Effects of Wastewater-Borne Nanoparticles of Silver and Titanium Dioxide on Survival, Growth, Reproduction and Biochemical Markers of Daphnia Magna

Silver (Ag) and titanium dioxide (TiO2) nanoparticles (NPs) are released into aquatic environments through wastewater treatment plants (WWTPs). Even though these NPs are mostly retained in WWTPs, a small fraction can be found in the released effluents and may exert toxic effects on aquatic biota. Currently, the available information about sublethal effects of wastewater-borne NPs on aquatic organisms is inconclusive and the importance of exposure media remains poorly understood. Previously, we demonstrated that rainbow trout juveniles chronically exposed to wastewater-borne AgNPs or TiO2NPs caused no effects on fish growth, but antioxidative stress mechanisms were triggered in fish organs. Accordingly, this study aimed to: (i) assess the chronic (21-d) effects of wastewater-borne AgNPs (0.3-23.5 µg.L-1 Ag) and TiO2NPs (2.7-3.9 µg.L-1 Ti) on survival, growth, and reproduction of Daphnia magna; (ii) determine the short-term (96-h) effects of the wastewater-borne AgNPs (30.3 µg.L-1 Ag) and TiO2NPs (6.3 µg.L-1 Ti) at the subcellular level (biochemical markers of neurotoxicity, anaerobic metabolism, and oxidative stress); and (iii) compare the effects obtained in (i ) and (ii) with the corresponding ones induced by effluent-supplemented and water-dispersed NPs. The total Ag and Ti levels were analytically quantified in all treatments. It was demonstrated that both wastewater-borne NPs are considered non-toxic to D. magna at the used concentration ranges, considering the endpoints for survival, growth, reproduction, and selected biochemical markers. Contrarily, when pristine forms of NPs were supplemented to effluents or water, concentration-dependent effects were noticed, particularly on the cumulative offspring of daphnids. The significant effects on anaerobic metabolism and detoxification pathways caused by the effluent itself indicate background toxicity. Bearing in mind the achievement of a well-founded risk assessment of NPs in the aquatic environment, this integrative approach comes up with with relevant information about the harmlessness of potentially transformed NPs present in environmental matrices like WWTP effluents