Phytoextraction for clean-up of low-level uranium contaminated soil evaluated

Spills in the nuclear fuel cycle have led to soil contamination with uranium. In case of small contamination just above release levels, low-cost yet sufficiently efficient remedial measures are recommended. This study was executed to test if low-level U contaminated sandy soil from a nuclear fuel processing site could be phytoextracted in order to attain the required release limits. Two soils were tested: a control soil (317 Bq 238U kg(-1)) and the same soil washed with bicarbonate (69 Bq 238U kg(-1)). Ryegrass (Lolium perenne cv. Melvina) and Indian mustard (Brassica juncea cv. Vitasso) were used as test plants. The annual removal of soil activity by the biomass was less than 0.1%. The addition of citric acid (25 mmol kg(-1)) 1 week before the harvest increased U uptake up to 500-fold. With a ryegrass and mustard yield of 15,000 and 10,000 kg ha(-1), respectively, up to 3.5% and 4.6% of the soil activity could be removed annually by the biomass. With a desired activity reduction level of 1.5 and 5 for the bicarbonate-washed and control soil, respectively, it would take 10-50 years to attain the release limit. However, citric acid addition resulted in a decreased dry weight production.     

Ecosystem carbon budgeting and soil carbon sequestration in reclaimed mine soil

Global warming risks from emissions of green house gases (GHGs) by anthropogenic activities, and possible mitigation strategies of terrestrial carbon (C) sequestration have increased the need for the identification of ecosystems with high C sink capacity. Depleted soil organic C (SOC) pools of reclaimed mine soil (RMS) ecosystems can be restored through conversion to an appropriate land use and adoption of recommended management practices (RMPs). The objectives of this paper are to (1) synthesize available information on carbon dioxide (CO2) emissions from coal mining and combustion activities, (2) understand mechanisms of SOC sequestration and its protection, (3) identify factors affecting C sequestration potential in RMSs, (4) review available methods for the estimation of ecosystem C budget (ECB), and (5) identify knowledge gaps to enhance C sink capacity of RMS ecosystems and prioritize research issues. The drastic perturbations of soil by mining activities can accentuate CO2 emission through mineralization, erosion, leaching, changes in soil moisture and temperature regimes, and reduction in biomass returned to the soil. The reclamation of drastically disturbed soils leads to improvement in soil quality and development of soil pedogenic processes accruing the benefit of SOC sequestration and additional income from trading SOC credits. The SOC sequestration potential in RMS depends on amount of biomass production and return to soil, and mechanisms of C protection. The rate of SOC sequestration ranges from 0.1 to 3.1 Mg ha(-1) yr(-1) and 0.7 to 4 Mg ha(-1) yr(-1) in grass and forest RMS ecosystem, respectively. Proper land restoration alone could off-set 16 Tg CO2 in the U.S. annually. However, the factors affecting C sequestration and protection in RMS leading to increase in microbial activity, nutrient availability, soil aggregation, C build up, and soil profile development must be better understood in order to formulate guidelines for development of an holistic approach to sustainable management of these ecosystems. The ECBs of RMS ecosystems are not well understood. An ecosystem method of evaluating ECB of RMS ecosystems is proposed.     

The United States Department of Energy's Regional Carbon Sequestration Partnerships program: a collaborative approach to carbon management

