Radionuclide Concentrations In Water Research Articles

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.

A new general dynamic model predicting radionuclide concentrations and fluxes in coastal areas from readily accessible driving variables

This paper presents a general, process-based dynamic model for coastal areas for radionuclides (metals, organics and nutrients) from both single pulse fallout and continuous deposition. The model gives radionuclide concentrations in water (total, dissolved and particulate phases and concentrations in sediments and fish) for entire defined coastal areas. The model gives monthly variations. It accounts for inflow from tributaries, direct fallout to the coastal area, internal fluxes (sedimentation, resuspension, diffusion, burial, mixing and biouptake and retention in fish) and fluxes to and from the sea outside the defined coastal area and/or adjacent coastal areas. The fluxes of water and substances between the sea and the coastal area are differentiated into three categories of coast types: (i) areas where the water exchange is regulated by tidal effects; (ii) open coastal areas where the water exchange is regulated by coastal currents; and (iii) semi-enclosed archipelago coasts. The coastal model gives the fluxes to and from the following four abiotic compartments: surface water, deep water, ET areas (i.e., areas where fine sediment erosion and transport processes dominate the bottom dynamic conditions and resuspension appears) and A-areas (i.e., areas of continuous fine sediment accumulation). Criteria to define the boundaries for the given coastal area towards the sea, and to define whether a coastal area is open or closed are given in operational terms. The model is simple to apply since all driving variables may be readily accessed from maps and standard monitoring programs. The driving variables are: latitude, catchment area, mean annual precipitation, fallout and month of fallout and parameters expressing coastal size and form as determined from, e.g., digitized bathymetric maps using a GIS program. Selected results: the predictions of radionuclide concentrations in water and fish largely depend on two factors, the concentration in the sea outside the given coastal area and/or adjacent coastal areas and the ecological half-life of the radionuclide in the sea. Uncertainties in these factors generally dominate all other uncertainties, e.g., concerning the surface water retention time, the settling velocity of the particulate fraction, the distribution coefficient regulating the fluxes in dissolved and particulate phases, the catchment area influences and the factors regulating biouptake and excretion of the radionuclide in fish. This means that the conditions in the sea are of paramount importance for the conditions in the coastal area, even for relatively enclosed coastal areas. This coastal model may be regarded as a tool for testing working hypotheses on the relative roles of different processes in different coastal areas. Such information is essential for getting realistic expectations of various remedial measures, such as coastal dredging discussed in this work.

A new generic sub-model for radionuclide fixation in large catchments from continuous and single-pulse fallouts, as used in a river model

This paper presents a new general sub-model for fixation in catchment areas to be used within the framework of a river model for substances such as radionuclides and metals from continuous and single-pulse fallouts. The model has been critically tested using data from 27 European river sites covering a very wide geographical area and contaminated by radiocesium and radiostrontium from the Chernobyl accident and from the nuclear weapons tests (NWT fallout). This modelling approach gives radionuclide concentrations in water (total, dissolved and particulate phases) at defined sites on a monthly basis. The overall river model is based on processes in the upstream river stretch and in the catchment area. The catchment area is differentiated into inflow (≈dry land) areas and outflow (≈wetland) areas. The model has a general structure, which can be used for all radionuclides or substances. It 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, catchment area, mean annual precipitation and fallout. Note that for large catchments, this model does not require data on the characteristic soil type or the percentage of outflow areas (wet lands) in the catchment, as in most previous models, since in practice it is very difficult to obtain reliable data on characteristic soil type or percentage of outflow areas, especially in large and topographically complex catchments. Modelled values have been compared to empirical data from rivers sites covering a wide domain (catchment areas from 3000 to 3,000,000 km2, precipitation from 400 to 1700 mm/year; fallouts from 1600 to 280,000 Bq/m2; altitudes from 0 to 1000 m.a.s.l. and latitudes from 41° to 72° N). The river model with its sub-model for fixation predicts close to the uncertainty factors given by the empirical data, which have been shown to be about a factor of 1.6 for 137Cs and a factor of 2.2 for 90Sr in river water. The obtained characteristic uncertainty factors for 137Cs from the Chernobyl fallout is 2.4, for 137Cs from the NWT fallout it is 1.3 and for the 90Sr results from the NWT fallout it is 3 using the new model.

