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Predictions of radionuclide dose rates to freshwater organisms can be used to evaluate the radiological environmental impacts of releases from uranium mining and milling projects. These predictions help inform decisions on the implementation of mitigation measures. The objective of this study was to identify how dose rate modelling could be improved to reduce uncertainty in predictions to non-human biota. For this purpose, we modelled the activity concentrations of 210Pb, 210Po, 226Ra, 230Th, and 238U downstream of uranium mines and mills in northern Saskatchewan, Canada, together with associated weighted absorbed dose rates for a freshwater food chain using measured activity concentrations in water and sediments. Differences in predictions of radionuclide activity concentrations occurred mainly from the different default partition coefficient and concentration ratio values from one model to another and including all or only some 238U decay daughters in the dose rate assessments. Consequently, we recommend a standardized best-practice approach to calculate weighted absorbed dose rates to freshwater biota whether a facility is at the planning, operating or decommissioned stage. At the initial planning stage, the best-practice approach recommend using conservative site-specific baseline activity concentrations in water, sediments and organisms and predict conservative incremental activity concentrations in these media by selecting concentration ratios based on species similarity and similar water quality conditions to reduce the uncertainty in dose rate calculations. At the operating and decommissioned stages, the best-practice approach recommends relying on measured activity concentrations in water, sediment, fish tissue and whole-body of small organisms to further reduce uncertainty in dose rate estimates. This approach would allow for more realistic but still conservative dose assessments when evaluating impacts from uranium mining projects and making decision on adequate controls of releases.

The Adverse Outcome Pathway (AOP) framework, a systematic tool that can link available mechanistic data with phenotypic outcomes of relevance to regulatory decision-making, is being explored in areas related to radiation risk assessment. To examine the challenges including the use of AOPs to support the radiation protection community, an international horizon-style exercise was initiated through the Organisation for Economic Co-operation and Development Nuclear Energy Agency High-Level Group on Low Dose Research Radiation/Chemical AOP Joint Topical Group. The objective of the HSE was to facilitate the collection of ideas from a range of experts, to short-list a set of priority research questions that could, if answered, improve the description of the radiation dose-response relationship for low dose/dose-rate exposures, as well as reduce uncertainties in estimating the risk of developing adverse health outcomes following such exposures. The HSE was guided by an international steering committee of radiation risk experts. In the first phase, research questions were solicited on areas that can be supported by the AOP framework, or challenges on the use of AOPs in radiation risk assessment. In the second phase, questions received were refined and sorted by the SC using a best-worst scaling method. During a virtual 3-day workshop, the list of questions was further narrowed. In the third phase, an international survey of the broader radiation protection community led to an orderly ranking of the top questions. Of the 271 questions solicited, 254 were accepted and categorized into 9 themes. These were further refined to the top 25 prioritized questions. Among these, the higher ranked questions will be considered as ‘important’ to drive future initiatives in the low dose radiation protection community. These included questions on the ability of AOPs to delineate responses across different levels of biological organization, and how AOPs could be applied to address research questions on radiation quality, doses or dose-rates, exposure time patterns and deliveries, and uncertainties in low dose/dose-rate effects. A better understanding of these concepts is required to support the use of the AOP framework in radiation risk assessment. Through dissemination of these results and considerations on next steps, the JTG will address select priority questions to advance the development and use of AOPs in the radiation protection community. The major themes observed will be discussed in the context of their relevance to areas of research that support the system of radiation protection.

Ectomycorrhizal (EM) fungi form symbioses with dominant tree families in boreal, temperate and tropical ecosystems and are important drivers of ecosystem function. EM fungal hyphae extend over a large area making them susceptible to enhanced radiation levels from naturally occurring or anthropogenically originating radioisotopes in the rhizosphere. In this study, the in-vitro effects of ionizing radiation on the growth and biomass of EM fungi Suillus luteus, S. bovinus and Rhizopogon luteolus were investigated. EM fungal cultures were exposed to gamma radiation from a 137Cs source for 137 h in darkness at 21 °C at dose rates of 404, 108.5 and 54.9 mGy h−1 resulting in total absorbed doses of 55.21, 14.82 and 7.50 Gy respectively. Cultures grown in the dark at 21 °C but not exposed to the 137Cs source served as the control. Our results show that EM fungi vary in their sensitivity to ionizing radiation. EM fungi used in this study produced melanin and reactive oxygen species scavenging enzymes such as catalase and superoxide dismutase as a response to ionizing radiation.

International audience; The ALLIANCE6 Strategic Research Agenda (SRA) initiated by the STAR7 Network of Excellence and integrated in the research strategy implemented by the COMET consortium, defines a long-term vision of the needs for, and implementation of, research in radioecology. This reference document, reflecting views from many stakeholders groups and researchers, serves as an input to those responsible for defining EU research call topics through the ALLIANCE SRA statement delivered each year to the EJP-CONCERT8 (2015-2020). This statement highlights a focused number of priorities for funding. Research in radioecology and related sciences is justified by various drivers, such as policy changes, scientific advances and knowledge gaps, radiological risk perception by the public, and a growing awareness of interconnections between human and ecosystem health. The SRA is being complemented by topical roadmaps that have been initiated by the COMET9 EC-funded project, with the help and endorsement of the ALLIANCE. The strategy underlying roadmap development is driven by the need for improved mechanistic understanding across radioecology. By meeting this need, we can provide fit-for-purpose human and environmental impact/risk assessments in support of the protection of man and the environment in interaction with society and for the three exposure situations defined by the ICRP (i.e., planned, existing and emergency). Within the framework of the EJP-CONCERT the development of a joint roadmap is under discussion among all the European research platforms and will highlight the major research needs for the whole radiation protection field and how these are likely to be addressed by 2030. © 2018 IOP Publishing Ltd.

Summary Flooded (paddy) rice (Oryza sativa) can take up ions from the irrigation water by foliar uptake via the exposed stem base. We hypothesised that the stem base uptake of radiocaesium (RCs) is a pathway for rice grown in RCs-contaminated environments. We developed a bi-compartmental device which discriminates the stem base from root RCs uptake from solutions, thereby using RCs isotopes (137Cs and 134Cs) with

The mutants Atnoa1 and Atnia1nia2noa1-2 having a defective chloroplast developmental process, showed enhanced chlorophyll levels when they were grown on Murashige and Skoog (MS) medium and on exposure with uranium (U) on Hoagland medium. Thus we hypothesized that these mutants probably produced NO in MS medium and on exposure with U. Wild-type Col-0, Atnoa1, Atnia1nia2noa1-2 plants were cultured on modified Hoagland and 1/10 MS media and NO generation in the roots of these mutants was monitored using NO selective fluorescent dyes, DAF-2DA and Fl2E. Both Atnoa1 and Atnia1nia2noa1-2 triple mutants produced NO as observed by increases in DAF-2T and Fl2E fluorescence when these mutants were grown on MS medium but not on Hoagland medium. In presence of NO scavenger, methylene blue (MB, 200 μM), DAF-2T and Fl2E fluorescence was completely abolished. On the other hand treatment of the plants with 25 μM U triggered NO generation. U-treated Atnoa1 and Atnia1nia2noa1-2 plants upregulated genes (POR B, POR D, CHL D) involved in the chlorophyll biosynthesis. From these results it was concluded that Atnoa1 and Atnia1nia2noa1-2 are conditional NO producers and it appears that NO generation in plants substantially depends on growth medium and NIA1, NIA2 or NOA1 does not appear to be really involved in NO generation in MS medium or after U exposure.

