Hyoe Takata

The IAEA handbook on radionuclide transfer to wildlife

An IAEA handbook presenting transfer parameter values for wildlife has recently been produced. Concentration ratios (CRwo-media) between the whole organism (fresh weight) and either soil (dry weight) or water were collated for a range of wildlife groups (classified taxonomically and by feeding strategy) in terrestrial, freshwater, marine and brackish generic ecosystems. The data have been compiled in an on line database, which will continue to be updated in the future providing the basis for subsequent revision of the Wildlife TRS values. An overview of the compilation and analysis, and discussion of the extent and limitations of the data is presented. Example comparisons of the CRwo-media values are given for polonium across all wildlife groups and ecosystems and for molluscs for all radionuclides. The CRwo-media values have also been compared with those currently used in the ERICA Tool which represented the most complete published database for wildlife transfer values prior to this work. The use of CRwo-media values is a pragmatic approach to predicting radionuclide activity concentrations in wildlife and is similar to that used for screening assessments for the human food chain. The CRwo-media values are most suitable for a screening application where there are several conservative assumptions built into the models which will, to varying extents, compensate for the variable data quality and quantity, and associated uncertainty.

Whole-body to tissue concentration ratios for use in biota dose assessments for animals

Environmental monitoring programs often measure contaminant concentrations in animal tissues consumed by humans (e.g., muscle). By comparison, demonstration of the protection of biota from the potential effects of radionuclides involves a comparison of whole-body doses to radiological dose benchmarks. Consequently, methods for deriving whole-body concentration ratios based on tissue-specific data are required to make best use of the available information. This paper provides a series of look-up tables with whole-body:tissue-specific concentration ratios for non-human biota. Focus was placed on relatively broad animal categories (including molluscs, crustaceans, freshwater fishes, marine fishes, amphibians, reptiles, birds and mammals) and commonly measured tissues (specifically, bone, muscle, liver and kidney). Depending upon organism, whole-body to tissue concentration ratios were derived for between 12 and 47 elements. The whole-body to tissue concentration ratios can be used to estimate whole-body concentrations from tissue-specific measurements. However, we recommend that any given whole-body to tissue concentration ratio should not be used if the value falls between 0.75 and 1.5. Instead, a value of one should be assumed.

Determination of 232Th in seawater by ICP-MS after preconcentration and separation using a chelating resin

This article describes an analytical method for the separation, preconcentration and determination of (232)Th in seawater samples at sub-ng/L levels using a NOBIAS CHELATE PA1 resin and a sector field (SF) inductively coupled plasma mass spectrometer (ICP-MS). The resin showed excellent adsorption of (232)Th at a low pH of 2.4 ± 0.4 in a relatively small volume (200 mL) of seawater. (232)Th adsorbed on the resin was easily eluted using 5 mL of 0.8M HNO(3). An enrichment factor of 40 was achieved for (232)Th analysis. Ethylenediamine-tetraacetic acid disodium salt dehydrate (EDTA) was used to investigate the effect of (232)Th-binding organic ligand on the retention of (232)Th on the chelating resin. Results obtained using acidified samples (pH of 2.4 ± 0.4) showed EDTA had no significant effect on (232)Th recovery, indicating that at this low pH, (232)Th was dissociated from the (232)Th-binding organic ligand and quantitatively retained on the NOBIAS CHELATE PA1 resin. The developed analytical method was characterized by a separation and preconcentration taking approximately 4h and a low detection limit of 0.0038 ng/L for (232)Th, and was successfully applied to the determination of (232)Th in seawater samples collected from coastal areas, Japan.

Concentration ratios of stable elements for selected biota in Japanese estuarine areas

For the estimation of radiation doses to organisms, concentration ratios (CRs) of radionuclides are required. In the present study, CRs of various elements were obtained as analogues of radionuclides for algae, molluscs, and crustaceans, in eight estuarine areas around Japan. The elements measured were Na, Mg, K, Ca, V, Mn, Fe, Co, Ni, Cu, Rb, Sr, Y, Mo, Cd, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Pb, and U. The geometric mean (GM) values of CRs (GM-CRs) for alkali and alkaline earth elements, Mo, and U for all biota, as well as V for crustaceans, were less than 100 L/kg, while GM-CRs for the other elements were higher. When the obtained GM-CRs were compared with the CRs recommended in IAEA Technical Report Series 422 for marine organisms, no big differences between them were found; however, several elements (i.e. Cd and U for algae, Mn for molluscs, and Pb for crustaceans) were lower than the recommended CRs. In the present study, conversion factors (the ratio of CR for the whole body to that for muscle) for molluscs and crustaceans were also calculated, since data on edible parts of these organisms are generally available in the literature. For crustaceans, GM conversion factors of all the elements were more than one. For molluscs, GM conversion factors of rare earth elements and U were slightly higher than those for crustaceans, while GM conversion factors of the other elements were almost the same and less than 10. These results indicate that some elements tend to be concentrated in the internal organs of biota collected in the estuarine areas. For environmental radiological assessment, conversion factors from tissue to whole-body CR values are useful parameters.

