Radium concentration factors in passionfruit (Passiflora foetida) from the Alligator Rivers Region, Northern Territory, Australia

Radium in New Zealand agricultural soils: Crop uptake and estimation of current and future ionising radiation dose

Crop uptake of ²²⁶Ra over a range of key New Zealand agricultural and horticultural growing areas was analysed to establish the dietary implications of an increase in soil ²²⁶Ra activity concentrations. Thirty crop samples, covering both feed and food commodities, were quantified for ²²⁶Ra activity concentrations, and concentration ratio (CRs) from the soil activity were calculated. The calculated CRs correlated with international default values for estimating crop uptake. Variation in CRs established that there was no increase in the crop activity concentration, relative to soil ²²⁶Ra from pasture foliage at a fertiliser impacted site, with a gradient of soil ²²⁶Ra activity concentrations. Based on the calculated CRs, the upper bound of the theoretical range of dietary exposures to ²²⁶Ra was 78.1 μSv/yr for teenage boys. Future forecasting of the increased dietary dose of ²²⁶Ra that might occur at the current soil loading rate, based on current fertiliser activity concentrations, confirmed that long-term loading of soil with ²²⁶Ra is unlikely to present a dietary risk. The forecast model calculated that the increase in dietary ionising radiation burden is unlikely to reach thresholds requiring regulatory intervention for two millennia.

Substratum influences uptake of radium-226 by plants

Radium-226, an alpha emitter with half-life 1600 years, is ubiquitous in natural environments. Present in rocks and soils, it is also absorbed by vegetation. The efficiency of ²²⁶Ra uptake by plants from the soil is important to assess for the study of heavy metals uptake by plants, monitoring of radioactive pollution, and the biogeochemical cycle of radium in the Critical Zone. Using a thoroughly validated measurement method of effective ²²⁶Ra concentration (EC_Ra) in the laboratory, we compare EC_Ra values of the plant to that of the closest soil, and we infer the ²²⁶Ra soil-to-plant transfer ratio, R_SP, for a total of 108 plant samples collected in various locations in France. EC_Ra values of plants range over five orders of magnitude with mean (min-max) of 1.66 ± 0.03 (0.020-113) Bq kg^-1. Inferred R_SP values range over four orders of magnitude with mean (min-max) of 0.0188 ± 0.0004 (0.00069-0.37). The mean R_SP value of plants in granitic and metamorphic context (0.073 ± 0.002; n = 50) is significantly higher (12 ± 1 times) than that of plants in calcareous and sedimentary context (0.0058 ± 0.0002; n = 58). This difference, which cannot be attributed to a systematic difference in emanation coefficient, is likely due to the competition between calcium and radium. In a given substratum context, the compartments of a given plant species show coherent and decreasing R_SP values in the following order (acropetal gradient): roots > bark > branches and stems ≈ leaves. Oak trees (Quercus genus) concentrate ²²⁶Ra more than other trees and plants in this set. While this study clearly demonstrates the influence of substratum on the ²²⁶Ra uptake by plants in non-contaminated areas, our measurement method appears as a promising practical tool to use for (phyto)remediation and its monitoring in uranium- and radium-contaminated areas.

Whole organism concentration ratios of radionuclides and metals in terrestrial vertebrates of an Australian tropical savanna environment

Preliminary values of whole organism concentration ratio (CR_wo-soil) were derived for terrestrial vertebrates of an Australian tropical savanna environment. Wildlife groups included bird, bat, ground-dwelling mammal and reptile. Sample data for some of the wildlife groups (bird and bat in particular) were limited. The bird and bat CR_wo-soil values were generally lower than the ground-dwelling mammal and reptile CR_wo-soil values based on the available data. Arithmetic mean CR_wo-soil values for two species of native marsupial and two species of non-native placental were not significantly different (p < 0.05) when tested using a one-way analysis of variance. The results hinted at possible sampling efficiencies for terrestrial vertebrates. However, verification with additional data was recommended. Used cautiously, the CR_wo-soil values may assist in environmental assessments of Australian uranium mining sites. They also enhance the available data on radionuclide transfer to wildlife for use internationally.

Influence of soil structure on the "Fv approach" applied to 238U and 226Ra

The soil-to-plant transfer factors were determined in a granitic area for the two long-lived uranium series radionuclides ²³⁸U and ²²⁶Ra. With the aim to identify a physical fraction of soil whose concentration correlates linearly with the plant concentration, the soil compartment was analyzed in various stages. An initial study identified the soil compartments as being either bulk soil or its labile fraction. The bulk soil was subsequently divided into three granulometric fractions consisting of: coarse sand, fine sand, and silt and clay. The soil-to-plant transfer of radionuclides for each of these three texture fractions was analyzed. Lastly, the labile fraction was extracted from each textural part, and the activity concentration of the radionuclides ²³⁸U and ²²⁶Ra was measured. In order to assess the influence of soil texture on the soil-to-plant transfer process, we sought to identify possible correlations between the activity concentration in the plant compartment and those found in the different fractions within each soil compartment. The results showed that the soil-to-plant transfer process for uranium and radium depends on soil grain size, where the results for uranium showed a linear relationship between the activity concentration of uranium in the plant and the fine soil fraction. In contrast, a linear relation between the activity concentration of radium in the plant and the soil coarse-sand fraction was observed. Additionally, the presence of phosphate and calcium in the soil of all of the compartments studied affected the soil-to-plant transfer of uranium and radium, respectively.

