The transfer of radionuclides from saltmarsh vegetation to sheep tissues and milk

Radionuclides released into the Irish Sea by the Sellafield reprocessing plant are deposited onto tide-washed pastures along the western coast of the United Kingdom. Many of these pastures are grazed by sheep or cattle. This paper describes a controlled feeding study, in which saltmarsh vegetation harvested from close to the Sellafield plant, was fed to lambs and adult female sheep for a period of 8 weeks. Activity concentrations of (60)Co, (95)Nb, (106)Ru, (134)Cs, (137)Cs, (238)Pu, (239,240)Pu and (241)Am were determined in edible tissues and transfer parameters estimated. The activity concentrations of some of the radionuclides will not have been in equilibrium with those in the diet. Nevertheless, the study was reasonably realistic in terms of agricultural management as the period of the study was similar to that for which lambs graze on the saltmarshes. A field study to determine the activity concentrations of (137)Cs and (239,240)Pu in the milk of ewes grazing a saltmarsh close to Sellafield is also described.     

Aspects of the uptake of radionuclides by sheep grazing on an estuarine saltmarsh. 2. Radionuclides in sheep tissues

The transfer ¹³⁷Cs, ²³⁸Pu, ^239/240Pu and ²⁴¹Am to sheep which graze a saltmarsh in the Esk estuary, 7 km south of the sellafield reprocessing plant in west Cumbria (UK), has been estimated.The concentrations of gamma-emitting radionuclides and of ²³⁸Pu, ^239/240Pu and ²⁴¹Am were measured in liver, lung, muscle, kidney and bone from saltmarsh ewes and lambs. ¹³⁷Cs concentrations in the soft tissues were similar in liver, lung and muscle but were consistently higher in kidney and much lower in bone. The highest concentration of the transuranics was found in liver.Transfer coefficients and concentration factors were calculated for both ewes and lambs. The concentration of ¹³⁷Cs in the tissues of 5-month old lambs was higher than in those of their mothers. Therefore, a higher transfer coefficient was obtained for lamb muscle (1·8 × 10^?1 d kg^?1) than for ewe muscle (6·4 × 10^?2 d kg^?1). Concentration factors were consistently higher for ¹³⁷Cs than for the transuranics.     

Constraints on the use of anthropogenic radionuclide-derived chronologies for saltmarsh sediments

Numerous studies have employed anthropogenic radionuclides deposited in accumulating sediments to derive chronologies for use in investigations of geomorphological processes and in reconstructing temporal trends in contaminant deposition. However, relatively few have interrogated their use in systems that erode as well as accrete sediment, or have addressed limitations in their applicability in systems that experience variable rates of accumulation. This paper examines the utility of Sellafield-derived radionuclides for reconstructing sedimentary processes in two contrasting saltmarsh systems in the south-west of Scotland. Sedimentation rates and patterns derived from the radionuclide chronologies are outlined and compared to results established through conventional geomorphological methods. The results confirm that the vertical distribution of anthropogenic radionuclides can be useful in determining sedimentation rates, but that these cannot always be used as indicators of contemporary processes, particularly where erosion is occurring. Their use is also limited unless profiles are obtained from spatially diverse geomorphological units. Integrating the use of chronologies with other independent methods secures more robust data for assessing both marsh sustainability and their longevity as radionuclide sinks.     

Variability in background levels of surface soil radionuclides in the vicinity of the US DOE waste isolation pilot plant

Concentrations of radionuclides were measured in soils from a grid of locations surrounding the US Department of Energy Waste Isolation Pilot Plant (WIPP) in southeastern New Mexico and from a grid on a reference site approximately 20 km southeast of the WIPP site. Each of the two grids has 16 sampling locations (grid nodes) systematically distributed within an area of 16.580 ha. Sampling was conducted prior to the arrival of the first waste shipment at WIPP. Thus, the 137Cs and 23,240Pu in the soil are expected to have been deposited as global fallout, although the Gnome Site, 8.8 km southwest of the WIPP, is also a potential source of 239,240Pu and fission products. The reference grid has significantly higher concentrations of fallout and natural radionuclides than the WIPP grid. Up to 80% of the total variability in radionuclide concentrations across the two grids is attributable to differences between grid nodes. Differences between replicates within a location account for 44-50% of the variability in concentrations of the uranium isotopes, but only 11-17% of the variability in the concentrations of the other radionuclides. Samples having similar abundance of radionuclides were spatially aggregated across the terrain. The activity concentrations of the radionuclides were strongly correlated with the concentrations of Al and Pb, and with the percentages of sand, silt and clay in the soil. Normalizing radionuclide concentrations to the concentration of Al or percent fine particles can help adjust for differences in soil textures among samples and facilitate the detection of gradients or temporal changes in soil concentrations.     

