Ethylenediaminetetraacetic Acid Extraction Research Articles

Assessment of Trace Metals Contamination, Species Distribution and Mobility in River Sediments Using EDTA Extraction.

The impact of the ethylenediaminetetraacetic acid (EDTA) on speciation image of selected trace metals (Zn, Cd, Cu, Pb) in bottom sediments was determined. The influence on the effectiveness of metal removal of extraction multiplicity, type of metal, extraction time and concentration of EDTA were analyzed. With the increase of extraction multiplicity, the concentration of EDTA and contact time, the efficiency of trace metals leaching increased. The speciation analysis revealed that EDTA not only leached metals from bioavailable fractions, but also caused the transition of the metals between the fractions. The biggest amounts of bioavailable forms were found for Cd, less for Zn. The amount of bioavailable fraction was the lowest for Cu and Pb. The two first-order kinetic models fitted well the kinetics of metals extraction with EDTA, allowing the metals fractionation into “labile” (Q1), “moderately labile” (Q2) and “not extractable” fractions (Q3).

Effects of EDTA and aqueous plants extract on the developmental and stress tolerance attributes of Spinacia oleracea and Brassica rapa under sewage water regime

Sewage water is causing a potential threat to agriculture sector due to industrial effluents having heavy metals. Present investigation was carried to study the role of ethylenediaminetetraacetic acid (EDTA) or aqueous extracts of Hyacinth and Hedychium on soil quality and growth of spinach and turnip plants irrigated with sewage water (SW). Treatment of plants with SW resulted in an increment of catalase (CAT), peroxidase (POD) and polyphenol oxidase (PPO) activities. However, EDTA or plant extracts further enhanced their activities. At both stages of development of the tested crops, a substantial increase was found in the content of proline and total phenols, indicating the strengthening of the antioxidant protection mechanism to boost the oxidative effects of SW stress. Sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) studies revealed considerable variation in the protein profile among the different treatments, with an expression of some unique proteins obvious with other treatments. SW treatments increased heavy metals (HM) content in soil and plants; however, EDTA or plant extracts greatly decreased the levels of HMs in both shoots and roots and soils. The present study results suggest that the application of EDTA or aqueous plant extracts can be a useful strategy for phytoextraction in areas irrigated with sewage water.

Influence of grinding conditions on the pulp chemistry and flotation of oxidised pyrite

The influence of grinding conditions on the pulp chemistry of oxidised pyrite and its subsequent flotation behavior was studied in this paper. The oxidised pyrite particles were ground with forged steel or 30% chrome steel either in atmosphere or in a nitrogen-rich environment in a Magotteaux Mill®. The in-situ pulp chemistry (i.e., dissolved oxygen, Eh, pH) was measured during grinding. The amount of iron and sulfur oxidation species in the solid and aqueous phases of the grinding slurry was determined using the EDTA (ethylene diaminetetra acetic acid) extraction technique. The flotation recovery of the dry grinding products and the grinding discharge in the absence and presence of a collector was determined. The results show that the flotation recovery of the ground samples relies on both the surface chemistry of the pyrite particles and the pulp chemistry of the discharge, which varies greatly between different grinding conditions. Grinding with forged steel under atmospheric environment and grinding with 30% chrome steel in a nitrogen-rich environment created a suitable pulp chemistry or produced little iron oxidation species, which are found to be the optimal grinding conditions for pyrite flotation.

Quantitative extraction of chromium VI and III from tanned leather: a comparative study of pretreatment methods

