A common combination of chemicals used to protect potato, dry bean, and tomato crops from bugs, weeds, and other pests seems to have a very unappetizing side effect. New research out of UCLA backs previous theories suggesting that exposure to pesticides could trigger Parkinson’s disease, a degenerative disorder of the central nervous system that can impair motor skill, speech, and other functions. The new study appeared in this month’s American Journal of Epidemiology. “We were able to show in humans what animal data had previously suggested,” says lead study author Sadie Costello, former doctoral student at UCLA who is now at the University of California, Berkeley. “Animal experiments are done in highly controlled environments in which exposure can be measured . . . the chance of actually seeing an effect in humans is not very high unless there is, in fact, quite a large effect.”
THE DETAILS: High rates of Parkinson’s disease have been reported in farmers and rural populations, raising suspicion that pesticides can trigger the disorder. In this study, researchers enrolled 368 longtime residents of California’s Central Valley who had been diagnosed with Parkinson’s and another 341 residents as a control group. Residents who lived within 500 meters of fields sprayed with the fungicide maneb and the herbicide paraquat between 1974 and 1999 had a 75 percent higher risk of developing Parkinson’s, compared with those who lived farther away. In people diagnosed with the disease before they were 60 years old, researchers found earlier exposure increased their risk for the disease as much as four- to sixfold. Exposure to just one type of pesticide increased their risk more than twofold.
“The results confirmed two previous observations from animal studies,” says Beate Ritz, the study’s senior author and professor of epidemiology at the UCLA School of Public Health. “One, that exposure to multiple chemicals may increase the effect of each chemical. That’s important, since humans are often exposed to more than one pesticide in the environment. And second, that the timing of exposure is also important.”