People who work near fields sprayed with pesticides face an increased risk for Parkinson's disease, a new study has found.

Not just agricultural workers but teachers, firefighters, clerks and others whose workplaces are near fields in California's Central Valley are at greater risk for the degenerative disorder of the central nervous system, according to researchers from the University of California, Los Angeles.

"This stuff drifts," the study's senior author, Dr. Beate Ritz, an epidemiology professor at the UCLA School of Public Health, said in a university news release. "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."

The study focused on three pesticides used on the fields: the fungicides maneb and ziram and the herbicide paraquat. The researchers estimated the exposure of 703 people who lived or worked in the area over a 25-year span, taking into account how far they were from the fields sprayed with the chemicals. About half of the people in the study had Parkinson's.

The risk for Parkinson's rose threefold for those who worked near fields sprayed with the three pesticides, the study found. Exposure to just ziram and paraquat raised risk by 80 percent. Earlier analysis by the researchers had found a 75 percent jump in risk for people who lived near fields where maneb and paraquat were sprayed.

The findings suggest that the chemicals act together in increasing the risk for Parkinson's, according to the study, published online in the European Journal of Epidemiology.

"Our estimates of risk for ambient exposure in the workplaces were actually greater than for exposure at residences," said Ritz. "And, of course, people who both live and work near these fields experience the greatest ... risk. These workplace results give us independent confirmation of our earlier work that focused only on residences, and of the damage these chemicals are doing."

SOURCE: University of California, Los Angeles, news release, May 26, 2011