In this study, seven pretreatment methods for chromium speciation in tanned leather were evaluated: acidic mineralization, ethylenediaminetetraacetic acid (EDTA) extraction, diethylenetriaminepentaacetic acid (DTPA) extraction, alkaline extraction (NH4OH), ammonium nitrate extraction (NH4NO3), water extraction, and phosphate buffer extraction. Acidic mineralization permitted the decomposition of the organic matter and ensured the complete digestion of leathers, giving access to the total content of chromium in each sample using inductively coupled plasma-atomic emission spectrometry (ICP-AES). From all the extractant media tested, EDTA proved to be the most efficient, allowing the extraction of Cr(VI) and Cr(III) as a Cr(III)-EDTA complex, quantitatively. Method validation is presented for EDTA extraction and direct mineralization. For the EDTA extraction, method detection limit (MDL) and method quantification limit (MQL) for total Cr in leather were 3.4 ppb and 11.2 ppb (µg of total Cr per L of extraction solution), respectively. Due to the lack of leather certified reference materials (CRMs) for Cr(VI), accuracy was evaluated by spiking leather samples with a Cr(VI) solution. The spike recovery of EDTA microwave assisted extraction ranged from 91.0 to 108.6%. Interday precision was also evaluated and all variation coefficients were below 5%, for both mineralization and EDTA extraction. This article provides an efficient procedure to extract quantitatively chromium from leather, while maintaining the speciation, which can be further followed by ion chromatography-inductively coupled plasma-mass spectrometry (IC-ICP-MS).

Differential flotation of pyrite and arsenopyrite: Effect of hydrogen peroxide and collector type

The present work investigates the role of hydrogen peroxide and collector type in differential flotation of pyrite and arsenopyrite model minerals without acid pretreatment. Ethylenediaminetetraacetic acid (EDTA) extraction and X-ray photoelectron spectroscopy (XPS) analysis were employed to determine the oxidation extent supplemented with zeta potential, UV–Vis and Time-of-Flight secondary ion mass spectrometry (TOF-SIMS) towards elucidating collector adsorption behaviour and surface species formation. The results showed higher extent of ferric hydroxide was generally observed for arsenopyrite compared to pyrite using EDTA extraction and XPS analysis. A 2 kg/t hydrogen peroxide addition and 120 g/t PAX collector concentration gave the best separation efficiency with 63.1% pyrite and 5.1% arsenopyrite recovery into the flotation concentrate. The addition of hydrogen peroxide (2 kg/t) had a minor effect on the mineral surface oxidation state according to XPS analysis. Thus, the oxidation of adsorbed xanthate ions into hydrophilic monothiocarbonate ion was the more apparent reason for remarkable arsenopyrite depression compared with pyrite. The observation was not affected with change in sequence of reagent addition and presents great opportunity in better, profitable processing of low-grade refractory auriferous sulphide ores.

A New Analytical Method for Calcium Quantification in Danio rerio Scales

The scale of Danio rerio is an ossified tissue which can be analyzed histologically, biochemically and immunohistochemically. In this paper, we describe and characterize the validation of a new colorimetric procedure for the quantification of the calcified component of the fish scale. This method is based on the use of alizarin red S (ARS) that specifically binds calcium of the bone matrix and ethylenediaminetetraacetic acid (EDTA), a chelating agent that competes with ARS for the binding of calcium. The release of ARS from the scale can be quantified by measuring the absorbance of the alizarin red contained in the EDTA extraction solution since it is proportional to scale calcium content, then it can be considered an index of the degree of mineralization of the scale itself. This new method has been proved to be accurate, precise, based on linear regression and allows a great characterization of scale mineral content. Then, it can be very helpful to evaluate the mineral alterations induced by different pathologies in bone metabolism studies.

Surface chemistry of oxidised pyrite during grinding: EDTA extraction analysis

This paper investigates the surface chemistry of oxidised pyrite under two different grinding conditions (forged steel grinding media and 30% chrome steel grinding media with nitrogen gas flow) using the ethylene diamine-tetra acetic acid (EDTA) extraction technique. The measurement of EDTA extractable iron and dissolved total sulfur (DTS) in the solid and aqueous phase of the grinding slurry enables us to decouple the relative intensity of the pyrite oxidation and galvanic interactions in the mill. It is found that the galvanic interaction predominates in the mill when pyrite samples are ground with forged steel media in the presence of sufficient dissolved oxygen. While the oxidation of pyrite becomes the predominant reaction when the concentration of dissolved oxygen is low in the mill. However, the oxidation of pyrite predominates in the mill when pyrite samples are ground with 30% chrome steel media regardless of the concentration of dissolved oxygen. Reducing the level of dissolved oxygen in the mill (e.g., purging the system with nitrogen gas) or applying less electrochemically active grinding media (e.g., high chrome steel) can reduce the hydrophilic species on the pyrite surface during grinding (e.g., iron hydroxides/oxyhydroxides). Hence, it would be expected to consequently increase the floatability of pyrite.

