Aquatic acute species sensitivity distributions of ZnO and CuO nanoparticles

Abstract

Metal oxide nanoparticles are increasingly being produced and will inevitably end up in the aquatic environment. Up till now, most papers have studied individual nanoparticle effects. However, the implementation of these data into a risk assessment tool, needed to characterise their risk to the aquatic environment, is still largely lacking. Therefore, aquatic species sensitivity distributions (SSDs) were constructed for ZnO and CuO nanoparticles and 5% hazard concentrations (HC5) were calculated in this study. The effect of individual nanoparticles on these SSDs was estimated by comparison with bulk SSDs. Additionally, the effect of nanoparticle dynamics (aggregation and dissolution) was considered by evaluating the effect of aggregate size on the toxicity, by estimation of the dissolved fraction and comparison with SSDs for ZnCl2 and CuCl2 inorganic salt. Bacteria, protozoa, yeast, rotifera, algae, nematoda, crustacea, hexapoda, fish and amphibia species were included in the analysis. The results show that algae (Zn) and crustacea (Zn, Cu) are the most sensitive species when exposed to the chemicals. Similar acute sensitivity distributions were obtained for ZnO nanoparticles (HC5: 0.06 with 90% confidence interval: 0.03–0.15mg Zn/l; 43 data points), bulk ZnO (HC5: 0.06 with CI: 0.03–0.20mg Zn/l; 23dps) and ZnCl2 (HC5: 0.03 with CI: 0.02–0.05mg Zn/l; 261dps). CuO nanoparticles (HC5: 0.15 with CI: 0.05–0.47mg Cu/l; 43dps) are more toxic than the bulk materials (HC5: 6.19 with CI: 2.15–38.11mg Cu/l; 12dps) but less toxic than CuCl2 (HC5: 0.009 with CI: 0.007–0.012mg Cu/l; 594dps) to aquatic species. However, the combined dissolution and SSD results indicate that the toxicity of these nanoparticles is mainly caused by dissolved metal ions. Based on the available information, no current risk of these nanoparticles to the aquatic environment is expected.