Seasonal effects, spatial distribution, and possible sources of microplastics in the Chao Phraya River estuary, Thailand

Abstract

Microplastics (MPs) in estuaries are sources of plastic debris that enter the marine environment. However, there is limited information on the seasonal effect on the accumulation of MPs in the estuaries of Thailand. The abundance and spatial distribution of MPs in the dry and wet seasons were investigated in the Chao Phraya River estuary, and possible emission sources were traced. Dominant factors affecting the distribution patterns of MPs have also been reported. All collected water samples contained MPs, with a mean abundance of 4.0 ± 2.8 × 10⁵ particles/km² in the wet season and 5.2 ± 3.3 × 10⁵ particles/km² in the dry season. Fragments were mostly observed, with polypropylene and polyethylene being the dominant polymers. The findings also showed that accumulation of MPs was directly influenced by the river discharge rate into the estuary. Further, the spatial distribution of MPs was closely related to seasonal variations in sea surface currents. Microplastic pollution status with seasonal variations and possible emission sources could provide important information to the government and local environmental organizations for MP pollution prevention and future MP studies in estuarine environments.

Graphical Abstract

Keywords:

• Microplastics
• estuary
• seasonal effects
• spatial distribution
• river discharge
• Chao Phraya river
• Thailand

Acknowledgments

The authors would like to thank Graham K. Rogers for editing and reviewing the English language.

Authors’ Contribution

Phyo Zaw Oo: Methodology, software, data curation, writing-original draft preparation. Suwanna Kitpati Boontanon: Conceptualization, funding acquisition, writing, review and editing, supervision. Narin Boontanon: Methodology and supervision. Shigeo Fujii: Reviewing, editing, and supervision. Shuhei Tanaka: Supervision.

Disclosure Statement

The authors declare no competing interests.

Data Availability

The data and materials for this study will be available from the corresponding author upon reasonable request.

Ethics Approval

This manuscript has not been published or presented elsewhere in part or entirety.

Consent for Publication

All authors agreed to publish this article in Marine Environmental Research.

Additional information

Funding

This work was funded by the On-site Laboratory Initiative of the Graduate School of Global Environmental Studies at Kyoto University. The required information and marine vessels were supported by the Regional Harbor Office (Samut Prakan branch).