Common and particular biochemical effects of gadolinium and yttrium in the bivalve mollusc Unio tumidus

Environmental concentrations of rare earth elements (REEs) are increasing rapidly due to their widespread application in modern technologies. Since the biological effects of REEs are expected to be like those of essential metals, the goal of this study was to verify the impact of selected REEs on the Zn-related biochemical characteristics in the bivalve mollusc Unio tumidus. The mussels were treated with environmentally relevant concentrations of gadolinium (GdCl3, 30 nM) and yttrium (YCl3, 30 nM) for 14 days. The accumulation of Gd, Y, Zn in the tissue (Zn-t), the level of metallothioneins (total MTSH and Zn-bound, ZnMT), as well as the redox state and enzyme activities, were studied in the digestive gland. Molluscs accumulated Gd, but not Y, in the tissue. Both exposures caused signs of neurotoxicity as indicated by choline esterase activity, and decreased Zn-t, whereas the level of ZnMT was unchanged (Gd-group) or decreased (Y-group). In both exposures, the concentrations of GSH, GSSG, MTSH, NADH, and NAD+, as well as the NADH/NAD+ ratio, increased dramatically and lipid peroxidation (TBARS) decreased, indicating a reductive shift and antioxidant activity. Specific effects of Gd included decreased lysosomal integrity and caspase-3 depletion. The Integrated Biomarker Response index (v. 2) indicated a stronger response to Gd. These findings highlight the interaction of REEs with essential metal biochemical targets, confirming the link between the effects of investigated REEs and Zn functionality in U. tumidus, and can contribute to the assessment of rare earths' impact in areas affected by mining or military activities.