Microplastics in the Northwestern Pacific: Abundance, distribution, and characteristics

Prevalence of microplastics (MPs) throughout the world's oceans has raised growing concerns due to its detrimental effects on the environment and living organisms. Most recent studies of MPs, however, have focused on the estuaries and coastal regions. There is a lack of study of MPs pollution in the open ocean. In the present study, we conducted field observations to investigate the abundance, spatial distribution, and characteristics (composite, size, color, shape and surface morphology) of MPs at the surface of the Northwestern Pacific Ocean. Samples of MPs were collected at 18 field stations in the Northwestern Pacific Ocean using a surface manta trawl with a mesh size of ~330 μm and width of 1 m from August 25 to September 26, 2017. The MPs were characterized using light microscopy, Micro-Raman spectroscopy, and scanning electron microscopy (SEM). Our field survey results indicate the ubiquity of MPs at all stations with an abundance from 6.4 × 10² items km^-2 to 4.2 × 10⁴ items km^-2 and an average abundance of 1.0 × 10⁴ items km^-2. The Micro-Raman spectroscopic analysis of the MPs samples collected during our field survey indicates that the dominant MPs is polyethylene (57.8%), followed by polypropylene (36.0%) and nylon (3.4%). The individual chemical compositions of MPs from the stations within the latitude range 123-146°E are comparable with each other, with PE being the dominating composition. Similar chemical fingerprints were observed at these field stations, suggesting that the MPs originated from similar sources. In contrast, the major MPs at the field stations adjacent to Japan is polypropylene, which may originate from the nearby land along the coast of Japan. Physical oceanography parameters were also collected at these stations. The spatial distribution of MPs is largely attributed to the combined effects of flow pattern, adjacent ocean circulation eddies, the Kuroshio and Kuroshio Extension system.