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Pathways to pesticide exposure

PHS project tracks paths of pesticide residue among highly exposed agricultural workers in Yakima Valley

March 4, 2004
Farm workers

Farm workers — like this woman in the Yakima Valley — who thin orchards are at greater risk for pesticide exposure than other orchard workers.

Photo courtesy of Dr. Gloria Coronado

Agricultural workers who perform thinning-removing young buds from or chard trees to increase the size of the remaining fruit-face a greater likelihood of pesticide exposure than other farm workers, according to a Public Health Sciences Division study published in the February issue of Environmental Health Perspectives.

The researchers found that workers who thinned orchards were more likely to have detectable levels of pesticides in their house and vehicle dust as compared to agricultural workers who did not perform orchard thinning. The study also found children of thinners are more likely to have detectable levels of pesticide metabolites in their urine than do children of non-thinners. These findings support the theory that agricultural workers may track home pesticides on their clothing and shoes.

"Most previous pesticide-exposure research on farm workers has focused on pesticide handlers, such as pesticide mixers, loaders and sprayers, but this study suggests that more research is needed regarding exposure patterns among other types of farm workers as well," said Dr. Gloria Coronado, lead author and staff scientist in the Cancer Prevention Program.

The study revealed that approximately 20 percent more thinners had pesticide residue in their home and vehicle dust as compared to non-thinners. The researchers also found the presence of a dimethyl urinary pesticide metabolite, called DMTP, more often in children of thinners (10 percent more) than in children of non-thinners.

Orchard thinners may be at higher risk for pesticide exposure because thinning usually takes place in the spring, when crops are sprayed to prevent pests.

Such workers also have substantial physical contact with fruits, leaves, twigs and branches that may contain pesticide residues. In addition, unlike pesticide handlers, thinners are not required by the U.S. Environmental Protection Agency to use protective equipment or undergo safety training.

"Unfortunately, we do not know the extent to which ongoing, low-level exposure to pesticides leads to adverse health consequences," said project leader Dr. Beti Thompson, an investigator in the PHS Division. "However, knowing exposure pathways helps us plan interventions to reduce exposure risk, which is particularly important for young children."

Tiny targets

Children are uniquely susceptible to home-pesticide exposure because they spend greater amounts of time on carpets and floors, often wear minimal clothing during the summer spray season (increasing their likelihood of skin exposure) and engage in hand-to-mouth behavior (increasing their likelihood of ingesting pesticides).

"Children are not small adults," Thompson said. "With less-developed immune systems than adults, children may be less able to clear pesticides from their bodies."

The project, conducted in eastern Washington's Lower Yakima Valley, involved 571 farm workers in 24 communities and labor camps who were interviewed about their pesticide-exposure patterns. Dust samples from households and vehicles of 213 randomly selected study participants were check-ed for the presence of six organophosphorous pesticides. Urine samples from these workers and family members (one adult and one child per household) were analyzed for the presence of five pesticide by-products.

Thinning was the second-most common farm task reported among those surveyed, accounting for about 64 percent of the workers. Those who worked directly with pesticides accounted for about 20 percent of those studied.

Larkin Strong and Ilda Islas in the PHS Division and Dr. William Griffith, UW Department of Environmental Health co-authored the analysis, which was funded by the EPA and the National Institute of Environmental Health Sciences.

The study is part of the University of Washington-based Center for Child Environmental Health Risks Research led by Dr. Elaine Faustman, professor of environmental and occupational health sciences at the UW School of Public Health and Community Medicine. It is the first study of its kind to search for evidence of a possible take-home pathway of pesticides, which exposes children to pesticide residues from their agricultural-worker parents.

Support for hypothesis

Previous reports from this project showed a significant association between urinary pesticide-metabolite levels in farm workers and children living in the same home. The reports associated the evidence of pesticide exposure in children with concentrations of various pesticide chemicals in house dust. These findings lend strong support for the hypothesis that a take-home pathway of pesticide exposure exists between agricultural workers and members of their households.

A local community-advisory board has worked with the researchers on all aspects of this ongoing project, from identifying questions for the pesticide-exposure surveys and helping to develop strategies for reducing pesticide exposure to communicating information about the project to agricultural workers throughout eastern Washington.

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