Chlorpyrifos-treated crops in the vicinity of surface water contamination in the San Joaquin Valley, California, USA.

Due to frequent contamination of streams in the San Joaquin Valley, California, USA, with the insecticide chlorpyrifos, researchers are working to identify crop-specific management practices that will reduce the offsite movement of this compound into surface waters. To guide this effort, crops treated with chlorpyrifos in the vicinity of contaminated streams were identified; walnut, alfalfa, and almond were the primary crops identified. Use was higher on walnut and almond, but due to irrigation practices offsite movement in surface runoff may be more likely from alfalfa. Based on these findings, development of management practices to reduce off-site movement of chlorpyrifos in irrigation runoff from treated alfalfa fields is recommended.

Detections of the neonicotinoid insecticide imidacloprid in surface waters of three agricultural regions of California, USA, 2010-2011.

Seventy-five surface water samples were collected from three agricultural regions of California and analyzed for the neonicotinoid insecticide imidacloprid. Samples were collected during California's relatively dry-weather irrigation seasons in 2010 and 2011. Imidacloprid was detected in 67 samples (89%); concentrations exceeded the United States Environmental Protection Agency's chronic invertebrate Aquatic Life Benchmark of 1.05 µg/L in 14 samples (19%). Concentrations were also frequently greater than similar toxicity guidelines developed for use in Europe and Canada. The results indicate that imidacloprid commonly moves offsite and contaminates surface waters at concentrations that could harm aquatic organisms following use under irrigated agriculture conditions in California.

Analysis of diazinon agricultural use in regions of frequent surface water detections in California, USA.

For five agricultural regions in California, USA, detection frequency of diazinon in surface water and several aspects of its use were determined from recent data (2005-2010): application method, product formulation and primary crops. Diazinon detection frequencies ranged from 10% to 91%. Application method and product formulations used were similar in all regions. The primary crops treated varied from lettuce (77%) in the regions with highest detections frequencies to tree crops (53%) in those with the lowest. The results suggest that the variation in diazinon detection frequencies likely was not due to the application method or formulation type.

Analysis of chlorpyrifos agricultural use in regions of frequent surface water detections in California, USA.

Chlorpyrifos is a common surface water contaminant in California, USA. We evaluated five years of chlorpyrifos use and surface water monitoring data in California's principal agricultural regions. Imperial County and three central coastal regions accounted for only 10% of chlorpyrifos statewide use, but displayed consistently high aquatic benchmark exceedances (13.2%-57.1%). In contrast, 90% of use occurred in Central Valley regions where only 0.6%-6.5% of samples exceeded aquatic benchmarks. Differences among regions are attributable to crop type, use intensity, irrigation practices and monthly application patterns. Application method did not appear to be a factor.