cnn7 Advisory Opinion for Carbon Tetrachloride .. *^ * ^l***^. • J
uu/ Office of Drinking Water
U.S. Environmental Protection Agency
Washington, D.C. 20460
AN OFFICE OF DRINKING WATER HEALTH EFFECTS ADVISORY
The Office of Drinking Water provides advice on health
effects upon request, concerning unregulated contaminants
found in drinking water supplies. This information suggests
the level of a contaminant in drinking water at which adverse
health effects would not be anticipated. A margin of safety
is factored in so as to protect the most sensitive members of
the general population. The advisories are called Suggested
No Adverse Response Levels (SNARLs). SNARLs have been calcu-
lated by EPA and by the National Academy of Sciences (NAS) for
selected contaminants in drinking water. An EPA-SNARL and a
NAS-SNARL may well differ due to the possible selection of
different experimental studies for use as the basis for the
calculations. Furthermore, NAS-SNARLs are calculated for
adults while the EPA-SNARLs are established for a 10 kg body
weight child. Normally EPA-SNARLs are provided for one-day,
ten-day and longer-term exposure periods where available data
exist. A SNARL does not condone the presence of a contaminant
in drinking water, but rather provides useful information, to
assist in the setting of control priorities in cases where
contamination occurs. EPA-SNARLs are provided on a case-by-
case basis in emergency situations such as spills and acci-
dents .
In the absence of a formal drinking water standard for
carbon tetrachloride the Office of Drinking Water has developed
EPA-SNARLs following the state-of-the-art concepts in toxicol-
ogy for non-carcinogenic risk for short and longer term
exposures. For carcinogenic risk, a range of risk estimates
is provided for life-time exposures discussed by the NAS
(1977) and the EPA Cancer Assessment Group (EPA, 1980b).
The EPA-SNARL calculations for short-term and chronic exposures
ignore the possible carcinogenic risk that may result for
those exposures. In addition, EPA-SNARLs usually do not
consider the health risk resulting from possible synergistic
effects of other chemicals in drinking water, food, and air.
EPA-SNARLs are not legally enforceable standards; they are
not issued as an official regulation, and they may or may
not lead ultimately to the issuance of national standards or
Maximum Contaminant Levels (MCLs). The latter must take
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into account occurrence, relative source contribution factors,
treatment technology, monitoring capability, and costs, in
addition to health effects. It is quite conceivable that
the concentration set for EPA-SNARL purposes might differ
from an eventual MCL. The EPA-SNARLs may also change as
additional information becomes available. In short, EPA-
SNARLs are offered as advice to assist those to protect
public health when dealing with specific contamination
situations.
General"Information:
Carbon tetrachloride, also known as tetrachloromethane
(CC1 ) is a colorless liquid at room temperature with a
characteristic, non-irritant odor. Its boiling point is
76.7°C and its specific gravity is 1.59 (20/4°C) (Kirk-
Othmer, 1979). Carbon tetrachloride is partly soluble in
water (0.8 g/liter at 25°C) (Kirk-Othmer, 1979), but more
soluble in other media, as determined by partition coefficient
studies: oil>blood>air>water (Morgan et al., 1972, Sato and
Nakajima, 1979). A concentration of 1 part per million in
air is equivalent to 6.3 mg/m . It is noteworthy that the
American Conference of Government Industrial Hygienists
(ACGIH), the National Institute for Occupational Safety and
Health (NIOSH), and the Occupational Safety and Health
Administration (OSHA) recommended threshold limit values
(TLV) for carboy tetrachloride as follows: 64.1 mg/m (10
ppm), 12.8 mg/m (2 ppm), and 64.1 mg/m (10 ppm), respectively.
The principal use of carbon tetrachloride (95%) is as an
intermediate in the production of chlorofluoromethanes,
which are used as propellants and refrigerants. Carbon
tetrachloride is also used in grain fumigation and as an
industrial solvent (Kirk-Othmer, 1979).
