Laboratory experiments to predict changes in radiocaesium root uptake after flooding events

Changes in soil solution composition after a flooding event were hypothesised to be one of the key factors in explaining changes in radiocaesium incorporation in the food chain in the areas affected by the Chernobyl accident. A laboratory methodology was set up to monitor changes in the soil solution composition after a sequence of flooding cycles. Experiments were performed using column and batch approaches on test soils with contrasting initial soil solution composition (high and low initial concentrations of K+). Results from column experiments indicated a potential increase in NH(4)(+) concentrations, a parameter which could lead to an increase in the radiocaesium root uptake. Batch results in the soil with high initial K+ concentration showed that after a number of flooding cycles, especially for high ratios of flooding solution/mass of soil, K+ concentration decreased sometimes below a threshold value (around 0.5-1 mmol l(-1)), a fact that could lead to an increase in radiocaesium transfer. For the soils with a low initial K+ concentration, the flooding solution increased K+ and NH(4)(+) values in the soil solution. The comparison of test soils with soils from Ukraine areas affected by flooding showed that the final stage in soil solution composition was similar in both cases, regardless of the initial composition of the soil solution. Moreover, the comparison with unflooded soils from the same area showed that potential changes in other soil parameters, such as (137)Cs activity concentration, clay content, and radiocaesium interception potential, RIP (a parameter that estimates the radiocaesium specific sorption capacity of a soil), should also be monitored for additional effects due to the flooding event. Therefore, the changes in the root uptake would depend on the resulting situation from changes in RIP, K+ and NH(4)(+) values in the soil solution.     

Adsorption and desorption of iodine by various Chinese soils: I. Iodate

In order to assess the adsorption of iodate by different soils from China, a series of batch experiments were conducted. It was found that soils rich in iron oxide had high affinity for iodate. Iodate adsorption isotherms could be well fitted with both Langmuir and Freundlich equations. Iodate adsorption by 20 different soils from China revealed that iodate adsorption was significantly correlated with soil organic matter negatively and positively with free iron oxide contents. At initial concentration of 4 mg I L(-1), iodate adsorption ranged between 9 and 34 mg kg(-1) soil. No correlation between iodate adsorption and cation exchange capacity and soil pH was found. For a single soil, there was a significant linear relationship between the amounts of iodate adsorbed and desorbed, but for a group of different soils, the relationship between the amounts of iodate adsorption and desorption followed a nonlinear relationship, the deviation mainly occurred at high adsorption side. The relationship between K(d) and free aluminum oxide and free iron oxide contents showed an exponential relationship for various soils with exception of the soil from Hetian in Xinjiang.     

The interaction of heavy metals with urban soils: sorption behaviour of Cd, Cu, Cr, Pb and Zn with a typical mixed brownfield deposit

This study investigated the sorption characteristics and release of selected heavy metals (Cd, Cu, Cr, Pb and Zn) from a typical urban soil material from a derelict brownfield site in Western Scotland, UK. The study aimed to evaluate contaminant interactions with an urban substrate, comprising a mix of mineral soil and residue materials (e.g. brick, concrete, wood). This type of material has received little consideration in the literature to date. Soil samples were subject to a sequence of test involving batch equilibration and dynamic leaching, in single (non-competitive) and multi-element (competitive) solutions. The batch experiments were carried out in unadjusted and close to soil field pH conditions (pH 2 and 7, respectively). The equilibrium adsorption capacity for heavy metals was measured and extrapolated using the Langmuir isotherm. The parameters of the isotherms x(m) (the maximum amount adsorbed per unit mass of adsorbent (mg/g)) and b (adsorption constant (m(3)/g)) were calculated for Cd, Cu, Cr, Pb as single-element and multi-element solutions. The adsorption from the single-element solution was more effective than adsorption under multi-element conditions, due to competitive effects. For example, the adsorption of copper from a single-element solution was over four times greater than for a multi-element solution. In the case of Cr and Zn, migration of metal from soil to solution was observed. Adsorption capacity at pH 2 followed the order Cr>Cu>Pb>Cd and at pH 7 Cd>Zn, with precipitation affecting Cu and Pb behaviour. During the column leaching experiment, most of the heavy metals were irreversibly bound to the soil, but in the case of Cr some movement from soil into solution was observed. The results also showed that Cd, Cu, Pb and Zn were removed from the solution and adsorbed on the soil. No significant difference in the metal removal from single- and multi-element solutions was observed. Overall, the urban residue behaved in a similar manner to mineral soils despite a significant component of anthropogenic solid materials.     