This paper reviews the Regional Carbon Sequestration Partnerships (RCSP) concept, which is a first attempt to bring the U.S. Department of Energy's (DOE) carbon sequestration program activities into the "real world" by using a geographically-disposed-system type approach for the U.S. Each regional partnership is unique and covers a unique section of the U.S. and is tasked with determining how the research and development activities of DOE's carbon sequestration program can best be implemented in their region of the country. Although there is no universal agreement on the cause, it is generally understood that global warming is occurring, and many climate scientists believe that this is due, in part, to the buildup of carbon dioxide (CO(2)) in the atmosphere. This is evident from the finding presented in the National Academy of Science Report to the President on Climate Change which stated "Greenhouse gases are accumulating in Earth's atmosphere as a result of human activities, causing surface air temperatures and subsurface ocean temperatures to rise. Temperatures are, in fact, rising. The changes observed over the last several decades are likely mostly due to human activities, ...". In the United States, emissions of CO(2) originate mainly from the combustion of fossil fuels for energy production, transportation, and other industrial processes. Roughly one third of U.S. anthropogenic CO(2) emissions come from power plants. Reduction of CO(2) emissions through sequestration of carbon either in geologic formations or in terrestrial ecosystems can be part of the solution to the problem of global warming. However, a number of steps must be accomplished before sequestration can become a reality. Cost effective capture and separation technology must be developed, tested, and demonstrated; a database of potential sequestration sites must be established; and techniques must be developed to measure, monitor, and verify the sequestered CO(2). Geographical differences in fossil fuel use, the industries present, and potential sequestration sinks across the United States dictate the use of a regional approach to address the sequestration of CO(2). To accommodate these differences, the DOE has created a nationwide network of seven Regional Carbon Sequestration Partnerships (RCSP) to help determine and implement the carbon sequestration technologies, infrastructure, and regulations most appropriate to promote CO(2) sequestration in different regions of the nation. These partnerships currently represent 40 states, three Indian Nations, four Canadian Provinces, and over 200 organizations, including academic institutions, research institutions, coal companies, utilities, equipment manufacturers, forestry and agricultural representatives, state and local governments, non-governmental organizations, and national laboratories. These partnerships are dedicated to developing the necessary infrastructure and validating the carbon sequestration technologies that have emerged from DOE's core R&D and other programs to mitigate emissions of CO(2), a potent greenhouse gas. The partnerships provide a critical link to DOE's plans for FutureGen, a highly efficient and technologically sophisticated coal-fired power plant that will produce both hydrogen and electricity with near-zero emissions. Though limited to the situation in the U.S., the paper describes for the international scientific community the approach being taken by the U.S. to prepare for carbon sequestration, should that become necessary.     

Ecosystem management based on ecosystem services and human activities: a case study in the Yanhe watershed

With activities that alter the structure and function of the habitat, humans have a direct impact on ecosystems and ecosystem services, i.e., the conditions and processes that sustain human life. In this study, 35 townships in the Yanhe watershed in the Loess Plateau of China were selected. The net primary production (NPP), carbon sequestration and oxygen production (CSOP), water conservation, and soil conservation were the ecosystem services selected and valuated. Human activity was quantified by an integrated human activity index (HAI) based on population density, farmland ratio, and the influence of road networks and residential areas. The NPP, CSOP, and water conservation showed a conspicuous spatial pattern fanning outward from the southwest, while the soil conservation showed an obscure spatial pattern distinguished primarily by the peripheral area surrounding the urbanized areas. Total ecosystem services in the Yanhe watershed demonstrated a decreasing pattern from south to north, and the HAI was in proportion to administrative and economic development. Based on the selected ecosystem services and HAI, we mapped the townships of the Yanhe watershed by cluster analysis, and provided sustainable ecosystem management suggestions, tailored to the social-ecological map.     

Depleted uranium particles in selected Kosovo samples

Selected soil samples, collected in Kosovo locations where DU ammunition was expended during the 1999 Balkan conflict, have been investigated by secondary ion mass spectrometry (SIMS), X-ray fluorescence imaging using a micro-beam (micro-XRF) and scanning electron microscopy equipped with an energy dispersive X-ray fluorescence detector (SEM-EDXRF), with the objective to test the suitability of these techniques to identify the presence of small DU particles and measure their size distribution and the 235U/238U isotopic ratio (SIMS). Although the results do not permit any legitimate extrapolation to all the sites hit by the DU rounds used during the conflict, they indicated that there can be "spots ' where hundreds of thousands of particles may be present in a few milligrams of DU contaminated soil. The particle size distribution showed that most of the DU particles were <5 microm in diameter and more than 50% of the particles had a diameter <1.5 microm. Knowledge on DU particles is needed as a basis for the assessment of the potential environmental and health impacts of military use of DU, since it provides information on possible re-suspension and inhalation.     

