Soil Matrix Effects Research Articles

Quantitative Analysis of Pb in Soil Using Laser-Induced Breakdown Spectroscopy Based on Signal Enhancement of Conductive Materials.

Studying efficient and accurate soil heavy-metal detection technology is of great significance to establishing a modern system for monitoring soil pollution, early warning and risk assessment, which contributes to the continuous improvement of soil quality and the assurance of food safety. Laser-induced breakdown spectroscopy (LIBS) is considered to be an emerging and effective tool for heavy-metal detection, compared with traditional detection technologies. Limited by the soil matrix effect, the LIBS signal of target elements for soil heavy-metal detection is prone to interference, thereby compromising the accuracy of quantitative detection. Thus, a series of signal-enhancement methods are investigated. This study aims to explore the effect of conductive materials of NaCl and graphite on the quantitative detection of lead (Pb) in soil using LIBS, seeking to find a reliable signal-enhancement method of LIBS for the determination of soil heavy-metal elements. The impact of the addition amount of NaCl and graphite on spectral intensity and parameters, including the signal-to-background ratio (SBR), signal-to-noise ratio (SNR), and relative standard deviation (RSD), were investigated, and the mechanism of signal enhancement by NaCl and graphite based on the analysis of the three-dimensional profile data of ablation craters and plasma parameters (plasmatemperature and electron density) were explored. Univariate and multivariate quantitative analysis models including partial least-squares regression (PLSR), least-squares support vector machine (LS-SVM), and extreme learning machine (ELM) were developed for the quantitative detection of Pb in soil with the optimal amount of NaCl and graphite, and the performance of the models was further compared. The PLSR model with the optimal amount of graphite obtained the best prediction performance, with an Rp that reached 0.994. In addition, among the three spectral lines of Pb, the univariate model of Pb I 405.78 nm showed the best prediction performance, with an Rp of 0.984 and the lowest LOD of 26.142 mg/kg. The overall results indicated that the LIBS signal-enhancement method based on conductive materials combined with appropriate chemometric methods could be a potential tool for the accurate quantitative detection of Pb in soil and could provide a reference for environmental monitoring.

A simple model of the soil freezing characteristic curve for saline soils with two freezing stages

Soil freezing characteristic curve (SFCC) describes the relationship between unfrozen water and subzero temperature, which is of significance for the simulation of heat, water, salt migration in cold regions. There are two phase transition stages in some saline soils, which is often explained by the phase equilibrium of bulk solution. However, the second phase transition and chemical characteristic of solute are ignored in the current coupling numerical models for freezing-thawing soils. The newest SFCC methods considering abovementioned two items are not applicable to numerical models due to complex calculation or irregularly changeable parameters. To solve those problems, a simple model was proposed in this paper. Firstly, the complete phase diagram of pore solution at icing stage was speculated from published experimental SFCCs of saline soils. Then, the temperatures of saline soils at freezing and eutectic points were quantitative expressed with phase diagram of bulk solution and SFCC of nonsaline soil, and the criteria determining whether single icing stage or icing-eutectic stage occurs in saline soils was proposed. A synthetic index was used to describe the effects of soil matrix and initial solute concentration on the exponent. Only three constant parameters were introduced to reflect the soil matrix effect on phase transition points of pore solution and the influence of chemical characteristic of solute on pore water freezing process. Finally, the model was validated by the experimental data of saline soils and showed good results and ease of use compared to a widely used theorical model for saline soil with single freezing stage and other two models both considering two phase transitions. The work provides a deeper view of freezing process in saline soils and promote the improvement of numerical simulation effect for heat, water and salt migration in seasonal freezing-thawing areas.

