CHLORDANE
EXPLANATION
Chlordane was evaluated for acceptable daily intake by the Joint
Meeting in 1963, and reviewed in 1970, 1977, and 1982 (Annex 1,
FAO/WHO, 1964, 1965a, 1968a, 1971a, 1978a, and 1983a). Toxicological
monographs were prepared in 1963, 1965, and 1967 (Annex 1, FAO/WHO,
1971b, 1978b, and 1983b). The 1982 Joint Meeting required submission
of a study of at least 90 days' duration in rats, using oxychlordane,
and the results of the long-term studies then on-going in Japan.
Submission of human monitoring data pertinent to oxychlordane and
trans-nonachlor was considered desirable. These and other studies
are summarized in this monograph addendum.
EVALUATION FOR ACCEPTABLE INTAKE
Biochemical aspects
Absorption, distribution, and excretion
In a comparative study, groups of three male Sprague-Dawley rats
and three male C57 BL/6 JX mice received single oral doses of
14C-cis-chlordane in corn oil (0-2 ml) and were sacrificed at
intervals over the ensuing week. Faeces and urine were collected at
12-hour intervals for three days and at 24-hour intervals thereafter,
and blood was collected at sacrifice.
The 14C-cis-chlordane was absorbed more quickly by rats than
mice; peak blood radioactivity occurred after two hours in rats
(81 mg/ml) and after eight hours in mice (112 mg/ml). The rate of
dissipation of these peak levels was also faster in rats than in mice
since, after 24 hours, 41% and 76% of peak levels remained in rats and
mice, respectively. The proportions of peak radioactivity remaining in
liver at this time were 11% and 19% in rats and mice, respectively.
Although there was significant individual variability among mice, the
elimination of radioactivity in urine and faeces was initially higher
in mice than rats. After three days, the cumulative faecal excretion
was 83% in both species, although urinary excretion remained lower in
rats. The results of this study indicate significant quantitative
differences in the absorption, distribution, and excretion of
cis-chlordane in rats and mice (Ewing et al., 1985).
Toxicological studies
Special study on cardiovascular effects
Groups of three male and three female baboons received technical
chlordane (0, 0.1, or 1.0 mg/kg b.w.) in a diet enriched in saturated
fat and cholesterol for 24 months. There were no significant effects
on the weight gain of treated animals. No significant effects of
treatment were found on the development of atherosclerosis, on the
lipid composition of the aortic intima, or on serum lipid or
lipoprotein concentrations. Similarly, there were no treatment-related
effects on the activities of mitochondrial enzymes of the heart or
liver. Only the high-dose chlordane treatment induced hepatic
cytochrome P-450 activity. No consistent haematological effects or
behavioural alterations were observed. Chlordane exposure had no
apparent effect on blood lipoproteins, arteries, or cardiac muscle of
the baboon (McGill et al., 1979).
Special study on inhalational toxicity
Rats
Groups of 35 male and 35 female Wistar (Crl:(WI) BR) albino rats
were exposed for eight hours per day, five days per week, to nominal
atmospheric concentrations of 0, 0.1, 1.0, or 10.0 µg/1 technical
chlordane for 13 weeks, and then sacrificed. Recovery groups of nine
males and nine females were held for 13 weeks after exposure before
sacrifice.
There were no clinical signs or deaths related to chlordane
exposure. Some high-dose males and females appeared to become more
sensitive to touch during the study, especially the females. There
were no treatment-related effects on food or water consumption or on
body-weight gain. Ophthalmoscopy findings were unremarkable.
Apparent treatment-related findings were leucocytosis,
cholesterolaemia, and elevation of serum glutamate dehydrogenase in
the early part of the study. There was a dose-related increase in
cytochrome-P450 levels at termination of exposure, which persisted for
10-11 days thereafter.
