Scientists in London have found that low-level exposure to organophosphate pesticides affect the brains and nervous systems of humans. Exposure to the chemicals was shown to affect memory and information processing capabilities.

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The nerve agents are widely used in agriculture, sold under a variety of names, and are favoured in part because they break down quicker than more persistent alternatives such as organochlorides (a group including the infamous DDT).

Researchers from UCL and the Open University evaluated data from 14 studies, which included over 1,600 participants. Lead author Dr Sarah Mackenzie Ross said her research was conducted so as to be more useful in informing public policy.

She said, "This is the first time anyone has analysed the literature concerning the neurotoxicity of organophosphate pesticides [in this way].The analysis reveals that the majority of well-designed studies undertaken over the last 20 years find a significant association between low-level exposure to organophosphates and impaired cognitive function."

Dr Mackenzie Ross added that pesticides prevent millions of people from starving to death and from contracting disease, but they can also be harmful to humans and animals. Organophosphate pesticides are the most widely used insecticides in the world, but the widely-available chemicals are derived from World War II nerve agents.

According to the World Health Organisation (WHO) organophosphate pesticides are one of the most hazardous pesticides to vertebrate animals, responsible for many cases of poisoning worldwide. The toxic effects of high level poisoning are well established but the possibility that long-term low-level exposure to OPs in doses below that causing acute toxicity causes ill health is controversial.

Dr Virginia Harrison, a co-author of the study said, "In the UK a number of occupational groups have expressed concern that their health has been affected by exposure to organophosphates. This includes sheep farmers, who between 1988 and 1991 were required to dip sheep yearly in pesticide formulations containing OPs." Between 1985 and 1998 more than 600 reports of ill health following exposure to sheep dip were received by a government adverse reaction surveillance scheme.

Although the domestic use of organophosphates has been banned in the EU, the pesticides are still used in agriculture, though their use has dropped off in recent years.

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