Freshwater Bivalve Coelatura aegyptiaca as a Sensitive Bioindicator for Zinc Oxide/ Chitosan Nanocomposites Toxicity

Abstract

Background: Freshwater bivalves are considered effective biomarkers for pollution in aquatic ecosystems. Despite advances in the use of zinc oxide nanoproducts in several sectors, such as food, industry, and medicine, paying attention to their environmental impacts is crucial. The objective of the study was to investigate the mechanisms of zinc oxide-chitosan nanocomposites (ZnO-CS NCs) ecotoxic in freshwater environments using freshwater bivalves Coelatora aegyptica as a sensitive indicator. Methods: After preparing and characterizing ZnO NPs and ZnO-CS NCs with transmission electron microscopy, ultraviolet spectroscopy, and X-ray diffraction, we exposed the bivalve to three different doses of ZnO NPs and ZnO-CS NCs (12.5, 25, and 50 mg/L) for 7 days. Results: ZnO-CS NCs concentrations significantly increased malondialdehyde and nitric oxide levels, whereas glutathione and catalase levels decreased in investigated organs. Furthermore, histological changes were detected in the tissues of the gills and mantle. Discussion: The bivalve organs had varying quantities of MDA, NO, GSH, and CAT. This could be related to the accumulation pattern of heavy metals in each organ, their close interaction with water, or the removal rates. Conclusion: We concluded from our findings that the toxicity of ZnO-CS NCs on freshwater bivalves causes histological alterations and an oxidative stress response. Moreover, Coelatura aegyptiaca was proposed as a highly sensitive bioindicator to monitor water contamination induced by diverse nanoparticles because it can accumulate and concentrate most pollutants, even at low concentrations. As a result, we recommend conducting additional studies with fresh bivalves to evaluate the aquatic ecosystem well and reduce water contamination at both local and worldwide levels.