Enhancement of Mass Interception Coefficient Data of Radiostrontium by Leafy Crops Using Global Fallout ⁹⁰Sr and Naturally Occurring ⁷Be

When artificial radionuclides are released into the atmospheric environment, one of the important processes by which they affect the human radiation dose is the direct deposition of the radionuclides onto crop surfaces. Because leafy vegetables are consumed while fresh and often raw, the mass interception coefficient [= concentration in food (Bq/kg dry mass (DM) or fresh mass)/total deposition (Bq/m2)] is a key parameter for estimating radionuclide concentrations in crops after the deposition of radionuclides on plant stands. However, such data are still sparse, especially for radiostrontium (89Sr and 90Sr). To enhance the mass interception coefficient data for leafy crops, we used global fallout 90Sr data in leafy crops harvested in 1963–1965 and the deposition data for the corresponding crop growing period. Geometric mean values of the mass interception coefficient of 90Sr for leafy crops were 2.8 m2 kg–1 DM for spinach, 0.60 m2 kg–1 DM for cabbage, and 1.3 m2 kg–1 DM for Chinese cabbage. For comparison, we measured naturally occurring 7Be in giant butterbur leaves, and the results showed that the data were similar to those of 90Sr for spinach. These data were similar to the previously obtained data by single spike radiotracer experiments. Therefore, in the case of nuclear emergency situations, mass interception coefficient data obtained using global fallout 90Sr and/or naturally occurring 7Be should be valuable to estimate radioactivity contamination levels of radiostrontium directly deposited on leafy crops

Estimation of Te-132 Distribution in Fukushima Prefecture at the Early Stage of the Fukushima Daiichi Nuclear Power Plant Reactor Failures

Tellurium-132 (¹³²Te, half-life: 3.2 d) has been assessed as the radionuclide with the third largest release from the Fukushima Daiichi Nuclear Power Plant (FDNPP) in March 2011; thus it would have made some dose contribution during the early stage of the reactor failures. The available data for ¹³²Te are, however, limited. In this study, available reported values of other isotopes of Te were compiled to estimate ¹³²Te concentration (in MBq m^–2). It was found that ¹³²Te and ^129mTe (half-life: 33.6 d) concentrations were well correlated (<i>R</i> = 0.99, <i>p</i> < 0.001) by <i>t</i> test. Thus, ¹³²Te concentrations on March 11, 2011 were estimated from ^129mTe using the concentration conversion factor (¹³²Te /^129mTe) of 14.5. It was also found that since deposited ^129mTe was well retained in the soil, the data collected in March–May of 2011 were applicable to ¹³²Te estimation. It was possible to obtain the first ¹³²Te concentration contour map for the eastern part of Fukushima Prefecture, including data from within the 20-km exclusion zone around the FDNPP, using these newly available estimated ¹³²Te data sets

Triple-Quadrupole Inductively Coupled Plasma-Mass Spectrometry with a High-Efficiency Sample Introduction System for Ultratrace Determination of ¹³⁵Cs and ¹³⁷Cs in Environmental Samples at Femtogram Levels

