Radiological risk assessment in the terrestrial ecosystem: comparative study of two software tools used for dose rate calculations

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.

Fundamentals of wildlife dosimetry and lessons learned from a decade of measuring external dose rates in the field

Methods for determining the radiation dose received by exposed biota require major improvements to reduce uncertainties and increase precision. We share our experiences in attempting to quantify external dose rates to free-ranging wildlife using GPS-coupled dosimetry methods. The manuscript is a primer on fundamental concepts in wildlife dosimetry in which the complexities of quantifying dose rates are highlighted, and lessons learned are presented based on research with wild boar and snakes at Fukushima, wolves at Chornobyl, and reindeer in Norway. GPS-coupled dosimeters produced empirical data to which numerical simulations of external dose using computer software were compared. Our data did not support a standing paradigm in risk analyses: Using averaged soil contaminant levels to model external dose rates conservatively overestimate the dose to individuals within a population. Following this paradigm will likely lead to misguided recommendations for risk management. The GPS-dosimetry data also demonstrated the critical importance of how modeled external dose rates are impacted by the scale at which contaminants are mapped. When contaminant mapping scales are coarse even detailed knowledge about each animal's home range was inadequate to accurately predict external dose rates. Importantly, modeled external dose rates based on a single measurement at a trap site did not correlate to actual dose rates measured on free ranging animals. These findings provide empirical data to support published concerns about inadequate dosimetry in much of the published Chernobyl and Fukushima dose-effects research. Our data indicate that a huge portion of that literature should be challenged, and that improper dosimetry remains a significant source of controversy in radiation dose-effect research.

Radioactivity and dose assessment of naturally occurring radionuclides in terrestrial environments and foodstuffs: a review of Bahi district, Tanzania

In this review, the online searchable research articles were scrutinized for the data presented in line with radioactivity and dose estimates from both terrestrial environments and foodstuffs from Bahi district and other parts of Tanzania. The data on natural gamma ray dose rates from Bahi localities were observed with variations among researchers. The observed ranges of radioactivity concentrations (Bq kg-1) in soil were 226Ra (28.5-57.4), 232Th (38.1-521.3), and 40K (562.9-665.0). Deep closed water wells with installed pumps from Ilindi and Bahi Mission reported radioactivity concentration of 238U 3.08 Bq L-1 and Ilindi swamps reported radioactivity concentrations of 226Ra 15.35 Bq L-1, whereas radioactivity concentrations of 238U in cereals were within the annual tolerable limits of 0.001-0.02 Bq kg-1. The quantity and accessibility of published studies, as well as the diversity of the data, point to the necessity for additional studies to be carried out in order to obtain comprehensive baseline data.

Risk Assessment of Exposure to Natural Radiation in Soil Using RESRAD-ONSITE and RESRAD-BIOTA in the Cobalt-Nickel Bearing Areas of Lomié in Eastern Cameroon

Nkamouna-Kongo is a cobalt–nickel deposit located in Lomié, Eastern Cameroon. Mining creates radiation exposure pathways that must be considered in risk management scenarios. RESRAD-ONSITE and RESRAD-BIOTA, developed by the US DOE, assess contaminated sites by deriving cleanup criteria and estimating the radiation dose and risk associated with residual radioactive materials using site-specific parameters. This paper evaluated the radiation dose in biota and the health risk from exposure to naturally occurring radionuclides. The activity of 226Ra, 232Th, and 40K was determined by γ-spectrometry. The internal doses were 2.13 × 10−07, 1.42 × 10−06, and 8.38 × 10−05 Gy d−1 for animals and 2.38 × 10−07, 2.04 × 10−06, and 9.07 × 10−05 Gy d−1 for plants. The maximum total dose of 0.7234 mSv yr−1 was obtained at t = 1 year. The external dose contribution obtained at t = 1 year for all nuclides summed and all component pathways was 0.4 mSv yr−1, above the background radiation dose limit of 2.5 × 10−01 mSv yr−1. A maximum cancer risk of 1.36 × 10−03 was observed at t = 1 year. It was also shown in the RESRAD calculations that the total cancer morbidity risks from plant ingestion, radon (independent of water), and external gamma exposure pathways were greater than those from other exposure pathways. The high risk calculated for 226Ra relative to 232Th and 40K makes it the primary human health concern in the study area. The use of a 1 m cover thickness would remediate the contaminated site to a dose on the order of 10−5 mSv yr−1 for a period of 0 to 100 years. The values of these doses are below the US DOE recommended limits.

