Evaluating the neurobehavioral toxicity of the neonicotinoid pesticide, thiamethoxam, in two fish species
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Thiamethoxam (TM) is a commonly used neonicotinoid pesticide that acts as a nicotinic acetylcholine receptor (nAChR) agonist. TM has been detected in surface waters at levels above aquatic life benchmarks and has raised concerns about its potential toxicity to fish. To address these concerns, the effects of chronic exposure to environmentally relevant concentrations of TM were determined in two fish species. Acute and chronic exposures to 0.02-163 μg TM/L were conducted in embryonic- and larval-stage fathead minnows and in embryonic-stage zebrafish. Endpoints to assess health and neurotoxicity were monitored throughout the duration of the exposure, including survival, hatching, foraging efficiency, embryonic motor activity, and predator escape behavior. TM-exposed fathead minnows experienced reductions in survival, changes to embryonic motor activity, and altered predator escape behavior while TM-exposed zebrafish embryos experienced reduced hatching rates and changes to the predator escape behavior. Lastly, molecular modeling was used to gain preliminary insight on the interactions of TM with the nAChR between organisms. While TM does not target fish, they still experience effects as a result of TM exposure. Taken together, this research indicates that further investigation of the effects of TM on fish is necessary to determine the impacts of this prevalent pesticide on the health of aquatic ecosystems.