At necropsy, increased liver weight in the high-dose groups was
accompanied by centrilobular enlargement of hepatocytes. Kidney
weights were increased in mid- and high-dose males at week nine and in
the high-dose groups at week 14. There was a tendency for increased
thyroid weight in exposed groups (Hardy et al., 1984).
Monkeys
An inhalation study was conducted with Macaca irus monkeys
using the same exposure regime as in the rat study just described.
Thus, groups of six male and six female monkeys were exposed to mean
atmospheric chlordane concentrations of 0, 0.1, 1.0, or 10 µg/l for
eight hours daily, five days per week, for 13 weeks.
There were no effects or clinical signs due to chlordane
exposure; food consumption and body-weight gain were unaffected.
Rectal temperatures were found to be slightly increased during
exposure, especially in the mid- and high-dose groups. Ophthalmoscopy
showed no treatment-related effects. No adverse effects were found on
pulmonary function (blood gases, lung function, and pulmonary
ventilation parameters). No consistent treatment-related effects on
haematological, serum biochemical, or urinalysis parameters were
found.
At necropsy, there were no significant macroscopic pathological
changes in any group, although treatment-group mean liver and thyroid
weights were greater than controls. No histopathological findings were
related to chlordane exposure (Hardy et al., 1984).
Special study on promotion of hepatic neoplasia
In the initiation phase, groups of 40 male B6C3F1 hybrid mice
received diethyl nitrosamine (0 or 200 ppm) in their drinking water
for 14 weeks. After four weeks' recovery on basal diet, the groups
received one of the following compounds in their diet for a further 25
weeks, as the promotion phase: technical chlordane (25 or 50 ppm),
technical heptochlor (5 or 10 ppm), DDT (50 ppm), or N-2-fluorenyl-
acetamide (150 ppm). In addition, some groups received the chemicals
before diethyl nitrosamine, to determine possible syncarcinogenic
effects. Randomly-selected mice from several of the groups were
sacrificed at weeks 14, 18, 26, and 34, and the remainder upon
completion of exposure. Prior to the interim kills (and at termination
with 8-10 mice), mice received s.c. injections of iron dextran (12.5
mg iron/100 gm b.w.) to produce hepatic siderosis for the subsequent
delineation of iron-excluding lesions.
Diethylnitrosamine initiation was indicated by the presence of
altered hepatic foci displaying abnormal alkaline phosphatase,
adenosine triphosphatase, glucose-6-phosphatase, gamma-glutamyl
transpeptidase, or iron accumulation in varying degrees. Abnormalities
of glucose-6-phosphatase were most marked. Neoplasia was not observed
at this stage.
At termination, most exposed animals exhibited reduced
body-weight gain, especially those in the high-dose chlordane and
heptochlor groups. Liver weights were increased in mice in those
groups which received diethyl nitrosamine followed by chlordane and
heptochlor, but not in animals in those groups receiving only
chlordane or heptochlor. While the number of hepatic foci found at
week 43 was less than that found 12 or 20 weeks after cessation of
exposure in mice given diethylnitrosamine alone, the number and size
of foci were increased by chlordane or heptochlor exposure in
initiated mice. N-2-Fluorenylacetamide increased the number, but not
the size, of hepatic foci in initiated mice, but exposure to DDT,
chlordane, heptochlor, or N-2-fluorenylacetamide alone did not
increase the number of foci compared to untreated controls.
Diethylnitrosamine produced squamous cell papillomas and
carcinomas in the forestomach and pulmonary adenomas in treated mice.
The incidence of hepatic neoplasms was particularly increased by
treatment with diethyl nitrosamine (40%) compared to untreated
controls (11%). Feeding of chlordane, heptochlor, DDT, or
N-2-fluorenylacetamide further increased not only the incidence of
hepatic neoplasms (to 66-85%), but also the multiplicity of liver
neoplasms. In each case the number of adenomas exceeded that of
adenocarcinomas. Mice given the higher doses of chlordane, heptochlor,
or N-2-fluorenylacetamide alone had the same incidence of hepatic
neoplasms as the controls, although the chlordane and heptochlor
treatment included hepatocyte hypertrophy with nuclear enlargement.