Galvanic interaction of pyrite with Cu activated sphalerite and its effect on xanthate adsorption

In the presence of Cu ions, a packed bed electrochemical reactor (PBER) was employed to deliberately avoid or induce galvanic coupling between pyrite and Cu‐activated sphalerite. The effect of galvanic interaction on Cu ions uptake and xanthate adsorption were investigated. Solution chemistry and surface chemistry studies (ethylenediaminetetraacetic acid extraction and time of flight secondary ion mass spectrometry) have observed that when sphalerite and pyrite were galvanically coupled, Cu ions migrated from the pyrite surface to the surface of the sphalerite. Along with the marked decrease in the adsorption of Cu ions on pyrite, xanthate adsorption on the minerals also dramatically dropped. The pseudo‐adsorption rate constant for the minerals in the mixed mode is only 0.0583 s‒1, much less than that in the decoupled mode, which is 0.1368 s ‒1. This testing program shows that the galvanic coupling of minerals contributes to more copper transfer and Cu ions preferentially adsorbed by sphalerite rather than pyrite. This affects the pyrite surface and causes it to become xanthate unflavoured.

Phytoavailability of potentially toxic elements from industrially contaminated soils to wild grass

Topsoil and grass samples from 14 sites located in different distances from three copper mining factories and a copper smelter were collected in Srednogorie, Bulgaria. The paper discusses results of studies on the mobility of potentially toxic elements (As, Cd, Cr, Cu, Mn, Ni, Pb, Zn) from contaminated soils to wild grass Cynodon dactylon in terms of transfer (TF: soil to plant) and phytoavailability (PF: EDTA (ethylenediaminetetraacetic acid)-soluble to plant) factors. Soils located close to mine and smelter factories were heavily contaminated by As and Cu reaching levels up to 500 mg/kg and 2400 mg/kg, respectively for As and Cu. At seven sites arsenic and copper in grass were over the normal levels (1 mg/kg As; 20 mg/kg Cu). The content of Cu in grass averaged 63 mg/kg exceeding the maximum allowable for sheep. Relationship between PF and TF values was found for As, Cd, Cu, Ni, Pb, Zn but not for Mn and Cr. To some extent the soil pH, TOM (total organic matter) and CaCO3 content are related to the phytoavailability of As, Cd and Cu since for Zn and Pb this relation is attributed to Al- and Fe-content of soil. Statistically significant correlation coefficients were determined between the EDTA-soluble fraction of soil and content in grass in the case of As, Cd, Cr, Cu, Mn and Pb indicating the suitability of the short procedure for phytoavailability studies of those elements. The application of hierarchical cluster analysis and self-organizing maps of Kohonen made it possible to reveal specific hidden relationships between the soil variables and transfer factors as well as between the sampling locations. This additional information helps in more detailed interpretation of phytoavailability and transfer processes in the region of interest.The novelty in this study is achieved by careful consideration of the possibility of using EDTA extracts of the toxic metals in investigating of the phytoavailability and transfer processes soil/plant. Additionally, chemometric expertise used makes it possible to differentiate the behavior of each toxic metal in the processes studied. The combination of easy option for rapid extraction and intelligent data analysis gives a new perspective for contributions in explanation of the complex interactions between soils and plants when assessing pollution events in a certain environment.

Structural characterization of alkali-soluble polysaccharides from Panax ginseng C. A. Meyer.

