Isolated and combined toxicity of PVC microplastics and copper on Pinctada fucata martensii: Immune, oxidative, and metabolomics insights

PVC microplastics (PVC MPs) and copper (Cu) are pervasive marine pollutants with significant ecological impacts. This study analyzed individual and combined effects of PVC microplastics (PVC MPs) at concentrations of 1 and 5 mg/L and copper (Cu) at concentration of 5 μg/L on immune response, oxidative balance, detoxification capacity, and hepatopancreas metabolomics in Pinctada fucata martensii. Pearl oysters were exposed to these stressors for 13 days, followed by a 7 days recovery phase. Immune enzymes: acidic phosphatase (ACP) and alkaline phosphatase (AKP); antioxidant enzymes: catalase (CAT), superoxide dismutase (SOD), and glutathione peroxidase (GPx); and detoxification enzyme: glutathione S-transferase (GST) were assessed, alongside hepatopancreas metabolomic profiling. Results showed that combined exposure (MPs + Cu) significantly elevated ACP and AKP activities compared to individual treatments, indicating enhanced immune activation. Oxidative stress biomarkers (CAT, SOD, GPx) were significantly higher in co-exposed groups, suggesting synergistic toxicity. Moreover, metabolomic analysis revealed significant alterations in key pathways, including glycerophospholipid metabolism, pentose and glucuronate interconversions, arachidonic acid metabolism, and phosphatidylinositol signaling, reflecting disruptions in membrane integrity, energy metabolism, and inflammatory responses. During recovery, enzyme activities and metabolite trends indicated partial physiological restoration, though co-exposed oysters exhibited prolonged metabolic disturbances. This study highlights the compounded toxicity of MPs and Cu, emphasizing their role in impairing bivalve health through oxidative stress, immune modulation, and metabolic disruption. The findings highlight the need for comprehensive risk assessments of marine pollutant interactions to mitigate ecological and aquacultural impacts.