The options adopted for recovery of agricultural land after the Chernobyl and Fukushima accidents are compared by examining their technical and socio-economic aspects. The analysis highlights commonalities such as the implementation of tillage and other types of countermeasures and differences in approach, such as preferences for topsoil removal in Fukushima and the application of K fertilizers in Chernobyl. This analysis shows that the recovery approach needs to be context-specific to best suit the physical, social, and political environment. The complex nature of the decision problem calls for a formal process for engaging stakeholders and the development of adequate decision support tools. Integr Environ Assess Manag 2016;12:662-666. © 2016 SETAC.

Food chain contamination with radiocaesium (RCs) in the aftermath of the Fukushima accident calls for an analysis of the specific factors that control the RCs transfer. Here, soil-to-plant transfer factors (TF) of RCs for grass were predicted from the potassium concentration in soil solution (mK) and the Radiocaesium Interception Potential (RIP) of the soil using existing mechanistic models. The mK and RIP were (a) either measured for 37 topsoils collected from the Fukushima accident affected area or (b) predicted from the soil clay content and the soil exchangeable potassium content using the models that had been calibrated for European soils. An average ammonium concentration was used throughout in the prediction. The measured RIP ranged 14-fold and measured mK varied 37-fold among the soils. The measured RIP was lower than the RIP predicted from the soil clay content likely due to the lower content of weathered micas in the clay fraction of Japanese soils. Also the measured mK was lower than that predicted. As a result, the predicted TFs relying on the measured RIP and mK were, on average, about 22-fold larger than the TFs predicted using the European calibrated models. The geometric mean of the measured TFs for grass in the affected area (N = 82) was in the middle of both. The TFs were poorly related to soil classification classes, likely because soil fertility (mK) was obscuring the effects of the soil classification related to the soil mineralogy (RIP). This study suggests that, on average, Japanese soils are more vulnerable than European soils at equal soil clay and exchangeable K content. The affected regions will be targeted for refined model validation.

Uranium (U) is a nonessential and toxic heavy metal and radioactive element. Nitric oxide (NO) and hydrogen peroxide (H 2 O 2 ) are intimately involved in the growth, development and metabolic function of plant cells. In addition to possible toxic activities, a role for these signalling molecules in the regulation of plant responses to toxic metals has been proposed. Here, we investigated the synthesis of NO and H 2 O 2 in Arabidopsis thaliana seedlings exposed to 25 μM U. We demonstrated that U induces NO and H 2 O 2 production in the roots and leaves. Addition of the NO releasing compound, sodium nitroprusside (SNP) as well as the NO synthase inhibitor (L-NAME) to the plants, resulted in a decrease of the U-induced NO production and both alleviated U toxicity as indicated by plant growth (leaf area and biomass). Treatment with L-NAME further resulted in the disappearance of the U-induced H 2 O 2 in the shoots of the plants. It appears that generation of NO and H 2 O 2 is intimately linked in the toxicity response of U-exposed A. thaliana plants.

The biological effects and interactions of different radiation types in plants are still far from understood. Among different radiation types, external gamma radiation treatments have been mostly studied to assess the biological impact of radiation toxicity in organisms. Upon exposure of plants to gamma radiation, ionisation events can cause, either directly or indirectly, severe biological damage to DNA and other biomolecules. However, the biological responses and oxidative stress related mechanisms under chronic radiation conditions are poorly understood in plant systems. In the following study, it was questioned if the Lemna minor growth inhibition test is a suitable approach to also assess the radiotoxicity of this freshwater plant. Therefore, L. minor plants were continuously exposed for seven days to 12 different dose rate levels covering almost six orders of magnitude starting from 80 μGy h(-1) up to 1.5 Gy h(-1). Subsequently, growth, antioxidative defence system and genomic responses of L. minor plants were evaluated. Although L. minor plants could survive the exposure treatment at environmental relevant exposure conditions, higher dose rate levels induced dose dependent growth inhibitions starting from approximately 27 mGy h(-1). A ten-percentage growth inhibition of frond area Effective Dose Rate (EDR10) was estimated at 95 ± 7 mGy h(-1), followed by 153 ± 13 mGy h(-1) and 169 ± 12 mGy h(-1) on fresh weight and frond number, respectively. Up to a dose rate of approximately 5 mGy h(-1), antioxidative enzymes and metabolites remained unaffected in plants. A significant change in catalase enzyme activity was found at 27 mGy h(-1) which was accompanied with significant increases of other antioxidative enzyme activities and shifts in ascorbate and glutathione content at higher dose rate levels, indicating an increase in oxidative stress in plants. Recent plant research hypothesized that environmental genotoxic stress conditions can induce endoreduplication events. Here an increase in ploidy level was observed at the highest tested dose rate. In conclusion, the results revealed that in plants several mechanisms and pathways interplay to cope with radiation induced stress.

© 2018, Springer International Publishing AG, part of Springer Nature. Aims: This study was established to better understand the mechanisms of the variable radiocaesium bioavailability observed in flooded rice. Methods: Paddy topsoils (n = 9) with contrasting soil properties were collected from the Fukushima-accident affected area, spiked with 134Cs and cropped in the greenhouse with rice under flooded conditions. Soil solution was collected. As a reference to earlier work, we cropped the same paddy soils and additional grassland soils (n = 22 in total) with ryegrass under unsaturated conditions. Results: Rice shoot 134Cs concentrations varied 110-fold among soils and were unrelated to soil solution 134Cs concentrations. However, the rice shoot 134Cs concentrations clearly increased with the soil solution 134Cs:K concentration ratio (R2 = 0.79; P < 0.001). The same trend was true for ryegrass shoot 134Cs concentrations, which were, on average, 4.1-fold larger than those for flooded rice at an equal soil solution 134Cs:K ratio. Conclusions: Soil solution radiocaesium and K concentrations explain the radiocaesium bioavailability to flooded rice, confirming established knowledge for ryegrass. Transport modelling suggests that the overall smaller 134Cs bioavailability to flooded rice than to ryegrass in unsaturated soils is related to the smaller K uptake rate of rice, alleviating K depletion in its rhizosphere with locally higher K+, blocking the root uptake of radiocaesium. ispartof: PLANT AND SOIL vol:428 issue:1-2 pages:415-426 status: published

International audience; Risks posed by the presence of radionuclides in the environment require an efficient, balanced, and adaptable assessment for protecting exposed humans and wildlife, and managing the associated radiological risk. Exposure of humans and wildlife originate from the same sources releasing radionuclides to the environment. Environmental concentrations of radionuclides serve as inputs to estimate the dose to man, fauna, and flora, with transfer processes being, in essence, similar, which calls for a common use of transport models. Dose estimates are compared with the radiological protection criteria for humans and wildlife, such as those developed by the International Commission on Radiological Protection. This indicates a similarity in the approaches for impact assessment in humans and wildlife, although some elements are different (e.g. the protection endpoint for humans is stochastic effects on individuals, whereas for wildlife, it is deterministic effects on species and ecosystems). Human and environmental assessments are consistent and complementary in terms of how they are conducted and in terms of the underlying databases (where appropriate). Not having an integrated approach may cause difficulties for operators and regulators, for communication to stakeholders, and may even hamper decision making. For optimised risk assessment and management, the impact from non-radiation contaminants and stressors should also be considered. Both in terms of the underlying philosophy and the application via appropriate tools, the European Radioecology Alliance (ALLIANCE) upholds that integration of human and ecological impact and risk assessment is recommended from several perspectives (e.g. chemical/radiological risks). © 2018, The International Society for Prosthetics and Orthotics.