High yield fission products, ¹³⁵Cs and ¹³⁷Cs, have entered the environment as a result of anthropogenic nuclear activities. Analytical methods for ultratrace measurement of ¹³⁵Cs and ¹³⁷Cs are required for environmental geochemical and nuclear forensics studies. Here we report a highly sensitive method combining a desolvation sample introduction system (APEX-Q) with triple-quadrupole inductively coupled plasma mass spectrometry (AEPX-ICPMS/MS) for the determination of ¹³⁵Cs and ¹³⁵Cs/¹³⁷Cs isotope ratio at femtogram levels. Using this system, we introduced only selected ions into the collision/reaction cell to react with N₂O, significantly reducing the isobaric interferences (¹³⁵Ba⁺ and ¹³⁷Ba⁺) and polyatomic interferences (^95,97Mo⁴⁰Ar⁺, ¹¹⁹Sn¹⁶O⁺, and ¹²¹Sb¹⁶O⁺). Compared to the instrument setup of ICPMS/MS, the APEX-ICPMS/MS enables a 10-fold sensitivity increase. In addition, an effective chemical separation scheme consisting of ammonium molybdophosphate (AMP) Cs-selective adsorption and two-stage ion-exchange chromatographic separation was developed to remove major matrix and interfering elements from environmental samples (10–40 g). This separation method showed high decontamination factors (10⁴–10⁷) for major matrix elements (Al, Ca, K, Mg, Na, and Si) and interfering elements (Ba, Mo, Sb, and Sn). The high sensitivity of APEX-ICPMS/MS and the effective removal sample matrix allowed reliable analysis of ¹³⁵Cs and ¹³⁷Cs with extremely low detection limits (0.002 pg mL^–1, corresponding to 0.006 Bq mL^–1 ¹³⁷Cs). The accuracy and applicability of the APEX-ICPMS/MS method was validated by analysis of seven standard reference materials (soils, sediment, and plants). For the first time, ultratrace determination of ¹³⁵Cs and ¹³⁵Cs/¹³⁷Cs isotope ratio at global fallout source environmental samples was achieved with the ICPMS technique

Method for Ultratrace Level ²⁴¹Am Determination in Large Soil Samples by Sector Field-Inductively Coupled Plasma Mass Spectrometry: With Emphasis on the Removal of Spectral Interferences and Matrix Effect

A new method using sector field-inductively coupled plasma mass spectrometry (SF-ICPMS) was developed for the determination of ²⁴¹Am in large soil samples to provide realistic soil-plant transfer parameter data for dose assessment of nuclear waste disposal plans. We investigated four subjects: extraction behaviors of interfering elements (Bi, Tl, Hg, Pb, Hf, and Pt) on DGA resin (normal type, abbreviated as DGA-N); soil matrix element removal (Mg, Fe, Al, K, Na) using Fe­(OH)₃, CaF₂, and CaC₂O₄ coprecipitations; Am and rare earth elements (REEs) separation on DGA-N and TEVA resins; and optimization of SF-ICPMS (equipped with a high efficiency nebulizer (HEN)) for Am determination. Our method utilized concentrated HNO₃ to leach Am from 2 to 20 g soil samples. The CaC₂O₄ coprecipitation was used to remove major metals in soil and followed by Am/interfering elements separation using the proposed UTEVA + DGA-N procedure. After a further separation of REEs on TEVA resin, ²⁴¹Am was determined by HEN-SF-ICPMS. This method eliminated the matrix effect in ICPMS ²⁴¹Am measurement for large soil samples. The high decontamination factors (DFs) of interfering elements enable their thorough removal, and in particular, the DF of Pu (7 × 10⁵) was the highest ever reported in ²⁴¹Am studies; thus, this method is capable of analyzing ²⁴¹Pu-contaminated Fukushima Daiichi Nuclear Power Plant (FDNPP) sourced soil samples. A low detection limit of 0.012 mBq g^–1 for ²⁴¹Am was achieved. The chemical recovery of Am (76–82%) was stable for soil samples. This method can be employed for the low level ²⁴¹Am determination in large size soil samples that are contaminated with ²⁴¹Pu

High-Performance Method for Determination of Pu Isotopes in Soil and Sediment Samples by Sector Field-Inductively Coupled Plasma Mass Spectrometry