Distribution coefficients (K d) of stable iodine in estuarine and coastal regions, Japan, and their relationship to salinity and organic carbon in sediments

The sediment–water distribution coefficient, Kd, is one of the most important parameters in radionuclide assessment models. In this study, we determined Kds of stable iodine (I) in estuarine and coastal regions. We studied 16 estuarine and coastal regions of Japan and obtained I data on water and sediments. Data on salinity, pH, dissolved organic carbon and dissolved oxygen in water, and organic carbon (OC) in sediments were also obtained as estuarine variables. Determined Kds of I in the Sagami River estuary decreased along the salinity gradient (salinity range, 0.1–33.8), indicating that salinity is one of the important factors controlling the Kd values; however, when the Kd values were compared among all the estuaries, the difference between minimum and maximum Kd values varied by about two orders of magnitude in a narrow salinity range of 30.0–34.4. A significant correlation between Kd value and OC content in sediments was observed in all the stations with a salinity of ≥30 except for stations in the Ishikari and Onga River estuaries. The exceptions are probably due to different sources of the sediments, which are explained by the results of relatively low I/OC ratios in sediments in those two estuaries, compared to the other estuaries. Thus, OC in sediments as well as salinity may be responsible for the variation of Kds of I in the estuarine and coastal regions.

Sediment-Water Distribution Coefficients of Stable Elements in Four Estuarine Areas in Japan

Sediment-water distribution coefficients (Kds) were obtained in estuarine areas of four A-class rivers in Japan. The total concentrations of stable elements and naturally occurring radionuclide (i.e., Na, Mg, K, Ca, V, Mn, Fe, Co, Ni, Cu, Rb, Sr, Y, Mo, Cd, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Pb, and U) in the estuarine water at each sampling point and in the corresponding sediment sample were measured. Kds of most of the elements varied within one order of magnitude regarding their differences between minimum and maximum values of each element at all the stations. However, a wide variation of Kds of Mn, Fe, Co, Cu, Rb, and La was observed. In addition, geometric means (GMs) of observed Kds were compared with the recommended values in the IAEA Technical Report Series 422 (TRS-422). The results showed that GMs of Kds for most of the elements agreed well with the recommended values, but GMs of Kds for Mn, Fe, and Cd were more than 10 times lower than the recommended values. The obtained Kd values could be important to investigate the behavior, transport, and fate of artificial radionuclide and to assess the radiological doses in estuarine areas.

A sensitive and simple analytical method for the determination of stable Cs in estuarine and coastal waters

A highly sensitive and simple analytical method is applied to the determination of Cs in estuarine and coastal waters. This analytical method combines adsorption of Cs on ammonium 12-molybdophosphate (AMP) and an ion exchange resin column, followed by subsequent ICPMS measurement. Significantly, the method requires a relatively small amount of sample volume (minimum volume: 20 mL) for the analysis by the selection of AMP with a low Cs impurity (0.02 ng-Cs mg−1-AMP). The method has a detection limit of 1.0 ng L−1 and a limit of quantification of 3.3 ng L−1 based on replicate analyses of purified water samples. A sample storage strategy is also investigated: no time dependent changes are found in the concentrations for acidified samples (pH 1.0–1.5) used immediately (storage: 0 day) to those stored for two months in a dark place at room temperature (4–20 °C) or in a freezer (ca. −20 °C). Respective Cs concentrations of 95.8 ± 0.9, 202.8 ± 3.6 and 197.0 ± 1.9 ng L−1 are obtained in estuarine water (SLEW-3), coastal seawater (CASS-4) and seawater (NASS-5) certified reference materials for heavy metals. In an application of the method to determination of Cs in estuarine and coastal regions of Japan, the obtained Cs concentrations vary from 11.2 to 306.4 ng L−1 at a salinity range of 0.1 to 33.6.

Bromine and iodine in Japanese soils determined with polarizing energy dispersive X-ray fluorescence spectrometry