Panax ginseng C. A. Meyer (ginseng) has been widely used as a herb and functional food in the world. Polysaccharides are the main active components of ginseng. In this paper, the polysaccharides were sequentially extracted by 50 mM Na2CO3, 1 M KOH and 4 M KOH from ginseng roots treated sequentially with hot water, α-amylase and ethylenediaminetetraacetic acid extraction. Na2CO3-soluble ginseng polysaccharide (NGP) was fractionated into one neutral and three acidic fractions by anion exchange and gel permeation chromatography. Fourier transform infrared, NMR and methylation analysis indicated acidic fractions in NGP were highly branched rhamnogalacturonan-I domains, with → 4)-α-GalpA-(1 → 2)-α-Rhap-(1 → disaccharide repeating units as backbone and β-1,4-galactan, α-1,5/1,3,5-arabinan and type II arabinogalactan as side chains. 1-KGP (1 M KOH-soluble ginseng polysaccharide) and 4-KGP (4 M KOH-soluble ginseng polysaccharide) were mainly composed of hemicellulose besides starch-like polysaccharides and minor pectin. Antibody detection, enzymic hydrolysis, high performance anion exchange chromatography and methylation analysis demonstrated xylan was the major component in 1-KGP, while xyloglucan was predominant in 4-KGP. Comparing the polysaccharides obtained by different solvent extractions, we have a comprehensive understanding about total ginseng polysaccharides.

Effect of surface oxidation on the flotation response of enargite in a complex ore system

In previous study, the selective separation of enargite from complex ore samples in a batch flotation system under controlled pulp potential was investigated (Tayebi-Khorami et al., 2017b). It has been found that it is possible to make a separation between enargite and the other copper minerals in a real ore system using pulp potential control. In this study, the effect of the surface chemistry on the floatability of enargite and pyrite in complex ore systems were investigated. Based on flotation behaviour, EDTA (Ethylenediaminetetraacetic acid) extraction, pulp potential measurement and pure mineral study, it was found that the galvanic interactions between sulphide minerals, and pulp potential conditions, determined the flotation performances of the ore samples. It was also concluded that enargite had the lowest rest potential compared to the other sulphide minerals, which caused strong galvanic interaction between enargite and pyrite. This study has an important implication in sulphide flotation where enargite is present in the ore samples.

Boron-bridged RG-II and calcium are required to maintain the pectin network of the Arabidopsis seed mucilage ultrastructure.

The structure of a pectin network requires both calcium (Ca2+) and boron (B). Ca2+ is involved in crosslinking pectic polysaccharides and arbitrarily induces the formation of an "egg-box" structure among pectin molecules, while B crosslinks rhamnogalacturonan II (RG-II) side chain A apiosyl residues in primary cell walls to generate a borate-dimeric-rhamnogalacturonan II (dRG-II-B) complex through a boron-bridge bond, leading to the formation of a pectin network. Based on recent studies of dRG-II-B structures, a hypothesis has been proposed suggesting that Ca2+is a common component of the dRG-II-B complex. However, no in vivo evidence has addressed whether B affects the stability of Ca2+ crosslinks. Here, we investigated the L-fucose-deficient dwarf mutant mur1, which was previously shown to require exogenous B treatment for phenotypic reversion. Imbibed Arabidopsis thaliana seeds release hydrated polysaccharides to form a halo of seed mucilage covering the seed surface, which consists of a water-soluble outer layer and an adherent inner layer. Our study of mur1 seed mucilage has revealed that the pectin in the outer layer of mucilage was relocated to the inner layer. Nevertheless, the mur1 inner mucilage was more vulnerable to rough shaking or ethylene diamine tetraacetic acid (EDTA) extraction than that of the wild type. Immunolabeling analysis suggested that dRG-II-B was severely decreased in mur1 inner mucilage. Moreover, non-methylesterified homogalacturonan (HG) exhibited obvious reassembly in the mur1 inner layer compared with the wild type, which may imply a possible connection between dRG-II-B deficiency and pectin network transformation in the seed mucilage. As expected, the concentration of B in the mur1 inner mucilage was reduced, whereas the distribution and concentration of Ca2+in the inner mucilage increased significantly, which could be the reason why pectin relocates from the outer mucilage to the inner mucilage. Consequently, the disruption of B bridges appears to result in the extreme sensitivity of the mur1 mucilage pectin complex to EDTA extraction, despite the reinforcement of the pectin network by excessive Ca2+. Therefore, we propose a hypothesis that B, in the form of dRG-II-B, works together with Ca2+to maintain pectin network crosslinks and ultimately the mucilage ultrastructure in seed mucilage. This work may serve to complement our current understanding of mucilage configuration.

