Bioaccumulation, transformation and toxicity of imidacloprid and dinotefuran in Eisenia fetida under single and binary exposure scenarios.

Earthworms (Eisenia fetida) were exposed to individual and binary mixture of imidacloprid (IMI) and dinotefuran (DIN) at 0.05 and 0.5 mg/kg for 28 days to investigate their bioaccumulation, transformation and toxicity. IMI was more easily absorbed by earthworms than DIN, and worms didn't accumulate or generate toxic metabolites. The obvious accumulation of neonicotinoids during later period caused significant neural dysfunction, especially when exposed to high-concentration IMI. Meanwhile, oxidative stress indicated by decreased SOD/CAT activity (33.2 %-68.1 %) and increased MDA (38.4 %-55.0 %) was induced by binary exposure with high-concentration IMI. By contrast, coelomocytes responded earlier and more strongly than oxidative responses. Coelomocytes' viability and mitochondrial membrane potential were inhibited (23.6 %-91.7 %) mainly by IMI and binary exposure. Coelomocytes' lactate dehydrogenase activity exerted a fluctuating pattern, suggesting irregular disturbance on cellular functions. This study highlights the role of coelomocytes and the need to consider binary/multiple scenarios and transformation of neonicotinoids in their risk assessment to earthworms. [Display omitted] • Imidacloprid was more easily taken up by earthworms than dinotefuran. • Earthworms didn't accumulate or generate toxic metabolites of IMI and DIN. • IMI and its co-exposure with DIN exerted evident neurotoxicity and oxidative stress. • Coelomocytes responded earlier to neonicotinoid exposure than histological enzymes. • Lactate dehydrogenase activity is a sensitive indicator for neonicotinoid exposure. [ABSTRACT FROM AUTHOR]