UCLA scientists have found that people whose workplaces were close to fields sprayed with the pesticides ziram, maneb and paraquat -- not just those who live nearby -- are at higher risk of developing Parkinson's disease, reported the Los Angeles Times.
The disease has been reported to occur at high rates among farmers and in rural populations, contributing to the hypothesis that agricultural pesticides may be partially responsible, said a UCLA news release about the study.
The researchers discovered that combined exposure to the three pesticides increased the risk of Parkinson's disease threefold, while combined exposure to ziram and paraquat alone was associated with an 80 percent increase in risk. The results appear in the current online edition of the European Journal of Epidemiology.
Scientists already knew that in animal models and cell cultures, such pesticides trigger a neurodegenerative process that leads to Parkinson's, a disorder of the central nervous system that impairs motor skills, speech and other functions and for which there is no cure.
In the past, data on human exposure had been unavailable, largely because it was too hard to measure an individual's environmental exposure to any specific pesticide.
"This stuff drifts," said Dr. Beate Ritz, senior author and a professor of epidemiology at the UCLA School of Public Health. "It's borne by the wind and can wind up on plants and animals, float into open doorways or kitchen windows — up to several hundred meters from the fields."
Ritz and her colleagues developed a geographic information system-based tool that estimates human exposure to pesticides applied to agricultural crops, according to the distance from fields on which pesticides are sprayed. This GIS tool combined land-use maps and pesticide-use reporting data from the state of California.
From 1998 to 2007, the researchers enrolled 362 people with Parkinson's and 341 controls living in the Central Valley, then obtained historical occupational and residential addresses from all the study participants. Employing their geographic information system model, they estimated ambient exposures to the pesticides ziram, maneb and paraquat, at work and home, from 1974 to 1999.
The data "suggests that the critical window of exposure to toxicants may have occurred years before the onset of motor symptoms, when a diagnosis of Parkinson's is made," the news release said.