[M-IS02] 地球科学としての海洋プラスチック

[MIS02-05] Plastic-Associated Radiocesium and Microbial Communities in Coastal Rivers of Fukushima, Japan

*Batdulam Battulga^1,2、Takahiro Nakanishi¹、Masataka Nakayama^1,3、Mariko Atarashi-Andoh ¹、Jun Koarashi¹ (1.Nuclear Science and Engineering Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan、2.Advanced Institute for Marine Ecosystem Change (WPI-AIMEC), Tohoku University, Sendai, Miyagi 980-8578, Japan、3.Arid Land Research Center, Tottori University, Tottori, 680-0001, Japan)

Plastic pollution is an alarming environmental issue. Surface alterations of plastics, such as degradation and biofilm formation, increase their ability to interact with pollutants in the environment. In 2011, the accident at the Fukushima Daiichi Nuclear Power Plant, triggered by the Great East Japan Earthquake, released large amounts of radionuclides, including radiocesium (¹³⁷Cs), into the environment. While numerous studies have reported activity concentrations and inventories of ¹³⁷Cs with comprehensive discussions, limited information is available on plastic-associated ¹³⁷Cs and the interaction mechanisms mediated by biofilms. This study aimed to evaluate plastic-associated ¹³⁷Cs and unravel the mechanisms of interaction to better understand the role of plastics on the radionuclide retention and transfer in the coastal ecosystem of Fukushima, Japan. Samples from the Kuma, Ukedo, Odaka, and Ohta Rivers were collected in 2022-2023. We analyzed plastics, water, sediment, and sand across different seasons for ¹³⁷Cs activity concentration and microbial composition. Biofilms were extracted from plastics using ultrasound-assisted extraction. A gamma-ray spectrometer and next-generation sequencing were used to analyze ¹³⁷Cs activity concentration and microbial communities, respectively. Although less than 220 mg of biofilm was extracted from up to 3,863 plastic particles, the mean activity concentration of ¹³⁷Cs in the extracted biofilm was 2,925 ± 34 Bq·kg⁻¹ (dry weight). The plastics with biofilms showed a mean concentration of 24.2 ± 0.3 Bq·kg⁻¹(dry weight). The highest ¹³⁷Cs concentrations were observed in the Kuma River. Plastics showed lower activity concentrations of ¹³⁷Cs compared to sand and sediment samples. Microbial patterns on plastics highlighted the unique microbial communities in the plastisphere. These results confirm the radioactivity of plastic debris within coastal areas of Fukushima and emphasize the need for further research on the long-term environmental impact of plastic-associated radionuclides.

Keywords: microplastics, biofilm, plastisphere, radiocesium (¹³⁷Cs), microbial community, coastal ecosystem