Screening plant species native to Taiwan for remediation of 137Cs-contaminated soil and the effects of K addition and soil amendment on the transfer of 137Cs from soil to plants

This study aims to screen plant species native to Taiwan that could be used to eliminate (137)Cs radionuclides from contaminated soil. Four kinds of vegetables and two kinds of plants known as green manures were used for the screening. The test plants were cultivated in (137)Cs-contaminated soil and amended soil which is a mixture of the contaminated one with a horticultural soil. The plant with the highest (137)Cs transfer factor was used for further examination on the effects of K addition on the transfer of (137)Cs from the soils to the plant. Experimental results revealed that plants cultivated in the amended soil produced more biomass than those in the contaminated soil. Rape exhibited the highest production of aboveground parts, and had the highest (137)Cs transfer factor among all the tested plants. The transfer of (137)Cs to the rape grown in the soil to which 100 ppm KCl commonly used in local fertilizers had been added, were restrained. Results of this study indicated that rape, a popular green manure in Taiwan, could remedy (137)Cs-contaminated soil.     

长江三角洲水田保护性耕作制度的碳收集效应估算

耕作制度对农田土壤有机碳的稳定和积累作用显著,探讨耕作制度演变下农田土壤碳库动态,将有助于农田土壤碳收集的技术选择及政策制定。利用已发表的田间定位试验数据,构建不同耕作制度下长江三角洲水田耕层土壤有机碳密度的估算模型。依据该区近20多年来耕作制度演变动态,对保护性耕作制度的土壤碳收集效应进行了初步估算。结果表明,油菜面积的扩大、小麦的少免耕和作物秸秆的还田分别约增加土壤耕层有机碳0.94 Tg、2.76 Tg和3.95 Tg,其中以麦稻复种转向油稻复种的单位面积碳收集效应为最高。最后,就碳收集效应估算的方法进行了相关讨论,并就土壤碳收集研究和如何提高土壤碳收集潜力提出了一些建议。     

Impact of arbuscular mycorrhizal fungi on uranium accumulation by plants

Contamination by uranium (U) occurs principally at U mining and processing sites. Uranium can have tremendous environmental consequences, as it is highly toxic to a broad range of organisms and can be dispersed in both terrestrial and aquatic environments. Remediation strategies of U-contaminated soils have included physical and chemical procedures, which may be beneficial, but are costly and can lead to further environmental damage. Phytoremediation has been proposed as a promising alternative, which relies on the capacity of plants and their associated microorganisms to stabilize or extract contaminants from soils. In this paper, we review the role of a group of plant symbiotic fungi, i.e. arbuscular mycorrhizal fungi, which constitute an essential link between the soil and the roots. These fungi participate in U immobilization in soils and within plant roots and they can reduce root-to-shoot translocation of U. However, there is a need to evaluate these observations in terms of their importance for phytostabilization strategies.     

Determination of the specific alpha activity of thick sources with a large area ZnS(Ag) scintillation detector

A method for determining the specific alpha activity of thick sources using a large area ZnS(Ag) scintillation detector is presented. In this method a quadratic relationship between the detector response and window thickness is assumed. This method provides a quick estimation of alpha activity in the sample, so it is an indicative method. The aim of this experimental work is to approve theoretical assumption and to develop a standard routine method for absolute alpha measurements of thick contaminated environmental sources. For this purpose reference material U(3)O(8) and spiked standards of soil were used. Measurements of contaminated soil samples from south Serbia showed the practical application of this method.     

农田固碳措施对温室气体减排影响的研究进展

农田是CO2,CH4和N2O三种温室气体的重要排放源,在全球范围内农业生产活动贡献了约14%的人为温室气体排放量,以及58%的人为非CO2排放,不合理的农田管理措施强化了农田温室气体排放源特征,弱化了农田固碳作用。土壤碳库作为地球生态系统中最活跃的碳库之一,同时也是温室气体的重要源/汇。研究表明通过采取合理的农田管理措施,既可起到增加土壤碳库、减少温室气体排放的目的,又能提高土壤质量。农田土壤碳库除受温度、降水和植被类型的影响外,还在很大程度上受施肥量、肥料类型、秸秆还田量、耕作措施和灌溉等农田管理措施的影响。本文通过总结保护性耕作/免耕,秸秆还田,氮肥管理,水分管理,农学及土地利用变化等农田管理措施,探寻增强农田土壤固碳作用,减少农田温室气体排放的合理途径。农田碳库的稳定/增加,对于保证全球粮食安全与缓解气候变化趋势具有双重的积极意义。在我国许多有关土壤固碳与温室气体排放的研究尚不系统或仅限于短期研究,这也为正确评价各种固碳措施对温室气体排放的影响增加了不确定性。     