A new generic sub-model for radionuclide fixation in large catchments from continuous and single-pulse fallouts, as used in a river model

This paper presents a new general sub-model for fixation in catchment areas to be used within the framework of a river model for substances such as radionuclides and metals from continuous and single-pulse fallouts. The model has been critically tested using data from 27 European river sites covering a very wide geographical area and contaminated by radiocesium and radiostrontium from the Chernobyl accident and from the nuclear weapons tests (NWT fallout). This modelling approach gives radionuclide concentrations in water (total, dissolved and particulate phases) at defined sites on a monthly basis. The overall river model is based on processes in the upstream river stretch and in the catchment area. The catchment area is differentiated into inflow (≈dry land) areas and outflow (≈wetland) areas. The model has a general structure, which can be used for all radionuclides or substances. It 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, catchment area, mean annual precipitation and fallout. Note that for large catchments, this model does not require data on the characteristic soil type or the percentage of outflow areas (wet lands) in the catchment, as in most previous models, since in practice it is very difficult to obtain reliable data on characteristic soil type or percentage of outflow areas, especially in large and topographically complex catchments. Modelled values have been compared to empirical data from rivers sites covering a wide domain (catchment areas from 3000 to 3,000,000 km 2, precipitation from 400 to 1700 mm/year; fallouts from 1600 to 280,000 Bq/m 2; altitudes from 0 to 1000 m.a.s.l. and latitudes from 41° to 72° N). The river model with its sub-model for fixation predicts close to the uncertainty factors given by the empirical data, which have been shown to be about a factor of 1.6 for 137Cs and a factor of 2.2 for 90Sr in river water. The obtained characteristic uncertainty factors for 137Cs from the Chernobyl fallout is 2.4, for 137Cs from the NWT fallout it is 1.3 and for the 90Sr results from the NWT fallout it is 3 using the new model.

A probabilistic approach to obtaining limiting estimates of radionuclide concentration in biota

The US Department of Energy has developed a graded approach for evaluating radiation doses to biota. Limiting concentrations of radionuclides in water, soil, and sediment were derived for twenty-three radionuclides. Four organism types (aquatic animals, riparian animals, terrestrial animals, and terrestrial plants) were selected as the basis for method development. While environmental transfer data needed for deriving biota tissue concentrations are available for aquatic animals and terrestrial plants, less information is available for terrestrial and riparian organisms. Two methods were applied and examined for their ability to provide estimates of organism:soil or organism:water concentration factors in lieu of measured data. The kinetic/allometric approach combined with a parameter uncertainty analysis provides a needed method to estimate concentration factors across multiple species with limited input data.

Derivation of a screening methodology for evaluating radiation dose to aquatic and terrestrial biota

The United States Department of Energy (DOE) currently has in place a radiation dose standard for the protection of aquatic animals, and is considering additional dose standards for terrestrial biota. These standards are: 10 mGy/d for aquatic animals, 10 mGy/d for terrestrial plants, and, 1 mGy/d for terrestrial animals. Guidance on suitable approaches to the implementation of these standards is needed. A screening methodology, developed through DOE’s Biota Dose Assessment Committee (BDAC), serves as the principal element of DOE’s graded approach for evaluating radiation doses to aquatic and terrestrial biota. Limiting concentrations of radionuclides in water, soil, and sediment were derived for 23 radionuclides. Four organism types (aquatic animals; riparian animals; terrestrial animals; and terrestrial plants) were selected as the basis for development of the screening method. Internal doses for each organism type were calculated as the product of contaminant concentration, bioaccumulation factor(s) and dose conversion factors. External doses were calculated based on the assumption of immersion of the organism in soil, sediment, or water. The assumptions and default parameters used provide for conservative screening values. The screening methodology within DOE’s graded approach should prove useful in demonstrating compliance with biota dose limits and for conducting screening assessments of radioecological impact. It provides a needed evaluation tool that can be employed within a framework for protection of the environment.

