An integrative method to quantify contaminant fluxes in the groundwater of urban areas

Background, Aims, and Scope  Groundwater in urban areas is often contaminated and emission sources can be located close to groundwater wells. The delineation of contaminant plumes is difficult because of the various potential emission sources. Thus, detection, quantification and remediation of contaminated sites in a city need more integrative approaches. Methods  A method has been developed which allows quantification of mass fluxes of contaminants in groundwater between control planes. Budget zones along the flow path are defined to calculate a contaminant balance and to quantitatively reveal input areas. Concentrations and water budgets are used to calculate mass balances for each contaminant. The city of Darmstadt (Germany) was chosen to evaluate the method. Results  The groundwater monitoring wells (GMWs) upstream of the city showed anthropogenically superposed background values for all naturally occurring inorganic species. The contaminant concentrations increased in the city (probably influenced by road traffic, gas stations, leaking sewers, etc.). Downstream from the city, concentrations usually decreased. Organic compounds typical for urban environments, such as polycyclic aromatic hydrocarbons (PAH), locally exceeded drinking water regulations. In GMWs with high concentrations of organic contaminants in the city or downstream from industrial areas, a significant increase in Fe²⁺ and Mn²⁺ could be observed, in some cases coinciding with a decrease in NO₃, SO₄ and an increase in NH₄. Discussion  For typical urban contaminants, a positive budget was calculated in several zones, which shows that emissions from urban sources are reaching the groundwater. Negative budgets can be mainly explained with diving plumes and degradation. The input calculated from the individual budget zones is usually higher than the input estimated from urban emissions. Differences between the calculated and the estimated input can be explained with additional sources or (bio)degradation processes. Conclusions  It was confirmed that high concentrations of contaminants do not necessarily correlate with high fluxes. Integrative approaches can reveal areas of high contaminant mass input. The results obtained with the new method are plausible compared to the land use and the estimated urban input. The concentration pattern of Fe²⁺, Mn²⁺, SO₄ and NO₃ is partly due to natural processes, triggered by the degradation of organic matter and organic contaminants. Recommendations  Since this method includes mass balances and flux calculations, avoiding an overestimation of single point contaminant concentration, it is recommended to use this approach to quantify groundwater contamination in cities. Further research is focusing on the role of urban soils as natural reservoirs for the input of contaminants.     

Feasibility of Field Portable Near Infrared (NIR) Spectroscopy to Determine Cyanide Concentrations in Soil

Vicinities of manufactured gas plants were often contaminated with solid iron?Ccyanide complexes as a result of the coal gasification process. During the remediation of affected soils, knowledge about contaminant concentrations is crucial, but laboratory methods are often expensive and time consuming. Rapid and non-destructive field methods for contaminant determination permit an analysis of large sample numbers and hence, facilitate identification of ??hot spots?? of contamination. Diffuse near infrared reflectance spectroscopy has proven to be a reliable analytical tool in soil investigation. In order to determine the feasibility of a Polychromix Handheld Field Portable Near-Infrared Analyzer (FP NIR), various sample preparation methods were examined, including homogenizing, sieving, drying, and grinding. Partial least squares calibration models were developed to determine near infrared (NIR) spectral responses to the cyanide concentration in the soil samples. As a control, the contaminant concentration was determined using conventional flow injection analysis. The experiments revealed that portable near-infrared spectrometers could be a reliable device for detecting cyanide concentrations >2,400?mg?kg^?1 in the field and >1,750?mg?kg^?1 after sample preparation in the laboratory. We found that portable NIR spectrometry cannot replace traditional laboratory analyses due to high limits of detection, but that it could be used for identification of contamination ??hot spots??.     

