Radionuclide Concentrations In Water Research Articles

Transfer of Metals Relevant to the Nuclear Fuel Cycle into Lumbriculus variegatus from Boreal Freshwater Sediments

Radioecological modeling requires information about the transfer of different elements and their radionuclides. These models have traditionally used radionuclide concentrations in water to predict concentrations in aquatic organisms. In addition, these models often assume this accumulation to be linear. In this study, we investigated the transfer of Ba, Co, Ni, Sr, U, and Zn from sediment and artificial freshwater to laboratory-reared benthic Oligochaeta (Lumbriculus variegatus). Total elemental concentrations were used as substitute measurements for specific radionuclides. The radioactive isotopes of these metals are an important part of the nuclear fuel cycle. During various parts of this cycle, they can end up in aquatic environments, mostly at low concentrations. Sediment samples were collected from three small lakes connected to a former uranium mine in Eastern Finland, as well as from a reference lake from a different drainage area nearby. A 28-day bioaccumulation experiment was conducted using collected samples and artificial freshwater. Concentrations measured from sediment, porewater, overlying water, and L. variegatus indicated importance of sediment as a source of uptake for all tested metals. Linear accumulation assumption (constant concentration ratio) also did not appear to be correct for most metals. Metal uptake by L. variegatus seemed to reduce at higher sediment concentrations for most metals, except for Ba and Co. Thus, the common assumptions related to radioecological modeling were not supported by our findings for majority of tested metals and accumulation sources. Further basic research is required to develop more accurate and robust radioecological models.

Sediments as sinks and sources of marine radionuclides: Implications for their use as ocean tracers

A Lagrangian transport model for the North Atlantic has been applied to simulate the historical releases of 137Cs, 129I and 236U from the European nuclear fuel reprocessing plants. Advection by currents, mixing and decay are included, as radionuclide interactions between water, sediments and suspended matter. The model was validated comparing predictions with measured radionuclide concentrations in water and sediments in several areas. 129I and 236U signals entering the Arctic Ocean have been compared with the input terms: the 236U signal is distorted, but the 129I signal preserves its shape. In the first moments after the releases, the sediments act as sinks for 236U, but not significantly for 129I and ultimately they become sources of 236U to the open sea. This results in a weaker correlation between input and output signals for 236U than for 129I. The same effects as for 236U have been found for 137Cs signal into the Arctic.

Biomonitoring of radioactive contamination using benthic invertebrate communities in Manzala Lake, Egypt

Manzala Lake, the largest in Egypt’s Nile Delta, has significant human activity. The Lake’s ecological condition has recently been impacted by a significant increase in agricultural, industrial, and urban wastewater discharge. Avaluable tool for monitoring the water quality of Manzal aLake is the sensitivity of invertebrate species to various types of pollution, such as radioactive contamination. Activity concentrations of radionuclides Radium-226 (226Ra),Thorium-232 (232Th), Potassium-40 ( 40K), and Caesium-137(137Cs) were measured in water, sediments and benthic invertebrate samples in 2020. The benthic community’s spatial distribution and the radionuclides’ bioaccumulation were evaluated to determine possible relationships.Thirty taxa of benthic invertebrates were recognised.The data illustrated that the mean activity concentratio nof radionuclides in water was in the order of 40K > 232Th >226Ra > 137Cs, which changed into 40K > 226Ra > 232Th > 137Csin the sediment and benthic invertebrates. Gastropoda and Ostracoda are the dominating groups of benthos in the lake and are related to the highest concentrations of radionuclides. The benthos species with shells dominated at the sites with the highest activity concentration of 226Ra, while soft-bodied organisms dominated in sites with the highest average 137Cs activity in these samples.

