Seasonal Distribution Characteristics of Microplastics Remaining on Sandy Beaches of Daebudo Island, Gyeonggi Province

Seasonal variation in the abundance and distribution of microplastics (MPs) in beach sediments was investigated for the Daebu island, Gyeonggi-do, South Korea. Beach surface sediments were sampled at five stations along the high strandline of the island beach in July and November 2013 and March 2014 to represent the summer, winter, and spring seasons, respectively. Six sizes ranging from 0.3 to 5 mm were classified and seven types of polymers were determined using FT-IR. The abundances of microplastics were 8,776-891,844 particles/ m2 in summer, 4,628-17,724 particles/m2 in winter, and 13,784-100,196 particles/m2 in spring with a predominant contribution of expanded polystyrene (EPS) of >95% in all seasons. Distinct seasonal differences were exhibited in the MPs abundance (i.e., 6-26 times higher in summer) and spatial distribution pattern (i.e., higher at northern stations in summer with southerly winds but southern stations in winter with northerly winds). On the other hand, similarities in size distribution as well as polymer composition were observed among seasons and stations. Particularly, there were good correlations between EPS of fishery-activity origin and non-EPS of inland origin. In conclusion, well-mixed currents seem to cause spatial and temporal homogeneity in size and polymer distribution, while different wind directions with seasons were likely to generate differences in the MPs abundance with time and space in the beach. However, whether the distribution characteristics of MPs on the beach sediments were determined by the direct reflection of those in flooding seawaters or by the redistribution of deposited MPs is unclear. Further study is required to identify the major mechanism.