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(P887) Partitioning of sediment-associated pesticides in California rivers.
LeBlanc, Lawrence*,1, Gunnarsson, Jonas2, Kuivila, Kathryn1, Weston, Donald2, Schroeder, Roy3, 1 U.S. Geological Survey, Sacramento, CA, USA2 University of California at Berkeley, Berkeley, CA, USA3 U.S. Geological Survey, San Diego, CA
ABSTRACT- Currently used hydrophilic pesticides have been detected on suspended sediments from the San Francisco Bay Estuary at concentrations above equilibrium with surrounding water in previous studies by the USGS San Francisco Bay Toxics Project. Modifications to our published sediment-associated pesticides (SAPs) method, particularly methods of extract cleanup, have lowered detection limits. This, along with an increase in the number of compounds that can be identified, has allowed more detailed investigations of partitioning and transport of SAPs. Ongoing studies are examining the partitioning of pesticides between sediments and water in two different agricultural regions in California. In northern California, water, and suspended and bedload sediments, were collected from the San Joaquin, Sacramento, and Napa Rivers after rainfall runoff events to capture recently transported material from upstream agricultural fields. Samples were also collected from the same sites in the summer when there is no storm runoff, and therefore when suspended sediments have a longer residence time in the system. In the Imperial Valley in southern California, these same matrices were collected along transects from the three rivers that flow into the Salton Sea. Sampling was performed in October and March to coincide with peak pesticide use. Sampling sites spanned a wide range of salinities (freshwater to 45‰) and suspended sediment concentrations (SSC = 30 mg/L to 300 mg/L) from upriver to offshore sites within the sea. Comparisons of SAP concentrations and partitioning are made between winter and summer in the northern rivers, and between low salinity high/SSC upriver sites and high salinity/low SSC sites in the Salton Sea. Comparisons of pesticide use patterns and concentrations between regions are also made.
Key words: pesticides, sediment, multiresidue analysis, partitioning
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