Toxicity of 12 metal-based nanoparticles to algae, bacteria and protozoa

Abstract

The use of metal-based nanoparticles (NPs) is increasing which leads to their release in water bodies via various waste streams, and thus warrants risk assessment. Consistent biological-effect data of NPs for environmentally relevant test species, which are accompanied by thorough characterization of NPs, are scarce but indispensable for understanding the possible risks of NPs. We composed and tested a library of 12 metal-based nanoparticles (Al₂O₃, Co₃O₄, CuO, Fe₃O₄, MgO, Mn₃O₄, Sb₂O₃, SiO₂, ZnO, TiO₂, WO₃ and Pd) using the alga Pseudokirchneriella subcapitata, three bacterial species (Vibrio fischeri, Escherichia coli, Staphylococcus aureus) and the protozoa Tetrahymena thermophila. The NPs were characterized for their physico-chemical properties, solubility and abiotic reactive oxygen species (ROS) production. Also, respective soluble salts were analysed for toxic effects. The algal growth inhibition assay has proven to be the most sensitive and yielded EC₅₀ values for 10 NPs ranging from 0.1 to 58 mg l⁻¹. Algal toxicity correlated with abiotic ROS production of NPs, and the majority of the NPs formed agglomerates that entrapped algal cells. Despite the different sensitivities, there was a common trend in the toxicity of the NPs across different species and test formats: CuO and ZnO had the highest toxicity (EC₅₀ values below 1 mg l⁻¹) among all organism groups except for the protozoa. The high toxicity was mostly due to the shedding of toxic concentrations of Zn and Cu ions; for most of the test species, Al₂O₃, SiO₂, WO₃ and Sb₂O₃ were not toxic below 100 mg l⁻¹ and MgO showed no adverse effects below 100 mg l⁻¹ to any test species in any test setting.