When aquatic exposure ends but effects persist: metal-dependent recovery dynamics

Emerging contaminants, such as rare earth elements and platinum group metals, have been receiving increasing attention from the international community due to their economic value and the consequent rise in their concentrations in the environment. Compared to classical contaminants, emerging contaminants pose an uncertain threat due to limited studies on their environmental fate and toxicological effects on organisms. Coastal and marine ecosystems are particularly vulnerable, given their high population density and industrial activities, which result in elevated inputs of these contaminants, mainly through domestic and industrial effluents. In this study, Mytilus galloprovincialis, a widely used bioindicator species in ecotoxicological surveys involving metals, was exposed for 14 days to relevant concentrations (20 μg/L) of yttrium (Y), platinum (Pt), and mercury (Hg), followed by a 14-day recovery period in uncontaminated seawater to assess the recovery and resilience of these organisms. A broad set of biomarkers was studied, from energy reserves and metabolic capacity, antioxidant responses, biotransformation enzymes, cellular damage, and neurotoxicity. The results revealed distinct metal-specific biochemical response and recovery patterns. Under the tested mass-based exposure conditions, Hg-exposed mussels exhibited the most persistent biochemical alterations, including depletion of energy reserves, oxidative stress-related responses, and cellular damage that remained evident after the recovery period. Exposure to Pt induced moderate biochemical adjustments, largely related to detoxification pathways, with limited reversibility after the recovery period. Exposure to Y led to milder responses, which were reversible during the recovery period. Overall, this study highlights differences in biochemical response trajectories between emerging and classical metals and underscores the importance of M. galloprovincialis as a bioindicator species for environmental monitoring. The findings further suggest that recovery potential depends on contaminant identity, exposure conditions and recovery dynamics, with relevant implications for ecological risk assessment and coastal pollution management.