Wild plant species in bio-indication of radioactive-contaminated sites around Jaslovské Bohunice nuclear power plant in the Slovak Republic

In a long-term study of contaminated soil around Jaslovské Bohunice nuclear power plant (NPP), 24 species of local flora were used to show impact of serious accidents from 1976 to 1977. The 19-km-long banks of the Jaslovské Bohunice NPP wastewater recipient have been identified as contaminated by (137)Cs. In total, more than 67,000m(2) of riverbanks have been found as being contaminated at levels exceeding 1Bq (137)Csg(-1) of soil. Used phytotoxic and cytogenetic "in situ" tests were extended by analyses of pollen grains. Although the dose of some samples of radioactive soil was relatively high (322kBqkg(-1)) no significant impact on the biological level of tested wild plant species was observed.     

Significant radioactive contamination of soil around a coal-fired thermal power plant

Soil samples were collected around a coal-fired power plant from 81 different locations. Brown coal, unusually rich in uranium, is burnt in this plant that lies inside the confines of a small industrial town and has been operational since 1943. Activity concentrations of the radionuclides 238U, 226Ra, 232Th, 137Cs and 40K were determined in the samples. Considerably elevated concentrations of 238U and 226Ra have been found in most samples collected within the inhabited area. Concentrations of 235U and 226Ra in soil decreased regularly with increasing depth at many locations, which can be explained by fly-ash fallout. Concentrations of 235U and 226Ra in the top (0-5 cm depth) layer of soil in public areas inside the town are 4.7 times higher, on average, than those in the uncontaminated deeper layers, which means there is about 108 Bq kg(-1) surplus activity concentration above the geological background. A high emanation rate of 222Rn from the contaminated soil layers and significant disequilibrium between 238U and 226Ra activities in some kinds of samples have been found.     

Global estimates of soil carbon sequestration via livestock waste: a STELLA simulation

It has become increasingly well documented that human activities are enhancing the greenhouse effect and altering the global climate. Identifying strategies to mitigate atmospheric carbon dioxide emissions on the national level are therefore critical. Fossil fuel combustion is primarily responsible for the perturbation of the global carbon cycle, although the influence of humans extends far beyond the combustion of fossil fuels. Changes in land use arising from human activities contribute substantially to atmospheric carbon dioxide; however, land use changes can act as a carbon dioxide sink as well. A soil carbon model was built using STELLA to explore how soil organic carbon sequestration (SOC) varies over a range of values for key parameters and to estimate the amount of global soil carbon sequestration from livestock waste. To obtain soil carbon sequestration estimates, model simulations occurred for 11 different livestock types and with data for eight regions around the world. The model predicted that between 1980 and 1995, United States soils were responsible for the sequestration of 444–602 Tg C from livestock waste. Model simulations further predicted that during the same period, global soil carbon sequestration from livestock waste was 2,810–4,218 Tg C. Our estimates for global SOC sequestration are modest in proportion to other terrestrial carbon sinks (i.e. forest regrowth); however, livestock waste does represent a potential for long-term soil carbon gain. SOC generated from livestock waste is another example of how human activities and land use changes are altering soil processes around the world. Readers should send their comments on this paper to: BhaskarNath@aol.com within 3 months of publication of this issue.     

Uptake of uranium and thorium by native and cultivated plants

Large part of available literature on biogeochemistry of uranium and thorium refers to the studies performed either in highly contaminated areas or in nutrient solutions that have been artificially ‘spiked’ with radionuclides. Effects of background levels of natural radioactivity on soil-grown plants have not been studied to the same extent. In this paper, we summarised results of greenhouse and field experiments performed by the author from 2000 to 2006. We examined some of the factors affecting transfer of U and Th from soil to plants, differences in uptake of these radionuclides by different plants, relationships between U and Th in soil and in plants, and temporal variations of U and Th in different plant species. Concentrations of radionuclides (critical point for experimental studies on biogeochemistry of U and Th - rare trace elements in non-contaminated regions) and essential plant nutrients and trace elements were determined by instrumental neutron activation analysis.     

