Computer graphics representation of a molecule of chlordane, an insecticide. Chlordane is an organochlorine insecticide, one of a group of compounds introduced in the 1940's which includes DDT. The idea of introducing chlorine atoms (light blue spheres) into molecules was to produce compounds that would not be readily broken down by soil organisms. Hence the organochlorines are known as persistent insecticides. Unfortunately, such persistence became reflected in the food chain, where accumulating concentrations of insecticides had disastrous toxic effects on bird and fish populations. Organochlorines were banned in many countries during the 1970's.