Seasonal variation of microplastics in seawater and zooplankton in Jiaozhou Bay, the Yellow Sea

Plastic pollution is a globally concerning issue in marine environments. There is currently little research about the seasonal changes in microplastics in coastal areas. Here, we report a seasonal study on the concentrations and characteristics of microplastics in the surface seawater and zooplankton of Jiaozhou Bay, a typical bay in the west Yellow Sea. The concentrations of microplastics in the surface water of Jiaozhou Bay were 0.063, 0.174, 0.094, and 0.050 pieces/m³ in February, May, August and November, respectively, with an annual average concentration of 0.095 pieces/m³, a low value compared with the plastic concentrations of other coastal areas. The size of the collected microplastics ranged from 346 to 155200 μm, with an average of 5093 μm. The overall percentages of fibers, fragments and plastic foams were 29%, 55% and 16%, respectively. Fragments were the most dominant shape in four seasons. Nine plastic polymers were detected from the surface water of Jiaozhou Bay. The dominant chemical composition was polypropylene (PP), accounting for 51.04% of polymers, followed by polyethylene (PE), accounting for 26.04% of polymers. The seasonal variation of plastic characteristics in Jiaozhou Bay, including the shape, color and chemical composition, was significant. The highest concentration of plastics occurred in May and the lowest concentration of plastics occurred in November. Strong rainfall resulted in an increase in the plastic concentration in May, and winds and eddies affected the spatial distribution of plastics in Jiaozhou Bay. Focused on the dominant zooplankton groups in Jiaozhou Bay, the morphology, color, size, chemical composition and quantity of MPs in zooplankton were investigated in Jiaozhou Bay. The results showed that the MPs in zooplankton of the Jiaozhou Bay were dominated by fibers. The proportions of fiber in February, May, August and November were 91%, 88%, 89% and 88%, respectively. The average size of MPs in zooplankton was 441±2, 468±2, 576±2, and 379±4μm in the four seasons. For the 2 common zooplankton groups in the 4 seasons, the MP/zooplankton was 0.3, 0.26, 0.17, 0.19 for copepod, and 0.22, 0.19, 0.17, 0.45 for chaetognath, respectively.