Sources•of•Exposure:
Carbon tetrachloride concentrations in the atmosphere are
relatively constant in most regions of the world (0.0008-0.0009
rog/m ) (EPA, 1980a) . However, extremely high concentrations
of carbon tetrachloride have been detected in urban atmospheres.
The highest reported concentration (0.113 mg/m ) was found in
a sample from Bayonne, New Jersey (Lillian, et al., 1975).
Carbon tetrachloride concentrations in U.S. drinking water
have generally ranged up to 6.4 ug/liter (EPA, 1980a). In
rare instances, industrial accidents have resulted in dramatic
increases in the concentration of carbon tetrachloride in
drinking water. Following an alleged spill of 70 tons of car-
bon tetrachloride into the Kanawha River, levels of carbon
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tetrachloride in drinking water reached 100 ug/liter (Landen,
1979). The inadvertant use of chlorine contaminated with car-
bon tetrachloride for the chlorination of drinking water in
Philadelphia and other Northeast locations also resulted in
high concentrations of carbon tetrachloride in drinking water
(up to 46 ug/liter) (EPA, 1977).
Pharmacokinetics:
In order to ascertain the absorption, distribution, and
elimination of radioactive carbon tetrachloride in animals,
McCollister, et al. (1951) designed experiments in which
rhesus monkeys inhaled a vapor concentration of 0.290 mg/1
(46 ppm) C-labeled carbon tetrachloride for periods of
139, 344, and 300 minutes. The authors made the following
observations: (a) of the total amount of carbon tetrachloride
inhaled, an average of 30% was absorbed; (b) the highest
concentration of radioactive material deposited in tissues
was found in the fat which had a distribution ratio of 7.94
(blood = 1); (c) c was found in the blood carbonate,
exhaled carbon dioxide and in urinary urea and carbonate;
and (d) the equivalent of at least 51% of the carbon tetra-
chloride absorbed during an inhalation period was estimated
to have been eliminated in the expired air within 75 days
following the end of the exposure. The remainder evidently
was excreted to a large extent in the urine and feces.
Among reported metabolic reactions in liver are conversion
to carbon dioxide (Rubinstein and Kanics, 1964), chloroform
(Butler, 1961), hexachloroethane (Fowler, 1969), carbonyl
chloride (phosgene) (Shah et al., 1979), and binding to
lipids and proteins (Glende, et al., 1976, Uehleke and
Werner, 1975).
Health-Effects;
Exposure to carbon tetrachloride is reported to produce
fatty liver, with centrilobular necrosis developing if expo-
sure is continued. In humans, this condition may be followed
by kidney failure. The histologic changes may be accompanied
by biochemical abnormalities including alterations in the
activity of the microsomal enzyme system, an increase in
triglycerides in the liver, and a decrease in protein synthesis
Short-Term•Exposure;
Lamson et al. (1928) studied the effects of carbon tetrachlor-
ide in patients receiving carbon tetrachloride and magnesium
sulfate orally as a treatment for hookworms. The authors
report the treatment of thousands of patients with a single
dose of 2.5-15 ml of carbon tetrachloride without any adverse
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effects. One man was reported to have safely ingested 40 ml
of carbon tetrachloride. However, an "extremely small" popu-
lation of adults died after receiving 1.5 ml of carbon tetra-
chloride; doses of 0.18-0.92 ml were reported to be fatal to
children. Alcohol consumption enhanced carbon tetrachloride-
induced toxicity in adults.
