Study Highlights Importance of Pesticide Worker Dermal Exposure and Limitations of Measurement Methods

Agricultural pesticide workers are not only exposed to pesticides from inhalation, but also through their skin. The dermal route of exposure to chlorpyrifos, a common agricultural pesticide, contributes substantially to workers’ total exposure, according to researchers from the Johns Hopkins Bloomberg School of Public Health and the U.S. Environmental Protection Agency (EPA), who analyzed agricultural test data provided by pesticide manufacturers. The study authors report that accurate methods for estimating dermal exposure are important because they form the basis for assessing and protecting worker health. The study is published in the current online issue of Annals of Occupational Hygiene.

“Although our study’s findings aren’t unexpected, they highlight the significance of dermal exposure among pesticide workers,” said Laura Geer, the study’s lead author and a PhD student in the Bloomberg School of Public Health’s Department of Environmental Health Sciences.

Geer explained that the EPA requires pesticide manufacturers to evaluate the potential for exposure to pesticide handlers. “Since there is a paucity of such data in the literature, we sought to mine these data. Our study demonstrates their utility and value to answer questions fundamental to dermal exposure and to protecting worker health,” she said. “For example, from these data, we were able to estimate the fraction of pesticide absorbed through the skin based on real-world agricultural worker monitoring.”

The authors analyzed data from five studies, including a total of 80 workers across nine states (Alabama, Virginia, Georgia, Texas, Arizona, Kentucky, Michigan, Florida and Ohio). The participants held a variety of pesticide-related jobs, including preparing pesticide formulations, loading the pesticide into application devices, applying the pesticide and inspecting crops after application.

The researchers found that dermal exposure represents a substantial portion of total exposure, even though exposure levels were found below current occupational health standards and guidelines. For nearly one-half of the workers monitored (34 out of 77) in this study, more chlorpyrifos was absorbed through the skin than was inhaled. The researchers compared methods for estimating worker exposure by comparing residues found on clothing to levels of pesticide metabolites in urine. They observed a substantial difference, indicating that researchers may not be able to precisely evaluate worker exposure using these methods.

This difference in estimates makes it difficult for researchers to reconcile exposure and dose, increasing the uncertainty in assessing worker risk and the development of effective protective strategies. The study authors recommend that additional work and research be done. The authors also note that their study demonstrates that the EPA’s Pesticide Registrant Database offers a unique and valuable resource to researchers for the purpose of improving methods for assessing exposure and protecting worker health. 

“Worker dermal exposure is under-appreciated in the United States. Our study brings to the forefront the potential for workplace chemicals to be absorbed through the skin and the need to develop better methods to assess this exposure, so that ultimately we can prevent it and protect worker health,” said Timothy J. Buckley, PhD, MHS, associate professor in the Bloomberg School of Public Health’s Department of Environmental Health Sciences and the study’s senior author.

The study was supported by the United States Environmental Protection Agency.

L.A. Geer, N. Cardello, J. D. Roberts and T. J. Buckley, from the Johns Hopkins Bloomberg School of Public Health, co-authored the study. Additional co-authors from the U.S. Environmental Protection Agency were M. J. Dellarco, T.J. Leighton and R.P. Zendzian.