Review and assessment of models used to predict the fate of radionuclides in lakes

A variety of models for predicting the behaviour of radionuclides in fresh water ecosystems have been developed and tested during recent decades within the framework of many international research projects. These models have been implemented in Computerised Decision Support Systems (CDSS) for assisting the appropriate management of fresh water bodies contaminated by radionuclides. The assessment of the state-of-the-art and the consolidation of these CDSSs has been envisaged, by the scientific community, as a primary necessity for the rationalisation of the sector. The classification of the approaches of the various models, the determination of their essential features, the identification of similarities and differences among them and the definition of their application domains are all essential for the harmonisation of the existing CDSSs and for the possible development and improvement of reference models that can be widely applied in different environmental conditions. The present paper summarises the results of the assessment and evaluation of models for predicting the behaviour of radionuclides in lacustrine ecosystems. Such models were developed and tested within major projects financed by the European Commission during its 4th Framework Programme (1994-1998). The work done during the recent decades by many modellers at an international level has produced some consolidated results that are widely accepted by most experts. Nevertheless, some new results have arisen from recent studies and certain model improvements are still necessary.     

Availability of 99Tc in undisturbed soil cores

Models for safety assessment of radioactive waste repositories need accurate values of the soil-to-plant transfer of radionuclides. In oxidizing environments, (99)Tc is expected to occur as pertechnetate ((99)TcO(4)(-)). Due to its high mobility, leaching of this element in the field might be important, potentially affecting the reliability of estimated transfer parameters of (99)Tc as measured in closed experimental systems such as hydroponics or pot experiments. The aim of this experiment was to measure the leaching of (99)Tc in undisturbed irrigated soil cores under cultivation as well as plant uptake and to study the possible competition between the two transfer pathways. Undisturbed soil cores (50 x 50 cm) were sampled from a Rendzic Leptosol (R), a colluvial Fluvic Cambisol (F) and a Dystric Cambisol (D) using PVC tubes (three cores sampled per soil type). Each core was equipped with a leachate collector at the bottom, allowing the monitoring of (99)Tc leaching through the cores. Cores were placed in a greenhouse and maize (Zea mays L., cv. DEA, Pioneer) was sown. After 135 d, maize was harvested and radioactivity determined in both plant and water samples. Results showed that during the growing period, leaching of (99)Tc was limited, due to the high evapotranspiration rate of maize. After harvest, leaching of (99)Tc went on because of the absence of evapotranspiration. Effective uptake (EU) of (99)Tc in leaves and grains was calculated. EU reached 70% of the input in the leaves and was not significantly different among soils. These results confirmed those obtained from pot experiments, even though leaching was allowed to occur in close-to-reality hydraulical conditions. As a consequence, it was concluded that pot experiments are an adequate surrogate for more complex "close-to-reality" experimental systems for measuring transfer factors.     

Human exposure to dioxins through the diet in Catalonia,Spain: carcinogenic and non-carcinogenic risk

The main objectives of this study were to estimate the dietary intake of dioxins by the population of Catalonia, Spain, to determine which food groups showed the greatest contribution to this intake, and to assess the health risks potentially associated with the dietary dioxin intake. From June to August 2000, food samples were randomly acquired in seven cities of Catalonia. Dioxin concentrations were determined in 108 samples belonging to the following groups: vegetables, fruits, pulses, cereals, fish and shellfish, meats and meat products, eggs, milk and dairy products, and oils and fats. Estimates of average daily food consumption were obtained from recent studies. Total dietary intake of dioxins for the general population of Catalonia was estimated to be 95.4 pg WHO-TEQ/day (78.4 pg I-TEQ/day), with fish and shellfish (31%), diary products (25%), cereals (14%) and meat (13%) showing the greatest percentages of contribution to dioxin intake. The contribution of all the rest of food groups to the total dietary intake was under 20%. The non-carcinogenic risk index of dioxin intake through the diet was in the range 0.34-1.36, while the carcinogenic risk level was 1,360 excess cancer over a lifetime of 70 years. Our results corroborate the decreasing tendency in dietary intake of dioxins found in recent studies (2000-2001) from various countries.     