Development of a dynamic food chain model for assessment of the radiological impact from radioactive releases to the aquatic environment

The software tool POSEIDON-R was developed for modelling the concentration of radionuclides in water and sediments as well as uptake and fate in the aquatic environment and marine organisms. The software has been actively advanced in the aftermath of the Fukushima Dai-ichi accident. This includes development of an uptake model for the benthic food chain, a kinetic-allometric compartment model for fish and recent advancements for the application of 3H. This work will focus on the food chain model development and its extension to key artificial radionuclides in radioecology such as 3H. Subsequently, the model will be applied to assess the radiological dose for marine biota from 3H, 90Sr, 131I, 134Cs and 137Cs released during and after the Fukushima Dai-ichi accident.The simulation results for 3H, 90Sr, 131I, 134Cs and 137Cs obtained from the coastal box (4-4 km) located at the discharge area of the Fukushima Dai-ichi NPP, and the surrounding regional box (15–30 km) are compared with measurements. The predictions are by and large consistent with experimental findings, although good validation for 3H, 90Sr and 131I is challenging due to lack of data. On the basis of the model predictions a dose assessment for pelagic and benthic fish is carried out. Maximum absorbed dose rates in the coastal box and the regional box are respectively 6000 and 50 μGy d−1 and are found in the pelagic non-piscivorous fish. Dose rates exceeding ICRP's derived consideration levels of 1 mGy d−1 are only found in the direct vicinity of the release and shortly after the accident. During the post-accidental phase absorbed dose rates consistently fall to levels where no deleterious effects to the marine biota are expected. The results also demonstrate the prolonged dose rate from 134Cs and 137Cs, particularly for benthic organisms, due to caesium's affinity with sediment, re-entry of caesium from the sediment into the food chain and external exposure from its high energetic gamma emissions. Uptake of non-organic tritium (HTO) and organically bound tritium (OBT) is modelled and shows some accumulation of OBT in the marine organism. However, dose rates from tritium, even during the accident, are low.

Баромембранный метод подготовки счётных образцов воды для измерения ультранизких концентраций радионуклидов

В работе показана возможность применения баромембранного метода для измерения ультранизких концентраций радионуклидов в воде пресноводных водоёмов. Актуальность задачи обусловлена необходимостью определения привноса радионуклидов в водные объекты, используемые предприятиями ядерно-топливного цикла. Радионуклиды естественного и техногенного происхождения, не связанные со сбросами предприятия, всегда присутствуют в таких водных объектах, формируя естественный или техногенно изменённый радиационный фон. Его наличие часто затрудняет идентификацию вклада сбросов предприятия в активность воды, так как штатные методы мониторинга характеризуются очень высоким порогом обнаружения радионуклидов. Традиционные способы определения фоновых концентраций радионуклидов требуют отбора минимум 500 л воды с последующим её выпариванием до образования сухого остатка, а на такую процедуру необходимо не менее пяти рабочих дней. Сократить затраты времени и энергии на выпаривание сотен литров воды можно путём предварительного концентрирования радионуклидов в меньшем объёме пробы баромембранным методом. Для его демонстрации применяли мобильную установку с осмотическими мембранами. Её начальная производительность составляет 6,0 л·мин−1. Осмотические мембраны позволяют разделить исходную пробу из водоёма на два компонента — деминерализованный пермеат и содержащий радиоактивные вещества концентрат. В зависимости от степени минерализации воды исследуемой пробы, установка позволяет проводить за 10–15 ч предварительное концентрирование 500 л до образца объёмом 20 л с минимальными потерями радионуклидов. Этот подход универсален и может быть применён для концентрирования растворённых солей любых тяжёлых металлов и прочих органических соединений. Он позволяет готовить счётные образцы водных проб в гораздо меньшие сроки, чем традиционный метод упаривания.

Accumulation and distribution of radionuclides in higher aquatic plants during the vegetation period

The long-term observations of the dynamics of 90Sr and 137Cs concentration, as well as the physicochemical forms of these radionuclides in 10 species of higher aquatic plants during the vegetation period of Glyboke Lake in the Chornobyl Exclusion Zone were presented. The accumulation of radionuclides depends on the influence of environmental factors and species characteristics of the studied plants. It has been shown that the accumulation of 90Sr and 137Cs by plants mainly occurs in accordance with the physiological stages of their development. Under conditions of intensive growth and accumulation of biomass in the juvenile period, plants disproportionately uptake 137Cs from the environment; during the seed ripening period at the stage of aging, plants mainly accumulate 90Sr, as evidenced by the non-correlation of this radionuclide concentration in water and plants in the considered periods. The specific features of the accumulation of radionuclides by plants were studied by the method of analysis of physicochemical forms, which consists in the sequential extraction of radionuclides from plant preparations and makes it possible to quantitatively investigate potentially exchange and fixed forms. The analysis of physicochemical forms confirmed the patterns of seasonal distribution of radionuclides, as well as their accumulation in cells, tissues and in the whole plant obtained from long-term observations.