Investigations of Thermoluminescence Dosimetry in the Techa River Flood Plain: Analysis of the New Results

The Techa river region was highly contaminated due to radioactive releases from a nuclear production facility in the period from 1949 to 1956. The inhabitants of the upper Techa river settlements received significant doses of external radiation. The majority of the houses in the upper Techa river villages were demolished after the evacuation of the population in 1956. Only three buildings (red-brick construction) in the former village of Metlino can still be used for thermoluminescence (TL) investigations in an external dose reconstruction study. The radiation source configuration changed in 1956 after an artificial reservoir was created next to Metlinsky pond. Preliminary TL studies showed good properties of the bricks that were sampled from the buildings. This paper presents an analysis of new results of TL investigations obtained on the samples collected from different walls of the buildings. The highest dose values in the range 1-4 Gy were found in bricks collected from the walls of building exposed to the artificial reservoir (Reservoir-10) and values of 1-1.5 Gy were found next to the Metlinsky pond shoreline. The measurements of the radiation source geometry were carried out simultaneously with the dose rates, radionuclide concentration in water and bottom sediments near the wall facing the old river bed. The measurements allow a validation of models used in the current Techa River Dosimetry System (TRDS-2000) to estimate external doses of the former inhabitants of the upper Techa riverside. In particular, the results can be applied for a more correct description of the source geometry in the settlement.

Study of caesium-137 in surface waters and sediments of the Tagus river

We have quantified the caesium-137 in surface waters and sediments in both the Portuguese and the Spanish sections of the Tagus River over six years. This river has its source in Spain, and of its 1100 km length about 230 km are in Portugal, 43 km serving as a natural frontier between the two countries. In the two regions under study the water flow is completely regulated by a chain of dams. There are three nuclear power plants, along the Spanish section of the river that might be sources of radioactive contamination. The Almaraz Nuclear Power Plant (ANPP) is the radioactive release source closest to Portugal. A concentration gradient of caesium was observed in the water, with the maximum values occurring at the sampling sites near the ANPP. However, there was no dependence of the caesium concentrations measured in the sediments on the proximity to the source. Instead, the values were related to the sediment type and its particle size. Distribution coefficients were evaluated in order to compare the radionuclide concentrations in water and sediments. In the calculation we took into account the time the caesium takes to move between these two media.

Determination of the admissable technogenic radioactive contamination of water in bays during the operation of nuclear objects in marine engineering

The various irradiation pathways due to radioactive contamination of water in bays (estuaries) are analyzed and the dose factors, characterizing the irradiation pathways considered, are determined for an extensive set of radionuclides. A method is proposed for determining the control concentration of radionuclides in water in reservoirs using the above-mentioned dose factors. The method is based on taking account of the professional work performed by workers. Critical population groups are identified on the basis of the irradiation pathways considered, and estimates of the control concentration of radionuclides in the water of a bay are made for these groups. 2 tables, 6 references.

Marine radioactivity assessment of Mururoa and Fangataufa atolls

The International Atomic Energy Agency (IAEA) carried out an international project ‘The Study of the Radiological Situation at the Atolls of Mururoa and Fangataufa’ with the aim of assessing the present and future radiological situation at the atolls and making recommendations for either monitoring or remedial actions if they are deemed necessary. The paper concentrates on marine radioactivity aspects and gives an estimation of present radionuclide concentrations in water, sediment and biota of the Mururoa and Fangataufa lagoons and the surrounding ocean. The dominant radionuclide in both lagoons is Pu in sediments (the total inventory is approximately 30 TBq). A decline in radionuclide concentrations has been observed in recent years in lagoon water, with the exception of 3H and 90Sr, for which a contribution from underground sources is to be expected. Radionuclide concentrations in biota from the lagoons and the surrounding ocean are low and consistent with previous measurements. The observed radionuclide concentrations in both lagoons imply that no radiological risk exists for hypothetical inhabitants of Mururoa and Fangataufa Atolls.

