Farming’s use of pesticides and herbicides tied to Parkinson’s risk

Higher disease rates seen in U.S. areas with highest use of these chemicals

Margarida Maia, PhD avatar

by Margarida Maia, PhD |

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People exposed to high levels of the pesticides and herbicides often used in farming have up to a 36% greater risk of Parkinson’s disease than those living in regions with the lowest exposure, a U.S. study reports.

The work, to be presented at the American Academy of Neurology (AAN) annual meeting in mid-April, adds to mounting evidence that exposure to environmental factors increases a person’s risk of developing or dying from Parkinson’s.

“Much more research is needed to determine these relationships and hopefully to inspire others to take steps to lower the risk of disease by reducing the levels of these pesticides,” Brittany Krzyzanowski, PhD, a research assistant professor of neuroepidemiology at Barrow Neurological Institute in Arizona, said in an academy news release.

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Pesticides, other common chemicals being seen as environmental risks

How exactly Parkinson’s develops still is unclear, but an interplay between genetics and environmental factors is thought to be behind the neurodegenerative disease.

Earlier work by Krzyzanowski has shown that breathing fine particulate matter — tiny air pollutant particles like PM2.5 — can place people at a higher risk of Parkinson’s.

For this study, Krzyzanowski reviewed a 2009 Medicare dataset covering more than 21 million people to determine the rate at which Parkinson’s is diagnosed across 10 U.S. regions, grouped by counties. The researcher then looked for a relationship between these rates and the use of 65 pesticides or herbicides.

Previous studies suggested that a number of agricultural chemicals not only increase a person’s risk of developing Parkinson’s, but also the likelihood of disease symptoms progressing faster once diagnosed.

“It’s concerning that previous studies have identified other pesticides and herbicides as potential risk factors for Parkinson’s, and there are hundreds of pesticides that have not yet been studied for any relationship to the disease,” Krzyzanowski said.

Krzyzanowski then geocoded people with Parkinson’s to regions with varied levels of exposure to these chemicals.

High risk particularly tied to heavy exposure to a pesticide, two herbicides

“In the Rocky Mountain and Great Plains region, we identified 14 pesticides associated with Parkinson’s,” she noted, adding that this region covers parts of Colorado, Idaho, Kansas, Montana, Nebraska, Nevada, New Mexico, North Dakota, Oklahoma, South Dakota, Texas, Utah, and Wyoming.

People living in counties with heaviest use of simazine, a herbicide applied to soil to control broadleaf and grass weeds, were 36% more likely to develop Parkinson’s than those in counties with the lowest exposure (411 vs. 380 new cases of Parkinson’s for every 100,000 people).

For the herbicide atrazine, the risk increased by 31% (475 vs. 398 new Parkinson’s cases per 100,000 people) in counties with the highest exposure, and for the insecticide lindane, it rose by 25% (386 vs. 349 new Parkinson’s cases per 100,000 people). Atrazine also is used to control broadleaf grasses and annual weeds, while lindane is used to keep pests away from fruit and vegetable crops and to treat farm animals.

“Our methods enabled us to identify parts of the nation where there was a relationship between most pesticides and Parkinson’s disease and subsequently pinpoint where the relationship was strongest so we could explore specific pesticides in that region,” Krzyzanowski said.

Findings were unchanged when the researchers considered other factors that could affect Parkinson’s risk, such as air pollution.

They noted that their study was limited by needing to rely on county-level estimates of pesticide or herbicide exposure, rather than person-level data.

The work was supported by the Michael J. Fox Foundation for Parkinson’s Research.