Selenium is essential for most of living organisms. In normoxic to moderately hypoxic freshwaters, Se exists predominantly in the (+VI) and (+IV) oxidation states as selenate and selenite respectively, whereas in the biota it is incorporated as Se (-II) or Se (0). At low concentrations, it acts against oxidative damages, but it may be toxic at higher levels. In filter feeders, such as the freshwater bivalve Corbicula fluminea, the ventilatory activity is a primary limiting step that controls the water influx and therefore the delivery of contaminants. A number of different parameters such as algal food density or presence of contaminant can influence the ventilation and hence the bioaccumulation potential of the contaminant. We report here a set of short-term experiments performed to study the effects of different forms of dissolved Se (selenite, selenate, selenomethionine) and algal-bound Se on the ventilatory activity of Corbicula fluminea and to evaluate the Se bioaccumulation. All experiments were performed on a 3-day exposure period after acclimatizing the organisms during a 7-day period to the synthetic water, at a regulated algal density. Both bioaccumulation and ventilatory activity of Se exposed groups, in comparison to these of the reference group, varied greatly according to the form of Se used.

Radionuclides can occur in the environment either through chronic releases of nuclear facilities, or due to incidents or accidents. In order to study there behaviors in the environment (migration, retention, transfer, ...) and in human organisms (metabolism, retention, excretion), it is of prime importance to know their solution chemistry, and more particularly thermodynamic equilibrium constants, allowing to calculate their speciation. In fact, speciation governs the migration, the bioavailability and the toxicity of elements. Moreover, this knowledge is also of great interest for decorporation or decontamination purposes. In this framework, a CEA working group on speciation has been created in order to share data both on thermodynamic constants and on analytical speciation methods, interesting chemists, environmentalists and biologists. It has been focused, in a first time, on actinides and a choice of specific ligands considered to be most representative of environmental and biological media. The thermodynamic database used is BASSIST (developed by CEA) in interaction with the speciation model JCHESS. Different examples are then presented on the selection of data (thermodynamic constants, ligands of interest) through benchmark exercises to test our state of knowledge in this area. Also, analytical methods to determine thermodynamic constants or direct speciation are discussed.

To meet the growing practical need in risk analysis in Russia health risk assessment tools and regulations have been developed in the frame of few federal research programs. One of the objectives and directions of this development is to produce common, unified basis of health risk analysis for different sources of risk. A specific risk index $\Re$ has been proposed for safety decision-making (establishing safety standards and other levels of protective actions, comparison of various sources of risk, etc.). The index $\Re$ is defined as the partial mathematical expectation of lost years of healthy life (LLE) due to exposure during a year to a risk source considered. The more concrete determinations of this index for different risk sources derived from the common definition of $\Re$ are given. Generic safety standards (GSS) for the public and occupational workers have been suggested in terms of this index. Secondary specific safety standards have been derived from GSS for ionising radiation and a number of other risk sources including environmental chemical pollutants. Other general and derived levels for decision-making have also been proposed including the “de-minimus" level. Some examples of risk comparison are demonstrated in the frame of different comparison tasks.

Radionuclides released to the environment may be present in different physico-chemical forms, ranging from ionic species to colloids, particles and fragments. Following releases during nuclear events such as nuclear weapon tests or use of depleted uranium munitions, and from nuclear accidents associated with explosions or fires, radionuclides such as uranium and plutonium are predominantly present as particles, mainly fuel particles. Similarly, radioactive particles are present in effluents from reprocessing facilities, and radioactive particles are observed in sediments in the close vicinity of radioactive waste dumped at sea. Thus, releases of radioactive particles occur far more often than earlier anticipated. Soils and sediments can act as a sink for colloids, particles and fragments, while contaminated soils and sediments may also act as a potential diffuse source, depending on particle characteristics and processes influencing particle weathering and remobilisation of associated radionuclides. To assess long-term impact from radioactive particle contamination, information on the source term is essential, i.e. activity concentrations and isotopic ratios as well as the particle size distribution, crystallographic structures and oxidation states influencing particle weathering rates and the subsequent mobilisation and biological uptake of associated radionuclides. The activity concentrations and the isotopic ratios will be source dependant, while particle characteristics will also reflect the release scenario, dispersion processes and deposition conditions. The present paper will summarise information on various nuclear sources summarise having released radioactive particles in the past


