Organophosphate (OP) insecticide use has decreased as pyrethroid and other insecticide use has increased, particularly in urban areas. Most recently, chlorpyrifos is being phased out in California in 2020, following the phase-out of diazinon for residential use in 2001 and chlorpyrifos for residential use in 2005. Many OPs are still used, but detections at SPoT sites have been reduced, and current concentrations are generally well below toxicity thresholds. Some early SPoT sediments from some agriculturally-influenced sites contained chlorpyrifos at concentrations that could have contributed to toxicity (Phillips et al. 2017), but further measurements of OPs were suspended after 2017 due to minimal detections and insufficient data to calculate trends. There were not enough data points to calculate statewide trends for chlorpyrifos, diazinon and malathion, and there were only three sites that had enough data points to calculate individual site trends for chlorpyrifos. All of these sites exhibited either stable trends or no trend.
Phillips BM, Anderson BS, Siegler K, Voorhees JP, Tadesse D, Weber L, Breuer R. 2017. Spatial and Temporal Trends in Chemical Contamination and Toxicity Relative to Land Use in California Watersheds: Stream Pollution Trends (SPoT) Monitoring Program. Fourth Report - Seven-Year Trends 2008-2014. California State Water Resources Control Board, Sacramento, CA.