Measured elemental transfer factors for boreal hunter/gatherer scenarios: fish, game and berries

Parameter Values for Estimation of Internal Doses from Ingestion of Radioactive Fallout from Nuclear Detonations

ABSTRACT

This paper suggests values or probability distributions for a variety of parameters used in estimating internal doses from radioactive fallout due to ingestion of food. Parameters include those needed to assess the interception and initial retention of radionuclides by vegetation, translocation of deposited radionuclides to edible plant parts, root uptake by plants, transfer of radionuclides from vegetation into milk and meat, transfer of radionuclides into non-agricultural plants and wildlife, and transfer from food and drinking water to mother's milk (human breast milk). The paper includes discussions of the weathering half-life for contamination on plant surfaces, biological half-lives of organisms, food processing (culinary factors), and contamination of drinking water. As appropriate, and as information exists, parameter values or distributions are specific for elements, chemical forms, plant types, or other relevant characteristics. Information has been obtained from the open literature and from publications of the International Atomic Energy Agency. These values and probability distributions are intended to be generic; they should be reviewed for applicability to a given location, time period, or season of the year, as appropriate. In particular, agricultural practices and dietary habits may vary considerably both with geography and over time in a given location.

A feasibility study on the determination of 90Sr food-chain transfer using stable strontium as a surrogate and neutron activation analysis

We evaluated the applicability of neutron activation analysis for investigating the potential mobility of ⁹⁰Sr in a pasture area in Hungary. To measure strontium concentrations, we made use of the ⁸⁴Sr(n,γ)⁸⁵Sr radiative capture reaction using neutron activation analysis and performed gamma spectroscopy using Compton-suppression techniques on the resulting 514.0 keV gamma ray. Our values for soil-to-plant transfer factors value of 1.6 (2.2) kg kg^-1 were in agreement with recommended values from the ICRP and IAEA, as well as similar studies performed by independent researchers. Our values for plant-to-animal transfer coefficients and concentration ratios varied from suggested values by several orders of magnitude to agreement with other values. Based on our results the utilized transfer of stable strontium could not be regarded as a convenient substitute to help clarify the long-term transfer of radioactive strontium in the environment, because short term dosing was applied. Neutron activation analysis provides a unique niche as a technique with very little chemical processing and short sample analysis times.

A geochemical perspective on the natural abundance of trace elements in beaver (Castor canadensis) from a rural region of southern Ontario, Canada

Chalcophile (Ag, Cd, Co, Cu, Mo, Ni, Pb, Se, Tl, Zn) and lithophile (Al, Ba, Ce, Cr, Cs, Fe, La, Li, Mn, Nd, Rb, Sr, V, Y) trace elements (TEs) were determined in kidney, liver and muscle of beaver (Castor canadensis) from a rural watershed in southern Ontario, Canada. To estimate the relative bioavailability of TEs in the landscape, they were also determined in the dissolved (<0.45 μm) fraction of water from the river where the animals were harvested. Concentration ratios (tissue/water) always showed the greatest enrichments for Cd (kidney, 1.1 × 10⁷; liver, 2.4 × 10⁶; muscle, 7.2 × 10⁵), most likely due to the metal binding properties of metallothioneins. Despite its potential toxicity, Tl also showed considerable enrichment: kidney, 4.2 × 10⁴; liver 1.2 × 10⁴; muscle 1.5 × 10⁴. Enrichments of Cs and Rb exceeded those of Tl in all three tissues, suggesting that the chemical similarity of their ionic species (Cs⁺, Rb⁺, Tl⁺) to K⁺ may be the key to their uptake. Lithophile elements of limited solubility in natural waters (Al, Ce, La, Nd) show moderate enrichments, despite the lack of physiological role. The smallest enrichments were found for Sr and Ba, the two TEs which are most abundant in the river. Of the TEs considered essential for animal nutrition, V was the least enriched in tissue relative to water (liver 19×, kidney, 33× and muscle 28×). Despite the lack of physiological function and absence of any known sources of contamination, Al, Ag, Cd, Ce, Cs, La, Pb, Rb, and Tl, are all enriched in beaver tissue, relative to water, by at least three orders of magnitude, due to natural processes. The widespread abundance of beaver in Canada combined with the growing need to manage their numbers in populated regions offer a unique opportunity for monitoring environmental quality in the riparian zone.

