DRAFT CRITERIA DOCUMENT
FOR 1,2-DICHLOROETHANE
FEBRUARY 1984
HEALTH EFFECTS BRANCH
CRITERIA AND STANDARDS DIVISION
OFFICE OF DRINKING WATER
U.S. ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C. 20460
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TABLE OF CONTENTS
I - Summary
II. General Information and Properties
III. Pharmacokinetics ,
IV. Human Exposure ,
V. Health Effects in Animals
v
VI. Health Effects in Humans .
VII. Mechanism of Toxicity
VIII. Quantification of Toxicological Effects,
IX. References
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1-1
I. Summary
1,2-Dichloroethane (ethylene dichloride, EDC, 1,2-DCE)
is the largest volume chlorinated organic chemical in
production, and thus has the potential for significiant
environmental pollution. Its use as an intermediate in
the manufacture of vinyl chloride constitutes the largest
volume of usage, but the many dispersive uses probably
contribute more significantly to human exposure. These
dispersive uses include fumigating stored grain, extracting
oil from seeds, manufacturing paints, coatings and adhesives,
cleaning textiles, cleaning polyvinyl processing equipment
and as a solvent for processing pharmaceutical products
and animal fats.
Despite its widespread use, little 1,2-DCE has been
detected in air, food or water except near point emission
sources. Most authorities consider that air is the
principal route of exposure, although environmental
sampling indicates that average exposure is minimal.
Fugitive emissions from industry and miscellaneous consumer
applications of products containing 1,2-DCE are more likely
to be the major sources of exposure to humans in non-industrial
settings.
1,2-DCE exhibits a high degree of toxicity in animals
and is a mutagen as well as an animal carcinogen. Most
studies reported in the literature are inhalation studies;
very little has been reported on ingestion toxicity other
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1-2
than carcinogenicity. Also, the exposure dose levels in the
inhalation studies have invariably been in a range not
normally encountered in the environment. Virtually nothing
is known of the more subtle toxicology of very low chronic
exposure to 1,2-DCE. Numerous instances of human toxicity
have been recorded, resulting from industrial exposures or
accidental or deliberate ingestion.
No definitive studies have been reported on the nature
or the extent of 1,2-DCE metabolism in humans after exposure.
On the basis of limited studies on animals, metabolites which
have been identified in vivo in mice and rats or in liver and
kidney crude enzyme systems in vitro are (1) 2-chloroethanol,
(2) 2-chloroacetic acid, (3) S-carboxymethylcysteine, (4)
thiodiacetic acid, (5) glycolic acid, (6) oxalic acid, (7) carbon
dioxide and (8) S,S-ethylene-bis-cysteine.
The National Academy of Sciences (NAS) Safe Drinking
Water Committee and EPA's Carcinogen Assessment Group (CAG)
have calculated projected incremental excess cancer risks
associated with the consumption of 1,2-DCE via drinking
water by mathematical extrapolation from high dose animal
studies using the linear, non-threshold multi-stage model
(NAS, 1979; Anderson, 1983). A range of 1,2-dichloroethane
concentrations was computed that would be estimated to increase
the risk of one excess cancer case per million (10^), per
hundred thousand (10^) or per ten thousand (10^) people
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1-3
over a 70-year lifetime, assuming daily consumption at the
stated exposure level. The Academy estimated, at the upper
95% confidence limit, that consuming two liters of 1,2-DCE
contaminated water per day over a lifetime having a 1,2-
dichloroethane concentration of 70 ug/1, 7ug/l or 0.7 ug/1
would result in one excess cancer per 10,000, 100,000 or
1,000,000 people exposed, respectively. Using the CAG approach,
it can be estimated at the upper 95% confidence limit that
consuming two liters of contaminated water per day over a
lifetime having a 1,2-dichloroethane concentration of 95 ug/1,
9.5 ug/1, 9-*§—ag^l or 0.95 ug/1 would result in one excess
cancer per 10,000 100,000 or 1,000,000 people exposed, respectively
Using methodology described in detail elsewhere, the EPA's
Carcinogen Assessment Group also has calculated estimated
excess cancer risk rates associated with 1,2-dichloroethane
in ambient water, extrapolating from data obtained in the
NTP bioassay in male rats { increased incidence of hemangio-
sarcomas)(U.S. EPA, 1980; NCI,1978). CAG employed the linear
non-threshold model to estimate the upper bound 95% confidence
limit of the excess cancer rate that would occur at a specific
exposure level for a 70 kg adult, ingesting 2 liters of water
and 6.5 g of fish and seafood/day ("fish factor"), over a 70-
year lifespan.
These estimates are summarized in Table 1-1.
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1-4
TABLE 1-1
Drinking Water Concentrations and Associated Cancer Risks
Excess Lifetime Range of Concentrations (ug/la)
Cancer Risk
CAGb CAGC NASq
10-4 94.0 59.9 70.0
10-5 9.4 6i0 7.0
10-6 0.94 0.6 0.7
a Assumes the consumption of two liters of water per day, except
for GAG*3 which also included "fish factor"; upper 95% confidence
limit
b (U.S.EPA,1980)
c (Anderson, 1983)
d (NAS, 1977;1980)
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II-l
II- General Information and Properties
1,2-Dichloroethane, the first chlorinated hydrocarbon
described in the chemical literature, was produced initially
by Dutch chemists in 1795 (Hardie, 1964). For more than a
century, little commercial use of the compound occurred. By
1970, however, such strong demand existed that 1,2-dichloroethane
was manufactured in greater tonnage than any other chlorinated
organic compound (Rothon, 1972). In 1975, 1,2-dichloroethane
was the sixteenth highest-volume chemical produced in the
United States (Hawley, 1977) . Previously regarded by some
investigators as an irritating but relatively non-toxic
liquid (Rothon, 1972), 1,2-dichloroetha'ne is now recognized
as a highly toxic material and a potential human carcinogen
and mutagen (Fishbein, 1976).
PHYSICAL PROPERTIES
1,2-Dichloroethane is a colorless, oily liquid that has
a sweet taste and an odor like chloroform (Hawley, 1977). It
is appreciably volatile, evaporating at a rate which is 0.788
times that of carbon tetrachloride or gasoline (Whitney,
1961). Air saturated with 1,2-dichloroethane contains 350
g/m3 at 20°C and 537 g/m3 at 30°C. Its solubility in water
is 9 g/1 at 20°C. (Irish, 1963). 1,2-Dichloroethane is
completely miscible with ethanol, chloroform, ethyl ether
and octanol (Windholtz, 1976). The log of the partition co-
efficient (log P) of 1,2-dichloroethane between octanol and
water is 1.48 (Radding et al., 1977).
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II-2
1,2-Dichloroethene forms an azeotrope with water which
distills at 71.9°C under a pressure of 1 atm. The binary azeotrope
contains 19.5% water. Fourteen other binary azeotropes are
known (Mitten et al.r 1970). A ternary azeotrope containing
78% 1,2-dichloroethane, 17% ethanol, and 5% water boils at 66.7°C.
1,2-Dichloroethane is a good solvent for fats, greases,
waxes, unvulcanized rubber, resins and many other organic
compounds (Bardie, 1964); however, its usefulness as a solvent
for cellulose ethers and esters is enhanced greatly by the
addition of methanol, ethanol or their acetates (Mitten et
al., 1970).
Other physical properties are listed in Table II-l.
CHEMICAL PROPERTIES
Dry 1,2-dichloroethane is stable at ambient temperature
but decomposes slowly in the presence of air, moisture and
light, forming hydrochloric acid and other corrosive products.
The decomposing liquid, which becomes darker in color and
progressively acidic, can corrode iron or steel containers.
This deleterious reaction is completely inhibited by small
concentrations of alkylamines (Hardie, 1964) .
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II-3
TABLE II-l
Physical Properties of 1,2-Dichloroethane
Molecular weight
Density at 20°C
Melting pointt °C
Boiling point, °C
Index of refraction at 20°C
Vapor pressure, torr
At 10.0°C
At 29.4°C
Solubility in water, ppm
At 20°C
At 30°C
Vapor density (air = 1)
Flash point, closed cup, °C
Ignition temperature, °C
Viscosity at 20°C, cP
Conversion factors at 25°C
and 760 torr
98.96
1.2351
-35.36
83.47
1.4448
40
100
8,690
9,200
3.42
13
413
0.840
1 mg/liter = 1 g/m3
= 247 ppm
1 ppm = 4.05 mg/m3 =
405 ug/liter
Source: Verschueren, 1977; Weast, 1977.
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II-4
Both chlorine atoms in 1 , 2-dichloroethane are reactive
and can be replaced by other substituents. This bifunctional
nature of 1 , 2-dichloroethane makes it useful in the manufacture
of condensation polymers (Rothon, 1972), Hydrolysis, with
slightly acidulated water at 160°C to 175°C and 15 atm pressure
or with aqueous alkali at 140°C to 250°C and 40 atm pressure,
yields ethylene glycol, HOCH2CH2OH. At 120°C, addition of
ammonia under pressure yields ethylenediamine, H2NCH2CH2NH2 •
1 ,1 ,2-Trichloroethane, CH2ClCHCl2r and other higher chloroethanes
are formed by chlorinating 1 , 2-dichloroethane at 50°C in
light from a mercury vapor lamp. 1 ,2-Dichloroe thane reacts
with sodium polysulfide to form polyethylene tetrasulfide and
with fuming sulfuric acid to give 2-chloroethylsulfuryl
chloride, CH2C1CH2OSO2C1 . With Friedel-Craf ts catalysis,
both chlorine atoms in 1,2-DCE can be replaced with aromatic
ring compounds; for example, with benzene, diphenylethane,
, is formed (Bardie, 1964).
CONTAMINANTS AND CHARACTERISTICS OF THE COMMERCIAL PRODUCT
Commercial 1 , 2-dichloroethane is usually technical grade
material that is 97% to 99% pure. Common commercial
specifications for this product include: (1) free from
suspended matter and sediment; (2) color, to pass test; (3)
distillation range, 82.5°C to 84.5°C at 760 torr; (4) specific
gravity at 20°C, 1.253 to 1.257; and (5) maximum activity,
as HC1 , 0.005%. Most commercial products contain about 0.1%
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II-5
by weight alkylamine to inhibit spontaneous decomposition
(Mitten et al., 1970). Uninhibited or impure 1,2-dichloroethane
may contain chlorine or hydrogren chloride that can corrode
iron or steel containers normally used to store or transport technical
grade material. Technical grade 1,2-dichloroethane is a
severe fire hazard and a moderate explosion hazard, but
spontaneous heating is not a problem. When subjected to
excessive heating, such as during a disaster, technical grade
1,2-dichloroethane may decompose, releasing hydrogen chloride
and phosgene, both of which are highly toxic (Sax, 1975).
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III-l
III. PHARMACOKINETICS
General
Very little is known of the tissue distribution,
accumulation, metabolism or biological half-life of dichloro-
ethane in the human after acute or chronic vapor inhalation,
the most common form of exposure. Few data are available on
metabolism after ingestion. From the few quantitative studies
in mice after intraperitoneal administration, a major route
of excretion of unchanged dichloroethane is via the lungs,
but the compound is readily and extensively metabolized
principally by the liver and to an unknown extent by other
tissues. Renal excretion is the important route of elimination
of end degradation products. Detailed information on the
mammalian biotransformation intermediates is not available,
although some principal metabolites have been identified and
several pathways of metabolism proposed. The importance of
greater knowledge of the biochemical mechanisms and pathways
of metabolism rest in the growing awareness that the intermediate
metabolites of dichloroethane probably are responsible for
the tissue and organ toxicities of the compound and also for
its carcinogenic potential. 1,2-Dichloroethane itself appears
to be only a weak mutagen, but at least four postulated
metabolites, namely, chloroacetaldehyde, chloroethanol,
S-chloroethylglutathione, S-chloroethylcysteine, have been
shown to be strong mutagens in bacterial test systems. In
addition, direct covalent binding of as yet unidentified
highly reactive metabolites to DNA and microsomal protein
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III-2
has been noted. Further research on the pharraacokinetics
and metabolism of dichloroethane is strongly indicated,
particularly with respect to low chronic exposures by inhalation
or ingestion, if rational and intelligent assessment of the
hazard potential of 1,2-DCE is to be made.
ABSORPTION AND DISTRIBUTION
Inhalation of 1,2-dichloroethane vapor in air is the
common route of exposure at work sites where this compound is
manufactured or used. Accidental or intentional ingestion of
1,2-dichloroethane is considered to be uncommon. Skin
absorption occurs but is negligible in most industrial vapor
exposure situations, although absorption may be significant
by this route with direct liquid contact (Irish, 1963).
No systematic studies of absorption, distribution or
excretion of 1,2-dichloroethane by humans have been reported.
However, once inhaled or ingested, 1,2-dichloroethane can be
expected to be distributed into virtually all body tissues.
The compound is appreciably soluble in water and very soluble
in lipid with partition coefficients at 25°C for olive oil/gas
and blood serum/gas of 164 and 30, respectively (Morgan et al.,
1972). As expected from its general anesthetic properties in
animals, 1,2-dichloroethane readily passes the blood/brain
barrier. Distribution is known to occur also into milk
(Urosov, 1953) and across the placental barrier into the
fetus (Vozovaya, 1975, 1976, 1977).
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III-3
Pulmonary excretion of dichloroethane, as with other
halogenated hydrocarbons, is undoubtedly the major route of
elimination of unmetabolized dichloroethane following exposure,
Urosov (1953) reported that women exposed to about 15.5 ppm
demonstrated initial concentrations in exhaled air of 14.5
ppm. The breath concentration declined to about 3 ppm 18
hours after exposure was terminated. Similar observations
have been made in animals (monkey, dog, cat, rabbit, rat and
guinea pig) in early investigations of the anesthetic
properties and toxicity of dichloroethane (Kistler and
Luckhardt, 1929; Lehman and Schmidt-Kehl, 1936; Heppel et
al., 1945). Yllner (1971a) found that up to 45 percent of an
intraperitoneal dose of 1,2-dichloroethane (0.17 mg/kg) was
recovered unchanged and excreted in the urine, indicating that
extensive biotransformation occurs in mice. The percentage
recovered in exhaled air unchanged increased with the dose
suggesting a limited capacity for biotransformation (Table
III-l) .
TABLE III-l
Percent Distribution of Radioactivity Excreted (48-hr)
by Mice Receiving 1,2-Dichloroethane-l^c*
14CO2 (exhaled air)
Dichloroethane
(exhaled air)
Urinary metabolites
0.05
13
11
73
Dose (g/kg)
0.10 0.14
8 4
21 46
70 48
0.17
5
45
50
*Adapted from Yllner (1971b)
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III-4
The accumulation of 1,2-dichloroethane in the milk of
cows fed with fumigated grain was studied by Sykes and Klein
(1957). These researchers administered the 1,2-dichloroethane
as a corn oil solution in sealed gelatin capsules. Two cows
received the equivalent of 100 ppm in 7 kg of grain concentrate
daily. Two other cows were fed the equivalent of 500 ppm for
the first 10 days , then 1000 ppm for an additional 12 days.
A fifth cow served as a control. Seven milk samples were analyzed
between the 3rd and 22nd days of the experiment. The concentra-
tion of 1,2-dichloroethane in the control sample varied from
0.0 to 0.10 ppm, with a mean of 0.06 ppm. The milk of cows
receiving 100 ppm daily contained from 0.10 to 0.29 ppm 1,2-DCE,
reaching a peak on the 5th day, then declining to the minimum.
The milk of cows receiving the higher dose of 1,2-dichloroethane
contained from 0.18 to 0.45 ppm. The highest concentration
was reached on the 9th day, after which a slow decline was
observed. No reduction in appetite or milk production occurred
during the experiment. Sykes and Klein (1957) also considered
the possibility that 1,2-dichloroethane is metabolized by cows
to a non-volatile organic chloride, but they were unable to
verify the presence of chloride in milk from a cow fed 1000
ppm 1,2-dichloroethane for 12 days.
METABOLISM AND DISPOSITION
Until recently, almost all of the volatile haloalkanes,
particularly those used as anesthetics, were considered to be
/
biologically inert substances eliminated from the body via
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III-5
the lungs without significant alteration. Considerable
evidence is now available to show that many of the volatile
industrial solvents as well as the most commonly used anesthetics
are metabolized appreciably in vivo (Van Dyke and Chenoweth,
1965; Cohen, 1971; Cascorbi et al., 1972). Some of the most
significant questions to be answered deal with the possible
toxic effects produced by metabolites of the haloalkanes on
liver and kidney as well as their mutagenic, teratogenic and
carcinogenic potential.
No definitive studies have been reported on the nature
or the extent of dichloroethane metabolism after human exposure.
Bryzkin (1945) reported that dichloroethane underwent rapid
transformation to an "organic chloride" in patients who subse-
quently died after ingesting 150 to 200 ml; dichloroethane
itself was not, however, found in tissues at autopsy. Current
information on mammalian metabolism of 1,2-dichloroethane
derives from only a few animal studies. Figure III-l shows
the probable mammalian biotransformation of this haloalkane
as determined from these studies. Metabolites which have been
identified in vivo in mice and rats, or in liver and kidney
tissue crude enzyme systems in vitro are: (1) 1-chloroethanol,
(2) 2-chloroacetic acid, (3) S-carboxymethylcysteine, (4)
thiodiacetic acid, (5) glycolic acid, (6) oxalic acid, (7)
carbon dioxide, (8) S,S-ethylene-bis-cysteine.
Main Pathway
The principal pathway of metabolism as shown in Figure
III-l and determined by Yllner (1971a, b) in mice, involves
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_,._ ^.A '.^s- '--
Figure 3 . Postulated Pathways of B ^transformation of Qlcnioroecndne
(based on a review of available studies;
(1) C1CH2-CH2C1
glutathione S-alkyltransferase
C1CH
9 '
hydrolytic
dehalogenation
(liver)
SG
(12)
(2)* C1CH2-CH2OH
glutathionase
alcohol
dehydrogenase
GS-CH2-CH2-SG (ID).
glutathionase
,, (liver, kidney)
H2C-S-CH2-CH(NH2)-COOH
H2C-S-CH2-CH(NH2)-COOH
(3) C1CH2-CHO
C1CH2-CH2-S-CH2-CH(NH2)-COOH
(13)
aldehyde
dehydrogenase
C1CH2-COOH
hydrolytic
glutathione
S-alkyltransferase
dehalogenation
(8)*
HOCH. • COOH -» CO
(5) GS-CH2-COOH
glutathionase
(liver, kidney)
(9)3
COOH
•
COOH
(5)* HQOC-CH(NH2)-CH2-S-CH2-COOH
deamination
decarboxylation
(7)* CH2-COOH
S
•
CH2-COOH
1. Dichloroethane
2. Chloroethanol
3. Chloroacataldehyde
4. Chloroacetic acid
5. S-carboxymethylglutathione
6. S-carboxymethylcysteine
7. Thiodiacetic acid
8. Glycolic acid
9. Oxalic acid
10. S-,S-ethylene-bis-g1utathione
11. S,S-ethylene-bis-cysteine
12. S-chloroethylglut3thione
13. S-cMoroethyl cysteine
-^alternative pathway (Johnson,
* metabolites which have been identified
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III-7
an initial hydrolytic dehalogenation to 2-chloroethanol,
conversion by alcohol and aldehyde dehydrogenases to
inonochloroacetic acid (a major urinary metabolite), with
further dehalogenation by enzymatic interaction of monochloro-
acetate with glutathione or cysteine to yield S-carboxymethyl-
cysteine and finally thiodiacetic acid. Yllner administered
dichloroethane-l^c and chloroacetate-l^c intraperitoneally
to mice and determined the metabolites in urine and exhaled
air. The results of his experiments are summarized in Table
III-l and III-2. Some 11 to 46 percent (increasing with
dose; Table III-l) of the injected dichloroethane was excreted
via the lungs unchanged; 5 to 13 percent was metabolized to
carbon dioxide and water, and the remainder, 50 to 73 percent
of the dose, was excreted as urinary metabolites. Table III-2
lists the metabolites identified in urine after dichloroethane
and chloroacetic acid administration.