Chemical fraction, leachability, and bioaccessibility of heavy metals in contaminated soils, Northeast China.

Heavy metals in urban soils may pose risks to both urban environment and human health. However, only a fraction of heavy metals in soil is mobile and/or bioavailable for plant uptake and human ingestion. This study evaluates the chemical fraction and potential mobility and bioaccessibility of heavy metals (Cd, Cr, Cu, Pb, and Zn) in the contaminated urban topsoils from steel-industrial city (Anshan), Northeastern China. Chemical forms of heavy metals in soils are determined using Tessier sequential extraction technique. The toxicity characteristic leaching procedure (TCLP), ethylenediaminetetraacetic acid (EDTA), and US Pharmacopeia methodology (USPM) are used to determine the operationally defined potentially mobile and bioaccessible metal fractions, respectively. Sequential extraction results show that Cd has the highest percentage of exchangeable form, whereas Cr primarily exists in residual form. The non-residual fraction of heavy metals increases in the order of Cr < Cu < Pb < Zn < Cd. The leachability of heavy metals evaluated by TCLP test indicates that Cd, Zn, Cu, and Pb have much higher mobile than Cr. The bioavailability of heavy metals determined by EDTA extraction decreases in the order of Pb > Cu ≅ Zn > Cd > Cr. The order of bioaccessibility determined by USPM extraction is Pb = Cu > Zn > Cd > Cr. The Cr exhibits the lowest leachability and bioaccessibility among the investigated metals. The Pb has the highest bioaccessibility, indicating higher potential hazard for the human health. There are significant relationships between the EDTA- and USPM-extractable metals (Cd, Cu, Pb, and Zn) and the sum of first three steps of sequential extraction. Highly significant correlation is found between amounts of EDTA-extractable Cd, Cu, Pb, and Zn and USPM-extractable metals. The result suggests that EDTA extraction can be helpful to estimate the bioaccessibility of heavy metals for human ingestion. Introduction of mobile and human bioaccessible concentrations into risk assessments can give more realistic implications for urban environmental management.

EDTA soluble chemical components and the conditioned medium from mobilized dental pulp stem cells contain an inductive microenvironment, promoting cell proliferation, migration, and odontoblastic differentiation.

BackgroundThe critical challenge in tissue engineering is to establish an optimal combination of stem cells, signaling morphogenetic molecules, and extracellular matrix scaffold/microenvironment. The extracellular matrix components of teeth may be reconstituted as an inductive microenvironment in an ectopic tooth transplantation bioassay. Thus, the isolation and identification of the chemical components of the inductive microenvironment in pulp/dentin regeneration will accelerate progress towards the goal of tissue engineering of the tooth.MethodsThe teeth demineralized in 0.6 M hydrochloric acid were sequentially extracted by 4.0 M guanidine hydrochloride (GdnHCl), pH 7.4, and 0.5 M ethylenediaminetetraacetic acid (EDTA), pH 7.4. The extracted teeth were transplanted into an ectopic site in severe combined immunodeficiency (SCID) mice with mobilized dental pulp stem cells (MDPSCs). The unextracted tooth served as a positive control. Furthermore, the soluble components for the inductive microenvironment, the GdnHCl extracts, or the EDTA extracts together with or without MDPSC conditioned medium (CM) were reconstituted systematically with autoclaved teeth in which the chemical components were completely inactivated and only the physical microenvironment was preserved. Their pulp/dentin regenerative potential and angiogenic potential were compared 28 days after ectopic tooth transplantation by histomorphometry and real-time RT-PCR analysis.ResultsExpression of an odontoblastic marker, enamelysin, and a pulp marker, thyrotropin-releasing hormone degrading enzyme (TRH-DE), was lower, and expression of a periodontal cell marker, anti-asporin/periodontal ligament-associated protein 1 (PLAP-1), was higher in the transplant of the EDTA-extracted teeth compared with the GdnHCl-extracted teeth. The autoclaved teeth reconstituted with the GdnHCl extracts or the EDTA extracts have weak regenerative potential and minimal angiogenic potential, and the CM significantly increased this potential. Combinatorial effects of the EDTA extracts and the CM on pulp/dentin regeneration were demonstrated in vivo, consistent with their in-vitro effects on enhanced proliferation, migration, and odontoblastic differentiation.ConclusionsThe EDTA-extracted teeth demonstrated significantly lower pulp/dentin regenerative potential compared with the GdnHCl-extracted teeth. The EDTA soluble chemical components when reconstituted with the physical structure of autoclaved teeth serve as an inductive microenvironment for pulp/dentin regeneration, promoting cell proliferation, migration, and odontoblastic differentiation.Electronic supplementary materialThe online version of this article (doi:10.1186/s13287-016-0334-z) contains supplementary material, which is available to authorized users.