Distribution coefficients of tin in Japanese agricultural soils and the factors affecting tin sorption behavior

Sorption behavior of tin (Sn) in Japanese agricultural soils was studied. Soil-soil solution distribution coefficient (K(d)) of Sn (K(d)-Sn) for 142 soil samples ranged between 128 and 1,590,000 L kg(-1) with the geometric mean of 12 400 L kg(-1). The K(d)-Sn values for Andosol tended to be higher than those of the other soil groups. Among the relationships between K(d)-Sn values and soil properties, a high correlation was observed for soil active-Al (Al-(hydr)oxide and Al-humus complex) amount and K(d)-Sn. The pH effect on Sn sorption was also investigated. The results suggested that the low pH condition enhanced the Sn sorption in soils. The soil-sorbed Sn fractions in each type of soil material were also evaluated with selective extraction methods. The results showed that most of the soil-sorbed Sn was as organic matter bound or Al/Fe-(hydr)oxide-bound forms.     

Detection of tritium sorption on four soil materials

In order to measure groundwater age and design nuclear waste disposal sites, it is important to understand the sorption behavior of tritium on soils. In this study, batch tests were carried out using four soils from China: silty clays from An County and Jiangyou County in Sichuan Province, both of which could be considered candidate sites for Very Low Level Waste disposal; silty sand from Beijing; and loess from Yuci County in Shanxi Province, a typical Chinese loess region. The experimental results indicated that in these soil media, the distribution coefficient of tritium is slightly influenced by adsorption time, water/solid ratio, initial tritium specific activity, pH, and the content of humic and fulvic acids. The average distribution coefficient from all of these influencing factors was about 0.1-0.2 mL/g for the four types of soil samples. This relatively modest sorption of tritium in soils needs to be considered in fate and transport studies of tritium in the environment.     

Cadmium desorption in sand

Desorption of cadmium (Cd) from sand was studied by both batch and flow-through methods. Batch experiments were conducted at three pH values (5.5, 6.0 and 6.5). In each case, the amount of Cd desorbed was low compared with the quantity of Cd adsorbed previously. Desorption of Cd in the batch experiments can be described adequately by a Freundlich isotherm. The Freundlich isotherm coefficient, Kf, increased with pH. Hysteresis between the sorption/desorption isotherms was observed in all batch experiments. Flow-through experiments in soil columns were conducted for the same three pH values, with the results used to determine transport and sorption/desorption parameters. Again, the desorption isotherms bore little resemblance to the corresponding adsorption isotherms. The experimental breakthrough curves were well fitted by a nonequilibrium desorption model, however the time scale of the desorption process was much larger than measured in batch experiments. This model was therefore rejected as lacking realism. A simple linear retardation (including hysteresis) model that utilises different isotherms was found to simulate column breakthrough curves well. The Freundlich isotherm coefficients, Kf, in all batch and flow-through desorption experiments were different to values evaluated from the corresponding adsorption experiments. However, in contrast to adsorption, desorption in flow-through experiments was not noticeably affected by changes in pH. The effect of pore-water velocity on desorption was also studied at pH 6.0. No trend was established between flow velocity and the desorption coefficient.     

Effect of pH on the sorption of uranium in soils

This work was undertaken to study the influence of soil type and chemical composition on uranium sorption ratios (SR in 1 kg-1) in order to reduce the uncertainty associated with this parameter in risk assessment models. Thirteen soil samples were collected from three different locations in France under different geological conditions. Clay content varied from 7.0 to 50.0%, pH ranged from 5.5 to 8.8 and organic matter content from 1.0 to 4.6%. Soils were incubated at room temperature in polyethylene packets for 28 days in the presence of 1 mg U kg-1 soil. Sorption ratio values varied from 0.9 to 3198 for all soils with no significant effect of soil texture or of organic matter. However, soil pH was highly linearly correlated with (log SR) as a probable consequence of the existence of different uranium complexes as a function of soil pH. The sorption behaviour differences between UO2(2+) and UO2(2+)-carbonate complexes are so great that any other effect of soil properties on U sorption is hidden. Thus, soil pH should be the focus variable for reduction of the uncertainty associated with the soil Kd value used in environmental risk assessments, even for reducing the uncertainty in site-specific Kd values.     