Uranium behaviour in soils is controlled by actions and interactions between physico-chemical and biological processes that also determine its bioavailability. In soil solution, uranium (+VI) aqueous speciation undergoes tremendous changes mainly depending on pH, carbonates, phosphates and organic matter. In a first approach, plants (Phaseolus vulgaris) were grown using hydroponics to allow an easy control of the composition of the exposure media. The latter, here an artificial soil solution, was designed to control the uranium species in solution. A geochemical speciation code was used to perform the solution speciation calculations. On this theoretical basis, three domains were defined for short-duration well-defined laboratory experiments in simplified conditions: pH 4.9, 5.8 and 7 where predicted dominant species are uranyl ions, hydroxyl complexes and carbonates respectively. For these domains, the influence of plant growth stage on transfer was determined. The Free Ion Model (or its derivated the Biotic Ligand Model) was tested to determine if U uptake was governed by the free uranyl species or if other metal complexes could be assimilated. The effect of different variables on root assimilation efficiency and phytotoxicity was explored: presence of ligands such as phosphates or carbonates and competitive ions such as Ca2+ at the 3 pHs. 


Because plants significantly affect radionuclides (RN) cycling and further dispersion into the biosphere, it is important to understand the biological factors influencing RN plant uptake, accumulation and redistribution. In this respect, mycorrhizal fungi are of particular interest. The effects of ecto-mycorrhizal (ECM) and arbuscular mycorrhizal (AM) fungi on the transport of uranium (U) or radiocaesium (Cs) were investigated both under pot and in vitro culture conditions. Results obtained in vitro demonstrated that AM hyphae can take up and translocate U and Cs towards roots, while this uptake and translocation were not perceptible using pot culture systems with soil. These contrasting results could be due to different experimental conditions, including the K level in the external solution and the bio-availability of Cs. The in vitro studies also indicated that root colonisation by AM fungi might limit U and Cs root transport. Under pot culture conditions, they appeared to significantly reduce root to shoot translocation of U. Under the same conditions, ECM transport of Cs was demonstrated, and appeared to be dependent on fungal species. A better estimation of the potential use of mycorrhizal fungi for the phytoremediation of RN-contaminated areas is now available and will be further discussed.

Within the framework of the Water Management Master plan, a bioindicator network (RINBIO) was deployed all along the French Mediterranean coast (1,800 km), using man-made cages containing mussels (Mytilus galloprovincialis) to assess contamination by heavy metals, persistent organic products and radionuclides. The caging technique compensated for the scarcity of natural shellfish stocks in significant parts of the coast and enable comparison between sites regardless of their physicochemical and trophic characteristics. Among the 103 stations of the entire program, 40 were selected for the measurement of anthropogenic radionuclides by high-efficiency gamma-spectrometry. Biometrics parameters of the each mussel samples, including `condition index' as an indicator of soft part growth, is correlated with radionuclides activities, to help correct raw data from differences in bioaccumulation between the various sites in relation to their trophic levels. A comprehensive picture of the distribution of radionuclides at such a large spatial scale is provided and the contribution of the Rhone River input, so far the main source for the coastal zone, is investigated.