Study of 210Po and 210Pb in the riverine environments of coastal Karnataka

Activity of ²¹⁰Po and ²¹⁰Pb were measured in soil and sediment samples collected from the major rivers Kali, Sharavathi and Netravathi of Coastal Karnataka. The activity of these two radionuclides were determined by radiochemical separation of ²¹⁰Po and counting the activity using a ZnS(Ag) Alpha counter. The activity of ²¹⁰Pb was higher than that of ²¹⁰Po in the riverine environs. The ²¹⁰Po and ²¹⁰Pb content in sediment was found to increase with silt/clay and organic matter contents. However no significant correlation was found between the activity ²¹⁰Po and ²¹⁰Pb with pH in sediments. The activity of ²¹⁰Po and ²¹⁰Pb and influence of physico-chemical parameters on these radionuclides were studied and discussed in this paper.     

Plutonium solubility in sediment pore waters

Using in situ porous cup samplers, dissolved Pu concentrations have been measured over a year in the pore waters from two contrasting sites in the valley of the River Esk, North West England. In saltmarsh sediments, dissolved Pu represents approximately 1 part in 10(6) of the total inventory. The Pu concentration in solution is in the range 1.1-3.5 mBq l-1, varying by a factor of 3 in the course of the year. Most of the changes in dissolved Pu coincide with changes in dissolved Fe and Mn concentrations, with Pu being low in the summer months when Fe and Mn are high. Nevertheless, there are a number of factors which make it unclear as to whether these patterns might be related to seasonal redox changes in the saltmarsh. At the highly organic, reducing reedbed site, the proportion of Pu in solution is typically around 1 part in 10(3), proportionately much higher than in the saltmarsh, giving concentrations ranging between 9.0 and 28.5 mBq l-1, and are apparently maintained by complexation to dissolved organic matter. There is no obvious seasonal pattern at the reedbed site nor is there any relation to any of the dissolved species measured (Fe, Mn, Na, DOC).     

Influence of soil texture on the distribution and availability of 238U, 230Th, and 226Ra in soils

The influence of soil texture on the distribution and availability of (238)U, (230)Th, and (226)Ra in soils was studied in soil samples collected at a rehabilitated uranium mine located in the Extremadura region in south-west Spain. The activity concentration (Bqkg(-1)) in the soils ranged from 60 to 750 for (238)U, from 60 to 260 for (230)Th, and from 70 to 330 for (226)Ra. The radionuclide distribution was determined in three soil fractions: coarse sand (0.5-2mm), medium-fine sand (0.067-0.5mm), and silt and clay (<0.067 mm). The relative mobility of the natural radionuclides in the different fractions was studied by comparison of the activity ratios between radionuclides belonging to the same radioactive series. The lability of these radionuclides in each fraction was also studied through selective extraction from the soils using a one-step sequential extraction scheme. Significant correlations were found for (238)U, (230)Th, and (226)Ra between the activity concentration per fraction and the total activity concentration in the bulk soil. Thus, from the determination of the activity concentration in the bulk soil, one could estimate the activity concentration in each fraction. Correlations were also found for (238)U and (226)Ra between the labile activity concentration in each fraction and the total activity concentration in bulk soil. Assuming that there is some particle-size fraction that predominates in the process of soil-to-plant transfer, the parameters obtained in this study should be used as correction factors for the transfer factors determined from the bulk soil in previous studies.     

Plutonium in sheep faeces as an indicator of deposition on vegetation

In order to study the deposition on vegetation of plutonium arising from the testing of nuclear weapons and discharges from nuclear facilities, sheep faeces were collected from the South-west and North of England. The plutonium content of faeces has been shown to be a reproducible and sensitive indicator of deposition on herbage and, with this technique, plutonium discharged from the Sellafield Works of British Nuclear Fuels LImited can be detected 60 km from the site. On moorland pastures the concentration of ^239+240Pu in faeces, expressed as activity per gram of ash, is roughly equal numerically to the deposit of plutonium on 1 m² of vegetation.Some of the plutonium ingested by a grazing sheep is absorbed and the highest concentrations are found in liver. The liver of a sheep grazing on pasture where the ^239+240Pu concentration in faeces was about 2 pCi (74 mBq) g⁻¹ of ash, was found to contain <1% of the Generalised Derived Limit for mutton and offal, and the meat <0·001%.     

