International Agency for Research on Cancer (IARC) - Summaries & Evaluations

Chlordane (Group 2B)
Heptachlor (Group 2B)

For definition of Groups, see Preamble Evaluation.

VOL.: 53 (1991) (p. 115)

: 57-74-9

Chlordane [technical grade]
: 12789-03-6

CAS No.: 5103-71-9

: 5103-74-2

: 5566-34-7

: 76-44-8

Heptachlor epoxide
: 1024-57-3

5. Summary of Data Reported and Evaluation

5.1 Exposure data

Chlordane has been used since the 1950s as a broad-spectrum contact insecticide, mainly for nonagricultural purposes and to a lesser extent on crops and on livestock. Since the mid-1970s, its use has generally been restricted to underground control of termites.

Heptachlor has been used since the 1950s as an insecticide in agriculture and in the control of termites and soil insects. Like chlordane, its use is now largely restricted to subsoil treatment for termites.

Chlordane and heptachlor have been formulated as granules, emulsifiable concentrates and solutions.

Both compounds can persist in soil for many years. Human exposure to chlordane and heptachlor occurs mainly during their application and in the air of buildings where they have been applied for termite control. When these compounds were used on crops, exposure may have occurred at much lower levels as a result of consumption of foods containing residues.

5.2 Carcinogenicity in humans

Case reports of leukaemia and other blood dyscrasias have been associated with exposure to chlordane/heptachlor, primarily in domestic situations.

Mortality from lung cancer was slightly elevated in two cohort studies of pesticide applicators and one of chlordane/heptachlor manufacturers. Termite control operators probably have greater exposure to chlordane than other pesticide applicators; however, in one study of applicators, the excess occurred only among workers who were not engaged in termite control. In the other study of applicators, the relative risk for lung cancer among workers engaged in termite control was similar to that of workers engaged in other pest control. Inconsistencies in these findings make it difficult to ascribe the excesses to exposure to chlordane.

Small excess risks for other cancers, including leukaemia, non-Hodgkin's lymphoma and soft-tissue sarcoma and cancers of the brain, skin, bladder and stomach were observed, with little consistency among studies.

5.3 Carcinogenicity in experimental animals

Chlordane, technical-grade chlordane, heptachlor, technical-grade heptachlor, heptachlor epoxide and a mixture of heptachlor and heptachlor epoxide have been tested for carcinogenicity by oral administration in several strains of mice and rats. These studies uniformly demonstrate increases in the incidence of hepatocellular neoplasms in mice of each sex. Increases in the incidence of thyroid follicular-cell neoplasms were observed in rats treated with chlordane and technical-grade heptachlor. An increased incidence of malignant fibrous histiocytomas was observed in one study in male rats treated with chlordane. A small increase in the incidence of liver adenomas was seen in one study in male rats treated with technical-grade chlordane.

5.4 Other relevant data

Metabolites of chlordane and heptachlor, like those of other chlorinated hydrocarbons, accumulate in human fat. Chlordane and heptachlor induce liver microsomal enzymes. The liver is the target organ for chronic toxicity.

No data were available on the genetic and related effects of chlordane or heptachlor in humans.

Chlordane and heptachlor did not cause dominant lethal effects in mice. Both compounds inhibited gap-junctional intercellular communication and induced gene mutations in rodent cells but did not induce unscheduled DNA synthesis. In plants, heptachlor induced mutations and chromosomal aberrations. Neither chlordane nor heptachlor was mutagenic to bacteria and neither damaged bacterial or plasmid DNA.

5.5 Evaluation

There is inadequate evidence in humans for the carcinogenicity of chlordane and of heptachlor.

There is sufficient evidence in experimental animals for the carcinogenicity of chlordane and of heptachlor.

Overall evaluation

Chlordane is possibly carcinogenic to humans (Group 2B).

Heptachlor is possibly carcinogenic to humans (Group 2B).

Subsequent evaluation: Vol. 79 (2001)

Previous evaluations: Vol. 20 (1979) (p. 45); Suppl. 7 (1987) (p. 146)

Synonyms for Chlordane

Synonyms for cis-Chlordane

Synonyms for trans-Chlordane

Synonyms for g-Chlordane

Synonyms for Heptachlor

Synonyms for Heptachlor epoxide

For definition of the italicized terms, see Preamble Evaluation.

Last updated: 20 November 1997

    See Also:
       Toxicological Abbreviations
       Chlordane and heptachlor  (IARC Summary & Evaluation, Volume 79, 2001)