Chemical fractionation of radium-226 in NORM contaminated soil from oilfields

Contamination of soil with ²²⁶Ra is a common problem in the oilfields, leading to costly remediation and disposal programmes. The present study focuses on the chemical fractionation and mobility of ²²⁶Ra in contaminated soils collected from an oilfield using a three-step sequential extraction procedure (BCR). The total activity concentrations of ²²⁶Ra in contaminated soils were measured and found to be in the range from 1030 ± 90 to 7780 ± 530 Bq kg^-1, with a mean activity concentration of 2840 ± 1840 Bq kg^-1. The correlation between the total concentration of ²²⁶Ra and soil properties, mainly pH, LOI, C_org, clay and Ca, was investigated using the principal component analysis method (PCA). The chemical fractionation of ²²⁶Ra was studied using the sequential extraction method (BCR). The highest fraction of ²²⁶Ra (27-65%) was found to be in the acid-reducible fraction, which suggests that ²²⁶Ra is mainly bound to FeMn oxides. The BCR method showed that high percentages of ²²⁶Ra were found to be in mobile soil phases (between 45 and 99%). Consequently, groundwater contamination could occur due to the remobilization of ²²⁶Ra from soils under normal environmental conditions. However, the obtained results could be useful to reduce the volume of NORM wastes generated from the oilfields and decision-making process for final treatment and disposal of NORM-contaminated soil.

A tool for calculating concentration ratios from large environmental datasets

This paper presents a tool for calculating concentration ratios from a large and structured environmental dataset of radionuclide activity and metal concentrations. The tool has been developed in MS Excel™ and includes a simple user interface for setting up queries. The tool is capable of matching environmental media samples to biota samples based on user-defined spatial and temporal criteria to derive a representative estimate of the environmental exposure conditions of an organism and its accumulation. Some potential benefits and uses of the tool are discussed.

A database of radionuclide activity and metal concentrations for the Alligator Rivers Region uranium province

This paper presents a database of radionuclide activity and metal concentrations for the Alligator Rivers Region (ARR) uranium province in the Australian wet-dry tropics. The database contains 5060 sample records and 57,473 concentration values. The data are for animal, plant, soil, sediment and water samples collected by the Environmental Research Institute of the Supervising Scientist (ERISS) as part of its statutory role to undertake research and monitoring into the impacts of uranium mining on the environment of the ARR. Concentration values are provided in the database for 11 radionuclides (²²⁷Ac, ⁴⁰K, ²¹⁰Pb, ²¹⁰Po, ²²⁶Ra, ²²⁸Ra, ²²⁸Th, ²³⁰Th, ²³²Th, ²³⁴U, ²³⁸U) and 26 metals (Al, As, Ba, Ca, Cd, Co, Cr, Cu, Fe, Hg, K, Mg, Mn, Na, Ni, P, Pb, Rb, S, Sb, Se, Sr, Th, U, V, Zn). Potential uses of the database are discussed.

Influence of group II metals on Radium-226 concentration ratios in the native green plum (Buchanania obovata) from the Alligator Rivers Region, Northern Territory, Australia

In this study, uptake of Ra from soil, and the influence of group II metals on Ra uptake, into the stones and edible flesh of the fruit of the wild green plum, Buchanania obovata, was investigated. Selective extraction of the exchangeable fraction of the soil samples was undertaken but was not shown to more reliably predict Ra uptake than total soil Ra activity concentration. Comparison of the group II metal to Ca ratios (i.e. Sr/Ca, Ba/Ca, Ra/Ca) in the flesh with exchangeable Ca shows that Ca outcompetes group II metals for root uptake and that the uptake pathway discriminated against group II metals relative to ionic radius, with uptake of Ca > Sr > Ba >> Ra. Flesh and stone analysis showed that movement of group II metals to these components of the plant, after root uptake, was strongly related. This supports the hypothesis that Sr, Ba and Ra are being taken up as analogue elements, and follow the same uptake and translocation pathways, with Ca. Comparison with previously reported data from a native passion fruit supports the use of total soil CRs on natural, undisturbed sites. As exchangeable CRs for Ra reach a saturation value it may be possible to make more precise predictions using selective extraction techniques for contaminated or disturbed sites.

228Ra and 226Ra measurement on a BaSO4 co-precipitation source

One of the most commonly-used methods for determination of ²²⁶Ra, particularly in water samples, utilises co-precipitation of Ra with BaSO₄, followed by microfiltration to produce a source for alpha counting. This paper describes two extensions to BaSO₄ co-precipitation methods which enable determination of ²²⁸Ra using the same source. The adaptations presented here do not introduce any contaminants that will affect the separation of radium or alpha counting for ²²⁶Ra, and can be used for re-analysis of already existing sources prepared by BaSO₄ co-precipitation. The first adaptation uses detection of ²²⁸Ac on the source by gamma spectrometry. The detection efficiency is high, allowing analysis of water samples at sufficiently low activity to be suitable in testing for compliance with drinking water quality standards. As ²²⁸Ac grows in quickly, taking less than 2 days to reach equilibrium with the ²²⁸Ra parent, this can also be useful in radiological emergency response situations. The second adaptation incorporates a method for the digestion of BaSO₄ sources, allowing separation of thorium and subsequent determination of ²²⁸Th activity. Although ingrowth periods for ²²⁸Th can be lengthy, very low detection limits for ²²⁸Ra can be achieved with this technique.