Microplastics in commercial bivalves from the upper gulf of Thailand: Do location, season, and species ecology matter to human dietary exposure?

Evaluating human food safety risks from microplastics (MPs) in seafood should avoid traditional pooled composite sampling, which introduces an artificial 100% prevalence baseline and skews downstream risk assessments. To overcome this, our study utilized an individual-centric approach to simultaneously track MP detection rates (P, %), mass concentrations (particles g −1 wet weight), and abundances (particles individual −1 ) from oysters ( Saccostrea forskalli ), green mussels ( Perna viridis ), blood cockles ( Tegillarca granosa ), and Venus clams ( Paratapes undulatus ) across wet and dry monsoonal regimes in Chonburi and Rayong provinces, Thailand. Individual independent replicate digestions revealed higher baseline detection frequencies in benthic clams and cockles (65.0%) than in suspended-culture oysters and mussels (55–58%). Cockles and clams exhibited significantly greater mass concentrations and abundances, suggesting habitats affect consumer exposure probabilities. There was no clear seasonal variation in contamination, except that wild-caught clams had greater MP in the wet than dry season, revealing higher dietary risks for wet-season wild catches. Multi-metric dietary analysis demonstrated that annual Estimated Daily Intakes in Thailand were highest for cockles and oysters due to local consumption preferences. Acute single-meal (100 g) profiling revealed that clams and cockles had higher MP contaminants, followed by mussels and oysters. An abundance approach shifted hazard maxima to cockles due to smaller sizes. Chonburi bivalves contained high-toxicity PVC, resulting in the Polymer Hazard Index classifying Chonburi's benthic bivalves as Level III “Strong Hazard” while Rayong cohorts remained at Level II “Moderate Hazard”. Our multi-metric analysis indicates seafood safety relates to the interplay of species ecology, consuming seasons, and locations.