Copper accumulation and toxicity in earthworms exposed to CuO nanomaterials: Effects of particle coating and soil ageing.

Engineered nanomaterials (ENMs) may be functionalised with a surface coating to enhance their properties, but the ecotoxicity of the coatings and how hazard changes with ageing in soil is poorly understood. This study determined the toxic effect of CuO ENMs with different chemical coatings on the earthworm (Eisenia fetida) in fresh soil, and then after one year in aged soil. In both experiments, earthworms were exposed for 14 days to the CuO materials at nominal concentrations of 200 and 1000 mg Cu kg-1 dry weight and compared to CuSO4. In the fresh soil experiment, CuO-COOH was found to be the most acutely toxic of the nanomaterials (survival, 20 ± 50%), with tenfold increase of total Cu in the earthworms compared to controls. Sodium pump activity was reduced in most CuO ENM treatments, although not in the CuSO4 control. There was no evidence of glutathione depletion or the induction of superoxide dismutase (SOD) activity in any treatment. Histology showed a mild hypoplasia of mucous cells in the epidermis with some nanomaterials. In the aged soil, the CuO-NH4+ was the most acutely toxic ENM (survival 45 ± 3%) and Cu accumulation was lower in the earthworms than in the fresh soil study. Depletion of tissue Mn and Zn concentrations were seen in earthworms in aged soil, while no significant effects on sodium pump or total glutathione were observed. Overall, the study showed some coating-dependent differences in ENM toxicity to earthworms which also changed after a year of ageing the soil.