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James Lovelock in the 1950s when he was at the National Institute for Medical Research at Mill Hill, North London.
Credit: Photograph courtesy of NIMR |
The breakdown of civil society in Central Europe at the end of the Second World War produced a major outbreak of typhus, an often fatal disease spread by body lice. This posed a major threat to the Allied armies, as did mosquito-borne malaria on the Pacific front. Both diseases were brought under control by killing the insects that carry them with a powerful new insecticide called DDT.
In the mid-1940s, DDT and several other new insecticides appeared almost miraculous. They killed hosts of harmful insects by simple contact and were harmless to mammals in comparison to earlier insecticides such as arsenic and nicotine. For his development of DDT, Paul Müller of Geigy was awarded the Nobel Prize for Medicine in 1948.
By the late 1950s, however, there was growing concern about DDT entering foods and thereafter climbing up the food chain. Some shipments of fruit and dairy products were impounded by customs on suspicion of being contaminated with insecticides. Alarmingly, DDT was even detected in the body fat of native people in Alaska, thousands of miles away from the main centres of pesticide use. Even more worryingly some marine species appeared to be affected by DDT at levels below one part per million, the existing level of detection by chemical analysis.
| Scientists have even discovered pollutants in the Greenland icecap |
Combining the new technique of chromatography with very sensitive devices called detectors solved the problem of detecting tiny amounts of pesticides. One of these detectors, the electron-capture detector (ECD), was particularly good for measuring very low levels of DDT. By the end of the 1960s, DDT and similar pesticides could be detected quickly and reliably at a level of parts per trillion, the equivalent of four kilograms of DDT in the entire Mediterranean Sea.
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An early version of the electron capture detector built by James Lovelock, around 1960.
Credit: Science Museum/Science & Society Picture Library |
Did this technological breakthrough make people more confident? Actually, no. Before the rise of DDT and the introduction of the ECD, the situation was simple. Existing techniques could only reliably measure pesticide residues in food down to a level of one part in a million (1 ppm). The authorities could act tough and set a ‘zero tolerance’ level, which in practice meant a level of 1 ppm, and everyone was happy, more or less.
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'Monster Soup commonly called Thames Water being a correct representation of that precious stuff doled out to us!',1828.
Credit: Science Museum/Science & Society Picture Library
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Once the new techniques made it possible to detect pesticides at a level a million times less than ever before, the concept of zero tolerance vanished. People began to worry more about pesticides as they were discovered in numerous places – including baby food, mother’s milk and schoolyards – even though the concentrations were extremely low. Using yet more sensitive chemical techniques, scientists have even discovered pollutants in the Greenland icecap.
The controversy over Alar, a fruit-ripening agent, illustrates the public disquiet over chemical residues on food. It is an emotional topic that is difficult to debate rationally – particularly for parents. As a society, we are still developing ways of coming to terms with these risks, however small they may be.
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