United States
Environmental Protection
Agency
Office of Health and
Environmental Assessment
Washington DC 20460
Research and Development
EPA/600/S6-87/004 Sept. 1987
&EPA Project Summary
Carcinogenicity Assessment of
Chlordane and Heptachlor/
Heptachlor Epoxide
Finis L Cavender, Brion T. Cook, and Norbert P. Page
Evidence pertaining to the carcino-
genicity of chlordane and heptachlor/
heptachlor epoxide is reviewed and
evaluated. The final report covers
studies completed before 1985. Case
reports and epidemiologic studies of
pesticide applicators and pesticide
manufacturing workers are reviewed,
but because of methodologic limita-
tions, these studies establish neither a
positive nor a negative association
between cancer and chlordane or
heptachlor/heptachlor epoxide expo-
sure. A number of independent studies
of laboratory animals, however, demon-
strates that chlordane and heptachlor/
heptachlor epoxide cause liver cancer
in mice and rats. Based on the ac-
cumulated evidence, chlordane and
heptachlor/heptachlor epoxide are
classified as probable human carcino-
gens. Group B2 using EPA's Guidelines
for Carcinogen Risk Assessment. The
carcinogenic potency of chlordane and
heptachlor/heptachlor epoxide is esti-
mated by fitting mathematical models
to the laboratory animal data. These
estimates indicate that chlordane and
heptachlor/heptachlor epoxide are
rather potent carcinogens, ranking in
the second quartile of potential car-
cinogens evaluated by EPA's Carcino-
gen Assessment Group. A separate
mutagenicity assessment of chlordane
and heptachlor/heptachlor epoxide is
attached as an appendix to the final
report. The report also includes an
extensive list of references pertinent to
the carcinogenicity of chlordane and
heptachlor/heptachlor epoxide.
This Project Summary was developed
by EPA's Office of Health and Environ-
mental Assessment, Washington, DC, to
announce key findings of the research
project that Is fully documented In a
separate report of the same title (see
Project Report ordering Information at
back).
Discussion
Qualitative Data
Human Studies
Case Reports
There were 11 case reports involving
CNS effects where the author looked at
the toxic effects of chlordane/heptachlor,
eight case studies involving blood
dyscrasias, and five case studies of
neuroblastomas in children with pre-/
postnatal exposure to chlordane or hep-
tachlor. The blood dyscrasias in children
included four cases of aplastic anemia
and one case each of refractory megalo-
blastic anemia, acute lymphoblastic
leukemia, acute stem-cell leukemia, and
acute myelomonocytic leukemia.
Epidemiologic Studies
Three epidemiologic studies of workers
exposed to chlordane and/or heptachlor
have been reported. One of these studies,
conducted in chlordane/heptachlor ap-
plicators, was considered inadequate in
sample size and duration of follow-up
since initial exposure. However, this study
showed increased mortality from bladder
cancer (SMR = 277, p < 0.05). A second
study showed an increased mortality from
lung cancer (SMR = 134), but the increase
was not statistically significant. The
mortality from cerebrovascular disease
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was statistically significant (SMR = 183,
p < 0.05). Of the 1,043 men involved in
the study, only one liver cancer was
reported. The third study involved 2,141
workers exposed to organochlorine pesti-
cides. One of the four plants involved in
pesticide manufacture produced chlor-
dane and one produced heptachlor. The
SMR for malignant neoplasms was 69 at
the chlordane plant and 91 at the
heptachlor plant. There was an excess
risk for cancer in various tissues; none
was statistically significant. The last two
studies were carried out in chlordane/
heptachlor manufacturing plants.
All of these studies have several limita-
tions. Neither the quantitative nor length
of exposure histories are available for
chlordane/heptachlor for the populations
studied. The workers were also exposed
to other pesticides and chemicals.
Adjustments for these other chemical
exposures and other confounding fac-
tors, like smoking and alcohol consump-
tion, were not considered in any of these
studies. All of the study populations were
small In the pesticide applicator study,
individual follow-up was not undertaken
and the data were missing on 103
percent of the decedents reported by the
Social Security Administration.
Because of these methodological
limitations and the limited data, it is
difficult to establish either a negative or
positive association between chlordane/
heptachlor and carcinogenicity. Hence,
these studies are considered inadequate
epidemiologic evidence.
Animal Studies
Chlordane
Mice. Four chlordane carcinogenesis
bioassays in mice have been reported.
