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

Publication date: 1 October 2016
Source:Talanta, Volume 159
Author(s): Liguo Cao, Jian Zheng, Hirofumi Tsukada, Shaoming Pan, Zhongtang Wang, Keiko Tagami, Shigeo Uchida
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 (1–2g). 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 (23.4–152Bq/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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