Yllner (1971a, b) proposed that the degradation of 1,2-
dichloroethane to 2-chloroacetic acid involves a primary
reacton in which chlorine is removed from one of the carbon
atoms (hydrolytic dehalogenation) to yield 2-chloroethanol.
As evidence for this reaction, he found chloroethanol to be a
metabolite (minor) in the urine (Table III-2) . Kokarovtseva
and Kiseleva (1978) also have identified chloroethanol in
the blood and in liver tissue of rats within one hour and
four 24-48 hours after oral administration of dichloroethane
(750 mg/kg). Heppel and Porterfield (1948) obtained an
enzyme preparation from rat liver capable of hydrolyzing the
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III-8
TABLE III-2
Percent Distribution of Radioactivity Excreted
(48-hr) as Urinary Metabolites by Mice Receiving
1,2-Dichloroethane-14c*
After After
dichloroethane chloroacetate
Metabolite (0.17 g/kg) (0.10 g/kg)
Chloroacetic acid 16 13
2-chloroethanol 0.3
S-carboxymethylcysteine 45 39
Conjugated S-carboxymethyl- 3 3
cysteine
Thiodiacetic acid 33 37
S,S-ethylene-bis-cysteine 0.9 —
Glycolic acid — 4
Oxalic acid — 0.2
*Adapted from Yllner (1971a, b)
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III-9
carbon-halogen bonds of chloro-derivatives of methane and
ethane. Dichloroethane was a substrate for this enzyme,
although the reaction product was not specifically identified
as chloroethanol. Furthermore, from a quantum chemical study
of the metabolism of a series of chlorinated ethane anesthetics,
Loew et al. (1973) concluded on theoretical grounds that the
initial metabolic reaction is a hydrolytic fission of a carbon-
chlorine bond with the formation of alcohols. The enzyme
or enzyme system for this primary reaction has not been
isolated or identified. There is little evidence that the
P-450 mixed-function oxidase system is followed. Van Dyke
and Wineman (1971) found that the enzyme system was similar
in function to a microsomal mixed-function oxidase system
requiring oxygen and NADPH and small amounts of cytosol.
This system slowly dechlorinated 1,2-di-36ci-ethane, but
was more active with 1,1-dichloroethane, 1,1,2-trichloro-
ethane and 1,1,2,2-tetrachloroethane. Cox et al. (1976)
studied the aerobic binding to microsomal P-450 of a series
of chloroalkanes. Whereas most of these compounds interacted
to give a Type 1 difference spectra associated with metabolism
of these substrates by direct C-hydroxylation, 1,2-dichloroethane
failed to give an observable interaction.
Following 2-chloroethanol formation, Yllner (1971a, b)
proposed that this alcohol was enzymatically converted to 2-
chloroacetic acid via 2-chloroacetaldehyde. Chloroacetic
acid was found as a major urinary metabolite of mice (Table
III-2).
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111-10
Johnson (1967) had observed that chloroethanol was
readily dehydrogenated to chloroacetaldehyde by purified
alcohol dehydrogenases from yeast or horse liver. Williams
(1959) previously had suggested that chloroacetic acid appeared
in vivo via chloroacetaldehyde. After dichloroethane adminis-
tration (0.17 mg/kg), Yllner found that chloroacetic acid
appeared in mouse urine in significant amounts within 24
hours where chloroethanol was only a minor metabolite (Table
III-2). In addition, Kokarovtseva and Kiseleva (1978)
observed that after oral administration of dichloroethane
(750 mg/kg) or 2-chloroethanol (80 mg/kg) to rats, the blood
level of 2-chloroethanol at 4 hours was 67.8 or 15.8 ug/ml,
respectively, and declined in accordance with first-order
kinetics with a half-life of about 9 hours. While chloro-
acetaldehyde and chloroacetic acid were not measured, these
investigators suggested that a conversion of chloroethanol to
chloroacetic acid occurred. The relatively low blood concen-
trations found after the large amounts of dichloroethane
ingested and the first-order kinetics of chloroethanol
metabolism were postulated to be due to initial sequestration
of dichloroethane in adipose and other tissues, with a gradual
diffusion redistribution as liver metabolism of dichloroethane
to chloroethanol and chloroethanol to chloroacetic acid
proceeded. Significant blood and liver tissue levels of
chloroethanol were found even 48 hours after dosing.
The urinary metabolites found in largest amount after
administration of 1,2-dichl.oroethane or 2-chloroacetic acid to
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III-ll
mice (Yllner, 1971a, b) are S-carboxymethylcysteine (ca.
40 percent) and thiodiacetic acid (ca. 35 percent) (Table
III-2). Yllner suggests that these metabolites arise from
enzymatic conjugation (S-alkyltransferase) of chloroacetic
acid with glutathione forming S-carboxymethylglutathione with
chloride excision. S-carboxymethylglutathione is converted by
glutathionase to S-carboxymethylcysteine, part of which is
further metabolized to thiodiacetic acid (Figure III-l).
Johnson (1966, 1967) has shown that S-carboxymethylglutathione
is rapidly degraded by rat kidney homogenate to yield glycine,
glutamic acid and S-carboxymethylcysteine. However, an
alternative scheme with chloroacetaldehyde conjugation has
been proposed by Johnson (1967). In his study of the metabolism
of orally administered 2-chloroethanol in the rat, Johnson
found that chloroethanol caused a rapid depletion of liver
glutathione with a concomitant formation of S-carboxymethyl-
glutathione. In vitro, the reaction with a rat liver cytosol
fraction required stoichiometric amounts of glutathione (1
mole) and NAD (2 moles). Since pyruvate was also required
for reaction, Johnson (1967) postulated that chloroethanol
was converted by alcohol dehydrogenase to chloroacetaldehyde
which then conjugated with glutathione to give S-formylmethyl-
i.
glutathione, and thence by an NAD-requiring dehydrogenation
to S-carboxymethylglutathione. Johnson (1966) also has
reported that chloroacetaldehyde is rapidly conjugated with
glutathione in vitro by a non-enzymatic reaction at pH 7.0.
Thus, Johnson concluded that this was probably the principal
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111-12
in vivo reaction in mammals. However, based on Yllner's
results with the metabolism of chloroacetic acid (Table III-2),
it appears likely that in vivo dehydrogenation of 2-chloroethanol
in mammals proceeds through chloroacetaldehyde to chloroacetate
before conjugation with glutathione occurs.
Recently, it also has been suggested by Rannug and Beije
(1979) that there are some similarities in the biotransformation
pathways of 1,2-chloroethane and vinyl chloride (Figure III-2).
Secondary Pathways
Yllner (1971a, b) observed that after dichloroethane
administration to mice some 5 to 15 percent (depending on dose)
was metabolized completely to C02 and water, and also that
after chloroacetate administration small amounts of glycolic
and oxalic acids appeared in urine (Tables III-l, III-2).
Since these acids are known to be metabolized with C$2'
Yllner (1971 a,b) proposed that chloroacetate is enzymatically
hydrolyzed to glycoiate by hydrolytic dehalogenation, a
portion of which is further oxidized to oxalic acid.
Yllner (1971a, b) found small amounts of S,S'-ethylene-
bis-cysteine in urine of mice injected with dichloroethane
(Table III-2) . This metabolite was believed to occur in
vivo from a reaction between dichloroethane and glutathione
catalyzed by the glutathione S-alkyltransferase previously
demonstrated in rat liver by Johnson (1966). The S,S'-ethy-
lene-bis-glutathione was presumed to be further degraded to
-------
HjC-CHCI - H^-CHCJ - OCH2-CHO^
Gly-C
aCH-j-CHjOH
•K3SH
^CH-CH2-S-CH2-CHO
:xn:
Gly -C
: XCH-CH2-S-CH2OH
Tv"1
7-Glu - N -IXl
H
Gly-C
+GSH
CH - CH2-S-CH2 -CH2C1
^
^ CM - CH2-S-CH2-COOH
COOH
\
CH - CH2-S-CHj - COOH
' fxiy^
NH,
COOH
s
CH -
/
NH,
-CH2 - CH2OH
COOH
\
CH - CH2 -S-CH2 -CHjOH
NHCOCH, - ' '
COOH
\
CH -
COOH
\
Ivuj
CH - CH2-S-CH2
NHCOCH,
HOOC -
-S-CH2 -COOH
;xv;
Figure £ - Suggested metabolic main pathways of vinyl chlor-
ide (I) and DCE (V) showing similarities and differences.
The illustrated pathways are in accordance with mutagenicity
data and data from metabolic studies (identified urinary
metabolites and depression of non-proteins sulfhydryl content
in vivo). The following symbols have been used: I, vinyl
chloride, II, chloroethylene oxide: III, chloroacetaldehyde;
IV, 2-chloroethanol; V, DCS; VI, £-(2-chloroethyl) gluta-
thione; VII, S-(2-chloroethyl) cysteine? VIII, N-acetyl-S-
(2-chloroethyl) cysteine; IX, £-(2-hydroxyethylT glutathione;
X, S^-(2-hydroxyethyl) cysteine; XI, N-acetyl-S-(2-hydroxy-
ethyl) cysteine; XII, £-(2-oxoethyl) glutathione; XIII, £-
(carboxymethyl) glutathione; XIV, S_-(carboxymethyl) cysteine;
XV, thiodiglycolic acid. (Rannug, V., and B. Beije. The
Mutagenic Effect of 1,2-Dichloroethane on Salmonella typhi-
murium. II. Activation by the isolated perfused rat liver.
Chem. Biol. Interaction 24:265-285, 1979).
-------
111-14
S,S'-ethylene-bis-cysteine. Nachtomi et al. (1966, 1970)
also found that an enzyme system from the soluble supernatent
fraction of rat liver catalyzed a reaction between dichloro-
ethane and glutathione to a small extent. The products were
S-betahydroxyethyl-glythione and S,S'-ethylene-bis-gluta-
thione. Earlier, Bray et al. (1952) had studied the dehaloge-
nation of dichloroethane and other halogenated hydrocarbons
by rabbit liver extracts. These workers found no evidence
for enzymatic dehalogenation of dichloroethane or chloroetha-
nol but suggested non-enzymatic dechlorination by direct
interaction with sulfhydryl groups (glutathione, cysteine),
a reaction which occurred with many compounds without the
liver extract. Morrison and Munro (1956) showed that such a
reaction occurs in vitro with cysteine to form S,S'-ethylene-
bis-cysteine. The tendency of 1,2-dichloroethane to injure
kidney tubules and cause pulmonary edema suggests that the
chlorinated compound is indeed capable of reacting with
sulfhydryl groups in vivo (Winteringham and Barnes, 1955).
The quantitative studies by Yllner (1971a, b) show that this
pathway involving direct reaction of dichloroethane with
glutathione or cysteine could only be a minor pathway.
-------
.IV-1
IV. HUMAN EXPOSURE
-------
V-l
V. HEALTH EFFECTS IN ANIMALS
General
The acute and chronic toxicity of 1,2-dichloroethane
exposure is not, in general, different from that observed
with other halogenated aliphatic hydrocarbons. Whereas high-
dose exposure to 1,2-dichloroethane causes immediate central
nervous system effects leading to unconsciousness, coma,
circulatory collapse and death, lower single or repeated
exposures result in abnormalities of the liver, kidneys, lungs,
heart, adrenals and gastrointestinal tract. These organ
systems show both morphological and functional abnormalities.
In part, the pathologic changes in the tissue can be ascribed
to the lipophilic and electrophilic nature of the compound,
but these adverse effects probably are related also to toxic
metabolic products since 1,2-dichloroethane is readily and
extensively metabolized. Most toxicities resulting from 1,2-
dichloroethane exposure are similar for different species
of animals, although there are a few manifestations which
are species specific. In the animal studies which have been
carried out to date, the exposure dose levels (over both
acute and chronic duration) have invariably been in a range
not normally encountered in the natural environment. Virtually
nothing is known of the subtle toxicology of low level chronic
exposures to 1,2-dichloroethane. Almost all toxicity studies
reported in the literature are based on inhalation exposures;
few studies have been made on toxicity resulting from ingestion,
particularly via drinking water.
-------
V-2
The narcotic properties of 1,2-dichloroethane have been
known for over 100 years, but its toxicity precludes its use
as an anesthetic agent. The central nervous system depression
observed in a variety of species of animals is characteristic
of compounds of the chloroethane series and of related
halogenated aliphatic hydrocarbon compounds. In addition to
central nervous system effects, other documented toxicity
associated with 1,2-dichloroethane exposure in laboratory
animals include damage to the liver, kidney, adrenal glands
and skin, as well as pathological changes in the cardiovascular,
hematological and immunological systems. A summary of these
effects as well as dose data appear in the text below and in
Tables V-l through V-3. Effects on reproduction and teratogenic
effects as well as mutagenicity and carcinogenicity are
discussed separately below.
Acute Toxicity
The principal acute effect of 1,2-dichloroethane in
mammals is central nervous system depression with unconsciousness
and coma resulting from exposure to high concentrations.
Visible signs of 1,2-dichloroethane poisoning include
restlessness, handling intolerance, abnormal weakness,
intoxication, dizziness, muscle incoordination, irregular
respiration and loss of consciousness. Deaths occurring
within a few hours after recovery from narcosis are usually
the result of shock or cardiovascular collapse; deaths
delayed by several days most often result from renal damage
-------
V-3
TABLE V-l
Correlation of Symptoms, Exposure
Time, and Concentration for Guinea
Pigs Inhaling 1,2-Dichloroethane
Average period necessary to produce symptom
at various concentrations (min)
Symptom
Nose and
eye irri-
tation
Unsteadi-
ness
Inability
to walk
Retching
Jerky, rapid
respiration
Uncon-
sciousness
2000 4000-
ppm 4500 ppm
6* 3-10 Z
20-45 8-18
a 30
a b
a b
a 30-40
10,000-
17,000 ppm
1-2
2-3
4-10
7-15
10-30
10-20
25,000- 60,000-
35,000 ppm 70,000 pp:
1-2 1
1-2 1-2
3-5 2-4
5-13 2-4
5-13 4-8
4-7 3-7
is symptom was not observed even after 480 min of exposure
is symptom was not observed even after 360 min of exposure,
Source: Adapted from Sayers et al., 1930.
-------
Mortality after single acute exposure to 1,2-dlchloroethane by inhalation
Animal
Mice
Rats
Guinea pig*
Rabbits
Raccoons
Cats
Hogs
Mice
Rats
Guinea pigs
Sources:
Number
22
19
20
16
IS
14
16
2
3
2
20
23
20
13
12
Adapted
Height
(8)
146
177
257
685
3.940
3,240
27,300
170
257
321
from Heppel
Tine Mortality
(he) ratio
1
2
7
3
1
7
7
7
• 7
7
7
2
7
4
7
et al.,
Exposure
22/22
19/19
20/20
1/2 15/16
1/2 0/15
14/14
12/16
0/2
0/3
2/2
Exposures
20/20
1/23
4/20
0/13
6/12
1945, Table 1, p.
0
to 3000 ppra
22
0
0
0
0
0
Q
to 1500 ppn
4
0
0
0
55. Reprinted by permission of
Cumulative mortaltiy
lat
day
19
19
1
11
7
0
20
0
2
1
2nd 3rd 4th
day day day
20
3 5 13
13 14
11 12
2
0 1
2 4
436
the publisher.
-------
V-5
TABLE V-3
Lethal Doses of 1,2-Dichloroethane
to Nonhuman Mammals
Species
Mouse
Rat
Guinea pig
Rabbit
Dog
Pig
aLCLo - lowest
LDLo - lowest
Category3
LCLo
LDLo
LDLo
LDLo
LDLo
LDLO
LD50
LCLo
LDLo
LCLo
LDLo
LD50
LDLo
LDLO
LCLO
published lethal
reported lethal
Dosage
5000 mg/m3
600 mg/kg
380 mg/kg
250 mg/kg
1000 ppm/4 hr
500 mg/kg
680 mg/kg
1500 ppm/7 hr
600 mg/kg
3000 ppm/7 hr
1200 mg/kg
860 mg/kg
2000 mg/kg
175 mg/kg
3000 ppm/7 hr
concentration in
dose by any route
Route
Inhalation
Oral
Subcutaneous
Intraperitoneal
Inhalation
Subcutaneous
Oral
Inhalation
Intraperitoneal
Inhalation
Subcutaneous
Oral
Oral
Intravenous
Inhalation
air;
other than
inhalation; LDso - median lethal dose by any route other
than inhalation.
Source: Adapted from NIOSH, 1977, p. 388.
-------
V-6
«
(Spencer et al., 1951; Irish, 1963). Despite these qualitative
statements, the manner in which 1,2-dichloroethane exerts its
lethal effects in mammals cannot always be easily identified
or characterized. For example, Heppel et al. (1946) stated,
"In spite of the fact that this important compound has been
extensively studied in this laboratory for nearly three years,
it must be admitted that the exact mechanism of death remains
obscure." Since that time, it has become generally accepted
that 1,2-DCE causes death by direct effects on the central
nervous system (CNS).
Weakness, disordered, vertiginous movement, persistent
thirst, eye and nasal irritation, static and motor ataxia,
retching movements and marked changes in respiration are
common signs of acute 1,2-dichloroethane poisoning in non-
human animals. Sayers et al. (1930) observed all of these
signs in guinea pigs after less than 10 minutes' exposure to
60,000 ppm 1,2-dichloroethane and in 25 minutes to 10,000 ppm
(Table V-l). However, no signs of poisoning were apparent
following exposure at 1200 ppm for 8 hours. Death occurred
in less than 30 minutes with animals exposed to 60,000 ppm
and usually after about a day following a 25-minute exposure
to 10,000 ppm. Congestion and edema of the lungs and genera-
lized passive congestion throughout the visceral organs were
commonly observed in animals that died during exposure.
Renal hyperemia and pulmonary congestion and edema were
typical conditions in animals that died one to eight days
following exposure. Similar histopathological lesions, as
-------
V-7
well as fatty degeneration of the myocardium and renal tubular
epithelium, also were reported by other observers who exposed
mice, rats, guinea pigs, rabbits, cats and dogs sufficiently
long to air containing 1000 to 3000 ppm 1,2-dichloroethane
(Heppel et al.r 1945, 1946; Spencer, et al., 1951).
The acute toxicity of 1,2-dichloroethane varies with
species and route of exposure. In general, it appears to be
more toxic to mammals than is carbon tetrachloride (Hofmann,
et al., 1971). Table V-2 summarizes mortality in seven species
of animals due to a single acute exposure by inhalation that
varied in duration from 1.5 to 7 hours. Few animals survived
exposure at 3000 or 1500 ppm for 7 hours, but death was
frequently delayed for days in some species. Congestion of
the viscera and degeneration of the liver and kidneys were
common findings among these animals (Heppel et al., 1945).
Data published by the National Institute for Occupational
Safety and Health (NIOSH, 1978) indicate that, for exposure
by inhalation, the lowest doses that are lethal for a variety
of common mammalian species range from about 1000 ppm for 4
hours to about 3000 ppm for 7 hours. In contrast, a dose of
175 mg/kg administered intravenously is lethal in the dog
(NIOSH, 1977). Other minimum lethal doses are indicated in
Table V-3.
