DDT: Angel or devil?

DDT was first thought to be a saviour but was then recast as a villain. Some say it now needs to be rehabilitated.

Insect pests eat crops and spread disease, and chemicals to kill them are potential life-savers as well as an aid to farmers. DDT (dichlorodiphenyltrichloroethane) was first made in 1874 by the German chemist Othmar Ziedler. Later, in the 1930s, Paul Müller and colleagues discovered its powerful insect-killing properties – for which they won a Nobel Prize.

DDT came into wide use in the Second World War to help prevent troops catching malaria, typhus and yellow fever. After the war, it was used widely in agriculture and to prevent insect-borne diseases. DDT may have saved more lives than any other single chemical.

Then the picture changed. DDT's long life meant that the chemical accumulated in the environment, and creatures high up a food chain could end up heavily loaded with DDT. It increased the chances of cancer in people. And it affected wildlife, as documented memorably in environmentalist Rachel Carson's classic 'Silent Spring' in 1962. By the early 1970s, there were bans on the use of DDT and similar compounds in many countries.

However, while there are alternatives for farmers in the USA and Europe who want to protect their crops, DDT is still one of the best and cheapest ways to kill mosquitoes. As yet there is no vaccine against malaria, which is spread by mosquito bites and kills more than a million people every year, mainly in Africa.

Some argue that a blanket ban on DDT is unjustified when it has the potential to do so much immediate good. The longer-term hazards may be worth the local gains.