International audience; This position paper gives an overview of how the COMET project (COordination and iMplementation of a pan-European instrumenT for radioecology, a combined Collaborative Project and Coordination and Support Action under the EC/Euratom 7th Framework Programme) contributed to the integration and sustainability of radioecology in Europe via its support to and interaction with the European Radioecology ALLIANCE. COMET built upon the foundations laid by the FP7 project STAR (Strategic Network for Integrating Radioecology) Network of Excellence in radioecology. In close association with the ALLIANCE, and based on the Strategic Research Agenda (SRA), COMET developed innovative mechanisms for joint programming and implementation of radioecological research. To facilitate and foster future integration under a common federating structure, research activities developed within COMET were targeted at radioecological research needs identified in the SRA. Furthermore, COMET maintained and developed strong mechanisms for knowledge exchange, dissemination and training to enhance and maintain European capacity, competence and skills in radioecology. In the short term the work to promote radioecology will continue under the H2020 project EJP-CONCERT (European Joint Programme for the Integration of Radiation Protection Research). The EJP-CONCERT project (2015-2020) aims to develop a sustainable structure for promoting and administering joint programming and open research calls in the field of radiation protection research for Europe. In the longer term, radioecological research will be facilitated by the ALLIANCE. External funding is, however, required in order to be able to answer emerging research needs. © 2018 IOP Publishing Ltd.

The potential of photosynthetic organisms to remediate radioactively contaminated water was evaluated for scenarios related to nuclear installations and included the following radionuclides: 137Cs, 134Cs, 136Cs, 90Sr, 131I, 239Pu, 241Am, 132Te/132I, 58Co, 60Co, 51Cr, 110mAg, 54Mn, 124Sb, 59Fe, 65Zn, 95Zr, and 95Nb. An extensive literature review was undertaken leading to the creation of a database including more than 20,000 entries from over 100 references in which terrestrial and aquatic plants, macro- and microalgae, cyanobacteria and biosorbents derived from these organisms were used to clean water from these specific radionuclides or their stable isotopes. In a first phase, the remediation potential of the organisms and biosorbents was evaluated for the individual elements based on parameters such as plant uptake, removal percentage, and bioconcentration factor, and for two radionuclide mixtures based on the ability of the organisms/biosorbents to work under mixture conditions. As the experimental and environmental conditions will influence the performance of the organisms and biosorbents, a literature-based evaluation of the most influencing or restricting parameters was made and water pH, competing ions, and the chemical modification of biosorbents showed to be of major importance. Finally, the most promising organisms and biosorbents were identified using a specifically developed selection procedure taking into account their performance and robustness. Ranking was done based on clear criteria with a distinct weight and scoring scheme. As such, 20 organisms/biosorbents were identified that showed high potential to clean waters contaminated with (mixtures of) radionuclides related to nuclear installations and which can be used for further experimental investigations.

International audience; Speciation modelling of uranium (as uranyl) and thorium, in four freshwaters impacted by mining activities, was used to evaluate (i) the influence of the co-contaminants present on the predicted speciation, and (ii) the influence of using nine different model/database combinations on the predictions. Generally, co-contaminants were found to have no significant effects on speciation, with the exception of Fe(III) in one system, where formation of hydrous ferric oxide and adsorption of uranyl to its surface impacted the predicted speciation. Model and database choice on the other hand clearly influenced speciation prediction. Complexes with dissolved organic matter, which could be simulated by three of the nine model/database combinations, were predicted to be important in a slightly acidic, soft water. Model prediction of uranyl and thorium speciation needs to take account of database comprehensiveness and cohesiveness, including the capability of the model and database to simulate interactions with dissolved organic matter. Measurement of speciation in natural waters is needed to provide data that may be used to assess and improve model capabilities and to better constrain the type of predictive modelling work presented here. © 2015 Elsevier Ltd.

Long-lived radionuclides such as (90)Sr and (137)Cs can be naturally or accidentally deposited in the upper soil layers where they emit β/γ radiation. Previous studies have shown that arbuscular mycorrhizal fungi (AMF) can accumulate and transfer radionuclides from soil to plant, but there have been no studies on the direct impact of ionizing radiation on AMF. In this study, root organ cultures of the AMF Rhizophagus irregularis MUCL 41833 were exposed to 15.37, 30.35, and 113.03 Gy gamma radiation from a (137)Cs source. Exposed spores were subsequently inoculated to Plantago lanceolata seedlings in pots, and root colonization and P uptake evaluated. P. lanceolata seedlings inoculated with non-irradiated AMF spores or with spores irradiated with up to 30.35 Gy gamma radiation had similar levels of root colonization. Spores irradiated with 113.03 Gy gamma radiation failed to colonize P. lanceolata roots. P content of plants inoculated with non-irradiated spores or of plants inoculated with spores irradiated with up to 30.35 Gy gamma radiation was higher than in non-mycorrhizal plants or plants inoculated with spores irradiated with 113.03 Gy gamma radiation. These results demonstrate that spores of R. irregularis MUCL 41833 are tolerant to chronic ionizing radiation at high doses.

The chemical speciation of uranium (U), and hence its toxicity, is strongly dependent on pH. However, oxidative stress responses after U exposure have mainly been investigated in Arabidopsis thaliana plants at pH 5.5, the ideal pH for growing plants in a hydroponic setup. As the pH of pore water can vary strongly, the aim of this study is to investigate oxidative stress responses induced in roots of A. thaliana plants exposed to different U concentrations at pH 4.5 and hence at a high free uraynl (UO 2 2+ ) concentration. In addition to analyzing growth reduction, effects were analysed at enzyme, metabolite and genetic level. Results indicate that U is highly toxic at low pH resulting in a significant decrease in fresh weight (EC50 value for root growth reduction: 28.14 ± 1.59 μM U). In addition, no intact RNA could be extracted from the roots exposed to 75 and 100 μM U and the ascorbate concentrations could not be determined in roots exposed to 50, 75 or 100 μM U indicating that the roots are seriously damaged. Concerning the antioxidative defence system, the involvement of miRNA398b/c in the regulation of the superoxide dismutase (SOD) response was observed after U exposure. As such, a significant increase in MIR398b / c expression was observed, accompanied by a decreased copper/zinc SOD ( CSD1 / 2 ) expression. The latter was compensated by an increased expression of iron SOD ( FSD1 ) to maintain the SOD capacity in the plastids. While the involvement of miRNA398b/c was already reported before under copper or cadmium stress, this is the first time that it is reported for U.

