HEALTHY FIELDS, SICK WATER: Pesticides implicated in Parkinson's Disease are believed to travel from farms to humans via private wells.
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Rural residents who drink water from private wells are much more likely to have Parkinson’s disease, a finding that bolsters theories that farm pesticides may be partially to blame, according to a new California study.

Nearly one million people in the United States--one of every 300--have the incurable neurological disease. Beginning with a slight tremor, Parkinson’s often progresses to severe muscle control problems that leave patients struggling to walk and talk.

Over the past few years, a growing body of evidence has led many experts to suspect that pesticides can attack developing brains, perhaps in the womb or infancy, leading to neurological diseases later in life. Many insecticides widely used on farms are potent neurotoxins, and lab animals exposed to mixes of them develop Parkinson’s symptoms. In addition, several previous studies of farmers and rural residents have reported a link.

The new study of more than 700 people in California’s Central Valley found that those who likely consumed contaminated private well water had a higher rate of Parkinson’s.

The risk was as much as 90 percent higher for those who had private wells near fields sprayed with the widely used insecticides propargite or chlorpyrifos.

People with Parkinson’s “were more likely to have consumed private well water, and had consumed it on average 4.3 years longer” than those who did not have the disease, said the scientists, led by UCLA epidemiology professor Beate Ritz, in their study published online in the journal Environmental Health Perspectives.

Unlike municipal water supplies, private wells are largely unregulated and are not monitored for contaminants. Many are dug at shallow depths of less than 20 yards, and some of the crop chemicals used to kill pests and weeds can seep into ground water.

The study participants lived in Fresno, Kern and Tulare counties—the heart of California’s farm belt. About 17 percent reported drinking private well water during the study period from 1974 through 1999.

Previous studies have reported connections between Parkinson’s and consumption of rural well water and pesticide use. The UCLA research, however, is the first to examine people’s proximity to specific chemicals and estimate their exposure. Incorporating a geographic information system and land use maps, the researchers based their analysis on California’s pesticide use records.

A weakness of the research is that the scientists do not know exactly what each person in the study was exposed to because private wells are not tested. Close proximity to sprayed fields does not necessarily mean their wells were contaminated.

The UCLA team examined state records identifying where pesticides were used between 1974 and 1999. They then compared the address of each participant in the study to those records.  From that, they estimated each person’s exposure via the air and the water based on how much pesticide was used within 500 meters of their homes.   

Jonathan Chevrier, a University of California at Berkeley postdoctoral researcher in epidemiology who did not participate in the research, said the new effort “is an interesting study” that “goes further than prior research” in connecting pesticides to Parkinson’s.

Most other studies had no exposure information at all, while the UCLA scientists tapped into the historical data, which Chevrier called “a major strength.” Nevertheless, he added, “it is important to note that the authors did not measure the water concentration of pesticides or determine the amount of well water participants consumed.”