Assessing year-round microplastic loading in the lower Brahmaputra River: A threat to aquatic environment

Rivers transport large quantities of microplastics (MPs) and suspended solids (SS) to the ocean. This study aimed to conduct a year-round analysis of MPs and total suspended solids (TSS) in the lower part of the Brahmaputra River in Bangladesh, estimate their outflow, and assess the resulting ecological risks. Fourier Transform Infrared Spectroscopy (FTIR) analysis identified nylon, polyethylene terephthalate, polypropylene, high-density polyethylene, and polystyrene polymers. The most common shape of MPs in the river water was fiber. Annually, 23.60 kg or 1.35 × 10⁴ trillion MPs and 2.08 × 10⁸ tons of SS outflows through this part of the river. Rainfall in the river basin is responsible for the high concentrations of MPs and TSS during the wet season. A species sensitivity distribution model based on toxicity data for freshwater species was used in this study to evaluate the ecological risks posed by MPs and SS. Risk assessment based on the risk quotient (RQ) suggests that MPs and SS pose potential risks to freshwater biota, particularly during the wet season. Overall, this study underscores the persistent presence of MPs throughout the year, highlighting the critical need for immediate and effective preventive measures to reduce MP pollution and protect freshwater biodiversity.