HS-SPME-GC-MS analysis of Cyprus vineyard soil for VOCs determination

In line with green chemistry principles, a headspace solid-phase microextraction gas chromatography-mass spectrometry (HS-SPME-GC-MS) method was developed and optimized to study the profile of biogenic volatile organic compounds (BVOCs) in soil samples from vineyards. The 75 µm CAR/PDMS fiber was selected for the identification of BVOCs in soil. The analytical method showed very good linearity (R2 ≥ 0.9914), sensitivity, and precision. Subsequently, soil matrix effect (ME) was examined on the BVOCs emission, through combined standard addition and internal standard (IS) calibration curves. The validated and optimized method was further applied in real soil samples from three vineyard areas of Cyprus (Omodos, Polemi, and Agros). Thirty-eight BVOCs were identified in total; among them acetone (0.65–5.96 μg/kg), hexane (0–0.50 μg/kg), heptane (0–0.18 μg/kg), trichloromethane (0.13–0.21 μg/kg), 1,2-dichloropropane (0.05–1.37 μg/kg), cyclohexane (0–0.26 μg/kg), benzene (0–0.51 μg/kg), toluene (0–0.54 μg/kg), p-xylene (0.15–0.97 μg/kg), and 1,3-di-tert-butyl-benzene (7.91–29.55 μg/kg) were quantified. The results revealed that the sampling vineyard location affects the BVOCs emissions in each soil. Also, vineyard elevation, soil pH, Ca, N, Zn, and Fe showed a significant correlation with the BVOCs emissions, which explains why vineyard soil regions are distinguished from each other, concluding that sample from Agros is the most abundant in BVOCs emissions.

Germanium speciation study in soil from an electronic waste processing plant area

PurposeGermanium (Ge) is known as a Technology Critical Element (TCE) and has been widely used in electronic and industrial products. Waste electronic and electrical equipment (WEEE) containing germanium goes to WEEE treatment plants. The transfer of Ge in the environment makes it necessary to get to know its mobility, reactivity, and chemical transformations in soil. The objective of this research was to develop a methodology for germanium speciation in soil under pressure from storage, processing, and recovery from electrowaste.Materials and methodsThirty soil cores (30 cm long) were collected from an area around a WEEE plant, using a Humax soil sampler. Soil magnetometry methods were used for the first time during the determination of soil sampling points for germanium. After basic physicochemical analysis (pH, Eh, total element concentration using the ICP-MS technique), soil samples were prepared for germanium speciation. The optimisation and validation of a methodology for determining Ge species in easily-leached fractions of soil collected from areas around an electrowaste plant, was studied using Ion Chromatography-Inductively Coupled Plasma-Mass Spectrometry (IC-ICP-MS). Chromatographic conditions were optimised, taking soil matrix effects into account. Optimised Ge extraction from the soil included: extraction time, type of extractants, extraction support using shaking, and ultrasound.Results and discussionThe Ge species (Ge(IV), monomethylgermanium (MMGe), and dimethylgermanium (DMGe)) were successfully separated after 12 min on a Dionex IonPac AS9-HC column with ammonium nitrate and potassium sodium tartrate as an elution phase. The highest extraction efficiency was achieved by using 100 mM NH4NO3 with 1 mM potassium sodium tartrate as an extractant, that washes out Ge from soils within 4 h. In most cases, the soils contained a Ge(IV) form. Germanium methyl derivatives were only found in a few soil samples. Our research showed that germanium concentration in the studied area was as high as 7.64 mg.kg−1, with an average concentration of 3.51 mg.kg−1. The results allowed the creation of a correlation matrix, which identified many strong correlations.ConclusionThis research confirmed the impact of a WEEE plant on the increase of the Ge content in topsoil, when in direct proximity. Increased germanium content occurred in soil samples located north of the emitter, which is consistent with the prevailing wind direction. The study confirmed that the soil magnetometry method is applicable for detecting TCE. Soil samples with the highest content of germanium had a very high magnetic susceptibility and there is a correlation between these parameters.

Evaluation of univariate and multivariate calibration strategies for the direct determination of total carbon in soils by laser-induced breakdown spectroscopy: tutorial

The correct choice of the calibration strategy method is a step that can ensure the accuracy of carbon determination in soils by laser-induced breakdown spectroscopy. In this paper, we evaluate and discuss the intrinsic characteristics of univariate and multivariate calibration strategies in overcoming soil matrix effects and their influence on the magnitude of calibration and prediction error values. The matrix-matching calibration with previous correction of Al spectral interference in the C I line at 193.03 nm was the best strategy of the 13 univariate models evaluated [root-mean-square error of calibration—(RMSEP)=0.2wt.%C]. In the multivariate evaluation of the 22 models obtained, the artificial neural network allowed obtaining a lower value of prediction error for C (RMSEP=0.1wt.%C) with very good accuracy (98%) for the set samples of validation. The observation of these results was justified considering the advantages and limitations of each calibration strategy explored.

