 1535 A ± Rannug et al. (1978)
TA 1535 P +
TA 1535 Pb +
reverse mutation bacteria S. typhimurium TA 1535 P + Rannug & Beije (1979)
reverse mutation bacteria S. typhimurium TA 1535 P + Reitz et al. (1982)
reverse mutation bacteria S. typhimurium TA 100 Pb + van Bladeren et al.
(1981a)
forward mutation fungi S. coelicolor A - Principe et al.
A. nidulans A - (1981)
sex-linked lethals insect D. melanogaster + Rapoport (1960); Shak-
arnis (1969, 1970);
King et al. (1979)
somatic cell mutation insect D. melanogaster + Nylander et al.
(1978)
forward mutation Chinese ovary cells in vitro P ++ Tan & Hsie (1981)
hamster A +
P + Zamora et al. (1983)
forward mutation human lymphoblastoid cell line A + Crespi et al. (1985)
AHH-1 and TK6 in vitro
somatic cell mutation mouse C57BL/6J Han (female) NA +? Gocke et al. (1983)
(spot test) x T stock (male)/embryos
---------------------------------------------------------------------------------------------------------
Table 10 (contd).
---------------------------------------------------------------------------------------------------------
Test description System description Activation Result Reference
Organism Strain/cell type system (S9)
---------------------------------------------------------------------------------------------------------
Chromosome/DNA damage
micronucleus test mice NMRI/polychromatic NA - King et al. (1979)
(ip or gavage exposure) erythrocytes
micronucleus test mice CBA/polychromatic NA - Jenssen & Ramel
(ip exposure) erythrocytes (1980)
dominant lethal mice ICR Swiss/germ cells NA - Lane et al. (1982)
(ip exposure)
alkaline DNA mice B6C3F1/liver in