Exposure of delta smelt to dissolved pesticides in 1998 and 1999

Delta smelt is a threatened species in the San Francisco Bay Estuary. Pesticide toxicity is a possible cause for the need to list this fish (Bennett and Moyle 1996; Moyle and others 1996). Numerous pesticides are transported into the estuary from area rivers (MacCoy and others 1995). However, there are minimal data to document the presence, or absence, of pesticides within delta smelt habitat, especially during their vulnerable early life stages. This study, conducted by the U.S. Geological Survey (USGS), documents the occurrence of pesticides within delta smelt habitat; specifically, the length and variability of their potential exposure to multiple dissolved pesticides.

This article reviews delta smelt habitat and early life stages followed by an explanation of the study design for assessing pesticide exposure. Results show the co-occurrence of multiple pesticides and delta smelt in their native habitat; these results are presented within the context of possible toxic effects to delta smelt. Finally, the annual variability of pesticide distributions is discussed.