Salt crust-assisted thermal decomposition method for direct and simultaneous quantification of polypropylene microplastics and organic contaminants in high organic matter soils

Direct quantitative analysis of soil polypropylene microplastics (MPs) via thermal method is still a challenge due to its sensitivity to the soil matrix during the thermal decomposition. In this work, the impact of soil organic matter (SOM) on MPs decomposition in real soil was estimated, and high SOM contents was found have significantly negative effect on the qualitative and quantitative analysis of PP. To solve this problem, a salt crust-assisted thermal decomposition method was developed to reduce the soil matrix effect. By adding salt solution and heating in appropriate temperature program, salt crust can be formed between MPs and soil matrix to isolate PP MPs and soils during the heating process, and thereby to avoid the influence of SOM. Thermal desorption/decomposition coupling with headspace solid phase microextraction (HS-SPME) was used extraction of MPs decomposition products. All the thermal decomposition products of PP were identified, several alkenes and dialkenes were selected as candidates for quantitative analysis, and 2,4,6,8,10-pentamethyltridec-1-ene with optimal linearity was finally established for quantification. Besides, this method was also established for simultaneous determination of PP MPs and organic contaminants (OCs) including PCBs and PAHs, since it is capable of providing a new approach for investigation of their interaction in real soil environment. A theoretical LOD of 0.002 wt% was obtained for PP MPs, and the LOD of OCs ranges from 0.05 to 1.87 ng/g. Determination of aged soil samples reveal that adsorption of OCs is not a predominating effect of MPs in soil environment, and MPs contaminants may reduce the soil retention capacity. This method provides a new approach for direct quantification of soil PP MPs, and applicable for investigation of the interactions between MPs and OCs in real soils.

Assessing Soil Key Fertility Attributes Using a Portable X-ray Fluorescence: A Simple Method to Overcome Matrix Effect

The matrix effect is one of the challenges to be overcome for a successful analysis of soil samples using X-ray fluorescence (XRF) sensors. This work aimed at evaluation of a simple modeling approach consisted of Compton normalization (CN) and multivariate regressions (e.g., multiple linear regressions (MLR) and partial least squares regression (PLSR)) to overcome the soil matrix effect, and subsequently improve the prediction accuracy of key soil fertility attributes. A portable XRF was used for analyzing 102 soil samples collected from two agricultural fields with contrasting soil matrices. Using the intensity of emission lines as input, preprocessing methods included with and without the CN. Univariate regression models for the prediction of clay, cation exchange capacity (CEC), and exchangeable (ex-) K and Ca were compared with the corresponding MLR models to assess matrix effect mitigation. The MLR and PLSR models improved the prediction results of the univariate models for both preprocessing methods, proving to be promising strategies for mitigating the matrix effect. In turn, the CN also mitigated part of the matrix effect for ex-K, ex-Ca, and CEC predictions, by improving the predictive performance of these elements when used in univariate and multivariate models. The CN has not improved the prediction accuracy of clay. The prediction performances obtained using MLR and PLSR were comparable for all evaluated attributes. The combined use of CN with multivariate regressions (MLR or PLSR) achieved excellent prediction results for CEC (R2 = 0.87), ex-K (R2 ≥ 0.94), and ex-Ca (R2 ≥ 0.96), whereas clay predictions were comparable with and without CN (0.89 ≤ R2 ≤ 0.92). We suggest using multivariate regressions (MLR or PLSR) combined with the CN to remove the soil matrix effects and consequently result in optimal prediction results of the studied key soil fertility attributes. The prediction performance observed for this solution showed comparable results to the approach based on the preprogrammed measurement package tested (Geo Exploration package, Bruker AXS, Madison, WI, USA).

Combination of cloud point extraction with single particle inductively coupled plasma mass spectrometry to characterize silver nanoparticles in soil leachates.