-------
V-8
The effects of acute exposure to 1,2-dichloroethane are
also strongly dependent on the concentration of the toxi-
cant. For example, when rats were exposed to air containing
1000 ppm 1,2-dichloroethane, 7.20 hours elapsed before half
the population died; however, with concentrations of 3000 and
12,000 ppm, the median lethal response times decreased to
2.75 and 0.53 hours, respectively (Spencer et al., 1951).
Similarly, when male guinea pigs were injected intraperi-
toneally with 150 or 300 mg/kg 1,2-dichloroethane in corn
oil, no noticeable hepatotoxic effects occurred; when 600
mg/kg was injected, a low order of damage occurred, as measured
by increased serum concentrations of ornithine carbamyl
transferase (DiVincenzo and Krasavage, 1974). 1,2-Dichloroethane
also exhibits concentration-dependent nephrotoxic characteristics
when it is injected intraperitoneally into male Swiss mice.
Plaa and Larson (1965) observed a progressive increase in the
number of mice (10%, 30% and 56%) having excessive urinary
protein, but not excessive urinary glucose, following
injection of 0.075, 0.2 and 0.4 ml of 1,2-dichloroethane per
kilogram of body weight. It should be noted, however, that
the last cited dose is well above the minimum lethal dose for
mice -
Duprat, et al. (1976) studied the irritant property of
1,2-dichloroethane and other simple chlorinated hydrocarbons
by making a single application or installation of the solvents
to the skin or eye of rabbits and then following the course of
the resulting lesions macroscopically and histologically.
-------
V-9
1,2-Dichloroethane was rated a primary irritant in both
applications but was considered less potent as a skin irritant
than perchloroethylene, chloroform, 1, 1, 2-trichloroethane,
trichloroethylene and methylene chloride- As an eye irritant,
1,2-dichloroethane was classified less potent than chloroform,
methylene chloride, dichloroethylene, trichloroethylene and
trichloroethane.
Although acute exposures to 1,2-dichloroethane produce
roughly similar responses in many mammalian species, the
systemic administration of this compound to dogs produces
one effect not ordinarily seen in other mammalian species:
clouding of the cornea. Typically, there is a necrosis of
the endothelium beginning in the basal portions of the cells,
followed by secondary swelling of the stroma, formation of
excess basement membrane and thickening of Descemet's layer.
This response also occurs in cats and rabbits when 1,2-
dichloroethane is injected directly into the anterior chamber
of the eye but not with systemic administration of the
compound. The unique response of the dog eye appears to
result from a greater amount of 1,2-dichloroethane coming in
contact with the dog endothelium rather than from any unusual
susceptibility of the eye itself (Heppel et al., 1944;
Kuwabara, et al., 1968).
Longer Term Exposures
Longer-term exposures of rats and guinea pigs to air
containing 100 ppm 1,2-dichloroethane for 7 hours per day.-
-------
V-10
five days per week for several months generally produced no
deaths and no evidence of adverse effects as judged by general
appearance, behavior, mortality, growth, organ function or
blood chemical chemistry (Heppel, et al., 1946; Spencer, et
al., 1951; Hofmann, et al., 1971 ). However, similar exposures
of rats, guinea pigs, rabbits and monkeys to air containing
400 or 500 ppm 1,2-dichloroethane usually resulted in high
mortality and a limited number of varying pathological findings,
including pulmonary congestion, diffuse myocarditis,
slight to moderate fatty degeneration of the liver, kidney,
adrenal and heart, and prolonged plasma prothrombin time
(Heppel, et al., 1946; Spencer, et al., 1951; Hofmann, et al.,
1971). Different effects were observed in rabbits exposed to
high concentrations of 1,2-dichloroethane for a few hours/day
over extended periods of time. After inhaling 3000 ppm
1,2-dichloroethane for 2 hours per day, five days per week for 90
days, rabbits exhibited varying degrees of anemia accompanied
by leukopenia and thromobocytopenia. In addition, there was
frequent hypoplasia of the granuloblastic and erythroblastic
parenchyma in the bone marrow. The cellular concentration of
leukolipids was reduced, but no change occurred in polysaccha-
rides, peroxidase, or ribonucleic acid. In view of these
findings, the authors suggested that 1,2-dichloroethane
might exert a direct poisoning effect on bone marrow (Lioia
and Elmino, 1959; Lioia, et al., 1959).
-------
V-ll
Reproduction and Teratology
In a series of studies, Vozovaya (1971, 1974, 1975,
1976) exposed female white rats (strain not stated) to air
containing 57 mg/m3 (14 ppm) 1,2-dichloroethane for 4 hours
per day, six days per week for six to nine months to determine
the effects of this compound on reproductive function of
these animals and on the development of progeny. Fertility
of the treated rats decreased and the number of still births
increased relative to controls. Viability of first generation
offspring decreased. First generation females exhibited
prolonged estrus and a high perinatal mortality rate. These
effects were augmented and others were observed when rats
were exposed in similar experiments to mixtures of 1,2-
dichloroethane (30 +_ 10 mg/m3) and gasoline (1210 + 70 mg/m3).
In particular, a decrease in the incidence of conception
occurred which was not seen during similar exposures to the
separate compounds. In addition, there was a significant
decrease in the viability of first generation offspring. For
example, at the end of the sixth month, mortality in the
group exposed to 1,2-dichloroethane alone was 25.0 +_ 6.92% as
compared with 5.4 + 3.75% in the controls (P < 0.05). However,
for the group exposed to the combination of 1,2-dichloroethane
and gasoline, mortality (P < 0.05) was 28.0 +_ 9.16% (Vozovaya,
1975) . In a later study in which 108 random-bred female white
rats were exposed to gasoline (31.0 +_ 33 mg/m3) and 1,2-dichloro-
ethane (15+3 mg/m3) separately and in combination 4 hours
-------
V-12
per day, six days per week for four months, Vozovaya (1976)
found increased numbers of degenerative follicles in the ovaries
of rats exposed to the mixture of compounds but not in ovaries
of rats exposed to the compounds separately. In the affected
rats, a high total embryonic mortality was caused by a high
rate of preimplantation deaths and also by a high rate of
resorptions of embryos at an early stage of development.
In other studies, Alumot and co-workers (1976) added
250 or 500 ppm 1,2-dichloroethane, with appropriate precaution
to avoid losses by volatilization, to the food of rats for two
years. No significant differences were found between these
animals and controls with respect to growth, feed consumption
or feed efficiency. At the levels tested, the added 1,2-
dichloroethane had no effect on male fertility or reproductive
activity of rats of either sex. Based on the results of this
study, the authors recommended an acceptable daily intake and
tolerance of 1,2-dichloroethane in human food of 0.07 mg/kg of
body weight and 10 ppm, respectively.
Inhaled 1,2-dichloroethane is transported into the uterus
and ovaries of non-pregnant rats. During pregnancy it passes
through the placental barrier of rats and is accumulated in
fetal tissues, especially the liver (Vozovaya and Malyarova, 1975)
Rao, et al. (1980) studied the effect of inhaled 1,2-
dichloroethane on embryonal and fetal development in rats and
rabbits and on the reproductive capacity of rats. For the
teratology studies, 16-30 pregnant Sprague-Dawley rats were
-------
V-13
exposed to 0, 100 or 300 ppm 7 hours/day on Days 6-15 of
gestation. Rabbits (19-21 per group) were exposed to the
same concentrations of dichloroethane on Days 6-18 of pregnancy.
Rats were sacrificed on Day 21, rabbits on Day 29 of gestation.
Ten of the 16 rats exposed to 300 ppm died. Animals in
this high dose group exhibited lethargy, ataxia, decreased body
weight and food consumption and vaginal bleeding prior to death.
No deaths occurred in the low dose group or the controls. Only
one rat in the high dose group exhibited implantation sites;
all implantations were resorbed. Exposure to 100 ppm did not
effect mean litter size, numbers of resorptions or fetal body
measurements. The number of litters/group was decreased (15/30
as compared with 22/30 in the control group). No teratological
changes were observed at any dose.
Three of 19 rabbits in the high dose group died, as did 4
of 21 in the low dose group. The incidence of pregnancy was
not affected, as it had been in the rat. There was no effect
on mean litter size, incidence of resorptions, fetal body
measurements or maternal body weights. In addition, no alteration
in the incidence of major malformations was observed at either
dose.
In the reproductive study, 20 Sprague-Dawley rats/sex/group
were exposed at levels of 0, 25, 75 or 150 ppm 1,2-dichloroethane.
During 60-day prebreeding period, the animals were exposed for
6 hours/day, 5 days/week. During the breeding period and gestation,
they were exposed 6 hours/day, 7 days/week. Females who delivered
litters were not exposed from Day 21 of gestation through the
-------
V-14
fourth day post-parturition so as to allow for delivery and
rearing of the offspring.
No significant changes in body weight occurred during the
prebreeding periods. Female body weights during gestation and
rearing of both F/la and F/lb litters were unaffected. Food
consumption by males in the 150 ppm dose group increased
significantly in the latter part of the study. In the females,
a decrease in food consumption occurred in the high and middle
dose groups during the first week, but returned to normal
afterwards. Of all the indices measured, only the average number
of pups per litter (both live and dead) at birth was significantly
lower in the 75 ppm group. Kidney weights of F/lb male in the
75 ppm group were significantly higher when measured at sacrifice
on Day 21 of age. No histological changes accompanied this change.
The only teratology/reproductive function study to date
which the test animals were exposed to 1,2-dichloroethane in
their drinking water was reported by Lane, et al, (1982). The
authors conducted a modified multigeneration reproduction study
which included screening for dominant lethal and teratogenic
effects. Male and female ICR Swiss mice received 1,2-dichloro-
ethane at concentrations of 0, 0.03, 0.09 or 0.29 mg/1 in
drinking solution (1% Emulphor in deionized water, v/v).
These concentrations were designed to correspond to daily
doses of 0,5,15 or 50 mg/kg bw. Two control groups were
used: 1) untreated, and 2) 1% Emulphor vehicle.
-------
V-15
The F/O mice were randomized into test groups of 10 males
and 30 females, acclimated for 2 weeks and then placed upon the
appropriate testing regimen. After 35 days on the test regimen,
the now 14-week olds were randomly mated to produce the F/1A
litters. Two weeks after weaning of the F/1A litters, the
F/O adults were rerandomized and remated to produce the
F/1B litters. Parental stock for the second generation was
drawn from these F/1B offspring. F/O females were rested
for 2 weeks following weaning of the F/1B pups. The offspring
from the F/1C mating were used in the dominant lethal and
teratology screening. By the end of the experiment, the F/O
adults had been exposed to 1,2-DCE in their drinking water
for a total of 25 weeks.
At weaning, the F/1B litters were culled to 30 females
and 10 males/group. Matings between siblings were avoided.
The F/1B weanings were placed on the testing regimen and
when reaching 14 weeks of age, were randomly mated to produce
the F/2A litters. Two weeks after these offspring were
weaned, the F/1B adults were remated randomly to produce the
F/2B offspring which were used in the dominant lethal and
teratology screening. By the end of the experiment, the
F/1B adults had been exposed to the drinking water solutions
for a total of 24 weeks.
Weekly body weight and twice-weekly fluid consumption
data were collected for the F/O and F/1B adult mice throughout
the study. The authors stated that there were no statistically
significant differences seen in either of these parameters.
-------
V-16
However, no data were presented in the paper so the reader
could not make a judgment about the validity of that conclu-
sion. Mortality rates in the same two adult groups also
were monitored. These are summarized in Table V-4. Significant
numbers of the animals in the low dose group of F/O adults
died (20% of the males, 13.3% of the females compared with
no male controls and only 3.3% of the female controls). How-
ever, this death rate appeared not to be dose-related, as it
did not increase at the higher two doses. Among the F/1B
adults, more controls died than did treated animals.
TABLE V-4
Percentage Mortality Among Males and Females
Ingesting 1,2-Dichloroethane
Mofified from Lane et. al, 1982
Concentration
Compound (mg/ml)
1 ,2-Dichloroethane 0.00C
(1,2-DCE) 0.00d
0.03
0.09
0.29
F/10 percentage
Mortality3
Males
0.0
0.0
20.0
0.0
0.0
Females
3.3
3.3
13.3
6.7
0.0
F/1B percentage
Mortality13
Males Females
20.0
0.0
0.0
0.0
0.0
7.4
0.0
3.3
3.3
0.0
A After 25 weeks of dosing.
b After 24 weeks of dosing.
c Naive control.
d 1% Emulphor vehicle control.
Adult reproductive performance was monitored in the F/O
and F/1B adults, as they produced the F/1A and F/1B generations
(F/O) and the F/2A generation (F/1B). The fertility and gesta-
tion indices (Fl and Gl, respectively) are shown in Table V-5.
No significant dose-related differences were seen in any
treatment group when compared with the controls.
-------
TABLE V-5
Reproductive Performance of
Adult Mice Ingesting 1,2-Dichloroethane
(Modified from Lane, et al, 1982)
Litter
Concentration
(mg/ml)
O.OOC
O.OOd
0.03
0.09
0.29
F/1A
Fia
90.0
93.3
89.3
82.8
90.0
GIb
92.6
82.1
92.0
83.3
85.2
F/1B
FI
70.0
76.7
89.3
62.1
70. a
F/2A
GI
71.4
78.2
84.0
94.4
90.5
FI
76.2
86.2
93.1
82.8
85.2
GI
100.0
96.0
81.5
100.0
78.3
3 FI (Fertility Index) = (No. females pregnant/no, females mated) X 100.
b GI (Gestation Index) = (No. females with live litters/no, females pregnant) X 100
c Naive control.
d Emulphor vehicle control.
-------
V-18
Twenty-one day litter survival studies were conducted on
litters of the F/1A, F/1B and F/2A generations. Litter size
was recorded on Days 0, 4, 7, 14 and 21. Offspring were
weighed collectively on Days 7 and 14 and individually on
Day 21. Viability and lactation indices (VI and LI, respectively)
also were calculated. 1,2-Dichloroethane, at the doses
administered, did not cause any significant adverse inter-
generational or transgenerational effects on mean litter
size at birth (Table V-6), mean postnatal body weights (Table
V-7) and survival indices (Table V-8). Values of the F/2A
postnatal body weights (Table V-7) and survival indices (Table
V-8) were decreased from the F/1A and F/1B values with few
exceptions. The decrease occurred in all groups, including
both controls, and thus was believed not to be treatment-related.
Necropsies of weanlings from these groups yielded no evidence
of dose-dependent gross pathology or congenital malformation.
Findings from the dominant lethal screening are presented
in Table V-9. Statistically significant effects in the
ratio of dead to live fetuses (DF/LF) were observed in both
generations. However, these effects did not appear to be
dose-related, since there were both increases and decreases
as observed when compared with the controls. The frequency
(F%) of dominant lethal factors in both generations was
minimal (-7 to +8).
-------
V-19
TABLE V-6
Mean Litter Size At Birth3 of
Mice Ingesting
1,2-Dichloroethane
(Modified from Lane, et al., 1982)
Litter
Concentration
Compound
1
, 2-Dichloroethane
(1,2-DCE)
0
0
0
0
0
(mg/ml)
.00b
.00C
.03
.09
.29
F/1A
13
12
13
12
11
.1 +
.0 +
.2 +
.9 +
.4 +
3.2
2.3
3.2
2.7
2.7
F/1B
13.1
12.1
12.5
10.5
10.4
+ 4.5
+ 3.0
+ 4.1
+ 4.4
+ 4.8
F/2A
11.8
12.2
11.3
12.3
12.6
+
•¥
Jf
+
+
2.
2.
3.t
2.
1.
a Mean pups per litter _+ SD.
b Naive control.
c 1% Emulphor vehicle control
-------
V-20
TABLE V-7
Mean Postnatal Body Weights3 of Offspring Of
Mice Ingesting 1,2-Dichloroethane
(Modified fron Lane, et alf 1982)
1,2-DCE concen-
tration
(mg/hil)
O.OQb
O.OQC
0.03
0.09
0.29
a Mean pup body
b Naive control
Day 7
4.8 + 1.0
4.8 + 0.5
4.8 -l- 0.5
4.7 + 0.7
5.1 + 0.6
weight (g)
»
F/1A
Day 14
7.1 + 1.3
7.5 + 0.7
7.1 + 0.8
7.4 + 1.1
7.1 + 0.9
+ SD.
l
Litter
F/1B F/2A
Day 21 Day 7 Day 14 Day 21 Day 7 Day 14 Day 21
11.0 + 2.4 4.8 + 0.8 7.7 + 1.5 12.0 + 1.5 3.7 -1- 1.2 5.2 + 2.2 7.1 + 3,
11.5 + 1.5 5.0 + 0.5 8.0 + 0.7 12.7 + 4.1 4.0 + 0.6 5.7 + 1.5 7.6 + 2,
10.5 + 1.8 5.0 -l- 0.4 7.9 + 0.7 12.2 + 1.3 4.7 + 0.9 7.0 + 1.6 9.7 + 2.
10.9 + 1.8 5.0 + 0.8 7.6 + 1.0 11.0 + 2.2 3.7 + 1.1 5.3 + 2.0 7.1 + 2,
10.7 + 1.7 4.9 + 0.7 7.8 + 1.4 11.0 -I- 2.3 4.4 + 0.5 6.6 + 0.9 8.9 + 1,
1% Emulphor vehicle control.
-------
-45-
TAHLE /'
Survival Indices for Litters of Mice Ingesting
1,2-Dichloroethanea
(Modified from Lane, et al», 1982)
Litter
F/1A
Compound
1 , 2-Dichloroethane
(1,2-DCE)
Concentration
(mg/ml)
0.00d
0.00°
0.03
0.09
0.29
VIb
97.2
97.5
98.1
94.3
93.0
LIC
94
98
97
97
97
.8
.2
.8
.5
.2
F/1B
VI
96
94
96
97
93
.9
.0
.7
.0
.1
LI
90
94
96
99
97
.4
.4
.4
.0
.7
F/2A
VI
88.5
89.6
91.8
89.6
92.3
LI
86
81
95
86
89
.3
.3
.0
.8
.6
a The F/1C and F/2B pregnancies were interrupted for dominant lethal and
teratology studies.
b VI (viability index) =
4 litter size) i
0 litter size)
ize if itA.*/-
ize)i-j// A
c LI (lactation index) =1 < p(Day 21 litter size)i~]/A/S '
f~ L(pups kept at Day 4)iJ' J]
U-l
d Naive control.
e 1% Emulphor vehicle control.
**;
'
-------
V-21
TABLE V-8
Survival Indices for Litters of Mice Ingesting
1,2-Dichloroethanea
(Modified from Lanef et al, 1982)
Litter
F/1A
Concentration
(mg/ml)
0.00d
O.OQC
0.03
0.09
0.29
VI b
97.2
97.5
98.1
94.3
93.0
Lie
94.8
98.2
97.8
97.5
97.2
F/1B
VI
96.9
94.0
96.7
97.0
93.1
LI
90.4
94.4
96.4
99.0
97.7
F/2A
VI
88.5
89.6
91.8
89.6
92.3
LI
86.3
81.3
95.0
86.8
89.6
a The F/1C and F/2B pregnancies were interrupted for dominant lethal am
teratology studies.
b VI (viability index)
(Day 4 litter size)i
(Day 0 litter size)i
N = No. litters
c LI (lactation index)
(Day 21 litter size)i
(pups kept at Day 4)i
d Naive control.
e 1% Emulphor vehicle control.