Chlordane, heptochlor, and DDT also increased the severity of cystic
changes found in the livers of all mice previously treated with
diethyl nitrosamine. Administration of the test chemicals in reverse
sequence did not increase the incidence of liver neoplasms over that
of controls.
The results of this study indicate that chlordane, heptochlor,
and DDT induce hepatocellular foci and enhance the development of
hepatocellular adenomas and adenocarcinomas in mice pre-treated with
diethylnitrosamine. However, the promotional effect seemed to be
specific to the liver (Williams and Numoto, 1984).
Long-term studies
Mice
In a combined chronic toxicity and carcinogenicity study, groups
of 80 male and 80 female Charles River ICR:SPF mice were fed technical
chlordane at dietary concentrations of 0, 1, 5, or 12.5 ppm for 104
weeks. An interim sacrifice of eight mice of each sex was conducted at
week 52. Chlordane had no apparent effect on the clinical condition of
the treated mice, and their mortality was unaffected. No consistent
influences on body-weight gain, food consumption, or food-conversion
efficiency were observed during treatment. Urinalysis and full
haematological examination, performed at weeks 52 and 104, were
unremarkable. There was a tendency for increased serum aspartate
aminotransferase and alanine aminotransferase among the mid- and
high-dose groups. Similarly, gamma-glutamyl transpeptidase values were
elevated among some high-dose females at 52 weeks.
At terminal sacrifice there was a dose-related increase in
hepatic size and relative and absolute liver weight in treated males;
treated females exhibited less of an increase in hepatic weight,
especially at the highest dose. Increased incidences of liver nodules
were found in mid- and high-dose groups, especially in male mice.
Histopathological lesions corresponding to the above changes were
found. In males, hepatocellular swelling, with associated changes to
hepatic cords and hepatocytes, increased in incidence from week 52 at
the high dose and from week 79 at the mid dose. Hepatocellular fatty
degeneration occurred at the high dose, while hepatocellular necrosis
was increased in incidence in the mid- and high-dose groups at
terminal sacrifice.
There were increased incidences of hepatocellular adenomas and
haemangiomas in the high-dose males at termination. Female mice
exhibited a dose-related increase in the incidence of hepatocellular
swelling, with a tendency for hepatocellular necrosis in only the
high-dose group. The incidence of hepatic tumours in female mice was
not increased by treatment. The results of this study indicate a
no-observed-effect level of 1 ppm (Ihui et al., 1983a).
Rats
Groups of 80 male and 80 female F-344 SPF rats were fed technical
chlordane in the diet at 0, 1, 5, or 25 ppm for 130 weeks before
sacrifice. Interim sacrifices of groups of eight males and nine
females were conducted at 26 and 52 weeks for pathological
investigation.
Treatment with chlordane produced no clinical signs of toxicity
and had no effect on mortality. Body weights, food consumption, and
food-conversion efficiency of treated animals were not consistently
different from controls. Urinalysis of sample groups of eight male and
eight female rats were unaffected by treatment after 26 and 52 weeks;
however, all groups exhibited proteinuria and haematuria at week 130.
Haematological and biochemical parameters, including serum hepatic
enzyme levels (aspartate and alanine aminotransferases, gamma-glutamyl
transpeptidase, and alkaline phosphatase), were not influenced by
treatment. Serum bilirubin levels were increased in mid- and high-dose
male groups at termination.
At necropsy significant increases in absolute and relative liver
weights in treated groups, as compared with controls, were noted;
absolute hepatic weights were increased in high-dose females at 26 and
52 weeks and in mid- and high-dose males at 130 weeks, while relative
liver weights were significantly increased in both high-dose groups.
