표층혼합층과 퇴적물 내 미세플라스틱 분포: 낙동강 하구역과 독도

Abstract

Plastic debris in the ocean are disposed mostly from land and fishing industries which are formed into micro sized plastics (<5 ㎜) by fragmentation though physiochemical process at the sea. In this study, the distribution and occurrence of microplastics in the sediment and surface mixed layer (SML) of the water column were compared between estuarine ecosystem and the open sea. Sediment and SML samples for Nakdong estuary were collected from 9 stations in May 2015 and May 2016, and samples for coastal waters around Dokdo island were collected from 4-6 stations in May and August of 2014 and 2015. The sediment samples were collected by van veen grab sampler, and SML samples were collected by net with mesh size of 200 ㎛, from depth of 10 m to surface. Sediment samples were analyzed using density separation method to increase the water density for the flotation of microplastics, then removed for filtration. Abundance of microplastic was analyzed by the following physical characteristics: fragment, expanded polystyrene, paint particles, and fiber. The average microplastic abundance for sediment sample in Nakdong estuary was 0.34 particles/g in May 2015, the majority of plastic consisted of fragment particles. Stations located innermost of the estuary (st. 7-9) had average microplastic abundance of 0.60 particles/g, highest in st.7 (0.87 particles/g), and microplastic abundance in the sediment gradually decreased to level of 0.02 particles/g towards the outer estuary, open sea. In relation to the sediment microplastics, microplastics in the SML had an opposite phenomenon, the majority plastic type was fiber. Outer estuary (st. 1-3, mean 19.09 particles/㎥) was ∼2.3 times higher than inner estuary (st. 7-9). This result can suggest that fiber microplastic particles flush out with hydrodynamic movement into the outer estuary while fragment microplastic particles may sinks to the sediment in relation with depth. The average microplastic exhibited seasonal variation in Dokdo Island, relatively higher abundance occurred in May than in August 2014. Fiber and fragment types of plastic was dominant in the waters surrounding Dokdo Island. Overall, the findings of the abundance of microplastic in both sediment and SML allows to predict the threatening bioavailability to marine organisms in future studies.