EFFECT OF BIFENTHRIN AND REDUCED SALINITY EXPOSURE ON LARVAL SHEEPSHEAD MINNOWS (<i>Cyprinodon variegatus</i>) and GRASS SHRIMP (<i>Palaemonetes pugio</i>)

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Hanson, Breanne Y
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As one of the ten fastest growing cities in the United States, Charleston, South Carolina is experiencing rapid rates of development along its coastline and waterways. Large-scale changes in land use lead to proportional increases in impervious ground cover, ultimately resulting in increased input of stormwater runoff into adjacent waterways. Stormwater runoff reduces salinity and increases contaminant loads as rainwater washes pollutants, including pesticides such as bifenthrin, into receiving waters. Numerous studies have demonstrated that rapidly reduced salinity and bifenthrin exposure independently threaten the integrity of ecologically and economically valuable estuarine ecosystems. The present study examined bifenthrin toxicity and the potential combined effect of reduced salinity for larval sheepshead minnows (<i>Cyprinodon variegatus</i>) and grass shrimp (<i>Palaemonetes pugio</i>). LC50 values were established in salinities of 20, 10, and 5 psu as 0.431, 0.415, 0.377 µg/L and 0.0065, 0.0064, 0.000109 µg/L for larval <i>C. variegatus</i> and <i>P. pugio</i>, respectively. Salinity did not have a significant effect on bifenthrin toxicity to larval <i>C. variegatus</i>, but mortality rates increased to 90% when larval <i>P. pugio</i> were exposed to 0.0015 µg/L of bifenthrin in 5 psu. Bifenthrin was detected in tidal creeks near urbanized areas in Charleston County at concentrations that exceed toxicity thresholds. Given that stormwater input is increasing as a result of increasing impervious cover, it is critical to understand how exposure to bifenthrin in low-salinity regimes affects estuarine organisms. The results of this study will benefit coastal resource management by providing new data on the toxicity of a common pesticide to larval estuarine organisms under a range of environmental conditions.
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