Evaluation of the effect of three constituent metals of monazita on the radiosensibility of human osteoblasts Publication date: November 2019 Source: Journal of Environmental Radioactivity, Volumes 208–209 Author(s): Lucas K. da F. Iwahara, Monica S. de Oliveira, Marcus A.V. de Alencar Abstract Thorium has gained notoriety in recent years, as a potential source of nuclear energy, substituting uranium in power plants. Monazite is an important source of thorium, as well of uranium and rare earths elements. Workers involved in the extraction and manipulation of this mineral are occupationally exposed to a range of metal mixtures containing thorium and to ionizing radiation. As an osteotropic substance, thorium is mostly deposited in bone tissue and may interfere in cellular radiosensitivity. A human osteoblast cell line was used to evaluate the effects of thorium (Th), cerium (Ce) and lanthanum (La) on cell radiosensivity, using proliferation as indicator. Assays were performed using cell cultures exposed to metals alone and metals combined with ionizing radiation. No stimulus of proliferation was observed when samples were exposed to metals or radiation alone. On the other hand, the metals were able to influence cell radiosensivity, in a concentration-dependent manner when metals and radiation were applied simultaneously. Samples irradiated and exposed to metals combinations revealed an interaction between them in all the tested arrangements (Th-Ce, Th-La, Th-Ce-La). All interactions proved to be of the antagonist type relative to the proliferation indicator, with a higher degree seen for the Th-Ce association. Such results showed the possibility that metal mixtures together with radiation may produce combined effects on osteoblasts, through modifications on the degree of radiosensivity. The results indicate the possibility of an enhancement in occupational risk for workers that manipulate monazite byproducts. Thus, the development of risk assessment models that include the evaluation of mixtures and their cytotoxic and radiotoxic effects on tissues and organs must be highlighted.

Time-dependent trends of artificial radionuclides in biota of the Yenisei River (Siberia, Russia) Publication date: November 2019 Source: Journal of Environmental Radioactivity, Volumes 208–209 Author(s): Tatiana A. Zotina, Elena A. Trofimova, Dmitry V. Dementyev Abstract We investigated time-dependent trends of artificial radionuclides in aquatic moss, zoobenthos (amphipods and caddisfly larvae), and three abundant wild fish species (Northern pike, Arctic grayling, and Siberian dace) inhabiting the Yenisei River in the vicinity of the radioactive discharge site in 2007–2015, in a period before and after the shutdown of the last nuclear reactor plant at the Mining-and-Chemical Combine (MCC), which occurred in 2010. From our research, we learned that concentrations of short-lived radionuclides, whose discharges to the Yenisei either stopped or declined after the shutdown of the reactor plant at the MCC (24Na, 46Sc,51Cr, 54Mn, 58Co, 59Fe, 60Co, 65Zn, 103Ru, 141,144Ce, 152,154Eu, 239Np), decreased in biota samples as well. The ecological half-life (EHL) of 65Zn (0.4–0.7 y) was similar to the physical half-life of this isotope, the EHLs of 60Co (1.2–2.1 y) and 152Eu (1.8 y) were shorter than the physical half-lives of these isotopes. Concentration of 137Cs did not decrease significantly in biota of the Yenisei after the shutdown of the last reactor plant because the discharges of this radionuclide to the Yenisei continued at the same level. On a longer-term scale (since 1973 and since 1991), concentration of 137Cs in fish muscle had significantly decreased, following the decrease in annual discharges of this radionuclide to the Yenisei, and the EHL of 137Cs was estimated as 6.5–12.8 y. Statistically significant correlation with annual discharges of 137Cs was revealed for the concentration of this radionuclide in grayling (whole bodies and muscle); dace (muscle), and amphipods. Despite their ability to accumulate high concentrations of 137Cs, aquatic moss and caddisfly larvae (analyzed together with their stony casings) were not sensitive to interannual fluctuations in the releases of this radionuclide to the Yenisei. Among the analyzed fish species of the Yenisei, the highest activity concentration of 137Cs was revealed in pike (body and muscle), indicating biomagnification of this radionuclide in the top level of the trophic chain.

