Heptachlor and heptachlor epoxide
(endorsed 1996)
Guideline
Heptachlor should not be detected in drinking water. If present in drinking water, heptachlor would not be a health concern unless the concentration exceeded 0.0003 mg/L.
If it is detected, remedial action should be taken to stop contamination. The limit of determination is 0.00005 mg/L (50 ng/L).
General description
Heptachlor is a broad spectrum insecticide used in Australia until September 1994 to protect wooden structures against termites. Its other former uses were withdrawn in the late 1970s and early 1980s. Heptachlor epoxide, an oxidation product of heptachlor, is not commercially available.
Heptachlor is moderately persistent in soil. It is transformed slowly to the epoxide, which is very resistant to further chemical or biological degradation.
Heptachlor has been detected at low nanogram per litre concentrations in water supplies in Europe and the United States. It has been found in a number of foods including human milk. The daily adult intake for heptachlor and the epoxide in the United States has been estimated at about 0.000007 mg/day (7 ng/day) and 0.0002 mg/day respectively. The 1990 Australian Market Basket Survey did not find heptachlor or the epoxide in any of the foods tested (NHMRC and NFA 1991).
Typical values in Australian drinking water
Heptachlor has not been detected in major Australian drinking water supplies.
Treatment of drinking water
No published reports are available on methods for the removal of heptachlor from drinking water supplies. Granular activated carbon would probably be effective.
Measurement
Heptachlor can be extracted from water using a nonpolar solvent such as pentane, and analysed using gas chromatography with electron capture detection (APHA Method 6630 Part B 1992). The limit of determination is 0.00005 mg/L (50 ng/L).
Health considerations
Heptachlor is absorbed rapidly from the gastrointestinal tract of rats and distributed throughout the body. It is metabolised to the epoxide and excreted in faeces.
Extensive reviews and summaries of the human and animal toxicology of heptachlor are available (IPCS 1984, JMPR 1991, IARC 1991, NHMRC 1992).
Heptachlor is acutely neurotoxic in animals and humans at high doses, and is hepatotoxic in animals. It caused liver tumours in mice, and in one study, thyroid follicular cell carcinoma in rats. At high exposure levels, heptachlor can affect the viability of the offspring of rodents and dogs.
Heptachlor has not been reported to be genotoxic or teratogenic in animals.
The International Agency for Research on Cancer has concluded that heptachlor is possibly carcinogenic to humans (Group 2B, inadequate evidence in humans, sufficient evidence in experimental animals) (IARC 1991).
Derivation of guideline
The health-based guideline value of 0.0003 mg/L for heptachlor and heptachlor epoxide was determined as follows:
where:
0.0001 mg/kg body weight per day is the maximum acceptable daily intake (ADI) based on a no-effect level of 0.025 mg/kg body weight per day from two studies using dogs (JMPR 1991).
70 kg is the average weight of an adult.
0.1 gives a guideline value based on 10% of the ADI.
2 L/day is the average amount of water consumed by an adult.
The maximum ADI value includes a safety factor of 200 (10 for interspecies variations, 10 for intraspecies variations and 2 for the inadequacy of the data base). No additional safety factors are necessary.
The World Health Organization guideline value of 0.00003 mg/L (30 ng/L) was determined using 1% of the ADI to allow for increased exposure from other sources. Such a low percentage of the ADI was considered inappropriate for Australia.
References
APHA Method 6630 Part B (1992). Organochlorine pesticides: Liquid–liquid extraction, gas chromatographic method I. Standard Methods for the Examination of Water and Wastewater, 18th edition. American Public Health Association, Washington.
IARC (International Agency for Research on Cancer) (1991). IARC Monographs on the Evaluation of Carcinogenic Risks to Humans: Occupational Exposures in Insecticide Application, and Some Pesticides. World Health Organization, IARC, 53.
IPCS (International Programme on Chemical Safety) (1984). Heptachlor. Environmental Health Criteria, 38. World Health Organization, I{CS.
JMPR (1991). Pesticide Residues in Food — 1991. Report of the Joint Meeting of the FAO Panel of Experts on Pesticide Residues in Food and the Environment and the WHO Expert Group on Pesticide Residues. Food and Agricultural Organization of the United Nations, FAO Plant Production and Protection Paper III, Rome.
NHMRC (National Health and Medical Research Council) (1992). Cyclodiene Insecticide Use in Australia. NHMRC, AGPS, Canberra.
NHMRC and NFA (National Health and Medical Research Council and National Food Authority) (1991). The 1990 Australian Market Basket Survey. NHMRC and NFA, AGPS, Canberra.
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