Behavior and distribution of plastic debris in the urban river in Mongolia

Remarkably high utility of plastics has promoted the drastic increase of plastic production and consumption over the last several decades, resulting in generation of large amount of plastic solid waste and further its accumulation in the environment.Although the majority of plastic debris in the marine environment derived from land-based sources, the transportation processes through river systems are unclear but important.Since plastic debris pose a threat to aquatic ecosystem, the current thesis aimed to identify behavior and distribution of environmental plastics in the Selenga River system, particularly along the Tuul River including Ulaanbaatar City of Mongolia.Plastic debris in the aquatic environment affected by plastic production and its waste generation was reviewed and its consequences relating to their behavior in the environment were pointed out in Chapter 1.There are no universally accepted methods to determine plastic debris.Considering many adopted methods for sampling, sample preparation and analyses of environmental plastics, validation and standardization of the most appropriate methods achieve high separation efficiency of plastic debris from the environmental matrix.The suitable methodological approaches for sampling, sample preparation and analysis of plastics in river environments were proposed and discussed in Chapter 2.Moreover, river shores and bottom sediments were selected as important sampling spots for the river environment to obtain comprehensive data of distribution pattern and degradation processes of environmental plastics based on hydrological and geographical backgrounds of the Selenga River and Tuul River systems.Nevertheless, from the methodological viewpoint, the carbonyl index was considered as a good indicator to identify plastic origins and surface deteriorations simultaneously.In chapter 3, abundance and distribution of visible plastic debris on the shores of Selenga River system were addressed to reveal the distribution pattern and fragmentation process of plastics in the river environment.Diversity in abundance and characteristics of the plastic debris on the river shore was probably reflected by multiple pathways of plastic debris in the river catchment.On-site fragmentation of plastic debris has been speculated in the foam and film morphotypes of plastics due to freeze-thaw and dry-wet cycles.Despite of occurrence of different morphotypes of mega-, macro-, meso-and micro-plastics on the river shores, micro sized polystyrene foam (PSF) have been considered as distinctive plastic debris in both the Selenga River system and the Tuul River system due to its predominant production and consumption in Mongolia.