Two widely-used pesticides could cause Parkinson’s disease

A mixture of the herbicide paraquat and the fungicide maneb have been found to kill key brain cells known as dopamine neurons, though neither substances can produce the effect when in isolation, according to the research team from the University of Rochester in New York State, USA. According to the researchers, this is one of the first studies to examine the effects of a combination of chemicals with regard to Parkinson’s disease.

Both pesticides are used by farmers on millions of acres in the US alone, with maneb being applied to crops such as potatoes, tomatoes, lettuce and corn, and paraquat being used on corn, soybeans, cotton and fruit.

“The environmental reality is that several of these chemicals are used on the same crops and in the same geographical locations,” said leader of the research team, Deborah Cory-Slechta, who is Professor of Environmental Medicine and Dean for research at the University of Rochester School of Medicine and Dentistry. “You’ve got to get rid of the weeds. Then the insects. Then funguses. These are different chemicals that do different things, but they’re often applied in the same fields.”

“In the real world, we’re exposed to mixtures of chemicals every day,” noted Cory-Slechta. “There are thousands upon thousands of combinations; I think what we have found is the tip of the iceberg. There are a dozen different fungicides related to maneb alone. I don’t think we just happened to pick the right chemicals to see such an effect.” Many pesticides are used in the agriculture-rich areas of the US, including the Midwest, California, Florida and the Northeast, corresponding to the areas of the country where people are more likely to die of Parkinson’s disease.

There is now growing agreement among scientists that the disease may be due to a combination of hereditary and environmental factors, say the researchers. They point out that this is similar to the effect seen with heart disease, where a patient might have both a family history and a sedentary lifestyle, or in cancer, where certain genes may make one prone to develop colon cancer and a poor diet makes the disease even more likely.

Further research is needed into how much people are actually exposed to the pesticides, says Cory-Slechta, pointing out that it is usually not clear exactly how much of a pesticide remains on crops by the time they reach the dinner table.

In November, in was reported in Nature Neuroscience that rotenone, a commonly used organic pesticide, induces the major features of Parkinson’s disease (see related story), and common hydrocarbon solvents have also been linked with the early onset of the disease (see related story).