The high variability of the soil-to-plant transfer factor of radiocaesium (RCs) compels a detailed analysis of the radiocaesium interception potential (RIP) of soil, which is one of the specific factors ruling the RCs transfer. The range of the RIP values for agricultural soils in the Fukushima accident affected area has not yet been fully surveyed. Here, the RIP and other major soil chemical properties were characterised for 51 representative topsoils collected in the vicinity of the Fukushima contaminated area. The RIP ranged a factor of 50 among the soils and RIP values were lower for Andosols compared to other soils, suggesting a role of soil mineralogy. Correlation analysis revealed that the RIP was most strongly and negatively correlated to soil organic matter content and oxalate extractable aluminium. The RIP correlated weakly but positively to soil clay content. The slope of the correlation between RIP and clay content showed that the RIP per unit clay was only 4.8 mmol g − 1 clay, about threefold lower than that for clays of European soils, suggesting more amorphous minerals and less micaceous minerals in the clay fraction of Japanese soils. The negative correlation between RIP and soil organic matter may indicate that organic matter can mask highly selective sorption sites to RCs. Multiple regression analysis with soil organic matter and cation exchange capacity explained the soil RIP ( R 2 = 0.64), allowing us to map soil RIP based on existing soil map information.

In the following study, dose dependent effects on growth and oxidative stress induced by -radiation were examined to gain better insights in the mode of action of -radiation induced stress in plant species. Radiostrontium (Sr-90) was used to test for -radiation induced responses in the freshwater macrophyte Lemna minor. The accumulation pattern of Sr-90 was examined for L. minor root and fronds separately over a seven-day time period and was subsequently used in a dynamic dosimetric model to calculate -radiation dose rates. Exposing L. minor plants for seven days to a Sr-90 activity concentration of 25 up to 25,000 kBqL(-1) resulted in a dose rate between 0.084 +/- 0.004 and 97 +/- 8 mGyh(-1). After seven days of exposure, root fresh weight showed a dose dependent decrease starting from a dose rate of 9.4 +/- 0.5 mGyh(-1). Based on these data, an EDR10 value of 1.5 +/- 0.4 mGyh(-1) was estimated for root fresh weight and 52 +/- 17 mGyh(-1) for frond fresh weight. Different antioxidative enzymes and metabolites were further examined to analyze if -radiation induces oxidative stress in L. minor. The authors thank the Research foundation-Flanders (FWO) (G.A040.11N) and the European Commission Contract Fission-2010-3.5.1-269672 Strategy for Allied Radioecology (www.star-radioecology.org) for financial support of this work. Belgian nuclear research institute (SCK.CEN) is further thanked for funding the PhD of A. Van Hoeck.

The activities of the phosphate industry may lead to enhanced levels of naturally occurring radioactivity in terrestrial and aquatic ecosystems. We performed a preliminary environmental risk assessment (ERA) of environmental contamination resulting from the activities of 5 phosphate fertiliser plants (located in Belgium, Spain, Syria, Egypt, Brazil), a phosphate-mine and a phosphate-export platform in a harbour (both located in Syria). These sites were selected because of the availability of information on concentrations of naturally occurring radionuclides in the surrounding environments. Assessments were generally performed considering highest environmental concentrations reported in the studies. The ERICA Tool, operating in a Tier 2 assessment mode, was used to predict radiation dose rates and associated risk to the selected reference organisms using the ERICA default parameter setting. Reference organisms were those assigned as default by the ERICA Tool. Potential impact is expressed as a best estimate risk quotient (RQ) based on a radiation screening value of 10 μGy h(-1). If RQ ≤ 1, the environment is considered unlikely to be at risk and further radiological assessment is not deemed necessary. Except for one of the cases assessed, the best estimate RQ exceeded 1 for at least one of the reference organisms. Internal exposure covered for 90-100 % of the total dose. (226)Ra or (210)Po were generally the highest contributors to the dose. The aquatic ecosystems in the vicinity of the phosphate fertiliser plants in Tessenderlo (Belgium), Huelva (Spain), Goiás (Brazil) and the terrestrial environment around the phosphate mine in Palmyra (Syria) are the ecosystems predicted to be potentially most at risk.

The biosphere is constantly exposed to ionising radiation, due to cosmic radiation and the presence of natural and anthropogenic radionuclides in the environment. The biological effects of the resulting radiation exposure are currently poorly understood in plants, due to a large influence of parameters such as species, cultivar, experimental setup and plant age on the response. In this study, 7-, 10- and 14-day-old Arabidopsis thaliana seedlings were exposed to 96 h and 168 h of 100 mGy h−1 chronic γ-radiation in a hydroponic setup. The response of growth, photosynthesis and the transcription of genes involved in DNA repair, cell cycle and signalling were measured. The results show that there is a difference in growth response between plants of different ages and decreasing radiosensitivity with increasing seedling age. This is linked to differences in regulation of DNA repair and cell cycle control at the transcriptional level.

To study the impact of environmental uranium (U) contamination, effects should be analysed at different environmentally relevant pH levels as the speciation of U, and hence its toxicity, is strongly dependent on the pH. As photosynthesis is a major energy producing process in plants intimately connected to plant growth and known to be susceptible to metal stress, the effects of different U concentrations on photosynthesis in 18-day-old Arabidopsis thaliana (Columbia ecotype) are investigated at two contrasting pH levels, pH 4.5 and pH 7.5. At pH 4.5, U is highly taken up by the roots but is poorly translocated to the shoots, while at pH 7.5, less U is taken up but the translocation is higher. The lower U concentrations in the shoots at pH 4.5 are accompanied by a more reduced leaf growth as compared to pH 7.5. In addition, U does not influence the photosynthetic machinery at pH 7.5, while an optimization of the photosynthesis takes place after U exposure at pH 4.5. As such, more of the absorbed quanta are effectively used for photosynthesis accompanied by a decreased non-photochemical quenching and an increased electron transport rate. Since the enhanced photosynthesis at pH 4.5 is accompanied by a decreased growth, we suggest that the energy produced during photosynthesis is used for defence reactions against U-induced oxidative stress rather than for growth. As such, a high discrepancy was observed between the two pH levels, with an optimized photosynthetic apparatus at pH 4.5 and almost no effects at pH 7.5.

