Characterization of microplastics in the surface seawater of the South Yellow Sea as affected by season

Microplastic pollution in global marine environments has attracted significant concerns; however, the environmental factors that influence the distribution and characteristics of microplastics are still unclear. In this study, 100 L of surface seawater samples collected from 16 different stations of the South Yellow Sea in January, April, and August 2018 were analyzed to investigate the relationship between spatio-temporal distribution of microplastics and environment variables. Results showed that the abundance of microplastics in January (6.5 ± 2.1 items/L) was higher than that in April (4.9 ± 2.1 items/L) and August (4.5 ± 1.8 items/L). On the whole, 78% of the total microplastics were <500 μm, ~90% were fibers, 73.2%-81.7% were transparent, and the two most abundant polymer types were polyethylene and polypropylene. The highest variability of microplastic characteristics (colour, size, and shape) and composition were observed in August, thereby showing the apparent features of terrestrial sources of microplastic pollution. Principal components analysis distinguished the spatio-temporal distribution of the microplastics, and significant difference in plastic sizes was found between microplastics in January and those in the other two months, which could be attributed to the Yellow Sea Warm Current and/or winter monsoon. Additionally, the abundance of microplastics, especially small-sized microplastics (<500 μm), was positively correlated with seawater salinity. These results suggest that microplastic pollution in surface waters of the South Yellow Sea varies with seasons owing to differences in the terrestrial sources and marine hydrological dynamics.