Influence of seasonal variations on the distribution characteristics of microplastics in the surface water of the Inner Gulf of Thailand

Abstract

This study collected 100–1000 L of surface water from 70 to 74 sites in the Inner Gulf of Thailand in both dry and wet seasons to investigate the relationship between the spatiotemporal distribution of microplastics and environmental variables. The quantity of microplastics in the wet season (34.59 ± 46.02 pieces/L) was significantly higher than the dry season (8.70 ± 15.34 pieces/L). Spatial distribution revealed an abundance of microplastics in river estuaries and seasonal current circulations. Polymeric characterization results showed that the plastic samples primarily consisted of polypropylene and polyethylene. New functional groups, including carbonyl, hydroxyl, and vinyl groups, were found in the chemical structures of the microplastic samples. The amount of freshwater runoff and the negative relationship with salinity confirmed that the river is the key factor in the transportation of microplastics to the coastal sea.