Assessing the ecotoxicity of commercial formulation based on Imidacloprid on the non-target freshwater planarian Girardia tigrina

Abstract

Imidacloprid (IMI) is among the most frequently detected insecticides in freshwater ecosystems near agricultural areas where it affects not only target insects, but also other non-target organisms. This study aimed to investigate the acute and chronic toxicity of a commercial insecticide formulation that uses imidacloprid as the active ingredient (Imidagold 700 WG®) on the non-target planarian Girardia tigrina. The ecotoxicological tests performed evaluated the survival, locomotor velocity, regeneration, and reproduction of planarians. In the acute toxicity test, the organisms were exposed to various concentrations of IMI ranging from 50 mg a.i./L to 527 mg a.i./L alongside a control treatment (ASTM only). For the chronic effect toxicity evaluation, planarians were exposed to concentrations ranging from 100 to 1,600 µg a.i./L in addition to the control treatment (ASTM, only). The estimated LC₅₀ at 24 and 48 hours for IMI was 114 and 94.29 mg a.i./L, showing low acute toxicity. However, decreased locomotor velocity and delayed regeneration of photoreceptors and auricles were observed for environmentally relevant concentrations equal or higher than 200 µg a.i./L. Reproduction was significantly impacted at the concentration of 200 µg a.i./L but not affected at higher concentrations, suggesting hormesis. Considering the planarians' importance in freshwater ecosystems and their position in the food chain, the detrimental effects induced by IMI may extend to freshwater communities and overall ecosystem functioning.