Evaluation of nitrate analysis using test strips: Comparison with two analytical laboratory methods

Abstract

Nitrate remains a contaminant of concern for users of well water. Well‐water evaluation, either to assess nitrate contamination or to evaluate sites prior to including them in a larger water quality study, often involves costly laboratory analysis. A cost effective alternative to laboratory analysis are dip‐style test strips. However, the accuracy of these types of products must be reliable, as failure to identify the contaminant may, for example, persuade a homeowner to neglect to have a potential problem further investigated. The testing of nitrate using such strips typically involves dipping the strip into the water sample and reading the color development after a specific period of time. The color development is then compared to a color scale which corresponds to concentration provided with the test. The results of these types of analysis are especially open to interpretation by the evaluator of the results. An experiment was conducted to evaluate test strips in which individuals or “readers” tested water samples collected in the field and nitrate standards prepared in the laboratory with nitrate test strips. The results obtained by the “readers” were compared to analysis of nitrate by high performance liquid chromatography and colorimetric analysis using a colorimetric ion analyzer. There was a good agreement between the “readers” results and the analytical methodologies used. Use of the test strips by non‐technical persons, such as homeowners, could provide an accurate determination of nitrate in well water without the expense involved in a detailed laboratory analysis. The test strips can also be relied upon to accurately determine nitrate concentration when screening wells prior to designing field experiments.     

The composition of precipitation at Snoqualmie Pass and Stevens Pass in the Central Cascades of Washington state

Bulk precipitation samples were collected weekly during the winters of 1984 and 1985 at two high elevation sites in the Washington Cascades. The Puget basin, west and upwind of the Cascade sites, includes an urban industrialized region with a variety of area and point sources of acidic oxides. The precipitation was found to be low in contaminant content with SO₄ ⁼ and NO₃ ^? concentrations as low or lower than those reported for remote pristine stations in the US or elsewhere. It is suggested that the reduced contaminant levels result from an interplay of the meteorological and washout factors unique to the region.     

Coastal Pollution and Potential Biomonitors of Metals in Mauritius

Contaminant metals are potentially toxic, accumulate in the sediment, are bioconcentrated by organisms and may cause health problems to humans via the food chain. Discharge of industrial wastewaters and untreated sewage pose a particularly serious threat to the coastal environment of Mauritius, but very little information exists on contaminant metals. This study aimed principally to assess such contamination by (i) reviewing available data, (ii) examining the results of metal (Cd, Cu, Cr, Pb and Zn) analysis in (a) seawater, sediment and biota from an island-wide survey of 20 sites in 1999–2000, (b) seawater from a water quality survey (high tide and low tide) in 2003 of a 10 km stretch of sewage-impacted coast. UNEP reference methods were used for sample collection and processing, and metal analysis was perfomed by flame atomic absorption spectrophotometry (AAS). Results were compared with established guidelines and data reported from elsewhere, and examined for suitable plant and animal species as biomonitors. The pioneering study by SOGETI (1995) provided indications of high marine sediment contamination in Mauritius compared to data reported from elsewhere. The 1999–2000 islandwide survey indicated even higher sediment contamination, namely at hotspots, requiring the use of sediment quality guidelines (SQG) for monitoring and assessment. Maximum metal concentrations from these two studies were as follows: 736 μgg^?1 Zn, 329 μgg^?1 Mn, 98.1 μgg^?1 Pb, 93.38 μgg^?1 Cu, 91.39 μgg^?1 Cr, 65.53 μgg^?1 Sn and 55.01 μgg^?1 Cd. Seawater contamination corresponded closely to the pattern of sediment contamination, both showing a downstream and away-from-the-outfall gradient. Applicable guidelines for seawater were exceeded at more than 50% of the sites around Mauritius with maximum concentrations of Cr, Cu, Zn, Pb and Cd as follows: 0.41, 0.352, 0.312, 0.247 and 0.232 mgl^?1, respectively. Maximum concentrations of Cu, Cd, Zn, Pb and Cr along the sewage-impacted shoreline occurred during low tide as follows: 0.454, 0.329, 0.259, 0.138 and 0.123 mgl^?1, respectively. The recommended limits for Cu, Cd and Zn were exceeded in all the samples. High tissue accumulation by marine biota corresponded to high levels of seawater and sediment contamination at hotspots. Species showing the highest potential as biomonitors (namely Ulva lactuca, Enteromorpha ramulosa, Crassostrea cuculatta, Isognomon isognomon and Echinometra mathaei) were identified based on their common occurrence, high bioconcentration potential and successful utilization in studies elsewhere. Enhanced levels of contaminant metals were recorded and suitable biomonitors were identified. It is advocated that a rigorous use of the suite of biomonitors proposed in this study and others later will allow identification of the different metal sources as well as provide an improved assessment of the magnitude of metal contamination in the coastal marine environment of Mauritius.     