Plutonium is extensively studied in radioecology (e.g., soil to plant transfer and radiological assessment) and geochemistry (e.g., sediment dating). Here, we reported a new chemical separation method for rapid determination of Pu in soil and sediment samples, based on the following investigations: extraction behaviors of interfering elements (IEs, for inductively coupled plasma mass spectrometry (ICPMS) measurement) on TEVA resin; decontamination of U using TEVA, UTEVA, and DGA resins; and the impact of coprecipitation on Pu determination. The developed method consists of four steps: HNO₃ leaching for Pu release; CaF₂/LaF₃ coprecipitation for the removal of major metals and U; the proposed TEVA + UTEVA + DGA procedure for the removal of U, Pb, Bi, Tl, Hg, Hf, Pt, and Dy; and ICPMS measurement. The accuracy of this method in determining ^239+240Pu activity and ²⁴⁰Pu/²³⁹Pu and ²⁴¹Pu/²³⁹Pu isotopic ratios was validated by analyzing five standard reference materials (soil, fresh water sediment, and ocean sediment). This method is characterized by its stable and high Pu recovery (90–97% for soil; 92–98% for sediment) and high decontamination factor of U (1.6 × 10⁷), which is the highest reported for soil and sediment samples. In addition, the short analytical time of 12 h and the method detection limits, which are the lowest yet reported in literature, of 0.56 μBq g^–1 (0.24 fg g^–1) for ²³⁹Pu, 1.2 μBq g^–1 (0.14 fg g^–1) for ²⁴⁰Pu, and 0.34 mBq g^–1 (0.09 fg g^–1) for ²⁴¹Pu (calculated on the basis of a 1 g soil sample) allow the rapid determination of ultratrace level Pu in soil and sediment samples

Determination of ¹³⁵Cs and ¹³⁵Cs/¹³⁷Cs Atomic Ratio in Environmental Samples by Combining Ammonium Molybdophosphate (AMP)-Selective Cs Adsorption and Ion-Exchange Chromatographic Separation to Triple-Quadrupole Inductively Coupled Plasma–Mass Spectrometry

Since the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident in 2011, the activity ratio of ¹³⁴Cs/¹³⁷Cs has been widely used as a tracer for contamination source identification. However, because of the short half-life of ¹³⁴Cs (2.06 y), this tracer will become unavailable in the near future. This article presents an analytical method for the determination of the long-lived ¹³⁵Cs (<i>t</i>_2/1 = 2 × 10⁶ y) and the atomic ratio of ¹³⁵Cs/¹³⁷Cs, as a promising geochemical tracer, in environmental samples. The analytical method involves ammonium molybdophosphate (AMP)-selective adsorption of Cs and subsequent two-stage ion-exchange chromatographic separation, followed by detection of isolated radiocesium isotopes via triple-quadrupole inductively coupled plasma–mass spectrometry (ICP-MS/MS). The AMP-selective adsorption of Cs and the chromatographic separation system showed high decontamination factors (10⁴–10⁵) for interfering elements, such as Ba, Mo, Sb, and Sn. Using ICP-MS/MS, only selected ions enter the collision/reaction cell to react with N₂O, reducing the isobaric interferences (¹³⁵Ba⁺ and ¹³⁷Ba⁺) and polyatomic interferences (⁹⁵ Mo⁴⁰Ar⁺, ⁹⁷ Mo⁴⁰Ar⁺, ¹¹⁹Sn¹⁶O⁺, and ¹²¹Sb¹⁶O⁺) produced by sample matrix ions. The high abundance sensitivity (10^–9 for the ¹³⁵Cs/¹³³Cs ratio) provided by ICP-MS/MS allowed reliable analysis of ¹³⁵Cs and ¹³⁷Cs isotopes with the lowest detection limits ever reported by mass counting methods (0.01 pg mL^–1 and 0.006 pg mL^–1, respectively). The developed analytical method was successfully applied to the determination of ¹³⁵Cs and ¹³⁷Cs isotopes in environmental samples (soil, litter, and lichen) collected after the FDNPP accident for contamination source identification

Isotopic Composition and Distribution of Plutonium in Northern South China Sea Sediments Revealed Continuous Release and Transport of Pu from the Marshall Islands