Atrazine, isoproturon, mecoprop, 2,4-D, and bentazone adsorption onto iron oxides

Iron oxides are important components influencing the adsorption of various inorganic and organic compounds in soils and sediments. In this study the adsorption on iron oxides of nonionic and ionic pesticides was determined as a function of solution pH, ionic strength, and pesticide concentration. The investigated iron oxides included two-line ferrihydrite, goethite, and lepidocrocite. Selected pesticides comprised atrazine (6-chloro-N2-ethyl-N4-isopropyl-1,3,5-triazine-2,4-diamine), isoproturon [3-(4-isopropylphenyl)-1,1-dimethylurea)], mecoprop [(RS)-2-(4-chloro-2-methylphenoxy)propionic acid], 2,4-D (2,4-dichlorophenoxyacetic acid), and bentazone [3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide]. The adsorption of the nonionic pesticides (atrazine and isoproturon) was insignificant, whereas the adsorption of the acidic pesticides (mecoprop, 2,4-D, and bentazone) was significant on all investigated iron oxides. The adsorption capacity increased with decreasing pH, with maximum adsorption reached close to the pKa values. The addition of CaCl2 in concentrations from 0.0025 to 0.01 M caused the adsorption capacity to diminish. The adsorption of bentazone was significantly lower than the adsorption of mecoprop and 2,4-D, illustrating the importance of a carboxyl group in the pesticide structure. The adsorption capacity on the iron oxides increased in the order: lepidocrocite < goethite < two-line ferrihydrite. The maximum adsorption capacities of meco-prop and 2,4-D on goethite were found to be equivalent to the site density of singly coordinated hydroxyl groups on the faces of the dominant (110) form, suggesting that singly coordinated hydroxyl groups are responsible for adsorption. Differences in adsorption capacities between iron oxides can be explained by differences in the surface site density of singly coordinated hydroxyl groups. The maximum measured adsorption capacity of mecoprop on two-line ferrihydrite was equivalent to 0.2 mol/mol Fe.     

Effects of sample storage on biosolids compost stability and maturity evaluation

Compost stability and maturity are important parameters of compost quality. To date, nearly all compost characterization has been performed using samples freshly collected because sample storage can affect compost stability and maturity evaluation. However, sample preservation is sometimes necessary, especially for scientific research purposes. There is little information available on the effects of sample storage on compost stability and maturity. Samples of biosolids compost with different levels of stability and maturity were collected from four compost facilities in Florida (referred to as Register, Winslow, Sunset, and Meadow). Comparisons of CO2 evolution, seed germination rate, and water-soluble organic carbon (WSOC) were made between fresh samples with short storage at 4 degrees C for less than 1 wk and air-dried or frozen compost samples stored for 1 yr. The effects of storage (air-dry or frozen) on the measured parameters depended on compost stability and maturity and on the compost material source. Frozen storage reduced the peak CO2 evolution of Register samples by 12 to 29%, while accumulated CO2 evolution was reduced by 43 to 64% and 110 to 277% with air-dry and frozen storage, respectively. The storage effect on CO2 evolution with more stable compost was inconsistent. Storage did not affect compost phytotoxicity, except for samples from the Sunset facility. Air-drying reduced the WSOC by up to 35%, and freezing increased it by up to 34%, while both storage methods had no significant effect on samples of low WSOC. Despite all these variations, WSOC had a significant and consistent relation to CO2 evolution and seed germination rates with R2 of 0.78 and 0.57, respectively, regardless of storage methods.     

Herbicide and nutrient transport from an irrigation district into the South Saskatchewan River

Pesticides and nutrients can be transported from treated agricultural land in irrigation runoff and thus can affect the quality of receiving waters. A 3-yr study was carried out to assess possible detrimental effects on the downstream water quality of the South Saskatchewan River due to herbicide and plant nutrient inputs via drainage water from an irrigation district. Automated water samplers and flow monitors were used to intensively sample the drainage water and to monitor daily flows in two major drainage ditches, which drained approximately 40% of the flood-irrigated land within the irrigation district. Over three years, there were no detectable inputs of ethalfluralin into the river and those of trifluralin were less than 0.002% of the amount applied to flood-irrigated fields. Inputs of MCPA, bromoxynil, dicamba and mecoprop were 0.06% or less of the amounts applied, whereas that for clopyralid was 0.31%. The relatively higher input (1.4%) of 2,4-D to the river was probably due its presence in the irrigation water. Corresponding inputs of P (as total P) and N (as nitrate plus ammonia) were 2.2 and 1.9% of applied fertilizer, respectively. Due to dilution of the drainage water in the river, maximum daily herbicide (with the exception of 2,4-D) and nutrient loadings to the river would not have resulted in significant concentration increases in the river water. There was no consistent remedial effect on herbicides entering the river due to passage of the drainage water through a natural wetland. In contrast, a considerable portion of the nutrients entering the river originated from the wetland.     