南京地区农田土壤和蔬菜重金属污染状况研究

采集了南京市5县4郊5个环境单元（矿冶区、交通干线、工厂周边、污灌地、农产品基地）共100个样点的农田土壤及部分蔬菜样品,测定了重金属（Pb、Cu、Zn、Cd）的质量分数。结果表明,土壤Pb、Cu、Zn、Cd 质量分数的变化范围分别为26.1~4 138.8、16.5 ~3 375.1、46.0~3 587.6、0.09~17.61 mg/kg。不同功能区土壤重金属含量存在明显差异,以矿区周边农田污染最为严重,其次为污灌地和公路沿线农田, 部分农产品基地存在轻度Cd污染,工厂周边农田土壤污染相对较小。19个样点的青菜地上部重金属Pb、Cu、Zn、Cd质量分数的变化范围分别为0.11~7.11、5.04~76.42、36.8~364.3、0.04~2.96 mg/kg,同样以矿区周边污染农田的青菜样本重金属含量最高。青菜重金属含量与土壤重金属生物有效性含量和总量之间呈极显著相关。不合理的矿业开采和冶炼是导致南京地区农田土壤和蔬菜重金属污染的重要原因。     

Retention of estrogenic steroid hormones by selected New Zealand soils

We performed batch sorption experiments for 17beta-estradiol (E2) and 17alpha-ethynylestradiol (EE2) on selected soils collected from dairy farming regions of New Zealand. Isotherms were constructed by measuring the liquid phase concentration and extracting the solid phase with dichloromethane, followed by an exchange step, and analysis by HPLC and UV detection. The corresponding metabolite estrone, (E1) formed during equilibration of E2 with soil was taken into account to estimate the total percentage recoveries for the compounds, which ranged from 47-105% (E2 and E1) and 83-102% (EE2). Measured isotherms were linear, although some deviation from linearity was observed in a few soils, which was attributed to the finer textured particles and/or the allophanic nature of the soils having high surface area. There was a marked difference in K(d)(eff) (effective distribution coefficient) values for E2 and EE2 among the soils, consistent with the soils organic carbon content and ranged from 14-170 L kg(-1) (E2), and 12-40 L kg(-1) (EE2) in the soils common for both compounds. The sorption affinity of hormones in the soils followed an order: EE2相似文献   

Impacts of sewage irrigation on heavy metal distribution and contamination in Beijing, China

A potential hazard to Beijing was revealed due to the accumulation trend of heavy metals in agricultural soils with sewage irrigation, which results in metal contamination and human exposure risk. Samples including soils and plants were collected to assess the impacts of sewage irrigation on the irrigated farming area of Beijing. Concentrations of the five elements Cd, Cr, Cu, Zn, and Pb were determined in samples to calculate the accumulation factor and to establish a basis for environmental protection and the suitability of sewage irrigation for particular land use in the urban-rural interaction area of Beijing. Using reference values provided by the Beijing Background Research Cooperative Group in the 1970s, the pollution load index (PLI), enrichment factor (EF), and contamination factor (CF) of these metals were calculated. The pollution load indices (sewage irrigation land 3.49) of soils indicated that metal contamination occurred in these sites. The metal enrichment (EF of Cd 1.8, Cr 1.7, Cu 2.3, Zn 2.0, Pb 1.9) and the metal contamination (CF of Cd 2.6, Cr 1.5, Cu 2.0, Zn 1.7, Pb 1.6) showed that the accumulation trend of the five toxic metals increased during the sewage irrigation as compared with the lower reference values than other region in China and world average, and that pollution with Cd, Cu, Zn, and Pb was exacerbated in soils. The distributions of these metals were homogeneous in the irrigation area, but small-scale heterogeneous spatial distribution was observed. Irrigation sources were found to affect heavy metal distributions in soils. It was suggested that heavy metal transfer from soils to plants was a key pathway to human health exposure to metal contamination. However, with the expansion of urban areas in Beijing, soil inhalation and ingestion may become important pathways of human exposure to metal contamination.     