The ^239+240Pu activities and ²⁴⁰Pu/²³⁹Pu atom ratios in sediments of the northern South China Sea and its adjacent Pearl River Estuary were determined to examine the spatial and temporal variations of Pu inputs. We clarified that Pu in the study area is sourced from a combination of global fallout and close-in fallout from the Pacific Proving Grounds in the Marshall Islands where above-ground nuclear weapons testing was carried out during the period of 1952–1958. The latter source dominated the Pu input in the 1950s, as evidenced by elevated ²⁴⁰Pu/²³⁹Pu atom ratios (>0.30) in a dated sediment core. Even after the 1950s, the Pacific Proving Grounds was still a dominant Pu source due to continuous transport of remobilized Pu from the Marshall Islands, about 4500 km away, along the North Equatorial Current followed by the transport of the Kuroshio current and its extension into the South China Sea through the Luzon Strait. Using a simple two end-member mixing model, we have quantified the contributions of Pu from the Pacific Proving Grounds to the northern South China Sea shelf and the Pearl River Estuary are 68% ± 1% and 30% ± 5%, respectively. This study also confirmed that there were no clear signals of Pu from the Fukushima Daiichi Nuclear Power Plant accident impacting the South China Sea

Effect of Ashing Temperature on Accurate Determination of Plutonium in Soil Samples

An acidic leaching method using HNO₃ is widely employed to release the global fallout Pu from soil samples for further chemical separations in radioecology and toxicology studies and in many applications using Pu as a useful tracer. In the method’s sample ash treatment step to decompose organic matter in soil, various ashing temperatures (400–900 °C) are used; however, the effect of ashing temperature on the accurate Pu analysis has not been well investigated. In this study, two standard reference soils (IAEA-soil-6 and IAEA-375) were used to determine the ashing temperature effect (from 375 to 600 °C) on the HNO₃ leaching method. The Pu analytical results of both standard reference materials showed that lower ^239+240Pu activity was observed when the ashing temperature exceeded 450 °C, and the ^239+240Pu activity continued to decrease as the ashing temperature was raised. Approximately 40% of the Pu content could not be leached out by concentrated HNO₃ after ashing for 4 h at 600 °C. The Pu loss was attributed to the formation of refractory materials, which are insoluble in HNO₃ solution. This hypothesis was confirmed by the XRD analysis of soil samples, which revealed that plagioclase-like silicate materials were formed after high-temperature ashing. To ensure Pu release efficiency in HNO₃ leaching, we recommend 450 °C as the ideal ashing temperature. This recommendation is also useful for analysis of other important artificial radionuclides (e.g., ¹³⁷Cs, ⁹⁰Sr, ²⁴¹Am) for which an ashing process is needed to decompose the organic content in soil samples

¹³⁵Cs/¹³⁷Cs Isotopic Ratio as a New Tracer of Radiocesium Released from the Fukushima Nuclear Accident

Since the Fukushima Daiichi nuclear power plant (FDNPP) accident in 2011, intensive studies of the distribution of released fission products, in particular ¹³⁴Cs and ¹³⁷Cs, in the environment have been conducted. However, the release sources, that is, the damaged reactors or the spent fuel pools, have not been identified, which resulted in great variation in the estimated amounts of ¹³⁷Cs released. Here, we investigated heavily contaminated environmental samples (litter, lichen, and soil) collected from Fukushima forests for the long-lived ¹³⁵Cs (half-life of 2 × 10⁶ years), which is usually difficult to measure using decay-counting techniques. Using a newly developed triple-quadrupole inductively coupled plasma tandem mass spectrometry method, we analyzed the ¹³⁵Cs/¹³⁷Cs isotopic ratio of the FDNPP-released radiocesium in environmental samples. We demonstrated that radiocesium was mainly released from the Unit 2 reactor. Considering the fact that the widely used tracer for the released Fukushima accident-sourced radiocesium in the environment, the ¹³⁴Cs/¹³⁷Cs activity ratio, will become unavailable in the near future because of the short half-life of ¹³⁴Cs (2.06 years), the ¹³⁵Cs/¹³⁷Cs isotopic ratio can be considered as a new tracer for source identification and long-term estimation of the mobility of released radiocesium in the environment