Do fungi need to be included within environmental radiation protection assessment models?

Assessment of background dose rate on non-human biota in a Mediterranean terrestrial ecosystem

The assessment of radiological impact to the environment is usually carried out by the dose rate estimation to hypothetical entities named Reference Animals and Plants (RAPs). There are many codes to carry out this assessment, which requires the definition of a scenario and using site-specific transfer parameters when possible. Transfer parameters present a geographical bias, as they are mostly derived from temperate and arctic climate datasets, but there is a scarcity of data for Mediterranean climates. In this study, a terrestrial Mediterranean scenario was defined using the distribution of activity concentrations of anthropogenic (90Sr, 137Cs) and naturally occurring radionuclides (40 K, 210Pb, 210Po, 226,228Ra, 235,238U, 232Th) in Cáceres province (Spain). Site-specific transfer factors, CRwo-media, defined as the ratio between the concentration in the whole organism and the medium (soil in this case) were considered. Dose rate assessments for terrestrial RAPs were carried out using Tier 3 in ERICA Tool, ranging 0.23-3.73 µGy/h which is below the screening level of 10 µGy/h. Therefore, no harmful effects are expected to occur. Internal dose rate predominates over external one because the main contributors are naturally occurring radionuclides (in most cases 40 K, 226,228Ra, 210Pb, 210Po), which are mostly α-emitting radionuclides. These results can be used for the evaluation of other radiological and nuclear installations in Mediterranean climates, as they set the background dose rate.

Bounding uncertainties around the conceptual representation of species in radiological assessment in the context of routine atmospheric release

Wildlife protection has become of regulatory interest since the International Commission on Radiological Protection (ICRP) developed an approach to assess the level of radiological protection specifically for animals and plants. For the purpose of demonstrating compliance with regulation to protect the environment against routine authorised discharges from nuclear facilities, the wide variety of biota inhabiting an ecosystem needs to be condensed to a limited set of representative organisms, as proposed by the ICRP with a set of 'reference animals and plants' which can be considered representative of many other species. It is now recommended in the International Atomic Energy Agency Safety Standards, and internationally accepted, that the use of such a limited number of organisms to represent a pool of species is adequate for radiation protection purposes, particularly in planned exposure situations. Adding site-specific species to that set of surrogate species can respond to various interests, such as ensuring a site-specific context to the assessment that addresses stakeholder interests and can aid in stakeholder consultation and risk communication. Moreover, there is a need to question whether the use of the set of surrogate organisms is conservative enough to cover a wider range of biodiversity. Previous studies partially answered this question and this paper adds a range of test cases. A selection of hypothetical representations of possible site-specific species are assessed on the basis of possible variations in size (mass) and occupancy habits. Dose rates are evaluated to determine the greatest difference between hypothetical organisms and those for reference organisms (ROs), considering radionuclides (RNs) potentially discharged in atmospheric routine release from different nuclear facilities. Differences observed in the results between hypothetical organisms and ROs were less than one order of magnitude in all cases, the difference being dependent on the RNs considered. These findings do not preclude the inclusion of site-specific species in environmental radiological assessments if it is considered necessary, but they provide reassurance that using ROs for radiological impact assessments in the case of routine atmospheric discharges is sufficient.

Natural radioactivity and total K content in wild-growing or cultivated edible mushrooms and soils from Galicia (NW, Spain)

The radioactive isotope, ⁴⁰K, of naturally occurring potassium (0.012%) is present in the Earth's crust in a low percentage of all potassium, leading to its presence in almost all foodstuffs. The impact of ⁴⁰K activity concentrations was assessed in wild and cultivated edible mushrooms and in growing substrates. Samples were analysed by gamma spectroscopy. In the wild mushroom species, the average activity concentration of ⁴⁰K was 1291 Bq kg^-1 dry weight (dw), approximately 140 Bq kg^-1 fresh weight (fw), with a range of average values per species from 748 in Lactarius deliciosus to 1848 Bq kg^-1 dw in Tricholoma portentosum. The cultivated species presented an average value of 1086 Bq kg^-1 dw; and the soils, compost of cultivation and wood of substrate are 876, 510 and 59.4 Bq kg^-1 dw, respectively. The total K content reached a maximum of 59,935 mg kg^-1 dw in T. portentosum. The transfer factors (TF > 1) suggested that mushrooms preferentially bioconcentrated ⁴⁰K. Cantharellus cibarius, Craterellus tubaeformis, Hydnum repandum and T. portentosum by most TF could be considered as bioindicators of ⁴⁰K. Taking into account that the annual radiation dose of ⁴⁰K due to the average consumption of mushrooms analysed (0.15 μSv/year) is very low, it can be concluded that the consumption of these mushrooms does not represent a toxicological risk for human health. Finally, according to the total K content, from the nutritional point of view, these mushrooms could be considered as a potential source of potassium for the human diet.

Radionuclides and stable elements in vegetation in Australian arid environments: Concentration ratios and seasonal variation

Data on the uptake of elements and radionuclides by flora from soils in arid environments are underrepresented in international databases, especially when comparing across seasons. This study improved the understanding on the uptake of natural uranium-series radionuclides, as well as more than 30 elements, in a range of Australian native flora species that are internationally representative of an arid/semi-arid zone (e.g. Acacia, Astrebla, Atriplex, and Dodonea). Results indicate that the soil-to-plant uptake ratios were generally higher when compared with international data for grasses and shrubs from more temperate environments. The majority of the elemental concentrations in grasses were higher in winter than in summer and the opposite trend was found in shrubs, which suggests that the season of collection potentially introduces variability in the reported concentration ratios. The data also suggest that grasses, being dominant and widespread species in arid zones, may be effective as a reference organism to ensure comparative assessment across sites of interest. The results of this study will improve the confidence of environmental assessments in arid zones.

210Po and 210Pb in forest mushrooms of genus Leccinum and topsoil from northern Poland and its contribution to the radiation dose

Wild growing mushrooms are traditional food items for man and also an important source of nutrients for small and big wildlife. Nevertheless, they can be species - specifically vulnerable for contamination with heavy metals and radionuclides. We studied a less known phenomenon of accumulation of highly toxic, the alpha-radiation emitter such as ²¹⁰Po and the beta emitter ²¹⁰Pb by three Leccinum mushrooms: orange oak bolete L. aurantiacum (Bull.) Gray (previous name Leccinum aurantiacum var. quercinum Pilát), foxy bolete L. vulpinum Watling and slate bolete L. duriusculum (Schulzer ex Kalchbr.) Singer. Fungal and soil materials were collected from areas of a different geochemical composition in the northern regions of Poland. In parallel evaluated was the risk to human consumer due to possible intake of ²¹⁰Po and ²¹⁰Pb with a mushroom meal. Results showed a heterogeneous distribution of ²¹⁰Po and ²¹⁰Pb activity concentrations within caps and stipes of fruiting bodies. Overall activity concentration for whole dried fungi material ranged from 0.59 ± 0.38 to 3.2 ± 0.2 Bq ²¹⁰Po kg^-1 and from 0.45 ± 0.04 to 3.1 ± 0.2 Bq ²¹⁰Pb kg^-1. Evaluation showed that Leccinum mushrooms consumed by locals in typical quantity of 0.5 kg (dry biomass) can contribute into annual effective radiation dose at 0.90-3.81 μSv from ²¹⁰Po decay and 0.31-2.14 μSv from ²¹⁰Pb decay, which is a small portion of the annual effective radiation dose of ²¹⁰Po and ²¹⁰Pb for human inhabiting the northern regions of Poland.