Erosion of atmospherically deposited radionuclides as affected by soil disaggregation mechanisms

The interactions of soil disaggregation with radionuclide erosion were studied under controlled conditions in the laboratory on samples from a loamy silty-sandy soil. The fate of 134Cs and 85Sr was monitored on soil aggregates and on small plots, with time resolution ranging from minutes to hours after contamination. Analytical experiments reproducing disaggregation mechanisms on aggregates showed that disaggregation controls both erosion and sorption. Compared to differential swelling, air explosion mobilized the most by producing finer particles and increasing five-fold sorption. For all the mechanisms studied, a significant part of the contamination was still unsorbed on the aggregates after an hour. Global experiments on contaminated sloping plots submitted to artificial rainfalls showed radionuclide erosion fluctuations and their origin. Wet radionuclide deposition increased short-term erosion by 50% compared to dry deposition. A developed soil crust when contaminated decreased radionuclide erosion by a factor 2 compared to other initial soil states. These erosion fluctuations were more significant for 134Cs than 85Sr, known to have better affinity to soil matrix. These findings confirm the role of disaggregation on radionuclide erosion. Our data support a conceptual model of radionuclide erosion at the small plot scale in two steps: (1) radionuclide non-equilibrium sorption on mobile particles, resulting from simultaneous sorption and disaggregation during wet deposition and (2) later radionuclide transport by runoff with suspended matter.     

Metal contamination of farming soils affected by industry

The contents of nine elements (As, Cd, Cr, Cu, Hg, Ni, Pb, Sb and Zn) have been assayed in the farming soils of Suszec commune (southern Poland). This area is affected by the main industrial centre of Poland (the Upper Silesian Industrial Region), the Czech Republic (Trzyniec smelter) and local contamination sources (coal mine). The contamination of the soils was assessed on the basis of geoaccumulation index, enrichment factor, contamination factor and degree of contamination. The tests revealed elevated contents of cadmium, lead, arsenic, antimony and mercury. The contents of the other elements were similar to the levels in the Earth's crust or pointed to metal depletion in the soil (EF<1).     

Effect of soil properties on arsenic fractionation and bioaccessibility in cattle and sheep dipping vat sites

Historical use of high arsenic (As) concentrations in cattle/sheep dipping vat sites to treat ticks has resulted in severe contamination of soil and groundwater with this Group-A human carcinogen. In the absence of a universally applicable soil As bioaccessibility model, baseline risk assessment studies have traditionally used the extremely conservative estimate of 100% soil As bioaccessibility. Several in-vitro, as well as, in-vivo animal studies suggest that As bioaccessibility in soil can be lower than that in water. Arsenic in soils exists in several geochemical forms with varying degree of dissolution in the human digestive system, and thus, with highly varying As bioaccessibility. Earlier batch incubation studies with As-spiked soils have shown that As bioaccessibility is a function of soil physicochemical properties. We selected 12 dipping vat soils collected from USA and Australia to test the hypothesis that soil properties exert a significant effect on As bioaccessibility in As-contaminated sites. The 12 soils varied widely in terms of soil physico-chemical properties. They were subject to an As sequential fractionation scheme and two in-vitro tests (IVGS and IVGIA) to simulate soil As bioavailability in the human gastrointestinal system. Sequential As fractionation results showed that the majority of the As measured in the dipping vat soils resided either in the Fe/Al hydroxide fraction, or the Ca/Mg fractions, or in the residual fraction. Water-extractable As fraction of the 12 soils was typically <10% of the total, reaching values up to 23%, indicating minimal leaching potential, and hence, lower risk of As-contamination from exposure to groundwater, typically used as drinking water in many parts of the world. Partial individual correlations and subsequent multiple regression analyses suggested that the most significant soil factors influencing As bioaccessibility were total Ca+Mg, total P, clay content and EC. Collectively, these soil properties were able to explain 85 and 86% of the variability associated with the prediction of bioaccessible As, using IVGS and IVGIA in-vitro tests, respectively. This study showed that specific soil properties influenced the magnitude of soil As bioaccessibility, which was typically much lower than total soil-As concentrations, challenging the traditional risk assessment guideline, which assumes that soil As is 100% bioaccessible. Our study showed that total soil As concentration is unlikely to provide an accurate estimate of human health risk from exposure to dipping vat site soils.     