Hydroxyl Radical Generation and Contaminant Removal from Water by the Collapse of Microbubbles Under Different Hydrochemical Conditions

The present study addresses the mechanism of hydroxyl radical (·OH) generation by the collapse of microbubbles in water solution. The influence of gas supply and flow rate, solution pH, and ionic strength on the aeration efficiency, free radical generation, and contaminant removal (take methylene blue as an example) are elucidated. The results showed that the degradation rate of methylene blue by ·OH increased with flow rate as well as in acidic or alkaline solutions compared to that in neutral conditions. ·OH was shown to be produced by the reaction between protons and oxygen radicals generated by the decomposition of O₂ rather than water molecules. A greater concentration of O₂ or H⁺ thus promoted the reaction, resulting in effective removal at a high flow rate or low pH. Nevertheless, there was considerable methylene blue removal at high pH, driven by the production of the dye cation through the dissociation of methylene blue and the high electronegativity of bubbles at high pH, thus enhancing interface adsorption and degradation, as well as by the high ionic strength of the solution helping to generate ultrafine bubbles and maintaining them through ionic shielding. The current work provides useful insights into the application of microbubble as a promising technique.     

三深度土壤水分传感器的研制及试验

针对当前植物根区不同深度下土壤含水量测量存在的传感器安装困难、对原位土壤扰动大以及传感器间一致性差等问题,该文基于阻抗法设计了一种三深度土壤水分传感器。该传感器不仅可以同时测量3个不同深度的土壤含水量,并且在安装时对原位土壤扰动极小。试验标定结果显示,该传感器具有较高的精度,所测的土壤含水量与烘干法所得的实际含水量非常吻合,决定系数R2和均方根误差(RMSE,root mean square error)分别达到0.996和0.013 cm3/cm3;传感器可适用于多种不同质地的土壤,在3种不同质地土壤中的输出灵敏度均大于1V/(cm3/cm3)。传感器的输出与土壤体积含水量呈现良好的线性关系,对黏土、砂土及壤土的决定系数R2分别达到0.983、0.965和0.975;土壤水分入渗试验结果进一步表明,该传感器性能良好,3个不同深度的传感器电极具有较高的一致性,在壤土和砂土样本中3个深度传感器电极的输出,相对误差分别小于2%和5%。     

利用自制压差装置测定水样含沙量的方法研究

[目的] 开展基于压差测定水样含沙量的方法研究,旨在寻求一种新方法以实现含沙量在野外的快速准确测定。[方法] 试验基于压差原理,选取4种土壤(土、风沙土、盐碱土与水稻土)分别预制11个含沙量梯度的含沙水样,使用数字式压差计测定含沙水样压强与大气压强之间的差值(简称压差),建立含沙量与压差的函数关系式。[结果] 含沙量与压差在0.01的水平下呈极显著线性正相关;对于其中3种含沙水样(土水样、盐碱土水样与水稻土水样),压差结合理论公式计算含沙量的方法具有可行性,最大相对误差绝对值小于15%,但不适用于风沙土水样。风沙土水样含沙量的测定最大相对误差绝对值高达39%。因此,为了缩小误差,试验通过测定纯水与含沙量为500 kg/m³的水样压差建立修正方程,再结合测定的压差值计算含沙量,发现最大相对误差绝对值小于8%。[结论] 基于压差测定水样含沙量的方法能较为准确地测定水样含沙量,可为水土保持监测等领域在野外便捷测定含沙量提供一种新思路与方法。     

