Salinity Changes the Dynamics of Pyrethroid Toxicity in Terms of Behavioral Effects on Newly Hatched Delta Smelt Larvae.

Amelie Segarra,Florian Mauduit,Nermeen R Amer,Nermeen R Amer,Felix Biefel,Felix Biefel,Richard E Connon,Michelle L Hladik,Susanne M Brander,Susanne M Brander

doi:10.3390/toxics9020040

Abstract

Salinity can interact with organic compounds and modulate their toxicity. Studies have shown that the fraction of pyrethroid insecticides in the aqueous phase increases with increasing salinity, potentially increasing the risk of exposure for aquatic organisms at higher salinities. In the San Francisco Bay Delta (SFBD) estuary, pyrethroid concentrations increase during the rainy season, coinciding with the spawning season of Delta Smelt (Hypomesus transpacificus), an endangered, endemic fish. Furthermore, salinity intrusion in the SFBD is exacerbated by global climate change, which may change the dynamics of pyrethroid toxicity on aquatic animals. Therefore, examining the effect of salinity on the sublethal toxicity of pyrethroids is essential for risk assessments, especially during the early life stages of estuarine fishes. To address this, we investigated behavioral effects of permethrin and bifenthrin at three environmentally relevant concentrations across a salinity gradient (0.5, 2 and 6 PSU) on Delta Smelt yolk-sac larvae. Our results suggest that environmentally relevant concentrations of pyrethroids can perturb Delta Smelt larvae behavior even at the lowest concentrations (<1 ng/L) and that salinity can change the dynamic of pyrethroid toxicity in terms of behavioral effects, especially for bifenthrin, where salinity was positively correlated with anti-thigmotaxis at each concentration.

Highlights

The Delta Smelt, Hypomesus transpacificus, is a pelagic fish species endemic to brackish and freshwater portions of the Sacramento River and the San Francisco Estuary (California, USA)
Average hatching was 94 ± 5% and 98 ± 2% at 9 dpf, and 97 ± 2% and 98 ± 2% at 12 dpf for batches used for the permethrin and bifenthrin exposures, respectively, and there were no differences across all exposure vessels (One-way ANOVA, p > 0.05)
All larvae from all conditions, in both experiments, exhibited a significant increase in movement in all light periods compared to dark cycles (Figure S1), confirming predictable behavior patterns previously verified for this species [47]

Summary

Introduction

The Delta Smelt, Hypomesus transpacificus, is a pelagic fish species endemic to brackish and freshwater portions of the Sacramento River and the San Francisco Estuary (California, USA). This fish has a migratory annual life cycle which follows the seasons and where life stages vary spatially across the San Francisco Bay Delta (SFBD). Salinity Unit; PSU), where resulting larvae remain until they become juveniles During late spring, they begin their migration downstream to low-salinity zones (1–6 PSU), where they continue to mature until the winter [2]. It was first classified as “threatened” under the Federal and State Endangered Species Act (ESA) in 1993, listed as “endangered”

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