A systematic review of microplastic pollution in rivers across Asia

Microplastics are widely distributed in the aquatic ecosystem globally. They pose potential risks and harm to the ecosystem and human health. Contamination of river environments by microplastics has raised concern due to its negative effect on the aquatic system. Asian rivers serve the world’s most populous continent, encompassing many developing countries experiencing rapid development and associated environmental challenges. In this article, we critically reviewed research papers published between 2011 and 2024 that reported microplastic contamination in major river systems across Asia. These papers examined the occurrence, distribution, sampling methods, sample preparation and identification techniques, and characterization of microplastics. Our review found that the majority of microplastic studies in Asian rivers have been conducted in China. Other countries reporting riverine microplastic pollution include India, Malaysia, Taiwan, Japan, South Korea, Thailand, Nepal, Iran, Pakistan, Hongkong, Vietnam, Cambodia, Bangladesh, Maldives, and Indonesia. The reported microplastic concentration varied widely, ranging from just a few particles to as high as 4,200,000 particles per cubic meter. Fibers were identified as the most dominant type of microplastics among fragments, foam, pellets, and film. A wide range of colors was observed, including red, black, blue, white, yellow, green, transparent, with white being the most prevalent one. Among the identified polymers, polypropylene was the most common in the river surface waters. Other reported materials included poly(ethylene-propylene), polyamide, polystyrene, polyurethane, cellulose, polyethylene terephthalate, silicone, polyester, rubber, and plastic coatings. Identified sources of microplastics identified domestic sewage, fishing, shipping activities, beautifying products and personal care products. Finally, this review highlights the urgent need for further research on microplastic pollution in Asian river system.