Mechanistic insights into single and mixed platinum group metal toxicity in Mytilus galloprovincialis: An integrated biomarker approach

Platinum group elements (PGEs), namely platinum (Pt), palladium (Pd), and rhodium (Rh), are increasingly recognized as emerging contaminants due to their extensive use in automotive catalysts, industry, and medicine. Their continuous release and accumulation in aquatic environments have raised ecotoxicological concerns, yet experimental data on their biological and interactive effects remain scarce. This study provides one of the first comprehensive evaluations of the sublethal and mixture effects of Pt, Pd, and Rh on the marine mussel Mytilus galloprovincialis, a sentinel species. Mussels were chronically exposed for 28 days to environmentally relevant concentrations (2, 20, and 200 μg/L) of each metal and to binary and ternary mixtures (20 μg/L each). A suite of biochemical biomarkers was analyzed, covering energy metabolism, antioxidant defenses, detoxification, and cellular damage, enabling a mechanistic understanding of metal-specific and mixture effects. Distinct dose-dependent responses emerged: Pt at low levels stimulated metabolism and antioxidant activity; Pd at high levels impaired energy reserves and mitochondrial efficiency; Rh caused oxidative damage to lipids and proteins. The Independent Action model revealed that interaction type and magnitude varied among mixtures. Synergistic effects predominated in Pt+Pd and Pt+Rh (≈50 % of biomarkers), while Pd+Rh showed mainly additive or synergistic patterns, and the ternary mixture (Pt+Pd+Rh) displayed mostly additive responses (50 %). Multivariate (PCO) and integrative (IBRv2) analyses confirmed distinct biochemical fingerprints for each exposure. Overall, this study pioneers the mechanistic evaluation of PGEs mixtures in marine organisms, highlighting their emerging and complex ecotoxicological risks.