Unraveling microplastic pollution patterns in sediments of a river system: The combined impacts of seasonal changes and waterway differences.

Microplastic (MP) distribution in river sediment, influenced by water regimes and pollution sources, remains understudied in the current literature. This study examines the combined impacts of seasonal variation and waterway differences on MP concentration in the sediment of the Saigon River and its tributaries, while identifying potential sources. Paired sediment samples were collected from eleven sites along the river and its tributaries during rainy and dry seasons. MPs from these 44 samples were separated, quantified, and characterized for a comprehensive assessment. The results revealed that MP concentrations in sediments ranged from 140 to 1200 items kg^-1, with predominant characteristics of fiber particles, white color, and particle sizes ranging from 200 to 500 μm. During the rainy season, MP concentrations were similar between the river (584 items kg^-1) and tributaries (553 items kg^-1), while during the dry season, tributaries exhibited statistically higher MP concentrations (737 items kg^-1) than the river (351 items kg^-1). Notably, the river, despite being farther from the sources, had a higher proportion of smaller MPs (<200 μm), while larger particles (>200 μm) were more prevalent in tributaries. These discrepancies are attributed to the combined impacts of water flow patterns and pollution sources, derived from residential, industrial, and agricultural activities. In brief, MP pollution in the river and tributary sediments is influenced by the interplay of seasonal variation and waterway characteristics, determined by water flow patterns and pollution sources. These findings emphasize the need for specific management strategies that account for spatial and temporal variations in MP distribution.