CA-0220

CA-0220 - Studies Relating Pesticide Concentrations to...

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Studies Relating Pesticide Concentrations to Potential Effects on Aquatic Organisms in the San Francisco Bay-Estuary, California by Kathryn M. Kuivila ABSTRACT A variety of pesticides are applied in large quantities to agricultural and urban areas in the Central Valley of California and are transported into the San Francisco Bay-Estuary dissolved in water and associated with suspended sediments. These pesticides can have deleterious effects on aquatic organisms. Three studies that relate pesticide concentrations to potential effects on aquatic organisms are currently underway by the U.S. Geological Survey’s San Francisco Bay-Estuary Toxic Substances Hydrology Project. These studies are (1) measuring the impacts of herbicides on phytoplankton primary production, (2) determining the exposure of Delta smelt to dissolved pesticides, and (3) assessing the effects of pesticides on the Asian clam, Potamocorbula amurensis . INTRODUCTION Large quantities of various pesticides are applied to agricultural and urban areas in the Central Valley of California that drain into the Sacramento-San Joaquin Delta (Delta) and then San Francisco Bay. Together, the Delta and San Francisco Bay are known as the San Francisco Bay-Estuary (Estuary). Several monitoring studies have measured elevated concentrations of dissolved pesticides in the Sacramento and San Joaquin Rivers, upstream of the Estuary (fig. 1) (MacCoy and others, 1995; Domagalski, 1996; Panshin and others, 1998). Fewer measurements of dissolved pesticides have been made in the Sacramento-San Joaquin Delta or farther downstream in the Estuary (fig. 1) (Kuivila and Foe, 1995; Kuivila and others, 1999). Pesticides also are transported into the rivers and Estuary associated with suspended sediments, but little is known about the concentrations and residence times of these pesticides (Domagalski and Kuivila, 1993; Bergamaschi and others, 1999; Bergamaschi and others, in press). Once in the aquatic environment, pesticides can have deleterious effects on aquatic organisms; controlling factors include the concentration, exposure time, and bioavailability of the pesticide of concern. When assessing a biological effect, it is important to use the appropriate endpoint or indicator. Endpoints reflect responses at various levels physiological, whole organism, population, and community. Field and laboratory studies can be used to assess effects of pesticides on aquatic organisms. Field studies take into account the complexity of the ecosystem, but that complexity makes it difficult to assign a single cause to an observed effect. In contrast, direct cause and effect are more easily shown in laboratory studies, but at the expense of oversimplifying the interrelations in the ecosystem. A combination of field and laboratory studies usually provides the most powerful approach. The purpose of this report is to summarize
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This note was uploaded on 12/06/2010 for the course GEOG 265 at USC.

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CA-0220 - Studies Relating Pesticide Concentrations to...

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