Vertical distribution and composition of microplastics in Korean coastal waters

Abstract

Vertical distribution and composition of microplastics were determined in four western and southern bays and two coastal areas of Korea in July and August, 2016. Collected seawater of 100 L from surface using stainless tray, middle and bottom using pump, was filtered through 20 μm hand-net. Volume-reduced samples were filtered through a 5 μm filter paper and plastic like particles on the filter papers were identified with a μFT-IR microscope. The microplastics in this study are divided into plastics and polytetrafluorethylene (PTFE) by polymer type because PTFE was easily fragmented by physical force. The abundance of microplastics from six regions of surface (n=31), middle (n=31) and bottom (n=31) was in the range of 460-5,480, 10-1,060 and 30-2,200 particle/m3 for plastics, and 0-860, 0-2,800 and 0-2,840 particle/m3 for PTFE, respectively. The mean abundance of plastics from surface waters (1,795±1,276 particle/m3) was significantly higher(p < 0.05) than those in middle and bottom (394±300 and 441±492 particle/m3). However the abundance of PTFE from surface (97.4±192 particle/m3) was significantly lower (p < 0.05) than those in bottom (619±774 particle/m3). The abundance of plastics was decreased by increasing water depth (p < 0.05), but this tendency did not show in the stations having thermocline layers. Among the four categories of microplastics (fragment, fiber, sphere, film), fragment type accounted fom using pump, was filtered through 20 μm hand-net. Volume-reduced samples were filtered through a 5 μm filter paper and plastic like particles on the filter papers were identified with a μFT-IR microscope. The microplastics in this study are divided into plastics and polytetrafluorethylene (PTFE) by polymer type because PTFE was easily fragmented by physical force. The abundance of microplastics from six regions of surface (n=31), middle (n=31) and bottom (n=31) was in the range of 460-5,480, 10-1,060 and 30-2,200 particle/m3 for plastics, and 0-860, 0-2,800 and 0-2,840 particle/m3 for PTFE, respectively. The mean abundance of plastics from surface waters (1,795±1,276 particle/m3) was significantly higher(p < 0.05) than those in middle and bottom (394±300 and 441±492 particle/m3). However the abundance of PTFE from surface (97.4±192 particle/m3) was significantly lower (p < 0.05) than those in bottom (619±774 particle/m3). The abundance of plastics was decreased by increasing water depth (p < 0.05), but this tendency did not show in the stations having thermocline layers. Among the four categories of microplastics (fragment, fiber, sphere, film), fragment type accounted f