Вміст радіонуклідів у фітопланктоні на різних ділянках Запорізького водосховища

The radionuclides, which have occurred in the aquatic ecosystem are quickly redistributed there. Most of them come through the water phase to the benthal deposit, while the other part of them accumulates in suspensions and hydrobionts. Even low concentrations of radionuclides in water contributes to its radioactive contamination that poses risks to the environment. The radionuclide contamination of freshwater ecosystems is particularly pressing issue, since water with low mineralization enhances the radionuclides activity in the sediments compared to the water by a factor of 10 or even more, and in the animals by hundreds and thousands of times. Phytoplankton is the fundamental autotrophic link of aquatic ecosystems. Due to a large total sorption surface, it is able to absorb, retain and transmit radionuclides along the food chains, leading to a deterioration of the environmental position of the reservoir. Phytoplankton was sampled in the summer of 2019 at 5 sites along the course of the Zaporizke reservoir, which differ in hydrological and hydrochemical conditions: Samara Bay, Festivalnyi pier, Monastyrsky island, creek of the Mokra Sura river and the lower section of the reservoir (near Viyskove village). The specific radioactivity of phytoplankton samples was determined using generally accepted radiochemical methods and gamma spectrometry. The specific radioactivity of radionuclides is given in bequerels per kilogram (Bq/kg) of fresh, natural weight. Statistical processing of research results was carried out using generally accepted methods of variation statistics for a small sample using the Excel 2010 software package. Purpose of the work. To determine the content of natural ( 232 Th, 226 Ra and 40 K) and artificial ( 137 Cs and 90 Sr) radionuclides in phytoplankton at different sites of the Zaporizke reservoir. The content of artificial radionuclides in the phytoplankton of the Zaporizke reservoir averaged as follows: 137 Cs – 7.61±0.501 Bq/kg; 90 Sr – 1.13±0.242 Bq/kg. The maximum values of the content of artificial radionuclides in phytoplankton were recorded in the area of the Festivalnyi pier and the minimum values were recorded near Viyskove village ( 137 Cs) and Samara bay ( 90 Sr). In total, phytoplankton has a relatively low content of artificial radionuclides, which is explained by its low content in water. Hydrobionts receive the main portion of radiation exposure from natural sources of radiation. About 300 natural radionuclides have been identified in the environment; among them 226 Ra, 232 Th and 40 K make a significant contribution to the total natural radioactivity. The specific activity of natural radionuclides in the water area of the Zaporizke reservoir on average was following: 226 Ra – 95.45±7,010 Bq/kg; 232 Th – 85.66±4,013 Bq/kg; 40 K – 185.26±23.74 Bq/kg. The lowest content of natural radionuclides was observed in the phytoplankton of the Samara bay. The maximum recorded specific activity of 226 Ra and 40 K was observed in the creek of the Mokra Sura river, which may indicate an increased content of radionuclides in the water of this river, because the river is polluted throughout its length by industrial, agricultural and municipal wastewater. It has been found that the specific activity of natural radionuclides 226 Ra, 232 Th and 40 K was 80-320 times higher than that of the artificial ones ( 90 Sr and 137 Cs). The distribution of radionuclides in the elements of the freshwater ecosystem is characterized by accumulation coefficients. According to the accumulation coefficients with respect to water, the sequence of accumulation of radionuclides in the phytoplankton of the Zaporizke reservoir has been arranged in descending order: 137 Cs> 232 Th> 226 Ra> 40 K> 90 Sr. The accumulation coefficients of 40 K and 90 Sr are 11-22 times less than those of 137 Cs and 232 Th, which is quite appropriately, because freshwater algae are more able to accumulate 137 Cs. For most of the radionuclides studied, the maximum values of accumulation coefficients have been recorded in phytoplankton in the area of the Festivalnyi pier ( 137 Cs, 90 Sr, 232 Th) and the creek of the Mokra Sura river ( 226 Ra, 40 K). The latter is associated with both the hydrochemical and hydrological conditions of these sites, and with increased anthropogenic impact, especially in the area of the river creek. The data obtained indicate that there is a potential threat of accumulation of radionuclides in phytoplankton and their transfer further along food chains. With reference to the above mentioned, it is important to monitor the content of radionuclides in phytoplankton in order to minimize their transmission through the food chain and preserve the biodiversity of aquatic ecosystems.