As photosynthesis is already known to be affected under various metal stresses, the aim of this study is to investigate uranium effects on photosynthetic parameters. Therefore, 18-day-old Arabidopsis thaliana seedlings were exposed to 50 μM uranium during 1–96 h. Uranium uptake, effects on growth parameters of roots and leaves and further responses on photosynthesis, pigment concentrations and lipid peroxidation in leaves were investigated. Uranium was highly taken up by the roots (50,352 ± 3383 μg g−1 DW at 96 h) causing complete growth arrest of the plants. Although uranium concentrations in the leaves remained low (15.0 ± 4.0 μg g−1 DW at 96 h), a remarkable photosynthetic response mechanism was observed. By chlorophyll fluorescence measurements it was observed that the potential photosynthetic efficiency (Fv/Fm) remained maximal while the effective efficiency of photosystem II (φPSII), which is a measure for the proportion of light absorbed by PSII used in photochemistry, even increased due to a decrease in non-photochemical quenching (NPQ), which indicates the conversion of excess energy into heat, but no alterations in non-regulated energy dissipation (NO). When measuring rapid light curves (RLC), giving the increase of the electron transport rate as function of irradiance, no differences were observed for the maximal electron transport rate (ETRmax) but an increase in α, representing the photosynthetic rate in the light-limited region of the RLC, was observed under uranium stress. We concluded that plant leaves start increasing their photosynthetic efficiency and decreasing their non-photochemical quenching under uranium stress.

An environmental risk assessment (ERA) was performed to evaluate the impact on non-human biota from liquid and atmospheric radioactive discharges by the Belgian Nuclear Power Plants (NPP) of Doel and Tihange. For both sites, characterisation of the source term and wildlife population around the NPPs was provided, whereupon the selection of reference organisms and the general approach taken for the environmental risk assessment was established. A deterministic risk assessment for aquatic and terrestrial ecosystems was performed using the ERICA assessment tool and applying the ERICA screening value of 10 μGy h −1 . The study was performed for the radioactive discharge limits and for the actual releases (maxima and averages over the period 1999–2008 or 2000–2009). It is concluded that the current discharge limits for the Belgian NPPs considered do not result in significant risks to the aquatic and terrestrial environment and that the actual discharges, which are a fraction of the release limits, are unlikely to harm the environment.

The application of nuclear energy and the use of radionuclides for industrial, medical and research purposes have caused significant contamination of certain sites and their environment, which could result in health problems for several centuries if nothing is undertaken to remedy these situations. Except for the immediate environment of the facility, where decontamination activities may be feasible and affordable, the contamination often extents over a vast area and decontamination would be costly and could result in vast amounts of waste. Therefore, more realistic yet efficient remediation options should be searched for of which phytomanagement is among the potential options. A number of phytomanagement approaches will be discussed.

Uranium (U) causes oxidative stress in Arabidopsis thaliana plants grown at pH 5.5. However, U speciation and its toxicity strongly depend on environmental parameters, for example pH. It is unknown how different U species determine U uptake and translocation within plants and how they might affect the oxidative defense mechanisms of these plants. The present study analyzed U uptake and oxidative stress-related responses in A. thaliana (Columbia ecotype) under contrasted U chemical speciation conditions. The 18-d-old seedlings were exposed for 3 d to 25 µM U in a nutrient solution of which the pH was adjusted to 4.5, 5.5, 6.5, or 7.5. Results indicate that there is a different rate of U uptake and translocation at the different pHs, with high uptake and low translocation at low pH and lower uptake but higher translocation at high pH. After U exposure, an increased glutathione reductase activity and total glutathione concentration were observed in U-exposed roots, pointing toward an important role for glutathione in the root defense system against U either by chelation or by antioxidative defense mechanisms. In leaves, antioxidative defense mechanisms were activated on U exposure, indicated by increased superoxide dismutase and catalase activity. As it seems that U toxicity is influenced by pH, it is important to consider site-specific characteristics when making U risk assessments. Environ Toxicol Chem 2013;32:2125–2133. © 2013 SETAC

Ecotoxicological research provides knowledge on ionising radiation-induced responses in different plant species. However, the sparse data currently available are mainly extracted from acute exposure treatments. To provide a better understanding of environmental exposure scenarios, the response to stress in plants must be followed in more natural relevant chronic conditions. We previously showed morphological and biochemical responses in Lemna minor plants continuously exposed for 7 days in a dose-rate dependent manner. In this study responses on molecular (gene expression) and physiological (photosynthetic) level are evaluated in Leminor plants exposed to ionising radiation. To enable this, we examined the gene expression profiles of irradiated Leminor plants by using an RNA-seq approach. The gene expression data reveal indications that Leminor plants exposed at lower dose rates, can tolerate the exposure by triggering acclimation responses. In contrast, at the highest dose rate tested, a high number of genes related to antioxidative defense systems, DNA repair and cell cycle were differentially expressed suggesting that only high dose rates of ionising radiation drive Leminor plants into survival strategies. Notably, the photosynthetic process seems to be unaffected in Leminor plants among the tested dose rates. This study, supported by our earlier work, clearly indicates that plants shift from acclimation responses towards survival responses at increasing dose rates of ionising radiation. (C) 2017 Elsevier B.V. All rights reserved.

When terrestrial environments get contaminated with long-lived gamma emitting radionuclides, plants that grow in these contaminated areas are exposed to gamma radiation during consecutive generations. Therefore it is important to evaluate the gamma induced stress response in plants in and between generations. The objective of this research is to reveal differences at the level of the antioxidative stress response between generations with a different radiation history. An experiment was conducted in which 7-days old Arabidopsis thaliana plants were exposed for 14 days to four different gamma dose rates: 22 mGy/h, 38 mGy/h, 86 mGy/h and 457 mGy/h. Two different plant groups were used: plants that were not exposed to gamma radiation before (P0) and plants that received the aforementioned gamma treatment during their previous generation (S1). Growth, the concentration of the antioxidants ascorbate and glutathione, a number of antioxidative enzyme activities and their gene transcript levels were analysed. A dose-rate dependent induction was seen for catalase (CAT) and guaiacol peroxidase (GPX) in the roots and for syringaldazine peroxidase (SPX) in the shoots. Differences between the two generations were observed for CAT and GPX in the roots, where a significantly higher activity of these reactive oxygen species (ROS) detoxifying enzymes was observed in the S1 generation. For SPX in the shoots, a dose dependent upregulation was observed in the PO generation. However, high SPX activities were present for all doses in the S1 generation. These differences in enzyme activity between generations for SPX and GPX and the involvement of these enzymes in cell wall biosynthesis, suggest an important role for cell wall strengthening in the response to gamma irradiation. (C) 2016 Elsevier Ltd. All rights reserved. This project was supported by the European project COMET (7th PCRD EURATOM Contract Number: Fission-2012-3.4.1-604794) (www.comet-radioecology.org) and the Belgian nuclear research centre (SCK CEN).

The potential radiological impact of releases from a low-level radioactive waste (Category A waste) repository in Dessel, Belgium on the local fauna and flora was assessed under a reference scenario for gradual leaching. The potential impact situations for terrestrial and aquatic fauna and flora considered in this study were soil contamination due to irrigation with contaminated groundwater from a well at 70 m from the repository, contamination of the local wetlands receiving the highest radionuclide flux after migration through the aquifer and contamination of the local river receiving the highest radionuclide flux after migration through the aquifer. In addition, an exploratory study was carried out for biota residing in the groundwater. All impact assessments were performed using the Environmental Risk from Ionising Contaminants: Assessment and Management (ERICA) tool. For all scenarios considered, absorbed dose rates to biota were found to be well below the ERICA 10 μGy h−1 screening value. The highest dose rates were observed for the scenario where soil was irrigated with groundwater from the vicinity of the repository. For biota residing in the groundwater well, a few dose rates were slightly above the screening level but significantly below the dose rates at which the smallest effects are observed for those relevant species or groups of species. Given the conservative nature of the assessment, it can be concluded that manmade radionuclides deposited into the environment by the near surface disposal of category A waste at Dessel do not have a significant radiological impact to wildlife.