Experimental values for 241Am and 239+240Pu Kd's in French agricultural soils

Experiments resulted in determination of K(d) values for (241)Am and (239+240)Pu in 6 soils whose characteristics are representative of agricultural soils found around French nuclear power plant sites. These experiments were conducted in stirred batch reactors and the sorption isotherms were plotted. For americium, the experimental K(d) values varied from 60 to 4000 Lkg(-1) (d.w.) and correlated well with soil pH, K(d) increased with increasing pH. As regards plutonium, the experimental K(d) values varied between 300 and 9600 Lkg(-1) and decreased with increasing total sand content. The estimation of the total residence time determined by using a particular and experimentally refined value for K(d)-with a model similar to those currently used for impact assessments-illustrates the importance of establishing values that are better suited to specific soils than generic values. Lastly, depending on the type of evaluation envisioned, it might be important to look for a specific value of K(d)-and even modelling-more suited to the specificity of the scenario studied, by performing more complex, or even in situ, experiments.     

A flow system for the determination of metal speciation in soil by sequential extraction

A flow extraction system with on-line and off-line flame atomic absorption spectrometric (FAAS) detection was developed to speed up, facilitate, and improve the accuracy of sequential extraction for metal speciation in solid materials. A flow extraction system with off-line detection was more advantageous than the on-line detection. In the proposed system, extraction was performed in a closed extraction chamber where extractants were flowing through sequentially. The extract from each extraction was collected in 4-10 fractions to obtain a total of approximately 180 ml for subsequent FAAS determination. The system is simple, easy to construct and operate. It has less risk of contamination and human error. A widely used three-step sequential extraction scheme was used to evaluate the novel system by analyzing Ca, Fe, Mn, Cu, and Zn in a certified reference material. The extraction time for three-step sequential extraction of soil sample was 4 h. The analytical results for Ca, Fe, Mn, Cu, and Zn of a soil certified reference material using the proposed system were compared with those of the conventional batch extraction.     

上海市崇明岛公路两侧土壤重金属污染研究

采集了上海市崇明岛陈海、北沿公路两侧土壤和灰尘样品270余个,测定了样品的Pb、Cd、Cu、 Zn和Cr重金属含量。结果表明,陈海和北沿公路两侧土壤重金属Pb、Cd、Cu、 Zn和Cr的平均含量达到277、0279、258、918和776 mg/kg,土壤Cd污染较严重。采集的路面灰尘样品Pb、Cd、Cu、 Zn和Cr的平均含量达到512、049、489、209和970 mg/kg,超过土壤背景值2~4倍,是土壤重金属的主要二次污染源。公路防护林体系较差的北沿公路路侧土壤纵向剖面（垂直于公路走向）重金属含量随距路肩距离增加呈指数下降,土壤重金属重污染区在距路肩15 m范围内。防护林体系较完善的陈海公路距路肩15 m范围内土壤重金属污染较小,土壤重金属重污染区出现在距路肩20~50 m范围内。     

Impact of water quality parameters on the sorption of U(VI) onto hematite

In this study, the sorption of U(VI) from aqueous solution on hematite was studied as a function of various water quality parameters such as contact time, pH, ionic strength, soil humic acid (HA) or fulvic acid (FA), solid content and temperature by using a batch technique. The results demonstrated that the sorption of U(VI) was strongly dependent on ionic strength at pH < 6.0, and outer-sphere surface complexation may be the main sorption mechanism. The sorption was independent of ionic strength at pH > 6.0 and the sorption was mainly dominated by inner-sphere surface complexation. The presence of HA/FA increases U(VI) sorption at low pH, whereas decreases U(VI) sorption at high pH. The thermodynamic parameters (ΔH⁰, ΔS⁰, and ΔG⁰) were calculated from the temperature dependent sorption isotherms, and the results suggested that U(VI) sorption was a spontaneous and endothermic process. The results might be important for the application of hematite in U(VI) pollution management.     

