Pesticide Exposure Near Workplace Linked to Parkinson’s Disease Risk

(Beyond Pesticides, May 31, 2011)

A study has found that people whose workplaces were close to fields sprayed with chemicals, not just those who live nearby, are at higher risk of developing Parkinson’s disease (PD). The pesticide chemicals in question include two fungicides -maneb (in the ethylene bisdithiocarbamate (EDBC) family and ziram (in the dimethylthiocarbamate family)- and the herbicide paraquat that appear to raise the risk of developing the movement disorder.

In a study published in the European Journal of Epidemiology, entitled, “Parkinson’s disease risk from ambient exposure to pesticides,” a team of researchers led by UCLA neurologist Beate Ritz, PhD found that exposures to the trio of pesticides are actually higher in workplaces located near sprayed fields than they were in residences. And the combination of exposure to all three pesticides, which act in different ways to harm brain cells involved in Parkinson’s disease, appears to be cumulative, the team led by Dr. Ritz concludes.

The study found that the combined exposure to pesticides ziram, maneb and paraquat near any workplace increased the risk of Parkinson’s disease threefold, while combined exposure to ziram and paraquat alone was associated with an 80% increase in risk. The researchers estimate exposures to the three chemicals that 703 study participants would have had between 1974 and 1999 while living and working in California’s agriculturally rich Central Valley. Of those, 362 participants already had been diagnosed with Parkinson’s, and the remainder had no sign of the disease. Among participants who had worked for long periods near fields in which all three chemicals were used on crops, rates of Parkinson’s disease are three times higher than among subjects whose exposure is less intensive.

In animal studies conducted as part of the research on agricultural chemicals and Parkinson’s disease, the researchers found that ziram was powerfully destructive to neurons that use the transmitter chemical dopamine to send messages. These brain cells are the ones that die off in regions of the brain that govern motor function, causing the tremors, unsteady gait and difficulty initiating movement that are the hallmarks of Parkinson’s.

“Our estimates of risk for ambient exposure in the workplaces were actually greater than for exposure at residences,” said Dr. Beate Ritz, senior author and a professor of epidemiology at the UCLA School of Public Health. “And, of course, people who both live and work near these fields experience the greatest PD risk. These workplace results give us independent confirmation of our earlier work that focused only on residences, and of the damage these chemicals are doing,” adds Dr. Ritz.

In addition, Dr. Ritz notes that this is the first study finding strong evidence in humans that associates the three chemicals in combination with a greater risk of Parkinson’s than exposure to the individual chemicals alone. Because these pesticides affect different mechanisms leading to cell death, they may act together to increase the risk of developing the disorder: Those exposed to all three experienced the greatest increase in risk.

In the past year, several studies have been published that link Parkinson’s disease to a combination of environmental risk factors such as pesticide exposure and genetic susceptibility. For example, residential exposure to an agricultural application of the fungicide maneb and the herbicide paraquat significantly increases the risk of developing Parkinson’s disease, according to a University of California, Berkeley study. A University of Texas study found a strong correlation between Parkinson’s disease patients and the use of the pesticide rotenone. In addition, Duke University and University of Miami researchers studying related individuals who share environmental and genetic backgrounds found a significant association between Parkinson’s disease and use of herbicides and insecticides, such as organochlorines and organophosphates. Farmworkers have nearly double the risk for the disease if exposed to pesticides, with a dose-effect for the number of years of exposure.

Source: LA Times