International audience; During the past decades, many specialised networks have formed to meet specific radioecological objectives, whether regional or sectorial (purpose-oriented). Regional networks deal with an array of radioecological issues related to their territories. Examples include the South Pacific network of radioecologists, and the European network of excellence in radioecology. The latter is now part of the European platform for radiation protection. Sectorial networks are more problem-oriented, often with wider international representativeness, but restricted to one specific issue, (e.g. radioactive waste, low-level atmospheric contamination, modelling). All such networks, while often working in relative isolation, contribute to a flow of scientific information which, through United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR's) efforts of synthesis, feeds into the radiation protection frameworks of protecting humans and the environment. The IUR has therefore prompted a co-construction process aimed at improving worldwide harmonisation of radioecology networks. An initiative based on an initial set of 15 networks, now called the IUR FORUM, was launched in June 2014. The IUR Forum agreed to build a framework for improved coordination of scientific knowledge, integration and consensus development relative to environmental radioactivity. Three objectives have been collectively assigned to the IUR FORUM: (1) coordination, (2) global integration and construction of consensus and (3) maintenance of expertise. One particular achievement of the FORUM was an improved description and common understanding of the respective roles and functions of the various networks within the overall scene of radioecology R&D. It clarifies how the various networks assembled within the IUR FORUM interface with UNSCEAR and other international regulatory bodies (IAEA, ICRP), and how consensus on the assessment of risk is constructed. All these agencies interact with regional networks covering different geographical areas, and with other networks which address specific topics within radiation protection. After holding its first Consensus Symposium in 2015, examining the possible ecological impact of radiation from environmental contamination, the IUR FORUM continues its work towards improved radiation protection of humans and the environment. We welcome new members. © The Author 2016.

We performed an Environmental Risk Assessment (ERA) to evaluate the impact on non-human biota from liquid radioactive effluents discharged by the Belgian Nuclear Power Plants (NPPs) of Doel and Tihange. A deterministic risk assessment for aquatic and terrestrial ecosystems was performed using the ERICA tool and applying the ERICA screening value of 10 µGy.h -1 . The ERA was performed for the radioactive discharge limits and for the actual releases (maxima and averages over the last 10 years, 1999-2008). All ERICA reference organisms were considered and depending on the assessment situation, additional reference organisms were included in the analysis. It can be concluded that the current discharge limits for the Belgian NPPs do not result in significant risks to the aquatic and terrestrial environment and that the actual discharges, which are a fraction of the liquid discharge limits, are unlikely to harm the environment.

This study aimed to investigate effects on growth and development and alterations in the nutrient profiles for Arabidopsis thaliana seedlings following uranium exposure. Seventeen-day-old Arabidopsis thaliana seedlings, grown in hydroponics, were exposed to 0, 0.1, 1, 10 and 100 μM uranium for one, three and seven days. Fresh weight of leaves and roots decreased after exposure to 100 μM uranium for one and three days and after exposure to 1, 10 and 100 μM uranium for seven days. Anthocyanous-colored leaves and stunted yellow roots were observed after exposure to 100 μM uranium. The uranium content of the roots highly increased but the root-to-shoot transfer of uranium was limited. Uranium exposure resulted in disturbed macro- and micronutrient profiles, especially following exposure to 100 μM. This study indicates that elevated uranium concentrations can cause important morphological and physiological effects and disturb the nutrient profiles in Arabidopsis thaliana seedlings.

The cellular redox balance seems an important modulator under heavy metal stress. While for other heavy metals these processes are well studied, oxidative stress related responses are also known to be triggered under uranium stress but information remains limited. This study aimed to further unravel the mechanisms by which plants respond to uranium stress. Seventeen-day-old Arabidopsis thaliana seedlings, grown on a modified Hoagland solution under controlled conditions, were exposed to 0, 0.1, 1, 10 and 100 μM uranium for 1, 3 and 7 days. While in Part I of this study oxidative stress related responses in the roots were discussed, this second Part II discusses oxidative stress related responses in the leaves and general conclusions drawn from the results of the roots and the leaves will be presented. As several responses were already visible following 1 day exposure, when uranium concentrations in the leaves were negligible, a root-to-shoot signaling system was suggested in which plastids could be important sensing sites. While lipid peroxidation, based on the amount of thiobarbituric acid reactive compounds, was observed after exposure to 100 μM uranium, affecting membrane structure and function, a transient concentration dependent response pattern was visible for lipoxygenase initiated lipid peroxidation. This transient character of uranium stress responses in leaves was emphasized by results of lipoxygenase (LOX2) and antioxidative enzyme transcript levels, enzyme capacities and glutathione concentrations both in time as with concentration. The ascorbate redox balance seemed an important modulator of uranium stress responses in the leaves as in addition to the previous transient responses, the total ascorbate concentration and ascorbate/dehydroascorbate redox balance increased in a concentration and time dependent manner. This could represent either a slow transient response or a stable increase with regard to plant acclimation to uranium stress.

When aiming to evaluate the environmental impact of uranium contamination, it is important to unravel the mechanisms by which plants respond to uranium stress. As oxidative stress seems an important modulator under other heavy metal stress, this study aimed to investigate oxidative stress related responses in Arabidopsis thaliana exposed to uranium concentrations ranging from 0.1 to 100 μM for 1, 3 and 7 days. Besides analyzing relevant reactive oxygen species-producing and -scavenging enzymes at protein and transcriptional level, the importance of the ascorbate–glutathione cycle under uranium stress was investigated. These results are reported separately for roots and leaves in two papers: Part I dealing with responses in the roots and Part II unraveling responses in the leaves and presenting general conclusions. Results of Part I indicate that oxidative stress related responses in the roots were only triggered following exposure to the highest uranium concentration of 100 μM. A fast oxidative burst was suggested based on the observed enhancement of lipoxygenase (LOX1) and respiratory burst oxydase homolog (RBOHD) transcript levels already after 1 day. The first line of defense was attributed to superoxide dismutase (SOD), also triggered from the first day. The enhanced SOD-capacity observed at protein level corresponded with an enhanced expression of iron SOD (FSD1) located in the plastids. For the detoxification of H2O2, an early increase in catalase (CAT1) transcript levels was observed while peroxidase capacities were enhanced at the later stage of 3 days. Although the ascorbate peroxidase capacity and gene expression (APX1) increased, the ascorbate/dehydroascorbate redox balance was completely disrupted and shifted toward the oxidized form. This disrupted balance could not be inverted by the glutathione part of the cycle although the glutathione redox balance could be maintained.

