Salinity modulation of neodymium and dysprosium toxicity in mussels: A comprehensive analysis of adult and sperm responses.

Neodymium (Nd) and dysprosium (Dy) are among the most commonly used rare earth elements (REEs) worldwide, leading to their increased concentrations in aquatic environments, with potential impacts on organisms. Additionally, organisms are also subjected to environmental stressors, such as salinity shifts, which can not only directly impact their health but also modulate the impacts of contaminants. Therefore, this study aimed to evaluate the effects of Nd and Dy on adult mussels and sperm of the species Mytilus galloprovincialis after 28 days and 30 min of exposure, respectively. Furthermore, the study assessed how salinity shifts influence the effects of these elements. To this end, histopathological and biochemical alterations were evaluated in adults, while biochemical and physiological changes were analyzed in sperm. To simplify data interpretation and understand the overall impact of each treatment, Multidimensional Scaling Analysis (MDS) and the Integrated Biological Index (IBR) were used. The MDS analysis identified three groups that were consistent with the IBR score. The first group, composed of the treatments at a salinity of 40, showed medium to severe effects. The second group was comprised of the treatments at control salinity (30), which presented the lowest IBR scores, indicating the least impact. The third group, which included the treatments at a salinity of 20, was associated with the most severe impacts, with Dy and Nd presenting the highest IBR scores. The results showed that salinity was the most predominant factor in this study, with the lower salinity being the most harmful. In addition, within each salinity level, Dy was the element that induced the highest response in this species. This study provides valuable information regarding the impacts of the interaction between REEs and salinity shifts, highlighting the importance of such research in mitigating the effects of pollution and climate change on marine ecosystems.