Potatoes And Pesticides Part Ways

Glenda García-Santos

Field To Plate Potatoes don't carry much chlorpyrifos, an insecticide sprayed in Colombia on the staple crop.

Scrubbing the outside of fruits and vegetables may not be good enough for potatoes, because some scientists have warned that root crops may carry pesticides in their flesh. But the first model to describe how pesticides travel through potato crops (Environ. Sci. Technol., DOI: 10.1021/es102907v) shows that the threat from at least one pesticide is low.

Led by Ronnie Juraske of the Swiss Federal Institute of Technology (ETH Zurich), the researchers monitored how farmers in Colombia applied the widely used organophosphate insecticide chlorpyrifos to their potato plants. The team logged mixing and spraying processes, as well as weather and other field conditions. Back in the lab, the researchers ground up potatoes -- cooked and raw, dirty and washed -- to examine how the skin and flesh might take up chlorpyrifos and other pesticides. The team used gas chromatography and high-performance liquid chromatography to measure pesticide levels in soil samples and in samples of potatoes at different stages of storage and preparation.

Levels of other pesticides, such as other pesticides applied by the farmer and residual DDT used long ago, appeared in the soil but not in the potatoes. Chlorpyrifos was an exception: it built up in raw potatoes. But Juraske's team determined that cooking the potatoes reduced the chlorpyrifos burden by 14%. In the end, cooked potatoes carried only 0.2% of the amount of chlorpyrifos allowed for a 60 kg person under the EU's daily intake limit of 0.1 mg/kg of body weight. Even long-term consumption of potatoes from Colombia, where they are a local staple, probably poses a negligible health threat, the researchers report.

The team used its data to create a model with different equations to describe the movement of pesticides through potato crops. The researchers want to use their model with other countries’ potato crops, as well as test it again in the same Colombian fields under different weather conditions.

Peter Fantke, a modeler at the University of Stuttgart, in Germany, praises Juraske's pesticide model for being "one of the few that focuses on what happens after direct application." Fantke and Juraske are working together to develop a model that could be applied anywhere for any crop. Fantke says that the potato model remains limited because it was calibrated to non-polar pesticides like chlorpyrifos and to spherical crops like potatoes. The model's underlying equations would need to be adjusted for polar and ionic pesticides, as well as for crops like carrots with different shapes, he says. In applying the conclusions to other pesticide-crop combinations, he says, "I would be quite careful."

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