More Research Links Pesticides to Parkinson’s Disease

(Beyond Pesticides, September 19, 2008)

Adding to the body of epidemiologic evidence linking pesticides to Parkinson’s Disease (PD), a recent study shows a correlation between 100 PD patients and the use of the pesticide rotenone. The study was conducted by physicians and researchers at The University of Texas Health Science Center at Tyler (UTHSCT) and an East Texas Medical Center physician. The study’s lead author is Aman Dhillon, MD, MS, assistant professor of occupational and environmental medicine at UTHSCT.

Rotenone is highly toxic to fish and insects, but mildly toxic to warm-blooded animals and humans. It is made from the roots of tropical plants and is used in home gardens and in fisheries management to remove unwanted fish species, said Jeffrey Levin, MD, MSPH, chair of UTHSCT’s Department of Occupational Health Sciences. Dr. Levin is a co-author of the study, published recently in the peer-reviewed Journal of Agromedicine.

A total of 184 people participated in the study: 100 had Parkinson’s disease and 84 did not, though they had other neurological disorders. All were patients of George M. Plotkin, MD, Ph.D., a neurologist with a special interest in Parkinson’s disease. Dr. Plotkin, medical director of the ETMC Movement Disorder Center, treats about 800 patients with Parkinson’s disease. He is a co-author of the study and also a clinical associate professor in UTHSCT’s Department of Occupational Health Sciences. “In this study, people with Parkinson’s disease were 10 times more likely to have used rotenone than individuals in the control group,” Dr. Levin said.

Parkinson’s is a neurodegenerative syndrome, affecting over 1.5 million people nationally, Dr. Plotkin said. There’s a higher incidence of Parkinson’s in certain industries, including farming and petroleum. Because Parkinson’s was first described at the peak of the Industrial Revolution, there has always been a suspicion that it is an “industrial disease,” reflecting the exposure history of those who contract it, he added.

“While epidemiologists have looked at a number of areas in the United States, this study is the first detailed account of exposure history in Parkinson’s patients, in East Texas, as compared with age-matched controls,” Dr. Plotkin said.

“The results are rather striking, and reflect our notion that environmental agents may well affect individuals predisposed to developing the disease. Future research will need to focus on determining how this happens, with the hope that more careful management of hazardous materials will reduce the chances of Parkinson’s disease developing in persons at risk,” he said.

Dr. Plotkin’s patients completed a 17-page questionnaire designed by study investigators about their everyday life, work history, and habits, as well as their current and past use of various pesticides. Each individual in the study was at least 50 years old and had lived in Northeast Texas for at least five years. If they had Parkinson’s, they had first been diagnosed with it at least five years ago.

Though pesticide use has been linked to Parkinson’s disease, this is one of the first studies to show a possible correlation between a specific pesticide, rotenone, and Parkinson’s disease in humans, Dr. Dhillon said. The study also revealed a weaker link between other pesticides and Parkinson’s disease. For example, people with Parkinson’s disease were twice as likely to have used pesticides with chlorpyrifos, such as Dursban, than individuals in the control group. Dursban and similar pesticides were banned by the U.S. Environmental Protection Agency in 2000 because of their potential to harm the developing brain and nervous system in children.

“It seems to be a combination of genes and environment that causes the development of Parkinson’s disease. This study examined one of many factors that may cause Parkinson’s,” Dr. Levin said. “Part of the role of public health is to identify the risk factors for disease. If we can identify them, then people can avoid risk factors such as rotenone and hopefully prevent the disease.”

Rotenone has been the subject of some debate before, including its use as a pesticide in California and being linked in previous studies to Parkinson’s. It is also toxic to nontarget species and further research could tie it more closely with Parkinson’s than it already is.

“The next step is to verify the results of this study. We think there’s potential to do a broader study examining more risk factors, with more individuals,” Dr. Levin said.