The strains tested include C57B1/6N,
CD-1, B6C3F1, and ICR. In C57B1/6N
mice fed 25 or 50 ppm for 18 months,
hepatocellular carcinomas were observed
in 27 percent (16) of the survivors. This
mouse strain rarely develops spontaneous
liver lesions. For CD-1 mice fed 5, 25, or
50 ppm for 18 months, liver nodules/
hepatocellular carcinomas were observed
in the 25 and 50 ppm groups. In B6C3F1
mice fed approximately 30 and 60 ppm
for 80 weeks and then held for 10 weeks,
hepatocellular carcinomas were observed
in both males and females. For ICR mice
fed 1, 5, or 12.5 ppm for 24 months,
hepatocellular adenomas and heman-
giomas were significantly increased (p <
0.001) in males receiving 12.5 ppm and
nonneoplastic liver lesions were present
in males fed 5 ppm and in females fed 5
or 12.5 ppm.
Rats. Four chlordane carcinogenesis
bioassays in rats have been reported. The
strains tested include albino, Osborne-
Mendel, and Fischer 344. Three of these
studies were considered adequate, and
one was inadequate. In albino rats fed
10, 20, 40, 80, 160, 320, 640, or 1280
ppm for 400 days, there were no treat-
ment-related tumors. In Osborne-Mendel
rats fed 5, 10, 30, 150, or 300 ppm for 2
years, hepatic toxicity was noted at 150
and 300 ppm, but no liver tumors were
noted. In Osborne-Mendel rats fed 203.5
or 407 ppm (males) or 120.8 or 241.5
ppm (females), respectively, for 80 weeks
and held for an additional 29 weeks, no
liver tumors were noted, but thyroid
tumors were significantly increased. In
light of historical data for Osborne-Mendel
rats, the thyroid tumors were not con-
sidered to be treatment-related. In Fischer
344 rats fed 1, 5, or 25 ppm for 130
weeks, there was a statistically significant
increase in hepatocellular adenomas,
which was considered by the authors as
weak evidence for carcinogenicity in
males fed 25 ppm. Hepatocellular swelling
was significant in females fed 25 ppm.
The hepatocellular adenomas occurred
only in males surviving longer than 104
weeks.
Heptachlor/Heptachlor Epoxide
Mice. Three heptachlor/heptachlor
epoxide carcinogenesis bioassays in mice
have been reported. The strains studied
include C3H, B6C3F1, and CD-1 mice. In
C3H mice fed 10 ppm of both heptachlor
and heptachlor epoxide for 2 years, benign
liver tumors/hepatocellular carcinomas
were reported in both male and female
mice. Hepatocellular carcinomas in
treated groups were generally large and
frequently multiple tumors, especially in
the epoxide group in respect to the con-
trols. For B6C3F1 mice fed technical grade
(containing 22 percent chlordane) at
concentrations of 6.1 or 13.8 ppm (males)
or 9 or 18 ppm (females), respectively, for
80 weeks and held for an additional 10
weeks, hepatocellular carcinomas were
significantly (p < 0.001) increased in
both male and female mice. In CD-1 mice
fed a mixture of heptachlor epoxide/
heptachlor (75:25) at concentrations of 1,
5, or 10 ppm for 18 months, nodular
hyperplasia/hepatocellular carcinomas
were noted at 5 and 10 ppm in both male
and female mice.
Rats. Five heptachlor/heptachlor
epoxide carcinogenesis bioassays in rats
have been conducted. The strains of rats
studied include Wistar, Osborne-Mendel,
CD, and CFN. In Wistar rats given 5 doses
of 10 mg/kg bw of heptachlor and held
for 106 to 110 weeks, no treatment-
related tumors were observed. For
Osborne-Mendel rats fed technical grade
heptachlor at concentrations of 38.9 or
77.9 (males) or 25.7 or 51.3 (females)
ppm, respectively, for 80 weeks and held
for 30 weeks, no liver tumors were noted,
although neoplastic nodules were found
in both treated and control rats. In CD
rats fed a mixture of heptachlor/hep-
tachlor epoxide (75:25) at concentrations
of 5, 7.5, 10, or 12.5 ppm for 2 years, no
liver tumors were noted, although non-
neoplastic lesions were noted in the livers
of rats fed 7.5, 10, or 12.5 ppm. In one
study using CFN rats fed 1.5, 3, 5, 7, or
10 ppm of heptachlor for 110 weeks, the
incidence of liver tumors was not statis-
tically different in treated and control
animals. In a second study using CFN
rats fed 0.5, 2.5, 5, 7.5, or 10 ppm of
heptachlor epoxide for 108 weeks, treat-
ment-related liver carcinomas were noted
by several pathologists.
