(Beyond Pesticides, September 16, 2009)
A new study published in the September issue of Archives of Neurology reports that the risk of Parkinsonism doubled with increased occupational exposure to pesticides, including eight agents associated with experimental Parkinsonism. These data add to the growing number of studies that lend credence to a causative role of certain pesticides in neurological disorders.
The study, “Occupation and Risk of Parkinsonism: A Multicenter Case-Control Study,” set out to investigate occupations, specific job tasks, or exposures and risk of parkinsonism in collaboration with eight movement disorders centers in North America including, the Parkinson’s Institute, CA, Department of Neurology, Baylor College of Medicine and Department of Neurology, Beth Israel Medical Center, New York. The investigation focused on five occupations previously suggested as posing an increased risk of Parkinsonism: agriculture, education, healthcare, welding, and mining. This examination of toxicant exposures included solvents and pesticides putatively associated with Parkinsonism. 519 people with Parkinson’s disease and 511 similar people who did not have Parkinson’s were studied.
Overall, the study finds that those whose jobs involve using pesticides are 80 percent more likely to develop the condition. The data reveals that any exposure to the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) almost triples the risk of Parkinsonism compared with individuals who report no exposure to the agent. The herbicide paraquat and the insecticide permethrin are also associated with a more than three-fold increased risk of Parkinson’s disease.
“Occupational pesticide exposure emerges as the most consistent etiologic association with Parkinsonism,” Caroline M. Tanner, MD, PhD, of the Parkinson’s Institute in Sunnyvale, CA. Those who worked in agriculture, education, health care, or welding but who had not been exposed to pesticides through their work were not likely to develop the disease. The researchers note that while they did not look at pesticide exposures such as hobby gardening or residential exposure, “because these exposures may affect many more subjects, future attention is warranted.”
Previous studies have linked pesticide exposure to the onset of Parkinson’s disease (PD), including several published this year alone. A similar study conducted by French researchers found that farmworkers who used insecticides had over a two-fold increase in the risk of PD. Another recent publication found that rural residents who drank contaminated well water had an increased (up to 90 percent) risk of developing PD. Exposure to the pesticides, paraquat and maneb, within 500 meters of an individual’s home, increased the risk of developing Parkinson’s by 75 percent, according to a University of California, Berkeley study. The Institute of Medicine (IOM) found suggestive but limited evidence that exposure to Agent Orange and other herbicides used during the Vietnam War is associated with an increased chance of developing ischemic heart disease and Parkinson’s disease in Vietnam veterans.
Parkinson’s Disease is the second most common neurodegenerative disease affecting more than one million people in the U.S. Parkinson’s disease occurs when nerve cells in the substantia nigra region of the brain are damaged or destroyed and can no longer produce dopamine, a nerve-signaling molecule that helps control muscle movement. All three pesticides in this study; 2,4-D, paraquat and permethrin, have effects on dopaminergic neurons. All three pesticides are currently registered for use in the U.S. 2,4-D is a herbicide most commonly found in many popular lawn care products, while permethrin is an insecticide (synthetic pyrethroid) found in many mosquito products and residential bug sprays. Both chemicals are already linked to cancer, endocrine disruption and other reproductive and developmental effects. Paraquat is a restricted-use pesticide (RUP) used primarily in agriculture.
For more on Parkinson’s disease, please read “Pesticides Trigger Parkinson’s Disease,” a review of published toxicological and epidemiological studies that link exposure to pesticides, as well as gene-pesticide interactions, to Parkinson’s disease and published in Pesticides and You (spring 2008).