Inter-cultivar variation in soil-to-plant transfer of radiocaesium and radiostrontium in Brassica oleracea

Radiocaesium and radiostrontium enter the human food chain primarily via soil-plant transfer. However, uptake of these radionuclides can differ significantly within species (between cultivars). The aim of this study was to assess inter-cultivar variation in soil-to-plant transfer of radiocaesium and radiostrontium in a leafy crop species, Brassica oleracea. This study comprised four independent experiments: two pot experiments in a controlled environment artificially contaminated with radiocaesium, and two field experiments in an area contaminated with radiocaesium and radiostrontium in the Chernobyl Exclusion Zone. Radiocaesium concentration ratios varied 35-fold among 27 cultivars grown in pots in a controlled environment. These 27 cultivars were then grown with a further 44 and 43 other cultivars in the Chernobyl Exclusion Zone in 2003 and 2004, respectively. In the field-grown cultivars radiocaesium concentration ratios varied by up to 35-fold and radiostrontium concentration ratios varied by up to 23-fold.In three of these experiments (one pot experiment, two field experiments) one out of the 27 cultivars was found to have a consistently lower radiocaesium concentration ratio than the other cultivars. The two field experiments showed that, five out of the 66 cultivars common to both experiments had consistently lower radiocaesium concentration ratios, and two cultivars had consistently lower radiostrontium concentration ratios. One cultivar had consistently lower radiocaesium and radiostrontium concentration ratios.The identification of cultivars that have consistently lower radiocaesium and/or radiostrontium concentration ratios suggests that cultivar selection or substitution may be an effective remediation strategy in radiologically contaminated areas. Future research should focus on plant species that are known to be the largest contributors to human dose

The transfer of 137Cs, Pu isotopes and 90Sr 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 here

The transfer of Cs-137 and Sr-90 to wild animals within the Chernobyl exclusion zone

More than 700 137Cs and 90Sr activity concentrations for the tissues of 8 species of mammals and 13 species of birds sampled from within the Chernobyl exclusion zone between 1988 and 2000 have been collated. These data present a useful contribution to the current development of environmental impact assessment approaches with regard to ionising radiation. Summarised transfer values are presented and discussed

Estimating the exposure of small mammals at three sites within the Chernobyl exclusion zone – a test application of the ERICA Tool

An essential step in the development of any modelling tool is the validation of its predictions. This paper describes a study conducted within the Chernobyl exclusion zone to acquire data to conduct an independent test of the predictions of the ERICA Tool which is designed for use in assessments of radiological risk to the environment. Small mammals were repeatedly trapped at three woodland sites between early July and mid-August 2005. Thermoluminescent dosimeters mounted on collars were fitted to Apodemus flavicollis, Clethrionomys glareolus and Microtus spp. to provide measurements of external dose rate. A total of 85 TLDs were recovered. All animals from which TLDs were recovered were live-monitored to determine 90Sr and 137Cs whole-body activity concentrations. A limited number of animals were also analysed to determine 239,240Pu activity concentrations. Measurements of whole-body activity concentrations and dose rates recorded by the TLDs were compared to predictions of the ERICA-Tool. The predicted 90Sr and 137Cs mean activity concentrations were within an order of magnitude of the observed data means. Whilst there was some variation between sites in the agreement between measurements and predictions this was consistent with what would be expected from the differences in soil types at the sites. Given the uncertainties of conducting a study such as this, the agreement observed between the TLD results and the predicted external dose rates gives confidence to the predictions of the ERICA Tool

Predicting the transfer of radionuclides to wildlife – an alternative to the concentration ratio

The commonly used models to assess radiation risk to wildlife all use the concentration ratio (CRwo) parameter to estimate whole-organism activity concentrations when measured data are unavailable. The CRwo relates the organism fresh mass activity concentration to the activity concentration in an environmental medium (e.g. typically soil for terrestrial ecosystems). Previously we demonstrated an alternative, taxonomic-based, approach for predicting Cs transfer to freshwater fish (Beresford et al. 2013), which removed the effect of site. In this paper we apply the same approach to terrestrial wildlife

Radionuclide activity concentrations in two species of reptiles from the Chernobyl exclusion zone

Assessments of radiation exposure of reptiles may be required in some countries as many species are protected. However, there are few data available for the transfer of radionuclides to them, especially in terrestrial ecosystems, and consequently, no specific peer reviewed reptile data have been used in the derivation of default transfer parameters in the ERICA Tool. Twenty samples of Lacerta agilis (sand lizard) and five of Natrix natrix (grass snake) were collected from two sites within the Chernobyl Exclusion Zone and analysed for Pu-isotopes, 137Cs and 90Sr. Corresponding activity concentrations for soil from the sampling sites were available. These data have been used to derive concentration ratios (CR) (i.e. reptile whole-body fresh weight activity concentration relative to the dry weight activity concentration in soil). CR values for N. natrix tended to be lower than those for L. agilis. The CR values derived in this paper will be used to improve the default values provided within the ERICA Tool. Whole-body activity concentrations determined in the reptile samples were broadly comparable with data available from the same sampling sites for small mammal species

Assessment of radionuclide export from Chernobyl zone via birds 18 years following the accident

In 2003–2005 we investigated current contamination of small birds in Chornobyl zone, as vertebrates with the largest diversity and biomass, and inherent season migrations. A whole-body live counting method was used to analyze 90Sr and 137Cs in the birds. Total number and biomass of small birds was estimated using 1) data of birds population density in different kinds of biogeocenosis, 2) ratio of biogeocenosises area at the zone, 3) data of biomass of species. We used GIS application, an electronic map of the Chernobyl zone contamination and 90Sr and 137Cs transfer factor “soil–bird” to calculate average contamination of birds at any location regardless they had been caught there or hadn't. According to our assessment total number of small birds by the end of breeding season in 2004 amount to at least 5.14 million individuals, total biomass – 134 tons, total stock of radionuclides – 74.7 MBq 90Sr and 55 MBq 137Cs. All these birds can export no more 80% of their initial contamination outside the zone. Together with total avian flow yearly passed through the region (2600 km2) they export up to 2.47 GBq 137Cs and 3.70 GBq 90Sr