Crop yields increased and it was also used to control malaria by killing mosquitoes. Muller was awarded the Nobel Prize in 1948.

However, in 1962, scientist Rachel Carson noticed that insect and worm-eating birds were dying in areas where DDT had been sprayed.

In her book Silent Spring she issued grave warnings about pesticides and predicted massive destruction of the planet's ecosystems unless the "rain of chemicals" was halted.

Pesticide manufacturers said that the minute amounts found in the environment couldn't possibly kill birds, but experiments demonstrated that even small amounts could affect the survival and reproduction of some species.

DDT had been transported over long distances in the atmosphere. It finally showed up in breast milk in very high concentrations. Because of its effect on reproduction, bald eagles, peregrine falcons and brown pelicans were almost eliminated.

DDT was finally banned for sale in Europe in the 1970s, but its damaging effects live on.

It was not until 2001 that new research linked DDT to low infant birth-weight and premature births in the U.S.

Find out more about WWF's efforts to phase out DDT

In the 1970s they were found to contaminate the enivronment and wildlife, and cause cancers and damage the immune and reproductive systems.

The production of PCB has been gradually banned across the world since the 1970s. However, they are still present in old electrical transformers and building materials - and in our bodies and those of wildlife.

PCBs, as a persistent and bioaccumlative chemical, is stored in body fat, so its concentration increases as it rises up the food chain. Huge quantities have escaped into the environment, where it continues to affect wildlife and humans.