Leveraging high spatiotemporal resolution data of pesticides applied to agricultural fields in California to identify toxicity reduction opportunities

Pesticides remain a leading environmental hazard, imperiling aquatic and terrestrial ecosystems. Reducing pesticide toxicity is hampered by the ability to evaluate toxicity over large extents, the spatiotemporal resolution of pesticide use data, the ability to assess cumulative toxicity, and the identification of health/economic contributions of different pesticide application sites. We introduce the Environmental Release Tool, a sub-tool of the Pesticide Mitigation Prioritization Model, to advance these four areas. Using daily pesticide use reports required for agricultural applicators in California, we quantify the applied toxicity of pesticides to fish as well as aquatic invertebrates, nonvascular plants, and vascular plants. With the tool’s ability to quantify applied toxicity for hundreds of pesticides and watersheds simultaneously, we explore the significance of accounting for cumulative applied pesticide toxicity for application sites and watersheds statewide. Our results show that 14 pesticides account for 99.9% of applied toxicity, and 16 of 432 application site types introduce 90% of toxicity for taxa investigated. We also find cumulative applied toxicity within watersheds was significantly greater (p <1.0 E-16) than the maximum impact pesticide for all taxonomic groups, with a mean-annual difference of 460–630%. While cumulative applied toxicity was significant, and sources varied in individual watersheds, the net applied toxicity can be approximated with a short list of active ingredients and site types.