Histopathological examination revealed a significantly-increased
incidence of hepatocellular swelling centered on hepatic nodules in
male and female high-dose rats and in some mid- and low-dose males,
towards the end of the study. There was also an increased incidence of
diffuse hepatocellular necrosis in some high- and some low-dose male
rats dying after week 79, but this lesion was not found at terminal
sacrifice. High-dose male rats also had an increased incidence of
hepatocellular adenomas. The incidences of mammary fibroadenoma and
adenoma were increased in treated females but not in a dose-related
manner. A no-effect level of 1 ppm was indicated by this study
(Ihui et al., 1983b).
Observations in humans
Clinical and epidemiological studies of chlordane exposure in man
have been reviewed (IARC, 1979; IPCS, 1984). Additional studies are
reviewed here.
Table 1 summarizes surveys of blood concentrations of workers
engaged in chlordane manufacture.
Table 1. Human blood chlordane concentrations in workers engaged in
chlordane manufacture
Blood chlordane concentration (ppb)
Number of
Year workers Range Mean
1975 50 0.7-32.0 6.6
1976 135 0.1-29.4 3.3
1979 109 0.8-76.9 11.2
Adipose tissue concentrations ranged from 900-6400 ppm with an
average concentration of 4067 ppm. Atmospheric concentrations in the
plant typically range from 10-550 µg/m3, although higher
concentrations may occur in certain areas. Significant surface
residues also contribute to exposure. Blood concentrations of
chlordane and heptochlor and their metabolites ranged from 0-75 ppb
(mean 1.5 ppb) among 411 pest-control operators (Khasawinah, 1986).
A survey of 567 randomly-selected serum samples collected from
citrus field workers found blood oxychlordane, heptochlor epoxide, and
trans-nonachlor concentrations, where detected, ranging from
0.2-2.9 ppb (Griffith & Duncan, 1985).
A recent survey of 22 male and 21 female volunteer Japanese city
dwellers has found the chlordane derivatives oxychlordane and trans-
nonachlor to be the main terminal residues in blood at concentrations
ranging from 0.18 - 1.16 mg/ml. A significant correlation was noted
between the concentrations of trans-nonachlor and oxychlordane,
between trans-chlordane and cis-chlordane, and between
trans-chlordane and cis-nonachlor. Dietary exposure seemed
to be the main source of the residues, although termite treatment of
dwellings remained a possible exposure source in some cases (Wariishi
et al., 1986).
Results of a large-scale human monitoring programme indicated
that the general U.S. population is exposed to relatively low levels
of trans-nonachlor and oxychlordane. Blood concentrations were
determined in approximately 21,000 individuals aged 12-74 years during
the period 1976-1980. In only 4.4% of the general population were
quantifiable levels of trans-nonachlor (median 1.4 ppb; range
1-17 ppb) found; the proportion of population subgroups that were
exposed increased with increasing age. Some 2.5% of the population had
quantifiable oxychlordane (median 1.7 ppb, range 1-23 ppb) or
heptochlor epoxide (median 1.7 ppb, range 1-23 ppb) in the blood
(Murphy and Harvey, 1985).
A follow-up prospective mortality study of workers occupationally
exposed to chlordane during manufacture during the period January 1946
to June 1985 has been reported. The study examined the rates of
overall mortality, cerebrovascular deaths, and cancer mortality in 800
employees with at least three months' exposure, in relation to
standard mortality ratios. Chlordane exposure was ranked by
consideration with the results of blood oxychlordane concentrations
previously determined.
Compared to other employees, production workers had less overall
mortality, with lower standard mortality ratios for both heart disease
and cancer. However, they did experience an apparent, although not
statistically significant, mortality excess from cerebrovascular
accident and trauma. Twenty cerebrovascular deaths occurred among 176
deaths, when 11.7 were to be expected.
This excess cerebrovascular mortality occurred in one
occupational subgroup with high pesticide exposure and in another with
low exposure. The apparent excess of cerebrovascular mortality
contrasts with the observed overall deficit of cardiovascular disease.
