Bifenthrin, a Ubiquitous Contaminant, Impairs the Development and Behavior of the Threatened Longfin Smelt during Early Life Stages

The development and behavior of the threatenedLongfin Smeltwere affected by the exposure to environmentally relevant concentrationsof bifenthrin, a ubiquitous contaminant. This suggests that bifenthrincould contribute to the observed population decline. The Longfin Smelt (Spirinchus thaleichthys) population in the San FransciscoBay/Sacramento-San Joaquin Delta(Bay-Delta) has declined to & SIM;1% of its pre-1980s abundanceand, as a result, is listed as threatened under the California EndangeredSpecies Act. The reasons for this decline are multiple and complex,including the impacts of contaminants. Because the spawning and rearingseasons of Longfin Smelt coincide with the rainy season, during whichconcentrations of contaminants increase due to runoff, we hypothesizedthat early life stages may be particularly affected by those contaminants.Bifenthrin, a pyrethroid insecticide commonly used in agriculturaland urban sectors, is of concern. Concentrations measured in the Bay-Deltahave been shown to disrupt the behavior, development, and endocrinesystem of other fish species. The objective of the present work wasto assess the impact of bifenthrin on the early developmental stagesof Longfin Smelt. For this, embryos were exposed to 2, 10, 100, and500 ng/L bifenthrin from fertilization to hatch, and larvae were exposedto 2, 10, and 100 ng/L bifenthrin from one day before to 3 days post-hatch.We assessed effects on size at hatch, yolk sac volume, locomotorybehavior, and upper thermal susceptibility (via cardiac endpoints).Exposure to these environmentally relevant concentrations of bifenthrindid not significantly affect the cardiac function of larval LongfinSmelt; however, exposures altered their behavior and resulted in smallerhatchlings with reduced yolk sac volumes. This study shows that bifenthrinaffects the fitness-determinant traits of Longfin Smelt early lifestages and could contribute to the observed population decline.