Heptachlor

Heptachlor is an insecticide. It was used against ants, termites, against mosquitos of the genus Anopheles, that can spread malaria and as a general pesticide. In humans, heptachlor damages the liver, and the central nervous system. It may cause cancer. It is sold as a powder. The Diels-Alder reaction is used to produce it. The compound is very stable and can stay in the environment for decades. 
Hepltachlor is one of the substances listed in the Stockholm Convention on Persistent Organic Pollutants.