Plastic debris is pervasive and persistent which allows its interaction with a range of organisms and organic and inorganic materials in the environment. Considering that plastics are considered carriers and vectors for pollutants in the aquatic environment, it is of utmost importance to elucidate the interaction between plastic debris and radionuclides. Because the accident at the Fukushima Daiichi Nuclear Power Plant caused by the Great East Japan Earthquake in 2011 led to the release of fission products, in particular radiocesium ($^{137}$Cs), into the environment, we aimed to elucidate the interaction between plastic debris and $^{137}$Cs in the environment. We selected the Kuma, Ukedo, Odaka, and Ohta Rivers of the Fukushima prefecture to collect environmental plastic and sediment samples. In addition, we adopted a newly developed ultrasound-assisted extraction technique to extract biofilm (a thin but robust layer of microbial cells embedded in an extracellular matrix) from plastics. The $^{137}$Cs activity concentrations in plastic-associated biofilms and river bottom sediments were determined by gamma-ray spectrometry. Our results indicate the dominance of common polymer types (i.e., polyethylene, polypropylene, polystyrene) of plastic debris in the river environments. Preliminary results of $^{137}$Cs analysis revealed that plastics serve as carriers for radionuclides mediated by biofilms in the coastal rivers.

Plastic debris in the aquatic environment receives special attention from scientific communities, whereas the radioactivity of environmental plastic and the dynamics of plastic-associated biofilm remain largely unknown. In this study, we addressed plastic-associated biofilms and bottom sediments from two contrasting coastal areas of Japan to elucidate their characteristics and interaction with radionuclides especially radiocesium ($^{137}$Cs) in the environment. We also explored stable isotope ($^{13}$C and $^{15}$N) signatures of the biofilm and sediment samples based on seasonal variations. Trace of $^{137}$Cs was observed in biofilm with an activity concentration of 292$\pm$19.4 Bq kg$^{-1}$ biofilm (dw) which correspond to 1.15$\pm$0.08 Bq kg$^{-1}$ plastic (dw).

Plastic waste is one of the high amounts of pollutants released from urban areas to the river. We had a field survey from urban rivers in Ulaanbaatar city, Mongolia. Ulaanbaatar occupies 0.03\% of the Mongolian territory, but 51\% of the total population lives in the city. We collected plastic samples from the 9 points at the river shore of Tuul and its tributaries. Distribution of plastic density was determined in the river shore sediment and in the river flow using a plankton net. River shore plastic items ranged between 0.82$\pm$0.34 and 13.72$\pm$10.53 item/m$^{2}$. Micro, meso, macro, and mega-sized plastics with the composition of fiber, film, foam, and fragments distributed more diversely in all sampling sites in the river shore.

Research cruises were conducted by the Shinsei Maru from October 7 to October 17, 2021, and from October 2 to 13, 2022, in the coastal waters off Fukushima Prefecture. Those cruises aimed to monitor radionuclide distribution and to clarify the dynamics of radionuclides in the coastal water and the environmental response of ecosystems after the Fukushima Daiichi Nuclear Power Plant accident in March 2011.

Plastic waste can be transferred to the river by wind, flood, and unexpected artificial disposal, which gives a negative impact on the environment and human health. Rivers collect plastic wastes from their watersheds according to geographical factors. Therefore, characterization of plastic distribution and composition with respect to land-uses can be understandable for fate of plastic wastes. Plastic debris surveyed from the main (Tuul river) and tributary river shores in Ulaanbaatar (UB) city, Mongolia from the upperstream to downstream to understand behavior and control of plastic waste along the major river in the urbanized city. The composition of collected plastics along the Tuul river in the UB city was composed of 63\% micro, 15\% of meso, 18\% of macro, and 5\% of mega-sized plastics on the number basis. Foam and films were dominant in the material-based fractions. The size distribution may vary according to catchment area and types of land-uses.

Plastic debris in the aquatic environment has become a growing concern due to their long-term ecological consequences. The current study is focused on microbial community composition on microplastics (MPs; sizes $<$5 mm) and characteristics of MP-associated biofilms in coastal river environments of Japan in order to understand the impact of MP-associated biofilms on aquatic organic matter cycling. The aims of the current study are i) extraction and characterization of microbial biofilms on MPs and ii) identification of diversity and composition of microbial communities on MP surfaces and in surrounding surface waters and sediments. The samples were collected from two coastal rivers during 2021-2022 on a seasonal basis. In this study, we proposed a new method to extract biofilms from MPs using ultrasound-assisted syringe treatment for isotopic analysis. Morphotypes of MPs and associated specific microbial taxa as well as seasonal differences were also observed.

Plastic debris has been recognized as one of the carriers of hazardous substances in the aquatic ecosystem due to its ubiquitous distribution and potential interaction with pollutants through developed biofilms. In this study, we aimed to extract biofilms from the environmental plastics using a newly developed extraction method and to determine the concentration of radiocesium ($^{137}$Cs) and stable isotope ratios ($\delta$$^{13}$C and $\delta$$^{15}$N) in the extracted biofilm samples. Visible plastics were collected from the mouths of coastal rivers in Ibaraki prefecture, Japan, and applied to the extraction procedures. After plastic and biofilm separation with ultrasonication, biofilm samples were collected by the two ways: freeze-drying (15.5-44.4 mg); and freeze-drying after syringe treatment (14.5-65.4 mg). The XRD diffractograms of biofilm samples confirmed that biofilms obtained by freeze-drying only were still heterogeneous and the agglomerations of organic substances, mineral particles, and small microplastics (MPs, $<$ 1 mm). The results also demonstrated that biofilm extraction was achieved by syringe treatment separating the mineral and small MPs particles, resulting in homogenous biofilms from the surface of plastics. Preliminarily results of $^{137}$Cs activity concentrations in heterogenous (ranging from 0.22 to 0.54 Bq g$^{-1}$) and homogenous (0.82$\pm$0.04 Bq g$^{-1}$) biofilm samples revealed that MPs serve as a carrier for $^{137}$Cs in the coastal river environment mediated by developed biofilms.