C14H9Cl5 (DDT)
The Chemistry
DDT is a cheap and effective insecticide. In insects, DDT opens sodium ion channels, which then fire spontaneously and causes spasms and death.
One of the concerning properties of DDT is that it does not break down in the environment or an organisms. It has low solubility in water and high solubility in fats. Thus, when animals ingest DDT, it mixes with the fat and eventually builds up in their fat tissue.
The History
DDT was first created in Germany in 1874 and later developed by Paul Müller in the 1930s. In World War II, Allied soldiers used DDT to control malaria, typhus, body lice, and bubonic plague. After the war, agricultural industries applied DDT as a pesticide, and DDT was a large part of the World Health's Organization's 1955 push to end malaria.
DDT was used as an insecticide in large scale agriculture.
In 1962, Rachel Carson published her famous Silent Spring, which illuminated the dangers of pesticides such as DDT. Laboratory experiments have shown that DDT causes cancer, mutations, and birth defects, and DDT was banned in the US in 1972 by the Environmental Protection Agency. However, DDT is still used in South America, Africa, and Asia.
For more info, the National Pesticide Information Center has a great fact sheet about DDT:
http://npic.orst.edu/factsheets/ddtgen.pdf