Prevalence of microplastic pollution in the Northwestern Pacific Ocean
People are increasingly aware of ubiquitous microplastic (MP) pollution in the world's ocean due to its far-reaching harmful impacts on marine ecosystem and potential hazards to human health, yet surprisingly comparatively limited studies about the abundance, source, transport, and fate of MPs in the Northwestern Pacific Ocean are available. We conducted the field survey of MPs pollution at the surface of the Northwestern Pacific Ocean between August 25 and September 26, 2017. MPs were collected from 18 sampling stations in the Northwestern Pacific Ocean using a manta trawl net with a mesh size of ∼330 μm and a rectangular net opening of 0.45 × 1 m. The abundance, shape, color, size, chemical composition, and surface morphology were characterized using light microscopy, μ-Raman spectroscopy, and scanning electron microscopy (SEM). The results show surface MPs at concentrations ranging over two orders of magnitude (6.4 × 102 to 4.2 × 104 particles km−2) and a mean abundance of 1.0 × 104 particles km−2. The most concentrated MPs were found at XTJ3-9, which may be associated with the convergence of surface currents collectively affected by the Kuroshio and its extension, adjacent eddies, and flow regimes. Polyethylene accounts for 57.8% of enumerated MPs, followed by polypropylene (36.0%) and nylon (3.4%). Pellets, sheets, lines, and films are major forms which may be linked to the breakdown of larger particles, aging processes, and movement over long distances by prevailing currents. Four possible MPs migration pathways were proposed based on the source-specific distribution, chemical fingerprints, size distribution patterns, and the observed physical oceanographic parameters.