Mixture toxicity study of metal oxide nanoparticles and chlorpyrifos on earthworms at low concentrations: a short-term exposure approach

Abstract Co-exposure soil studies of pollutants are necessary for an appropriate ecological risk assessment. Here, we examined the effects of two-component mixtures of metal oxide nanoparticles (NPs, ZnO or goethite) with chlorpyrifos (CPF) under laboratory conditions in short-term artificial soil assays using Eisenia andrei earthworms. We evaluated effects on metal accumulation, oxidative stress enzymes, and neurotoxicity related biomarkers in single and combined toxicity assays. Exposure to ZnO NPs increased Zn levels compared to control in single and combined exposure (ZnO NPs + CPF) at 72 h and 7 days, respectively. In contrast, there was no indication of Fe increase in organisms exposed to goethite NPs. One of the most notable effects on oxidative stress biomarkers was produced by single exposure to goethite NPs. This shows that the worms were more sensitive to goethite NPs than to ZnO NPs, regardless of nano-structure. Statistically significant differences between single and combined exposure were found for catalase and superoxide dismutase (goethite NPs) and for glutathione S-transferase (ZnO NPs) activities, mostly at 72 h. Acetylcholinesterase and carboxylesterase activities indicated that ZnO NPs were not neurotoxic to earthworms and similar degrees of inhibition were observed after single CPF and ZnO NPs + CPF exposure. These findings suggest a necessity to evaluate mixtures of NPs with co-existing contaminants in soil, and that the nature of metal oxide NPs and exposure time are relevant factors to be considered when assessing combined toxicity, as it may have an impact on ecotoxicological risk assessment.