Test of existing mathematical models for atmospheric resuspension of radionuclides

Atmospheric resuspension of radionuclides can be a secondary source of contamination after a release has stopped, as well as a source of contamination for people and areas not exposed to the original release. A test scenario based on measurements collected after the Chernobyl accident was used to evaluate existing mathematical models for contaminant resuspension from soil, to examine resuspension processes on both local and regional scales, and to investigate the importance of seasonal variations of these processes. Model predictions from 15 participants were compared with measured air concentrations and resuspension factors to investigate and explain the discrepancies both among model predictions and between model predictions and observations and thus to evaluate the predictive capabilities and drawbacks of commonly used generic resuspension models. The empirical models tested can give predictions within an order of magnitude of observations or better if adequately calibrated for site-specific conditions, but they do not describe the process-level events or account for spatial heterogeneity or temporal variations.     

Seasonal variations in radionuclide transfer in a Mediterranean grazing-land ecosystem.

We made quarterly determinations of the transfer coefficients and effective transfer coefficients for the radionuclides 137Cs, 90Sr, 40K, 226Ra, 228Ra and 228Th over a full annual cycle, in a Mediterranean grazing-land ecosystem. The input and output fluxes of the radionuclides between the different compartments of this ecosystem were quantified for the following processes: root uptake; variation in root and aerial biomass; pasture production; translocation; leaf fall; efflux due to grazing action; resuspension and subsequent aerial deposition of radionuclides. We observed there to be a marked seasonal variation for this type of ecosystem in both the transfer coefficients and the radionuclide fluxes, which impedes the soil-plant transfer being characterized on the basis of values that are constant with time.     

Kinetics of the adsorption and desorption of radionuclides of Co, Mn, Cs, Fe, Ag and Cd in freshwater systems: experimental and modelling approaches

The sorption and release kinetics of 54Mn, 58Co, 59Fe, 109Cd, 110mAg and 134Cs by freshwater suspended particles were investigated to better identify the biogeochemical processes involved and to obtain suitable data for improving models describing radionuclide migration in freshwater streams. In order to observe any seasonal variability in the interaction of radionuclides with natural particles, experiments were performed both in winter and in summer during a phytoplanktonic bloom. Two kinetic models are compared in this paper: the "one-step reversible" model, based on the hypothesis that the transfer of radionuclides between water and suspended solids is governed by a reversible reaction, and the "two-successive-step reversible" model, which assumes two distinct types of sites or reactions on the solid phase. The "one-step reversible" model is generally unable to describe properly the exchange kinetics; this result shows that at least two processes are generally involved in radionuclide exchange between water and suspended particles. On the contrary, a model involving the existence of two successive reversible reactions properly simultes both the sorption and release kinetics. The determination of the kinetic coefficients allows quantitative assessment of the relative importance and kinetics of the processes. In particular, it has been shown that, except for Cs and Cd, major fractions of the radionuclides are associated at equilibrium with particulate sites involving strong interactions. The kinetics to reach this equilibrium depend on seasonal conditions, especially for Co and Mn: the transfer of Co and Mn to particulate sites involving strong interactions is much slower in winter. The distribution of the radionuclides between water and particulate sites involving weak interactions also shows seasonal variations for Co, Mn, Fe and Ag: the capacity to associate radionuclides is much higher in summer for Co and Mn, while the inverse tendency is observed for Fe and Ag. For Cs and Cd, no significant seasonal differences were observed.     

Behaviour and transport of radionuclides in soil and vegetation of a sand dune ecosystem

A sand dune ecosystem in the vicinity of the British Nuclear Fuels reprocessing plant at Sellafield, Cumbria, UK was used to examine the spatial, temporal and depth distributions of 134Cs, 137Cs, 238Pu, 239 + 240Pu and 241Am in soil and in two species of vegetation (Festuca rubra, Ammophila arenaria). Core samples showed evidence of the accumulation of radionuclides derived mainly from sea-to-land transfer. Accumulated deposits of radioactivity (0-0.1 m) lie within the range: 1.1-3.4 Bq kg-1 (134Cs), 260-440 Bq kg-1 (137Cs), 31-40 Bq kg-1 (238Pu), 150-215 Bq kg-1 (239 + 240Pu) and 190-240 Bq kg-1 (241Am). Soil profiles showed greater activity concentrations in their deeper regions and this is attributed to leaching of radionuclides in percolating drainage water accentuated by the coarse texture, low organic matter and clay mineral content of coastal sands. Radionuclide activity concentrations in F. rubra and A. arenaria were similar, in the ranges 20-70 Bq kg-1 (137Cs), 1-5 Bq kg-1 (238Pu), 10-30 Bq kg-1 (239 + 240Pu) and 10-65 Bq kg-1 (241Am). Clear temporal and spatial variations were observed in both species of vegetation, reflecting the weather conditions antecedent to the sampling period and the influence of sea-to-land transfer. Concentration ratios (vegetation:soil) for activity concentrations in the two species were similar, in the ranges: 0.05-0.14 (137Cs), 0.025-0.097 (238Pu), 0.022-0.057 (239 + 240Pu) and 0.025-0.212 (241Am).     

