Microplastics in the Water of Transboundary Lake Khanka and Rivers of Its Basin

A novel assessment of the content of microplastics in the surface waters of Lake Khanka and its tributaries is performed. Collection, preparation, and analysis of samples were carried out in 2021‒2022. Five geographical sites were selected (the source of the Sungacha River, the mouth of the Spasovka River, the Vostochnyi cordon, the Ilistaya River, and the Komissarovka River) as areas most susceptible to pollution. Scanning spectrophotometry with an AIM-9000 SHIMADZU IR microscope detected the presence of microplastic particles (MPs) in all the water samples. The microplastics are predominantly of mixed and synthetic nature; the concentration varies depending on the season, amounting to 6–27 units/m3 in the spring–summer and 5–24 units/m3 in the autumn–winter sampling period. The detected microplastics are of mostly secondary origin and are overwhelmingly identified as fibers. Spectral analysis of the particles show that polyester and organic fibers are the most common types of microplastics. An increased concentration of microplastics is observed at the mouths of the Spasovka and Komissarovka rivers; in the area of the Vostochnyi cordon, which is located in the eastern coastal region of the lake on the territory of the Khanka Nature Reserve; and at the source of the Sungacha, the drainage river of Lake Khanka. It is concluded that the likely sources of microplastic pollution in Lake Khanka and rivers of its basin are runoff from wastewater treatment plants carried in by river flow, runoff from agricultural land, and precipitation and/or untreated wastewater. A comparative analysis of the surface waters of Lake Khanka, the Hai River (China), the Songhua River (China), and rivers of Japan and South Korea is performed. In all the considered water bodies, the predominant type of microplastics is fibers of synthetic origin. The average concentration of microplastics in Lake Khanka is found to be noticeably lower than in the other water bodies, with only that in the Hai River lower.