Measurement and calculation of radionuclide concentration ratios from soil to grass in semi-natural terrestrial habitats in Greece

The results of the measurements of radionuclide transfer from soil to vegetation (Poaceae spp.) that conducted during 2010-2014, in free-ranged grazing regions in Greece, are presented in this work. The specific activities of ¹³⁷Cs, ²²⁶Ra, ²²⁸Ra and ²²⁸Th radionuclides were measured and the activity concentrations were calculated in samples of soil and grass obtained from several studied regions in Greece. The respective soil-to-plant radionuclide transfer parameters (as Concentration Ratio) were calculated and the results were analyzed in terms of spatial deviation caused by the different climate type among the studied regions, provided that the same plant and soil types are studied. The Concentration Ratios ranged from 0.02 to 2.5 for ¹³⁷Cs, 0.01 to 0.7 for ²²⁶Ra, from 0.07 to 1.1 for ²²⁸Ra, and, from 0.08 to 0.17 for ²²⁸Th. Although, the concentration ratios of the primordial radionuclides show some consistency among the different regions, significant differences are observed for ¹³⁷Cs, which may be particularly attributed to the different climatic types (according to the Koppen-Geiger climate classification) that govern these regions.

Determination and mapping of the spatial distribution of cesium-137 in the terrestrial environment of Greece, over a period of 28 years (1998 to 2015)

In this study, we are applying the GIS techniques in order to record the data that have been collected for cesium-137, over the for the period 1998 to 2015, for the terrestrial environment in Greece. Following the Chernobyl Nuclear Power Plant (CNPP) accident in 1986, extended fieldwork was conducted for the determination of cesium-137 concentrations in the terrestrial environment. In 2011, in the light of the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, new campaigns were organized in order to assess the variation in cesium-137 activity concentrations. The measured data, combined with data taken from the databases of the Environmental Radioactivity Laboratory (NCSR'Demokritos', in Athens, Greece), as well as, from the European Atlas of Cesium Deposition on Europe, are being used for the spatial distribution analysis of cesium-137 in the country. Furthermore, are used for the temporal analysis of this radionuclide in a long-term basis. Moreover, we are using the ERICA Assessment Tool for the calculation of the dose rate that the studied organisms (plants of Poaceae spp. and mammals of Bovidae spp.) receive due to the exposure to cesium-137. All gathered information provides us with thematic maps, designed through the GIS techniques, that allow for an appropriate representation of cesium-137 presence in the country nowadays. This study provides an insightful view of the behavior of this anthropogenic radionuclide that is useful for future research in order to elucidate its behavior in long-term periods. The knowledge of the environmental fate of radionuclides is important because it contributes to the projection of long-term risks resulting from radionuclide releases, as well as, for the selection of cost-effective remediation strategies. Furthermore, it provides the opportunity to conduct a comprehensive risk assessment in the region, as the studied organisms were exposed to low-level ionizing radiation. But, as it was shown, on the level of ecosystem, no significant impact was estimated. However, regarding the future objectives, further consideration of the exposure levels should be considered while taking also into account the exposure to natural and background radiation and the exposure to spontaneous emission of anthropogenic radionuclides, especially if we want to consider the eventual effects of protracted low-level ionising radiation on the various levels of life's organization.