Evaluation of Environmental Hazards of Nanocomposite Use for Wastewater Treatment ^†

Antibiotics are not completely metabolized nor degraded in traditional wastewater treatment, leaving a large proportion of them in the wastewater. Consequently, water bodies become reservoirs of antibiotics, where antibiotic resistance can develop. Therefore, a new strategy for the efficient, selective, and cost-effective removal of antibiotics from wastewater is being developed within the ANTIBIO project [1] using imprinted magnetic nanomaterials. However, in order to apply the new materials on a large scale, their potential harm to the environment has to be evaluated. We used aquatic ecotoxicology tests according to OECD/ISO to evaluate the environmental hazard of the novel nanocomposites. We used bacteria Vibrio fischeri, water fleas Daphnia magna and algae Raphidocelis subcapitata to study the toxicity of the nanocomposites as well as their component materials, including organic polymers, TiO₂, ZnO and magnetite (Fe₃O₄). The studied concentration range was 0.01–100 mg/L. Out of the tested samples, only ZnO was toxic to all organisms, with EC₅₀ values (mg/L) 3.9 for V. fischeri, 3.3 for D. magna and 0.1 for R. subcapitata. When the inhibition was calculated based on mg Zn per liter, ZnO and ZnSO₄ were equally toxic, indicating the shedding of Zn ions as a possible mechanism of ZnO toxicity. Magnetite was toxic to algae, with an EC₅₀ value of 2.2 mg/L; however, the composite containing magnetite core was not harmful to algae. In contrast to our previous studies [2,3,4], TiO₂ did not inhibit algal growth at 100 mg/L and the entrapment of algal cells within TiO₂ aggregates was not witnessed. According to our results, the organic polymers as well as the TiO₂ produced within this study are not environmentally harmful, while the toxicity of ZnO has to be considered when designing nanocomposites.