Pesticide sprays encourage life-threatening bacteria to grow on crops, a researcher in Canada has discovered. The bugs could pose a threat to people eating raw fruit and vegetables such as strawberries, raspberries and lettuce.

Alarmed by the rise in cases of food poisoning caused by fresh produce, Greg Blank and his colleagues at the University of Manitoba in Winnipeg wondered if contaminated sprays could be to blame. To find out, they prepared formulations of a dozen or so common herbicides, fungicides and insecticides approved for spraying on raw fruit or vegetables.

After diluting each with water, they added strains of bacteria that cause food poisoning. These included Shigella, Salmonella, Listeria and Escherichia coli O157:H7 which can cause kidney failure.

The researchers found that bacteria thrived in around a third of the pesticides, growing best in the fungicide chlorothalonil, the weedkiller linuron and the insecticides permethrin and chlorpyrifos. "Numbers could increase one-thousandfold," says Blank. Salmonella, E. coli and Shigella grew best, he says, particularly on chlorothalonil.

Blank acknowledges that when farmers irrigate their crops they may spray on far larger volumes of contaminated water. What's different with pesticides, he says, is that the bacteria multiply in tanks where the solution is stored, and so can reach far higher concentrations. He is now investigating whether the bugs survive to the point of consumption.

Ross Dyer, technical manager of the Crop Protection Association in Britain, says that the problem is caused by farmers using dirty water rather than by the pesticides: "If the water supply is contaminated, it's that that's supplying the bacteria in the first place."

Author: Andy Coghlan

New Scientist issue: 7 OCTOBER 2000

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