N = No.litters. P
kept at Day 4 =
-------
V-22
TABLE V-9
Results of Dominant Lethal Screening in Females
Mated to Males Ingesting 1,2-Dichloroethane
(Modifified from Lane, et al., 1982)
Concentration
(mg/ml)
F/1C
Mating
F/2B
Mating
O.OQC
O.OQd
0.03
0.09
0.29
O.OQC
0.00d
0.03
0.09
0.29
Nunber
pregnant
17
19
16
23
17
15
25
27
24
16
Fertility
Index9
56.7
63.3
66.6
76.7
56.7
62.5
83.3
90.0
80.0
63.3
Resorp- Live
Implants^ tions" fetuses*5
14.1
14.0
14.0
14.5
13.2
12.2
11.6
12.3
12.0
10.9
1.4
0.7
1.6
0.9
0.6
1.0
0.8
0.9
1.7
0.1
12.7
13.3
12.4
13.6
12.5
11.2
10.8
11.4
. 10.3
10.8
DF/LF
23/216
13/252*
26/198*
21/312
11/213
15/168
19/271
23/309
40/247*
2/172*
DF > 1
9/8
11/8
8/8
16/7
7/10
3/12
9/16
14/13
12/12
2/14
DF > 2
6/11
2/17
1/15
5/18
2/15
1/14
3/22
5/22
5/19
0/16
FL%
-1.89
2.60
-6.77
1.42
3.21
-2.14
8.13
4.02
alndices defined:
Fertility index= number of females pregnant x 100
number of females available
DF/LF = total number of dead fetuses
total number of live fetuses
DF >_ 1 = total number of females with one or more dead fetuses
total number of females with zero dead fetuses
- continued next page -
-------
V-23
DF ^ 2 = total number of females with two or more dead fetuses
total number of females with less than two dead fetuses
FL% (frequency of dominant lethal factors)= II - mean live fetuses, treatmentlx 100 (Ehling et al., 1978)
L_ mean live fetuses, naiveJ
b Mean value per dam.
c Naive control.
d 1% Etnulphor vehicle control.
* Significantly different from control at p <0.05.
Vehicle controls were compared to naive controls;
treatment groups were compared with their vehicle controls.
-------
V-24
Maternal ingestion of 1,2-dichloroethane did not produce
any apparent adverse reproductive effects (Table V-10) or
increased incidences of fetal visceral or skeletal abnormalities
(Table V-ll). The authors concluded, therefore, that, at the
doses tested, 1,2-dichloroethane did not present a hazard to
reproduction and development.
CARCINOGENICITY
Because of its structure, 1,2-dichcloroethane has been
classified as a substance having limited suspicion of carcino-
genicity (U.S. EPA, 1977c); nonetheless, several studies
have addressed the carcinogenic potential of this compound.
In an inhalation study lasting 212 days, Spencer et al.
(1951) found no evidence of carcinogenic activity when Wistar
rats were exposed 151 times to 200 ppm 1,2-dichloroethane
for 7 hours per day. More recently, in an inhalation study
at the Montedison Research Institute in Bologna, Maltoni (as
cited in Albert, 1978) separately exposed 90 male and 90
female Swiss mice and Sprague-Dawley rats 7 hours daily, five
times weekly, to 0, 5, 10, 50, or 150 ppm 1,2-dichloroethane.
Initially, the highest exposure was 250 ppm, but this was
reduced after ten weeks to 150 ppm because the animals could
not tolerate the higher concentration. After exposure of 1
1/2 years' duration, surviving animals were to be held until
the end of their natural lives. In an interim report after
78 weeks of exposure and 26 weeks of observation, Maltoni
-------
V-24A
TABLE V-10
Results of Teratology Screening in Females Ingesting 1,2-Dichloroethane
(Modified from Lane, et al., 1982)
Concentration
(mg/fail)
No. of
liters
Fecundity
Index3
Implants^
Resorp-
tions"
Live
fetuses^
DF/LF a
DF I3
DF 2a M:Fa
Fl/C
mating
F/2B
mating
0.03
0.09
0.29
0.00C
0.03
0.09
0.29
9
8
10
6
8
9
6
4
9
6
90.0
100.0
100.0
100.0
80.0
100.0
100.0
100.0
100.0
85.7
12.0
12.1
14.9
13.8
13.4
14.1
14.5
16.0
13.1
13.0
1.8
5.6
2.5
5.3
1.0
1.0
2.7
0.8
2.7
0.7
10.2
6.5
12.4
8.5
12.4
13.1
11.8
15.2
10.5
12.3
16/92
47/51*
25/121*
32/51
8/99*
4/5
6/2
6/4
5/1
3/5
1/8
6/2*
5/5
3/3
2/6
49:51
59:41
48:52
48:52
43:57
9/118
17/71*
3/61*
24/94
5/74*
7/2
3/3
2/2
5/4
5/1
2/7
2/4
1/3
2/7
0/6
47:53
39:61
57:43
46:54
49:51
AIndices defined: Fecundity index = percentage of copulation plug-positive females bearing live fetus(es) at
sacrifice. DF/LF= ratio of dead fetuses to live fetuses. M:F = ratio of live male to
female fetuses expressed as a percentage of the total number of live fetuses.
bMean value per dam.
cl% Naive control.
dl% Fjnulphor vehicle control.
*Significantly different from control at p£ 0.05. Vehicle controls were compared to naive controls; treatment
groups were compared with their vehicle controls.
-------
V-25
TABLE V-ll
Distribution of Visceral and Skeletal Malformations Among Fetuses/Litters
of Females Ingesting 1,2-DCE
(Modified fron Lane, et al., 1982)
F/1C litters
Cone. (mg/fal)i
Total No. fetuses/total No.
litters:
O.OOa
92/9
O.OOQb 0.03
51/8
121/10
0.09
51/6
0.29
99/8
O.OOa
118/9
F/2B litters
0.00b
71/6
0.03
61/9
0.09
94/9
0.29
74/6
Visceral malformations
Total number examined
Hydrocephalus
Cleft palate
33/8
0/0
0/0
19/7
0/0
0/0
• 46/9
1/1
0/0
18/4
0/0
0/0
29/7
0/0
0/0
38/9
0/0
0/0
24/5
0/0
0/0
20/4
0/0
0/0
29/8
Q/o
0/0
24/6
0/0
0/0
Atrial, ventricular, or cardiac
hypertrophy
Malrotation of the heart
Hydronephros is
Dilated renal pelvis
Dilated bladder
Cryptorchidism/hialpositioned
testis
0/0
0/0
1/1
0/0
0/0
1/1
0/0
0/0
0/0
1/1
0/0
0/0
1/1
0/0
0/0
0/0
0/0
0/0
0/0
0/0
0/0
2/1
0/0
0/0
0/0
0/0
0/0
1/1
0/0
0/0
0/0
0/0
0/0
1/1
0/0
0/0
1/1
0/0
0/0
0/0
0/0
0/0
0/0
0/0
0/0
0/0
1/1
0/0
1/1
0/0
0/0
0/0
0/0
0/0
0/0
0/0
0/0
0/0
0/0
0/0
Skeletal malformations
Total number examined
Dyplastic skull
Dysplastic supraoccipital
region
Microagnathia
Asymetric stenebrae
Bifid sternebrae
Hypoplastic sternebrae
Extra ribs
Wavy ribs
(c) 80/9
0/0
3/2
0/0
24/6
8/3
3/1
2/2
0/0
47/5
0/0
3/2
0/0
9/4
1/1
0/0
1/1
0/0
41/4
0/0
0/0
o/o •
2/2
7/2
0/0
0/0
0/0
65/8
0/0
2/2
0/0
9/5
4/3
0/0
2/2
1/1
50/6
1/1
1/1
0/0
16/6
5/3
1/1
2/2
0/0
aNavie control.
bi* Fimilnhor vehicle control.
-------
V-26
indicated that he "has found no evidence of any exceptional
tumors in rats or mice" (Albert, 1978). This conclusion was
qualified as "almost conclusive." The animals were allowed
to live until spontaneous death.
After more than 60,000 pathologic slides were examined,
the authors concluded the 1,2-DCE did not show carcinogenic
effects under the experimental conditions (Maltoni, et al.,
1980). The negative results may be explained by the fact
that Maltoni, et al. did not follow NCI guidelines in the
conduct of their study. On the other hand, Maltoni, et al.,
(1980) noted several factors which could be involved: the
route of administration of 1,2-DCE; the purity of the compound
used; the possibility of laboratory pollution; the size of
both treated and control animal groups; the professionality
of the study team, the different strains of animals used;
and the possible differences in pathological interpretation.
In 1977, Theiss et al. reported on an investigation of
the carcinogenic potential of 1,2-dichloroethane and other
organic contaminants of U.S. drinking water by injecting the
compounds intraperitoneally into six- to eight-week-old strain
A/St male. Each dose of reagent grade 1,2-dichloroethane
was injected into groups of 20 mice three times a week for 24
injections. Three dose levels were used: 20, 40, and 100
mg/kg in each injection; 100 mg/kg was the maximum tolerated dose.
Tricaprylin was used as the vehicle. Twenty-four weeks after
the first injection, the mice were sacrified and their lungs
-------
V-27
% -*-*.
were placed in Tellyesniczky1s fluid. After 48 hours the
lungs were examined microscopically for surface adenomas.
The frequency of lung tumors in each group was compared
with that in a vehicle-treated control group by means of the
Student's "t" test. The incidence of lung tumor increased
with dose, but none of the groups had pulmonary adenoma
responses that that were significantly greater (P < 0.05)
than that of the vehicle-treated control mice.
NCI Bioassay
Two studies of the carcinogenicity of 1,2-dichloroethane
were performed for the National Cancer Institute (NCI) by the
Hazleton Laboratories, Inc., Vienna, Virginia. The results
of both were released by NCI on September 26, 1978. In one
of these studies, 200 8-week-old Osborne-Mendel rats were
exposed to technical grade 1,2-dichloroethane delivered by
oral intubation. Fifty rats of each sex separately received
either the maximum tolerated dose (95 mg/kg daily, time-
weighted average dosage over a 78-week period) or one-half of
this dose. Twenty rats of each sex served as untreated
controls, and an equal number were given the vehicle (corn
oil) by intubation. Survival of male rats exposed to the
high dose was low: 50% (25/50) were alive by week 55, but
only 16% (8/50) lived to week 75. None survived the study.
Male rats in other groups fared better: in the low dose
group, 52% (26/50) survived at least 82 weeks, and, in the
untreated control group, 50% (10/50) survived at least 87
weeks. The survival rate of female rats exposed to the high
-------
V-28
dose was 50% (25/50) by week 57 and 20% (10/50) by week 75.
Half (25/50) of the female rats in the low-dose group survived
at least 85 weeks. Terminal survival times for all
groups are shown in Table V-12.
Gross necropsies were performed on animals dying during
the experiment or killed at the end. Twenty-eight organs,
as well as all tissues containing visible lesions, were
fixed in 10% buffered formalin, embedded in paraplast and
sectioned for microscopic examination. Diagnoses of any
tumors and other lesions were coded according to the Systema-
tized Nomenclature of Pathology of the College of American
Pathologists, 1965. Squamous-cell carcinomas of the fore-stomach
occurred in 18% of the high-dose males and in 6% of the low-dose
males but were not found in the controls. The Cochran-Armitage
test included a significant positive association between dosage
and the incidence of squamous-cell carcinomas in these animals.
The Fisher exact test also confirmed the significance of these
results (P = 0.001) when comparison was made between the
high-dose group and the pooled vehicle control group. Only
one squamous-cell carcinoma of the fore-stomach occurred in
the exposed female rats and none were found in the controls
(Table V-13).
-------
V-29
TABLE V-12
Terminal Survival of Rats in
Experimental and Control Groups
Involved in Carcinogenicity
Studies with 1,2-Dichloroethane
MALES FEMALES
Animals
Group Weeks in alive at Weeks in
study end of study study
Untreated
controls* 106 4/20 (20%) 106
Vehicle 110 4/20 (20%) - 110
controls
Low-dose 110 1/50 (2%) 101
group
High-dose 101 0/50 (0%) 93
group*5
Animals
alive at
end of study
13/20 (65%)
8/20 (40%)
1/50 (2%)
0/50 (0%)
a Five male and female rats were sacrificed at 75 weeks of
study.
b All animals in this group died before the bioassay was
terminated.
Source: Adapted from Albert, 1978, Table I, p. 15.
-------
V-30
TABLE V-13
Squamous-cell Carcinomas of the Forestomach
in 1,2-Dichloroethane-treated Rats
Rats with squamous-cell
Group ' carcinoma of forestomach
Males
Untreated controls 0/20 (0%)
Vehicle controls 0/20 (0%)
Low-dose group 3/50 (6%)
High-dose group 9/50* (18%)
Females
Untreated controls 0/20 (0%)
Vehicle controls 0/20 (0%)
Low-dose group 1/49 (2%)
High-dose group 0/50 (0%)
a A squamous-cell carcinoma of forestomach metastasized
in one male of high-dose group.
Source: Adapted from National Cancer Institute, 1978.
-------
V-31
Hemagiosarcomas also occurred in exposed male and female
rats but not in the control animals (Table V-14). They were
seen in the spleen, liver, adrenals, pancreas, large intestine
and abdominal cavity. Low-dose animals had higher incidences
of hemangiosarcoma than high-dose animals. The Cochran-
Armitage test indicated a significant (P = 0.021) positive
association between dosage and the incidence of circulatory
system hemangiosarcoma in males, but not females, when dosed
groups were compared with the pooled vehicle control group.
The Fisher exact test confirmed these findings with statistically
significant probability values as follows: P = 0.016 for
high-dose males versus pooled control and P = 0.003 for low-
dose males versus pooled control.
The NCI rat study also showed significant increases in
the incidence of mammary adenocarcinomas in treated female
rats. In the high-dose group, tumors were noticed as early
as 20 weeks after treatment. Eventually 36% (18/50) of this
group developed lesions (Table V-15). The Cochran-Armitage
test indicated significant (P = 0.001) positive association
between the dosage and the incidence of mammary carcinomas
when results were compared with either control group. The
Fisher exact tests were significant when compared with the
high-dose group and either the matched vehicle group (P =
0.001) or the pooled vehicle control group (P = 0.002).
Historically, adenocarcinomas of the mammary gland occur in
2% (4/200) of the vehicle control females.
-------
V-32
TABLE V-14
Hemangiosarcomas in 1,2-Dichloroethane-treated Ratsa
Males Females
Low-dose High-dose*3 Low-dosec High-dose
11/50 (22%) 5/50 (10%) 5/50 (10%) 4/50 (8%)
a No hemangiosarcomas were found in male or female controls,
b Only 49 animals were examined for hemangiosarcomas of the
spleen and adrenals and 48 for hemangiosarcomas of the
pancreas.
c Only 48 animals were examined for hemangiosarcomas of the
large intestine.
Source: Adapted from National Cancer Institute, 1978
-------
V-33
TABLE V-15
Adenocarcinomas of the Mammary Gland
in 1r2-Dichloroethane-treated Female Rats
Untreated
controls
Vehicle
controls
1,2-Dichloroethane-
treated rats
Low-dose
High-dose
2/20 (10%)
0/20 (0%)
1/50 (2%)
18/50 (36%)
Source: Adapted from NCI, 1978.
In summary, the NCI study indicates a positive association
between exposure to 1,2-dichloroethane and the incidence
in male, but not female, rats of squamous-cell carcinomas of
the forestomach and hemangiosarcomas of the circulatory
system. The study also statistically links an incrased
incidence of adenocarcinomas of the mammary gland in female
rats with exposure to technical grade 1,2-dichloroethane.
Analysis of purity performed by NIOSH after completion of the
bioassay showed that there was about 99% 1,2-DCE, along with
chloroform as the major contaminant as well as 12 other
minor contaminants (Hooper, et al., 1980).
The second NCI carcinogenic study of 1,2-dichloroethane
used 200 5-week-old B6C3F1 mice instead of rats. Fifty male
and female mice were administered technical grade 1,2-dichloro-
ethane in maximum tolerated doses or in half of the maximum
tolerated dose by oral intubation. For male mice this dose
-------
V-34
was 195 or 97 mg/kg/day, but for female mice it was 299 or
149 mg/kg/day (time-weighted average dose over a 78-week
period). Twenty mice of each sex were used as untreated
controls, and an equal number were given the vehicle (corn
oil) by oral intubation. As in the NCI rat study, gross
necropsy was performed on each animal that died or was killed
at the end, and similar histopathologic examinations were
made.
Hepatocellular carcinomas occurred in all male mice
(Table V-16), but only two were seen in females. The number
of hepatocellular carcinomas in the high-dose male group were
significantly greater than those in the control groups. The
Cochran-Armitage test indicated a positive dose-response
association with either the matched (P = 0.025) or the pooled
(P = 0.006) controls. The Fisher exact test also yielded a
significant (P = 0.009) comparison of the high-dose to the
pooled control group.
A large number of alveolar/bronchiolar adenomas were
also observed in the mouse study. They were present in 31%
of the male (15/48) and female (15/48) high-dose mice. None
occurred in the untreated or vehicle control males, and only
one appeared in each female control group (Table V-17). The
Cochran-Armitage test showed a significant (P = 0.005) positive
dose-response association when either high-dose male or female
groups were compared with appropriate untreated or vehicle
control groups. The Fisher exact test also indicated that
-------
V-35
TABLE V-16
Hepatocellular Carcinomas in
1,2-Dichloroethane Treated Mice
Group Mice with hepatocellular
carcinomas
Male
Untreated controls 2/17 (12%)
Vehicle controls 1/19 (5%)
Low-dose group 6/47 (13%)
High-dose group 12/48 (25%)
Female
Untreated controls - 0/19 (0%)
Vehicle controls 1/20 (5%)
Low-dose group 0/50 (0%)
High-dose group 1/47 (2%)
Source: Adapted from NCI, 1978.
-------
V-36
TABLE V-17
Alveolar/Bronchiolar Adenomas in Mice
Treated with 1,2-Dichloroethane
Mice with
Group alveolar/bronchiolar
adenomas
Male
Untreated controls 0/17 (0%)
Vehicle controls 0/19 (0%)
Low-dose group 1/47 (2%)
High-dose group 15/48 (31%)
Females
Untreated controls 1/19 (5%)
Vehicle controls 1/20 (5%)
Low-dose group 7/50 (14%)
High-dose group 15/48 (31%)
Source: Adapted from NCI 1978.
-------
V-37
both high-dose groups had a significantly (p = 0.016) higher
incidence rate than either of the control groups, but this
test attributed no statistical significance to the incidence
of alveolar/bronchiolar adenomas in the low-dose female mice,
Squamous-cell carcinomas of the forestomach occurred in
ten of the mice treated with 1,2-dichloroethane and in two
of the controls (Table V-18). The Cochran-Armitage test
indicated a significant (P = 0.035) positive association
between dosage and the incidence of these lesions when dosed
female groups were compared with the pooled vehicle control,
but the Fisher exact tests did not confirm this association.
TABLE V-18
Squamous Cell Carcinomas of the Forestomach in
1,2-Dichloroethane Treated Mice
Group Mice with squamous-cell
carcinoma of forestomach
Male
Untreated controls 0/17 (0%)
Vehicle controls 1/19 (5%)
Low-dose group 1/46 (2%)
High-dose group 2/46 (4%)
Female
Untreated controls 0/19 (0%)
Vehicle controls 1/20 (5%)
Low-dose group 2/50 (4%)
High-dose group 5/48 (10%)
Source: Adapted from NCI, 1978.
-------
V-38
A statistically significant positive association between
dosage and the incidence of mammary adenocarcinomas in female
mice was also reported. These malignancies occurred in 18%
(9/50) of the low-dose mice (P = 0.001, Cochran-Armitage
test; P = 0.039, Fisher exact test) and 15% (7/48) of the
high-dose mice (P = 0.003, Cochran-Armitage test). No
adenocarcinomas of the mammary gland occurred in either the
pooled vehicle controls (0/60) or the matched vehicle controls
(0/20) (NCI, 1978).