Computerized Map of Risk to Manage Wildlife Species in Urban Areas

For the last 20 years, human–wildlife conflicts have been rapidly increasing in towns. Although people want “greener” cities, the expansion of disliked species causes problems that are difficult to manage and to reduce. The complexity of the numerous factors involved in these human–wildlife relations needs the development of a comprehensive tool for urban planners. Today, with the development of computers and geographical information systems, it is easier to analyze and combine different spatial data as methods used for the management of risks in studies of natural hazards. Here we present a method for assessing and mapping the risk in cases of human–wildlife conflict. An application to starling management in a town in western France will show the efficiency of our methods to combine information given by a network of experts and to highlight higher risk sites. The map of risk provides a spatial result useful for comprehension, communication between people and agencies, and public education.     

Airborne surveys of Swiss nuclear facility sites

Annually since 1989, biannually since 1994, the environs (approximately 50 km2) of the Swiss nuclear facilities are surveyed (by helicopters) flying the same survey lines. The equipment and the data processing software used for these surveys were built and developed at the Institute of Geophysics, ETH Zurich. For mapping of man-made radiation at or around nuclear facility sites a pixel representation and the MMGC (man-made gross count) ratio is used. So far no artificial radioactivity that could not be explained by the Chernobyl event (1986) or by earlier nuclear weapon tests was detected outside the fenced sites of the nuclear facilities.     

Extraction of full absorption peaks in airborne gamma-spectrometry by filtering techniques coupled with a study of the derivatives. Comparison with the window method

In this paper, an adaptation of a spectral profile analysis method, currently used in high-resolution spectrometry, to airborne gamma measurements is presented. A new algorithm has been developed for extraction of full absorption peaks by studying the variations in the spectral profile of data recorded with large-volume NaI detectors (16 l) with a short sampling time (2 s). The use of digital filters, taking into consideration the characteristics of the absorption peaks, significantly reduced the counting fluctuations, making detection possible based on study of the first and second derivatives. The absorption peaks are then obtained by modelling, followed by subtraction of the Compton continuum in the detection window. Compared to the conventional stripping ratio method, spectral profile analysis offers similar performance for the natural radioelements. The 137Cs 1SD detection limit is approximately 1200 Bq/m2 in a natural background of 200 Bq/kg 40K, 33 Bq/kg 238U and 33 Bq/kg 232Th. At low energy the very high continuum leads to detection limits similar to those obtained by the windows method, but the results obtained are more reliable. In the presence of peak overlaps, however, analysis of the spectral profile alone is not sufficient to separate the peaks, and further processing is necessary. Within the framework of environmental monitoring studies, spectral profile analysis is of great interest because it does not require any assumptions about the nature of the nuclides. The calculation of the concentrations from the results obtained is simple and reliable, since only the full absorption contributions are taken into consideration. A quantitative estimate of radioactive anomalies can thus be obtained rapidly.     

Exposure of workers in mineral processing industries in Brazil

The mining, milling and processing of uranium and thorium bearing minerals may result in radiation doses to workers. A preliminary survey pilot program, that included six mines in Brazil (two coal mines, one niobium mine, one nickel mine, one gold mine and one phosphate mine), was launched in order to determine the need to control the radioactive exposure of the mine-workers. Our survey consisted of the collection and analysis of urine samples, complemented by feces and air samples. The concentrations of uranium, thorium and polonium were measured in these samples and compared to background data from family members of the workers living in the same dwelling and from residents from the general population of Rio de Janeiro. The results from the coal mines indicated that the inhalation of radon progeny may be a source of occupational exposure. The workers from the nickel, gold and phosphate mines that were visited do not require a program to control internal radiological doses. The niobium mine results showed that in some areas of the industry exposure to thorium and uranium might occur.