Effect of California’s 2020 Chlorpyrifos Ban on Urinary Biomarkers of Pesticide Exposure in Agricultural Communities

In 2020, California banned the sale and agricultural use of chlorpyrifos, an organophosphate pesticide (OP) associated with neurotoxicity and other adverse health outcomes. We primarily assessed changes in chlorpyrifos associated with this policy and secondarily explored how other OP exposures changed. The participants were from California’s Central Valley, 18 years or older, and English- or Spanish-speaking. The surveys and urine samples were collected pre-ban (December 2020) and post-ban (February–April 2022). The urine samples were analyzed for a chlorpyrifos-specific metabolite (TCPy), six dialkyl phosphates (DEP, DMTP, DETP, DMDTP, DMP, DEDTP), and total DE and DM. The pre- and post-ban metabolite concentrations were compared via Wilcoxon signed-rank tests and natural log-transformed paired differences in linear mixed effects regression, adjusted for covariates. Forty-nine participants had repeated biomarker data. The mean age of the study population was 46.8 years (SD: 16), 61% female, 67% Spanish-speaking, 100% Hispanic/Latino(a), and 47% had less than a high school education. Six urinary metabolites (TCPy, DEP, DMP, DMTP, total DE and total DM) had sufficient variation for further analysis, while DMDTP, DEDTP, and DETP were undetected. The paired differences in adjusted models showed statistically significant increases in TCPy and DMP associated with the policy change (e.g., TCPy estimated ratio of geometric means: 4.53 (95% CI 2.66, 7.69)) Reductions in metabolites of chlorpyrifos exposure were not observed following California’s chlorpyrifos ban, suggesting ongoing exposure to chlorpyrifos from other sources.