Distribution of Microplastics in Freshwater, Brackish Water, and Seawater Along the Lower Nakdong River

Microplastics can cause physical, chemical and biological problems for organisms in water. In this study, we investigated the level of microplastic pollution in freshwater, brackish water, and seawater in the downstream of Nakdong river in Korea. After density separation and organic matter removal, the collected water was checked for the quantity, size, type, shape, and color of microplastics in the water using an FTIR microscope and a digital microscope. The amount of microplastics was found to be relatively high in seawater, with an average of 9.5 MPs/L in fresh water, 13.5 MPs/L in brackish water, and 20.5 MPs/L in sea water. Microplastic sizes above 50 ㎛ and below 100 ㎛ were most widely distributed in freshwater, brackish water, and seawater. The proportion of microplastics above 50 ㎛ and below 100 ㎛ was confirmed to be freshwater (38.6 %), brackish water (47.8 %), and seawater (65.3 %). Microplastic types were abundant in the following order: PP>PE>PET>PVC>Nylon in freshwater, brackish water, and seawater. The form of microplastics was confirmed in the following order: Fiber>Film>Fragment>Sphere in freshwater, brackish water, and seawater. The main colors of microplastics are blue and black, while yellow, white, and transparent microplastics were also found. Through this study, it was confirmed that microplastics can flow into freshwater, brackish water, and seawater due to various causes such as nearby industrial areas, roads, and trails. And it was confirmed that the level of microplastic pollution gradually increases from land to sea. The results of this study can be used as research data on microplastics in freshwater, brackish water, and seawater, and are expected to be helpful in preventing microplastic pollution in surface waters.