The toxicity and oxidative stress responses of 19-day old Arabidopsis seedlings induced by U (66 μM) and Cd (20 μM) alone or in a binary mixture set-up (equitoxic mixture) are studied in function of time. After 48h a significant decrease in root and shoot growth and a simultaneous increase in anthocyanin production was evident in all treated plants.Production of O− 2 or H2 O2 was visualized by staining freshly harvested leaves with nitrobluetetrazolium or diaminobezidine, respectively. With this method production of O− 2 was only significantly measurable after 168 h treatment which coincides with a significant decrease in biomass production and probably also plant cell death. For Cd treated plants a significant increase in H2 O2 production was measurable from 24h onwards. In contrast, a similar H2 O2 production could not be measured in U or U + Cd treated plants. Both water and lipophilic soluble antioxidants significantly increased in U treated plants after 48 h. These high antioxidant levels might detoxify potential H2 O2 produced in the U treated plants. In contrast for Cd treated plants only after 168h a significant increase in water soluble antioxidants was measured whereas no difference in the lipophilic fraction was visible.

An exercise to compare 10 approaches for the calculation of unweighted whole-body absorbed dose rates was conducted for 74 radionuclides and five of the ICRP's Reference Animals and Plants, or RAPs (duck, frog, flatfish egg, rat and elongated earthworm), selected for this exercise to cover a range of body sizes, dimensions and exposure scenarios. Results were analysed using a non-parametric method requiring no specific hypotheses about the statistical distribution of data. The obtained unweighted absorbed dose rates for internal exposure compare well between the different approaches, with 70% of the results falling within a range of variation of ±20%. The variation is greater for external exposure, although 90% of the estimates are within an order of magnitude of one another. There are some discernible patterns where specific models over- or under-predicted. These are explained based on the methodological differences including number of daughter products included in the calculation of dose rate for a parent nuclide; source-target geometry; databases for discrete energy and yield of radionuclides; rounding errors in integration algorithms; and intrinsic differences in calculation methods. For certain radionuclides, these factors combine to generate systematic variations between approaches. Overall, the technique chosen to interpret the data enabled methodological differences in dosimetry calculations to be quantified and compared, allowing the identification of common issues between different approaches and providing greater assurance on the fundamental dose conversion coefficient approaches used in available models for assessing radiological effects to biota. © 2010 Springer-Verlag.

Accumulation and distribution of uranium in roots and shoots of four plants species differing in their cation exchange capacity of roots (CECR) was investigated. After exposure in hydroponics for seven days to 100 μmol U L −1 , distribution of uranium in roots was investigated through chemical extraction of roots. Higher U concentrations were measured in roots of dicots which showed a higher CECR than monocot species. Chemical extractions indicated that uranium is mostly located in the apoplasm of roots of monocots but that it is predominantly located in the symplasm of roots of dicots. Translocation of U to shoot was not significantly affected by the CECR or distribution of U between symplasm and apoplasm. Distribution of uranium in roots was investigated through chemical extraction of roots for all species. Additionally, longitudinal and radial distribution of U in roots of maize and Indian mustard, respectively showing the lowest and the highest translocation, was studied following X-ray fluorescence (XRF) analysis of specific root sections. Chemical analysis and XRF analysis of roots of maize and Indian mustard clearly indicated a higher longitudinal and radial transport of uranium in roots of Indian mustard than in roots of maize, where uranium mostly accumulated in root tips. These results showed that even if CECR could partly explain U accumulation in roots, other mechanisms like radial and longitudinal transport are implied in the translocation of U to the shoot.

The objective of this study was to compile data, based on an extensive literature survey, for the soil solid–liquid distribution coefficient ( K d ) and soil-to-plant transfer factor (TF) for nickel. The K d best estimates were calculated for soils grouped according to texture and organic matter content (sand, loam, clay and organic) and soil cofactors affecting soil–nickel interaction, such as pH, organic matter, and clay content. Variability in K d was better explained by pH than by soil texture. Nickel TF estimates were presented for major crop groups (cereals, leafy vegetables, non-leafy vegetables, root crops, tubers, fruits, herbs, pastures/grasses and fodder), and also for plant compartments within crop groups. Transfer factors were also calculated per soil group, as defined by their texture and organic matter content. Furthermore an evaluation of transfer factor dependency on specific soil characteristics was performed following regression analysis. The derived estimates were compared with parameter estimates currently in use.

The applicability of biodegradable amendments in phytoremediation to increase the uptake of uranium (U), cadmium (Cd), chromium (Cr), copper (Cu), lead (Pb) and zinc (Zn) by Indian mustard (Brassica juncea) and ryegrass (Lolium perenne) was tested in a greenhouse experiment. Plants were cultivated during one month on two soils with naturally or industrially increased contaminant levels of U. Treatments with citric acid, NH4-citrate/citric acid, oxalic acid, S,S-ethylenediamine disuccinic acid (EDDS) or nitrilotriacetic acid (NTA) at a rate of 5 mmol kg(-1) dry soil caused increases in soil solution concentrations that were up to 18 times higher for U and up to 1570 times higher for other heavy metals, compared to the controls. Shoot concentrations increased to a much smaller extent. With EDDS, 19-, 34-, and 37-fold increases were achieved in shoots of Indian mustard for U, Pb and Cu, respectively. The increases in plant uptake of Cd, Cr and Zn were limited to a factor of four at most. Ryegrass generally extracted less U and metals than Indian mustard. Despite a marked increase of U and metal concentrations in shoots after addition of amendments, the estimated time required to obtain an acceptable reduction in soil contaminant concentrations was impractically long. Only for Cu and Zn in one of the studied soils, could the Flemish standards for clean soil theoretically be attained in less than 100 years.

The reactive oxygen species (ROS)-signaling pathway is very important in heavy metal toxicity. Induction of the antioxidative defense mechanism, comprising ROS-scavenging enzymes and metabolites, in plants after environmental uranium contamination has been insufficiently studied in the past. This study aimed to analyze oxidative stress related responses in Arabidopsis thaliana after uranium exposure. Seventeen-day-old seedlings were exposed to 0, 0.1, 1, 10 and 100 μM uranium for 3 days. After exposure to 100 μM uranium, a decrease in fresh weight for leaves and roots was observed, leaves colored anthocyanous and roots were stunted and yellow. To reveal the importance of oxidative stress in uranium toxicity, alterations in ROS-scavenging enzymes were studied at protein and transcriptional level. Superoxide dismutase (SOD) capacities increased in leaves and roots after exposure to 100 μM uranium but no differences were observed for catalase (CAT) capacities. Transcript levels of different SODs located at various cellular compartments were affected depending on the place of action. Gene expression of CAT in leaves and roots was also affected after uranium exposure. Results indicate that oxidative stress plays an important role in uranium toxicity but suggest that plant responses differ for leaves and roots.

The biological responses induced by low-dose chronic gamma exposure of hydroponically grown Arabidopsis thaliana , irradiated during a full life cycle (seed to seed) were investigated. Applied dose rates were 2300, 375 and 85 µGray h-1 . Plants (roots and shoots) were harvested after 24 day (inflorescence emergence), at 34 days (∼50% of flowers open) and at 54 days (silice ripening). Gamma exposure significantly reduced root weight compared to the control but no clear effect of dose rate level on root dry weight was observed. Leaf weight was significantly reduced at the highest irradiation level, only after 54 days exposure. ED-10 was estimated at 10 µGy h-1 . Seed germination was not affected by gamma irradiation. For several of the stress enzymes studied enzyme capacity was generally stimulated at the low and intermediate gamma irradiation level compared to the control and highest irradiation level. No pattern was observed in concentration or reduction state of the non-enzymatic antioxidants, ascorbate and glutathione. Lipid peroxidation products in leaves were present highest at full flowering and decreased with exposure level at this growth stage. At the other two growth stages, lipid peroxidation products were unaffected by gamma treatment.

