Characteristic of spatiotemporal distribution of microplastics in surface microlayer in southern coast of South KoreaCharacteristic of spatiotemporal distribution of microplastics in surface microlayer in southern coast of South Korea

Abstract

Microplastics, less than 1 mm in size, have been recently recognized as marine pollutants of significant concern due to their persistence, ubiquity, toxic potential, and their ability to act as vectors for transfer of absorbed and additive toxic chemicals to marine organisms. Floating of plastics on sea surface is affected by the density of the plastic materials. For example, polyethylene, polypropylene and expanded polystyrene which are generally less dense than sea water is likely to become floating debris. There is a microlayer in the sea surface formed by the surface tension of water with thickness of 1 mm. Sea surface microlayer is a habitat of a variety of life and accumulates light particles as well as pollutants deposited from the atmosphere and buoyant from water column. So the place is used for researching of pollutants. Considering the size and specific gravity of the microplastics, they are also expected to be accumulated within the microlayer. In this study, microplastic debris was quantitatively determined in surface microlayer at 21 stations in southern coast of South Korea in May (dry season) and July (rainy season), 2012, which is receiving Nakdong River discharge. The microplastics in the microlayer samples were extracted using the surface tension. The specially fitted 2 mm mesh sieve was dipped into the sea surface for 100 times, then the trapped water within mesh space was collected in the range of 2.2-2.8 L per site in the stainless steel tray and transferred to the 1 L polyethylene bottle. In the laboratory, the microlayer sample was filtered, using a glass fiber filter and counted using a dissecting microscope. Microplastic abundances in microlayer are in the range of 50-110 particles/L in May and 55-132 particles/L in July. Even if the average of microplastics (110±45 particles/L) in May was higher than those (132±106 particles/L) in July, there is not a statistical signification. Among four categories of microplastics (fragment, fiber, sheet and spherule), fragment type accounted for 80% in May and 98% in July. Small size microplastics down to 0-100 &#61549 m class are dominant in all the samples. Microplastics are relatively abundant at stations near shore in comparison with offshore stations. Abundances of microplastics in microlayer were folders or orders of magnitude higher than those in top 20 cm surface water collected by filtering (0.7 &#61549 m pore), a hand net (50 &#61549 m mesh) and a manta trawl net (330 &#61549 m).