Heavy Metal Concentration Survey in Soils and Plants of the Les Malines Mining District (Southern France): Implications for Soil Restoration

Mining activities generate spoils and effluents with extremely high metal concentrations of heavy metals that might have adverse effects on ecosystems and human health. Therefore, information on soil and plant metal concentrations is needed to assess the severity of the pollution and develop a strategy for soil reclamation such as phytoremediation. Here, we studied soils and vegetation in three heavily contaminated sites with potential toxic metals and metalloids (Zn, Pb, Cd, As, TI) in the mining district of Les Malines in the Languedoc region (southern France). Extremely high concentrations were found at different places such as the Les Aviniéres tailing basins (up to 160,000 mg kg^?C1 Zn, 90,000 mg kg^?C1 Pb, 9,700 mg kg^?C1 of As and 245 mg kg^?C1 of Tl) near a former furnace. Metal contamination extended several kilometres away from the mine sites probably because of the transport of toxic mining residues by wind and water. Spontaneous vegetation growing on the three mine sites was highly diversified and included 116 plant species. The vegetation cover consisted of species also found in non-contaminated soils, some of which have been shown to be metal-tolerant ecotypes (Festuca arvernensis, Koeleria vallesiana and Armeria arenaria) and several Zn, Cd and Tl hyperaccumulators such as Anthyllis vulneraria, Thlaspi caerulescens, Iberis intermedia and Silene latifolia. This latter species was highlighted as a new thallium hyperaccumulator, accumulating nearly 1,500 mg kg^?C1. These species represent a patrimonial interest for their potential use for the phytoremediation of toxic metal-polluted areas.     

Impact of coal combustion waste on the microbiology of a model aquifer

The effects of water infiltration into an alkaline coal combustion waste burial site on the chemical and microbiological aspects of a meso-scale (2.44 m diameter × 4.6 m, height, 65 tonne) model aquifer were analyzed. The spatial and temporal effects of the alkaline leachate on microbial activity, numbers and diversity were examined in the model and compared with uncontaminated control materials. Within the saturated zone below the waste there was a pH gradient from 12.4 at the water table, immediately below the waste, to 6.0 at 3.5 meters from the waste, and elevated levels of arsenic and strontium in the pore waters. Microtox testing of the contaminated pore waters indicated high toxicity (a gamma value of 1 at dilutions of 45 to 110 fold). The leachate contamination was associated with a reduction in bacterial [³H] leucine incorporation from a high of 267 fmol g^?1 h^?1 in sediments below the contaminant plume to undetectable in the contaminated zone. In comparison, leucine incorporation rates in control column sediments were 899 fmol g^?1 h^?1. Similar toxic effects were evident in reduced total direct and culturable counts of bacteria. Observations also indicated a reduction in microbial diversity and development of alkaline-tolerant microbial communities. These results indicated that any failure of confinement technologies at disposal sites would adversely affect both the chemistry and microbiology of the underlying saturated zone.     

Parameterization of the MACRO model to represent leaching of colloidally attached inorganic phosphorus following slurry spreading

Abstract. The dual porosity soil water and contaminant transport model MACRO was tested for its suitability to represent water flows and leaching of phosphorus (P) through field drains following spreading of slurry. These flows are characterized by very high loadings of P, including a high proportion in colloidally attached form, for about one week following winter spreading of slurry, followed by quite a rapid decline to the low background level. Use was made of the option in MACRO for representing colloid facilitated contaminant transport. The model simulates transport through macropores and soil matrix pores (micropores) of contaminant carrying colloids, as well as trapping of colloids by straining and filtration using an adaptation of standard filtration equations. Calibration involved selecting soil hydraulic parameters, colloid filtration coefficients and P sorption characteristics for two soils from measured and literature values. Both P in solution and P attached to colloids were represented in simulated outputs. Reasonable agreement was found between simulated and measured water and leached P flows. Work with the model suggests that macropore flow through the soil to field drains of colloidally transported P is an important component of water pollution associated with slurry spreading     

