Heptachlor was commercially introduced as a non-systemic contact insecticide in 1945. It was also a major constituent (about 10 %) of technical chlordane. Heptachlor was used for agricultural
purposes, soil and seed treatment, wood protection and termite- and household insect control. It has been banned for use in the European Union since 1984 and in most other countries worldwide
because of the persistency in the environment of the two break-down products heptachlor epoxide and photoheptachlor. All these compounds are lipophilic and particularly heptachlor epoxide and
photoheptachlor tend to accumulate in the food chain.
Heptachlor shows moderate acute toxicity and heptachlor epoxide and photoheptachlor are more toxic than heptachlor. In mammals, the main target organs are the nervous system and the liver, but
also the reproductive and the immune system are affected. Heptachlor and heptachlor epoxide cause liver tumours in mice, but are not genotoxic. Heptachlor is classified by IARC as possibly
carcinogenic to humans (group 2B). Heptachlor is moderately or highly toxic to fish exposed via water, but no data from oral studies have been found.
Amongst the species studied, the domestic hen is the most sensitive species and egg production and hatchability are the critical endpoints. Total heptachlor (sum of heptachlor and heptachlor
epoxide) is not frequently found in feed commodities. When present, it is mostly in fish derived products and only very infrequently in feed materials of plant origin. Heptachlor epoxide is the
predominant contaminant. The concentrations found in feed are in the low mg/kg range and thus well below those that have been found to cause adverse effects in animals. The half-life of total
heptachlor varies from several days in rodents up to more than 20 weeks in non-lactating cattle. Following heptachlor exposure, only heptachlor epoxide is found in milk and eggs. The present
dietary exposure of the adult population to total heptachlor is below 1 ng/kg b.w. per day, which is two to three orders of magnitude below the tolerable daily intake of 0.0001 mg/kg b.w. as
established by WHO in 2006.