Dissolved Pesticides in Weekly Water Samples from the NAWQA California Stream Quality Assessment (2017)

Dissolved pesticides were measured in weekly water samples from 85 wadeable streams in Central Coastal California over a variable six-week period during March–May, 2017, as part of the California Stream Quality Assessment (CSQA) study conducted by the U.S. Geological Survey's (USGS) Regional Stream-Quality Assessment (RSQA) Project. The 85 streams consisted of 40 urban sites (5–100% urban land in the lower basin), 9 agricultural sites, 24 mixed land-use sites, and 12 undeveloped sites. Water samples were filtered (0.7 micrometers) and analyzed for 253 pesticide compounds by direct-injection liquid chromatography with tandem mass-spectrometry (LC-MS/MS). Two similar LC-MS/MS methods were used: a broad-spectrum (223 compounds) method in use since 2012 and a newly developed method for 30 new-generation fungicides and diamide and neonicotinoid insecticides. This Data Release provides sampling-site locations, analyte information, concentration data for pesticide compounds in environmental weekly water samples, quality-control data for the new method (to supplement previously published quality control data for the standard method), aquatic-life benchmark and Pesticide Toxicity Index toxicity concentration values that were used to assess potential toxicity, estimates of agricultural and nonagricultural pesticide-use data, and streamflow data for gaged sites, in support of the journal article, “New-generation pesticides are prevalent in California’s Central Coast streams,” by Sandstrom, M.W., Nowell, L.H., Mahler, B.J., and Van Metre, P.C.