Modeling Water Quality Impacts of Petroleum Contaminated Soils in a Reservoir Catchment

Soil contamination due to spills or leaks of crude oils andrefined hydrocarbons is a common problem. Estimation of spillvolume is a crucial issue in order to determine the expectedcontaminating life span of contaminated soils. The directprocedure to determine the amount of hydrocarbon in soil is to measure the concentration of total petroleum hydrocarbon (TPH) in soil samples. The primary objective of this study was toassess the potential effects of oil contaminated soils on thewater quality of Devegecidi dam reservoir. For this purpose,limited spill data available were evaluated and soil samplingstudies were conducted in the Beykan oil field to analyze forTPH on oil contaminated soils. Available spill and measured soilTPH data were used in a subsequent modeling study to assess thereservoir water quality impacts due to dissolved mass leachingfrom hydrocarbon contaminated soils. Evaluation of availablespill data between 1989 and 1995 revealed that a total of 252recorded spills resulted in a net spill of 395 tons. The majortypes of oil spills were identified as well heads (WH), returnlines/flow lines (RL/FL), and power oil lines (POL). A total of211 soil samples was collected at selected well heads andanalyzed for TPH in the laboratory. TPH results revealed aconcentration range between 600 and 115 500 mg kg^-1 with a meanconcentration of 20 300 mg kg^-1. Modeling studies focused onbehavior assessment and involved two major components. The firstcomponent is a soil-leaching submodel for estimating theleachate concentration and contaminant mass leaching out of thecontaminated soil body. The second component is a reservoirwater quality submodel assuming complete-mix conditions forestimating the changes of hydrocarbon concentration in thereservoir water as a function of time. These two components arecoupled via a mass inflow term present in the reservoir waterquality model, accounting for contaminant mass loadingcontributed by the leaching of contaminated soil. Simulation runs performed under conservative conditions assuming an annualaverage oil spill volume of 95 tons and the minimum reservoirvolume of 7.3 × 10⁶ m³ revealed that there isno imminent threat to reservoir water quality from the dissolved phase contaminants soils. Limited amount of availablemeasurements of TPH concentrations in soil samples and benzeneconcentrations in reservoir water samples supported model results.     

Initial sample extract stock concentration affects in vitro bioassay-based toxicological risk characterization

Purpose

Bioassays have become an alternative for sediment risk profiling, including potential compliance with sediment quality criteria (SQC). In vitro functional bioassays have evolved through standardization and validation towards a confident toxicological hazard estimate of sediments. Sample preparation is a key aspect for the improvement of bioassays. It is a standard practice to use a high single-stock concentration of extracts to further dilute test concentrations from and carry out the analysis. This study was carried out to demonstrate that high a contaminant load in a sediment extract (>20 g sediment equivalents (SEQ) ml^?1) oversaturates solubility in carrier solvents and overloads the clean-up columns, potentially resulting in an under- or overestimation of the quantified dioxin-like toxic potency.

Materials and methods

Cleaned nonpolar sediment extracts were prepared from samples collected from various locations in Luxembourg. The influence on the quantified toxic potency of the initial stock concentration, sonication assisted dissolution and exposure period in an in vitro bioassay for dioxin-like toxic potency (Bio-TEQ) was evaluated, as well as its impact on the sediment risk characterization according to SQC.

Results and discussion

Stock sonication before serial dilution strongly reduced the standard variation of the outcomes. Higher initial stock concentrations (>20 g SEQ ml^?1 for contaminated sediments) produced significantly lower Bio-TEQs g SEQ^?1 compared to those obtained with initial stock concentrations of 2 g SEQ ml^?1, probably due to solvent oversaturation. An initial stock concentration of 2 g SEQ ml^?1 is low enough to prevent mis-estimation, but 20 or even 200 g SEQ ml^?1 might be used when quantification of Bio-TEQ is required. The overload of extract on clean-up columns caused an overestimation of the dioxin-like potency probably due to PAH-induced false-positive responses.

