Temporal trends analysis of 2004 to 2012 toxicity and pesticide data for California's Central Valley water quality coalitions.

This study was designed to assess temporal trends of 2004-2012 toxicity data from three water column tests, one sediment test and concentrations of three pesticides from four Central Valley Water Quality Coalitions in California. Major conclusions based on this extensive toxicity and pesticide data from 150 mainstem and tributary sites showed a significant decline in toxicity over 9 years from Ceriodaphnia dubia water column toxicity tests and a significant decline in toxicity from three water column and one sediment toxicity test combined. The organophosphate insecticides diazinon and chlorpyrifos also showed a significant decline in concentrations from 2004 to 2012 and also a significant decline in the percent of samples that exceeded water quality objectives for both of these insecticides. The analysis conducted did not show any cases of either increased toxicity or pesticide concentrations over the 9-year period. The final conclusion from this analysis is that water quality conditions in the Central Valley Region of California, as measured by the toxicity and pesticide data from this study, have improved from 2004 to 2012.