On the role of 210Bi in the apparent disequilibrium of 210Pb-210Po at sea Publication date: November 2019 Source: Journal of Environmental Radioactivity, Volumes 208–209 Author(s): Suk Hyun Kim, Gi-Hoon Hong Abstract The disequilibrium of the grandparent-daughter pair 210Pb (t1/2=22.3 years)-210Po (t1/2=138 days) has been used to estimate the export fluxes of particulate organic carbon in the ocean using particulate-matter-associated 210Po. 210Po is produced from 210Bi, not from 210Pb. The half-life of 210Bi (t1/2=5.01 days) is sufficiently long compared to the rates of biological particle formation and decomposition or dissolution occurring at sea. The role of 210Bi has not yet been assessed quantitatively in the apparent disequilibrium between 210Pb and 210Po, partly due to the non-existence of 210Bi depth profile measurements at sea up to now. However, greater affinity of 210Bi over 210Po and 210Pb was found recently in coastal waters and phytoplankton 207Bi uptake experiments. Build upon these findings, we developed a primitive and simple analytical approach to elucidate the role of 210Bi in the 210Po-210Pb pair in the ocean using a simplified two-box irreversible steady-state ocean model. We assumed that the activity concentrations in the dissolved and particulate phases of 210Pb, 210Bi, and 210Po in a given water column are solely determined by the concentration of the particles, their input and output, the distribution coefficients between dissolved and particulate phases, and decay constants of these radionuclides in the steady-state ocean. The 210Bi contribution to the 210Pb-210Po activity difference in seawater is found to be significant, therefore, it needs to be considered in estimating particle fluxes using 210Pb-210Po secular equilibrium at sea.

Transport and fate of 137Cs in the Mediterranean and Black Seas system during 1945–2020 period: A modelling study Publication date: November 2019 Source: Journal of Environmental Radioactivity, Volumes 208–209 Author(s): R. Bezhenar, V. Maderich, A. Schirone, F. Conte, V. Martazinova Abstract The compartment model POSEIDON-R with an embedded dynamic food web model was used to assess 137Cs distributions in the Mediterranean and Black Seas during 1945–2020 due to the weapon testing and accident at the Chernobyl nuclear power plant. Three maximums of contamination of surface waters can be identified from 1950 in the Mediterranean Sea system. Two of them (in 1959 and 1963) were caused by atmospheric deposition due to the nuclear weapon testing. Third maximum in 1986 was related with the Chernobyl accident. Maximum of inventory of 137Cs in the Mediterranean Sea (11461 TBq) was achieved in 1968, whereas secondary maximum caused by Chernobyl accident in 1986 was almost the same (11460 TBq). The corresponding maximum in the Black Sea (3703 TBq) was reached in 1986. It is approximately two times larger than nuclear weapon tests maximum. The results of simulations conducted with generic parameters agreed well with measurements of 137Cs concentrations in the water, bottom sediments, and in marine organisms. The inventory in the Mediterranean Sea is most sensitive to the global deposition, whereas water exchange with Atlantic Ocean and the Black Sea plays minor role. The cumulative individual dose for the period 1945–2020 from consumption of marine products contaminated by 137Cs was in the range 41–130 μSv in the Mediterranean Sea and 213–274 μSv in the Black Sea. The dose increased up to 40% due to Chernobyl accident in the Mediterranean countries and 66–103% in the Black Sea countries comparatively with dose from the global deposition. A useful application of the modelling for monitoring purposes was selection of representative regions in the Mediterranean Sea (5 regions) and in the Black Sea (4 regions) using “etalon” method for classification.

Improved approach for LSC detection of 35S aiming at its application as tracer for short groundwater residence times Publication date: November 2019 Source: Journal of Environmental Radioactivity, Volumes 208–209 Author(s): M. Schubert, J. Kopitz, K. Knöller Abstract The knowledge of groundwater residence times in (vulnerable) aquifers is essential for the sustainable management of the associated groundwater resources. A powerful tool for related investigations is the application of naturally occurring radioisotopes as water age indicators. However, due to the limited number of suitable (i.e. omnipresent, short-lived and easily detectable) radionuclides only few studies focus on groundwater ages below one year. A natural radionuclide that does have the potential to cover this time range is 35S (87.4 day half-life). 35S is continually produced in the upper atmosphere and transferred with the rain to the groundwater. Since no natural sources of 35S exist in the subsurface the decrease of the 35S activity concentration in such young groundwater can be used for the determination of its age. Still, 35S activities in precipitation (and hence even more in groundwater) are very low and necessitate appropriate analytical protocols based on liquid scintillation counting (LSC). This turns out to be challenging due to the required large sample volumes and due to potentially high SO42− loads of the samples, both limiting the range of possible applications of 35S as indicator for short groundwater residence times. In the paper we present an improved straightforward LSC based approach for the detection of 35S in natural water samples. We recommend using Insta-Gel Plus as scintillation cocktail for allowing a homogeneous suspension of 35S-containing BaSO4 in the cocktail. The recommended improvements in instrument setting concern the LSC (TriCarb 3170 Tr/SL) counting window, the pulse decay discriminator setting and the delay before burst setting. The settings allow measuring low activity concentrations of 35S, which was previously pre-concentrated from natural water samples, containing SO42− loads of up to 1500 mg with a reasonably high statistical reliability.