Radionuclides in waters and suspended sediments in the Rhone River (France) - Current contents, anthropic pressures and trajectories

The Rhone River is one of the most nuclearized river in the world. Radionuclide concentrations in water and suspended sediments transferred to the marine environment were intensively monitored in this river over the last decades (2002–2018). Over this period of time, >12 and 25 time integrating samples were collected each year in filtered waters and suspended sediments, respectively, and analyzed for their radionuclide contents at ultra-trace levels by using top performance analytical tools. While >60% of plutonium, americium, cesium, cobalt, silver, beryllium and actinium radioisotopes are carried by sedimentary particles, sodium, tritium, antimony and strontium are mainly exported as dissolved species (>90%) due to their low affinity with particles. Most natural radionuclides contents show low seasonal variation. No significant trends are observed over the last two decades for these elements, even for 40K widely used in fertilizers after the middle of the last century, indicating that the basin has currently converged towards geochemical equilibrium for all of them. In contrast, the concentrations of numerous anthropogenic radionuclides originating from nuclear industries significantly declined since the beginning of the 2000s. Assuming no change of the current anthropic and climatic pressures over the next decades, apparent periods, i.e. the time required for a reduction by half the concentrations in the downstream part of the Rhône River, would be close to 6 years for most artificial radionuclides, except for tritium and other artificial radionuclides conveyed to the river by soil leaching and erosion (90Sr, 241Am, plutonium isotopes) which would be far longer. Referring to regional referential backgrounds, only few anthropogenic radionuclides specifically produced by nuclear industries are still detectable at the downstream part of the Rhone River and excess contents of tritium, 238Pu and 241Am are observed in filtered waters.

Feasibility evaluation of a direct detection method of alpha particles in water using YGAG plate with pulse shape analysis

Ce doped (YGd)3(GaAl)5O12:Ce (YGAG) is a ceramic scintillator with high light output, and its decay times are different between alpha particles and gamma photons or beta particles. This characteristic may be applied to the direct measurement of alpha particles in water where the gamma photons or beta particles become background counts. Thus we proposed a radiation detector using a YGAG plate dipped in water that contained alpha radionuclides to detect alpha particles in water. The scintillation photons from the YGAG plate were detected by a position sensitive photomultiplier tube (PSPMT) set in water that contained alpha radionuclides. A YGAG plate (20 × 20 × 0.5 mm) was set on the bottom of a glass cup filled with water containing alpha radionuclides that emit alpha particles. The alpha particles near the YGAG plate were detected by the scintillator, and the scintillation light was detected by the PSPMT . For radon-containing water sampled from a hot spring, pulse shape spectra showed two peaks: one for the alpha particles and another for the beta particles and the gamma photons. By pulse shape discrimination for the peak of the alpha particles, their count rate decreased with a decay of Rn-222 (3.8 days). For tap water, the pulse shape distribution showed only one peak and the count rate was almost constant, indicating these counts were mainly from the background beta particles or gamma photons. We could show a detection principle for alpha radionuclides in water and this detection principle for alpha radionuclides in water might be a new method for estimating the alpha radionuclide concentration in water.

THE CURRENT STATE OF PREPAREDNESS OF THE ROSPOTREBNADZOR INSTITUTIONS FOR PROVISION OF THE RADIATION SAFETY FOR THE 2018 WORLD FOOTBALL CHAMPIONSHIP

This study is focused on the main activities on provision of the radiation safety as a part of sanitary surveillance and radiation terrorism counteraction during the 2018 World Football Championship. The main activities at the preparatory stage are collection and analysis of information on the potentially dangerous sources of ionizing radiation in the regions of the Russian Federation hosting the 2018 World Football Championship; control of compliance to the sanitary rules of the projects of the allocation of X-ray screening units and their commissioning; radiation control as a part of the commissioning of the sport facilities after construction/reconstruction; sanitary control of the allocation of X-ray screening units on the sport and infrastructure facilities; organization-methodical activities. During the World Football Championship it is planned to carry out the radiation control in monitoring points and the control of the concentration of radionuclides in water and food stuff samples. In the framework of the radiation terrorism countermeasures, the main activities of the provision of the radiation safety are the radiation control on the infrastructure facilities, remote points of inspection and entry points to the sport facilities; full-time emergency preparedness. A brief evaluation of the equipment of the Rospotrebnadzor radiation control laboratories in the regions of the Russian Federation hosting the 2018 World Football Championship and their preparedness for the provision of the radiation safety is also presented in the paper.