The expansion of silver nanoparticle (AgNP) applications in industry as antibacterial agents has generated an increment of their presence in the environment. Once there, their behavior is not clear because they can undergo different transformation processes that affect their transport, mobility, bioavailability, and toxicity. Therefore, the characterization and quantification of these emerging contaminants are important to understand their behavior and the toxicity effects that can be exerted on living beings. Single particle inductively coupled plasma mass spectrometry (SP-ICPMS) has demonstrated its ability to characterize and give quantitative information on AgNPs in aqueous samples. However, sometimes, the discrimination of the signal corresponding to AgNPs from the signal of dissolved species (Ag(I)) is a challenge. In the present contribution, it is shown that the presence of high amounts of Ag(I) hamper silver nanoparticle size and nanoparticle concentration determination in aqueous samples by SP-ICPMS. To facilitate signal discrimination of both chemical forms, the combination of cloud point extraction (CPE) with SP-ICPMS was studied. CPE experimental conditions to separate AgNPs from Ag(I) were assessed and adapted taking into account the characteristics of the SP-ICPMS technique. CPE and soil matrix effects on particle size were evaluated, showing that particle size was not modified after being in contact with soil matrix and after being separated by CPE. Additionally, frequently used calculation methods for SP-ICPMS data treatment were assessed. Finally, the potential of the developed methodology CPE-SP-ICPMS was evaluated in aqueous soil leachates contaminated with mixtures of AgNPs/Ag(I).

Possible soil tension controls on the isotopic equilibrium fractionation factor for evaporation from soil

AbstractThe stable isotopes of hydrogen and oxygen (δ2H and δ18O) are useful conservative tracers for tracking the movement of water in soil. But although the tracking of water infiltrating through the soil profile and its movement as run‐off and groundwater recharge are well developed, water movement through the soil can also include evaporative fractionation. Soil water fractionation factors have, until now, been largely empirical. Unlike open water evaporation where temperature, humidity, and vapour pressure gradient define fractionation, soil water evaporation includes fractionation by soil matrix effects. These effects are still poorly characterized. Here, we present preliminary results from a simple laboratory experiment with four soil admixtures with grain sizes that range from sand to silt and clay. Our results show that soil tension seems to control the isotope fractionation of resident soil water. The relationship between soil tension and equilibrium fractionation appears to be independent of soil texture and appears well supported by thermodynamic theory. Although these results are preliminary, they suggest that future work should go after soil tension effects as a possible explanatory factor of soil water and water vapour fractionation.

Development and application of a dispersive solid-phase extraction method for the simultaneous determination of chloroacetamide herbicide residues in soil by gas chromatography-tandem mass spectrometry (GC-MS/MS)

ABSTRACTIn this study, a convenient and sensitive analytical method based on dispersive solid-phase extraction (dSPE) and gas chromatography-tandem mass spectrometry in tandem was developed for the simultaneous determination of six chloroacetamide herbicides (acetochlor, alachlor, metolachlor, metazachlor, butachlor and pretilachlor) in soil. Parameters that could influence the extraction efficiency such as the varieties of solvents, the amount of solvents and sorbents were investigated. The optimized extractions were performed by mixing 5.0 g of dried soil with 10.0 mL acetonitrile, 10.0 mL deionized water and 4.0 g sodium chloride, and then the extract was purified with 50.0 mg N-propyl ethylenediamine (PSA), 50.0 mg C18, 10.0 mg graphitized carbon black (GCB) and 100.0 mg MgSO4 (5:5:1:10). At 5.0, 25.0 and 100.0 ng g−1 fortification levels for each analyte, the average obtained recoveries ranged from 87.7% to 108.0% with relative standard deviation (RSD) between 3.8% and 10.9%. The soil matrix effect of the six compounds were lower than 11.0%. The linear relation was observed in the range of 5.0–500.0 ng g−1 and the correlation coefficient (R2) of these compounds were higher than 0.998. The detection limits (LODs) were in the range of 0.2–1.0 ng g−1, and the limits of quantification (LOQs) were between 0.8 and 2.2 ng g−1. Comparing with the gas chromatography-electron capture detector (GC-ECD), the GC-tandem mass spectrometry (MS/MS) method can improve the anti-interference ability and thus get better separation of the chloroacetamide herbicides. Additionally, this method was verified to fit for soil samples with broad organic matter range (16.2 to 83.0 g kg−1). The developed method was successfully applied for analysing 26 field soil samples collected from Dianchi lake basin in the southeast of China. About 42.0% soil samples were detected with these herbicides, of which butachlor was the most frequently detected and the highest concentration was up to 137.0 ng g−1 in rape soil.

