Primarily used to kill soil insects and termites, heptachlor has also been used more widely to kill cotton insects, grasshoppers, other crop pests, and malaria carrying mosquitoes.
It is believed to be responsible for the decline of several wild bird populations, including Canadian Geese and American kestrels in the Columbia River Basin in the U.S. The geese died after eating seeds treated with levels of heptachlor lower than the usage levels recommended by the manufacturer, indicating that even responsible use of heptachlor may kill wildlife.
Laboratory tests have also shown high doses of heptachlor to be fatal to mink, rats, and rabbits, with lower doses causing adverse behavioral changes and reduced reproductive success.
Heptachlor is classified as a possible human carcinogen, and some two dozen countries have either banned it or severely restricted its use.
Food is the major source of exposure for humans, and residues have been detected in the blood of cattle from the U.S. and from Australia.