Comparative ecotoxicity of the nano Ag, TiO2 and ZnO to aquatic species assemblages

Abstract

Ecotoxicological testing of engineered nanoparticles (ENPs) began some years ago, but satisfactory knowledge of their environmental effects is still far from acceptable. In this study, the effects of three ENPs, i.e. nano silver (nAg), nano titanium-dioxide (nTiO2) and nano zinc-oxide (nZnO) on surface waters were examined using Species Sensitivity Distributions (SSD) models. Ecotoxicity data (acute EC50/LC50/IC50) from 44 scientific publications were evaluated. The nAg proved to be the most toxic among the three examined ENPs, followed by nZnO and nTiO2 with HC5 values of 0.00015, 0.275, and 3.246 (mg/L), respectively. Risk Quotient (RQ) values of nAg, nTiO2 and nZnO showed irrelevant risk (RQ<0.001) for surface waters in Europe and the USA. However, the risk is expected to increase in the future. No clear relationship was found between toxicity and taxonomical position of the tested species. Some cladoceran species seem to be more sensitive to nAg and nTiO2 than other tested organisms, such as microorganism, plant and animal species. Investigation of the published test results of nAg for Daphnia magna, showed that the filtration of the stock solution before testing has statistically significant effect on the toxicity. Our results clearly show that current methods used for ecotoxicological testing of the nano Ag, TiO2 and ZnO are not yet suitable for standardisation.