The influence of the development of temperate fruit tree species on the potential for their uptake of radionuclides

This paper reviews the published literature that describes the phenological development of above and below ground organs of temperate fruit trees (top fruit), particularly with respect to apple (Malus domestica). Critical information is presented which is considered appropriate in developing an understanding of the potential for top fruit species to take up radionuclide contaminants from the atmosphere and the soil. Information is cited on how climatic and edaphic factors influence the growth and development of temperate fruit trees, the phenological production of their leaf area and the development and growth of their fruit and hence the potential for foliar and fruit uptake of radionuclides from the atmosphere. The study also reports on the importance of the distribution and phenological development of roots in the soil and the potential for their uptake of radionuclides from the soil. The effects of above and below ground management procedures, within temperate fruit orchards, on potential radionuclide uptake are also considered. It is concluded that the potential for the uptake of radionuclides by temperate fruit tree species will depend on a number of phenological and physiological factors. For uptake from the soil these factors include; root distribution and density in the soil profile, seasonal changes in the production and distribution of roots, and the presence and amount of water in the soil. These factors are themselves influenced by rootstock type and its growth vigour, scion type and its growth vigour, tree age, spacing of trees in the orchard, orchard management practices (presence or absence of weeds or grass under the trees) and soil type and depth. Direct uptake by the shoot, however, will be influenced by the climatic conditions at the time of exposure and the presence of foliage. Deposition and uptake are likely to change with leaf area development and the ability of radionuclides to penetrate the cuticle of the leaf changes with seasonal development. Transport of radionuclides to the fruit may also depend on the time of season, as the importance of the xylem and phloem transport routes can change with the growth and development of the fruit.     

Radiochemical analyses for environmental radiological studies at nuclear power stations

The analytical procedures used in a program of radiological monitoring studies at nuclear power stations are discussed. Samples of in-plant and effluent liquids, gases, and airborne particles were analyzed by radiochemical methods or by gamma-ray spectrometry. These procedures were modified for environmental media, including air, airborne particles, vegetation and food, milk, animal tissue, water, soil and sediment, generally by analyzing larger samples, enhancing the purification procedures, and increasing the detection sensitivity. Emphasis was placed on analyzing special samples for effluent radionuclides not routinely monitored, such as gaseous H-3, C-14, and Kr-85, and on measuring radionuclides at very low concentrations in media of possible dosimetric significance, such as radioiodine in milk. Measurements at these low levels permitted comparisons of source terms with environmental radioactivity in terms of calculational models.     

基于MODIS-EVI和CI的洞庭湖流域植被指数对气象干旱的响应

基于洞庭湖流域2000~2012年98个气象站点的综合气象干旱指数（CI）和MODIS增强型植被指数（EVI）数据，对研究时段内生长季干旱强度和EVI时空变化特征，典型春、夏、秋季干旱年月和湿润年月干旱强度和EVI的空间分布及相关性进行分析，旨在研究EVI指数能否反映大范围气象干旱事件，探讨该指数作为流域干湿状况度量标准的潜力。结果表明：（1）在年际变化上，EVI在2001、2005、2009年出现低谷值，与其对应年份的干旱强度出现高峰值；在季节变化上，干旱强度的高值段主要集中在夏秋季，低值段主要集中在冬春季；夏季EVI值最大，冬季EVI值最小；（2）去除年际变化和季节性影响的生长季干旱强度、EVI和森林覆盖率年际波动变化明显，并且干旱强度高峰值的年份对应EVI和森林覆盖率出现低值的年份；（3）典型干旱年月干旱强度高值区的空间分布与EVI距平低值区的空间分布存在高度一致性，其中夏、秋季干旱年月的干旱强度和EVI的相关系数分别通过了0.01、0.1的显著性水平检验；（4）除部分地区外，典型春夏秋季湿润年月的干旱强度空间分布与EVI距平的空间分布对应较差，两者的相关系数未通过显著性检验。上述结果表明，在典型干旱年月，流域植被的生长状况能够响应大范围的区域气象干旱情况。     

