Study GW17/GW17A: Groundwater Protection List Monitoring for Imidacloprid
Abstract
Groundwater Protection Program (GWPP) staff from the California Department of Pesticide Regulation’s (DPR) Environmental Monitoring Branch (EM) sampled 69 wells between June 2017 (GW17 Study) and November 2019 (GW17a Study) to determine if agricultural uses of imidacloprid resulted in contamination of groundwater. For this study, wells were sampled in moderate to high use sections of Fresno, Kern, Madera, Monterey, San Luis Obispo, Santa Barbara, and Tulare counties. Imidacloprid was detected above the reporting limit in five wells located in Fresno, Santa Barbara, and Tulare counties, with concentrations ranging from 0.054 to 0.124 parts per billion (ppb), while trace concentrations (between the reporting limit and method detection limit) were detected in nine wells located in Fresno, Monterey, Santa Barbara, and Tulare counties. Fifty-five of the wells were also analyzed for imidacloprid degradates, and since there were no detections, the degradates were not analyzed for in subsequent samples. Several other pesticides, mostly 6800(a)-listed pesticides or degradates, were also detected in the counties monitored. All pesticides detected in this study were below the established drinking water quality standards.