To summarize, the NCI study indicated statistically
significant association between oral intubation exposure to
1,2-dichloroethane and the incidence of alveolar/bronchiolar
adenomas in both male and female mice. The study also
established a statistically significant relationship between
oral intubation exposure and the occurrence of hepatocellular
carinomas in male mice. No such relationship was found for
female mice, nor was an unequivocal association found between
oral intubation exposure to 1,2-dichloroethane and the
occurrence of squamous-cell carcinomas of the forestomach in
either male or female mice.
The NCI bioassay had some major experimental design
flaws. The rats treated with 1,2-dichloroethane and the
vehicle control rats were housed in the same room as other
rats intubated with 1,1-dichloroethane, dibromochloropropane,
trichloroethylene and carbon disulfide. Untreated control
rats were housed in a different room along with other rats
-------
V-39
intubated with 1,1,2-trichloroethane and tetrachloroethylene
(NCI, 1978) .
All mice used in the 1,2-dichloroethene study were housed
in the same room as other mice intubated with 1,1,2,2-
tetrachloroethane, chloroform, allyl chloride, chloropicrin,
dibromochloropropane, 1,2-dibromoethane, 1,1-dichloroethane,
trichloroethylene, 3-sulfolene, iodoform, methylchloroform,
1,1,2-trichloroethane, tetrachloroethylene, hexachloroethane,
carbon disulfide, trichlorofluoromethane and carbon tetrachloride
(NCI, 1978).
The high dose rats showed a significant dose-related
increase in mortality (P < 0.001). The results were skewed
particularly because the vehicle control had a greater
mortality than low dose males early in the study. High dose
male rat survival was low, 50% dead by week 55 and 89% dead
by week 75 (Table V-12).
The rats, in general, appeared to suffer from chronic
murine pneumonia ranging from 70% in high dose females to 95%
in vehicle control females. Male rats appeared to have some
hematopoietic system effects as observed primarily in the
spleen: 16% and 12% in low and high-dose male rats, respectively,
vs. 5% in vehicle controls. The female rats had 12% and 40%
in the low and high-dose, respectively, vs. 10% in vehicle
controls. In males, 12% of the low-dose and 16% of the
high-dose vs. 0% in the vehicle controls had adverse circula-
tory system effects. The females had 6% and 16% adverse
-------
V-40
effects in the low and high-dose, respectively. In the liver,
excluding fatty metamorphosis, there were 8% and 14% adverse
effects in the high and low dose, respectively, vs. 0% in the
vehicle controls for males and 8% and 16% in the high and low-
dose, respectively, vs. 5% in the vehicle controls for females.
There were reported endocrine effects in the male rat of
14% and 16% in the low and high dose respectively vs. 0% in
the vehicle controls.
The mice also suffered from chronic murine pneumonia.
The untreated and vehicle controls, even though housed in the
same room, did not suffer from pneumonia.
In the female mouse, the integumentary system, 14% and
6% with low and high dose, respectively, was affected. At
the high dose, the urinary bladder (10%) was affected.
A carcinogenic bioassay of 1,2-DCE by inhalation was
carried out by Maltoni, et al. (1980). Four groups of 180
Sprague-Dawley rats and four groups of Swiss mice of both
sexes were exposed to four 1,2-DCE concentrations: 250-150
ppm, 50 ppm, 10 ppm, 5 ppm or 0 ppm respectively, for 7 hours
daily, 5 days a week, for 78 weeks. The 250 ppm exposure had
to be reduced to 150 ppm after several days because of severe
toxic effects on the animals, particularly the mice. Two
groups of 180 rats and one group of 249 mice served as
controls. At the end of the exposure period, the animals
were allowed to live until spontaneous death. No specific
types of tumors were found in treated animals of either
species. No relevant changes in the incidences of tumors
-------
V-41
normally occurring in the Sprague-Dawley rats, apart from a
non dose-correlated increase in mammary tumors when compared
with the controls. This was due to enhanced numbers of
fibromas and fibroadenomas as opposed to malignant tumor types,
On the basis of data gathered to date, it appears that
1,2-dichloroethane is an animal carcinogen when administered
by the oral route. No significant increase in the incidence
of tumors has been observed in animals exposed via inhalation.
Several explanations have been proposed to reconcile these
apparent discrepancies, such as a difference in responsiveness
by the strains of test animals studied .and the route of
exposure affecting the carcinogenicity of the substance.
There are several studies reported in the literature
which demonstrate covalent binding of 1,2-dichloroethane to
macromolecules, including DNA (Banerjee and Van Duuren, 1979;
Guengerich, et al., 1980; DiRenzo, et al., 1982). The work
of Banerjee and Van Duuren was designed to determine if
1) 1,2-DCE interacts with microsomal proteins of the liver,
its principal target organ in the mouse, 2) if it binds to
DNA in the absence or presence of microsomes and 3) if a
correlation can be shown between binding and carcinogenicity.
Microsomal protein preparations were obtained from young
B6C3F1 mice. DNA was isolated from salmon sperm. Each
preparation was incubated individually with [14C] 1,2-DCE in
the presence of native or denatured hepatic microsomes (2 mg
protein) from male B6C3F1 mice. No detectable radioactivity
was measured in preparations utilizing denatured microsomes,
-------
V-42
but considerably binding was observed to both liver microsomal
proteins (19,000 + 2,300 dpm/mg protein) and to sperm DNA
(570 + 2 dpm/mg protein) in the presence of the native
microsomal preparation.
Banerjee and Van Duuren (1979) also did comparative in
vitro studies with hepatic microsomal protein preparations
from B6C3F1 mice and Osborne-Mendel rats. The results can be
seen in Table V-19. Hepatic microsomal protein from mice bound
eight and six times more 1,2-DCE than did microsomal protein
from male and female rats, respectively. This result is
statistically significant for both the males and females of
these species (P < 0.001). The covalent binding of [14c] 1,2-
DCE was five times greater to DNA in the presence of microsomes
from male B6C3F1 mice ,than in the presence of microsomes from
male Osborne-Mendel rats, whereas 1,2-DCE was bound 2.5 times
greater to DNA in the presence of microsomes from female mice
than from female rats. This result was also statistically
significant: P < 0.001 for males and P < 0.02 for females.
These observations are similar to those reported earlier by
the same authors for trichloroethylene (Banerjee and Van
Duuren, 1978). In both studies, significantly greater binding
of 14C-compound was noted in the target organ proteins of
mice which are susceptible to compound-induced hepatocellular
carcinoma than for Osborn-Mendel rats which are resistant to
liver carcinoma by TCE or 1,2-DCE. These observations lend
support to the hypothesis that a correlation exists between
binding to DNA and the compound-induced carcinogenicity.
-------
V-43
TABLE V-19
In vitro Binding of EDC to Hepatic Microsomal Protein from
B6C3Fi mice and Osborne-Mendel Rats and to Salmon Sperm DNA
[I4c]EDC bound to macromolecules3
Species nmole/mg protein nmole/mg DNA
male female male female
B6C3F1 mice 1.75+0.15 1.23+0.17 0.05+0 0.05+0
Osborne-Mendel rats 0.22+0.04 0.21+0.03 0.01+0 0.02+0
a The results for mice are the average +SD of 3 males and 3 females;
the results for rats are the average +_SD of 7 males and 5 females.
Three analyses were performed for each animal.
(Modified from Banerjee and Van Duuren, 1979).
-------
V-44
Similar studies have been conducted by Guengerich, et al.
(1981) in Sprague-Dawley rats. Microsomal and cytosolic
fractions of liver homogenates were prepared from phenobarbi-
tal-treated males. Little irreversible binding of 1,2-DCE to the
microsomal preparations was observed in the absence of NADPH;
irreversible binding was linear with respect to time over the 90
minute testing period in the presence of NADPH. Liver micro-
somes catalyzed the NADPH dependent metabolism of 1,2-dichloro-
^
ethane to metabolites irreversibly bound to calf thymus
DNA. Cytosolic fractions also catalyzed binding of the
compound to DNA in a reaction enhanced by GSH. Both reactions
were linear with respect to time for 150 minutes of incubation.
Pretreatment of rats with phenobarbital increased microsomal
rates of total non-volatile product formation two-fold and
irreversible binding to protein four-fold, but did not
significantly affect covalently binding to DNA.
DiRenzo, et al. (1982) also showed that in vitro covalent
binding to calf thymus DNA by 1,2-dichloroethane occurred
following activation by hepatic microsomes isolated from
phenobarbital-treated rats (strain not named). The degree
of binding to form a DBA-adduct was considerably lower for
1,2-DCE than for most of the other compounds tested (see
Table V-20). This could be due, in part, to the fact that
only a relatively small fraction of 1,2-DCE is metabolized
to active metabolites by the microsomal fraction. The
greater conversion occurs in the presence of the cytosolic
-------
V-45
TABLE V-20
Microsonal Bioactivation and Covalent Binding of Aliphatic
Halides to Calf Thymus DMA
Aliphatic halides Binding to ENA
1 , 2-Dibromoethane
Bronotrichlorone thane
Chloroform
Carbon tetrachloride
Trichloroethylene
1,1, 2-Trichloroethane
Di chlorone thane
Halothane
1 ,2-Dichloroethane
1,1, 1-Tr ichloroe thane
0.52+0.14(6)
0.51+0.18(6)
0.46+0.13(6)
0.39+0.08(6)
0.36+0.14(7)
0.35+0.07(7)
0.11+0.05(6)
0.08+0.01(6)
0.06+0.02(6)
0.05+0.01(3)
*nnol bound/fag DNA/h. Values are the mean +_ standard deviation for the
number of experiments in parentheses.
(Modified from DiRenzo, et al.f 1982)
-------
V-46
fraction. Thus, proportoinately less active metabolite
would have been available with which adducts with DNA
would be formed.
MUTAGENICITY
There are a number of studies which demonstrate a positive
correlation between mutagenicity and carcinogenicity (Ames,
1979). In addition, there is evidence accumulated in mammals
that most environmental carcinogens require bioactivation.
Therefore, the identification of carcinogens by mutagenicity
tests may be largely dependent upon the particular test system
which is used. Table V-21 shows the results obtained with
1,2-dichloroethane in a number of short-term test systems.
1,2-Dichloroethane was shown to inhibit the growth of
DNA polymerase-deficient Escherichia coli (P01A~) (Brem,
et al., 1974). E_. Coli bacteria which are deficient in the
enzyme DNA polymerase are sensitive to the inhibitory
actions of chemicals which attack cellular DNA because
they are unable to repair damage to their DNA.
In the bacterium Salmonella typhimurium, 1,2-dichloroethane
produced a dose-dependent, although relatively weak, direct
mutagenic effect in standard mutagenicity tests (Brem, et al.,
1974; Simmon, et al., 1978). However, when further studies
were undertaken, 1,2-dichloroethane was found in most of
them to be activated to a highly mutagenic metabolite, when
metabolized by enzymes in the soluble fraction (S-9) of the
rat liver cell. (Kanada and Uyeta, 1978; Rannug, et al.,
1978; Rannug and Beije, 1979). In addition, the mutagenic
-------
TABLE V-21
Results of 1,2-Dichloroethane in Short-term Assys
Assay System
A. Prokaryotic Mutagenesis:
Salmonella
Effect*
Measured
n
n
n
n
n
ii
E. Coli, PolA+/PolA-
M
.Lysis K39(a)
B. Drosophila
sex-linked recessive
lethal test (larvae and
adults)
Results
Weakly +
highly + (activated)
+ (with S-9)
+ (TA 100)
-i- (with activation)
- (with induced S-9)
+ (with S-9)
+ (with S-9 + GSH)
- (no S-9)
- (with/without S-9)
+ (lethal mutation)
+ (eye-color marker)
References
Brem, et al., 1974
Rannug and Beije, 1979
(Canada and Uyeta, 1978
Simmon, et al., 1978
Guengerich, et al., 1980
King, et al., 1979
McCann, et al., 1975
Rannug, et al., 1978
Brem, et al., 1974
Brem, et al., 1974
Kristofferson, 1974
(abstract - no details
available)
Rapoport, 1960
Shakarnis, 1969
Nylander, et al., 1978
King, et al., 1979
* G = genotoxic;
+ = positive;
NG = non-genotoxic
- = negative
-------
(Table V-21 continued)
Assay System
C. DNA Binding
D. Barley kernels
E. Saccharomyces cerevisiae
F. Mouse micronucleus test
G. Allium root tip
H. Pulmonary tumor induction
in Strain A mice
Effect*
Measured
NG?
NG
NG
Results*
+ (In vitro, naked
Calf thyraus DNA,
with NADPH + S-9)
+ (In vitro, naked
with calf thymus DNA,
NADPH + cytosolic
fraction)
+ (minor covalent
binding to naked
calf thymus DNA
with S-9)
+ (Covalent binding
to DNA)
+(increased t's of
recessive lethal
mutations)
Weakly +
References
Guengerich, et al.,
1980
DiRenzo, et al., 1982
Banerjee and
VanDuuren, 1979
Ehrenberg, et al.,
1974
Simmon, unpublished
(cited in Simmon, 1980)
King, et al., 1979
Kristofferson, 1974
(abst.) (no details
available)
Theiss, et al., 1977
f
03
-------
V-49
metabolite was assumed to be a glutathione conjugate, which
when synthesized and tested was highly mutagenic (Rannug
and Beije, 1979; Guengerich, et al. 1980). This was surprising
because compounds which are conjugated with glutathione are
usually considered to be rendered less reactive and quickly
and harmlessly excreted from the body. However, in this
case, displacement of one reactive chlorine group by glutathione
actually causes the other chlorine to become more reactive,
and the compound formed is highly mutagenic. Also, a synthetic
glutathione conjugate of this type was demonstrated to be
directly mutagenic.
In other investigations of its mutagenic activity, 1,2-
dichloroethane produced single-strand breaks in DNA of hamster
cells and chromosomal aberrations in barley kernels (Ehrenberg,
et al., 1974). The mutagenic effectiveness of 1,2-dichloro-
ethane was reported to be 100 times greater than expected
from the frequency of initial reactions with DNA. Displacement
of a chlorine is thought to result in this amplification of
effectiveness.
These findings concur with those indicating that displacement
of one chlorine by glutathione, as shown by Rannug and co-workers
51978) leads to a more reactive derivative.
1,2-Dichloroethane has also been shown to be mutagenic
in Drosophila melanogaster (Rapoport, 1960; Nylander, et al.
1978; King et al., 1979). Nondisjunction and recessive sex-
linked lethal mutations were induced in Drosophila treated
-------
V-50
with 1t2-dichloroethane through their food supply (Shakarnis,
1969). A high frequency of mutations was also produced in a
sex-linked genetaically unstable Drosophila system (Nylander,
et al, 1978). Mutation was measured by the frequency of somatic
mutations for eye pigment. Metabolic activity in Drosophila was
suggested.
The synthetic reaction product of 1,2-dichloroethane and
cysteine is a relatively strong mutagen in Drosophila and in
Arabidopsis, as well as in Salmonella typhimurium (Rannug et
al., 1978).
Other possible metabolites of 1,2-dichloroethane,
chloroethanol and chloracetaldehyde, are highly mutagenic.
Chloracetaldeyde is a direct-acting mutagen in Salmonella
(McCann et al. ,M975) .
\
-------
VI-1
VI. HEALTH EFFECTS IN HUMANS
General
1,2-Dichloroethane is toxic to humans when it is ingested,
inhaled or absorbed through skin or mucous membranes (Sax,
1975). The primary effects of acute or chronic exposure to
1,2-dichloroethane are central nervous system depression,
gastrointestinal upset and injury to the liver, kidneys,
lungs, and adrenals (Irish, 1963).
Acute Toxicity
Oral ingestion of 1 or 2 ounces, about 400 to 800 mg/kg
body weight, of 1,2-dichloroethane by an adult male is fatal
(NIOSH, 1978). Clinical symptoms of acute 1,2-dichloroethane
poisoning by ingestion usually appear within 2 hours after
exposure. Typically, they include headache, dizziness,
general weakness, nausea, vomiting of blood and bile, dilated
pupils, heart pains and constriction, pain in the epigastric
region, diarrhea and unconsciousness. Pulmonary edema and
increasing cyanosis often are observed. If exposure is
sufficiently brief, these symptoms may disappear when the
individual is no longer exposed (Wirtschafter and Schwartz,
1939; McNally and Fostvedt, 1941). However, persistent
effects occur with sufficient exposure. Autopsies frequently
reveal hyperemia and hemorrhagic lesions of vital organs,
especially the stomach, intestines, heart, brain, liver and
kidney. Not all instances of 1,2-dichloroethane ingestion
are fatal, but death has resulted in the majority of reported
-------
VI-2
cases. Most often these deaths were attributed to circulatory
and respiratory failure (Budanova, 1965; Yodaiken and Bancock,
1973; Luzhnikov et al.f 1976; Zhizhonkov, 1976). Hypermia
and hemorrhaging into the tissues of the visceral organs and
lungs is often revealed at autopsy (Martin et al, 1969;
Yodaiken and Babcock, 1973; Bryzhin, 1975). The symptoms
described here observed in humans, including a prolonged latent
period in certain of the clinical manifestations and delayed
death, as well as the autopsy findings, are supported by
animal data.
Exposure to 4000 ppm of 1,2-dichloroethane vapor for 1
hour produces serious illness in humans (Association of the
Pesticide Control Officials, Inc., 1966). However, two men
exposed experimentally in 1930 to 1200 ppm of 1,2-dichloroethane
for 2 minutes apparently suffered little discomfort, except
that the odor of 1,2-dichloroethane was extremely noticeable
(Sayers et al., 1930). The effects of acute exposure by
inhalation are similar to those described for ingestion,
but the primary target appears to be the central nervous
system (Patterson et al., 1975). Neural depression increases
with the amount of 1,2-dichloroethane absorbed (Stewart,
1967). Damage to the liver, kidneys and lungs also occurs;
reports of leukocytosis and elevated serum bilirubin are
common.
The absorption of 1,2-dichloroethane through skin
produces effects similar to those reported for inhalation,
-------
VI-3
but large doses are required to cause serious systemic
poisoning.
Brief contact of 1,2-dichloroethane with skin
seldom causes serious difficulties; however, repeated or
prolonged contact results in extraction of normal skin oils
and can cause cracking (Wirtschafter and Schwartz, 1939;
Duprat, et al., 1976). Although pain, irritation and
lacrimation normally occur when 1,2-dichloroethane contacts
eye tissue, significant damage usually occurs only if
the compound is not promptly removed by washing (Irish, 1963).
Chronic Toxicity
Few reports of chronic ingestion of 1,2-dichloroethane
were found, but a few. reports of repeated exposures to low
concentrations of 1,2-dichloroethane by inhalation or skin
absorption have been published. Chronic exposures to 1,2-
dichloroethane by inhalation or absorption usually result
in progressive effects that closely resemble the effects
described for acute exposure, especially neurological
changes, loss of appetite, gastrointestinal problems,
irritation of the mucous membranes and liver and kidney
impairment. The concentrations and exposure times associated
with the onset of chronic symptoms in humans are difficult
to deduce from the existing literature. In general, low level
exposures of 10 to 100 ppm for durations of a few days to a
few months appear to be characteristic of most reports.
Fatalities may occur following such exposures, but they are
-------
VI-4
more frequently associated with acute rather than chronic
poisonings (Irish, 1963).
