Twenty-six farm pesticides were included in the study, although six with widespread use were studied individually to look for connections to Parkinson’s. The goal was to identify specific pesticides that may warrant further investigation.
People drinking well water within 500 meters of a dozen or more of the pesticides had a 66 percent greater rate of Parkinson’s, the study says. Airborne exposure only slightly increased the risk.
The strongest link to the disease was for propargite. Those who had wells near fields sprayed with the chemical had a 90 percent higher risk of having Parkinson’s, according to the study.
About half a million pounds of propargite were sprayed on California crops in 2007, mostly on nuts, corn and grapes, according to the state Department of Pesticide Regulation’s database.
Propargite, sold under the names Omite and Comite, has been used on crops since 1969, but many uses, including the spraying of many fruits and beans, were rescinded by the U.S. Environmental Protection Agency in 1996 due to the cancer risk. The EPA, however, in 2001 approved its continued use on restricted crops and reported that levels in drinking water are below levels of concern, based on the cancer risk.
Other strong links were found for the insecticides methomyl and chlorpyrifos, which increased the risk of Parkinson’s by 67 percent and 87 percent. Chlorpyrifos, sold under the names Dursban and Lorsban, was banned in the United States for residential use in 2001 but is still widely used on cotton, corn, fruit trees and other crops. Methomyl is highly restricted because of its toxicity and is mostly used on alfalfa.
In recent years, scientists have gathered a large amount of human and animal evidence suggesting that exposure to agricultural pesticides, particularly early in life, may play a major role in who gets Parkinson’s.
University of Rochester scientists found that newborn mice exposed to a mix of two commonly used pesticides—maneb and paraquat—developed Parkinson’s symptoms as they aged. Earlier this year, Ritz and colleagues reported similar human results after investigating Central Valley residents exposed to those same two pesticides.
Parkinson’s is caused when nerve cells die in an area of the brain, called the substantia nigra, that produces dopamine. As dopamine decreases, messages from the brain that control how and when the body moves are blocked.
Only a small percentage of those with the disease share a gene or family history of the disease. Experts say the cause of the vast majority is probably due to a combination of genetic and environmental factors.
This article originally ran at Environmental Health News, a news source published by Environmental Health Sciences, a nonprofit media company.