Assessment of soil erosion rates in a Mediterranean cultivated and uncultivated soils using fallout 137Cs Publication date: November 2019 Source: Journal of Environmental Radioactivity, Volumes 208–209 Author(s): M. Meliho, A. Nouira, M. Benmansour, M. Boulmane, A. Khattabi, N. Mhammdi, A. Benkdad Abstract Fallout radionuclides, such as 137Cs, have been recognized as a valuable means for studying soil erosion processes. In this study, the 137Cs technique was used to assess soil erosion magnitude and to investigate the effectiveness of terrace cultivations in the High Atlas of Morocco, particularly, the Ourika watershed. 137Cs depth distribution profiles were established along slope gradients associated with land use considering cereal crop, arboriculture and native forests. Along the slope gradient, depth distribution profiles highlight dissimilarities reflecting differences in land use, topographic roughness, soil particle distribution and stoniness. 137Cs inventory decreases exponentially with depth and its penetration increases along the slope. It becomes higher at the bottom of the slope, with penetration reaching 30 cm. 137Cs mass activity and inventory significantly decrease in cultivated terraces, compared to native forest. Although the pattern of 137Cs gain/loss varied according to topography, soil properties and vegetation cover, showing eroding and aggrading profiles, most samples had 137Cs values lower than the reference value, suggesting net-loss of soil as a consequence of erosion processes. The net erosion rates were estimated about 8.5 and 6.0 t ha−1 yr−1 in cereal crop and arboriculture agrosystems, respectively, whereas in the forest, the net erosion rate was lower at about 4.2 t ha−1 yr−1. Soil loss on agricultural terraces is not significantly above tolerable erosion rates for Morocco (<7 t ha−1 yr−1), particularly for arboriculture terraces. A strong correlation was observed between 137Cs and both soil organic carbon and slope gradient, in uncultivated area, whereas, there was no correlation for cultivated terraces. Terraced arboriculture systems should be encouraged for better soil preservation against water erosion in the Ourika watershed.

Radon diffusion coefficients and radon resistances of waterproofing materials available on the building market Publication date: November 2019 Source: Journal of Environmental Radioactivity, Volumes 208–209 Author(s): Martin Jiránek, Veronika Kačmaříková Abstract This paper presents radon diffusion coefficient values and radon resistance values determined for 650 widely-used waterproofing materials divided into 29 groups according to their chemical composition. The reliability of two different approaches for determining the radon resistance is discussed, and differences between the two approaches are identified. A comparison between the radon resistances of waterproofing materials and the requirements prescribed by various building standards indicates that some requirements are unnecessarily strict. It is shown that the most effective approach for setting the requirements is to prescribe several minimum radon resistance values in dependence on the parameters of the building and the subsoil. Graphical abstract

