Influence of aged and non-aged environmentally relevant microplastics on zinc removal from aqueous media by Daphnia magna

Recent studies have highlighted the potential of Daphnia magna (D. magna) as a bio-based tertiary system for improving treated water quality. However, further research is needed to study the impact of micropollutants on these planktonic crustaceans. The present work provides an in-depth investigation of how microplastics (MPs), emerging contaminants of high-environmental interest, can influence the removal of Zn²⁺ (selected as a pollutant model) from water by D. magna individuals. With this purpose, true-to-life MPs were obtained by micronizing commercially available plastic devices of different polymers (polyethylene, polypropylene, and polystyrene) and sizes (<63 µm and 63–80 µm). Additionally, the produced MPs were exposed to UV radiation to simulate aging processes in natural environments that can lead to changes in their physicochemical properties, and their bioavailability and toxic effects to organisms. An integrated analytical framework combining complementary techniques was employed, including confocal microscopy to detect and localize MPs in D. magna individuals, infrared spectroscopy to characterize structural changes in aged and non-aged MPs, and inductively coupled plasma optical emission spectroscopy (ICP-OES) for quantitative determination of zinc in aqueous samples and digested organisms. Results showed that although the presence of MPs does not significantly affect Zn²⁺ removal from the aqueous media, MP polymer type or aging state affects Zn²⁺ accumulation in the living organisms. On the contrary, the effect of MP size seems to be negligible, at least in the studied size range (<63 versus 63–80 µm).