A study on evaluating the distribution characteristics of microplastics entering the East Sea of Korea

Abstract

Marine microplastic pollution is a recognized global environmental problem. Microplastics entering the ocean are found from the surface to the bottom of the seafloor. Buoyant microplastics are also widely present in the water column due to various biological and physical factors. This study was conducted to determine the distribution and characteristics of microplastics in the water column entering the East Sea and to estimate the amount of input. The study was conducted in Sep. 2022 and Apr. 2023 at three stations located in the southeastern of Korea. Seawater samples were collected 100-200 liters from six water layers, and microplastics were analyzed by μFT-IR. The average concentration of microplastics in seawater collected in Sep. 2022 and Apr. 2023 was 247-757 n/m³ and 308-737 n/m³, respectively. Microplastic concentrations in seawater showed an overall decreasing trend with distance from the coast. No vertical pattern of concentration distribution of microplastics along the water column was observed. Polymer compositions varied, with September 2023 samples containing polypropylene (PP), polyethylene vinyl acetate (PEVA), polyethylene (PE), Alkyd, and polyester (PES)/polyethylene terephthalate (PET). In April 2023, Alkyd, PP, PEVA, PES/PET, and PE prevailed. PP is the dominant polymer detected in the water column, although it is positively buoyant due to its low density compared to seawater. The alkyd polymer, prominently detected in Apr. 2023, mostly exhibited small sizes ranging from 20-200 μm, with red and green colors being predominant(>90%).The microplastics entering through seawater at the beginning of the East Sea are a combination of land-based sources close to the land and ship activities at sea, and the input rate calculated from the flow velocity data at this point was 14.19 × 10⁷ particles per second. Future research should focus on seasonal variations, as well as vertical and horizontal distribution patterns, to refine input estimations further.