Historical trends analysis of 2004 to 2009 toxicity and pesticide data for California's central valley.

The goals of this study were to conduct temporal trends analysis of 2004-2009 toxicity and pesticide data sets for four Central Valley Water Quality Coalitions in California. The general conclusions from analysis of 6 years of toxicity and pesticide data from these Central Valley Coalitions is that a significant decline has occurred with Ceriodaphnia toxicity, diazinon concentrations and chlorpyrifos concentrations. There was no data to support a significant increase in toxicity or pesticide concentrations from any of the data sets analyzed from 2004 to 2009. In addition, the percent of diazinon and chlorpyrifos samples exceeding water quality objectives of these organophosphate insecticides has also declined significantly from 2004 to 2009. Interpretation of all toxicity and pesticide data used in this analysis within a "weight of evidence context" suggests that water quality conditions have generally improved in the Central Valley Region of California from 2004 to 2009.