Spatio-temporal dynamics and flux of microplastics in the lower Ganges-Brahmaputra-Meghna River system and estuary

Rivers are major pathways of land-based plastic debris to the oceans, but limited data exist for microplastic (MP) flux from large river systems. This study examines the spatial and seasonal dynamics of MPs in the Ganges-Brahmaputra-Meghna (GBM) River system and estuary, a key contributor to global marine plastic pollution. MP abundances ranged from 1.53 to 8.13 items/L in the dry season and 2.67 to 7.67 items/L in the wet season, with no significant overall seasonal difference (p > 0.05). The dominated shape and color were fiber and blue, respectively, with the size class of 0.02–0.5 mm being predominant. The prevalent polymers during both seasons were rayon and polyethylene. MP transported into the Bay of Bengal (BoB) were calculated as 9.42 × 10¹² items/day (1.17 tons/day) during dry season and 33.95 × 10¹² items/day (10.78 tons/day) in wet season indicating that a substantial amount of MPs are being input to marine environment from GBM River system compared with other rivers globally. Risk assessments indicated high contamination levels (CF, PLI, and HI) and substantial ecological risks (RI) values in the entire study area with maximum pollution level gradient at the Ganges, Meghna and GBM confluence. These findings contribute important quantitative information on spatio-temporal patterns and load of MP, necessary for validation of global-level MP flux models and the development of focused mitigation strategies within the GBM basin.