Distribution and characterization of microplastics in marine sediments from coastal and offshore in South Korea

The seafloor is considered the ultimate repository for microplastics in the environment. Sediment can accumulate microplastics over extended periods due to low degradation rates under poor light and oxygen-deficient conditions. We conducted an intensive assessment survey to determine the levels, distribution profiles, and contamination characteristics of microplastic in the seafloor of coastal and offshore areas. The study focused on a coastal bay (Masan Bay) and an offshore area (East Sea). Surface sediment samples were collected using Van Veen Grab and box core samplers in Masan Bay (n=27) and the East Sea (n=47) from 2022 to 2023. Microplastics were detected in all sediment samples collected from Masan Bay and the East Sea, with concentrations ranges of 3,189-75,375 n/kg and 892-43,209 n/kg, respectively. The overall microplastic abundance was higher in the coastal bay compared to the offshore area, with a negative gradient in microplastic concentration observed from inside to outside of the bay. Among the various polymers, polyethylene, polypropylene, polyester, and polyethylene terephthalate exhibited concentration gradients. These results indicates that land-based human activities are a significant source of microplastic in the marine environment. Fragment-type microplastics were predominant in both the coastal bay and offshore area, while fibers were relatively more abundant in the coastal bay. Low-density polymers such as polyethylene, polypropylene, and polyethylene vinyl acetate were relatively abundant in the coastal region, while high-density small microplastics were more prevalent in the offshore area. Exceptionally high microplastic abundances were found at a dumping site and its surrounding areas, with spherical polystyrene being particularly abundant. Also see: https://micro2024.sciencesconf.org/559369/document