Parkinson's, Dementia, & Mental Health
Risk of Parkinson’s Disease Triples for Those Who
Worked Near Pesticide Spraying
Study first to implicate pesticide ziram, as part
of the problem with fungicide maneb and herbidice paraquat
May 26, 2011 - In April 2009, researchers at UCLA
announced they had discovered a link between Parkinson's disease and two
chemicals commonly sprayed on crops to fight pests. A new study expands
the list of dangerous chemicals and widens the areas where they are
dangerous.
That 2009 epidemiological study didn't examine
farmers who constantly work with pesticides but people who simply lived
near where farm fields were sprayed with the fungicide maneb and
the herbicide paraquat. It found that the risk for Parkinson's
disease for these people increased by 75 percent.
The follow-up study adds two new twists. Once again
the researchers returned to California's fertile Central Valley, and for
the first time have implicated a third pesticide, ziram, in the
pathology of Parkinson's disease.
Second, instead of looking just at whether people
lived near fields that were sprayed, they looked at where people worked,
including teachers, firefighters and clerks who worked near, but not in,
the fields.
They found that the combined exposure to ziram,
maneb and paraquat near any workplace increased the risk of Parkinson's
disease (PD) threefold, while combined exposure to ziram and paraquat
alone was associated with an 80 percent increase in risk.
The results appear in the current online edition of
the European Journal of Epidemiology.
"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."
In addition, Ritz noted, this is the first study
that provides strong evidence in humans that the combination of the
three chemicals confers 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.
"Our results suggest that pesticides affecting
different cellular mechanisms that contribute to dopaminergic neuron
death may act together to increase the risk of PD considerably," said
Ritz, who holds a joint appointment in the UCLA Department of Neurology.
Scientists knew that in animal models and cell
cultures, such pesticides trigger a neurodegenerative process that leads
to Parkinson's, a degenerative disorder of the central nervous system
that often impairs motor skills, speech and other functions and for
which there is no cure. The disease has been reported to occur at high
rates among farmers and in rural populations, contributing to the
hypothesis that agricultural pesticides may be partially responsible.
In the past, data on human exposure had been
unavailable, largely because it had been too hard to measure an
individual's environmental exposure to any specific pesticide.
"This stuff drifts," Ritz said. "It's borne by the
wind and can wind up on plants and animals, float into open doorways or
kitchen windows — up to several hundred meters from the fields."
So several years ago, Ritz and her colleagues
developed a geographic information system–based tool that estimates
human exposure to pesticides applied to agricultural crops, according to
the distance from fields on which pesticides are sprayed. This GIS tool
combined land-use maps and pesticide-use reporting data from the state
of California.
Each pesticide-use record includes the name of the
pesticide's active ingredient, the amount applied, the crop, the acreage
of the field, the application method and the date of application.
From 1998 to 2007, the researchers enrolled 362
people with Parkinson's and 341 controls living in the Central Valley,
then obtained historical occupational and residential addresses from all
the study participants. Employing their geographic information system
model, they estimated ambient exposures to the pesticides ziram, maneb
and paraquat, both at work and home, from 1974 to 1999.
The results reaffirmed what their previous research
had suggested, that the data, "suggests that the critical window of
exposure to toxicants may have occurred years before the onset of motor
symptoms, when a diagnosis of Parkinson's is made."
Knowing that the fungicide ziram is commonly used
in agriculture and suspecting its relationship to Parkinson's, Ritz
turned to her colleague Jeff Bronstein, a UCLA professor of neurology
and co-author of the study, for confirmation.
His lab performed a genetic screen using
genetically modified cells to identify pesticides that inhibit the
breakdown of important proteins such as alpha-synuclein. Ziram was one
of the best inhibitors they identified; they found, in fact, that
synuclein accumulated in dopamine neurons, selectively killing them.
When it was given systemically to rodents, it reproduced many of the
features of Parkinson's disease.
"So the present study clearly demonstrates that
exposure to ziram in humans is associated with a significant increased
risk of developing PD," Bronstein said.
Funding for the study was provided by the National
Institute of Environmental Health Sciences, he National Institute of
Neurological Disorders and Stroke, the U.S. Department of Defense
Prostate Cancer Research Program, and the American Parkinson's Disease
Association.
Other authors included lead author Anthony Wang
(UCLA), Sadie Costello (UC Berkeley) and Myles Cockburn and Xinbo Zhang
(University of Southern California). The authors declare no conflict of
interest.
The UCLA School of Public Health is dedicated to
enhancing the public's health by conducting innovative research;
training future leaders and health professionals; translating research
into policy and practice; and serving local, national and international
communities.
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