In the frame of the IRSN Chernobyl Pilot Site Project, a waste trench containing hot particles was instrumented to study the fate of radioactive pollutants. Results have shown the formation of a 90Sr plume in the downstream aquifer, mainly present in the Aeolian layer after 15 years. Laboratories experiments were performed to analyse the transport of 90Sr and 137Cs in the Aeolian sand in both saturated and unsaturated conditions. Batch experiments were performed to study the chemical equilibrium state of the soil/solution system under static conditions. Stirred flow-through reactor experiments were performed to study the kinetics and reversibility of sorption reactions at the surface of solid particles under dynamic conditions. Column experiments in the structured porous media were also performed in saturated and unsaturated flow conditions. Experimental data pointed out a non-linear, instantaneous and reversible sorption process of 90Sr. 137Cs exhibits a non-linear behaviour with a partial irreversible sorption process. A suitable cation-exchange model was used to describe the solute/soil reactions. The former model was coupled with transport models to describe behaviour of 90Sr and 137Cs in both saturated and unsaturated steady flow conditions. Main transport parameters were identified and discussed. An effective simple Kd type approach to describe radionuclides transport properties under unsaturated conditions was evaluated

It is well known that the bioavailability of artifical radionuclides such as 90Sr, 137Cs and 239+240Pu in contaminated soils depends on the source term origin of the contamination. Altough the behaviour of the mentioned radionuclides in the soil is also influenced by the time passed from the contamination event and the characteristics of the contamination receiving soils. The objective of the present work is to analyse the different bioavailability and possible chemical-physical associations of 90Sr, 137Cs, and 239+240Pu in soils located in different Spanish ecosystems (Almeria and Cáceres provinces) by application of a sequential extraction procedure based on the NIST standard sequential extraction protocol. The resulting fractions obtained are: a) water soluble and exchangeable, b) associated to organic matter, and c) residual fraction. They will be studied jointly with the polluting sources (deposit of nuclear fallout-50s and 60s, Palomares accident in 1966 and the cesium release by Acerinox in 1998) in each ecosystem to interpret the observed behaviour of radionuclides.

The basis premise of many radiological assessments is the assumption that the transfer of many radionuclides from soil to herbage and hence animal derived food products is a positive linear relationship for a given set of ecological conditions. However, a number of authors have published results, which they conclude demonstrate non-linear transfer of radiocaesium to plants and animals with transfer being highest when soil concentrations are lowest. Whilst we may expect non-linear transfer of radionuclides under homeostatic control or present in comparatively large chemical quantities, there appears no credible hypothesis to support such an observation for radiocaesium. In this paper we review those articles, which have reported non-linear radiocaesium transfer and also analyse novel data. We argue that saturation of Cs uptake as suggested by some other authors is unlikely. Sampling bias, statistical data distribution and countermeasure application are suggested as potential contributors. However, we have not been able to provide a conclusive reason for such observations. Given the important implications for foodchain modelling further consideration of available data is required to more comprehensively answer this question

The nuclear accident that occurred in Palomares in 1966 caused the release of plutonium weapon grade particles into a Mediterranean ecosystem, and consequently, urban and farming areas were contaminated with this material. Several studies focused on the characterization and behaviour of transuranides have been carried out in the area. In this work, the solubility evolution of plutonium is analysed for a period of more than 30 years, as well as the influence that the incorporation of cow urine into organic fertilizers has on the solubility of the mentioned element. The average value of the plutonium solubility in water determined in five samples was 0.0082% in 1986. However, determinations carried out in samples taken in 1999 and 2000 indicated an increase of the plutonium solubility of two orders of magnitude. In order to check the influence of organic fertilizers on the solubility of plutonium, a solubility test was carried out using cow urine as extracting solution. The results show that the solubility of plutonium can reach a value equal to 14%, which is similar to the one obtained with sodium pyrophosphate acting as extracting solution. Thus, these results are a clear warning of what might happen if organic fertilizers are used in transuranic-contaminated soils.

