Microplastic ingestion and trait-weighted ecological risk assessment framework for intertidal invertebrates of the Cox’s Bazar Coast, Bay of Bengal

Microplastic pollution poses an increasing ecological threat to coastal ecosystems, yet organism-level exposure and risk in intertidal invertebrates from South Asia remain poorly documented. This study assesses MP ingestion and ecological risk across four major invertebrate groups (gastropods, bivalves, crabs, and barnacles) collected from 15 geo-referenced sites along the Cox’s Bazar coast, Bay of Bengal. A total of 132 MPs were recovered from invertebrate tissues, dominated by fibers (81%), followed by fragments (14%), films (4%), and foams (1%), with white and black particles most frequently observed. Fourier-transform infrared spectroscopy (FTIR) confirmed polyamide (48%) and polyethylene (42%) as the predominant polymers, with minor contributions from polypropylene and rare polyurethane. Multivariate analyses indicated consistent patterns linking fibrous morphotypes, dominant polymers, and specific invertebrate taxa, while spatial variation in MP burden was evident among sites. Ecological risk was evaluated using the Pollution Load Index (PLI), Polymer Hazard Index (PHI), and a newly developed Invertebrate Microplastic Hazard Index (IMHI), a trait-weighted framework integrating MP abundance, polymer hazard, and particle characteristics. Gastropods exhibited the highest MP burdens and associated risk scores, whereas crabs and barnacles showed lower but compositionally distinct exposures. Overall, the results highlight taxon-specific ingestion patterns and demonstrate the utility of a trait-weighted index as a screening tool for organism-level MP risk assessment in coastal ecosystems. • Intertidal invertebrates along the Cox’s Bazar coast show widespread microplastic ingestion across taxa and anthropogenic gradients. • Fibers dominated recovered microplastics, with polyamide and polyethylene indicating strong textile, fishing, and packaging inputs. • A novel trait-weighted Invertebrate Microplastic Hazard Index (IMHI) integrates abundance, polymer hazard, and particle traits at the organism level. • Multivariate ordination (PCA, HCA, RDA, CCA) resolved taxon-specific exposure pathways and spatial contamination structure. • Combining IMHI with multivariate analysis improves identification of ecologically meaningful risk patterns beyond particle counts alone.