Pesticide Action Network

By Margaret Reeves

This kind of evidence can't be ignored. Scientists report that the risk of Parkinson’s Disease is significantly greater for individuals with a history of exposure to pesticides. They reached this conclusion after reviewing data from six decades of research.

The results were strongest for exposure to weedkillers and insecticides—not so strong for those pesticides designed to kill disease-causing fungi. And the risk was greatest when exposure was associated with work activities, such as applying pesticides in the field.

Many studies have linked pesticides and Parkinson’s in recent years, including one in 2006 that found individuals who applied pesticides more than 400 days in their lifetime had nearly double the risk of Parkinson’s, compared to those who had applied pesticides for fewer days.

More recently we reported on a study showing that the combination of commonly used pesticides can triple Parkinson's risk, and another identifying the mechanism through which pesticide exposure may trigger onset of the disease.

Strong evidence from population studies

This latest review is significant because it looked at (and compared) a range of population studies.

The three types of studies reviewed include:

1. Case–control studies, in which people with the disease are compared with disease-free individuals that are otherwise similar

2. Cohort studies, which evaluate the risks of acquiring the disease among people disease-free individuals who share other characteristics such as age, occupation or exposure within a defined period

3. Cross-sectional studies, which describe all individuals in a selected population, often used to describe absolute or relative risks of a disease.

One 2009 study in California’s Central Valley showed a link between pesticide-contaminated drinking water and development of Parkinson's. The Central Valley is notorious for having some of the highest rates of pesticide use in the country. Researchers found that high levels of well-water contamination with methomyl, chlorpyrifos and propargite increased the relative risk of Parkinson's by 70–90 percent.

For me, this issue hits close to home. Two members of my immediate family have struggled with Parkinson's. Although my grandmother didn't spend a lifetime on a farm, she did spend a few years. It just makes me wonder—could her disease have been prevented?

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