Suspended microplastics during a tidal cycle in sea-surface waters around Chao Phraya River mouth, Thailand

Roochira Sukhsangchan, Rangsiwut Keawsang, Suchai Worachananant, Thon Thamrongnawasawat, Jitraporn Phaksopa*

ABSTRACT: The study investigated the influence of tides (low and high) on composition and abundance of microplastic. Suspended microplastics (MP) were sampled in surface waters around the Chaophraya River mouth in Upper Gulf of Thailand using Neuston trawl (330-?m mesh) during tidal cycle at both tides in rainy season (August) of 2019. The abundance and types of microplastic had been analyzed. Overall, the concentration of MP during spring tide was significantly lower than the concentration during neap tide (p < 0.01). Suspended microplastic particle concentration ranged from 16.74 to 59.06 pieces per 100 m3 (spring tide) and 43.26 to 126.13 pieces per 100 m3 (neap tide). Concentration of MP found during flood tide was higher which suggested marine derived MP. Dominant samples identified under stereomicroscope were fibers and film. Using Fourier transform infrared spectrophotometry, the majority of the particles was identified as polypropylene. The effect of the tidal amplitude was an important factor determining the extent of the variations in microplastic abundance, which was stronger between the lower low tide and the higher high tide.

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^a	Department of Marine Science, Faculty of Fisheries, Kasetsart University, Bangkok 10900 Thailand

* Corresponding author, E-mail: jitraporn.p@ku.th

Received 28 May 2020, Accepted 10 Oct 2020