Bifenthrin, a current-use pyrethroid insecticide, has been repeatedly identified as a major contributor to toxicity in urban and residential stream sediment. Within an urban stream multiple stressors exist. However, other than pesticides, the influence of secondary stressors on bifenthrin toxicity has not been studied. The goal of this project was to study how dissolved ions, based on the model salt KCl, influence bifenthrin toxicity. The presence of these dissolved ions could influence bifenthrin toxicity either through joint action as a secondary toxicant or through changing the partitioning or bioavailability of bifenthrin between the sediment matrix and overlying water or pore water. The first objective was to determine if mixtures of bifenthrin and KCl, a commonly utilized reference toxicant, display additive toxicity to the benthic invertebrates Hyalella azteca and Chironomus dilutus using concentration addition and independent action mathematical models. The second objective of the present study was to examine how KCl dissolved in the overlying water influences partitioning and bioavailability of a pyrethroid (bifenthrin). Joint toxicity of bifenthrin and KCl was less than predicted by both concentration addition and independent action models. However, both models predicted the joint toxicity within a factor of two. Partitioning of bifenthrin was not significantly influenced by KCl concentrations based on K(oc) determinations and desorption to Tenax beads. This indicates that the fate and bioavailability of bifenthrin are not likely different in aquatic environments with varying dissolved ion concentrations. Therefore, the toxicological interaction that results in the antagonistic joint action between bifenthrin and KCl is likely due to the physiological effects of exposure to hypertonic solutions of KCl rather than alterations to bifenthrin bioavailability.
2010 Elsevier Ltd. All rights reserved.