From sub-individual responses to ecological risk through an integrative framework based on the Health Status Index...

Understanding how sub-individual disturbances propagate to organism-level functions remains a central challenge in ecotoxicology, particularly for benthic species exposed to emerging contaminants. In this study, the effects of barium chloride (BaCl₂) were investigated in the clam Ruditapes decussatus using an integrative framework combining biochemical, lipidomic and functional endpoints. A total of 80 clams were exposed for five days to 0, 20, 40 and 80 mg/L BaCl₂ (n = 20 per treatment), and analyses were conducted on whole soft tissues to capture organism-wide responses. Exposure induced a marked oxidative imbalance, reflected by concentration-dependent increases in H₂O₂, lipid peroxidation products (LOOH and MDA) and protein oxidation (PCO), together with contrasted antioxidant responses. GSH, MT, vitamin C, SOD, GPx and GST increased, reflecting activation of antioxidant and detoxification pathways, whereas CAT and FRAP declined. Nevertheless, the overall response profile revealed that these compensatory mechanisms became insufficient at higher exposure levels, resulting in progressive physiological deterioration. Lipid remodeling was also pronounced, with decreases in saturated and monounsaturated fatty acids and a concomitant increase in polyunsaturated fatty acids, suggesting membrane adjustment and increased susceptibility to oxidative damage. At the functional level, burrowing performance was progressively impaired, while filtration activity exhibited a non-monotonic response, with stimulation at 20 mg/L followed by a decline at 80 mg/L. Multivariate analysis revealed a clear separation of treatments along a contamination gradient, with 20 mg/L occupying an intermediate position between control and highly stressed organisms. This pattern was supported by the Health Status Index, which decreased from 0.59 in controls to -0.79 at 80 mg/L, indicating a progressive shift from physiological balance to systemic stress. Overall, these findings demonstrate a hierarchical cascade linking oxidative disturbance, lipid remodeling and functional impairment. These results highlight the value of integrating sub-individual and functional endpoints for the ecological risk assessment of emerging contaminants. Such an approach may improve the early detection of contaminant-induced stress in coastal ecosystems and support environmental monitoring and management strategies for benthic communities.