Supporting Evidence
Mutagenicity
The published literature on mutageni-
city tests of chlordane and heptachlor/
heptachlor epoxide is quite similar, with
most studies reporting results on both
chemicals. Generally, the results have
indicated that these chemicals are not
mutagenic in bacteria or in mammalian
cells in culture, and do not induce DNA
repair, as measured by unscheduled DNA
synthesis in rodent hepatocytes. While
dominant lethal tests in mice have been
negative for both chemicals, the absence
of direct cytogenetic tests in both germinal
and somatic cells precludes a conclusion
as to their potential for causing chro-
mosomal aberrations.
Structural Relationship
Three compounds, structurally related
to chlordane/heptachlor/heptachlor
epoxide, have induced malignant liver
tumors in animals. Aldrin, dieldrin, and
chlorendic acid have produced liver
tumors in mice and chlorendic acid has
also produced liver tumors in rats.
Quanf/faf/ve Analysis
In the absence of information on human
absorption, tissue distribution, metabo-
lism, and excretion, this assessment
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makes no adjustment for potential dif-
ferences between animals and humans.
Chlordane
Five data sets involve chlordane: male
and female CD-1 mice, male and female
B6C3F1 mice, and male F344 rats. The
most sensitive sex and strain tested is
male CD-1 mice. From these, the potency
is estimated at 4.7 per mg/kg/day.
The most sensitive species tested is
mice. There are four potency estimates,
ranging from 4.7 down to 0.25 per
mg/kg/day, with a geometric mean of
1.3 per mg/kg/day. This geometric mean
from mice is consistent with potency
estimate from rats of 1.1 per mg/kg/day.
Because humans may be as sensitive as
the most sensitive animal species, the
potency for the general population is
estimated at 1.3 per mg/kg/day.
These estimates are plausible upper
bounds for the increased cancer risk from
chlordane, meaning that the true risk is
not likely to exceed these estimates and
may be lower. These estimates supersede
the potency of 1.61 per mg/kg/day pre-
viously calculated by the EPA.
The molecular potency index, which is
the potency expressed in terms of
molecular weight, has been used to rank
suspect carcinogens according to potency.
The index is computed by multiplying the
general-population potency by the mole-
cular weight. The molecular potency index
for chlordane is 5.2 x 102 per mmol/kg/
day. This places chlordane in the upper
middle quartile of suspect carcinogens
ranked by the Carcinogen Assessment
Group (CAG)
Heptachlor
Four data sets involve heptachlor: male
and female C3H mice, and male and.
female B6C3F1 mice. The most sensitive
sex and strain tested is female C3H mice.
From these, the potency is estimated at
14.9 per mg/kg/day.
The most sensitive species tested is
mice. There are four potency estimates,
ranging from 14.9 down to 0.83 per
mg/kg/day, with a geometric mean of
4.5 per mg/kg/day. Because humans
may be as sensitive as the most sensitive
animal species, the potency for the gen-
eral population is estimated at 4.5 per
mg/kg/day.
These estimates are plausible upper
bounds for the increased cancer risk from
heptachlor, meaning that the true risk is
not likely to exceed these estimates and
may be lower. These estimates supersede
the potency of 3.37 per mg/kg/day pre-
viously calculated by EPA.
The molecular potency index for hep-
tachlor is 1.7 x 103 per mmol/kg/day.
This places heptachlor in the upper
middle quartile of suspect carcinogens
ranked by the CAG.
Heptachlor Epoxide
Five data sets involve heptachlor
epoxide: male and female C3H mice, male
and female CD-1 mice, and female CFN
rats. The most sensitive sex and strain
tested is female C3H mice. From these,
the potency is estimated at 36.2 per
mg/kg/day.
The most sensitive species tested is
mice. There are four potency estimates,
ranging from 36.2 down to 1.0 per
mg/kg/day, with a geometric mean of
9.1 per mg/kg/day. This geometric mean
from mice is consistent with the potency
estimate from rats of 5.8 per mg/kg/day.
Because humans may be as sensitive as
the most sensitive animal species, the
potency for the general population is esti-
mated at 9.1 per mg/kg/day.
These estimates are plausible upper
bounds for the increased cancer risk from
heptachlor epoxide, meaning that the true
risk is not likely to exceed these estimates
and may be lower. These estimates
supersede the potency of 57.86 per
mg/kg/day previously calculated by the
EPA.
The molecular potency index for hep-
tachlor epoxide is 3.5 x 103 per mmol/
kg/day. This places heptachlor epoxide
in the most potent quartile of suspect
carcinogens ranked by the CAG.
