Sublethal Effects of Chronic Exposure to Neonicotinoid Pesticides on Aquatic Organisms

Background/Need: Neonicotinoid insecticides were designed to specifically target the nervous system of invertebrate pests (specifically the nicotinic Acetylcholine receptor, nAChR) and deemed not overtly toxic to vertebrates. Initially hailed as an exceptional replacement for older insecticides, their reputation was quickly tarnished by their association with honeybee declines and impacts on other non-target terrestrial insects. Following decades of widespread use, neonicotinoids are now major contaminants of concern in aquatic ecosystems, and their impacts on the aquatic community are not fully understood.

Thiamethoxam (TM) and imidacloprid (IM) are found above ecological threshold levels in groundwater and surface waters in Wisconsin, particularly within the Central Sands Region. This poses a potential risk to aquatic invertebrates, and emerging evidence suggests that fish may be susceptible to adverse effects following chronic exposure to these insecticides.

Objectives: The overall objectives of our work were to better understand the chronic toxicity of TM and IM to key aquatic species within the Central Sands Region of Wisconsin, as well as an additional fish species that is a model organism in aquatic toxicology. Since neonicotinoids are commonly found in mixtures that are dominated by TM and IM, we also evaluated the toxicity of these compounds in mixtures.

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