Microplastic contamination in the Karnaphuli River, Bangladesh: a case study of exposure pathways in data-scarce tropical river systems

ABSTRACT Graphical summary of microplastic pollution in the Karnaphuli River. It illustrates sources such as industrial discharge, municipal waste, and urban runoff, transport through water and sediments, ingestion by fish, and human exposure through fish consumption, highlighting a source-to-human pathway. Microplastic (MP) pollution is an emerging environmental concern in the Global South, yet its implications for human exposure remain insufficiently understood. This study presents a systematic literature review following Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, applying a Source–Pathway–Receptor (SPR) framework to synthesize current evidence on MP occurrence, transport, and biological uptake in the Karnaphuli River, a highly industrialized system in Bangladesh. Available studies consistently report a predominance of synthetic fibres and fragments, largely associated with textile discharge, municipal wastewater, and urban runoff. Spatial evidence suggests downstream accumulation, with estuarine zones functioning as important depositional environments. The synthesis indicates that both the water column and sediments act as key pathways facilitating MP ingestion by freshwater and estuarine fish. In the local context, the consumption of small indigenous species and dried fish (Shutki), often eaten whole, represents a plausible route of human exposure. Experimental studies further suggest that MPs may release associated chemical additives under gastrointestinal conditions, indicating the potential for combined physical and chemical exposure. Despite increasing research since 2022, significant gaps remain, particularly in freshwater fish data and quantitative exposure assessment. Overall, the Karnaphuli River basin may represent a potential MP exposure hotspot, highlighting the need for source-level mitigation and integrated environmental–health research.