M.J. Madruga

226Ra bioavailability to plants at the Urgeiriça uranium mill tailings site.

Large amounts of solid wastes (tailings) resulting from the exploitation and treatment of uranium ore at the Urgeiriça mine (north of Portugal) have been accumulated in dams (tailing ponds). To reduce the dispersion of natural radionuclides into the environment, some dams were revegetated with eucalyptus (Eucalyptus globolus) and pines (Pinus pinea). Besides these plants, some shrubs (Cytisus spp.) are growing in some of the dams. The objective of this study is to determine the 226Ra bioavailability from uranium mill tailings by quantifying the total and available fraction of radium in the tailings and to estimate its transfer to plants growing on the tailing piles. Plant and tailing samples were randomly collected and the activity concentration of 226Ra in plants (aerial part and roots) and tailings was measured by gamma-spectrometry. The exchangeable fraction of radium in tailings was quantified using one single step extraction with 1 mol dm-3 ammonium acetate (pH = 7) or 1 mol dm-3 calcium chloride solutions. The results obtained for 226Ra uptake by plants show that 226Ra concentration ratios for eucalyptus and pines decrease at low 226Ra concentrations in the tailings and appear relatively constant at higher radium concentrations. For shrubs, the concentration ratios increase at higher 226Ra solid waste concentrations approaching a saturation value. Percentage values of 16.0 +/- 8.3 and 12.9 +/- 8.9, for the fraction of radium extracted from the tailings, using 1 mol dm-3 ammonium acetate or calcium chloride solutions, respectively, were obtained. The 226Ra concentration ratios determined on the basis of exchangeable radium are one order of magnitude higher than those based on total radium. It can be concluded that, at a 95% confidence level, more consistent 226Ra concentration ratios were obtained when calculated on the basis of available radium than when total radium was considered, for all the dams.

The "AQUASCOPE" simplified model for predicting 89,90Sr, 131I, and 134,137Cs in surface waters after a large-scale radioactive fallout.

Simplified dynamic models have been developed for predicting the concentrations of radiocesium, radiostrontium, and 131I in surface waters and freshwater fish following a large-scale radioactive fallout. The models are intended to give averaged estimates for radionuclides in water bodies and in fish for all times after a radioactive fallout event. The models are parameterized using empirical data collected for many lakes and rivers in Belarus, Russia, Ukraine, UK, Finland, Italy, The Netherlands, and Germany. These measurements span a long time period after fallout from atmospheric nuclear weapons testing and following the Chernobyl accident. The models thus developed were tested against independent measurements from the Kiev Reservoir and Chernobyl Cooling Pond (Ukraine) and the Sozh River (Belarus) after the Chernobyl accident, from Lake Uruskul (Russia), following the Kyshtym accident in 1957, and from Haweswater Reservoir (UK), following atmospheric nuclear weapons testing. The AQUASCOPE models (implemented in EXCEL spreadsheets) and model documentation are available free of charge from the corresponding author.

Environmental radioactivity monitoring in Portugal

Environmental radioactivity monitoring in Portugal is a nationwide programme that consists of two complementary (sparse and dense) sampling networks established following the EURATOM recommendations [2000/473/EURATOM-Commission Recommendation of 8 June 2000, Official Journal of the European Commission, no. 191, 27 June 2000]. This paper describes the aim of the monitoring programme, how it was implemented, the sampling locations, the type of samples, the analytical and measurement methods and the quality control programmes. Some representative results are also discussed. Based on the monitoring data it can be concluded that the Portuguese population has not been exposed to radioactivity levels that require any radiological protection measures.

Solid phase speciation of radiocaesium in bottom sediments

A comprehensive laboratory study is presented on the solid-phase speciation of ionic radiocaesium in bottom sediments (riverine, lacustrine, estuarine) covering some 75 samples of widely differing textural properties and originating from various locations in Europe. Sediments are characterised in terms of cation exchange capacities, exchangeable potassium and ammonium and specific radiocaesium sorption properties. It is shown that radiocaesium is quantitatively retained in the specific sorption sites associated with the micaceous clay minerals in the sediments. The practical consequences of this finding are discussed in terms of a predictive equation allowing forecasting of radiocaesium levels in the watercolumn or in the interstitial fluid of the sediment.

The influence of particle size on radionuclide activity concentrations in Tejo River sediments.