In addition to the above, information concerning
biochemical changes and microscopic lesions resulting from
exposure to 1,2-dichloroethane is increasing (Yodaiken and
Babcock, 1963; Bonitenko, 1974). Unfortunately, the available
information concerning the toxicology of 1,2-dichloroethane
in humans is concerned with poisoning at higher concentrations
or doses (NIOSH, 1978). The more subtle toxic effects
which may result from chronic low level environmental
exposure have not been reported. Of particular interest is
the accumulation of 1,2-dichloroethane in the body with chronic
low level exposure, which is suggested from the water/air,
blood/air, olive oil/air, olive oil/water, and olive/oil
blood partition coefficients (Morgan, et al, 1972; Sato and
Nakajima, 1979). 1,2-Dichloroethane does concentrate in milk
(Urosova, 1953; Sykes and Klein, 1957). More studies are
required to gather information related to chronic low
level exposures.
Sice 1,2-dichloroethane is both water soluble and
lipid soluble, disposition after lung absorption of 1,2-
dichloroethane in the body is widespread, and hence the
toxic effects are related to virtually every organ system.
The toxic consequences which have been seen in human subjects
exposed to 1,2-dichloroethane vapors are similar to those
seen following ingestion and include: cardiovascular disorders
-------
VI-5
with increased heart rate, fluctuations in blood pressure,
changes in blood components and damage to the myocardium, a
characteristic narcotic effect on the central nervous system
with nausea, vomiting, headache, dizziness, unsteady gait,
dilated pupils, pathological reflexes, unconsciousness and
coma, changes in the gastrointestinal tract with gastroenteritis,
chest and stomach pains, cyanosis and pulmonary edema,
damage to kidney function and signs of liver damage
(Wirtschafter and Schwartz, 1939; Gaurino, et al, 1959).
Autopsy findings in fatal cases following acute
poisoning include extensive bleeding into the tissues of
all organs, inflammation, congestion, degeneration and
necrosis in the liver, hemorrhaging of respiratory mucosa,
hemorrhaging, swelling and inflammation of the lungs,
degeneration of the myocardium, and hemorrhaging, inflamation
and swelling of the kidney (Brass, 1949; Troisi and Cavallazi,
1961).
Odor is not a dependable guide for avoiding dangerous
chronic exposures to 1,2-dichloroethane. Although some
individuals can detect as little as 3 ppm under laboratory
conditions, others consider it barely detectable at 50 or
100 ppm (Hoyle, 1961; Verschueren, 1977), The odor of
1,2-dichloroethane is generally considered unmistakable at
180 ppm, but even at this concentration, it may not be
considered unpleasant. In addition, it is easy to become
adapted to odor at low concentrations (Irish, 1963).
-------
VI-6
Poisoning Incidents and Case Histories - More than 100
cases histories of fatal and non-fatal 1,2-dichloroethane
poisonings have been reported in some detail in the literature,
In almost all cases involving ingestion of 1,2-dichloroethane
(approximately 30), death resulted. The amounts of 1,2-
dichloroethane consumed by the victims varied from "one
sip" to 100 ml or more. Age varied from 1.5 years to
about 80. Signs and symptoms included: violent vomiting,
nausea, collapse and unconsciousness. Death usually occurred
within two days of exposure, but, in a few instances, it was
delayed up to six days.
More than 70 cases of acute inhalation exposures to
1,2-dichloroethane are described in the literature (see
Table VI-1); only a small fraction of these, about 13%,
resulted in fatalities. In general, acute inhalation
exposures have been work-related and associated with the
use of end products containing 1,2-dichloroethane. Most
fatalities have been adult males. Symptoms and signs
associated with acute inhalation exposures are generally
similar to those previously described. In lethal exposures
by inhalation, death does not occur as rapidly as in lethal
exposures by ingestion. However, most victims succumb
within two weeks.
Among recorded case histories, most victims of acute
inhalation poisoning recovered and were released as clinically
normal a few days after exposure. Only a few follow-up
-------
VI-7
TABLE VI-1
Cases of Fatal 1,2-Dichloroethane Ingestion
Patient
Anount of Chemical
taken into the body
(if known)
Onset and
Progression
of symptoms
Reference
63-year-
old man
2 onces
1-1/2-year-
old boy
1-1/2-year-
4 males 20-29
years old
53-year-
old man
1 sip
Unknown
150-200 ml
Unknown; maybe
on several
occasions
2 hours
Nausea; faintness;
vomiting; dazed;
cyanotic: dilated
pupils; coarse rales;
weak, rapid pulse;
dark brown liquid
stools; increased
cyanosis; pulse and
heart sounds absent;
dypspnea; death 22 hours
after ingestion
Extreme weakness;
comatose; vomiting;
death the next day
Coma; anuria;
pneumonia
3-4 hours
Symptoms not reported;
death 10, 15,33, and
35 hours after ingestion
Inattentive; sleepy;
excitement; uncon-
sciousness; rapid,
irregular breathing;
cyanosis; completely
dilated pupils; light
pulse; heart and
respiratory failure;
lung edema; death at
least 10 hours after
ingestion.
Hueper and
Smith,
1945
Keyzer,
1944
Meurs,
1944
Bryzhin,
1945
Bloch,
1046
-------
VI-8
TABLE VI-1 (Continued)
Patient
Amount of Chemical
taken into the body
(if known)
Onset and
Progression
of symptoms
Reference
43 -year-
old man
alcoholic
43-year-
old man,
alcoholic
55-year-
old man,
asthmatic
4 drinks diluted
with orange juice
4 drinks diluted
with orange juice
20 ml
Unconsciousness;
death 8 hours after
ingestion
Confusion; deep
sleepiness; uncon-
sciousness; vomiting
with blood; death 24
hours after ingestion
Epigastric pain;
extreme dizziness;
sleepnessness; vomit-
ing; slow pulse; death
24 hours after ingestion
Hulst,
1946
Hulst,
1946
Roubal,
1947
16-year-
old man
50 ml
Vomiting; epigastric pain;
fourth day: muscle spasms,
hiccups, pulse 108, no eye-
lid response to light; death
91 hours after ingestion
Stuhlert,
1949
Man
Unknown
Violent vomiting;
painful visceral
cramps; extreme
weakness; pale,
cyanotic; weak,
rapid pulse; weak
heart sounds; rales;
dyspnea; increased
cyanosis and dyspnea,
and weakening pulse;
death 20 hours after
ingestion
Stuhlert,
1949
-------
VI-9
TABLE VT-1 (Continued)
Patient
Amount of Chemical
taken into the body
(if none)
Onset and
Progression
of Symptoms
Reference
Man
Unknown
50-year-
old man
30 ml
Man
About 20 ml
Man
30-year-
old man
About 20 ml
40 ml
Violent vomiting;
circulatory failure
and death 39 hours
after ingestion
30 minutes Lochlead
Unconsciousness; and Close,
vomiting, cyanosis; 1951
dilated, fixed pupils;
pulmocary edema, extreme
•dyspnea; death 10 hours
after ingestion
1 hour Flotow
Collapse; repeated 1952
vomiting; after 12
hours blue lips, diffi-
culty breathing; death
13 hours after ingestion
Death within 12 hours of
ingestion
Slight cough; Garrison
reddened conjuctivae; and
shock; weak, rapid Leadingham
pulse (100); regained 1954
consciousness after 3
hours; hyperactivity
alternating with semi-
comatose condition; death
28 hours after ingestion
-------
VI-10
TABLE VI-1 (Continued)
Patient
Anount of Chemical
taken into the body
(if known)
Onset and
Progression
of symptoms
Reference
Nan
2-year-
old boy
79-year-
old man
1 sip
2-year-
old boy
1 sip
23-year-
1 sip
2 hours
Violentely ill; shock
cyanosis; pulmonary
edema; light coma;
vomiting and diarrhea;
low blood pressure; severe
albuminuria; death at 19
hours after ingestion
2 hours
Violently vomiting; 20
hours after ingestion;
restlessness, cramps;
death occurred approxi-
mately 21 hours after
ingestion during convulsions
Void ting; weakness;
pale, cyanotic;
scarcely conscious;
vagueness; rapid, regular
pulse (136); blood pressure
not measureable; died 40 hours
after ingestion with heart and
circulatory failure
Vomiting; diarrhea;
tonic spasms; increasing
loss of consciousness;
dyspnea; impaired circu-
lation; death 20 hours after
ingestion
1 hour
Dizziness; nausea;
unconsciousness;
vomiting; cyanosis;
no pupil reaction; no
corneal reflex; difficult
breathing; strong motor
unrest; death after 8
hours due to respiratory
and circulatory failure
Hubbs and
Prusmack,
1955
Durwald,
1955
Weiss,
1957
Reinfried,
1958
-------
VI-11
TABLE VI-1 (Continued)
Patient
Amount of Chemical
taken into the body
(if known)
Onset and
Progression
of symptoms
Reference
63-year-
old man
1 or 2 sips
3 men, 19-27
years old
70, 80 and 100 ml
32-year-
old man,
8 ml
27-year-
old man
Half a glass
Shortly after inges- Freundt
tion; unconsciousness; et al.
soon regained conscious- 1963
ness, strong vomiting;
period of improvement;
10.5 hours after ingestion
unconscious; blood pressure
falling; 14 hours after
ingestion death resulting from
circulatory failure
Few minutes Kaira,
Vomiting; weakness;
dizziness; lost can-
sciousness; deaths
occurred 5-8 hours
after ingestion
Immediate Bogoyav-
Burning sensation in lenski,
mouth throat, stomach; et al.
drank milk and vomited; 1968
weakness; speach retar-
dation; lethargic; asthenic;
cold sweat; heart sounds
muffled; weak and rapid
pulse; 22 hours after inges-
tion excitation, restlessness,
delirium, face flushed, coarse,
systolic murmur, respiratory
depression, circulatory weak-
ness , anuria, then death 56
hours after ingestion
2.5 hours
unconsciousness; vomiting
of dark vomitus; regained
consciousness after 12 hours,
burning sensation in digestive
tract; dyspnea; nausea; cynosis;
respiratory rate 32/minute; moist
rales in lungs; heart sounds muf-
fled; pulse 102, extrasystoles;
anuria; death 19 hours after
ingestion
-------
VI-12
TABLE VI-1 (Continued)
Patient
Amount of Chemical
taken into the body
(if known)
Onset and
Progression
of symptoms
Reference
80-year-
old man
50 ml
57-year-
old man
40 ml
18-year-
old man
50 ml
14-year-
old boy
15 ml
Elevated serum Secchi et
enzymes-—LDH, SCOT al. 1968
SGPT, alkaline phos-
phatease, glutamic
dehydrogenase, RNAase;
death a few hours after
ingestion
Somnolence; vomiting; Martin et
sinus tachycardia (100); al. 1969
ventricular extrasystoles;
return of consciousness
14 hours after ingestion
dyspnea; loss of blood
pressure; cardiac arrest;
death 24 hours after ingestion
1 hour Schoenborn
Somnolent; cyanotic; et al.
4 hours later foul 1970
smelling diarrhea;
5.5 hours later shock
of circulatory system;
death after 17 hours in
irreversible shock
Within 2 hours severe Yodaiken
headache; staggering; and
lethargy; periodic Babcock,
vomiting; blood pres- 1973
sure drop; oliguric;
increasingly dyspenic,
somnolent and oliguric;
ecchymoses; sinus brady-
cardia; cardiac arrest;
pulmonary edema; refractory
hypotension; death on 6th day
-------
VI-13
case studies have been made to determine if long-term effects
develop from acute inhalation exposure to 1,2-dichloroethane.
In a few poorly documented instances, chronic changes in
the central nervous system appear to have persisted 1 to 18
years following exposure (Smirnova and Granik, 1970). In
the most serious case, illness was accompanied by encephalitis
and injury to the subcortical region that improved only
slowly during 14 years. It is uncertain, however, that
exposures were only to 1,2-dichloroethane. Further studies
of delayed effects of acute inhalation exposures to
1,2-dichloroethane are needed.
Recent Studies
Since 1970, several comprehensive studies have been
published which detailed the human toxicity of 1,2-
dichloroethane in the acute as well as the chronic forms.
Summarized in Table VI-2 are the symptoms of acute
1,2-dichloroethane poisoning from ingestion in 118 patients
and the clinical findings in these patients reported by
Akimov et al. (1976, 1978). The amount of compound swallowed
ranged from 20 to 200 ml. The patients were divided into
three groups—mild, moderate, and severe—the severity of
the symptoms do not necessarily correlate with the amount
ingested.
-------
VI-14
TABLE VI-2
Symptoms and Clinical Findings of Acute
Peroral 1,2-Dichloroethane Poisoining
(translated from Akimov et al., 1976, 1978)
Simp tons
Degree of severity of
Poisoning
Mild Moderate Severe
Total Nunber
of Patients,
absolute (%)
Dichloroethane odor
in mouth
Dry skin
Mucosal cyanosis
Respiratory disorders
Tachycardia
Arterial hypotension
Loss of consciousness
Mydriasis
Horizontal nystagmus
Speech disorders
Muscular hypotonia
Decrease in tendon
reflexes
Presence of pathologic-
reflexes
17
10
81
108 (91)
15
2
3
12
3
-
6
8
4
2
2
10
2
4
5
4
1
10
4
6
4
5
64
76
63
57
81
49
69
16
15
52
48
89 (75)
80 (67)
70 (59)
74 (62)
88 (74)
50 (42)
85 (72)
28 (23)
25 (21)
58 (46)
55 (46)
8 (6)
Convulsions
9 (7)
-------
VI-15
TABLE VI-2 (Continued)
Symptoms
Degree of severity of
poisoining
Mild Moderate Severe
Total Number
of patients,
absolute (%)
Cerebellar disorders:
Ataxia 8
Romberg's sign 9
Intention tremor 13
Adnodochokinesis 7
Dysmetria 5
Extrapyramidal disorders:
Pare nictation 2
Hypomimia 4
Bradykinesia 3
Delirious hallucina- 1
tions
7-
9
9
7
4
2
5
4
18
21
29
16
11
9
19
11
33 (27)
39 (33)
51 (43)
30 (25)
20 (16)
13 (11)
28 (23)
18 (15)
4 (3)
-------
VI-16
The most common effects in mild to severe 1,2-
dichloroethane poisoning were a pronounced odor on the
patient's breath, cyanosis, difficulty in breathing,
tachycardia, hypotension, mydriasis, loss of muscle tone
and a decrease in tendon reflexes. Neurological syndromes
involving disturbances in consciousness, mental disorders,
cerebellar and extrapyramidal abnormalities were often
noted (Table VI-3).
The neurological symptoms in mild poisoning disappeared
4 to 5 days after the onset. These disorders were more
prolonged in moderate poisoning, and a cerebellar syndrome
was observed for up to two weeks in some patients from
this group. The neurological disorders in the group of
patients who were severely poisoned were characterized by
loss of consciousness, muscle hypotonia, a decrease in tendon
and periosteal reflexes, the onset of pathological reflexes
in the feet and convulsions. The cerebellar and extrapyramidal
disorders, which lasted for 2 to 3 weeks, were more pronounced.
Shchepotin and Bondarenko (1978) described acute
toxicity to 1,2-dichloroethane in 248 patients, males and
females between the ages of 15 and 72. The majority of
these patients (85 percent) suffered harmful effects resulting
from oral ingestion of the liquid chemical, while toxicity
followed inhalation of vapors in 15 percent. The length
of inhalation of 1,2-dichloroethane was, on the average,
20 to 30 minutes. However, concentrations of the inhaled
1,2-dichloroethane vapors were not reported.
-------
VI-17
TABLE VI-3
Characteristics of the Basic Forms of Damage
to the Nervous System in Acute Dichloroethane Poisoning
(translated from Akimov et al., 1978)
Severity of damage
Mild
Medium
Severe
Euphoria
Hallucinations
Mild nystagmus
Reduction of
abdominal
and sole
reflexes
Moderate atactic
symptoms
Deafness
Hallucinations
Psychomotor excitation
Mydriasis
Persistent nystagmus
Muscular hypotonia
Reduction of abdominal
and sole reflexes
Reduction of reflexes
of extremities
Pronounced atactic
symptoms
Hypomimia
Bradykinesia
Stupor, coma
Mydriasis
Persistent
nystagmus
Reduction of
corneal
reflexes
Muscular
hypotonia
Reduction of
abdominal
and sole
reflexes
Reduction of
reflexes of
extremities
Toxic convulsions
Pronounced atc-
tic symptoms
Hypomimia
Bradykinesia
Dysarthria
Dysarthria
-------
VI-18
Four main clinical syndromes were identified with 1,2-
dicloroethane poisoning in these patients. The hepatic and
cardiovascular systems were affected most often following
central nervous system disorders. Renal dysfunction was
also observed. Neurological disorders were noted in all
patients. These included unconsciousness (narcotic effect)
and respiratory inhibition via depression of the medullary
center of the brain. A syndrome of acute cardiovascular
insufficiency developed in 60 percent of the patients
including arrhythmias and a fall in both systolic and
diastolic blood pressure, with reduction of cardiac output
and decreased peripheral resistance. In 35 percent of the
patients, a syndrome of liver dysfunction was evident. The
liver was enlarged, hyperbilirubinemia was severe, and
serum albumin and asparagine transaminase activities were
increased.
With inhalation poisoning, in particular, the kidneys
were affected. This is explained by the relatively high
arterial blood flow (20 percent of cardiac output) perfusing
the kidneys. Nephropathology in these patients was manifested
by oliguria, proteinuria, azotemia and acute renal failure
with disturbances of acid base balance.
Of interest was a common syndrome of gastroenteritis
not only in the patients poisoned by ingestion, but also
in the patients poisoned by inhalation, although the degree
of gastroenteritis was milder in those patients poisoned by
inhalation.
-------
VI-19
Shchepotin and Bondarenko (1978) attempted to correlate
the severity of 1r2-dichloroethane poisoning with the
concentrations of 1,2-dichloroethane in blood and urine as
determined by gas chromatography. While a severe clinical
course of poisoning was sometimes noted with high concentrations
in blood and urine, no correlation between severity and DCE
levels in body fluids was established. Similarly, no direct
correlation between severity of poisoning and the amount of
1,2-dichloroethane inhaled was evident.
Bonitenko (1974, 1977), in a description of 1,2-
dichloroethane toxicity in 32 patients, compared the severity
of clinical symptoms of poisoning with concentrations of
the chemical in the blood. Coma was associated with blood
concentrations of 15-30 mg percent, and the level at which
consciousness returned corresponded to levels below 8-10 mg
percent. The method of measurement was not described.
These investigators determined at autopsy that the level in
adipose tissue was 68 mg per 100 gm of tissue while the
corresponding level in blood was only 1.2 mg percent.
Luzhnikov et al. (1970), in a study of a series of 110
patients, observed clinical symptoms similar to those reported
by Akimov et al. Within the first hours following exposure,
77 percent of these patients demonstrated acute gastritis
with vomiting, neurological disorders including coma (81
percent), acute cardiovascular insufficiency (57 percent),
hepatitis (56 percent) with liver enlargement and functional
-------
VI-20
abnormalities (abnormal bromosulfonphthalein clearance,
plasma bilirubin and plasma glutamine-asparagine transaminase
levels). Clinical symptoms of poisoning were observed with
only minimal concentrations of 1,2-dichloroethane in the
blood (0.5 mg percent). Coma developed at a blood concen-
tration as low as 5 to 7 mg percent and higher. Gas-liquid
chromatography was utilized to measure the concentration
of 1,2-dichloroethane. Differences in analytical methodology
may help to explain the apparent discrepancy in the values
associated with development of coma given by Bonitenko and
those reported by Luzknikov et al. Time of sampling may
also affect the resulting concentration measurement.
