Microplastics in seawater and zooplankton from the Yellow Sea

Marine plastic pollution is a worldwide problem. Microplastics (MPs) are the predominant form of marine plastic debris, a form small enough to be ingested by and potentially harm marine organisms. It is urgent to develop ecologically relevant metrics for the risk assessment of MPs based on in situ data, especially for coastal areas. For the first time, we performed a comprehensive study of the characteristics of MPs in seawater and zooplankton in the Yellow Sea. For MPs in seawater, the average concentration is 0.13 ± 0.20 pieces/m³, dominated by fragments (42%). The average size is 3.72 ± 4.70 mm, with the most frequent size appearing at 1200 μm. The major polymer types are polypropylene and polyethylene, accounting for 88.13% in total. The distribution of MPs in seawater is patchy, with high MP concentrations close to the coastal cities. The average concentration of MPs in 11 total zooplankton groups is 12.24 ± 25.70 pieces/m³. The average size is 154.62 ± 152.90 μm, with 90% being <500 μm. Fiber is the dominant shape of MPs found in zooplankton, accounting for 46%, but the composition of the polymer type is diverse. The retention of MPs in zooplankton depends on the taxa and their abundance in the Yellow Sea. Siphonophorea, Copepoda, Euphausiacea and Amphipoda are the main repositories compared to other groups, achieving 3.57, 2.44, 1.41 and 1.36 pieces/m³, respectively. The high concentration area of MPs in zooplankton appeared near the adjacent waters of the Yangtze estuary. These results prove that zooplankton act as a repository for MPs in coastal waters. The retention of MPs in zooplankton is recommended as a key index for further ecological risk assessment of MPs.