Digital version of the European Atlas of natural radiation

The European Atlas of Natural Radiation is a collection of maps displaying the levels of natural radioactivity caused by different sources. It has been developed and is being maintained by the Joint Research Centre (JRC) of the European Commission, in line with its mission, based on the Euratom Treaty: to collect, validate and report information on radioactivity levels in the environment of the EU Member States.This work describes the first version of the European Atlas of Natural Radiation, available in digital format through a web portal, as well as the methodology and results for the maps already developed. So far the digital Atlas contains: an annual cosmic-ray dose map; a map of indoor radon concentration; maps of uranium, thorium and potassium concentration in soil and in bedrock; a terrestrial gamma dose rate map; and a map of soil permeability.Through these maps, the public will be able to: familiarize itself with natural environmental radioactivity; be informed about the levels of natural radioactivity caused by different sources; have a more balanced view of the annual dose received by the European population, to which natural radioactivity is the largest contributor; and make direct comparisons between doses from natural sources of ionizing radiation and those from man-made (artificial) ones, hence, to better assess the latter.Work will continue on the European Geogenic Radon Map and on estimating the annual dose that the public may receive from natural radioactivity, by combining all the information from the different maps. More maps could be added to the Atlas, such us radon in outdoor air and in water and concentration of radionuclides in water, even if these sources usually contribute less to the total exposure.

Cesium-137 of Chernobyl origin in lake–river systems of Eastern Fennoscandia: 30 years after the accident

Contamination of waters of lake–river systems after many-year migration of 137Cs in water bodies was studied. In lakes with the 137Cs fallout density lower than 8 kBq m–2, the radionuclide concentrations in water after 24–29 years did not exceed 2–3 Bq m–3, and at a fallout level of 37 kBq m–2 it was in the range 11–34 Bq m–3. The natural half-clearance time Т of lake waters from 137Cs was 6–7 years at the exposure of up to 20 years. The 137Cs migration in the lake–river systems that occurred during ~30 years did not lead to structural changes in the water contamination: The initially low 137Cs level in lake waters did not become high, and vice versa. Among rivers feeding Lake Ladoga, the 137Cs level in the Vuoksa River is ~3 times higher than in waters of the Volkhov and Svir rivers. During the period 1988–2015, 21.3 TBq of 137Cs was supplied to Lake Ladoga with Vuoksa waters. The Vuoksa source from the Saima lake system with increased contamination with 137Cs of Chernobyl origin leads to long-term supply of this radionuclide to Lake Ladoga.

Reference levels of radioactive contamination of water bodies based on the environmental criteria

Quantitative environmental criteria for the radiation protection of aquatic ecosystems, namely, reference concentrations of radionuclides in water are developed. If activity concentrations of radionuclides do not exceed these levels, aquatic biota can be considered completely protected from the negative effects of ionizing radiation. Reference concentrations of radionuclides in environmental objects can be compared directly with the measurement data on radioactive contamination parameters that allows using them for the monitoring data interpretation. Reference concentrations of anthropogenic radionuclides in the sea and fresh water are calculated using the environmental criteria and are compared to the values of reference concentrations computed using the hygienic criterion. It is demonstrated that the current levels of concentration of 90Sr, 137Cs, and tritium in the seas, rivers, and lakes of Russia are considerably lower than the values of reference concentrations of these radionuclides calculated using the environmental criterion.

Distribution of natural and artificial radioactivity in soils, water and tuber crops.