Measurements of cesium in Arctic beluga and caribou before and after the Fukushima accident of 2011

Concern from northern communities following the Fukushima Daiichi nuclear accident of March 2011 has prompted a reassessment of the safety of their traditional foods with respect to radioactivity levels. To this end, a study was conducted to measure the levels of radionuclides in Arctic caribou (Rangifer tarandus) and beluga (Delphinapterus leucas). The main radionuclide of concern is cesium-137, which is easily transferred through the lichen-caribou food chain. Previous studies have been conducted on the cesium-137 levels in Canadian caribou herds from 1958 to 2000, allowing researchers to determine the amount of cesium-137 in caribou specifically attributable to atmospheric weapons testing and the Chernobyl nuclear accident in 1986. In this study, samples of lichens, mushrooms, caribou, beluga and beluga prey collected before and after the Fukushima accident were analyzed for radioactivity levels. Samples were processed and measured using gamma ray spectroscopy to identify the radionuclides present and determine the radioactivity concentration. Both calibration standards and Monte Carlo simulations were used to determine the efficiency of the detectors for the samples, taking into account differences in individual sample sizes as well as matrices. In particular, a careful analysis of the atomic composition of lichens and mushrooms was performed to ensure the efficiencies for these sample types were correct. A comparison of the concentrations from before and after the accident indicated that there was no increase in radioactivity as a result of the atmospheric plume from the Fukushima accident. Some cesium-137, likely attributable to fallout from atmospheric weapons testing of the 1950s and 1960s (since there was no cesium-134 measured in the samples), was measured in the post Fukushima caribou and beluga whale samples; however, this amount was determined to be insignificant for any radiological concern (9.1 ± 1.8 and 0.63 ± 0.23 Bq kg^-1 ww respectively). The activity concentrations of cesium-137 was about 200 times smaller than that of natural radioactive potassium in the beluga samples. Both the caribou and beluga results showed that these foods continue to be a healthy food choice for northern Canadians with respect to radioactivity, and this result has been communicated to the nearby northern communities and stakeholders.

The transfer of (137)Cs, Pu isotopes and (90)Sr to bird, bat and ground-dwelling small mammal species within the Chernobyl exclusion zone

Protected species are the focus of many radiological environmental assessments. However, the lack of radioecological data for many protected species presents a significant international challenge. Furthermore, there are legislative restrictions on destructive sampling of protected species to obtain such data. Where data are not available, extrapolations are often made from 'similar' species but there has been little attempt to validate this approach. In this paper we present what, to our knowledge, is the first study purposefully designed to test the hypothesis that radioecological data for unprotected species can be used to estimate conservative radioecolgical parameters for protected species; conservatism being necessary to ensure that there is no significant impact. The study was conducted in the Chernobyl Exclusion Zone. Consequently, we are able to present data for Pu isotopes in terrestrial wildlife. There has been limited research on Pu transfer to terrestrial wildlife which contrasts with the need to assess radiation exposure of wildlife to Pu isotopes around many nuclear facilities internationally. Our results provide overall support for the hypothesis that data for unprotected species can be used to adequately assess the impacts for ionising radiation on protected species. This is demonstrated for a range of mammalian and avian species. However, we identify one case, the shrew, for which data from other ground-dwelling small mammals would not lead to an appropriately conservative assessment of radiation impact. This indicates the need to further test our hypothesis across a range of species and ecosystems, and/or ensure adequate conservatism within assessments. The data presented are of value to those trying to more accurately estimate the radiation dose to wildlife in the Chernobyl Exclusion Zone, helping to reduce the considerable uncertainty in studies reporting dose-effect relationships for wildlife. A video abstract for this paper is available from: http://bit.ly/1JesKPc.