Soil availability,plant uptake and soil to plant transfer of 99Tc--a review

The fission yield of 99Tc from 239Pu and 235U is similar to that of 137Cs or 90Sr and it is therefore an important component of nuclear weapons fall-out, nuclear waste and releases from nuclear facilities. There is particular current interest in 99Tc transfer from soil to plants for: (a) environmental impact assessments for terrestrial nuclear waste repositories, and (b) assessments of the potential for phytoextraction of radionuclides from contaminated effluent and soil. Vascular plants have a high 99Tc uptake capacity, a strong tendency to transport it to shoot material and accumulate it in vegetative rather than reproductive structures. The mechanisms that control 99Tc entry to plants have not been identified and there has been little discussion of the potential for phytoextraction of 99Tc contaminated effluents or soil. Here we review soil availability, plant uptake mechanisms and soil to plant transfer of 99Tc in the light of recent advances in soil science, plant molecular biology and phytoextraction technologies. We conclude that 99Tc might not be highly available in the long term from up to 50% of soils worldwide, and that no single mechanism that might be easily targeted by recombinant DNA technologies controls 99Tc uptake by plants. Overall, we suggest that Tc might be less available in terrestrial ecosystems than is often assumed but that nevertheless the potential of phytoextraction as a decontamination strategy is probably greater for 99Tc than for any other nuclide of radioecological interest.     

Soil management practices for sustainable agro-ecosystems

A doubling of the global food demand projected for the next 50 years poses a huge challenge for the sustainability of both food production and global and local environments. Today’s agricultural technologies may be increasing productivity to meet world food demand, but they may also be threatening agricultural ecosystems. For the global environment, agricultural systems provide both sources and sinks of greenhouse gases (GHGs), which include carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O). This paper addresses the importance of soil organic carbon (SOC) for agro-ecosystems and GHG uptake and emission in agriculture, especially SOC changes associated with soil management. Soil management strategies have great potential to contribute to carbon sequestration, since the carbon sink capacity of the world’s agricultural and degraded soil is 50–66% of the historic carbon loss of 42–72 Pg (1 Pg=10¹⁵ g), although the actual carbon storage in cultivated soil may be smaller if climate changes lead to increasing mineralization. The importance of SOC in agricultural soil is, however, not controversial, as SOC helps to sustain soil fertility and conserve soil and water quality, and organic carbon compounds play a variety of roles in the nutrient, water, and biological cycles. No-tillage practices, cover crop management, and manure application are recommended to enhance SOC storage and to contribute to sustainable food production, which also improves soil quality. SOC sequestration could be increased at the expense of increasing the amount of non-CO₂ GHG emissions; however, soil testing, synchronized fertilization techniques, and optimum water control for flooding paddy fields, among other things, can reduce these emissions. Since increasing SOC may also be able to mitigate some local environmental problems, it will be necessary to have integrated soil management practices that are compatible with increasing SOM management and controlling soil residual nutrients. Cover crops would be a critical tool for sustainable soil management because they can scavenge soil residual nitrogen and their ecological functions can be utilized to establish an optimal nitrogen cycle. In addition to developing soil management strategies for sustainable agro-ecosystems, some political and social approaches will be needed, based on a common understanding that soil and agro-ecosystems are essential for a sustainable society.     

The co-application of earthworms (Dendrobaena veneta) and compost to increase hydrocarbon losses from diesel contaminated soils

