Microplastics Contamination and Potential Health Risks in the Newly Identified Oyster Crassostrea (Magallana) saidii from Malaysia’s Muar River Estuary

Microplastics (MPs) are widespread in aquatic environments, raising serious ecological and food safety concerns. This study investigated the occurrence, abundance, and physical characteristics of MPs in Crassostrea (Magallana) saidii , C. (M.) saidii, a newly recognized oyster species native to the Muar River estuary in Malaysia. Oysters from three age categories (juvenile, young, and adult) were collected and assessed for MPs using chemical digestion and density separation. MPs abundance increased with oyster age, from 3.4 ± 0.7 MPs in juveniles to 11.6 ± 2.6 MPs in adults, with fibers (58.3%) and black particles predominating (48%). Human health risk assessment was performed using three integrated indicators: the Estimated Daily Intake (EDI), Contamination Magnitude per Particle Index (CMPI), and Polymer Hazard Index (PHI). The EDI values ranged from 0.097 and 0.433 particles/kg of body weight/day, under typical (20 g/day) and high (50 g/day) consumption scenarios. CMPI (0.16–0.52) and PHI (13.85–16.70) values indicated low to moderate polymer-related hazards that increased with oyster age. These findings establish C. (M.) saidii as a promising bioindicator of estuarine MPs contamination and emphasize the importance of continuous monitoring to safeguard seafood safety in Malaysian waters.