Microplastics Pollution in the Seto Inland Sea and Sea of Japan Surrounded Yamaguchi Prefecture Areas, Japan: Abundance, Characterization and Distribution, and Potential Occurrences

Marine microplastics pollution has been an emerging global threat. This study investigated microplastics pollution in the ‘Seto Inland Sea (SIS)’ and ‘Sea of Japan (SJ)’ surrounded Yamaguchi prefecture areas in Japan. The density separation method was applied to extract microplastics from sea surface sediment and water samples. Polymeric compounds were identified through ATR-FTIR analysis. The average microplastic abundances were 112.57 ± 121.30 items/kg in sediment and 57.46 ± 20.82 items/L in water. Abundance comparisons revealed similar level of pollution in both sea areas and medium to high-level pollution than others around the world. Characterization revealed that fragments and small microplastics (< 1,000 µm) predominated sediments. Fragments and films were major shapes in the SIS sediments while only fragments predominated the SJ sediments. Large microplastics (1,000–5,000 µm) fibers predominated water in all the areas. Transparent microplastics predominated both the sediments and water. Polyethylene, polyvinyl alcohol, and polypropylene were major polymers in sediments while polyethylene terephthalate and polyethylene predominated water. No significant correlations of microplastics abundances and characteristics were observed between sediment and water. Anthropogenic activities and environmental factors were speculated to be the main sources of microplastics in these areas. Overall, this study indicated that microplastics pollution in these marine areas could be an alarming environmental problem.