Stewart, et al. (1961) reported the toxic effects of experi-
mental exposure of human volunteers to carbon tetrachloride
vapor. Health males, 30-59 years of age, were exposed to
concentrations of 63, 69, and 309 mg/m of carbon tetrachloride
(99% pure) in an exposure chamber for 180 minutes at the two
lower doses or 70 minutes at the highest dose. All subjects
had undergone periodic physical examinations; some participated
in more than one of the exposure experiments, which were con-
ducted 4 weeks apart. Six subjects exposed to the highest
concentration experienced no nausea or lightheadedness, and
carbon tetrachloride was not detected in blood and urine dur-
ing or after exposure (the detection limit was 5 ppm). One
of these six subjects had an increased level of urinary uro-
bilinogen 7 days after exposure. In addition, two of four sub-
jects exposed to the highest concentration and monitored for
serum iron showed a decrease within 48 hours after exposure.
Carbon tetrachloride was also not detected in the blood or
urine of volunteers exposed at 63 or 69 mg/m , and the volun-
teers reported no physiologic effects. No changes in blood
pressure, serum transaminase levels, or urinary urobilinogen
levels were noted.
Effects of acute exposure to low levels of carbon tetrachloride
in rats were reported by Korsrud et al. (1972). Male Wistar
rats (260-400 g; 8-10 animals per treatment group) were admin-
istered single oral doses of carbon tetrachloride (0 to 4000
mg/kg bw) in corn oil (5 ml/kg bw). The rats were fasted for
6 hours before dosing and for 18 hours afterward, and then
killed. Assays included liver weight and fat content, serum
urea and arginine levels, and levels of nine serum enzymes,
produced mainly in the liver. At 20 mg/kg bw there was histo-
pathologic evidence of toxic effects on the liver. At 40 mg/kg
bw, liver fat, liver weight, serum urea, serum arginine, and
levels of six of the nine liver enzymes were increased. At
higher doses the remaining three enzyme levels were also ele-
vated. The histologic changes seen at the minimum effect
level, 20 mg/kg bw, included a loss of basophilic stippling,
a few swollen cells, and minimal cytoplasmic vacuolation.
Murphy and Malley (1969) investigated the effects of single
oral doses of carbon tetrachloride on the corticosterone-
inducible liver enzymes, tyrosine-«C-ketoglutarate transamin-
ase, alkaline phosphatase, and tryptophan pyrrolase in rats.
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Specifically, groups of 4-7 male rats were administered by
gavage 400, 800, 1600, 2400, or 3200 mg/kg undiluted carbon
tetrachloride. Single doses of 400 mg/kg or greater of carbon
tetrachloride increased liver tyrosine-o<-ketoglutarate trans-
aminase and alkaline phosphatase, but not tryptophan pyrrolase
activity within 5 hours.
Carcinogenicity
Oral administration of carbon tetrachloride has been shown to
be carcinogenic in rats, mice, and hamsters. In all three
species, liver neoplasms developed although hamsters appeared
to be the most sensitive.
Weekly administration of carbon tetrachloride (20 mg/kg bw)
by gavage to 10 male and 10 female Syrian hamsters for 7 weeks,
followed by 10 mg/kg bw weekly for an additional 23 weeks,
produced liver cell carcinomas in 5 male and 5 female hamsters
that survived 13-25 weeks after cessation of treatment. No
data on control animals were provided (Delia Porta, et al.,
1961).
Two groups of 50 Osborne-Mendel rats of each sex were adminis-
tered carbon tetrachloride in corn oil by gavage five times
weekly for 78 weeks. Two doses were given to each sex: 47 or
94 mg/kg for males and 80 or 160 mg/kg for females. Both
sexes exhibited statistically significant (P < .05) numbers
of hepatocellular carcinomas at the low and high doses (males,
2/49, 2/50; females, 4/50, 2/49, respectively) as compared to
the pooled controls (males, 1/99; females, 0/98) (NCI, 1976).
In another study, 50 hybird B6C3F1 mice of each sex were
dosed by gavage five times weekly for 78 weeks with 1,250 or
2,500 mg/kg bw of carbon tetrachloride in corn oil. After
90-92 weeks, hepatocellular carcinomas developed in all males
(49) and females (40) in the low-dose group and in 47 of 48
males and 43 of 45 females in the high-dose group. The inci-
dences in the control group were 3 of 18 males and 1 of 18
females. In this experiment, carbon tetrachloride was used
as a positive control (NCI, 1976).
