Seasonal variations and spatial distribution of microplastics in tributary rivers and the Mekong mainstream in Ubon Ratchathani, Thailand

Pawena Limpiteeprakan; Sanga Tubtimhin; Pawena Limpiteeprakan; Sanga Tubtimhin

doi:10.3934/environsci.2026014

AIMS Environmental Science

2026, Volume 13, Issue 2: 348-361. doi: 10.3934/environsci.2026014

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Research article

Seasonal variations and spatial distribution of microplastics in tributary rivers and the Mekong mainstream in Ubon Ratchathani, Thailand

College of Medicine and Public Health, Ubon Ratchathani University, Ubon Ratchathani-34190, Thailand

Received: 30 January 2026 Revised: 30 March 2026 Accepted: 14 April 2026 Published: 24 April 2026

Microplastic (MP) pollution has emerged as a growing environmental concern in freshwater ecosystems, yet data from northeastern Thailand, a key hydrological region within the Mekong River Basin, remain limited. In this study, we investigated the abundance, characteristics, and seasonal variations of microplastics in six tributary rivers and four Mekong mainstream sites in Ubon Ratchathani Province. Surface-water samples were collected during the dry (April 2021) and wet (October 2021) seasons using a surface-trawl microplastic sampler, and particles were isolated through density separation and oxidative digestion before identification by FTIR spectroscopy. Nine polymer types were detected across all sites and seasons, with polypropylene (PP) and polyethylene (PE) as the predominant polymers. Seasonal differences were evident, with fragment-shaped MPs more abundant in the wet season, reflecting intensified hydrodynamic fragmentation, while fibers and sheets were more prevalent during the dry season. Tributary sites exhibited consistently higher MP abundances than Mekong mainstream sites, highlighting the importance of localized land-based inputs such as municipal wastewater, stormwater runoff, and urban activities. Overall, the findings demonstrate that hydrological conditions and land-use characteristics influence microplastic distribution within the region. This study provides baseline data for northeastern Thailand and contributes to understanding microplastic distribution in the Mekong River Basin.
- microplastics,
- Mekong River,
- seasonal variation,
- terrigenous input,
- polymer composition
Citation: Pawena Limpiteeprakan, Sanga Tubtimhin. Seasonal variations and spatial distribution of microplastics in tributary rivers and the Mekong mainstream in Ubon Ratchathani, Thailand[J]. AIMS Environmental Science, 2026, 13(2): 348-361. doi: 10.3934/environsci.2026014

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Abstract

Microplastic (MP) pollution has emerged as a growing environmental concern in freshwater ecosystems, yet data from northeastern Thailand, a key hydrological region within the Mekong River Basin, remain limited. In this study, we investigated the abundance, characteristics, and seasonal variations of microplastics in six tributary rivers and four Mekong mainstream sites in Ubon Ratchathani Province. Surface-water samples were collected during the dry (April 2021) and wet (October 2021) seasons using a surface-trawl microplastic sampler, and particles were isolated through density separation and oxidative digestion before identification by FTIR spectroscopy. Nine polymer types were detected across all sites and seasons, with polypropylene (PP) and polyethylene (PE) as the predominant polymers. Seasonal differences were evident, with fragment-shaped MPs more abundant in the wet season, reflecting intensified hydrodynamic fragmentation, while fibers and sheets were more prevalent during the dry season. Tributary sites exhibited consistently higher MP abundances than Mekong mainstream sites, highlighting the importance of localized land-based inputs such as municipal wastewater, stormwater runoff, and urban activities. Overall, the findings demonstrate that hydrological conditions and land-use characteristics influence microplastic distribution within the region. This study provides baseline data for northeastern Thailand and contributes to understanding microplastic distribution in the Mekong River Basin.

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