Excerpt: Scientists have shown that the
combination of two widely used agricultural pesticides-but neither
one alone-creates in mice the exact pattern of brain damage that
doctors see in patients with Parkinson's disease. The research
offers the most compelling evidence yet that everyday
environmental factors may play a role in the development of the
disease.
The latest findings of the team led by Deborah Cory-Slechta,
Ph.D., professor of environmental medicine and dean for research
at the University of Rochester School of Medicine and Dentistry,
appear in the Dec. 15 issue of the Journal of Neuroscience. The
scientists caution that more studies are necessary to explain the
link, since it's probable that many factors contribute to a
complex disease like Parkinson's, and they say it's unlikely that
the pesticides on their own actually cause the disease.
Cory-Slechta's team studied the effects of a mixture of two
very common agrichemicals, the herbicide paraquat and the
fungicide maneb. Each is used by farmers on millions of acres in
the United States alone: Maneb is applied widely on such crops as
potatoes, tomatoes, lettuce and corn, and paraquat is used on
corn, soybeans, cotton, fruit, and a variety of other products. In
the experiment, mice exposed to either one had little or no brain
damage, but mice exposed to both share a significant trait with
people in the very early stages of the disease: Though they appear
healthy, key brain cells known as dopamine neurons are dying. The
mice exposed to the mixture carried nearly all of the molecular
hallmarks of Parkinson's disease as seen in humans.
"The environmental reality is that several of these
chemicals are used on the same crops and in the same geographical
locations. 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," says
Cory-Slechta, who was joined in the research by graduate student
Mona Thiruchelvam and faculty members Eric Richfield, Raymond
Baggs, and A. William Tank.
The study is one of the first to examine the effects of such
chemicals in tandem. Cory-Slechta notes that current regulations
and determinations of safety levels are usually based on the
effects of single chemicals. "In the real world, we're exposed to
mixtures of chemicals every day. There are thousands upon
thousands of combinations; I think what we have found is the tip
of the iceberg," she says. "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."
Maneb, paraquat, and many other pesticides are used in the
same agriculture-rich areas of the country, including the Midwest,
California, Florida and the Northeast. The map of their use
mirrors areas of the country where people are more likely to die
of Parkinson's disease.
Several epidemiological studies have hinted at a role for
pesticides in the development of the disease. Studies have found
that farmers, people who live in rural areas, and people who drink
well water are more likely to have the disease than people who
don't. In addition, just last month, scientists at Emory
University presented evidence that rats given a steady dose of the
natural pesticide rotenone, used on home-grown fruits and
vegetables, develop Parkinson's-like symptoms. Cory-Slechta's
study, which used much lower levels of chemicals than the Emory
research, is the first to link a combination of more widely used
pesticides to the disease.
"No one has looked at the effects of studying together some
of these compounds that, taken by themselves, have little effect,"
says Cory-Slechta. "This has enormous implications." (...)
