Posted on February 19, 2016 · Posted in Drift, Risk Assessment

Multiple exposures to different pesticide chemicals are common and arise from use of pesticide products comprised of mixtures of active and other ingredients, as well as co-application of different pesticide products. Interactive effects of chemicals range from additive effects (where the toxicity is simply the sum  of the toxicity of the two chemicals) to antagonistic effects (where one chemical is detoxified and excreted more quickly in the presence of another) to synergistic effects (where one chemical enhances the toxicity of another). Such interactive effects are well-studied in the world of pharmaceuticals, but knowledge of interactions of pesticide chemicals is sorely lacking because the regulatory authorities conduct risk assessments  assuming exposure to only a single chemical.

PRI has been working with the UCLA Sustainable Technology and Policy Program (STPP) to evaluate what is known about interactive effects and make recommendations for changes in the regulatory system to account for these exposures. The resulting report, Exposure and Interaction: The Potential Health Impacts of Using Multiple Pesticides, explores the issue of multiple pesticide exposures through a case study of three commonly used pesticides in California, chloropicrin, 1,3-dichloropropene (Telone®), and metam sodium.

Exposure and Interaction

Fumigant pesticides are highly drift-prone because they are gaseous chemicals (or nearly so) at ambient temperatures and applied at high application rates (50-400 lbs/acre). Primarily used for strawberries, carrots, tomatoes, orchards, and vineyards, fumigants are injected into the soil prior to planting to kill soil pests. Often two fumigants are co-applied to enhance efficacy. All of the fumigants assessed are carcinogens, and two of the three are strong respiratory irritants, indicating the potential for at least additive effects.  The assessment of the health effects of mixtures is not a part of the current regulatory process, but should be, since these exposures are common.

PRI developed a map of fumigant use in California by week to allow people who live in high fumigant-use areas to assess their potential exposure to multiple fumigants at different times of year. Read the report to find out more.

This work was funded by the Clarence E. Heller Charitable Foundation.

About the Author

Susan Kegley is Principal and CEO of Pesticide Research Institute. She is a PhD Organic chemist with expertise in pesticide chemistry, fate and transport and toxicology of organic chemicals, and U.S. pesticide regulation.