The application of Biolog EcoPlate™ for community-level physiological profiling of soils is well documented; however, the functional diversity of aquatic bacterial communities has been hardly studied. The objective of this study was to investigate the applicability of the Biolog EcoPlate™ technique and evaluate comparatively the applied endpoints, for the characterisation of the effects of metal oxide nanoparticles (MONPs) on freshwater microbial communities. Microcosm experiments were run to assess the effect of nano ZnO and nano TiO₂ in freshwater at 0.8–100 mg/L concentration range. The average well colour development, substrate average well colour development, substrate richness, Shannon index and evenness, Simpson index, McIntosh index and Gini coefficient were determined to quantify the metabolic capabilities and functional diversity. Comprehensive analysis of the experimental data demonstrated that short-term exposure to TiO₂ and ZnO NPs affected the metabolic activity at different extent and through different mechanisms of action. TiO₂ NPs displayed lower impact on the metabolic profile showing up to 30% inhibition. However, the inhibitory effect of ZnO NPs reached 99% with clearly concentration-dependent responses. This study demonstrated that the McIntosh and Gini coefficients were well applicable and sensitive diversity indices. The parallel use of general metabolic capabilities and functional diversity indices may improve the output information of the ecological studies on microbial communities.

After more than a decade of studying the ecotoxicity of graphene oxide nanomaterials (nGOs), it has been concluded that there is limited information available regarding the environmental risk of graphene-based materials. Since existing ecotoxicological studies of nanomaterials have produced contradictory results, it is recommended that case-by-case studies should be conducted to evaluate their effects. This can be carried out by employing several methods, testing species from different trophic levels, and conducting community studies. Our goal was to evaluate the toxicity effects of two GOs (AF 96/97 and PM 995) derived from different graphite precursors on various test organisms from diverse trophic levels (bacteria, protozoa, a freshwater microbial community, plants, and invertebrate animals) in aquatic environments. We compared the effects of both nGO types and estimated the predicted no-effect environmental concentration (PNEC) values to determine their potential environmental risk. Our findings demonstrated the need for a complex ecotoxicity toolkit since the ecotoxicity results varied based on the test organism, the selected endpoints, and the test method used. Additionally, we found that toxicity effects were dependent on the concentration and characteristics of the specific nGO type used, as well as the exposure time. We estimated the PNEC values for GO AF 96/97 and GO PM 995 in the aquatic compartment to be 8 ng/L and 4 ng/L, respectively. Even after applying the worst-case scenario approach, the tested nGOs pose no environmental risk.