In comparison to the U.S. male population, overall cancer
mortality was slightly reduced in production workers and was at the
expected level for others. No type of cancer consistently occurred and
there seemed to be an inverse relationship between cancer mortality
and length of employment. The results of this study do not suggest any
association between occupational exposure to chlordane and human
mortality or cancer incidence (Shindell and Ulrich, 1986).
A further follow-up study of the mortality of pesticide
applicators has been conducted. Termite-control operators with a high
probability of exposure to chlordane and hepatochlor were identified
among a cohort of 16,126 male pesticide applicators employed in the
period January 1968 to September 30, 1981. Although ascertainment was
incomplete, the overall number of deaths among the cohort and the
termite-control operators was less than expected. No single cause of
death was significantly elevated, although the incidences of cancers
of the lung, skin, and bladder were each slightly increased among the
cohort, rather than the termite-control operators. Thus, there was no
apparent association between chlordane exposure and increased
mortality or human cancer in this study (McMahon et al., 1986).
COMMENTS
A comparative study of absorption, distribution, and excretion of
orally-administered cis-chlordane (alpha-chlordane) in rats and mice
indicated significant qualitative differences. It remains uncertain,
however, whether one of these species is a better animal model for
humans than the other.
As previously noted, there has been uncertainty over the
potential for chlordane, and to a lesser extent, heptochlor and/or
their metabolites, to accumulate in tissues. The presence of
trans-nonachlor and oxychlordane in human milk and adipose tissue
has been previously recognized (IPCS, 1984). The 1982 JMPR noted the
significant differences in the metabolism of chlordane by rats and
humans, but was concerned that metabolites such as trans-nonachlor
could accumulate in human tissues.
Recent human data suggest the presence of low blood levels of
cis- and trans-oxychlordane and cis- and trans-nonachlor and
their metabolites in the general population. These studies do not
indicate that either trans-nonachlor or oxychlordane are
accumulating in human tissues to a significant extent. Hence, the need
for further study with oxychlordane in rats has been superseded.
An inhalation study indicates that the monkey, Macaca irus, is
less susceptible to chlordane toxicity than rats. A study in baboons
did not indicate that low dietary levels of chlordane adversely
influenced serum lipoprotein or cholesterol levels, or the development
of atherosclerosis.
The recent chronic feeding study in rats has confirmed and
extended the results of previous studies. Proliferative lesions in the
liver were seen at a significant level at 25 ppm in male rats. Hepatic
changes, suggestive of an adaptive response, occurred at lower doses,
but these were not considered to represent an adverse toxicological
effect.
A further chronic feeding study has again confirmed the liver as
the target organ for chlordane toxicity in mice. Liver tumours
occurred in male mice at 12.5 ppm, but significant hepatic changes
were seen at lower doses. Chlordane seems to act as a tumour promoter
in the mouse liver.
Additional epidemiological data from two mortality studies of
occupationally-exposed individuals do not suggest that chlordane
exposure adversely affects the mortality or development of
cardiovascular diseases or cancer. However, the value of these data is
limited by relatively small group-sizes and uncertainty of duration
and degree of exposure.
The temporary ADI was converted to an ADI at a lower level.
TOXICOLOGICAL EVALUATION
LEVEL CAUSING NO TOXICOLOGICAL EFFECT
Mice: 1 ppm in the diet, equal to 0.12 mg/kg b.w./day.
Dogs: 3 mg/kg in the diet, equal to 0.075 mg/kg b.w./day.
Rats: 1 ppm in the diet, equivalent to 0.05 mg/kg b.w./day.
ESTIMATE OF ACCEPTABLE DAILY INTAKE IN MAN
0-0.0005 mg/kg b.w.
FURTHER WORK OR INFORMATION
STUDIES WHICH WILL PROVIDE INFORMATION VALUABLE FOR THE CONTINUED
EVALUATION OF THE COMPOUND
Further human monitoring data.
