Center News

Dangerous path of pesticides

March 6, 2003
Miguel Juarez and Lower Yakima Valley farm worker

Miguel Juarez (left), program assistant for the pesticide study, discusses the "take-home" pathway with a Lower Yakima Valley farm worker. The study found significant levels of pesticide byproducts in the urine of farm workers' children.

Photo courtesy Dr. Beti Thompson

Farmers in Washington's Lower Yakima Valley bring their work home with them - literally.

A recent Public Health Sciences Division study found significant levels of pesticide by-products in the urine of farm workers' children, suggesting that parents exposed to contaminants in the field track these chemical agents into the home.

Led by Dr. Beti Thompson and colleagues in PHS, the study revealed a high association between the level of pesticide metabolites in farm workers' homes and concentrations of pesticide breakdown products in children's urine. They also found a high association between contaminated dust in farmworker vehicles and in farm workers' homes.

In addition, researchers found that field workers reported high levels of exposure to pesticides while harvesting and thinning crops and that many employers did not provide adequate resources for hand washing.

Published in the January edition of the Journal of Occupational and Environmental Medicine, the study is the first to look for evidence to support the existence of a long suspected "take-home" pathway for the transmission of pesticides from the field into the home. The research was conducted as the baseline component of a project that will assess the effect of an educational intervention strategy on reducing levels of pesticide exposure among farm workers and their families.

Environmental-agency funding

The overall five-year study is funded by the National Institute of Environmental Health Science (NIEHS) and the Environmental Protection Agency (EPA) and is a component of the Center for Child Environmental Health at the University of Washington, headed by Dr. Elaine Faustman.

Dr. Richard Fenske and colleagues at UW School of Public Health and Community Medicine performed the chemical analysis of dust and urine samples.

"The findings are disturbing, particularly because we don't really know what levels of exposure to organophosphorus pesticides could lead to harmful effects on children's health," Thompson said.

"Through ongoing and future studies, we hope to better assess the effects of these chemicals on children and to implement interventions that will protect the children and their families from exposure to pesticides."

Because of their higher rates of metabolism, less mature immune systems and different hand-to-mouth behaviors compared to adults, children are likely to be particularly susceptible to potential harmful effects - including cancer and developmental and neurological defects - of exposure to toxic chemicals. The EPA sets exposure thresholds for potential toxicants, such as pesticides, based on animal studies.

Residents' health concerns

Thompson, who has conducted several cancer-prevention research studies in the Lower Yakima Valley, said that what initially prompted the Fred Hutchinson/UW study were health concerns by residents. The valley is one of the nation's primary fruit-growing regions and has a population that is more than 50 percent Hispanic, including many who are involved in agricultural work.

"As part of a separate research project, we had been conducting focus groups and qualitative research to understand the community," Thompson said. "The issue that would come up again and again was pesticides. Residents wanted to know how pesticides are related to cancer and expressed concern about their health and that of their children.

"At the same time, NIEHS and the EPA began to solicit research proposals for centers for child health. Researchers at the UW wanted to respond to that and contacted us because it required a community intervention component. Once we began to meet, it became clear that the Lower Yakima Valley was an ideal site to initiate a project on pesticide research."

Between June and October 1999, interviewers questioned 571 farm workers - more than 85 percent of whom were Hispanic - in 16 communities and eight labor camps in the Lower Yakima Valley. Interviewers were bilingual community members who were hired and trained by the research project staff. A community advisory board of area residents worked closely with the research team on all aspects of the project, including development of survey questions, planning of the intervention strategy and dissemination of the study's results.

Participants were asked about the type of work they performed, perceived pesticide exposure and protective practices at work and home. Urine samples were collected from an adult and a young child in each home. Also, dust samples were collected from the home and the commuting vehicle.

Although about one third of the respondents handled pesticides, two thirds of the respondents reported that pesticides touched their clothing daily. Among pesticide handlers, 87 percent had access to water for hand washing; 79 percent reported that soap was available for hand washing.

Dust samples were evaluated for six organophosphorus pesticides, and urine samples were analyzed for five metabolites of the pesticides. One such pesticide, azinphosmethyl, was found at relatively high concentrations in house and vehicle dust, suggesting that the vehicle used for travel to and from work carried the chemical, as did the workers themselves. Azinphosmethyl is used more than any other pesticide on apple, cherry and pear crops in Washington state.

High correlation

There was a high correlation between pesticide-metabolite levels - some of which were present at significant levels - in child and adult urine.

Thompson said urine metabolites have not yet been measured for community residents who are not farm workers. Without such measurements, it is difficult to say with certainty whether children can be exposed to pesticides via other sources, such as diet or drift from spraying on fields.

The research team just completed an educational intervention strategy designed to minimize the exposure of farm workers and their families to pesticides. Researchers provided information at community health fairs, in-home "health parties," at schools and in one-on-one encounters in residents' homes. Analysis to assess the effectiveness of the intervention will be completed later this year.

The scientists also plan studies to evaluate the effects of pesticides on children. One proposed study would compare children who are and are not exposed to pesticides to determine whether exposure is associated with developmental delays or neurological impairment.

"The literature is sparse on this," Thompson said. "We're only just beginning to understand the effect of such chemicals on children's health."

Thompson said that residents were not surprised by the results of the baseline analysis.

"Many of the community members said, 'We already know this. Now, what can we do to change this?' We hope that our intervention will make a difference."

Fred Hutchinson Cancer Research Center is a world leader in research to prevent, detect and treat cancer and other life-threatening diseases.