Integrated assessment of microplastic contamination in bank sediments of urban Rivers in Khulna, Bangladesh

Abstract

Microplastic pollution has emerged as a growing environmental concern in freshwater ecosystems, particularly in rapidly urbanizing regions of developing countries. This study provides the first integrated assessment of microplastic contamination in the bank sediments of the Bhairab and Rupsha Rivers in Khulna, Bangladesh, combining quantitative distribution analysis with comprehensive physicochemical characterization. Sediment samples collected from ten locations along both rivers were analyzed using a modified NOAA extraction protocol, followed by FTIR, Raman spectroscopy, SEM-EDX, and XRD investigations. Microplastic abundance ranged from 5 ± 2.8 to 24 ± 7.8 particles kg−1 dry weight, with the highest concentrations recorded at RupshaGhat and Fulbari Gate Ghat, indicating strong anthropogenic influence. A clear upstream-to-downstream enrichment trend was observed. Fragments constituted the dominant morphology (51%), while the 2–3 mm size fraction and colored particles (86%), particularly red microplastics, were most prevalent. Spectroscopic analyses identified polypropylene (PP) and polyethylene terephthalate (PET) as the dominant polymer types, primarily originating from household plastic products and single-use beverage containers. SEM-EDX and XRD results revealed significant environmental weathering and semi-crystalline polymer characteristics. Although the Pollution Load Index classified all sites within Risk Category I (slight contamination), the zone-level PLI of 2.1 indicates emerging ecological pressure. The novelty of this work lies in its multi-technique characterization approach and spatial risk assessment of urban river sediments in southwestern Bangladesh. These findings provide critical baseline data for microplastic monitoring, support evidence-based waste management strategies, and contribute to the development of sustainable policies for protecting freshwater ecosystems and ensuring a safe ecological environment.