Effects of sediment-bound bifenthrin on gizzard shad and plankton in experimental tank mesocosms

Abstract

We examined the effects of bifenthrin, a synthetic pyrethroid insecticide, on gizzard shad (Dorosoma cepedianum) and plankton in an 8-d experiment using 16 outdoor tank mesocosms (5.5 m3). The replicated design included six treatments of sediment-bound bifenthrin (0-7,750 ng/L), a sediment-free control treatment, and a fish-free control treatment (with untreated sediment). The 8-d LC50s for gizzard shad were 521 and 207 ng/L, using bifenthrin concentrations in water 1 h after addition and average concentrations during the study, respectively. In the presence of bifenthrin, gizzard shad exhibited abnormal stress behaviors, including swimming slowly, gulping near the water surface, opercle flaring, and head shaking. Bifenthrin significantly reduced copepod nauplii density and turbidity, increased rotifer density and Secchi depth, and affected chlorophyll.