Polystyrene microplastic induced immunotoxicity and redox dysregulation in the tropical sand star Astropecten euryacanthus of the Bay of Bengal: An integrated biomarker approach

Polystyrene microplastics (PS-MPs) are emerging contaminants increasingly detected in coastal ecosystems, but quantitative information on PS-MP-associated immunotoxicity in tropical benthic asteroids of the Bay of Bengal remains limited. This study hypothesised that exposure to experimental PS-MP concentrations, which exceed typical environmental concentrations, would disrupt immune regulation and redox homeostasis in the tropical sea star Astropecten euryacanthus. Adult specimens were exposed to PS-MPs (0.25, 0.5, and 1 mg/L) for 7 and 14 days under controlled laboratory conditions to assess immunophysiological and oxidative stress responses. PS-MP exposure increased total coelomocyte abundance, indicating an activated cellular immune response. Flow cytometry revealed a reduction in G1-gated blast-like cells from 8.87% to 2.84% and an increase in G3-gated petaloid cells from 8.88% to 20.15% at 1 mg/L, indicating marked changes in coelomocyte population distribution. Oxidative imbalance was evident from increased superoxide anion production and intracellular reactive oxygen species, particularly in G1-gated coelomocytes. Superoxide dismutase and catalase activities declined, whereas glutathione-S-transferase activity increased, suggesting differential regulation of antioxidant and detoxification pathways. The integrated biomarker response (IBR/n) provided a descriptive representation of the combined biomarker responses and demonstrated concentration- and exposure-duration-dependent variation in the overall biomarker profile. Future studies should evaluate chronic responses to lower, environmentally relevant PS-MP concentrations, particularly because the concentrations examined in the present study represent acute dose exposure scenarios relative to field concentrations. Collectively, These findings suggest the biomonitoring potential of A. euryacanthus for evaluating microplastic-associated environmental risks in tropical benthic habitats of coastal ecosystem.