Investigation of the promotional activity of chlordane on the
diethylnitrosamine-induced liver tumours in a species other than the
mouse, with special emphasis on cytochrome P-450 induction.
REFERENCES
Ewing, A.D., Kadry, A.M., & Dorough, H.W., 1985. Comparative
disposition and elimination of chlordane in rats and mice.
Toxicology Letters, 26, 233-239.
Griffith, J. & Duncan, R.C., 1985. Serum organochlordane residues in
Florida citrus workers compared to the National Health and
Nutrition Examination Survey sample. Bull. Environ. Contam.
Toxicol., 35, 411-417.
Hardy, C.J., Clark, G.C., Street, A.E., Read, L.E., Gopinath, C.,
Gregson, R.L., & Down, W.H., 1984. Chlordane, a 90-day inhalation
toxicity study in the rat and monkey. Unpublished report by
Huntingdon Research Centre, Huntingdon, Cambridgeshire, England.
Submitted to WHO by Velsicol Chemical Corp., Chicago, IL, USA.
IARC, 1979. IARC monographs on the evaluation of the carcinogenic risk
of chemicals to man: some halogenated hydrocarbons. Chlordane.
International Agency for Research on Cancer, Lyon,
Volume 20, pp. 45-65.
IPCS, 1984. Chlordane, Environmental Health Criteria No 34.
International Programme on Chemical Safety, WHO, Geneva.
Ihui, S., Hayakawa, T. Yonemura, T., Takamura, F., Takahashi, Y., &
Yamazaki, K., 1983a. Twenty-four month chronic toxicity and
tumourigenicity test in mice by chlordane technical. Unpublished
report by Research Institute for Animal Science in Biochemistry
and Toxicology. Submitted to WHO by Velsicol Chemical Corp.,
Chicago, IL, USA.
Ihui, S., Hayakawa, T., Yonemura, T., Takamura, F., Takahashi, Y., &
Hashizume, M., 1983b. Thirty-month chronic toxicity and
tumourigenicity test in rats with chlordane technical.
Unpublished report by Research Institute for Animal Science in
Biochemistry and Toxicology. Submitted to WHO by Velsicol
Chemical Corp., Chicago, IL, USA.
Khasawinah, A.M., 1986. Plant workers and pest control operators
exposure to chlordane and heptachlor. Unpublished report.
Submitted to WHO by Velsicol Chemical Corp., Chicago, IL, USA
McGill, H., Mott, G.E., Kruski, A.W., Montiel, M.M., Stavinoha, W.B.,
Coelho, A.M., Carey, K.D., & McMahan, C.A., 1979. Pilot study of
the effects of pesticides on blood lipoproteins, arteries and
cardiac muscle of baboons. Unpublished report by University of
Texas Health Science Center and Southwest Foundation for Research
and Education. Submitted to WHO by Velsicol Chemical Corp.,
Chicago, IL, USA
McMahon, B., Wang, H., & Monson, R., 1986. A second follow-up of
mortality in a cohort of pesticide applicators. Unpublished
report. Submitted to WHO by Velsicol Chemical Corp.,
Chicago, IL, USA
Murphy, R. & Harvey, C., 1985. Residues and metabolites of selected
persistent halogenated hydrocarbons in blood specimens from a
general population survey. Environmental Health Perspectives,
60, 115-120.
Shindell, S. & Ulrich, S., 1986. Mortality of workers employed in the
manufacture of chlordane: An update. J. Occup. Med., In Press.
Wariishi, M., Suzuki, Y., & Nishiyama, K., 1986. Chlordane residues in
normal human blood. Bull. Environ. Toxicol., 36, 635-643.
Williams, G.M. & Numoto, S., 1984. Promotion of mouse liver neoplasms
by the organochlorine pesticides chlordane and heptachlor in
comparison to dichlorodiphenyltrichloroethane. Carcinogenesis,
5, 1689-1696.