モンゴルの都市河川におけるプラスチックごみの動態と分布

首都大学東

Abundance of microplastics in sediments from the urban river in Mongolia

Microplastics (MPs) are ubiquitous pollutants of the aquatic environment; however, the behavior of these materials in freshwater environments is largely unknown. The present study aimed to identify types of MPs and quantify their concentration in the river bottom sediment in the Tuul River, northern central part of Mongolia. The goal was also to analyze and evaluate the behavior of MPs. Six sampling plots were chosen as the research objectives, which were close to the junctions between tributaries and the main river of Tuul in the capital of Mongolia,Ulaanbaatar. All sediment samples contained MPs with an average concentration of 603±251 items kg−1. The major morphotype was synthetic fibers, which originated from polyester and polyamide polymers. While the size of MPs ranged between 28.4 µm and 3409.1 µm, most of these materials varied between 100 and 200 µm. Furthermore, the finer the particle sizes of sediments, the higher the number of detected MPs. Distribution of the MPs in the study area indicates that the point-source of MPs such as wastewater treatment plant strongly affects their concentration. However, domestic wastes (i.e., plastic litter) impact the distribution of MPs as non-point sources

Plastic-associated metal(loid)s in the urban river environments of Mongolia

The widespread distribution of plastic debris in riverine environment is one of the major concerns of environmental pollution because of its potential impact on the aquatic ecosystem. In this study, we investigated the accumulation of metal(loid)s on polystyrene foam (PSF) plastics collected from the floodplain of the Tuul River of Mongolia. The metal(loid)s sorbed on plastics were extracted from the collected PSF via sonication after peroxide oxidation. The size-dependent association of metal(loid)s with plastics indicates that PSFs act as vectors for pollutants in the urban river environment. The mean concentrations of metal(loid)s (i.e., B, Cr, Cu, Na, and Pb) indicate a higher accumulation of the metal(loid)s on meso-sized PSFs compared with macro- and micro-sized PSFs. In addition, the images from scanning electron microscopy (SEM) indicated not only the degraded surface of plastics showing fractures, holes, and pits but also the adhered mineral particles and microorganisms on the PSFs. The interaction of metal(loid)s with plastics was probably facilitated by the physical and chemical properties of altered surface of plastics through photodegradation, followed by an increase in surface area by size reduction and/or biofilm development in the aquatic environment. The enrichment ratio (ER) of metals on PSF samples suggested the continuous accumulation of heavy metals on plastics. Our results demonstrate that the widespread plastic debris could be a carrier of hazardous chemicals in the environment. Considering that the negative impacts of plastic debris on environmental health are major concerns to be addressed, the fate and behavior of the plastics especially their interaction with pollutants in aquatic environments should be further studied