洞庭湖湿地土壤持水能力及其影响因素研究

土壤持水能力是反映土壤调节水文和供给植物耗水的重要指标，受土壤有机质、容重、机械组成和植物地下生物量的直接或间接影响。与森林和农田生态系统相比，湿地土壤持水能力关注较少。于2010年12月，对洞庭湖湿地3种主要植被（苔草、芦苇和杨树）土壤持水能力、土壤理化性质和地下生物量进行了调查，并采用主成分分析对影响土壤持水能力的主要环境因子进行了分析。结果表明：除非毛管孔隙度外，3种植被上层土壤的总孔隙度、毛管孔隙度、田间持水量和含水量差异显著，均为苔草＞芦苇=杨树，而中、下层无显著差异。沙粒为苔草≥杨树≥芦苇，而粗粉粒、细粉粒和粘粒均为杨树≥芦苇≥苔草；容重为杨树≥芦苇＞苔草，有机质为苔草=芦苇＞杨树。各级别生物量在植被类型大小顺序不一：总地下生物量、0～1 mm和＞5 mm径级地下生物量均以芦苇最大，而1～5 mm径级地下生物量则以苔草最大。主成分分析表明，上层土壤，容重、有机质和1～5 mm径级地下生物量是影响其持水能力的主要因素，而中层土壤和下层土壤，环境因子对土壤持水能力的影响很小。此研究对于洞庭湖生物多样性保护和湿地管理政策的制定具有重要意义     

基于MODIS数据的安徽省植被水分利用效率时空变化及影响因素

水分利用效率是衡量生态系统碳水循环耦合程度的重要指标。基于MODIS数据、土地覆盖类型数据和气象数据，估算安徽省植被水分利用效率(WUE），采用趋势分析法和相关分析法对安徽省2000~2014年植被WUE的时空格局、变化趋势及影响因素进行研究。研究表明:（1）不同植被类型的WUE年均值差异明显，常绿阔叶林和常绿针叶林的WUE均值较高，分别达到1.66和1.69 gC?mm-1?m-2，而耕地的年均WUE最低，各植被类型的年均WUE按照“常绿针叶林>常绿阔叶林>灌木>草地>落叶阔叶林>针阔混交林>耕地”的顺序递减。植被年均WUE具有较强的空间分异性规律，整体上呈现南北高中间低的趋势，植被WUE的高值区主要分布在大别山区和皖南山区，分布范围与常绿针叶林、常绿阔叶林的分布范围基本一致。（2）安徽省2000~2014年植被WUE年内变化呈现出“增加-减小-增加-减小”的M状“双峰型”趋势，具有明显的季节差异，呈现出春季＞秋季＞夏季＞冬季的特征，各季节植被WUE的均值分别占植被WUE的32.58%、24.91%、29.27%、13.24%。（3）安徽省植被WUE动态变化受到降水影响显著的区域占比3.88%；气温显著影响的区域占比2.19%；降水显著影响的地区主要分布在林地范围内，温度显著影响的地区则位于耕地范围内，降水和气温综合显著影响所占面积最小，为0.11%；而植被WUE受气温和降水影响均不显著占比为93.82%；整体上，安徽省大部分地区的植被WUE变化主要受非气候因素影响。     

Assessment of the radiological impacts of historical coal mining operations on the environment of Ny-Alesund, Svalbard

Mineral extraction activities, such as those conducted by oil, gas and coal industries, are widespread throughout the Arctic region. Waste products of these activities can result in significant contributions to the radioactive burden of the surrounding environment due to increased concentrations of naturally occurring radioactive materials (NORM) to levels that would not normally be found in the environment. Coal mining operations commenced in the early 1900s on Svalbard and have been conducted at a variety of locations on the archipelago since then. Coal contains radionuclides of the uranium and thorium series as well as 40K. Extraction and processing of coal can result in releases of these radionuclides to the broader environment with subsequent impact on the human and non-human inhabitants of the area. This paper presents the results of a study on environmental radioactivity resulting from historical coal mining operations conducted at Ny-Alesund, Spitsbergen, in the Svalbard archipelago. Activity concentrations of radionuclides found in materials associated with these operations are presented as well as the results of a spatial dosimetric survey conducted over an area affected by coal mining.     

Interception of dry and wet deposited radionuclides by vegetation

Interception of dry and wet deposited radionuclides by vegetation is a key process in radioecological models that assess ingestion doses to the population following releases of radionuclides to the atmosphere. Radionuclides may be deposited during precipitation or as dry particles. Interception of wet deposited radionuclides is the result of a complex interaction of the vegetative development of the plant canopy, the amount of rainfall, and the chemical form of radionuclides. For the interception of dry deposits, particle size is a key parameter; interception is more effective for small particles and reactive gases. Due to the dependence on plant development, interception of both dry and wet deposits is subject to pronounced seasonality.     

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.