| Abstract | This research examines the abundance and transport pathways of microplastics (MPs) in the Bangkok Metropolitan Region (BMR), Thailand, with a focus on three main urban sources: domestic, agricultural, and livestock wastewater. Despite the rapid urbanization in Southeast Asia, there is a lack of comprehensive frameworks for understanding how MPs are introduced and transported within urban water systems. This study fills that gap by measuring seasonal MP fluxes at the source. Primary data were collected through seasonal field sampling across three decentralized domestic wastewater sites, two poultry breeding farms, and two agricultural runoff sites. Laboratory analysis involved organic digestion, density separation, and microscopic identification, with chemical validation via FTIR. MP characteristics were dominated by synthetic polymers, primarily polyethylene (PE) in domestic and agricultural sources, while polystyrene (PS) was most prevalent in livestock wastewater. Across all streams, small particles (10–500 m) and fibers were the most common forms, with white and transparent being the dominant colors, followed by blue. The average microplastic generation concentration in terms of particles per liter for domestic waste water are 15.46 for dry season and 7.09 for wet season; 1.43 for and 5.38 for dry season and wet season of agricultural waste water; 5.54 and 16.13 for dry and wet season of livestock waste water. Mass balance analysis estimated a total annual MP flux from domestic sources alone at approximately 10,83,142.05 million particles/yr, with over 39,21,902.233 million particles/yr retained in sewage sludge. From agricultural waste water sources (considering the paddy fields only) the MPs flux is 1082.94 million particles/yr and from livestock 10,473.32 million particles/yr annually. The study emphasizes that the direct release of uncollected domestic wastewater and agricultural runoff is a key pathway for MPs entering aquatic environments. These findings offer essential data for policymakers to create targeted mitigation measures and enhance water governance, supporting Sustainable Development Goals (SDG 11 and 14). |
