|October 5, 2000
(New Scientist) - 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