水環境汚染の評価に向けた海洋マイクロプラスチックの分析

Microplastics in environments is an important class of plastic litter that has attracted great attention as emerging pollutants in recent years. In this study, we conducted a preliminary field survey in aquatic environments. The identification and analysis of drifting microplastics residue in surface seawater collected from urban areas were performed. Drifting samples were taken from three stations in Tokyo Bay, using a plankton net. At first, samples on grass fiber filters were visually sorted to pick up substances supposed to be microplastics. The substances were then analyzed by FT-IR to identify the polymer of microplastics (polyethylene (PE), polypropylene (PP), and (polystyrene) propylene (PS)). As results, microplastics were found at all studied stations with the total number of 414 particles, which suggest that they ubiquitously distribute in aquatic environments. Secondary microplastics were frequently detected in samples. In addition, the size distributions of microplastic particles showed that relatively small sizes of particles (0.5–1 mm) were very abundant (51.4 %) compared to lager particles. These results suggest that the fragmentation of large plastic litter in environments is an important source of microplastic. As for the polymer composition microplastic, PE was predominantly detected, accounting for 60.1 % of the identified microplastics, followed by PP (27.3 %) and PS (12.6 %). The results in this study imply needs for investigating the environmental fates of microplastic particles as well as pollutants accumulated on drifting microplastics.