Sediment samples from Tejo River were analyzed for (228)Ra, (226)Ra, (137)Cs and (40)K by HPGe gamma spectrometry. The activity concentration data were statistically analyzed. The activity concentrations values were in the range of about two orders of magnitude for each radionuclide. The influence of the particle size on the radionuclide concentrations was observed. The different environmental origins of the radionuclides (228)Ra, (226)Ra, (137)Cs and (40)K, in the sediments were demonstrated through correlation analysis. Cluster analysis showed a close relationship between (228)Ra and (226)Ra and a different behavior for (40)K. The data obtained in this study provides useful information on the background radioactivity of the studied area and can be further used for radiological mapping of the Tejo River.

Caesium-137 and Strontium-90 temporal series in the Tagus River: experimental results and a modelling study

The objective of this work consisted of analysing the spatial and temporal evolution of two radionuclide concentrations in the Tagus River. Time-series analysis techniques and numerical modelling have been used in this study. (137)Cs and (90)Sr concentrations have been measured from 1994 to 1999 at several sampling points in Spain and Portugal. These radionuclides have been introduced into the river by the liquid releases from several nuclear power plants in Spain, as well as from global fallout. Time-series analysis techniques have allowed the determination of radionuclide transit times along the river, and have also pointed out the existence of temporal cycles of radionuclide concentrations at some sampling points, which are attributed to water management in the reservoirs placed along the Tagus River. A stochastic dispersion model, in which transport with water, radioactive decay and water-sediment interactions are solved through Monte Carlo methods, has been developed. Model results are, in general, in reasonable agreement with measurements. The model has finally been applied to the calculation of mean ages of radioactive content in water and sediments in each reservoir. This kind of model can be a very useful tool to support the decision-making process after an eventual emergency situation.

Contamination of Hydrographic Bassins in Uranium Mining Areas of Portugal

The uranium-radium mining industry generated about six million tons of radioactive by-products composed mainly by the tailings of uranium milling facilities and by fine mud deposits resulting from treatment of acid mine waters. Most of these radioactive materials are deposited on the ground in the village of Urgeirica, near Viseu, and are currently exposed to weathering. Following rains, leaching and surface runoff of these tailings drain into a stream, Ribeira da Pantanha that joins the river Mondego. In this river a wide artificial lake, Barragem da Aguieira, is the main water reservoir for the centre region of the country. Other rivers flowing through the mining region, namely the rivers Dao, Vouga and Tavora, may also receive drainage from the areas of old uranium mines. The radioactive contamination that uranium mining and milling wastes may have originated in rivers and water reservoirs is assessed.

Development of a couple of methods for measuring radon exhalation from building materials commonly used in the Iberian Peninsula

Radon is considered to be the main contributor to the worldwide population exposure to natural sources of radiation and so a lot of efforts have been made in most countries to assess indoor radon concentrations. Radon exhales from the earths surface and is part of the radioactive decay series of uranium, which is also present in building materials. In this work, measurements of radon exhalation rates in building materials commonly used in the Iberian Peninsula have been carried out by using two different methods: active and passive techniques. In the first technique, the radon exhalation rate was measured following the radon activity growth as a function of time, by using a continuous radon monitor. The second technique is based on integrated measurements by using solid-state nuclear track detectors and a Spark Counter reading equipment. The results obtained by both measuring methods were found to be consistent.

Naturally‐Occurring Radionuclides In Drinking Water From Surface And Groundwater Reservoirs

Radioactivity in water for human consumption is under closer scrutiny than ever before and many countries adopted guideline values based on total alpha and total beta activity measurements. Although most waters from surface circulation meet these guidelines, it is frequently found that groundwater exceed guideline values. Results of water analyses by alpha spectrometry clarified that the main radionuclides present are from the uranium decay series, such as uranium isotopes, radium (226Ra), radon (222Rn), and also 210Pb and 210Po. Occasionally, groundwater displayed 226Ra concentrations higher than 1 Bq L−1 and 222Rn concentrations above 1000 Bq L−1. Nevertheless, lack of conformity of these waters with guidelines adopted, generally, is not due to anthropogenic inputs.

Release of 137 Cs from plant mass in course of biodegradation

AbstractThis investigation was focused on the role of humic acid-like compounds during the biodegradation of plant mass contaminated with 137Cs. The experiments were set up to distinguish cases of external and internal contamination. The results showed that 137Cs was associated with humic acid-like compounds in eluates from biomass and especially with their lighter fraction. The 137Cs in detritus was markedly mobile and only minor amounts were retained in biomass. These two variants differed in the rate of 137Cs release: while in the internally contaminated biomass the rate decreased during composting, in the externally contaminated biomass the rate increased.