Determining baseline radiation levels in marine biota - A comparison of SE Queensland commercial species.

Limited data exists on the contribution to radiological dose to members of the public from ingestion of radioactivity in seafood in the Australian diet. There is also a lack of data available to assess the radiological dose to marine fauna in Australian waters. Natural and anthropogenic radionuclides and trace metals were measured in the edible flesh of prawns to determine the radiological dose to humans. The remaining tissues were combined and analysed to enable uptake and environmental radiological doses to be assessed. Although in international studies, the edible flesh is generally measured to determine radiation dose or ingestion of trace metals, the effects of preparation and cooking techniques are rarely assessed. In this study, cooking and preparation techniques that may influence the radiological dose to humans were assessed. Eggs were also removed from a selected number of samples to assess the potential dose in sensitive developmental tissues and possible implications for environmental effects. Order of magnitude differences in 210Po activity concentrations and Cd concentrations were observed between whole animals and the edible flesh of Australian caught King (Melicertus spp.) and Tiger (Penaeus spp.) prawns, with the hepatopancreas primarily responsible for this difference. Most 210Po was unsupported by 210Pb and activity concentrations of all other radionuclides measured (137Cs, 210Pb, 226Ra, 232Th, and 238U) were very low. The major contribution to radiation dose via the ingestion pathway and to the organism itself was from 210Po. Cooking techniques that may lead to leaching of 210Po from the hepatopancreas could substantially increase the radiological dose from ingestion of this isotope. Organism dose estimates using different input assumptions in the radiological assessment tool "ERICA", including site-specific tissue activity concentrations with site- or region-specific media concentrations, were compared with ERICA default distribution coefficients (Kd) and concentration ratios.

Whole organism to tissue concentration ratios derived from an Australian tropical dataset.

Whole organism to tissue concentration ratios (CRwo-tissue) were derived for six wildlife groups (freshwater birds, freshwater bivalves, freshwater fishes, freshwater reptiles, freshwater vascular plants and terrestrial mammals). The wildlife groups and data represented species common to tropical northern Australia. Values of CRwo-tissue were derived for between 6 and 34 elements, depending upon wildlife group. The values were generally similar to international reference values. However, differences for some element-tissue combinations could affect radiation dose estimates for wildlife in certain environmental exposure situations, including uranium mining, where these data are intended to be applied.

Comparison of radium-228 determination in water among Australian laboratories.

The National Health and Medical Research Council and Natural Resource Management Ministerial Council of Australia developed the current Australian Drinking Water Guidelines which recommend an annual radiation dose value of 1 mSv year-1. One of the potential major contributors to the radiation dose from drinking water is radium-228, a naturally occurring radionuclide arising from the thorium decay series. Various methods of analysing for radium-228 in water have been established and adapted by analytical radiochemistry laboratories. Seven laboratories in Australia participated in analysing radium-228 spiked water samples with activity concentrations ranging from 6 mBq L-1 to 20 Bq L-1. The aim of the exercise was to compare and evaluate radium-228 results reported by the participating laboratories, the methods used and the detection limits. This paper presents the outcome of the exercise.

Natural radionuclides and stable elements in weaver ants (Oecophylla smaragdina) from tropical northern Australia.

Natural radionuclides and stable elements were measured in weaver ants, leaves and soils collected from three sites in tropical northern Australia. Radionuclide concentration ratios for ants relative to soil were derived from the measurements and used to refine the current environmental radiological assessment for remediation of Ranger uranium mine. Use of site-specific concentration ratios for weaver ants gave a more conservative estimate of environmental exposure to the arthropod wildlife group than use of default concentration ratios in the ERICA Tool. This was primarily because the 226Ra concentration ratio for weaver ants was more than 7 times greater than for generic arthropods.

Estimating doses from Aboriginal bush foods post-remediation of a uranium mine.

This paper presents a calculator to facilitate assessments of ingestion doses from Aboriginal bush foods. The calculator combines information on traditional diet and land use with radionuclide concentration ratios and ingestion dose coefficients to estimate doses. The calculator was applied to the planned remediation of Ranger uranium mine to derive a set of scaling factors between radionuclide activity concentrations in environmental media and ingestion dose from bush foods. The scaling factors can be used to estimate doses from bush foods once the post-remediation radiological conditions of the mine and surrounding environment are known.

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.

Alligators and Crocodiles Have High Paracellular Absorption of Nutrients, But Differ in Digestive Morphology and Physiology.

Much of what is known about crocodilian nutrition and growth has come from animals propagated in captivity, but captive animals from the families Crocodilidae and Alligatoridae respond differently to similar diets. Since there are few comparative studies of crocodilian digestive physiology to help explain these differences, we investigated young Alligator mississippiensis and Crocodylus porosus in terms of (1) gross and microscopic morphology of the intestine, (2) activity of the membrane-bound digestive enzymes aminopeptidase-N, maltase, and sucrase, and (3) nutrient absorption by carrier-mediated and paracellular pathways. We also measured gut morphology of animals over a larger range of body sizes. The two species showed different allometry of length and mass of the gut, with A. mississippiensis having a steeper increase in intestinal mass with body size, and C. porosus having a steeper increase in intestinal length with body size. Both species showed similar patterns of magnification of the intestinal surface area, with decreasing magnification from the proximal to distal ends of the intestine. Although A. mississippiensis had significantly greater surface-area magnification overall, a compensating significant difference in gut length between species meant that total surface area of the intestine was not significantly different from that of C. porosus. The species differed in enzyme activities, with A. mississippiensis having significantly greater ability to digest carbohydrates relative to protein than did C. porosus. These differences in enzyme activity may help explain the differences in performance between the crocodilian families when on artificial diets. Both A. mississippiensis and C. porosus showed high absorption of 3-O methyl d-glucose (absorbed via both carrier-mediated and paracellular transport), as expected. Both species also showed surprisingly high levels of l-glucose-uptake (absorbed paracellularly), with fractional absorptions as high as those previously seen only in small birds and bats. Analyses of absorption rates suggested a relatively high proportional contribution of paracellular (i.e., non-mediated) uptake to total uptake of nutrients in both species. Because we measured juveniles, and most paracellular studies to date have been on adults, it is unclear whether high paracellular absorption is generally high within crocodilians or whether these high values are specific to juveniles.

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.

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

In this study, uptake of Ra from soil into the edible fruit of the wild passionfruit species Passiflora foetida was investigated, using selective extraction from the soil samples. A wide range of environmental exposure conditions were represented by the locations that were sampled, including both natural soils, and soils influenced by past and present uranium mining activities. The bioavailable (226)Ra fraction in soils was found to be a better predictor of (226)Ra fruit activity concentrations than the total soil activity concentration, or any of the other fractions studied. Concentration Factors (CFs) derived using the bioavailable fraction varied by only a factor of 7 between different locations, whereas CFs derived using other fractions and total soil varied by up to two orders of magnitude. CFs were highest for those soils containing the lowest concentrations of Mg, Ca and Ba, and approached a saturation value at higher soil concentrations. This finding suggests that group II elements influence radium uptake, most likely the result of increased pressure on the plant to take up essential nutrient group II elements from soil with the lower concentrations, with Ra being taken up as an analogue element. It is also possible that at higher concentrations of bioavailable Ca and Mg in the soil, these ions will outcompete Ra for adsorption sites in the soil and/or on the root surfaces. The study also shows that (228)Ra can potentially be a significant contributor to ingestion doses and should also be considered when assessing committed effective doses from the ingestion of fruits.