Plastics and biodegradable plastics: Ecotoxicity comparison between polyvinylchloride and Mater-Bi® micro-debris in a freshwater biological model

The improper release of plastic items and wastes is nowadays one of the main environmental and social problems, whose solution or mitigation represents a great challenge worldwide. In this context, the growing use of the so-called biodegradable plastics could represent a possible solution in the short to mediumterm. The few information known about the ecological impact of these materials on freshwater organisms, especially the ones relative to the micro-debris derived from their aging, prompted us to study the comparison of the sub-lethal effects eventually caused by plastic and biodegradable plastic micro-debris on the mussel Dreissena polymorpha, which represents an excellent biological model for the freshwater ecosystems. We selected two powders of polyvinylchloride (PVC) and Mater-Bi (R) administered at 1mg/L to D. polymorpha specimens in semi-static conditions for 14 days. The presence of micro-debris was evaluated on mussel tissues and pseudo-faeces using advanced microscopy techniques. The sub-lethal effects were investigated on exposed mussels at 6 and 14 days using a suite of biomarkers of cellular stress, oxidative damage, and genotoxicity. Lastly, we compared the ecotoxicity of these two materials integrating each endpoint in the Biomarker Response Index. Microscopy observations highlighted the surprising absence of micro-debris in the gut lumen and tissues of exposed mussels, but the presence of both PVC and Mater-Bi (R) micro-debris in the pseudo-faeces, suggesting a possible efficient elimination mechanism adopted by mussels to avoid the micro-debris gulping. Consequently, we did not observe significant sub-lethal effects, except for the glutathione-S-transferase activity modulation after 6 days of exposure.