Aquatic acute species sensitivity distributions of ZnO and CuO nanoparticles.

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: 0.03-0.15 mg Zn/l; 43 data points), bulk ZnO (HC5: 0.06 with CI: 0.03-0.20 mg Zn/l; 23 dps) and ZnCl2 (HC5: 0.03 with CI: 0.02-0.05 mg Zn/l; 261 dps). CuO nanoparticles (HC5: 0.15 with CI: 0.05-0.47 mg Cu/l; 43 dps) are more toxic than the bulk materials (HC5: 6.19 with CI: 2.15-38.11 mg Cu/l; 12 dps) but less toxic than CuCl2 (HC5: 0.009 with CI: 0.007-0.012 mg Cu/l; 594 dps) 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.