Soil invertebrate toxicity and bioaccumulation of nano copper oxide and copper sulphate in soils, with and without biosolids amendment

Abstract

The fate, toxicity and bioaccumulation of copper oxide nanoparticles (nCuO) was investigated in soil, with and without biosolids amendment, through chronic exposures using the earthworm, Eisenia andrei, and the collembolan, Folsomia candida. The effects of copper sulphate (CuSO₄) were included so as to compare the behavior of nCuO to a readily soluble counterpart. The fate of nCuO was evaluated through characterization of dissolved and nano-particulate fractions (via single particle ICP-MS) as well as extractable Cu²⁺ throughout the duration of select tests. Neither Cu form was particularly toxic to F. candida, but effects on E. andrei reproduction were significant in all treatments (IC50 range: 98 - 149 mg Cu kg^-1 dry soil). There were no significant differences in toxicity between the Cu forms, nor in extractable Cu²⁺ activities, indicative that particle dissolution within the soil and, subsequent activity of Cu²⁺ was likely the primary mode of toxicity in the nCuO exposures. The presence of biosolids did not significantly alter toxicity of nCuO, but did affect Cu²⁺ activity over time. Bioaccumulation of total Cu in E. andrei when exposed to nCuO (kinetic bioaccumulation factor (BAF_k): 0.80 with biosolids and 0.81 without) was lower than exposure to CuSO₄ (BAF_k: 2.31 with biosolids and 1.12 without). Enhanced dark-field hyperspectral imaging showed accumulation of nCuO along the epidermis and gut of E. andrei, with trace amounts observed in muscle and chloragogenous tissue, providing evidence of nCuO translocation within the organism. The present study demonstrates that the current risk assessment approach for trace metals in the environment, based on substance solubility and bioavailability of the dissolved free ion, are applicable for nCuO exposure to soil invertebrates, but that the rate of particle dissolution in different soil environments is an important factor for consideration.

Keywords: Bioaccumulation; Bioavailability; Nano-copper; Nanomaterials; Soil invertebrates; Toxicity.