U.S. GEOLOGICAL SURVEY
U.S. Environmental Protection Agency
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Abstract
As part of a collaborative study involving the United States Geological Survey Toxics
Substances Hydrology Project (Toxics Project) and the University of California, Davis, Bodega Marine
Laboratory (BML), water samples were collected at three sites within the San Joaquin River Basin of
California and analyzed for dissolved pesticides. Samples were collected during, and immediately after,
the first significant rainfall (greater than 0.5 inch per day) following the local application of dormant
spray, organophosphate insecticides during the winters of 2000 and 2001. All samples were collected in
conjunction with fish-caging experiments conducted by BML researchers. Sites included two locations
potentially affected by runoff of agricultural chemicals (San Joaquin River near Vernalis, California, and
Orestimba Creek at River Road near Crows Landing, California, and one control site located upstream of
pesticide input (Orestimba Creek at Orestimba Creek Road near Newman, California). During these experiments,
fish were placed in cages and exposed to storm runoff for up to ten days. Following exposure, the fish were
examined for acetylcholinesterase concentrations and overall genetic damage. Water samples were collected
throughout the rising limb of the stream hydrograph at each site for later pesticide analysis. Concentrations
of selected pesticides were measured in filtered water samples using solid-phase extraction (SPE) and gas
chromatography-mass spectrometry (GC/MS) at the U.S. Geological Survey organic chemistry laboratory in Sacramento,
California. Results of these analyses are presented.
CONTENTS
Abstract
Introduction
Purpose and Scope
Acknowledgments
Study Design and Methodology
Selection of Sampling Sites
Generalized Sampling Methods
Sampling Methods at the Three Sites
Vernalis
Orestimba
Upper Orestima
Sample Processing and Analysis
Dissolved-Pesticide Concentrations
References Cited
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