DDT or dichloro-diphenyl trichloroethane was the first important synthetic pesticide (organo chlorine) discovered in 1939 by a Swiss chemist Paul Muller. It was toxic to wide range of insect pests ("broad spectrum") yet appeared to have low toxicity to mammals. It was persistent i.e. didn't break down rapidly in the environment, so that it didn't have to be reapplied often. DDT was so effective at killing pests and thus boosting crop yields and was so inexpensive to make that its use quickly spread over the globe. Farmers used more and more DDT throughout the $1950 \mathrm{~s}$ and 1960 s to get an increased yield of crop.