Activity concentrations of radionuclides in water, soil and tuber crops of a major food-producing area in Ghana were investigated. The average gross alpha and beta activities were 0.021 and 0.094 Bq/L, respectively, and are below the guidelines for drinking water and therefore not expected to pose any significant health risk. The average annual effective dose due to ingestion of radionuclide in water ranged from 20.08 to 53.45 μSv/year. The average activity concentration of (238)U, (232)Th, (40)K and (137)Cs in the soil from different farmlands in the study area was 23.19, 31.10, 143.78 and 2.88 Bq/kg, respectively, which is lower than world averages. The determined absorbed dose rate for the farmlands ranged from 23.63 to 50.51 nGy/year, which is within worldwide range of 18 to 93 nGy/year. The activity concentration of (238)U, (232)Th, (40)K and (137)Cs in cassava ranges from 0.38 to 6.73, 1.82 to 10.32, 17.65 to 41.01 and 0.38 to 1.02 Bq/kg, respectively. Additionally, the activity concentration of (238)U, (232)Th, (40)K and (137)Cs in yam also ranges from 0.47 to 4.89, 0.93 to 5.03, 14.19 to 35.07 and 0.34 to 0.89 Bq/kg, respectively. The average concentration ratio for (238)U, (232)Th and (40)K in yam was 0.12, 0.11 and 0.17, respectively, and in cassava was 0.11, 0.12 and 0.2, respectively. None of the radioactivity is expected to cause significant health problems to human beings.

Radionuclides in bats using a contaminated pond on the Nevada National Security Site, USA

Perched groundwater percolating through radionuclide contamination in the E Tunnel Complex on the Nevada National Security Site, formerly the Nevada Test Site, emerges and is stored in a series of ponds making it available to wildlife, including bats. Since many bat species using the ponds are considered sensitive or protected/regulated and little information is available on dose to bats from radioactive water sources, bats were sampled to determine if the dose they were receiving exceeded the United States Department of Energy dose limit of 1.0E-3 Gy/day. Radionuclide concentrations in water, sediment, and flying insects were also measured as input parameters to the dose rate model and to examine trophic level relationships. The RESRAD-Biota model was used to calculate dose rates to bats using different screening levels. Efficacy of RESRAD-Biota and suggested improvements are discussed. Dose to bats foraging and drinking at these ponds is well below the dose limit set to protect terrestrial biota populations.

Analyses of radionuclides in soil, water, and agriculture products near the Urgeiriça uranium mine in Portugal

Analyses of soils, irrigation waters, agriculture products (lettuce), green pasture, and cheese were performed in samples collected in the area of the old Urgeirica uranium mine and milling facilities, Centre-North of Portugal, in order to assess the transfer of uranium series radionuclides in the environment and to man. Soils close to milling tailings display an enhancement of radioactivity. In the drainage basin of the stream Ribeira da Pantanha, receiving drainage from the tailings piles and discharges from the acid mine water treatment plant, there was enhancement of uranium series radionuclide concentrations in water and suspended matter. Agriculture products from kitchen gardens irrigated with water from the Ribeira da Pantanha show an increase of radioactivity, mainly due to uranium isotopes. Agriculture products from other kitchen gardens in this area, irrigated with groundwater, as well pasture and cheese produced locally from sheep milk did not show enhanced radionuclide concentrations. In the Urgeirica area, some soils display radionuclide concentrations higher than soils in reference areas and, in agriculture products grown there, 226Ra was the radionuclide more concentrated by vegetables. Through ingestion of these products 226Ra may be the main contributor to the increment of radiation dose received by local population.

A simplified model to evaluate the radiological impact of an accident with a nuclear reactor submerged at the sea

There are various scenarios dealing with releases of radionuclides in a water body, for example, accidents in nuclear power plants located in coastal areas, on margins of rivers or lakes. Meager attention has been given, however, to potential accidents with nuclear reactors submerged at sea. The latter type of accidents may occur with partial or total loss of the nuclear reactor core to the adjacent waters. In addition to initial instantaneous releases, one may estimate delayed sources based on rates of leaching or dissolving solid materials which are part of the core. Transport equations were used to estimate concentrations of radionuclides in water. Time dependent functions of concentrations of radionuclides in the aquatic food chain reflect the absorption and elimination processes in the flora and fauna. However, to avoid the multi-parametric complexity which can be inserted in these processes, the model takes into proper consideration in a simplified way the transfer of radionuclides through trophic levels. The model avoids the need to analyze step-by-step the details of transfer factors used to determine radionuclide accumulation in fish, crustaceans, mollusks, and algae. This simplified model may help authorities in the case of an accident with a nuclear reactor submerged at sea.