Optimization of portable X-ray fluorescence spectrometry for the assessment of soil total copper concentrations: application at an ancient smelting site

Copper (Cu) is the earliest anthropogenic metal pollutant, but knowledge of Cu soil concentrations at ancient metalworking sites is limited. The objective of this work was to examine the ability of portable X-ray fluorescence to quantify Cu in soils at such sites. Using a Bruker Tracer III-SD pXRF, we examine factory “scan” settings versus simple instrument parameter changes (a reduction in energy settings from 40 to 12 kV) to target analysis for Cu. We apply these to a set of uncontaminated samples (n = 18, < 92 mg Cu kg−1) from Central Thailand and compare results to standard wet chemistry analysis (aqua regia digestion and ICP-OES analysis). We then apply the optimized method to a set of highly contaminated samples (n = 86, < 14,200 mg Cu kg−1) from a known ancient smelting site. We demonstrate that simple changes to factory recommended “scan” settings can double the sensitivity of Cu determination via pXRF (“optimized limit of determination” of 19.3 mg kg−1 versus an initial value of 39.4 mg kg−1) and dramatically improve the accuracy of analysis. Changes to other results for other elements are variable and depend on concentration ranges, soil matrix effects, and pXRF response for the individual element. We demonstrate that pXRF can accurately determine Cu across a wide concentration range and identify grossly contaminated soil samples. We conclude that pXRF is a useful tool to rapidly screen and analyse samples at remote sites and can be applied to ancient metalworking sites. Simple optimization of the pXRF settings greatly improves accuracy and is essential in determining comparative background concentrations and “unaffected” areas. Application to other elements requires further element and matrix specific optimization.

Quantification of naphthalene in soil using solid-phase microextraction, gas-chromatography with mass-spectrometric detection and standard addition method

Development of simple, fast and accurate methods for quantification of volatile organic compounds (VOCs) in soil samples is important for providing greater efficiency of analytical laboratories in Kazakhstan and other developing countries. Naphthalene is a model polycyclic aromatic hydrocarbon (PAH), belonging to a group of compounds of significant concern due to environmental impact. Solid-phase microextraction (SPME) is an optimal method for solvent-free automated sample preparation for determination of VOCs in environmental samples. In this work, the method for quantification of naphthalene in soil based on headspace SPME, gas chromatography with mass spectrometric detection, and standard addition calibration was developed. The parameters of SPME and sample equilibration after spiking with standards were optimized for better control of the soil matrix effect. The SPME temperature 80 °C provided the greatest accuracy of naphthalene responses for soils with different matrix and humidity. Equilibration of soil samples after spiking with standards for 6 h at 80 °C provided stabilization of responses in soils with different matrix and water content. The greatest accuracy and precision were achieved after equilibration of the samples for 8 h. The method provides recoveries of 105-119% in the concentration range 0.01-0.1 ng g-1 with detection limit 0.001 ng g-1. The developed method was applied for quantification of naphthalene in real soil samples collected in Almaty, Kazakhstan. The measured concentration of naphthalene in real soil samples varied in the range of 1.4 to 47 ng g-1. In five out of ten collected soil samples concentration exceeded a maximum permissible concentration of 15 ng g-1.

Application of a mobile laser-induced breakdown spectroscopy system to detect heavy metal elements in soil.

