Heptachlor in freshwater and marine water

​Toxicant default guideline values for protecting aquatic ecosystems

October 2000

Extracted from Section 8.3.7 ‘Detailed descriptions of chemicals’ of the ANZECC & ARMCANZ (2000) guidelines.

The default guideline values (previously known as ‘trigger values’) and associated information in this technical brief should be used in accordance with the detailed guidance provided in the Australian and New Zealand Guidelines for Fresh and Marine Water Quality.

Description of chemical

Most organochlorine pesticides have been phased out of use in recent years, mainly because of their residual properties and potential for bioaccumulation. The guideline trigger values stated are for toxicity only and need to be adjusted for bioaccumulation where appropriate. Where the statistical distribution method was used, figures quoted are the 95% protection levels, usually applicable to slightly to moderately disturbed systems although 99% protection figures are recommended for chemicals that bioaccumulate.

Heptachlor (CAS 76-44-8) is a cyclodiene organochlorine insecticide first introduced by Velsicol Chemical Corp. Its IUPAC name is 1,4,5,6,7,8,8-heptachloro-3a-4,7,7a-tetrahydro-4,7-methanoindene, formula is C10H5Cl7 and molecular weight is 373.3. It has very low solubility in water (56 µg/L at 25°C) (Tomlin 1994) and log Kow of 5.3 to 5.6 (Hansch et al. 1995).

Uses and environmental fate

Heptachlor was used on a variety of soil insect pests in areas not involving food or food crops, particularly subterranean termites and ants. It was its residual action that made the use of heptachlor and related cyclodienes attractive for sub-floor treatment against termites and it was registered for that use through much of Australia until December 1995.

Heptachlor is very persistent in soil with a DT50 around 9 months. The principle metabolite in animals is heptachlor epoxide (Tomlin 1994).

Levels of heptachlor in red morwong Cheilodactylus fuscus caught off Sydney’s sewer outfalls, prior to construction of the deep ocean outfalls, contained levels of heptachlor up to 2.6 mg/kg, 52 times the maximum residue level (ANZEC 1991). Levels have declined markedly since opening the deep ocean outfalls (Scanes & Phillip 1995). The current analytical practical quantitation limit (PQL) for heptachlor in water is 0.05 µg/L (NSW EPA 2000).

Aquatic toxicology

Toxicity of many species noticeably increased with duration of exposure. For some species of crustaceans, 96-hour LC50 values were between 5 and 28 times lower than the 24-hour LC50s from the same experiment. Heptachlor was highly toxic to most test species.

Freshwater fish: 13 species, 96-hour LC50 of 6.2-102 µg/L. Figures above 150 µg/L were reported for three of these species.

Chronic no observed effect concentration (NOEC) (280-day mortality) of 0.86 µg/L for Pimephales promelas gave an acute-to-chronic ratio (ACR) of 65.

Freshwater crustaceans: six species, 48 to 96-hour LC50 or EC50 (immobilisation) of 0.5 to 56 µg/L. There was an outlying figure for Daphnia pulex of 404 µg/L (above water solubility). Crayfish and shrimp were most sensitive (two species 0.5 to 1.8 µg/L). A 64-day chronic NOEC for D. magna of 12.5 µg/L was reported.

Freshwater insects: three species, 96-hour EC50 (immobilisation) of 0.9 to 80 µg/L.

Freshwater molluscs: one species, 96-hour LC50 of 1450 µg/L, above water solubility.

Freshwater algae: one species, 48-hour EC50 (growth) of 28 to 38 µg/L.

Marine fish: eight species, 48 to 96-hour LC50 of 0.85 to 10 µg/L.

Marine crustaceans: four species, 48 to 96-hour LC50 of 0.03 to 3.4 µg/L. Higher 96-h LC50 figures were reported for the Australian amphipod Hyale crassicornis (28 to 39 µg/L) and two crab species, 55 µg/L. NOEC figures (5 days) for immobilisation of. H. crassicornis were 8 to 32 µg/L (Australian data).

Marine molluscs: one species, 96-hour EC50 growth of 1.5 to 16 µg/L.

Australian and New Zealand data

Marine data for the amphipod H. crassicornis were available; 96-hour LC50 of 28 to 39 µg/L and 5-day NOEC (immobilisation) of 8 to 32 µg/L.

Factors that modify toxicity

Johnson and Finley (1980) reported that an increase in test temperature from 7°C to 29°C caused a 4.8-fold increase in toxicity (decrease in LC50) to Lepomis microlophus. However, no effect was noted with rainbow trout Oncorhynchus mykiss between 2°C and 18°C. Toxicity of heptachlor to rainbow trout did not change with hardness between 44 and 272 mg/L CaCO3 (Johnson & Finley 1980).

Johnson and Finley (1980) reported results for pond treatments with heptachlor between 12.5 and 50 µg/L. Up to 100% mortalities of fish and invertebrates occurred within 7 days but invertebrate populations recovered by 28 days. Liver lesions in fish were noted from 14 to 56 days after treatment. Toxic responses of bluegills Lepomis macrochirus fed diets containing 5 to 25 mg/L heptachlor were similar to those in fish from the ponds.


A freshwater moderate reliability guideline figure of 0.09 µg/L was calculated for heptachlor using the statistical distribution method at 95% protection and an ACR of 7.5. The 99% protection level is 0.01 µg/L and is recommended as the trigger value for slightly-moderately disturbed systems.

Less marine data were available and a marine low reliability trigger value of 0.0004 µg/L was derived using an AF of 10 and an ACR of 7.5. This figure should only be used as an indicative interim working level.

These figures do not account for bioaccumulation. Users are advised to apply the 99% protection level for slightly-moderately disturbed systems if there are no data to adjust for bioaccumulation at the specific site (Section of the ANZECC & ARMCANZ 2000 guidelines).


ANZEC 1991. Persistent organochlorine compounds in the marine environment. Australian and New Zealand Environment Council, Australian Government Publishing Service, Canberra.

ANZECC & ARMCANZ 2000. Australian and New Zealand Guidelines for Fresh and Marine Water Quality, Australian and New Zealand Environment and Conservation Council and Agriculture and Resource Management Council of Australia and New Zealand, Canberra.

Hansch C, Leo A & Hoekman D 1995. Exploring QSAR. Hydrophobic, electronic, and steric constants. American Chemical Society, Washington, DC.

Johnson WW & Finley MT 1980. Handbook of acute toxicity of chemicals to fish and aquatic invertebrates. US Department of the Interior, Fish and Wildlife Service, No 137, Washington DC.

NSW EPA 2000. Analytical Chemistry Section, Table of Trigger Values 20 March 2000, LD33/11, Lidcombe, NSW.

Scanes PR & Phillip N 1995. Environmental impact of deepwater discharge of sewage off Sydney, NSW, Australia. Marine Pollution Bulletin 26, 687-691.

Tomlin C 1994. The pesticide manual: A world compendium. 10th edn, British Crop Protection Council & Royal Society of Chemistry, Bath, UK.