Abstract The bromine (Br) and iodine (I) status of Japanese soils was investigated by analyzing around 900 soil samples and related materials with polarizing energy dispersive X-ray fluorescence spectrometry (EDXRF). The samples consisted of the following five groups: (1) 468 soil samples collected from 70 sites in the mainland of Japan (mainland soils); (2) 139 agricultural soils collected nationwide; (3) 93 samples taken from the southwestern island (island soils); (4) 52 coastal marine sediments; and (5) 137 tsunami deposits by the 2011 off the Pacific coast of Tohoku Earthquake. The geometric mean of Br was highest in marine sediments (30.6 mg kg−1), followed by that in island soils (24.8 mg kg−1), although the difference between these two groups was not significant. The values for the other three groups were significantly lower at p < 0.05 by Welch’s t test, and were in the following order: mainland soils (10.4 mg kg−1) > tsunami deposits (8.52 mg kg−1) > agricultural soils (7.86 mg kg−1). For I, the geometric mean of island soils (31.9 mg kg−1) was significantly higher than that of other soils at p < 0.05 by Welch’s t test, and was more than three times higher than that of mainland soils (9.11 mg kg−1), which was the second highest group. The values for the other three groups were in the following order: marine sediments (5.68 mg kg−1) > tsunami deposits (4.66 mg kg−1) > agricultural soils (3.50 mg kg−1). The contents of I were higher than those of Br for around two thirds of the island samples. As a result, the geometric mean of the Br/I ratio was less than 1.0 only in this group. The contents of both elements were significantly higher in upland soils than in paddy fields soils. These differences could be partly attributed to the higher ratio of Andosols containing higher amounts of Br and I in upland samples, in addition to the difference in the chemical forms of both elements in paddy field and upland samples. The correlation coefficients among rare earth elements, for example, were more than 0.9 for a considerable number of combinations, whereas more than 80% of the absolute values of correlation coefficients for Br and I against 60 other elements were less than 0.4. These results strongly suggest that the behavior of Br and I in the terrestrial environments differs considerably from that of most other metallic elements.

A new approach to evaluate factors controlling elemental sediment–seawater distribution coefficients (Kd) in coastal regions, Japan

In numerical models to simulate the dispersion of anthropogenic radionuclides in the marine environment, the sediment-seawater distribution coefficient (Kd) for various elements is an important parameter. In coastal regions, Kd values are largely dependent on hydrographic conditions and physicochemical characteristics of sediment. Here we report Kd values for 36 elements (Na, Mg, Al, K, Ca, V, Mn, Fe, Co, Ni, Cu, Se, Rb, Sr, Y, Mo, Cd, I, Cs, rare earth elements, Pb, (232)Th and (238)U) in seawater and sediment samples from 19 Japanese coastal regions, and we examine the factors controlling the variability of these Kd values by investigating their relationships to hydrographic conditions and sediment characteristics. There was large variability in Kd values for Al, Mn, Fe, Co, Ni, Cu, Se, Cd, I, Pb and Th. Variations of Kd for Al, Mn, Fe, Co, Pb and Th appear to be controlled by hydrographic conditions. Although Kd values for Ni, Cu, Se, Cd and I depend mainly on grain size, organic matter content, and the concentrations of hydrous oxides/oxides of Fe and Mn in sediments, heterogeneity in the surface characteristics of sediment particles appears to hamper evaluation of the relative importance of these factors. Thus, we report a new approach to evaluate the factors contributing to variability in Kd for an element. By this approach, we concluded that the Kd values for Cu, Se, Cd and I are controlled by grain size and organic matter in sediments, and the Kd value for Ni is dependent on grain size and on hydrous oxides/oxides of Fe and Mn.

Distribution coefficients (Kd) of strontium and significance of oxides and organic matter in controlling its partitioning in coastal regions of Japan

The Fukushima Daiichi Nuclear Power Plant accident in March 2011 resulted in the release of large quantities of a long-lived radioactive strontium (i.e. (90)Sr; half-life: 28.8 y) into the coastal areas of Japan. (90)Sr release was dispersed and mixed into the water column, and will eventually be deposited into sediment. Because factors controlling seawater-sediment partitioning in the coastal marine environments are not fully understood, we developed seawater-sediment distribution coefficients, Kd (L/kg), for Sr in coastal regions of Japan by means of sediment-water partitioning experiments. (85)Sr was used as a radiotracer and conditions were designed to mimic the environmental systems of the sampling sites as closely as possible. Experimentally determined Kd values (Kd-ex) varied between 0.3 and 3.3 L/kg (mean, 1.4 L/kg), and the variation in Kd-ex was attributed to the percentage of Sr in the exchangeable fraction in the sediment. Kd-ex values were used, along with the measured concentrations of (88)Sr, a stable naturally occurring Sr isotope in seawater and sediment, to estimate the concentrations of exchangeable Sr in the sediment. Estimates ranged from 2.1 to 24.3 μg/kg, or 1.3-15.7% of the total (88)Sr concentration in the sediment. Significant correlations existed between the estimated concentrations of exchangeable Sr, and the organic matter and the oxide/hydrous oxide contents. When organic contents were greater than 0.38%, Sr binds to organic surface sites more strongly than to the other sites. Results indicate that binding of Sr to the surface of sedimentary particles was influenced by grain size, iron and manganese oxides, and organic matter. Furthermore, the information presented here could be useful to estimate Kd values for anthropogenic (90)Sr in sediment in the coastal marine environment.