Division of Agriculture and Natural Resources
University of California
Division of Agriculture and Natural Resources

Santa Maria farmers and farmworkers assist in UC pesticide-exposure research

Farmworkers harvest strawberries at DB Specialty Farms in Santa Maria.
A group of Santa Maria farmworkers has volunteered to participate in a UC study to determine whether they are exposed to hazardous pesticide residues when harvesting strawberries.

The study is led by Robert Krieger, UC Cooperative Extension specialist in the Department of Entomology at UC Riverside. Krieger is an expert in environmental and occupational toxicology.

This summer, Krieger and a team of researchers spent nearly three weeks in Santa Maria with workers at DB Specialty Farms. The workers wear gloves as they pick strawberries. Before each break, their gloves are collected and frozen for later lab analysis.

“We’ve found that pesticides are transferred to the gloves during normal work and we’re measuring the amounts that are transferred in hopes that we can use it to measure total exposure,” Krieger said. “The real question is how much exposure occurs, how much is OK, and how little occurs under normal conditions of use.”

The team is also collecting samples of strawberries harvested by the workers and samples of leaves.

In order to understand uptake and excretion, the workers are asked to collect urine for 24-hour periods after working in sprayed fields. To be certain any sign of pesticides in the urine came from work exposure, the researchers have also collected 24-hour urine samples from spouses or roommates of the field workers to assess dietary or home exposure.

“The levels of exposure are determined by how much is applied, how much remains on the crop and how much is transferred to people. We’ve independently measured those and came up with an assessment of how much a person is exposed to during their normal work,” Krieger said.

The research focuses on two pesticides: the organophosphate malathion and the pyrethroid fenpropathrin. After the pesticides are applied, there is a three-day waiting period before harvest gets under way. In the project, as soon as the workers are back in the field, the monitoring begins.

Studies that Krieger has conducted over the past 18 years show that low, safe levels of pesticide are absorbed and rapidly excreted by harvesters. Breakdown products of the pesticides – parts of the pesticide molecule that are not toxic – can be measured in the urine, but it is not known whether the pesticide broke down on the plant, before the workers were exposed, or if the workers’ metabolism broke down the pesticides.

“Those breakdown products are not toxic, but if they are absorbed, they will appear in the urine and we can’t tell whether a plant made it or a person made it and that complicates our analysis and that’s one of the new areas that we’re investigating in 2012,” Krieger said.

By comparing the gloves, fruit, leaves and urine and using sophisticated metabolic chemistry in the laboratory analyses, the researchers will be able to reconstruct how much exposure there was during the work day.

If the research concludes that analyzing gloves is a useful way to measure worker exposure, gloves could become an important tool for farmers and regulators. Another probable area of impact from the study is in verifying the levels of exposure, which the researchers are finding to be very low.

“These workers have very low levels of pesticide exposure. And in fact, they’re the best-studied workers with respect to pesticide exposure in agriculture,” Krieger said. “That gives us confidence that the exposure is not having a health impact.”

Definitive results from the August study are expected in about six months.

The research program has been sponsored by strawberry growers of the California Strawberry Commission and the Personal Chemical Exposure Program, UC Riverside. The current Santa Maria research is possible by the involvement of DB Specialty Farms and Safari Farms of Santa Maria, and PrimusLabs.

The research was approved by the Institutional Review Board of UC Riverside and the California Environmental Protection Agency. All the participation is voluntary and the farmworkers and their spouses or roommates are compensated for the inconvenience of urine collection. They receive $25 for each 24-hour collection and a $100 bonus for completing all 10 urine collections.

In addition to the extra pay, the study volunteers benefit by helping improve pesticide safety for themselves and their colleagues.

“These workers are doing a service to other workers by allowing us to measure the amount of exposure that occurs during normal work,” Krieger said.

View video of the on-farm research below:

Posted on Thursday, August 23, 2012 at 11:24 AM

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