99Tc and 79Se, two long-lived radionuclides, are supposed to be highly mobile in soils, because of their anionic forms. Their behaviours in the soil are often considered only from a physico-chemical point of view, although the microorganisms can affect either directly or indirectly their speciation. This study demonstrates the role of the microbial compartment in the retention of Se and Tc in soil by comparing experiments with soils constrained to different microbiological status (sterile / raw / amended). Kd coefficients for Se and Tc were determined in batch experiments, whereas transport of Se and Tc was investigated through column leaching experiments. Kd for Se was enhanced for the raw soil without amendment compared to the value obtained for the sterilised soil. The retention of Se was higher again in the amended soil. Besides, a biofilm, which can directly retain Se, was obtained at the entrance of the amended soil column. This effect was less obvious for Tc in batch experiments, but was revealed by leaching experiments where a high quantity of Tc was retained in the amended soil columns. These results give strong evidence that microorganisms are responsible for a greater retention of Se and Tc in soil.

In surface soils, the native physical and chemical properties of the abiotic components control most of the sorption-desorption processes. Moreover, micro-organisms may significantly modify the speciation of trace elements and/or radionuclides and subsequently determine their fate, to a large extent. Micro-organisms, mainly bacteria and fungi, develop many strategies that may affect indirectly or directly the behaviour of trace elements. Due to their activity, changes in the pore-water composition, e.g. pH, redox-potential, may occur in relation with organic acid production or solid phase alteration, reduction or oxidation of metallic oxi-hydroxides, and mineralization of organo-metallic complexes. Micro-organisms may also directly modify the speciation of radionuclides as a result of bio-accumulation in living cells, biosorption on cellular components, direct reduction or oxidation, biomethylation, etc. Each one of these microbial processes may either increase or decrease radionuclide mobility, depending on the element, the soil reactivity and the environmental conditions. The resulting effect of these processes is still poorly known. This literature review intends to present a comprehensive overview of the role of micro-organisms on radionuclide mobility. It aims at classifying these elements, regarding to their potential sensitivity to these microbial processes. It summarizes the theoretical effect of these mechanisms, resulting in a potential increase or decrease of the solid-liquid distribution. The environmental significance of such processes for various biogeochemical radionuclides cycles still remains to be confirmed by experiments. (This study is part of a research program supported by Andra).

This paper presents new data on concentration factors (CFs: concentration kg-1 biota/concentration l-1 seawater) for several marine species-radionuclide pairs, in three regions: coastal waters of Ireland, eastern Irish Sea and coastal waters of Norway. The CFs were estimated using data from long-term monitoring programmes, obtained for radiological protection purposes. The practical constraints of using such data sources are discussed. CFs were obtained for a range of fin fish, crustaceans, molluscs and brown seaweed, for one or more of the following radionuclides: 99Tc, 137Cs, $^{239,240}$Pu and 241Am. In general, there was a relatively high degree of variability in the values obtained, and it was not possible to discern systematic regional or time-dependent differences. However, for two datasets in the eastern Irish Sea (137Cs in winkles and crabs) and a number of datasets (137Cs in various species of fish) in the western Irish Sea there was a statistically significant increase in the CF over the monitoring periods. Significant gender differences were found for 99Tc in lobster. The results are compared with current IAEA recommendations and are discussed in relation to the influence of contemporaneous discharges and the possible impact of remobilised radionuclides on bioavailability.


Cellular growth and intracellular concentrations of selenite in the unicellular green alga Chlamydomonas reinhardtii showed considerable variability between replicates at ambient concentrations of Se that became toxic to the alga. However, growth inhibition was well correlated to the cellular quota of selenite; the correlation between absorbed selenite and toxicity was better than the simple correlation between ambient selenite and toxicity usually used to express metal toxicity, suggesting selenite toxicity is mainly linked to intracellular accumulation. It is usually expected that effects of contaminants on organisms depend on internal concentrations. These results confirm this hypothesis.

