Mixture toxicity study of two metal oxide nanoparticles and chlorpyrifos on Eisenia andrei earthworms

Abstract

Co-exposure soil studies of pollutants are necessary for an appropriate ecological risk assessment. Here, we examined theeffects of two-component mixtures of metal oxide nanoparticles (ZnO NPs or goethite NPs) with the insecticide chlorpyrifos(CPF) under laboratory conditions in short-term artificial soil assays using Eisenia andrei earthworms. We characterized NPsand their mixtures by scanning electron microscopy, atomic force microscopy, dynamic light scattering and zeta potential,and evaluated effects on metal accumulation, oxidative stress enzymes, and neurotoxicity related biomarkers in single andcombined 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 exposedto goethite NPs. One of the most notable effects on oxidative stress biomarkers was produced by single exposure to goethiteNPs, showing that the worms were more sensitive to goethite NPs than to ZnO NPs. Acetylcholinesterase and carboxylesteraseactivities indicated that ZnO NPs alone were not neurotoxic to earthworms, but similar degrees of inhibition wereobserved after single CPF and ZnO NPs + CPF exposure. Differences between single and combined exposure were foundfor catalase and superoxide dismutase (goethite NPs) and for glutathione S-transferase (ZnO NPs) activities, mostly at 72 h.These findings suggest a necessity to evaluate mixtures of NPs with co-existing contaminants in soil, and that the nature ofmetal oxide NPs and exposure time are relevant factors to be considered when assessing combined toxicity, as it may havean impact on ecotoxicological risk assessment.