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Water-Resources Investigations Report 03-4088

Evaluation of Diazinon and Chlorpyrifos Concentrations and Loads, and other Pesticide Concentrations, at Selected Sites in the San Joaquin Valley, California, April to August, 2001

By Joseph L. Domagalski and Cathy Munday

Prepared in cooperation with the
California Department of Pesticide regulation


Twelve sites in the San Joaquin Valley of California were monitored weekly during the growing and irrigation season of 2001 for a total of 51 pesticides and pesticide degradation products, with primary interest on the concentration, load, and basin yield of organophosphorus insecticides, especially diazinon and chlorpyrifos. Diazinon was detected frequently, up to 100 percent of the time, at many of the sampling sites, but with generally low concentrations. For all sites, 75 percent of all measured diazinon concentrations were less than 0.02 mg/L, and 90 percent of all measured diazinon concentrations were less than 0.06 mg/L. The highest diazinon concentrations were measured in samples from two west-side tributaries to the San Joaquin River, Orestimba Creek, and Del Puerto Creek. The median concentration of chlorpyrifos was at or less than the laboratory reporting limit (0.005 mg/L) for most sites with the exceptions of two tributaries to the San Joaquin River: Orestimba Creek and the Tuolumne River. For all sites, 75 percent of all measured chlorpyrifos concentrations were less than 0.03 mg/L and 90 percent of all measured chlorpyrifos concentrations were less than 0.07 mg/L. The total load of diazinon out of the basin was just over 7 kilograms, which accounted for about 0.17 percent of the total agricultural applications. The diazinon load from the monitored upstream tributaries accounted for about 50 percent of the load at the mouth of the San Joaquin River. The streamflow from the selected monitored tributaries accounted for about 83 percent of the streamflow at the mouth of the San Joaquin River. The total load of chlorpyrifos out of the basin was 3.75 kilograms, and this accounted for approximately 0.007 percent of the total amount applied. Other pesticides that were frequently detected during this study included herbicides such as metolachlor, simazine, and trifluralin, and insecticides such as carbaryl, carbofuran, and propargite. At Orestimba Creek, DDE, a degradation product of DDT, was detected at a frequency of 95 percent.

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wri03_4088.pdf 6.1MB

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Description of Study Area
Methods and Quality Control
Sample Collection Methods
Integrated Grab Samples
Midpoint Grab Samples
Dip Samples
Calculation of Loads and Yields
Quality Control Data and Sample Types
Field Blank Samples
Replicate Samples
Spiked Samples
Sample Processing and Analysis and Laboratory Quality Control
Field-Level Quality Control Data Analysis
Blank Samples
Routine Quality Control Replicate Samples
Replicate Samples Comparing Collection Methods at San Joaquin River near Crows Landing
Comparison of Sample-Collection Methods
Spiked Samples
Surrogates Added to All Samples
Results and Discussion
Discharge and Pesticide Loads
Comparison of Detected Pesticides to Applications
Summary and Conclusions
References Cited


Send questions or comments about this report to the author, J.L. Domagalski at 916.278.3077

For more information about USGS activities in California, visit the USGS California District home page.

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Last modified: Thursday, September 01 2005, 05:08:58 PM
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