DDT

Insecticide discovered in 1939 by Swiss chemist Paul Müller. It is useful in the control of insects that spread malaria, but resistant strains develop. DDT is highly toxic and persists in the environment and in living tissue.

The Stockholm Convention, which came into force in 2004, calls for a complete ban on DDT and eleven other organic pollutants. However, public-health use of DDT in tropical countries (where the threats of mosquito-borne infections such as malaria far outweigh any concerns over DDT's toxicity) remains exempt from the ban until a viable alternative has been found.