The feasibility of using composted civic waste for the remediation of a soil contaminated with petroleum hydrocarbons (extractable petroleum hydrocarbons (EPH) 10+/-1.8 g kg(-1) and total 16 USEPA PAH 1.62+/-0.5 g kg(-1)) was assessed. The effects of compost to soil ratio, in combination with and without earthworm presence (Dendrobaena veneta), upon the loss of contaminants were determined for EPH (GC-FID) and PAH (GC-MS), respectively. Increasing the ratio of compost substrate to hydrocarbon impacted soil (1:0.5, 1:1, 1:2 and 1:4 (soil:compost wt/wt)) in the absence of earthworms resulted in significantly (p<0.05) greater losses of both EPH and SigmaPAH after an 84 d incubation period, when compared to the soil only control. Where earthworms were present without compost, EPH losses were significantly (p<0.05) enhanced in the soil only treatment (33.4+/-5.3% residual) compared to the soil only control (54.4+/-5.3% residual). However, PAH loss in the soil only treatment (with-earthworm presence) were only slightly enhanced (65.3+/-9.3% residual), with respect to the soil only control (69.2+/-6.4% residual). Synergistic benefits of both earthworm and compost presence were most significant for PAHs (p<0.05), and less so for EPH. (14)C-respirometer studies, to establish catabolic competence in terms of microbial mineralisation of key hydrocarbons, complemented the hydrocarbon analysis.     

Changes in 137Cs concentrations in soil and vegetation on the floodplain of the Savannah River over a 30 year period

(137)Cs released during 1954-1974 from nuclear production reactors on the Savannah River Site, a US Department of Energy nuclear materials production site in South Carolina, contaminated a portion of the Savannah River floodplain known as Creek Plantation. (137)Cs activity concentrations have been measured in Creek Plantation since 1974 making it possible to calculate effective half-lives for (137)Cs in soil and vegetation and assess the spatial distribution of contaminants on the floodplain. Activity concentrations in soil and vegetation were higher near the center of the floodplain than near the edges as a result of frequent inundation coupled with the presence of low areas that trapped contaminated sediments. (137)Cs activity was highest near the soil surface, but depth related differences diminished with time as a likely result of downward diffusion or leaching. Activity concentrations in vegetation were significantly related to concentrations in soil. The plant to soil concentration ratio (dry weight) averaged 0.49 and exhibited a slight but significant tendency to decrease with time. The effective half-lives for (137)Cs in shallow (0-7.6 cm) soil and in vegetation were 14.9 (95% CI=12.5-17.3) years and 11.6 (95% CI=9.1-14.1) years, respectively, and rates of (137)Cs removal from shallow soil and vegetation did not differ significantly among sampling locations. Potential health risks on the Creek Plantation floodplain have declined more rapidly than expected on the basis of radioactive decay alone because of the relatively short effective half-life of (137)Cs.     

Arbuscular mycorrhizas contribute to phytostabilization of uranium in uranium mining tailings

Uranium (U) tailings pose environmental risks and call for proper remediation. In this paper medic and ryegrass plants were used as host plants to examine whether inoculation with an AM fungus, Glomus intraradices, would help phytostabilization of U tailings. The need of amending with uncontaminated soil for supporting plant survival was also examined by mixing soil with U tailing at different mixing ratios. Soil amendment increased plant growth and P uptake. Ryegrass produced a more extensive root system and a greater biomass than medic plants at all mixing ratios. Medic roots were extensively colonized by G. intraradices whereas ryegrass were more sparsely colonized. Plant growth was not improved by mycorrhizas, which, however, improved P nutrition of medic plants. Medic plants contained higher U concentrations and showed higher specific U uptake efficiency compared to ryegrass. In the presence of U tailing, most U had been retained in plant roots, and this distribution pattern was further enhanced by mycorrhizal colonization. The results suggest a role for AM fungi in phytostabilization of U tailings.     

Characterization of uranium and plutonium containing particles originating from the nuclear weapons accident in Thule, Greenland, 1968

To improve long-term radioecological impact assessment for the contaminated ecosystem of Bylot Sound, Greenland, U and Pu containing particles have been characterized with respect to particle size, elemental distribution, morphology and oxidation states. Based on scanning electron microscopy with XRMA, particles ranging from about 20 to 40 microm were isolated. XRMA and mu-XRF mapping demonstrated that U and Pu were homogeneously distributed throughout the particles, indicating that U and Pu have been fused. Furthermore, mu-XANES showed that U and Pu in the particles were present as mixed oxides. U was found to be in oxidation state IV whereas Pu apparently is a mixture of Pu(III) and Pu(IV). As previous assessments are based on PuO2 only, revisions should be made, taking Pu(III) into account.