A greenhouse experiment was set up to evaluate the potential of enhanced phytoextraction to clean up U and heavy metal contaminated soils. One soil had a naturally high U concentration; the other soil was impacted by the radium extraction industry. Enhancement of solubility and uptake by plants (ryegrass and Indian mustard) was monitored after addition of 5 chemical amendments: citric acid, ammonium citrate-citric acid mixture, oxalic acid, EDDS and NTA. Solubilisation and uptake were highly influenced by the amendment applied and soil-plant combinations. For U, citric acid, the ammonium citrate-citric acid mixture or EDDS were most effective in increasing U uptake. EDDS was most effective in increasing Cu in mustard and ryegrass and Pb in ryegrass shoots. For other metals, increase in uptake was limited to at most a factor 5. Percentages annually removed with biomass ranged from 0.0002% to 1.52%., and were lowest for U, Cr and Pb and highest for Cd. A targeted 10% reduction in soil contaminant would require 7 years for Cd, 35 and 52 years for Cu and Zn, 203 and 384 years for U and Pb and 9433 years for Cr. Phytoextraction is hence not a feasible technique to decontaminate historically contaminated soils.

The measurement of diffusive gradients in thin films (DGT) has been proposed as a surrogate for metal uptake by plants. A small-scale experiment was performed to test the predictive capacity of the DGT method with respect to uranium and heavy metal availability and uptake by ryegrass. Correlation analysis was performed to compare the results obtained with the DGT device with more conventional bioavailability indices: concentration in pore water or in selective extractants. Six soils with different histories of uranium contamination and with distinct soil characteristics were screened. For uranium, the bioavailability indices evaluated were highly correlated, indicating that uranium pools assessed were at least partially comparable. For heavy metals, bioavailability indices were hardly correlated. Uranium concentration in the pore water was a better predictor for uranium uptake than amount recovered following selective extraction. The concentration measured with DGT (CDGT ) was also highly correlated with plant uptake. However, the significance level was sensitive to the value of the diffusion coefficient (pH dependent or not) used to calculate CDGT . For the heavy metals screened, only in the case of Cd was uptake predicted by CDGT .

The production of reactive oxygen species (ROS) and the induction of the antioxidative defense mechanism are very important in heavy metal toxicity. In this study, biological effects induced after uranium contamination were investigated for Arabidopsis thaliana. Three-week-old seedlings were exposed for 4days to 100microM U in an adjusted Hoagland solution. Uranium exposure caused a decreased growth of leaves (38%) and roots (70%) and a modified nutrient profile was observed. Investigation of lipid peroxidation products indicated a significant increase of membrane damage. Important ROS-producing and -scavenging enzymes were studied at transcriptional and protein level to investigate the importance of the ROS-signature in uranium toxicity. Elevated gene expression was observed for NADPH-oxidase, a ROS-producing enzyme. Changes in gene expression for different ROS-scavenging enzymes as Cu/ZnSOD, FeSOD and APX were also observed. Analysis of enzyme capacities showed little effects after uranium contamination. Higher ascorbate levels in uranium exposed leaves suggested an increase of antioxidative defense via the ascorbate-glutathione pathway after uranium exposure. Theoretical calculations indicated rapid formation of uranium-phosphate precipitates if normal phosphate concentrations are used. Precipitation tests recommend the use of 25microM P in combination with 100microM U to inhibit uranium precipitation. Because this combination was used for uranium toxicity investigation, the influence of this low phosphate concentration on plant growth and oxidative stress had to be evaluated. Minor differences between low phosphate (25microM P) and high phosphate (100microM P) treatments were observed justifying the use of the low phosphate concentration in combination with uranium.

Chelate-assisted phytoextraction has been proposed as a potential tool for phytoremediation of U contaminated sites. In this context, the effects of five biodegradable amendments on U release in contaminated soils were evaluated. Three soils were involved in this study, one with a relatively high background level of U, and two which were contaminated with U from industrial effluents. Soils were treated with 5 mmol kg − 1 dry weight of either citric acid, NH 4 -citrate/citric acid, oxalic acid, S , S -ethylenediamine disuccinic acid or nitrilotriacetic acid. Soil solution concentration of U was monitored during 2 weeks. All amendments increased U concentration in soil solution, but citric acid and NH 4 -citrate/citric acid mixture were most effective, with up to 479-fold increase. For oxalic acid, S , S -ethylenediamine disuccinic acid and nitrilotriacetic acid, the increase ranged from 10-to 100-fold. The highest concentrations were observed 1 to 7 days after treatment, after which U levels in soil solution gradually decreased. All amendments induced a temporary increase of soil solution pH and TOC that could not be correlated with the release of U in the soil solution. Thermodynamic stability constants (log K ) of complexes did not predict the relative efficiency of the selected biodegradable amendments on U release in soil solution. Amendments efficiency was better predicted by the relative affinity of the chelate for Fe compared to U.

The present study aimed to quantify the influence of soil parameters on uranium uptake by ryegrass. Ryegrass was established on eighteen distinct soils, spiked with 238 U. Uranium soil-to-plant transfer factors (TF) ranged from 0.0003 to 0.0340 kg kg � 1 . There was no significant relation between the U soil-to-plant transfer (or total U uptake or flux) and the uranium concentration in the soil solution or any other soil factor measured, nor with the U recovered following selective soil extractions. Multiple linear regression analysis resulted in a significant though complex model explaining up to 99% of variation in TF. The influence of uranium speciation on uranium uptake observed was featured: UO22 , uranyl carbonate complexes and UO2PO4 seem the U species being preferentially taken up by the roots and transferred to the shoots. Improved correlations were obtained when relating the uranium TF with the summed soil solution concentrations of mentioned uranium species. 2006 Elsevier Ltd. All rights reserved.

Present study aims to quantify the influence of soil parameters on soil solution uranium concentration for (238)U spiked soils. Eighteen soils collected under pasture were selected such that they covered a wide range for those parameters hypothesised as being potentially important in determining U sorption. Maximum soil solution uranium concentrations were observed at alkaline pH, high inorganic carbon content and low cation exchange capacity, organic matter content, clay content, amorphous Fe and phosphate levels. Except for the significant correlation between the solid-liquid distribution coefficients (K(d), L kg(-1)) and the organic matter content (R(2)=0.70) and amorphous Fe content (R(2)=0.63), there was no single soil parameter significantly explaining the soil solution uranium concentration (which varied 100-fold). Above pH=6, log(K(d)) was linearly related with pH [log(K(d))=-1.18 pH+10.8, R(2)=0.65]. Multiple linear regression analysis did result in improved predictions of the soil solution uranium concentration but the model was complex.