Foamed plastic debris in aquatic systems has become one of the emerging global contaminants. In this study, the behavior of polystyrene foam (PSF) and microplastics (MPs) adhered on the PSFs were investigated on the Tuul River shore in Ulaanbaatar, the capital city of Mongolia. The micro-sized (<5 mm) PSF, which was the dominant PSF over 600 pieces in 100 m², have accumulated along the shoreline of Tuul River. Carbonyl index (CI) was calculated to evaluate the surface oxidation of macro-sized (20–100 mm), meso-sized (5–20 mm), and micro-sized PSFs and confirm the relative aging depending on photodegradation. CI ranged from 0.00 to 1.09 in the sampled PSFs, whereby the degraded PSFs with high CI were distributed on the shore of downstream of sewer drainage. Micro-sized PSFs showed a wide range of CI and a relatively high average value of CI as compared to those of meso and macro PSFs. Most of PSFs aggregated with MPs and the adhered MPs have been ubiquitously detected from the surface of PSFs. Adhered micro-sized plastics explored from the surface of PSFs with various sizes, except for mega-sized (>100 mm) PSF, ranged from 5 to 141 items per piece of PSF fragment. The aggregates of PSFs and MPs were common status of PSFs during their transportation. The present findings, which indicated a high concentration of adhered MPs, raise an environmental concern about the widespread aquatic plastic pollution.

水生系统中的泡沫塑料碎片已成为新兴的全球污染物之一。在这项研究中，在蒙古首都乌兰巴托的Tuul河沿岸调查了聚苯乙烯泡沫（PSF）和微塑料（MPs）粘附在PSF上的行为。微型（<5 mm）PSF，在100 m ^2中超过600件是主要的PSF，已在图尔河沿岸堆积。计算羰基指数（CI）来评估宏观尺寸（20–100 mm），中等尺寸（5–20 mm）和微观尺寸的PSF的表面氧化，并根据光降解来确认相对老化。在采样的PSF中，CI的范围从0.00到1.09，从而具有较高CI的降解PSF分布在下水道排水的下游海岸。与中型和大型PSF相比，微型PSF表现出宽泛的CI和较高的CI平均值。从PSF的表面普遍检测到大多数与MP聚集的PSF和粘附的MP。从各种尺寸的PSF的表面探索粘附的微型塑料，除了超大型（> 100 mm）PSF之外，每片PSF碎片的含量为5到141件。PSF和MP的聚集体是PSF在运输过程中的常见状态。目前的发现表明粘附的MP的高度集中，引起了对广泛的水生塑料污染的环境关注。