Mutagenicity:
S;'cerevisiae, strain D7, incubated with three concentrations
of carbon tetrachloride (21, 41, or 54 mM) showed significantly
increased frequencies of mitotic gene conversion and recombi-
nation at the highest dose compared to the control (Callen
et al. 1980). Incubation of S; typhimurium strain G46 and
E;"coli strain K12 with carbon tetrachloride in the presence
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of a metabolic activation system containing mouse liver micro-
somes produced no mutagenic effects. No data on dose levels,
cytotoxicity, or controls were reported, however (Kraemer et
al. 1974). Carbon tetrachloride also proved negative as a
mutagen in S;-typhimurium strain TA 1535 (McCann et al. 1975)
at a maximum dose of 10 nM, at which less than 70 revertants
per plate were produced. The compound was tested with a meta-
bolic activation system, but additional experimental details
were not reported.
Teratogenictty/Reproductive"Effects;
Exposure of pregnant Sprague-Dawley rats to 1,890 or 6,300
mg/m of 99.9% carbon tetrachloride for 7 hours/day on days
6-15 of gestation were reported to produce both fetotoxic
and teratogenic effects (Schwetz et al. 1974). At the low
and high concentrations, 22 and 23 litters, respectively,
were examined. Fetal body weight and crown-rump length were
significantly reduced from control values at both concentrations.
At the higher dose the incidence of sternebral abnormalities,
including bipartite and delayed ossification, was significantly
increased over those in controls. Total skeletal abnormalities
were significantly increased in the 1,890 mg/m group, but
not at the higher dose (Schwetz et al. 1974). In contrast,
another study reported no significant teratogenic effects
following exposure of 25 pregnant Sprague-Dawley rats to
pure carbon tetrachloride at 1,575 mg/m , 8 hours per day
for 5 consecutive days between 10 and 15 of gestation (Oilman,
1971). No convincing explanation is available to explain
this discrepancy at this juncture.
When three groups of rats were given carbon tetrachloride
(2,400 mg/kg bw) intraperitoneally for 10, 15, or 20 days,
testicular and seminal vesicle weights were decreased in all
rats. The number of animals per group was not specified. In
addition, histologic examination of the testes revealed no
damage in animals treated for 10 days; an increase in lumen
size and a decrease in spermatogenic cells at 15 days; and
atrophy of the tubules and an increase in lumen size at 20
days (Kalla and Bansal, 1975).
EPA-SNARL•Developmentt
The available data suggest that the EPA-SNARL for carbon tetra-
chloride should be based on the potential of this compound to
cause liver damage. This decision is justified by the follow-
ing factors:
1. The liver appears to be the most sensitive indicator of
carbon tetrachloride toxicity.
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2. Carbon tetrachloride-induced hepatic liver damage has
been reported after a single low-level exposure by inges-
tion.
One-Day•EPA-SNARL t
The lowest acute oral dose of carbon tetrachloride reported
to cause an adverse effect was 20 rag/kg bw in rats (Korsrud
et al. 1972). This dose produced minimal damage to the liver
as indicated by histologic examination (i.e., a loss of
basophilic strippling, a few swollen cells, and minimal cyto-
plasmic vacuolation). Several higher and lower doses (0 to
4000 mg/kg) were also tested in that study, so a dose-response
relationship could be developed. For these reasons, 20 mg/kg
bw carbon tetrachloride will be used in the development of
the EPA-SNARL. Because the data are for animals rather than
humans and only one species (rat) was considered, a safety
factor of 1000 will be used.