Conclusions

Higher contaminant load in the initial extracts from sediments affects the reliability of in vitro Bio-TEQ sediment quantification. Advice is given on how to avoid underestimation because of extract oversaturation, avoid overestimation because of overload of clean-up columns and reduce variability by applying sonication in standard testing protocols for risk characterization and quantification of the sample’s toxic potency. Taking into account the new aspects revealed in this study, in addition to important issues for quality control that are already included, the in vitro bioassays based on Bio-TEQs can be applied in a comprehensive monitoring program to determine whether sediments comply with health and safety standards for humans and the environment.     

An electrohydrodynamic technique for removal of moisture from soil samples

Abstract

Removal of moisture from soil is of great importance in research, and any attempt in improving the existing soil drying techniques would be desirable. Evaporation rates of water from six soil samples of varying organic matter content were determined gravimetrically while exposed simultaneously to bipolar ions produced by corona electrodes and a thallium‐204 beta‐ray source. These devices produced ion fluxes of 2.63 × 10¹² positive and 2.68 × 10¹² negative ions cm^‐2 s^‐1 in air at the soil surface. Argon (A), dry air, and nitrogen (N) gases were used as ionization media for moisture loss studies. The rate of moisture loss was found to be the lowest in N. The water vapour fluxes from the exposed soil samples were enhanced by a factor of at least three compared to control samples under ambient conditions.     

Comparability of and Alternatives to Leaching Tests for the Assessment of the Emission of Inorganic Soil Contamination (11 pp)

Goal, Scope and Background

The suitability of leaching tests for the assessment of soil water concentrations is a controversial issue. The aim of this paper is to review and critically discuss the applicability and comparability of leaching tests in the scope of groundwater risk assessment of inorganic contamination and to discuss soil water sampling methods as alternative.

Main Features

First, the theoretical background of leaching tests and the main leaching controlling parameters (pH, redox, ionic strength, reaction kinetics, surface, and speciation) are discussed. Experience with common batch leaching tests (the German DEV S4 test (S4), saturation soil extraction (SSE), ammonia nitrate extraction (ANE), and pHstatic tests) are compiled and an emphasis is set on the comparability of the results of batch leaching tests. Additionally, the comparability between batch tests and column tests is discussed and comparison studies are reviewed. As a feasible alternative, soil water sampling strategies (the suction cup method and centrifugation) are outlined.

Results and Conclusions

For an expedient application of leaching tests, it is crucial to identify the main release controlling parameters, which can be both site and contaminant specific. Possible controlling parameters are, for example, pH, redox conditions, specific surface area of the investigated material, liquid to solid-ratio, ionic strength, cation exchange capacity, DOC, speciation, temperature and contact time. It depends on the release process of the contaminant in the investigated material, which parameters are influencing the release predominantly. The following questions have to be answered: Is the release process availability controlled or solubility controlled and are there kinetic limitations? Suction cups are particularly useful for long-term monitoring. In contrast, centrifugation is a fast and simple method to sample soil water also at larger and heterogeneous sites. SSE or similar batch tests for coarse material are suitable if the soil water cannot be investigated directly. Contaminant concentrations of the SSE fit best to contaminant concentrations in soil water compared to other leaching tests. Concentrations measured with S4 tests are usually significantly lower than in real soil water due to the unrealistically high liquid to solid-ratio. The ANE is used for the evaluation of plant uptake. It does not represent realistic soil water concentrations. Cationic contaminants are usually significantly higher concentrated in ANE eluates. pHstatic tests provide an evaluation of the pH dependency of contaminant release and buffer capacity of the investigated material. It provides indications to release processes and often explains deviations in the results of different leaching tests. Previous practical experience and fundamental research studies show that a conversion of leaching test results, as is proposed by the (already withdrawn) DIN V 19735, is impossible. Correlations of results from different methods, regarding different kinds of materials and different sites, are not significant. This is due to different leaching processes.

