Banned Pesticide May Be Linked to Parkinson's Disease
Effects of dieldrin persist for years after exposure, study suggests
THURSDAY, Sept. 14, 2006 (HealthDay News) -- A now-banned pesticide that still lingers in the environment could be damaging human brain cells and prompting the onset of Parkinson's disease, a new study suggests.
Animal and human cadaver studies appear to link exposure to dieldrin, an organochlorine pesticide, with Parkinson's disease, researchers say.
"We can't say at this point that pesticides cause Parkinson's disease, but we feel it accelerates the process," said Kurt Pennell, an associate professor at the School of Civil and Environmental Engineering at Georgia Institute of Technology, Atlanta.
Pennell and his group report that levels of dieldrin in the autopsied brain tissue of 14 Parkinson's patients were more than three times those of 12 similarly aged people who didn't have the disease.
The researchers also exposed mice to repeated low-level doses of dieldrin to simulate environmental exposure that humans might encounter. The mice's brain tissue showed significant reductions in the uptake of dopamine, a neurotransmitter. And, levels of carbonyls -- a marker of oxidative stress -- were increased substantially in the brain of dieldrin-treated mice, Pennell reported.
"Our research shows that elevated levels of dieldrin are associated with Parkinson's disease in humans, which is supported by an animal model study that correlates low-level exposure to dieldrin with early markers of Parkinson's disease," he explained.
The researchers presented their findings Thursday at the American Chemical Society annual meeting, in San Francisco.
Dieldrin was banned in the 1987 but, Pennell said, "It's very persistent and remains in the ground. It accumulates in lipid tissues, including the brain."
Parkinson's disease, a neurodegenerative disorder, affects an estimated 500,000 people in the United States, and about 50,000 new cases are reported annually. These numbers are expected to increase as the population ages. The disorder appears to be slightly more common in men than women, and the average age of onset is about 60, according to the U.S. National Institute of Neurological Disorders and Stroke.
Prior epidemiological and laboratory studies have suggested a link between chronic exposure to persistent organic pollutants, such as polychlorinated biphenyls (PCBs), and Parkinson's disease.
Dr. Rajesh Pahwa is director of the Parkinson Disease and Movement Disorder Center at the University of Kansas Medical Center, in Kansas City. He said that while the study isn't "major news, it is interesting in that it shows postmortem Parkinson's disease patients' brains had higher levels of pesticide compared to normal controls. And this study has confirmed other work correlating pesticide exposure with the illness."
But, Pahwa added, "This is a small [study] and questions remain. For example, were the Parkinson's brains more exposed to these chemicals or were the Parkinson's patients unable to clear or metabolize the dieldrin?"
Pahwa suggested that the causes of Parkinson's are most likely complex, and may be due to a combination of genetic and environmental factors. "Maybe these studies could lead us to a biomarker for the disease or for people who are being exposed to the disease," he said.
Pennell said, "It is hard to say that exposure to dieldrin is causal, but as people live longer they're more likely to get Parkinson's." That means exposure becomes more relevant. "Baby boomers could have been exposed to these chemicals before they were banned and now as they age, we could see more disease."
Dieldrin and other banned pesticides should dissipate in the environment during the next few decades and become less of a factor in the development of Parkinson's disease, said study researcher Gary Miller, an associate professor of environmental and occupational health at Emory University.
"Today, people are being exposed to much lower levels of pesticides than people were 30 or 40 years ago," Miller said in a prepared statement. "I would predict that over the course of the next several decades that we will see a decrease in the incidence of Parkinson's disease."
For more on the possible link between pesticides and Parkinson's disease, visit the Harvard School of Public Health.