In calculating the EPA-SNARL, children are assumed to be the
exposure subjects, since research in animals has indicated
that young animals may be more sensitive than adults to the
toxic effects of carbon tetrachloride (Cagen and Klassen,
1979). Furthermore, due to the lipophilic nature of this
chemical, it is assumed that 100% of carbon tetrachloride is
absorbed through the gastrointestinal tract.
Accepting 20 mg/kg as the minimal toxic effect dose, calcula-
tions of an EPA-SNARL for a 10 kg child, consuming one liter
of water, are given below:
Calculations:
2e-mg/kg-x-10e%-x-10-kg _ Q 2 ma/liter
1 liter/day x 1000 ~ °'2 m9/1:Lter
liter/day
20 mg/kg = minimal toxic effect dose
100% = assumed absorption rate
10 kg = weight of child
1 liter/day — assumed water consumption by a 10 kg child
1000 = safety factor
Ten-Day ~SNARL;
In the absence of long-term (10-day) ingestion studies, the
10-day SNARL is thus calculated by dividing the 1-day SNARL
of 0.2 rag/liter by 10:
O.-2-mg/liter = ^ mg/liter
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It should be noted that NAS used a similar approach for the
calculation of their 7-day NAS-SNARLs. However, additional
pharmacokinetics data are needed to calculate scientifically
valid 10-day SNARLs.
The National Academy of Sciences has calculated SNARLs for
carbon tetrachloride of 14 mg/liter for 1-day exposure and 2
mg/liter for 7-day exposure (NAS, 1980), in contrast to the
EPA-SNARLs developed in this report of 0.2 mg liter for 1-
day exposure and 0.02 mg/liter for a 10-day exposure. The
reasons for this discrepency are threefold: different data
bases were used, the NAS-SNARL was calculated for a 70 kg
adult rather than a 10 kg child, and the adult was assumed
to consume 2 liters of water per day as compared to 1 liter
per day for a child. The NAS-SNARLs are based on the data
of Murphy and Malley (1969), who reported liver effects in
rats 5 hours after a single oral dose of carbon tetrachloride
of 400 mg/kg bw. The study used in the EPA-SNARL reported
toxic liver effects at the lower dose of 20 mg/kg bw (Korsrud
et al. 1972). This difference, coupled with EPA's choice
of a child rather than an adult as representative of the
population most sensitive to exposure to carbon tetrachloride
in water, accounts for the difference in SNARL values.
Long-Term•EPA-SNARL:
Insufficient data on chronic exposure to carbon tetrachloride
are available to develop a long-term EPA-SNARL for this com-
pound .
Quantification-of"Carcinogenic"Risk;
Because of positive results in animal carcinogenicity studies,
carbon tetrachloride can be considered a suspect human car-
cinogen. Data from these animal studies have been used by
NAS and the EPA Carcinogen Assessment Group (CAG) to calculate
the number of additional cancer cases that may occur when car-
bon tetrachloride is consumed in drinking water over a 70-year
lifetime. As shown in Table I, using the NAS and CAG data,
estimates of additional carcinogenic risk following the expo-
sure of humans to carbon tetrachloride may be derived.
The criteria for the CAG and NAS risk calculations differ in
several respects: (1) NAS used the multistage model, while
CAG used an "improved" multistage model, (2) NAS used the data
set from the National Cancer Institute (NCI) study in male
rats while CAG used the data set from NCI's study in male mice.
The levels estimated by CAG thus resulted in a carbon tetra-
chloride concentration 1/llth that was estimated by NAS for
identical cancer risks (EPA, 1980b).
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Table I. Estimates of Additional Carcinogenic Risk
Following Exposure of Humans to Carbon
Tetrachloride in Drinking Water*
Carbon Tetrachloride Concentrations
(ug/liter)
CAG NAS
(95% (95%
Excess cancer confidence confidence
risk/lifetime limit) limit)
10~4 40 450
10~5 4 45
10~6 0.4 4.5
* An average daily drinking water consumption of 2 liters per
day was assumed.