Conclusions
Based on the accumulated evidence,
chlordane is a probable human car-
cinogen, classified in Group B2 under the
EPA's Guidelines for Carcinogen Risk
Assessment. Animal studies provide suf-
ficient evidence for carcinogenicity:
chlordane increased the incidence of liver
carcinomas in C57B1/6N, CD-1, and
B6C3F1 mice; liver adenomas and
hemangiomas in ICR mice; and liver
adenomas in Fischer 344 rats. Epidemio-
logic studies provide inadequate evidence
due to methodology and data limitations.
According to the criteria in the guide-
lines, the above evidence puts chlordane
in Group B2. However, the guidelines
allow for the possibility of downgrading
the classification from Group B2 to Group
C when the only tumor response is that
of mouse liver tumors in strains with
high background rates, or when war-
ranted by a number of other factors. In
the case of chlordane these conditions do
not apply, since chlordane caused tumors
in C57B1 /6N mice — which do not have
a high background rate — and caused
tumors in rats as well. Other pertinent
evidence includes highly significant tumor
responses, up to 77 percent increased
incidence over controls, increased in-
cidence in both males and females,
increased incidence at medium and high
doses, a dose-related increase in the
proportion of malignant tumors, and in-
duction of tumors by structurally related
chemicals. In light of these factors, down-
grading is clearly not warranted, and
chlordane remains in Group B2.
For chlordane, the carcinogenic poten-
cy, averaging estimates from the most
sensitive species tested, is 1.3 per
mg/kg/day. The potency using the most
sensitive sex and strain is 4.7 per
mg/kg/day. These are plausible upper
bounds for the increased cancer risk from
chlordane, meaning that the true risk is
not likely to exceed these estimates and
may be lower. The molecular potency
index for chlordane is 5.2 x 102 per
mmol/kg/day. This places chlordane in
the second (upper middle) quartile of
suspect carcinogens ranked by the Car-
cinogen Assessment Group (CAG).
Heptachlor/heptachlor epoxide is a
probable human carcinogen, classified in
Group B2 under the EPA's Guidelines for
Carcinogen Risk Assessment. Animal
studies provide sufficient evidence for
carcinogenicity: heptachlor/heptachlor
epoxide increased the incidence of liver
carcinomas in C3H, CD-1, and B6C3F1
mice and in CFN rats. Epidemiologic
studies provide inadequate evidence due
to methodology and data limitations.
The guidelines consider this evidence
sufficient for Group B2, but they allow
downgrading from Group B2 to Group C
when the only tumor response is that of
mouse liver tumors in strains with high
background rates, or when warranted by
a number of other factors. The evidence,
however, shows highly significant tumor
responses, increased incidence in both
males and females, increased incidence
at medium and high doses, and induction
of tumors by structurally related chemi-
cals. In light of these factors, downgrading
is clearly not warranted, and heptachlor/
heptachlor epoxide remains in Group B2.
For heptachlor, the carcinogenic po-
tency, averaging estimates from the most
sensitive species tested, is 4.5 per mg/
kg/day. The potency using the most
sensitive sex and strain is 14.9 per
mg/kg/day. These are plausible upper
bounds for the increased cancer risk from
heptachlor, meaning that the true risk is
not likely to exceed these estimates and
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may be lower. The molecular potency
index for heptachlor is 1.7 x 103 per
mmol/kg/day. This places heptachlor in
the second quartile of suspect carcino-
gens ranked by the CAG.
For heptachlor epoxide, the carcino-
genic potency, averaging estimates from
the most sensitive species tested, is 9.1
per mg/kg/day. The potency using the
most sensitive sex and strain is 36.2 per
mg/kg/day. These are plausible upper
bounds for the increased cancer risk from
heptachlor epoxide, meaning that the true
risk is not likely to exceed these estimates
and may be lower. The molecular potency
index for heptachlor epoxide is 3.5 x 103
per mmol/kg/day. This places heptachlor
epoxide in the most potent quartile of
suspect carcinogens ranked by the CAG.
Finis L. Cavender, Bnon T. Cook, and Norbert P. Page are with Dynamac
Corporation. Rockville, MD 20852.
Dharm V. Singh is the EPA Project Officer (see below).
The complete report entitled "Carcinogenicity Assessment of Chlordane and
Heptachlor/Heptachlor Epoxide." (Order No. PB 87-208 757/AS; Cost:
$24.95, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Office of Health and Environmental Assessment
U.S. Environmental Protection Agency
Washington. DC 20460
U.S. OFFICIALS
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
Penalty for Private Use $300
EPA/600/S6-87/004
' 0000329 PS
A6ENCT
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