Environmental radiological risk assessment of a coal ash and slag disposal site with the use of the ERICA Tool Publication date: November 2019 Source: Journal of Environmental Radioactivity, Volumes 208–209 Author(s): Božena Skoko, Dinko Babić, Gordana Marović, Sanja Papić Abstract The aim of this study was to assess the environmental radiological risk of coal ash and slag to terrestrial wildlife. The research site used in this study was a disposal site of coal ash and slag with enhaced content of uranium decay chain radionuclides. With the use of the ERICA Tool, total dose rates to wildlife and risk of resultant radiobiological effects were estimated. As input data for the assessment, experimental activity concentrations of 238U, 226Ra and 210Pb in coal ash and slag and best estimates of activity concentrations for related daughter radionuclides and 235U decay chain were used. Where possible, the experimental data for activity concentrations of 238U, 226Ra and 210Pb in plants and related concentration ratios were used. Results were compared to background dose rates, also estimated by the Tool. The Tool's assessment data indicated internal exposure as the prevalent exposure pathway with 226Ra and 210Po as the main dose contributors. Also, the contribution of 235U decay chain to the total dose rate was not negligible since for some organisms it represented up to 11% of the total dose rate. The risk of an occurrence of radiobiological effects in plants on the coal ash and slag disposal site can be considered negligible since the estimated total dose rates were below the screening dose of 10 μGyh−1 and near the dose rates estimated for plants in the control area. However, the estimated dose rates for reference animals and Lichen & Bryophytes were above the screening dose rate for most organisms and on average 13 times higher than the estimated background dose rates. At the given dose rates, an occurrence of different radiobiological effects could not be excluded for animals in close contact with coal ash and slag such as earthworms and small burrowing mammals. A separate assessment performed on an example of reference plants showed that the use of activity concentrations in organisms as input data can result in an order of magnitude smaller estimates of dose rates in comparison to activity concentration in coal and ash as input data. Our study highlighted the need for experimental data in radiological risk assessments to mitigate the conservatism of the ERICA Tool and its tendency to overestimate dose rates.

Moving radiation protection on from the limitations of empirical concentration ratios Publication date: November 2019 Source: Journal of Environmental Radioactivity, Volumes 208–209 Author(s): N.A. Beresford, N. Willey Abstract Radionuclide activity concentrations in food crops and wildlife are most often predicted using empirical concentration ratios (CRs). The CR approach is simple to apply and some data exist with which to parameterise models. However, the parameter is highly variable leading to considerable uncertainty in predictions. Furthermore, for both crops and wildlife we have no, or few, data for many radionuclides and realistically, we are never going to have specific data for every radionuclide - wildlife/crop combination. In this paper, we present an alternative approach using residual maximum likelihood (REML) fitting of a linear mixed effects model; the model output is an estimate of the rank-order of relative values. This methodology gives a less uncertain approach than the CR approach, as it takes into account the effect of site; it also gives a scientifically based extrapolation approach. We demonstrate the approach using the examples of Cs for plants and Pb for terrestrial wildlife. This is the first published application of the REML approach to terrestrial wildlife (previous applications being limited to the consideration of plants). The model presented gives reasonable predictions for a blind test dataset.

Experimental study on the use of granulometric speciation for the radiometric dating of recent sediments Publication date: November 2019 Source: Journal of Environmental Radioactivity, Volumes 208–209 Author(s): Juan Mantero, José M. Abril Hernández, Rafael García-Tenorio, Emmanuel Klubi, Elvis Nyarko Abstract Theoretical and experimental studies have shown that activity concentrations of fallout radionuclides (such as 137Cs and excess 210Pb) decrease with particles size in aqueous suspensions. This paper is aimed at reviewing the theoretical fundamentals for granulometric speciation of radionuclides, and at exploring its practical use in the analytical context of gamma spectrometry for the radiometric dating of recent sediments, with view to: i) improving the detection of 137Cs (since its use as independent chronostratigraphic mark is challenging in the southern hemisphere because its low fallout rate), ii) supporting refined CIC models and normalization techniques in 210Pb-based radiogeochronologies. The work uses surface sediments sampled from the Tinto Estuary (SW Spain), affected by mining and phosphate-fertilizer industries, and from the Ankobra Estuary (Ghana), affected by intensive artisanal gold-mining. Granulometric classes have been separated by a sieving column with decreasing mesh sizes and the obtained cumulative percentage of mass mathematically described by a Rosin-Rammler particle-size distribution. The target radionuclides for gamma spectrometry were 210Pb, 226Ra and137Cs, complemented with 40K, 234Th and 228Ra. Results revealed that, far from ideal experiments, under actual environmental conditions the increase in activity concentrations with decreasing particle sizes is too moderate, and in general they are affected by larger counting uncertainties due to the small available amount of mass. Indeed, there was no correlation between grain-size and 137Cs concentrations (p = 0.25), and similarly for excess 210Pb (p = 0.53). No effect of the organic matter content was observed in 137Cs (p = 0.58) and excess 210Pb (p = 0.85) concentrations. Present results pose some concerns to the general use of granulometric speciation in the context of gamma spectrometry for supporting the radiometric dating of recent sediments. A detailed discussion on the use of normalization methods is also presented.