The chronic effects of CuO and ZnO nanoparticles on Eisenia fetida in relation to the bioavailability in aged soils.

The bioavailability and bioaccumulation of metal-based engineered nanoparticles (ENPs) in soils need to be evaluated in environmentally relevant scenarios. The aim of this study was an analysis of potentially available metal-component ENPs (nano-ZnO and nano-CuO) in soils. Earthworms (Eisenia fetida) were used to examine the bioaccumulation potential of ENPs. Micro-particles (micro-ZnO and micro-CuO) and metal salts (ZnCl and CuCl) were used to evaluate the nano-effect and the activity of dissolved ions, respectively. Zn- and Cu-compounds were added to sandy loam and silt loam at a concentration of 10 mg kg. The bioavailable fractions of metals were extracted from soil using HO, MgCl with CHCOONa or EDTA. EDTA was the most effective extractant of Zn and Cu (10.06-11.65 mg Zn kg and 2.69-3.52 mg Cu kg), whereas the HO-extractable metal concentration was at the lowest level (1.98-2.12 mg Zn kg and 0.54-0.82 Cu mg kg). The bioavailable metal concentrations were significantly higher in silt loam than sandy loam soil, which was related to the higher pH value of silt. There were no significant differences between the Zn content in the earthworms incubated in the two soils, which may confirm the auto-regulation of the Zn content by earthworms. However, the bioaccumulation of Cu was strongly correlated with the extractable Cu concentrations. The juvenile earthworms accumulated Cu and Zn more than adults. Based on our results, aging neutralized the differences between the ionic and particulate effects of metal-compounds.