In this work, a mobile laser-induced breakdown spectroscopy (LIBS) system has been successfully applied to in situ analysis of heavy metals in soil samples. The LIBS system had two working methods, which were a fixed measuring method and a handheld method. For the fixed measuring method, a simple sample pretreatment was needed to reduce the soil matrix effect generated by moisture and porosity. Experiments proved that this method could be used to semi-quantitatively detect heavy metals when combined with the traditional calibration curve method. The limits of detection for copper, lead, and zinc were all below 10 mg/kg, which satisfied the need of heavy metal detection in soil. Principal component analysis was used for soil classification, which helped to build appropriate calibration curves. On the basis of soil classification, accurate and rapid detection of heavy metals in soil is feasible. For the handheld method, spectrum intensity and stability decreased significantly compared with the fixed measuring method. However, by using the internal standard method, the stability of LIBS data was improved significantly to 6%. For soil samples with serious heavy-metal pollution, the measurement errors were less than 12%, which indicated that handheld LIBS was effective to monitor heavy-metal pollution in soil. The research results provide application support for rapid and on-site monitoring of heavy metals in soil.

Investigation of the effect of soil matrix on flow characteristics for soil and rock mixture

The flow characteristic is important to soil and rock mixture (SRM). Seepage of SRM includes a combination interaction between soil matrix, rock blocks and rock–soil interfaces. Properties of soil matrix play crucial role in controlling the flow rule of SRM, yet the effects of different kinds of soil matrix in SRM on its flow mechanism are still poorly understood. In this work, the authors present the results of a state-of-the-art investigation on the flow properties of SRM with clay, mucky soil and fine sand matrix. A self-developed servo-controlled large-scale permeability testing system was used to carry out the flow test. From the test results, the flow rules are different for SRM with different kinds of soil matrix. For a matrix composition of clay and mucky soil, the flow law follows the non-Darcy law; however, it follows Darcy's law for the SRM with a fine sand matrix. The non-Darcy flow properties are studied with the Forchheimer equation to obtain the permeability coefficient for SRM with different rock block percentages.

Rapid determination of acid herbicides in soil by liquid chromatography with tandem mass spectrometric detection based on dispersive solid phase extraction

This study determined twenty six the highly sensitive phenoxy, pyridines, aliphatic and aromatic acid compounds in soil with a liquid chromatography tandem mass spectrometry. The samples were prepared by modified quick, easy, cheap, effective, rugged and safe (QuEChERS) analytical procedure in solid samples. Herbicides extraction effectiveness was evaluated at three different spiking levels (0.01, 0.1 and 1.0mgkg−1). Fourteen different dispersive solid-phase extraction (d-SPE) sorbents in clean-up step were tested. The QuEChERS protocol with acidic alumina provided the highest number of pesticides with recoveries in the 70–120% range. The soil matrix effect was evaluated and for the majority of compounds were not significant, showing suppression or enhancement (±81–123%). The precision calculated as relative standard deviation (RSD) was below 22%. The linear relation was observed in the range 0.01–2.0mgkg−1 and the correlation coefficient R>0.999. The expanded measurement uncertainty was estimated as being on average, and was between 9% and 33%. The validated method was employed in the analysis of 309 real soil samples.

The soil matrix increases microbial C stabilization in temperate and tropical forest soils

Microbial biomass represents a substantial source of labile C contributing to soil organic matter (SOM) maintenance. Microbial residues may associate with the soil matrix through a variety of mechanisms, reducing its bioavailability and increasing its persistence in soil. Our objective was to examine soil matrix effects on the stability of non-living microbial C inputs in two contrasting forest ecosystems by following microbial residues (Fungi, Actinobacteria, Gram-positive bacteria (Gm +), Gram-negative bacteria (Gm −)) into SOM fractions in a temperate forest in California (CA) and a tropical forest in Puerto Rico (PR) for 3 and 2 years, respectively. We isolated 3 SOM fractions: (i) free light fraction (FLF), (ii) occluded light fraction (OLF), and (iii) dense fraction (DF). Additionally, we characterized SOM fraction chemistry to infer quality and source of native fraction SOM. Our results showed greater stabilization as mineral-associated microbial C (i.e., as DF and OLF), compared with loose detrital C (i.e., FLF). There was no microbial group effect (i.e., differences in fraction C recovery among different microbial cell types). Our findings suggest that mineral association is more important for stabilizing non-living microbial C in soil than the cellular structure of the initial source of microbial inputs, with site specific edaphic factors as the major controllers of the amount of microbial residues stabilized.