Setting standards for the safe level of radioactive contamination of water and bottom sediments in bodies of water

In this paper, we propose standards which can be used to simply and reliably monitor the content of technogenic radioactive substances in rivers and other bodies of water. We introduce the concept of “maximum safe concentration” and “reference monitored concentration” of radionuclides in water, and also the “maximum concentration of radionuclides in bottom sediments.” To determine the maximum safe concentration of radionuclides in water, we have used the basic public health principle established in NRB-96: to not exceed the limit of an effective dose of 1 mSv/y for external and internal radiation exposure for a critical population group, considering overall water use. To define the degree of radioactive contamination of the bottom of bodies of water, we propose using the maximum concentration of radionuclides in bottom sediments: a concentration less than that for which the bottom sediments may be classified in the category of “low activity solid radioactive wastes” according to OSP-72/87. We offer a calculation scheme and numerical values for the proposed standards for some radionuclides most frequently encountered in practice and examples of their use.

A collective model for predicting the long-term behaviour of radionuclides in rivers

Here I describe a collective model to predict the long term behaviour of 90Sr in river catchments. The model is applied to 11 Italian rivers contaminated by 90Sr due to nuclear explosions in the atmosphere over past decades. The uncertainty at the 68% confidence level of the model, when used as a generic tool for evaluating the concentration of the radionuclide in water, is a factor 1.8 around the predicted values. The reliability of the model output is due to the mutual compensation effects of different phenomena occurring in the catchments that lead to ‘collective’ behaviours which are scantily variable and uncertain despite the large range of catchment characteristics. The model is based on the assumption that the time behaviour of the 90Sr (Bq s −1) transported by water, following a single pulse of radionuclide deposition, is the sum of some exponential components. In the present paper the components were supposed characterised by the following decay constants: λ 1 = 2.3 × 10 −7 s −1, λ 2 = 4.2 × 10 −9 s −1 and λ 3 = 4.2 × 10 −10 s −1. The average value of 90Sr transfer coefficient from the catchment to the river, that, in the case of a pulse deposition, is approximately equal to the ratio between the radionuclide concentration in water and the deposition, is estimated to be 0.2 m −1.

A predictive model for the behavior of radionuclides in lake systems.

This paper describes a predictive model for the behavior of 137Cs in lacustrine systems. The model was tested by comparing its predictions to contamination data collected in various lakes in Europe and North America. The migration of 137Cs from catchment basin and from bottom sediments to lake water was discussed in detail; these two factors influence the time behavior of contamination in lake water. The contributions to the levels of radionuclide concentrations in water, due to the above factors, generally increase in the long run. The uncertainty of the model, used as a generic tool for prediction of the levels of contamination in lake water, was evaluated. Data sets of water contamination analyzed in the present work suggest that the model uncertainty, at a 68% confidence level, is a factor 1.9.

Concentrations of radionuclides in Lake Ontario water from measurements on water treatment plant sludges

The purpose of this investigation was to compare the results of indirect measurements of radionuclide concentrations in water with those measured directly. The levels of 137Cs and 226Ra in western Lake Ontario nearshore waters were derived from high-resolution γ-spectrometric measurements on aluminum hydroxide sludge samples obtained from four water treatment plants. The concentrations of 137Cs evaluated by this indirect technique averaged 0.036 compared with 0.023 pCi l −1 measured directly, while those of 226Ra averaged 0.047 compared with the direct measurement of 0.03 pCi l −1. The concentrations of a number of other radionuclides at these locations were also calculated from the sludge γ-ray measurements.

RADIATION DOSE TO THE HUMAN INTESTINAL TRACT FROM INTERNAL EMITTERS.

AbstractInternational (ICRP) recommendations for maximum permissible concentration of various radionuclides in water and air are based on a Standard Man model of average behavior. Previous work with animals has shown a high degree of variation among subjects where the intestinal tract was the critic