Heptachlor is a banned pesticide that persists in the environment. It enters water through agricultural runoff and is highly toxic, linked to cancer in humans.

Heptachlor, a chlorinated cyclodiene insecticide, was widely used from the 1950s to 1970s for termite control and crop protection. Despite being banned in most countries, it persists in the environment due to its chemical stability. It primarily enters water systems through agricultural runoff and soil erosion. Heptachlor is typically measured in parts per billion using gas chromatography. Its persistence and ability to bioaccumulate make it a significant environmental concern, even years after its use was discontinued.