Recommendation

. For short-term risk assessment, soil water should be sampled and investigated directly by suction cups (for monitoring purposes) or centrifugation (for inventory purposes). If this is not possible, the SSE or analogous batch tests for coarse material with a narrow L/S ratio should be applied. A suggestion could be a modified saturation soil extraction where a soil column is saturated and the eluate is removed by suction at the bottom of the column. With this method, an unsaturated column test could follow in the same vessel. In order to assess the long-term leaching behavior, total contents of the investigated material have to be taken into account additionally. Furthermore, it is essential to understand the dominant physical and chemical release processes and to figure out the main leaching controlling parameters. Therefore, the following methods are recommended: pHstatic tests at different pH values provide an insight to leaching processes and possible future leaching scenarios. Batch tests similar to the S4 procedure with different L/S ratios are useful to find out whether the release process is solubility or availability controlled. Additionally, this method allows the determination of maximum solubility and maximum availability, respectively. Furthermore, unsaturated column tests provide an insight into leaching processes and releasable amounts even though they require great experimental effort. Other leaching tests like S4 or ANE are not suitable for the estimation of soil water concentrations.     

适用于梯级泵站压力管道的传感器优化布置方法

为解决梯级泵站压力管道传感器优化布置问题,提出一种基于有效独立-总位移法的传感器优化布置方法。该方法针对有效独立法所选测点能量较小的缺陷,将测点的总位移以权重的方式加入传感器优化过程中,并保留有效独立法的优点,最终得到独立性较好且满足能量要求的测点。以景泰压力管道为例,运用该方法进行传感器优化布置,并与传统有效独立法比较,通过模态置信准则、Fisher信息矩阵值、最大奇异值比以及总位移等指标评价2种方法的优劣。结果表明,有效独立-总位移法得到的测点在满足独立性的前提下,增加了测点信息量,可观性更好。优化前后实测数据的比较分析,表明该方案对实际结构检测具有较好的适用性,是一种实用有效的传感器优化布置方法。     

Preconcentration/Cleanup Studies of Tin from Environmental Water Samples by Oxidized Multiwall Carbon Nanotubes Packed Column and its Determination by ETAAS

The use of multiwall carbon nanotubes (MWCNT) as an efficient solid extractor in preconcentration/cleanup studies for tin determination in water samples by electrothermal atomic absorption spectrometry (ETAAS) is proposed. In the proposed method, tin adsorption onto MWCNT was carried out by percolating the solution previously buffered (pH 4.79 with 0.24 mol?L^?1 acetic acid/acetate buffer) at 4.0-mL?min^?1 flow rate, followed by elution with 1.0 mL of 2.7 mol?L^?1 HNO₃. Factors such as sample pH, preconcentration/cleanup flow rate, type and concentration of eluent, and buffer concentration were appraised and optimized from chemometric tools based on fractional factorial design and Doehlert design. A limit of detection of 0.73 ??g?L^?1 and precision (n?=?8) assessed as relative standard deviation of 8.6% and 7.0% for tin concentration of 8.0 and 43.0 ??g?L^?1, respectively, were achieved. Foreign metallic ions (Ni²⁺, Pb²⁺, Co²⁺, Zn²⁺, Cd²⁺, Mn²⁺, and Fe³⁺) were checked as potential interferents, and no interference was observed up to an analyte/interference ratio of 1:10 (m/v). Direct tin determination by ETAAS in water samples containing high salt amount is drastically affected by background signal. However, previous cleanup of sample by MWCNT has promoted a significant improvement and makes the method useful for tin monitoring in water samples (mineral, lake, mine, and natural waters) by ETAAS. Quantitative recovery values ranging from 91.5% to 103.0% attested the applicability of the proposed preconcentration/cleanup for tin determination in water samples.     