Luzhnikov and co-workers (1974, 1976) also investigated
the toxic effects of 1,2-dichloroethane on the myocardium in
at least 160 patients. These workers developed a concept
of "exotoxic shock," that is, hemodynamic shock due to the
toxic effects of a chemical on the myocardium. During the
compensatory phase of shock, total peripheral resistance
was 15 to 25 percent higher than normal, arterial blood
pressure was normal or increased slightly, while cardiac
output and blood volume were decreased significantly. In
decompensated shock, pronounced and progressive hypotension
was observed, cardiac output was decreased 30 to 70 percent
and peripheral resistance was either unchanged or slightly
decreased. Electrocardiographic (ECG) changes including
arrhythmias were observed in both compensated and decompensated
shock.
-------
VI-21
In analyzing the myocardial function, definite changes
in the cardiac cycle were found in the compensated shock
phase: isometric contraction was decreased, expulsion time
(ventricular emptying period) was increased, intraventricular
pressure was increased and asynchronous contractions
occurred. In the decompensated exotoxic shock phase,
myocardial contractile force was markedly decreased during
ventricular systole and prolonged periods of asynchronous
contractions were observed. The authors noted that a 25-30
percent increase in peripheral resistance for a prolonged
period will produce the observed left sided heart failure,
especially after the observed kidney lesions appear as an
additional contributing factor (Luzhnikov et al., 1974, 1975).
Morphological examination of the myocardium at autopsy
showed significant edema in the cells of the capillary
endothelium and stenosis of the capillary lumina. The
micro-circulatory vessel changes also were accompanied by
pronounced edema of the myocardial interstices with
accumulation of polymorphonuclear leucocytes and microfocal
hemorrhages. Histological examination showed a diminished
presence of glycogen and degenerative changes of varying
degrees in the cardiac muscle. Mitochondrial damage was
indicated by a decrease in enzyme activities.
Toxicity in Infants and Children
1,2-Dichloroethane poisoning in children presents a
clinical syndrome similar to that seen in adults. Hinkel
-------
from an exposure to a "nerve balsalm" medicine which was 75
percent 1,2-dichloroethane. The features of clinical
toxicity are summarized in Table VI-4. Within an hour after
exposure, severe and persistent vomiting occurred. Immediately,
or even after an interval of 10 to 12 hours, various degrees
of narcotic effects were present. The symptoms ranged from
somnolence to coma; less frequently, motor unrest, reflex
increases and convulsions occurred. Indications of circulatory
failure were also present. The manifestations of toxicoses
in the child thus correspond to those observed in adults.
The disturbances in kidney and liver function which are
observed in the adult were less frequent in the children
poisoned from the "nerve balsalm." However, corresponding
investigations have not been undertaken in all instances.
Tachycardia indicated that the effect of 1,2-dichloroethane
on the heart was similar to that of chloroform, although
no ventricular fibrillation was recorded. The blood changes
were not exceptional. In particular, there was no leukocytosis
or erythrocyte and hemoglobin increase which have been
described by others. Electroencephalograms were not routinely
performed; however, in the patients for which they were
recorded, the EEC's proved to be normal. The gross and
histopathological findings were the same as those described
for 1,2-dichloroethane poisoning elsewhere in the literature.
-------
TABLE VI-4
4.
5.
6.
SUMMARIZATION OF THE CLINICAL SYMPTOMS IN CHILDHOOD
(adapted from Hinkel, 1965)
Appearance of the Gastrointestinal Circulatory Clinical
Cases clinical symptoms symptoms CNS symptoms symptoms interval
1 . immediately
2. 1 hour
3. 1/2 hour
severe vomiting
severe vomiting
Severe vomiting
later diarrhea,
incon-
spicuous
unrest,
slugglish
pupil react-
tion
soporose to
comatose
circulatory
insufficiency
circulatory
insufficiency
circulatory
insufficiency
not pre-
sent
not pre-
sent
not pre-
sent
Blood Liver & Kid-
picture ney findings
no find-
ings
no find-
ings
urine no
findings
urine no
findings
Details
easy
course
easy
course
exitus
2 hours
immediately
1 hour
pressure pain in
abdomen, liver
swelling
severe vomiting
severe uninter-
rupted vomiting
somnolent, circulatory not pre- no find- urine, no survived
reflex and insufficiency sent ings findings
tonus increase
somnolent to circulatory 12 hours no find-
soporose insufficiency ings
albumi-
nuria,
leukocyturia,
retention of
substances
normally in
urine
survived
somnolent to circulatory 12 hours
soporose to sufficiency
exitus
7.
1/4 hour
severe vomiting
staggered
gait, somno-
lence
circulatory
insufficiency
8 hours leukocy- no find-
tosis with ings
left dis-
placement
survi-
ved
-------
VI-2 4
In spite of the fact that some of the characteristic changes
of 1,2-dichloroethane poisoning were not present, the
diagnosis of oral hydrocarbon intoxication was indicated.
The toxic lethal dose in children is less than for
adults, ranging from 0.03 to 0.9 gm/kg. However, this oral
dose level did not always cause death.
Infant exposure to 1,2-dichloroethane with subsequent
toxic effects can occur via the milk of nursing mothers who
heve been exposed to the compound. Urusova (1953) demonstrated
the presence of 1,2-dichloroethane in the milk of nursing
mothers who were exposed to the chemical by inhalation or
cutaneous absorption in an industrial setting. Samples of
breast milk and exhaled air from the lungs usually were
taken immediately after work and at periods up to 2 1/2 hours
after work exposure. 1,2-Dichloroetahne was found in the
breast milk within 5 minutes after the ending of the work
period, peaking 1 hour post work exposure. A similar pattern
was found for breath analysis. A concentration of 1,2-
dichloroethane in the work atmosphere was determined to be
0.063 mg/liter (0.016 ppm). After exposure to this atmos-
pheric concentration for one hour, 0.58 mg/liter (0.014 ppm)
was found in the expired air, and 0.54 to 0.64 mg percent
was found in the breast milk. In many cases, 1,2-dichloro-
ethane was detected in the mothers' milk 18 hours after work had
ended. The concentration ranged between 0.2 to 0.63 mg
percent, whereas the breath concentration of 1,2-dichloroethane
-------
VI-2 5
was 0.009 to 0.017 mg/liter (0.002 to 0.004 ppra). 1,2-Dichloro-
ethane was blown out of the milk by an air stream at the rate
of 1 liter/hour with heating in a water bath to 50° and was
concentrated in alcohol. The amount of dichloroethane was
determined by Ginzburg's method. The exhaled air was collected
through the exhalation valve of a gas mask. The dichloroethane
was absorbed and concentrated in alcohol and determined by
the same method.
1,2-Dichloroethane also has been found in cows' milk which
provides another source for exposure in infants and young
children (Sykes and Klein, 1957).
Microscopic Pathology and Cellular Toxicity
Within the last few years, increasing interest has
been expressed in the toxic manifestations of 1,2-dichloroethane
exposure at the cellular and biochemical levels. As noted
above, Luzhnikov et al. have described the histological
changes in myocardial tissue (1974, 1976). Yodaiken
and Babcock (1973) described clinical features and pathologic
findings in detail for a case of fatal poisoning. The
significant abnormalities related to the liver, kidneys and
adrenal glands. Microscopically, extensive liver parenchymal
cell necrosis was found with only scattered vacuolated
cells and occasional islets of surviving cells located near
or around central veins and portal triads. Fat stains
confirmed the presence of lipid in the vacuoles. The
kidneys were yellow and swollen. The glomerulae were intact
-------
VI-26
although focal epithelial cell necrosis was observed. Marked
degenerative changes were found in the descending proximal
limb and the thick ascending limb of the nephrons. Lipid
staining showed extensive fat droplet accumulation most
marked in cortical areas but present throughout the tubular
structure. The adrenals microscopically showed vascular
congestion and well-marked focal degenerative cell damage
in all zones of the cortex. The prominent clinical chemistry
before death was hypoglycemia and hypercalcemia (Yodaiken
and Bancock, 1973).
Schoenborn et al. (1970) found disseminated intravascular
coagulation in a single acute fatality of 1,2-dichloroethane
poisoning. But, unlike Martin's observations in 1968, this
patient did not show an increased tendency to bleed.
Luzhnikov et al. (1974) studied the coagulability
of blood in 30 patients. In 1,2-dichloroethane poisoning,
they found an increased amount of heparin in the blood.
Also observed was an increase in fibrinolytic activity, a
prolonged clotting time and an increased prothrombin index,
all of which are in accord with hemorrhaging or increased
tendency toward hypocoagulation.
Bonitenko et al. (1974, 1977) have shown that the
leucocyte count in the blood of patients poisoned with 1,2-
dichloroethane increases as a function of severity of
poisoning (see Table VI-5). In addition, increases in serum
aminotransferase enzyme activities correlates with severity
of poisoning (Table VI-6). These latter effects are related
-------
VI-27
TABLE VI-5
Mean Number of Leukocytes in the Blood as a Function
of the Severity of the 1,2-Dichloroethane Poisoining
(Bonitenko et al., 1977)
Degree of Me_an Std. Dev,
poisoning x m
Mild 6800 240
Moderate 9200 330
Severe 12000 360
-------
VI-28
TABLE VI-6
Mean Serum Aminotransferase Values in the Early Stages
of 1,2-Dichloroethane Poisoning (U per ml)
(Bonitenko et al.f 1977)
Degree of
poisoning
Alanine-aminotrans-
ferase (SCOT)
Aspartate-amino-
transferase (SGPT)
mean
x
Std dev
m
Mild
Moderate
Severe
39
62
117
4.9
7.1
12.5
mean
x
Std. Dev.
m
32.7 5.2
50.2 7.3
107 13.2
-------
VI-2 9
to organ damage, particularly to damage in the liver. The
blood leucocyte and serum enzyme activity provide a means
of early evaluation of the degree of 1,2-dichloroethane
poisoning and institution of appropriate therapy.
Epidemiology - The earlier available reports of chronic
exposure to 1,2-dichloroethane are complicated by concurrent
exposure of the subjects to other organic chemicals. Hence
the description of observed toxic effects encountered in
these reports cannot be ascribed entirely to 1,1-dichloroethane,
These reports may, however, have certain value in suggesting
the synergistic toxicities which may occur with simultaneous
multi-chemical exposure, and are, therefore, summarized below.
Forty-eight cases of poisoning in Italy by a fumigant
mixture of 75 percent 1,2-dichloroethane and 25 pecent
carbon tetrachloride were reported by DiPorto and Padellaro
(1959). Mild, moderate and severe pathological syndromes
were described. Central nervous system effects and
gastrointestinal disorders were seen commonly in these patients.
The effects were mild for 28, moderate to severe for 16 and
fatal for 4 persons. Clinical findings included acute
hepatorenal insufficiency with the implications associated
with this syndrome. In addition, necrotic and hemorrhagic
lesions in the liver, primarily in the centrolobular cells,
necrosis of the tubular epithelium in the kidneys, as well
as proliferative changes in the glomeruli including
multinucleated cells, were found in the fatal cases.
-------
VI-30
In the same year, Cetnarowicz (1959) published a study
of Polish workers employed by an oil refinery that used a
4:1 mixture of 1,2-dichloroethane and benzene as a processing
fluid. After a two- to eight-month exposure to 10 to 200
ppm 1,2-dichloroethane in the work site air, 16 workers on
one shift experienced a general reduction in body weight
of 2 to 10 kg; four had tender, slightly enlarged livers,
seven had tenderness of the epigastrium and most had
elevated urobilinogen levels in the urine. Thirteen of
the workers had normal levels of erythrocytes and hemoglobin,
but only nine showed a normal distribution of white blood
cells. Other workers had abnormal levels of serum bilirubin,
albumin, globulin, fibrin and blood non-protein nitrogen.
In general, about half of the workers had some loss of
liver function, and nearly one-third experienced changes
in the gastrointestinal tract, sinus bradycardia or hemato-
poietic system. It should be noted, however, that some of
the reported blood changes could reflect benzene poisoning
rather than 1,2-dichloroethane poisoning.
Khubutiya (1964) studied hematologic changes in an
unspecified number of 1,2-dichloroethane workers. Blood
cell morphology, color index, red blood cell count and
hemoglobin content were recorded. Samples from about one-
third of the workers contained hyperchromic erythrocytes
without megaloblasts. Nearly half of the blood samples
showed moderate to high sedimentation rates induced by an
-------
aosoiute neutropniiia ana aosojiuce xyiupnopeaia was
Moderate or marked monocytosis was frequently observed.
\
Turk's cells occurred in the peripheral blood of one worker
in five. The number of platelets was frequently reduced.
Khubutiya attributed both the monocytosis and the Turk's
cells to stimulation of the reticuloendothelial system by
long, unspecified exposures to 1,2-dichloroethane.
Brzozowski et al. (1954) reviewed the health status
and work practices of Polish agricultural workers who used
1,2-dichloroethane as an insecticide. The liquid was
brought to the field in barrels and was then poured by
hand into a series of holes. Skin absorption, which
resulted from spillage on clothes and shoes, was probably
as significant a contribution to exposure as inhalation.
Air concentrations of 1,2-dichloroethane were estimated at
15 to 60 ppm. Signs and symptoms of exposure were reported
in 90 of 118 workers. The most common subjective complaints
were conjunctival congestion, reddening of the pharynx,
bronchial symptoms, metallic taste in the mouth, headache,
weakness, nausea, abdominal and epigastric pains, tachycardia,
dyspnea after effort and burning and reddening of skin.
Liver function tests were significantly abnormal in 70
percent of those tested.
No changes were found in the blood or functions of
internal organs of 100 factory workers exposed to 1,2-
dichloroethane for six months to five years at concentrations
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VI-3 2
of 25 ppm or less (Rozenbaum, 1947). However, functional
disturbances of the nervous system occurred in several
workers, including heightened lability of the autonomic
nervous system, diffuse red dermatographism, muscular
swelling, bradycardia and increased sweating.
Kozik (1975) reported a study of a group of workers in
a Russian aircraft industry chemically exposed to 1,2-dichloro-
ethane during the manufacture of soft rubber tanks. He
compared findings in this group to those for the workers in
the entire factory. He looked at morbidity and temporary
loss of ability to work for the two groups.
Concentrations of 1,2-dichloroethane varied from 5 to
40 ppm and persisted for 70% to 75% of the working time of
the exposed group. Total morbidity, acute gastrointestinal
disorders, neuritis, radiculitis and other diseases were
generally more pronounced among workers exposed to 1,2-
dichloroethane than among other workers in the factory.
Among 83 exposed workers, 19 were found to have diseases
of the liver and bile ducts, 13 had neurotic conditions,
11 experienced autonomic dystonia, 10 had goiter or hyper-
thyroidism and 5 reported asthenic conditions.
No epidemiological studies of 1,2-DCE other than in
industrial exposures have been reported.
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VI I-1
VII. MECHANISMS OF TOXICITY
The cellular mechanisms of toxicity of 1,2-dichloroethane
remain to be investigated. However, a few generalizations
may be made. 1,2-DCE causes acute toxicity via direct
effects on the central nervous system (CNS). The morphological
evidence shows that 1,2-DCE produces adverse effects on
the lungs, liver, heart, adrenals and kidneys.
The signs and symptoms of acute toxicity of 1,2-DCE
vary depending on the species, route of administration and
concentration or dose. Depending upon the intensity of the
exposure and the species of the animal, the liver may show
fatty degeneration or slight congestion with slight
parenchymal degeneration. The kidney often shows signs of
moderate inflammatory irritation with moderate exposure,
but with more severe poisoning, tubular damage ranges from
slight parenchymal degeneration to complete necrosis with
interstitial edema, congestion and hemorrhage. Plaa and Larson
(1965) observed an increase in urinary protein due to the
nephrotoxic effect of 1,2-DCE.
When administered perorally, 1,2-DCE produces direct
irritation of the gastrointestinal tract with cellular
mucosal damage, probably due in part to the solubility
properties of the chemical (Parker, et al., 1979). Kistler
and Luckhardt (1929) found hemorrhages in the mesentery and
in the intestinal mucosa. Pre-neoplastic and malignant
lesions of the gastrointestinal tract were observed in
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VI I-2
rodents exposed to 1,2-DCE by gavage in the NCI bioassays
(NCI, 1978) .
Pulmonary congestion and edema are very frequent
findings whether the exposure to 1,2-DCE is by inhalation
or orally (Parker, 1979). Like chloroform, 1,2-DCE may
have direct effects on the functional properties of the
heart. Heppel, et al. (1945, 1946) and Hofmann, et al.
(1971) observed fatty degenerative changes in the myocardium
of the guinea pig after inhalation exposure.
Metabolite Toxicity and Protection
The 1,2-dichloroethane metabolites, chloroacetaldehyde,
chloroethanol (oral LD$Q for rats - 95 mg/kg), and chloroacetic
acid (oral LDso for rats - 76 mg/kg) are several times more
toxic than dichloroethane itself (oral LD$Q for rats - 770 mg/kg)
(Woodward et al., 1941; Heppel et al., 1945, 1946; Ambrose,
1950; Hayes et al., 1973). Johnson (1967) suggests that chloro-
acetaldehyde may be the toxic metabolite, since this very
reactive compound is capable of both enzymatic and non-enzymatic
interaction with cellular sulfhydryl groups. However,
Yllner (1971a, b) found that chloroacetic acid also reacted
extensively with sulfhydryl compounds in vivo. Heppel, et
al. (1945, 1946) found a high mortality (35 percent) in
rats given 1.3 g/kg of 1,2-DCE orally. Mortality was
reduced by pre- or post-administration of methionine,
cysteine, cystine and other sulfhydryl compounds. Sulfur-
containing amino acids, cystine and methionine, also protected
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VI I-3
young rats from inhalation exposure. This protective
effect of sulfhydryl compounds is clearly related to the
marked depletion of glutathione levels that occurs in the
livers of rats given 1, 2-dichloroethane, chloroethanol or
chloroacetaldehyde (Johnson, 1965, 1967).
Johnson (1965, 1966, 1967) observed that, within 2
hours, a single oral dose of 1,2-dichloroethane (4 millimoles/kg)
reduced the level of liver glutathione in rats to 52% of
that in controls. 2-Chloroethanol (0.67 millimole/kg)
similarly lowered glutathione levels to 17% of control
values with formation of S-carboxymethylglutathione.
Reduction of liver glutathione may have serious toxicological
consequences because the liver is more susceptible to
injury in the absence of this compound (Hayes, 1975) .
Johnson (1965, 1967) also noted that the morbidity and
mortality of young rats given chloroethanol orally was
reduced by concomitant administration of ethanol. He
postulated that the protective effect of ethanol was due to
simple substrate competition for alcohol dehydrogenase
which catalyzes the conversion of chloroethanol to
chloroacetaldehyde. Ethanol also inhibited early effects
of chloroethanol on liver glutathione depletion in these
animals. This author suggests also that the minimal toxicity
observed with chronic low inhalation doses of dichloroethane
in different animal species by Heppel et al. 1946) may be
explained simply by the rapid replenishment of tissue
glutathione.
-------
VI I-4
Over the past several decades, scientists have conducted
a great deal of research in an effort to establish the
mechanism(s) by which chemical substances exert their
carcinogenicity- The somatic cell mutation theory of
carcinogenicity suggests that for a carcinogenic response
to occur, an irreversible change must occur in the cell
which results in proliferation of a neoplasm. This change
reflects a mutational event in the DNA of that cell, suggesting
that the chemical carcinogen must interact directly with or
otherwise alter the DNA to initiate the change. In recent
years, however, some substances have been shown to be carcino-
genic, but by mechanisms in which there apparently is no
direct interaction with or alteration of the DNA of the cell
by the substance. Presumably, these compounds are not capable
of initiating the alteration of a normal cell to a neoplastic
one, but can facilitate expression of a neoplastic response
in latent cells. On the basis of these purported differences
in mechanisms, carcinogens now are often classified into two
broad categories: genotoxic and epigenetic or non-genotoxic.
