Common and specific effects of gadolinium and yttrium separately, and jointly with nifedipine, on the bivalve mollusc Unio tumidus

Environmental concentrations of rare earth elements (REEs) are increasing rapidly due to their unique properties and widespread application in modern technologies. Since the biological effects of REEs are expected to be similar to those of essential metals and cause oxidative stress, the goal of this study was to verify these directions of their impact in the bivalve mollusc Unio tumidus. The mussels were treated with gadolinium (Gd, 30 nM), yttrium (Y, 30 nM), and their mixture (Mix) with the Ca-channel blocker nifedipine (NFD, 10 µM) for 14 days. The distribution of zinc (Zn), involving metallothioneins (MT), as well as the redox state and signs of toxicity, was analysed in the digestive gland. The visible changes due to Gd accumulation, unlike those of Y, were observed in the tissue and were accompanied by a decrease in lysosomal integrity. Both Gd and Y increased the total MT (MTSH) concentration without increasing ZnMT levels. The presence of NFD alleviated the effects of single exposures to Gd or Y on MT and Gd accumulation. It induced approximately 2-fold increases in Cyp450-dependent EROD, caspase-3, and GTPase activities, indicating a Ca-dependent and Zn-related mode of action for the studied REEs. All exposures elevated GSH, GSSG, NAD, and NAD+ levels, as well as the NADH/NAD+ ratio, while decreasing lipid peroxidation (TBARS), indicating a reductive shift and cholinesterase inhibition. Discriminant analysis separated toxicant groups, and IBRv2 showed that the Gd group had the most significant impact on molluscs.