Observations of the behaviour of large cores of soil during drainage, and the calculation of hydraulic conductivity

This paper reports observations on the behaviour of large cores of undisturbed clay-loam soil during the drainage of water under an imposed step in potential. Rates of outflow and the matric potential at various points in the core were recorded during drainage. The volumes of ‘macropore-channels’(large, continuous voids) were estimated to be 0.005 m³ m^?3 in a subsoil sample, and 0.026 m³ m^?3 in a topsoil sample from arable land. The calculated values of hydraulic conductivity were found to vary with the size of the step in potential imposed on the sample at the start of each drainage experiment. The available evidence suggested that the apparent K/Ψ_m relationship was influenced by the rate that air could enter the soil to replace water during drainage. The degree of restriction on air movement was affected by the initial drainage behaviour, and this varied with the imposed step in potential.     

Remediation of Perfluorooctane Sulfonate in Contaminated Soils by Modified Clay Adsorbent—a Risk-Based Approach

Perfluorooctane sulfonate (PFOS), which has numerous uses besides being an ingredient in the formulation of aqueous film-forming foams, is considered as an emerging pollutant of increasing public health and environmental concern due to recent reports of its worldwide distribution, environmental persistence and bioaccumulation potential. In an attempt to recommend a ‘risk-based’ remediation strategy, this study investigates the removal of PFOS from impacted waters and fixation of PFOS in impacted soils using a novel modified clay adsorbent (MatCARE?, patent number 2009905953). Batch adsorption tests demonstrated a much faster adsorption kinetics (only 60 min to reach equilibrium) and remarkably higher PFOS adsorption capacity (0.09 mmol g^?1) of the MatCARE? compared to a commercial activated carbon (0.07 mmol g^?1). Treatability studies, performed by treating the PFOS-contaminated soils with the MatCARE? (10 % w/w) and then incubating at 25 and 37 °C temperatures maintaining 60 % of the maximum water holding capacity of the soils for a period of a year, demonstrated a negligible release (water extractable) of the contaminant (only 0.5 to 0.6 %). The fixation of PFOS in soils by the new adsorbent was exothermic in nature. Soils with higher clay and organic matter content, but lower pH values, retained PFOS to a much greater extent. A cost analyses confirmed that the MatCARE^TM could be an economically viable option for the ‘risk-based’ remediation of PFOS in contaminated waters and soils.     

Element (Ag, Cd, Cu, Pb, Sb, Tl and Zn), element ratio and lead isotope profiles in a sediment affected by a mining operation episode during the late 19th century

Mining operations at Mårsätter in 1877–81 resulted in increased metal loading to a small lake, notably as sulphidic tailings. The event is taken as an opportunity to study the present environmental impact of a historical single major metal release. Lake water and four sediment cores were sampled and analysed for principal and trace elements in solid and aqueous phases as well as general hydrochemical conditions. Chronologies were determined from ²⁰⁶Pb/²⁰⁷Pb ratios and historical records. Ordinary sedimentation after the event has lead to that the tailings are found as a distinct layer at a depth of 18–22 cm in the sediment. The layer is characterized by elevated metal concentrations in the solid and pore water phases, respectively, circum neutral pH and sulphate concentrations below detection. Geochemical modelling indicated a preference for carbonate equilibrium in the waste while sulphides prevailed above it. It is concluded that the growth of the ordinary sediment on top of the waste has lead to a physicochemical barrier that seals of the waste from the overlying sediment. Chemical or physical rupture of the barrier will release the metals to downstream regions. According to the chronologies at least three sources have contributed to the present elevated levels of metals, in additions to the release of tailings. Copper from a historical blast furnace prior to the event at Mårsätter, transport from mineralized parts of the watershed and release of contaminated water from present mining operations maintain elevated levels of notably zinc, silver, cadmium and lead. At present less than 10% of the lead content at the sediment/water interface comes from atmospheric deposition. Increased levels of antimony and thallium were not observed prior to ca 1950.