John Wiley & Sons, Ltd.

Effects of salinity acclimation on the endocrine disruption and acute toxicity of bifenthrin in freshwater and euryhaline strains of Oncorhynchus mykiss

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The pyrethroid insecticide, bifenthrin, is frequently detected at ng/L concentrations in tributaries of the San Francisco Bay Delta (SFBD). The estuary is also experiencing increasing salinity through climate change and water redirection. To evaluate the impacts of hypersaline conditions on bifenthrin toxicity in anadromous salmonids of the SFBD, a 14‐day laboratory exposure was performed using two strains of O. mykiss (rainbow trout and steelhead) acclimated to freshwater, 8 g/L, and 17g/L salinity. The fish were then exposed to nominal concentrations of 0, 0.1, and 1.5 µg/L bifenthrin. Rainbow trout exhibited significant mortality following exposure to 1.5 µg/L (1.07 ± 0.35 measured) bifenthrin in freshwater. Elevated levels of Na+/K+ATPase (NKA) α1A mRNA subunit expression was observed in the gill of rainbow trout acclimated to hypersaline conditions relative to freshwater animals. No significant difference was noted in NKA subunit levels in brains of either strain in freshwater or hypersaline conditions. Likewise, significant differences were not observed in plasma VTG or steroid hormone concentrations in either strain whether maintained in fresh or saltwater. Saltwater acclimation significantly reduced NADPH‐catalyzed biotransformation of bifenthrin in liver microsomes of rainbow trout, but not steelhead. This study showed that relative to steelhead, rainbow trout have different responses to bifenthrin acute toxicity as well as different rates of hepatic bifenthrin biotransformation and regulation of NKA subunits in gills. These data indicate that significant differences exist between the strains and that animal life history may have important impacts on the susceptibility of each strain to environmental contaminants. Environ Toxicol Chem © 2013 SETAC

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