EPA's Ambient Water Quality Criteria for carbon tetrachloride
(EPA, 1980a^-based on increased lifetime cancer risk estimates
of 10 , 10 , and 10 , are as follows: 4.0, 0.40, and 0.04
ug/liter, respectively. It is noteworthy that these concentra-
tion levels were derived by assuming a lifetime consumption
of both drinking water (2 liters/day) and aquatic life (6.5
g fish and shellfish/day) grown in waters containing the
corresponding carbon tetrachloride concentrations. Thus,
these criteria do not apply to drinking water per se.
Analysis;
Carbon tetrachloride (and 47 other halogenated organics) in
water can be analyzed by a purge and trap method (Method
502.1) described by the EPA Environmental Monitoring and
Support Laboratory (EPA, 1980c). This method can be used to
measure purgeable organics at low concentrations. Using a
sample size of 5 ml, purgeable organic compounds are trapped
on a Tenax GC-containing trap at 22°C using a purge gas rate
of 40 ml/min for 11 minutes. The trapped material is then
heated rapidly to 180°C and backflushed with helium at a
flow rate of 20-60 ml/min for 4 minutes into the gas chromato-
graphic analytical column. The programmable gas chromatograph
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used is capable of operating at 40° 4; 1° C. The primary
analytical column is stainless steel packed with 1% SP-1000
on Carbopack B (60/80) mesh (8 ft. x 0.1 in. I.D.) and is
run at a flow rate of 40 ml/min. The temperature program
sequence begins at 45°C for 3 minutes, increases 8°C/min to
220°C, and is then held constant for 15 minutes or until all
compounds have eluted. A halogen-specific detector with a
sensitivity to 0.10 mg/liter and a relative standard deviation
of 10% must be used. The optional use of GC/MS techniques
of comparable accuracy and precision is acceptable.
Treatment;
The information available on the removal of carbon tetrachlor-
ide from drinking water is limited. However, based upon
data obtained from industrial waste treatment, conventional
treatment processes are not very effective in the removal of
this compound. An isotherm study of carbon tetrachloride on
Filtration 400 activated carbon (GAG) showed that at an _
equilibrium concentration range of 3 x 10~ to 2.6_x 10
mol/1 a maximum surface concentration of 2.6 x 10 mol/g
was obtained (NAS, 1979). Studies have also been conducted
to evaluate aeration and adsorption processes in the removal
of this compound. It was found that powdered activated
carbon (PAC) at 2 to 4 mg/1 is not effective in treating
contaminated river water containing 16.3 mg/1 of carbon
tetrachloride. After PAC, coagulation, settling and filtration,
the finished water still contains 16.0 mg/1 (EPA, 1980d).
Aeration by diffused air aerator in a laboratory study was
found to be more successful. At 4:1 air-to-water ratio, a
91 percent removal efficiency of the carbon tetrachloride
was achieved (EPA, 1980d). Adsorption by GAG in a pilot
scale study revealed that carbon tetrachloride at an average
concentration of 12 mg/1 (Cincinnati tap water) was reduced
to less than 0.1 ug/1 for 3 weeks with a 5-min. empty bed
contact time (EBCT) and between 14 and 16 weeks with a 10-
min. EBCT.
Conclusions"and•Recommendations;
From data on the lowest acute dose of carbon tetrachloride
producing health effects in rats (20 mg/kg bw), a 1-day EPA-
SNARL of 0.2 mg/liter and a 10-day EPA-SNARL of 0.02 mg/liter
have been calculated. Insufficient data on chronic exposure
to carbon tetrachloride are available to calculate a long-
term SNARL for this compound. Carcinogenic effects of
carbon tetrachloride were not considered in the preparation
of these SNARLs. Possible risks associated with carcinogenicity
as derived from the data calculated by the National Academy
of Sciences and EPA Carcinogen Assessment Group are discussed.
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