Assessment of Radionuclide Concentrations in Water Supply from Bore-holes in Ogbomosoland, Western Nigeria

The level of radionuclide concentration in water from bore-holes in selected areas of Ogbomosoland, a region consisting of five local governments, was determined. Concentration of 238U, 232Th, and 40K was determined for the water samples from eight bore-holes around Ogbomosoland by γ-ray spectrometry with a high-purity germanium (HPGe) detector connected to a multichannel analyzer. All the water samples from these bore-holes were found to contain acceptable levels of radionuclides with mean activity values of 3.98 ±0.26, 11.00 ±2.58, and 17.73 ± 5.04 Bql -1 for 40K, 232Th, and 238U, respectively showing that the mean activity of 238U for all the samples is the highest when compared with those of 40K and 232Th. Water samples from Ikoyi had the highest radionuclide content although 40K concentration was below detectable level. Water samples from Gambari were next to Ikoyi in radionuclide content, followed by Saja, Ajinopai, Kajola, Isale-Ora, Iresa-Apa, and Owode in that order. The mean absorbed dose rate for all the area is 0.123 mSvyr-1 which is very low when compared to the recommended limit of 1mSvyr-1 for bore-hole water. Overall, the radionuclide concentration of the bore-hole water supply in Ogbomosoland is, negligible and poses no radiological hazards to the public.

Radionuclides from past uranium mining in rivers of Portugal

During several decades and until a few years ago, uranium mines were exploited in the Centre of Portugal and wastewaters from uranium ore milling facilities were discharged into river basins. To investigate enhancement of radioactivity in freshwater ecosystems, radionuclides of uranium and thorium series were measured in water, sediments, suspended matter, and fish samples from the rivers Vouga, Dão, Távora and Mondego. The results show that these rivers carry sediments with relatively high naturally occurring radioactivity, and display relatively high concentrations of radon dissolved in water, which is typical of a uranium rich region. Riverbed sediments show enhanced concentrations of radionuclides in the mid-section of the Mondego River, a sign of past wastewater discharges from mining and milling works at Urgeiriça confirmed by the enhanced values of 238U/ 232Th radionuclide ratios in sediments. Radionuclide concentrations in water, suspended matter and freshwater fish from that section of Mondego are also enhanced in comparison with concentrations measured in other rivers. Based on current radionuclide concentrations in fish, regular consumption of freshwater species by local populations would add 0.032 mSv a −1 of dose equivalent (1%) to the average background radiation dose. Therefore, it is concluded that current levels of enhanced radioactivity do not pose a significant radiological risk either to aquatic fauna or to freshwater fish consumers.

A new general mechanistic river model for radionuclides from single pulse fallouts which can be run by readily accessible driving variables

This paper presents a new general, process-based river model for substances such as radionuclides from single pulse fallouts. The new model has been critically tested using data from 13 European rivers contaminated by radiocesium from the Chernobyl accident. This modelling approach gives radionuclide concentrations in water (total, dissolved and particulate phases; and also concentrations in sediments and fish, but the latter aspects are not discussed in this paper) at defined river sites. The model is based on processes in the upstream river stretch and in the upstream catchment area. The catchment area is differentiated into inflow (≈dry land) areas and outflow (≈wetland) areas. The model also accounts for time-dependent fixation of substances in the catchment. The catchment area sub-model is based on a previous catchment model, which has been tested with very good results for radiocesium, radiostrontium and Ca-concentrations (from liming operations). The new river model is simple to apply in practice since all driving variables may be readily accessed from maps and standard monitoring programs. The driving variables are: latitude, altitude, continentality, catchment area, mean annual precipitation, soil type (percentages or organic and sandy soils), fallout and month of fallout. Modelled values have been compared to independent empirical data from 10 rivers sites (91 data on radiocesium in water) covering a wide domain (catchment areas from 4000 to 180 000 km 2, precipitation from 500 to 960 mm/yr and fallout from 1700 to 660 000 Bq/m 2). The new model predicts very well – when modelled values are compared to empirical data, the slope is perfect (1.0) and the r 2-value is 0.90. This is good giving the fact that there are also uncertainties in the empirical data, which set a limit to the achieved predictive power, as expressed by the r 2-value.