Common and Particular Biochemical Effects of Gadolinium and Yttrium in the Bivalve Mollusc Unio tumidus

ABSTRACT

Environmental concentrations of rare earth elements (REEs) are increasing rapidly due to their widespread application in modern technologies. Because 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 (GdCl ₃ , 30 nM) and yttrium (YCl ₃ , 30 nM) for 14 days. The accumulation of Gd, Y, Zn (Zn‐t) in the tissue, 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, whereas the concentration of Y was below the limit of detection (< 0.2 μg/g FW). Correspondingly, Gd induced the specific responses: decreased lysosomal integrity and caspase‐3 depletion. However, both exposures affected the concentration and distribution of Zn in the tissue. They increased 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 effective antioxidant protection. Nevertheless, choline esterase activity decreased in both exposures. The Integrated Biomarker Response index (v.2) indicated a stronger response to Gd. These findings highlight interactions between REEs and essential metal‐based biochemical targets in U. tumidus and can contribute to the assessment of rare earths' impact in areas affected by mining or military activities.