Exposure to permethrin or chlorpyrifos causes differential dose- and time-dependent behavioral effects at early larval stages of an endangered teleost species.

Pc Mundy,N Fangue,Ke Huff Hartz,Ca Fulton,Re Connon,Sm Brander,Mj Lydy,Tc Hung

doi:10.3354/esr01091

Abstract

Pyrethroid and organophosphate pesticides are two of the most commonly used classes of insecticide worldwide. At sublethal concentrations, permethrin (a pyrethroid) and chlorpyrifos (an organophosphate) impact behavior in model fish species. We investigated behavioral effects of environmentally relevant concentrations of permethrin or chlorpyrifos on early larval delta smelt Hypomesus transpacificus, a Critically Endangered teleost species endemic to the San Francisco Bay Delta, California, USA. Using a photomotor behavioral assay of oscillating light and dark periods, we measured distance moved, turn angle, meander, angular velocity, rotations, thigmotaxis (time spent in the border versus center), and swim speed duration and frequency. The lowest concentrations of permethrin used in the tests (0.05 and 0.5 μg l−1) caused significant increases in distance moved at 72 and 96 h, respectively. At 48, 72, and 96 h of exposure, 5 μg l−1 of permethrin caused a hyperactive state in which the larvae significantly decreased thigmotaxis, quickly turning in short bouts of activity, characterized by significant increases in rotations and freezing events. Larvae exposed to 0.05 μg l−1 chlorpyrifos significantly increased thigmotaxis at 72 and 96 h. In response to 5 μg l−1 chlorpyrifos, larvae significantly increased velocity at 72 h exposure, and significantly increased freezing events at 96 h. Behavioral data on larval delta smelt exposed to contaminants present in their limited habitat have the potential to aid evaluations of the suitability of spawning and rearing habitats for this endangered species, thus improving conservation management strategies focused on this sensitive life stage.

Highlights

Two of the most common insecticide groups used worldwide are pyrethroids and organophosphates
The mechanism of action (MOA) of permethrin is generally accepted to be the binding of voltage gated sodium ion channels (VGSCs), delaying closure of the channel, resulting in prolonged depolarization of neurons, resulting in convulsions and death (Soderlund 2012)
Larval zebrafish Danio rerio exposed to 25 μg l−1 permethrin decreased thigmotaxis, defined here as the affinity of an organism to preferentially remain near the boundaries of an environment, as opposed to the center (Nunes et al 2020)

Summary

Introduction

Two of the most common insecticide groups used worldwide are pyrethroids and organophosphates. Endang Species Res 44: 89–103, 2021 ture (Mackay et al 2014, DiBartolomeis et al 2019) Both categories of insecticide are of concern to aquatic organisms, and have been shown to be toxic to fish (Giesy et al 1999, Weston et al 2015b). Because permethrin is used heavily in agricultural and urban applications, it often enters watersheds and can be found in sediment and surface waters in the ng l−1 to μg l−1 range (You & Lydy 2006, Delgado-Moreno et al 2011, Weston et al 2014, Deanovic et al 2018). Permethrin is considered a Type I pyrethroid insecticide, as it lacks an α-cyano group on the phenoxybenzyl moiety (Soderlund 2012). Exposure of larval zebrafish to anxiolytic or anxiogenic compounds has been found to enhance or attenuate thigmotaxis, respectively (Schnörr et al 2012)

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