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A New approach to extracting biofilm from environmental plastics using ultrasound-assisted syringe treatment for isotopic analyses

環境プラスチックからバイオフィルムを分離回収する新しい方法

Battulga, B. ; 安藤 麻里子  ; 小嵐 淳   

Battulga, B.; Atarashi-Andoh, Mariko; Koarashi, Jun

本研究では、マイクロプラスチックの表面に形成されるバイオフィルム(有機付着物)の特性を明らかにするための第一ステップとして、バイオフィルムを分離回収する手法を開発した。茨城県内の河川において、大きさ、色、組成の異なる様々なマイクロプラスチック試料を採取した。それらの試料に超音波処理を行った後、シリンジを用いた方法により有機付着物を溶液として分離回収した。バイオフィルム由来の有機物から放射性セシウムが検出され、マイクロプラスチックが河川生態系における放射性核種の輸送媒体としての役割を果たすことが示唆された。また、有機物の安定炭素・窒素同位体の分析にも成功した。本手法は、マイクロプラスチックの状態や環境中における物質循環への寄与を解明するために有効である。

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.

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