The mechanisms by which a compound exerts its
carcinogenicity rarely can be determined by the chronic
testing of whole animals such as is done in the NTP bioassay.
Thus, a large number of short-term in vitro and in vivo
assay systems have been developed for the purpose of
elucidating mechanisms. Since most of the in vitro testing
systems measure mutational events, and many carcinogens are
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VI I-5
mutagens, it is becoming accepted that positive results in
these test systems may indicate genotoxicity. The decision
as to whether a substance is genotoxic can be made qualitatively
on the basis of several criteria: 1) a reliable, positive
demonstration of genotoxicity in appropriate prokaryotic
and eukaryotic systems in vitro; 2) studies on binding to
DNA and 3) evidence of biochemical or biologic consequences
of DNA damage (Weisburger and Williams, 1981).
No single test system appears capable of detecting all
carcinogens that are genotoxic. Therefore, a number of
scientists have proposed testing batteries such that results
from each test within the battery, when evaluated as a
whole, may allow one to make a conclusion about the mechanism
of carcinogenicity of a particular compound. 1,2-Dichloro-
ethane has not been systematically studied in any specific
battery of tests, but has been evaluated in a number of
test systems that have been proposed for inclusion in one
or more batteries. Table V-21 lists the results obtained
with 1,2-dicloroethane in a number of these short-term
test systems. Each test system is designated as measuring
genotoxic or nongenotoxic events. In addition, there is
recorded a positive or negative result for 1,2-dichloroethane
in the test system as well as the reference citation. Most
of the studies have appeared in the peer-reviewed literature.
When considering the body of data as a whole, it
becomes evident that 1,2-dichloroethane probably exerts its
carcinogenicity primarily via genotoxic mechanism(s).
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VIII-1
VIII. Quantification of Toxicological Effects
The quantification of toxicological effects of a chemical
consists of an assessment of the non-carcinogenic and carcino-
genic effects. In the quantification of non-carcinogenic
effects, an Adjusted Acceptable Daily Intake (AADI) for the
chemical is determined. For ingestion data, this approach
is illustrated as follows:
Adjusted ADI - (NOAEL or MEL in mg/kg)(70 kg)
(Uncertainty factor)(2 liters/day)
The 70 kg adult consuming 2 liters of water per day is used
as the basis for the calculations. A "no-observed-adverse-effect-
level" or a "minimal-effect-level" is determined from animal
toxicity data or human effects data. This level is divided
by an uncertainty factor because, for these numbers which are
derived from animal studies, there is no universally acceptable
quantitative method to extrapolate from animals to humans,
and the possibility must be considered that humans are more
sensitive to the toxic effects of chemicals than are animals.
For human toxicity data, an uncertainty factor is used to
account for the heterogeneity of the human population in
which persons exhibit differing sensitivity to toxins. The
guidelines set forth by the National Academy of Sciences
(Drinking Water and Health, Vol. 1, 1977) are used in estab-
lishing uncertainty factors. These guidelines are as follows:
an uncertainty factor of 10 is used if there exist valid
experimental results on ingestion by humans, an uncertainty
factor of 100 is used if there exist valid results on long-
-------
VII1-2
term feeding studies on experimental animals, and an uncertainty
factor of 1000 is used if only limited data are available.
In the quantification of carcinogenic effects, mathematical
models are used to calculate the estimated excess cancer
risks associated with the consumption of a chemical through
the drinking water. EPA's Carcinogen Assessment Group has
used the multistage model, which is linear at low doses and
does not exhibit a threshold, to extrapolate from high dose
anjlmal studies to low doses of the chemical expected in the
environment. This model estimates the upper bound (95%
confidence limit) of the incremental excess cancer rate that
would be projected at a specific exposure level for a 70 kg
adult, consuming 2 liters of water per day, over a 70 year
lifespan. Excess cancer risk rates also can be estimated
using other models such as the one-hit model, the Weibull
model, the logit model and the probit model. Current
understanding of the biological mechanisms involved in cancer
do not allow for choosing among the models. The estimates
of incremental risks associated with exposure to low doses
of potential carcinogens can differ by several orders of
magnitude when these models are applied. The linear, non-
threshold multi-stage model often gives one of the highest
risk estimates per dose and thus would usually be the one
most consistent with a regulatory philosophy which would
avoid underestimating potential risk.
The scientific data base, which is used to support the
estimating of risk rate levels as well as other scientific
-------
VIII-3
endeavors, has an inherent uncertainty. In addition, in
many areas, there exists only limited knowledge concerning
the health effects of contaminants at levels found in drinking
water. Thus, the dose-response data gathered at high levels of
exposure are used for extrapolation to estimate responses at
levels of exposure nearer to the range in which a standard
might be set. In most cases, data exist only for animals; thus,
uncertainty exists when the data are extrapolated to humans.
When estimating risk rate levels, several other areas of
uncertainty exist such as the effect of age, sex, species
and target organ of the test animals used in the experiment,
as well as the exposure mode and dosing rates. Additional
uncertainty exists when there is exposure to more than one
contaminant due to the lack of information about possible
additive, synergistic or antagonistic interactions.
Non-carcinogenic Effects
The non-carcinogenic toxic effects of 1,2-dichloroethane
(1,2-DCE) in humans and other animals from both acute and
longer-term exposures at relatively high levels include
central nervous system (CNS) depression, liver and kidney
damage, gastrointestinal distress, adrenal and pulmonary
effects and circulatory disturbances. The appearance and
intensity of these effects are dependent upon dose and duration
of exposure. Death following high level acute exposures
usually results from respiratory or circulatory failure.
Delayed fatalities usually are due to renal damage. Fatty
degeneration in the liver, heart and adrenals also have been
observed.
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VIII-4
- No information is available on the existence of any sub-
group of the human population which is likely to be more
susceptible to the toxicity of 1,2-dichloroethane, nor is
there any information on the nature of interaction between
1,2-DCE and other chemicals during multiple chemical exposure.
Reported minimum acute lethal doses in non-human mammals
range from 600 to 2000 mg/kg (see Table VIII-1). Humans, however,
may be more sensitive to the acute effects of this substance
as there exists a case report describing the death of an
adolescent male following ingestion of about 350 mg/kg of
the solvent (Yodaiken and Babcock, 1973).
Some of the effects occurring after extended exposure in
animals to 1,2-dichloroethane are described below in the
section on Quantification of Non-carcinogenic Effects. Different
effects were noted in rabbits exposed to 3000 ppm 1,2-DCE for
2 hr/day, 5 days/week for 90 days( Lioia and Elmino, 1959;
Lioia, et al, 1959). These authors reported that the animals
exhibited varying degrees of leukopenia and thrombocytopenia. In
addition, there was frequent hypoplasia of the granuloblastic
and erythroblastic parenchyma in the bone marrow. The cellular
concentration of leukolipids was reduced, but no changes occurred
in polysaccharides, peroxidase or RNA. The investigators suggested
that 1,2-DCE might exert a direct poisoning effect on bone
marrow.
-------
VIII-5
Table VIII-1
Acute Lethal Doses of 1,2-Dichloroethane in Animals
Species Category3
Mouse
Rat
Guinea pig
Rabbit
Dog
Pig
LCLQ
LDL0
LDL0
LDL0
LCL0
LDL0
LD50
LCL0 . -
LDL0
LCL0
LDL0
LD50
LDL0
LDL0
LCL0
Dosage
5000 mg/m3
600 mg/kg
380 mg/kg
250 mg/kg
1000 ppm/4 hr
500 mg/kg
680 mg/kg
1500 ppm/7 hr
600 mg/kg
3000 ppm/7 hr
1200 mg/kg
860 mg/kg
2000 mg/kg
175 mg/kg
3000 ppm/7 hr
Route
Inhalation
Oral
Subcutaneous
Intraperitoneal
Inhalation
Subcutaneous
Oral
Inhalation
Intraperitoneal
Inhalation
Subcutaneous
Oral
Oral
Intravenous
Inhalation
aLCLQ:lowest published lethal concentration in air; LDLQ: lowest
reported lethal dose by any route other than inhalation;
median lethal dose by any route other than inhalation.
Source: NIOSH, 1977, p.388
-------
VIII-6
Quantification of Non-carcinogenic Effecfts
The only toxicological study published to date in which
the test animals were exposed to 1,2-dichloroethane in their
drinking water was reported by Lane, et al. (1982). The
duration of dosing varied from 5 to 25 weeks, depending upon
the particular protocol used. The authors conducted a multi-
generation reproductive study which included screening for
dominant lethal and teratogenic effects. Male and female
ICR Swiss mice received the test substance at concentrations
of 0, 0.03, 0.09 or 0.29 mg/1 (0, 5, 15, or 50 mg/kg/day).
Under the conditions of this study, there appeared to be no
dose-dependent effects upon fertility, gestation, viability
or lactation indices. Weight gain and pup survival were not
affected adversely. No significant dominant lethal or tera-
togenic effects occurred in either of the two generations
tested. The no-effect level of 50 mg/kg may not be the
highest no-effect level since no higher doses were given.
If one were to use the results of this study to derive an
acceptable daily intake (ADI) for non-carcinogenic toxicity,
it might be developed as follows:
ADI: 50 mg/kg/day X 100% =0.05 mg/kg/day(or 3.5 mg/day
100 X 10 for a 70 kg adult)
Where: 50 mg/kg/day = No-observed adverse effect level (NOAEL)
for reproductive and teratogenic effects
70 kg = weight of protected individual
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VIII-7
100% = percentage of dose absorbed
100 = uncertainty factor, appropriate for use with
NOAEL from animal data, and no equivalent
human data
10 = uncertainty factor, for less than lifetime
exposure
The study by Alumot, et al. (1976), in which 250 or 500
ppm 1,2-dichloroethane was added to the feed of rats for up
to two years, yielded no significant differences between
treated and control animals. Even though the authors
recommended an acceptable daily intake (ADI) of 25 mg/kg,
inadequacies in the conduct and reporting of the study exist,
rendering this, experiment inappropriate for use in the deriva-
tion of an ADI.
Longer-term inhalation exposures (up to eight months) to
100 ppm 1,2-dichloroethane for 6 to 7 hours/day, 5 days/week
in a variety of animal species yielded no adverse effects as
measured by general appearance, behavior, mortality rates,
growth rates, organ function and blood clinical chemistry in
separate studies reported by Heppel, et al., 1946, Spencer,
et al., 1951 and Hofmann, et al., 1971. Exposures at higher
levels (400-500 ppm) for the same duration did result in
increased mortality and some pathological findings, including
pulmonary congestion, diffused myocarditis, slight to moderate
fatty degeneration of the liver, kidney, adrenal and heart as
well as increased prothrombin time. If one were to use the
NOEL of 100 ppm identified in these three studies to derive an
ADI for non-carcinogenic effects, the ADI might be developed
-------
VIII-8
as follows:
ADI: 405 mg/m3 X 1 m3/hr X6hrX0.3X5 = 0.00745 mg/kg/day
100 X 10 X 7 (or 0.521 mg/day
for a 70 kg adult)
Where: 405 mg/m3 = NOAEL of 100 ppm (1 ppm = 4.05 mg/m3)
1 m3/hr = respiratory rate of adult human (pulmonary rate/
body weight ratio assumed to be the same for
humans and test animals)
6 hours « exposure duration/day
5/7 = conversion of 5 day/week dosing to daily for
7 day/week
0.3 = fraction of test substance absorbed (assumed)
100 = uncertainty factor, appropriate for use with NOAEL
from animal data and no equivalent human data
10 = uncertainty factor, for less than lifetime exposure
From the data presented above, it is obvious that alter-
ations in reproductive function do not represent the most sensitive
end point of toxicity to this substance. The end-points
identified in the inhalation studies are,for now, more appropriate
indicators of 1,2-dichloroethane's noncarcinogenic toxicity.
Therefore, the ADI derived from this series of studies will
be used to develop an Adjusted ADI for noncarcinogenic
effects for 1,2-dichloroethane. Assuming that there is no
exposure to 1,2-dichloroethane from other sources, the
Adjusted ADI would be derived thusly:
7.45 ug/kg/day x 70 kg x 100% = 0.260 mg/1
2 1
Where: 7.45 ug/kg/day * ADI for 70 kg adult
-------
VIII-9
70 kg = body weight of protected individual
100% = assumed percentage contribution to total
exposure by drinking water
21= volume of drinking water imbibed/day by
70 kg adult
The Adjusted ADI is derived to reflect allowable daily
exposure of a 70 kg adult drinking two liters of water
per day, and whose sole source of exposure to 1,2-dichloro-
ethane is via that drinking water. This calculation does not
reflect the associated carcinogenic risk.
Carcinogenic Effects
Near lifetime exposure to 1,2-dichloroethane has been shown
to significantly increase tumor incidences at several sites
in both rats and mice when administered by gavage, but not
following inhalation exposures in these species (different
strains) or thrice weekly intraperitoneal injections as
measured by observing the incidence of lung adenomas in
Strain Amice (NCI, 1978; Maltoni, et al., 1980; Theiss, et
al., 1977). Negative results in the Strain A mouse system,
however, are not considered to be sufficient evidence that a
compound is not a carcinogen.
1,2-DCE at doses of 47 or 95 mg/kg/day was administered
in corn oil by gavage five times weekly to 50 Osborne-Mendel
rats of each sex per group for 78 weeks followed by an
observation period of 23 weeks for males and 15 weeks for
females. A statistically significant increase in the incidence
of squamous cell carcinoma of the forestomach and hemangiosarcoma
of the circulatory system was observed in male but not female
-------
rats (P < 0.04). The female rats had a significantly increased
incidence of adenocarcinoma of the mammary glands (P < 0.002)
(NCI, 1978).
In a complementary gavage study, 50 hybrid B6C3F1 mice
of each sex per group were dosed five times weekly for 78
weeks with 195 or 97 mg/kg/day in corn oil for male mice and
299 or 149 mg/kg/day in corn oil for female mice. The mice
were observed for 12 to 13 weeks following cessation of the
treatment. A statistically significant increase in the
incidence of mammary adenocarcinoma (P < 0.04) and endometrial
stromal polyps or sarcomas (P < 0.016) was seen in the female
mice; the incidence of alveolar/bronchiolar adenomas was
increased in both sexes (P < 0.028) (NCI, 1978).
In an inhalation study, Swiss mice or Sprague-Dawley rats
of each sex were exposed to 607.5, 202.5, 40.5, or 20.3 mg/m3
of 1,2-DCE for 7 hours daily, 5 days per week for 78 weeks
(Maltoni, et al., 1980). At the end of exposure period, the
animals were allowed to live out their natural lives. In no
case did the incidence of a particular type of tumor appear
to be dose-related. In this interim report, the authors
concluded that 1,2-DCE was not carcinogenic under the conditions
of their experiment.
Several explanations have been proposed to reconcile the
differences in the results of the gavage and inhalation
studies. These are presented in some detail in Chapter V.
-------
In spite of the purported inadequacies of the bioassay,
NCI did conclude that under the conditions of the study, 1,2-
dichloroethane was carcinogenic to Osborne-Mendel rats and to
B6C3F1 mice (NCI, 1978). The National Academy of Sciences Safe
Drinking Water Committee, in its updated assessment of the
toxicity of 1,2-dichloroethane, recommended that additional
long-term oral ingestion studies employing several species
of animals be conducted to determine if 1,2-DCE is a carcinogen,
and, if so, which organs are involved in different species,
the nature of uptake, metabolism and accumulation of DCE and
its metabolites, and minimum times and doses of DCE required
to induce tumors (NAS, 1980).
On the basis of the results of the NCI bioassay, the
International Agency for Research on Cancer (IARC) concluded
that there was sufficient evidence for 1,2-dichloroethane's
carcinogenicity in test animals. For compounds classified
as having sufficient evidence of carcinogenicity in animals,
but lacking adequate data in humans (which would be the case
for 1,2-dichloroethane), IARC states that "it is reasonable,
for practical purposes, to regard such chemicals as if they
presented a carcinogenic risk to humans" (IARC, 1979).
1,2-Dichloroethane was shown to be carcinogenic by the
oral route, the same route by which individuals would be
exposed to 1,2-dichloroethane when it is present in their
drinking water. Therefore, one must determine whether or not
a carcinogenic risk exists and, if so, estimate the magnitude
of that risk to individuals drinking water which contains
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VIII-12
measurable levels of this substance.
1,2-DCE has been studied in a variety of short-term
test systems which evaluate the mutagenic potential of the
compound and/or its potential for interaction with DNA.
The results of these studies are summarized in Table V-21.
Positive results in certain of these test systems are considered
to be predictive of carcinogenic potential.
When considering the body of data as a whole, it becomes
evident that 1,2-dichloroethane possesses the potential to
exert its carcinogenicity via genotoxic mechanism(s).
Quantification of Carcinogenic Effects
Using methodology described in detail elsewhere, the
EPA's Carcinogen Assessment Group (CAG) has calculated estimated
incremental excess cancer risks associated with exposure to
1,2-dichloroethane in ambient water, extrapolating from
data obtained in the NTP Bioassay in male rats with this
compound (increased incidence of hemangiosarcomas) ( U.S.
EPA, 1980; NCI, 1978). CAG employed a linear, non-threshold
multistage model to estimate the upper bound 95% confidence
limit of the excess cancer rate that would occur at a specific
exposure level for a 70 kg adult, ingesting 2 liters of
water and 6.5 g of fish and seafood/day ("fish factor"),
every day over a 70-year lifespan.
The National Academy of Sciences (NAS, 1980) and
EPA's CAG (Anderson, 1983) have estimated upper 95%
confidence limit excess cancer risk rates associated with
consumption of 1,2-dichloroethane via drinking water alone.
-------
VIII-13
Each group used the linearized, non-threshold multistage
model. HAS derived its estimates using data from the NCI
bioassay showing an increased incidence of squamous cell
carcinomas of the forestomach in male rats, mammary tumors
in female rats and mice, endometrial tumors in female mice
and lung adenomas in mice of both sexes. CAG generated its
estimates based upon 1) mammary adenocarcinomas in female
mice, 2) mammary adenocarcinomas in female rats, 3) squamous
cell carcinomas in the forestomach of male rats, and 4) a
combined risk incorporating the above three as well as the
heraangiosarcomas in male rats. It is this combined risk
( 4)) that the ODW has chosen to represent CAG's extrapolation
for drinking water.
In all three instances, a range of 1,2-dichloroethane
concentrations were computed that would be estimated to
increase the risk by one excess cancer per million (10^),
per one hundred thousand (105) and per ten thousand (104) in the
population over a 70-year lifetime assuming daily consumption
of 2 liters of water by a 70 kg adult at the stated exposure
level. The ranges of concentrations and associated estimated
risks are summarized in Table VIII-2.
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VIII-14
Table VIII-2
Drinking Water Concentrations and Estimated Excess Cancer Risks
Range of Concentrations (ug/l)a
Excess Lifetime
Cancer Risk
10-4
10-5
10-6
0
CAGb
94
9.4
0.94
0.00
CAGC
59.9
6.0
0.6
0.00
NASd
70
7
0.7
0.00
a Assumes the consumption of two liters of water per day by 70
kg adult over a lifetime; number represents 95% upper bound
confidence limit
b (U.S. EPA, 1980)
c (Anderson, 1983)
d (NAS, 1980)
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IX-1
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