Simultaneous determination of radiocesium (135Cs, 137Cs) and plutonium (239Pu, 240Pu) isotopes in river suspended particles by ICP-MS/MS and SF-ICP-MS

• A method for simultaneous determination of Pu and radiocesium isotopes was developed.
• High DFs for U, Ba, Mo, Sb and Sn were achieved.
• The developed method was applied to river suspended particles in Fukushima.
• Spatial distribution of 135Cs/137Cs atom ratios was investigated in Fukushima.

Due to radioisotope releases in the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident, long-term monitoring of radiocesium (135Cs and 137Cs) and Pu isotopes (239Pu and 240Pu) in river suspended particles is necessary to study the transport and fate of these long-lived radioisotopes in the land-ocean system. However, it is expensive and technically difficult to collect samples of suspended particles from river and ocean. Thus, simultaneous determination of multi-radionuclides remains as a challenging topic. In this study, for the first time, we report an analytical method for simultaneous determination of radiocesium and Pu isotopes in suspended particles with small sample size (1–2 g). Radiocesium and Pu were sequentially pre-concentrated using ammonium molybdophosphate and ferric hydroxide co-precipitation, respectively. After the two-stage ion-exchange chromatography separation from the matrix elements, radiocesium and Pu isotopes were finally determined by ICP-MS/MS and SF-ICP-MS, respectively. The interfering elements of U (238U1H+ and 238U2H+ for 239Pu and 240Pu, respectively) and Ba (135Ba+ and 137Ba+ for 135Cs and 137Cs, respectively) were sufficiently removed with the decontamination factors of 1–8×106 and 1×104, respectively, with the developed method. Soil reference materials were utilized for method validation, and the obtained 135Cs/137Cs and 240Pu/239Pu atom ratios, and 239+240Pu activities showed a good agreement with the certified/information values. In addition, the developed method was applied to analyze radiocesium and Pu in the suspended particles of land water samples collected from Fukushima Prefecture after the FDNPP accident. The 135Cs/137Cs atom ratios (0.329-0.391) and 137Cs activities (23.4–152 Bq/g) suggested radiocesium contamination of the suspended particles mainly originated from the accident-released radioactive contaminates, while similar Pu contamination of suspended particles caused by the accident could be neglected as the 240Pu/239Pu atom ratios (0.182–0.208) were within the range of global fallout.

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