Remediation of PAH-contaminated soils by magnetite catalyzed Fenton-like oxidation

This is the premier study reporting the degradation of polycyclic aromatic hydrocarbons (PAHs) through Fenton-like oxidation catalyzed by magnetite. Kinetic degradation of PAHs was studied at circumneutral pH by treatments: (i) H2O2+soluble FeII (F), (ii) H2O2+magnetite as iron source (FL) and (iii) H2O2 alone without catalyst (HP). Results show that oxidation of a model PAH compound (fluorenone) spiked on sand resulted in its complete removal by FL treatment but degradation did not exceed 20% in HP or F systems. However, in two PAHs polluted soils (sampled from coking plant sites), negligible oxidation of 16 PAHs was observed regardless of the catalyst used: soluble FeII or magnetite. Then organic extract separated from these soils was added to sand and after evaporation of the solvent, oxidation was performed which resulted in more than 90% of PAHs removal by FL as compared to 15% by F or HP systems. These removal extents decreased by a factor of two when the organic extracts were oxidized in the presence of original soil. PAHs degradation extent was improved in soils pre-treated with availability-enhancement agents such as ethanol or cyclodextrin. Degradation was non-selective and no by-products were observed by GC–MS and μFTIR. Treatment efficiency was highly limited by PAHs availability in soils and the soil matrix effect. This study points out the promising efficiency of magnetite for PAHs oxidation at circumneutral pH over soluble FeII in contaminated soils, and has important implications in the remediation of contaminated soils.

The role of internal standards and their interaction with soils impact accuracy of volatile organics determinations

Both US Environmental Protection Agency (EPA) SW-846 Methods 8260C/5035 and 8261A include mixing soil with water and addition of internal standards prior to analyses but the equilibration of internal standards with the soil is not required. With increasing organic carbon content and no effort to equilibrate internal standards with the matrix, results are less likely to be accurate. Adding internal standards to soils prior to diluting the sample with water gives more accurate determinations but less reliable quality control (QC). Extending times for equilibration of internal standards improves accuracy but is conducive to analyte degradation not normally observed during analyses. Soil-matrix effects on a given analyte can be greatly understated using a single internal standard as described in Method 8260C while the use of multiple internal standards as described in Method 8261A is more accurate. Method 8261A's reporting error when spiking soils before adding water provides confidence intervals with accuracy near the experimental rule (75.2, 95.7 and 99.5%) with the exception of two analytes that require overnight equilibration.

Rapid Test Methods for the Field Screening of Heavy Metals in Soil Samples

In the present work, rapid test methods for field screening of soil for Cu, Ni, and Pb content are presented. They are based on commercially obtainable Microquant tests (Merck, Germany), which are originally developed for water analysis. The same type of color reaction was also used for the determination of heavy metals in soil extracts: Reagents to form colored metal complexes are cuprizone for Cu, dimethylglyoxime for Ni, and dithizone for Pb. The experimental conditions for the colorimetric determination of these metals in the soil extracts were studied and additionally modified. An aqua regia solution (HCl/HNO3, 3:1) was used for the rapid extraction of metals from soil. To establish accuracy, results obtained with the proposed test methods were compared with those obtained with the standard laboratory method using microwave digestion and flame atomic absorption spectrometry (FAAS). Real soil samples containing metals at background levels generally yielded approximately 50% of the total content obtained with the standard FAAS method. High recovery values of spiked samples confirm that the colorimetric methods are unaffected by soil matrix effects.

Improvement of ELISA analysis for soil residue analysis by reducing soil matrix effects

Improvement of the commercially available fenitrothion-ELISA kit for soil residue analysis was examined. Recovery trials were conducted with 5 soils spiked at 0.5 μg/g soil. Interference of soil matrix was not adequately removed by the addition of synthetic zeolite in extraction, although it reduced Ca2+ concentration. Ultrafiltration at 9 kDa after dilution of the soil extracts gave enough results to compare with those obtained by gas chromatography. It was suggested that overestimation in ELISA was caused by high-molecular-weight humus-like compounds in soil extracts.