Transfer factors to Whitetail deer: comparison of stomach-content, plant-sample and soil-sample concentrations as the denominator

A recent study measured transfer factors for 49 elements in hunter-killed Whitetail deer (Odocoileus virginianus), using concentrations in the stomach content as the substrate/denominator to compute muscle/vegetation concentration ratios (CR(m-stomach)) and daily fractional transfer factors (Ff). Using the stomach content ensured an accurate representation of what the deer ate, except that it was limited in time to the vegetation selected by the animal just before it was killed. Here, two alternatives are considered, one where the feed is represented by samples of 21 different vegetation types that deer may have eaten in the area (CR(m-plant)), and the other is using soil concentration in the region as the denominator (CR(m-soil)). The latter is the formulation used in the ERICA tool, and other sources, for risk assessment to non-human biota. Across elements, (log) concentrations in all the media were highly correlated. The stomach contents had consistently higher ash and rare earth element concentrations than the sampled (and washed) vegetation and this was attributed to soil or dust ingestion. This lends credence to the use of soil-based CRm-soil values, despite (or more accurately because of) the inclusive yet gross simplicity of the approach. However, it was clear that variation of CR(m-soil) values was larger than for CR(m-stomach) or CR(m-plant), even if soil load on vegetation was included in the latter values. It was also noted that the variation in CR(m-soil) computed from the product of CR(m-plant) and CR(plant-soil) (where CR(plant-soil) is the plant/soil concentration ratio) was somewhat larger than the variation inherent in CR(m-soil) data. Thus it is reasonable to estimate CR(m-soil) from CR(m-plant) and CR(plant-soil) if observed CR(m-soil) values are not available, but this introduces further uncertainty.

Evaluating summarised radionuclide concentration ratio datasets for wildlife

Concentration ratios (CR(wo-media)) are used in most radioecological models to predict whole-body radionuclide activity concentrations in wildlife from those in environmental media. This simplistic approach amalgamates the various factors influencing transfer within a single generic value and, as a result, comparisons of model predictions with site-specific measurements can vary by orders of magnitude. To improve model predictions, the development of 'condition-specific' CR(wo-media) values has been proposed (e.g. for a specific habitat). However, the underlying datasets for most CR(wo-media) value databases, such as the wildlife transfer database (WTD) developed within the IAEA EMRAS II programme, include summarised data. This presents challenges for the calculation and subsequent statistical evaluation of condition-specific CR(wo-media) values. A further complication is the common use of arithmetic summary statistics to summarise data in source references, even though CR(wo-media) values generally tend towards a lognormal distribution and should, therefore, be summarised using geometric statistics. In this paper, we propose a statistically-defensible and robust method for reconstructing underlying datasets to calculate condition-specific CR(wo-media) values from summarised data and deriving geometric summary statistics. This method is applied to terrestrial datasets from the WTD. Statistically significant differences in sub-category CR(wo-media) values (e.g. mammals categorised by feeding strategy) were identified, which may justify the use of these CR(wo-media) values for specific assessment contexts. However, biases and limitations within the underlying datasets of the WTD explain some of these differences. Given the uncertainty in the summarised CR(wo-media) values, we suggest that the CR(wo-media) approach to estimating transfer is used with caution above screening-level assessments.

Verification of radionuclide transfer factors to domestic-animal food products, using indigenous elements and with emphasis on iodine

Recent reviews have established benchmark values for transfer factors that describe radionuclide transfer from plants to animal food product such as milk, eggs and meat. They also illustrate the paucity of data for some elements and some food products. The present study quantified transfer data using indigenous elements measured in dairy, poultry and other livestock farms in Canada. Up to 62 elements are reported, with particular emphasis on iodine (I) because of the need to accurately assess the behaviour of (129)I from disposal of nuclear fuel waste. There was remarkable agreement with the literature values, and for many elements the present study involved many more observations than were previously available. Perhaps the most important observation was that product/substrate concentration ratios (CR) were quite consistent across species, whereas the traditional fractional transfer factors (TF, units of d kg(-1) or d L(-1)) necessarily vary with body mass (feed intake). This suggests that for long-term assessments, it may be advisable to change the models to use CR rather than TF.