Abstract
Metallic nanomaterials (MNM) like cobalt oxide (nano-Co3O4) are currently attracting enormous interest owing to their unique size and shape-dependent properties and potential applications in various sectors. The aims of this study were to assess the toxicity of nano-Co3O4 and to propose a risk limit through the estimation of a Predicted No Effect Concentration (PNEC) for this MNM to soil biota. For this purpose, a battery of sub-lethal ecotoxicological tests was performed to assess the influence of this MNM on four plant species (endpoints: germination and growth) and two invertebrate species (endpoints: avoidance and reproduction) following standard protocols. Further, biochemical endpoints (acetylcholinesterase [AChE], catalase [CAT], glutathione-S-transferase [GST] activity, and lipid peroxidation [LPO]) were also assessed in Eisenia andrei, one of the invertebrate species tested, in order to contribute for refining the PNEC value. The recorded data showed a significant inhibition in the germination of L. lycopersicum and in the growth of Z. mays, even at the lowest concentration tested (269.3 mg kg−1 soildw of nano-Co3O4). Concerning the soil invertebrates, the results showed only significant avoidance (p < 0.05) by E. andrei in the soil contaminated with the highest concentration tested (1000 mg kg−1 soildw of nano-Co3O4), while no significant ecotoxicological effect on reproductive outputs of both species was recorded. However, the data reported for AChE, CAT, GST, and LPO showed significant effects at the range of concentrations tested in E. andrei. Thus, we recorded, the occurrence of oxidative stress and the enhancement of lipid peroxidation, on this invertebrate species. The data obtained in this study supports the proposal of a PNEC value of 9.1 mg kg−1 soildw for nano-Co3O4 in soil. The integration of data from biochemical endpoints allowed the refinement of the PNEC value and to obtain a more protective threshold.
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