Pesticides Common in California Estuary

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Pesticides were observed frequently in water, sediment, and the tissue of resident aquatic organisms from an agriculturally dominated estuary along the central California coast according to a collaborative study by U.S. Geological Survey (USGS) and University of California, Davis scientists published in Marine Pollution Bulletin.

USGS scientist dissecting a summer flounder

USGS scientist dissecting a summer flounder. Photo Credit: James Orlando, USGS.

The estuary and lagoon, near Guadalupe, provide nursery and foraging habitat for numerous marine and estuarine fish and other aquatic animals including the endangered tidewater goby fish. Three fungicides, an herbicide, and two organophosphate insecticides were observed frequently in the study area. Pesticides found in the water increased during the summer months as pesticide application increased in the adjacent agricultural watershed; pesticides in bed sediment decreased with increasing distance from potential sources. Fish and sand crabs collected from the mouth of the estuary accumulated a number of pesticides in their tissues. This is the first study to document the occurrence of many current-use pesticides, including fungicides, in tissue. Limited information is alsoavailable documenting the accumulation and effects of pesticides on aquatic organisms, especially in small, agriculturally dominated estuaries.

In estuaries receiving runoff from agricultural areas, management practices are being implemented by State and local agencies to reduce the load of pesticides to estuaries. This study provides a baseline that will allow resource managers to track changes in ecosystem performance with changes in pesticide contamination levels. The approach developed in this study will help resource managers and scientists assess the health of coastal environments.

The California State Water Resources Control Board, USGS Cooperative Water Program, and USGS Toxic Substances Hydrology Program provided the funding for this work.


Anderson, B., Phillips, B., Hunt, J., Siegler, K., Voorhees, J., Smalling, K., Kuivila, K., and Adams, M., 2010, Watershed-scale evaluation of agricultural BMP effectiveness in protecting critical coastal habitats--Final report on the status of three coastal estuaries: Central Coast Regional Water Quality Control Board, San Louis Obispo, Calif., 117 p.