Microplastic pollution in coastal Cox's Bazar, Bangladesh: Quantification, distribution, and characteristics

This study assessed microplastic (MP) pollution in coastal sediments and nearshore seawater along Cox's Bazar, Bangladesh, integrating spatial quantification with morphology, polymer fingerprinting, and a weathering or oxidation proxy. Surficial sediments (n=18; high-tide line [HTL] and low-tide line [LTL]) and seawater (n=12) were collected from Laboni, Sugandha, and Kolatoli beach points. Microplastics were isolated via density separation and wet peroxide oxidation, enumerated by stereomicrocopy, and characterized using scanning electron microscopy (SEM). Polymer composition was confirmed using ATR-FTIR with library matching, and oxidative weathering was evaluated using a carbonyl index (CI). MP abundance differed significantly between HTL and LTL across all sampling locations (p<0.05), indicating shoreline deposition as a key accumulation pathway. Sediment MPs were highest at Laboni HTL (44.0±15.9 items kg -1 ) and lowest at Kolatoli LTL (3.3±1.2 items kg -1 ). Seawater MPs exhibited a similar spatial variation, with the highest concentration at Laboni (17.3 ± 6.1 items L⁻ 1 ) and the lowest at Kolatoli (8.7 ± 5.8 items L⁻ 1 ). Fibrous morphotypes dominated across the matrices, and colored particles accounted for 57% of the observed MPs. ATR-FTIR identified polyethylene (41%) and polyvinyl chloride (29%) as predominant polymers. CI results indicated advanced oxidation in PET relative to polyolefins, suggesting heterogeneous aging and a variable interaction potential with contaminants. In summary, Cox's Bazar serves as a key sink and redistribution area for microplastics, highlighting the importance of implementing targeted coastal waste management strategies, tourism industry interventions, and sustained monitoring frameworks.