A critical review of the bioavailability and impacts of heavy metals in municipal solid waste composts compared to sewage sludge

The content, behaviour and significance of heavy metals in composted waste materials is important from two potentially conflicting aspects of environmental legislation in terms of: (a) defining end-of-waste criteria and increasing recycling of composted residuals on land and (b) protecting soil quality by preventing contamination. This review examines the effects of heavy metals in compost and amended soil as a basis for achieving a practical and sustainable balance between these different policy objectives, with particular emphasis on agricultural application. All types of municipal solid waste (MSW) compost contain more heavy metals than the background concentrations present in soil and will increase their contents in amended soil. Total concentrations of heavy metals in source-segregated and greenwaste compost are typically below UK PAS100 limits and mechanical segregated material can also comply with the metal limits in UK PAS100, although this is likely to be more challenging. Zinc and Pb are numerically the elements present in the largest amounts in MSW-compost. Lead is the most limiting element to use of mechanically-segregated compost in domestic gardens, but concentrations are typically below risk-based thresholds that protect human health. Composted residuals derived from MSW and greenwaste have a high affinity for binding heavy metals. There is general consensus in the scientific literature that aerobic composting processes increase the complexation of heavy metals in organic waste residuals, and that metals are strongly bound to the compost matrix and organic matter, limiting their solubility and potential bioavailability in soil. Lead is the most strongly bound element and Ni the weakest, with Zn, Cu and Cd showing intermediate sorption characteristics. The strong metal sorption properties of compost produced from MSW or sewage sludge have important benefits for the remediation of metal contaminated industrial and urban soils. Compost and sewage sludge additions to agricultural and other soils, with background concentrations of heavy metals, raise the soil content and the availability of heavy metals for transfer into crop plants. The availability in soil depends on the nature of the chemical association between a metal with the organic residual and soil matrix, the pH value of the soil, the concentration of the element in the compost and the soil, and the ability of the plant to regulate the uptake of a particular element. There is no evidence of increased metal release into available forms as organic matter degrades in soil once compost applications have ceased. However, there is good experimental evidence demonstrating the reduced bioavailability and crop uptake of metals from composted biosolids compared to other types of sewage sludge. It may therefore be inferred that composting processes overall are likely to contribute to lowering the availability of metals in amended soil compared to other waste biostabilisation techniques. The total metal concentration in compost is important in controlling crop uptake of labile elements, like Zn and Cu, which increases with increasing total content of these elements in compost. Therefore, low metal materials, which include source-segregated and greenwaste composts, are likely to have inherently lower metal availabilities overall, at equivalent metal loading rates to soil, compared to composted residuals with larger metal contents. This is explained because the compost matrix modulates metal availability and materials low in metals have stronger sorption capacity compared to high metal composts. Zinc is the element in sewage sludge-treated agricultural soil identified as the main concern in relation to potential impacts on soil microbial activity and is also the most significant metal in compost with regard to soil fertility and microbial processes. However, with the exception of one study, there is no other tangible evidence demonstrating negative impacts of heavy metals applied to soil in compost on soil microbial processes and only positive effects of compost application on the microbial status and fertility of soil are reported. The negative impacts on soil microorganisms apparent in one long-term field experiment could be explained by the exceptionally high concentrations of Cd and other elements in the applied compost, and of Cd in the compost-amended soil, which are unrepresentative of current practice and compost quality. The metal contents of source-segregated MSW or greenwaste compost are smaller compared to mechanically-sorted MSW-compost and sewage sludge, and low metal materials also have the smallest potential metal availabilities. Composting processes also inherently reduce metal availability compared to other organic waste stabilisation methods. Therefore, risks to the environment, human health, crop quality and yield, and soil fertility, from heavy metals in source-segregated MSW or greenwaste-compost are minimal. Furthermore, composts produced from mechanically-segregated MSW generally contain fewer metals than sewage sludge used as an agricultural soil improver under controlled conditions. Consequently, the metal content of mechanically-segregated MSW-compost does not represent a barrier to end-use of the product. The application of appropriate preprocessing and refinement technologies is recommended to minimise the contamination of mechanically-segregated MSW-compost as far as practicable. In conclusion, the scientific evidence indicates that conservative, but pragmatic limits on heavy metals in compost may be set to encourage recycling of composted residuals and contaminant reduction measures, which at the same time, also protect the soil and environment from potentially negative impacts caused by long-term accumulation of heavy metals in soil.     