The fifth framework EU project BORIS (Bioavailability Of Radionuclides In Soils: role of biological components and resulting improvement of prediction models) had three scientific objectives. The first was to improve understanding of the mechanisms governing the transfer of radionuclides to plants. The second was to improve existing predictive models of radionuclide interaction with soils by incorporating the knowledge acquired from the experimental results. The last and third objective was to extract from the experimental results scientific basis for the development of bioremediation methods of radionuclide contaminated soils and to apprehend the role of additional non-radioactive pollutants on radionuclide bioavailability. This paper is focused on the second objective. The purpose of the BORIS assessment model is to describe the behaviour of radionuclides in the soil-plant system with the aim of making predictions of the time dynamics of the bioavailability of radionuclides in soil and the radionuclides concentrations in plants. To be useful, the assessment model should be simple and use only a few parameters, which are commonly available or possible to measure for different sites. The model shall take into account, as much as possible, the results of the experimental studies and the mechanistic models developed in the BORIS project. The adopted approach was to introduce in the assessment model a quantitative relationship between bioavailability of the radionuclides in soil and the soil properties. To do this an operational definition of bioavailability was proposed. Here, operational means experimentally measurable, directly or indirectly, and that the bioavailability can be translated into a mathematical expression. This paper describes the reasoning behind the chosen definition of bioavailability and how it was used in the assessment model.

The biogeochemical behaviour of americium in subsurface soils plays a dominant role on its potential migration, but is currently poorly known. This research investigates the relevant processes controlling americium biogeochemical speciation in the rhizosphere of an agricultural soil. Lixiviation tests were performed on columns packed with a calcareous soil contaminated with 241Am, under steady-state unsaturated or saturated hydric flow conditions. The columns were percolated with various soil solutions, containing citrate and/or glucose to simulate root exudates. The bio-physico-chemical parameters of the outlet solutions were monitored continuously. The percolation of a solution in equilibrium with the soil or containing low exudate concentrations (10-4 M) released less than 5 mBq/cm3 of americium. Poor remobilisations were also observed when injecting 10-2 M glucose solutions, despite effective glucose microbial degradation, production of secondary ligands, and important chemical changes. On the contrary, percolation of 10-2 M citrate solution released 1000 times more americium, in accordance with previous studies. 10000 times greater releases were observed when glucose was added to citrate at 10-2 M. The remobilisation of americium resulting from both dissolution of calcite and iron oxides, and complexation by citrate, as well as the applicability of simple parameterisation of partition coefficient are discussed.

A set of countermeasures aimed at reducing 137Cs uptake by plant products includes agrochemical measures based on changes in the soil properties after the application of ameliorants. The dynamic models for studying the effect of the application of potassium fertilizers and dolomite powder on 137Cs accumulation in plants are presented. Conceptual approaches to the development of models are based on the identification of mechanisms governing a complex of physico-chemical processes in soil after the use of ameliorants. The developed models were parameterized for soils of the coniferous forest located in the Bryansk region in area suffered from the radioactive fallout after the Chernobyl accident. Effects of ameliorants and time of their application on 137Cs behaviour in the soil-plant system are assessed. The contribution of soil chemical and biological processes to the decrease in the radionuclide uptake by plants is estimated.

The absorption behavior of technetium (Tc) and rhenium (Re) through plant roots was studied using nutrient solution culture. Radish samples, grown in culture solutions for 20-30 days in a greenhouse, were transferred into plastic vessels containing nutrient solutions contaminated with multitracer solutions including 95mTc and 183Re. The plant samples were grown individually for 1-7 days under laboratory conditions. The activities of radionuclides in nutrient solutions and oven-dried plant parts (roots, fleshy roots and leaves) were measured with Ge detecting systems. The concentrations of 95mTc and 183Re in the nutrient solutions after harvesting the plants were almost the same as those in the initial solution, though about 2 mL of the nutrient solution was lost per day per plant pot due to transpiration. Possibly, the radionuclides were taken up with water through the plant roots. The distributions of Tc and Re in the plants showed no differences, thus, soluble Tc and Re absorption mechanisms by plant samples were the same. It is suggested that Re could be used as a geochemical tracer for Tc in soil environments.