Adsorption models of Cs radionuclide and Sr (II) on some Egyptian soils

Distribution of cesium (¹³⁴Cs and ¹³⁷Cs) and strontium (Sr-II) between soil/water phases depends on many factors such as concentration of these ions between phases, the cation exchange capacity (CEC) of the soil as well as its clay content, chemical composition (especially Na, K, Ca, and Mg ions), grain size distribution, calcite, iron oxide content, and organic coatings. Distribution coefficients (Kd) of cesium (labeled with ¹³⁷Cs) and strontium were measured on the grain size distributions ≥32 μm of four soil samples. These soils were obtained from four different locations within Inshas site in Egypt and three groundwater samples were obtained from the same site locations. X-ray diffraction showed that the soil samples consisted mainly of quartz mixed with the minor amounts of kaolonite and clay minerals. Sorption experiments were carried out at strontium aqueous concentrations range 10⁻⁷ to 10⁻⁴ mol l⁻¹. The CEC and Kds for cesium and strontium were measured at the same metal concentrations range. Distribution coefficients of cesium were found to be influenced by the composition of the soil, while the distribution coefficients of strontium were found to depend on calcium concentrations in the soil/groundwater system. The aim of this study was to determine the safety assessment of disposal ¹³⁷Cs radionuclide and Sr(II) in the aquifer regions inside the Inshas site. Sequential extraction tests showed that, strontium was associated with the carbonate fractions and majority of cesium was sorbed on the iron oxides and the residue.     

Cesium and strontium sorption by selected tropical and subtropical soils around nuclear facilities

The dynamics of Cs and Sr sorption by soils, especially in the subtropics and tropics, as influenced by soil components are not fully understood. The rates and capacities of Cs and Sr sorption by selected subtropical and tropical soils in Taiwan were investigated to facilitate our understanding of the transformation and dynamics of Cs and Sr in soils developed under highly weathering intensity. The Langmuir isotherms and kinetic rates of Cs and Sr sorption on the Ap1 and Bt1 horizons of the Long-Tan (Lt) and the A and Bt1 horizons of the Kuan-Shan (Kt), Mao-Lin (Tml) and Chi-Lo (Cl) soils were selected for this study. Air-dried soil (<2 mm) samples were reacted with of 7.5 × 10⁻⁵ to 1.88 × 10⁻³ M of CsCl (pH 4.0) or 1.14 × 10⁻⁴ to 2.85 × 10⁻³ M of SrCl₂ (pH 4.0) solutions at 25 °C. The sorption maximum capacity (q_m) of Cs by the Ap1 and Bt1 horizons of the Lt soil (62.24 and 70.70 mmol Cs kg⁻¹ soil) were significantly (p < 0.05) higher than those by the A and Bt1 horizons of the Kt and Cl soils (26.46 and 27.49 mmol Cs kg⁻¹ soil in Kt soil and 34.83 and 29.96 mmol Cs kg⁻¹ soil in Cl soil, respectively), however, the sorption maximum capacity values of the Lt and Tml soils did not show significant differences. The amounts of pyrophosphate extractable Fe (Fe_p) were correlated significantly with the Cs and Sr sorption capacities (for Cs sorption, r² = 0.97, p < 1.0 × 10⁻⁴; for Sr sorption, r² = 0.82, p < 2.0 × 10⁻³). The partition coefficient of radiocesium sorbed on soil showed the following order: Cl soil ? Kt soil > Tml soil > Lt soil. It was due to clay minerals. The second-order kinetic model was applied to the Cs and Sr sorption data. The rate constant of Cs or Sr sorption on the four soils was substantiality increased with increasing temperature. This is attributable to the availability of more energy for bond breaking and bond formation brought about by the higher temperatures. The rate constant of Cs sorption at 308 K was 1.39-2.09 times higher than that at 278 K in the four soils. The activation energy of Cs and Sr sorbed by the four soils ranged from 7.2 to 16.7 kJ mol⁻¹ and from 15.2 to 22.4 kJ mol⁻¹, respectively. Therefore, the limiting step of the Cs⁺ or Sr²⁺ sorption on the soils was diffusion-controlled processes. The reactive components, which are significantly correlated with the Langmuir sorption maxima of Cs and Sr by these soils, substantially influenced their kinetic rates of Cs and Sr sorption. The data indicate that among components of the subtropical and tropical soils studied, short-range ordered sesquioxides especially Al- and Fe-oxides complexed with organics play important roles in influencing their capacity and dynamics of Cs and Sr sorption.