Adsorption of copper sulphate on PGM-bearing ores and its influence on froth stability and flotation kinetics

Copper sulphate is used as an activator in the flotation of base metal sulphides as it promotes the interaction of collector molecules with mineral surfaces. It has been used as an activator in certain platinum group mineral (PGM) flotation operations in South Africa although the mechanisms by which improvements in flotation performance are achieved are not well understood. Some investigations have suggested these changes in flotation performance are due to changes in the froth phase rather than activation of minerals by true flotation in the pulp zone. In the present study, the effect of copper sulphate on froth stability was investigated on two PGM containing ores, namely Merensky and UG2 (Upper Group 2) ores from the Bushveld Complex of South Africa. Froth stability tests were conducted using a non-overflowing froth stability column. Zeta potential tests and ethylenediaminetetraacetic acid (EDTA) tests were used to confirm the adsorption of reagents onto pure minerals commonly found in the two ores. The results of full-scale UG2 concentrator on/off copper sulphate tests are also presented. The UG2 ore showed a substantial decrease in froth stability in the order of reagent addition: no reagents>copper>xanthate>copper+xanthate, while Merensky ore showed a slight decrease. It was shown through zeta potential measurements that copper species were to be found on plagioclase, chromite, talc and pyrrhotite surfaces and through EDTA extraction that this copper was in the form of almost equal amounts of Cu(OH)2 and chemically reacted copper ions on the Merensky and UG2 ore surfaces. In certain cases, the presence of copper sulphate and xanthate substantially increased the recovery, and therefore the implied hydrophobicity, of pure minerals in a frothless microflotation device. It was, therefore, proposed that increases in hydrophobicity beyond an optimum contact angle for froth stability, were the cause of instabilities in the froth phase and these were found to impact grade and recovery in a full-scale concentrator. Differences in the extent of froth phase effects between the different ores can be attributed to differences in mineralogy.

Quantifying arsenate partitioning in aquatic systems: Narrowing the laboratory-real world gap with kinetic sediment extractions and the Diffuse Layer Model

Many studies have proposed that silicic acid and phosphate (PV) can displace arsenic sorbed to iron oxides leading to elevated As concentrations in aquatic systems. While surface complexation models are adept at quantifying sorption to synthetic oxides in laboratory systems their application to complex natural systems remains challenging. In this study we provide a systematic approach to developing a robust use of models for understanding AsV distribution in natural systems in which hydrated iron oxides are the main adsorptive phase. The Waikato River provides a useful laboratory for this work because it contains high H4SiO4, AsV and PV loadings due to geothermal and agricultural inputs. A 15min oxalate extraction and a 48h ethylenediaminetetraacetic acid (EDTA) extraction of river sediment contained the same ratios of As:Fe, P:Fe and Si:Fe. Both of these extracts target the poorly ordered iron oxide phases (typically ferrihydrite) and by following the release of elements over time in the EDTA extraction it was possible to demonstrate that the extracted As, P, and Si were associated with the ferrihydrite. This demonstrates for the first time that a single oxalate extraction can quantify ferrihydrite sorbed H4SiO4, As and PV and provides a basis to quantify the role of these ligands in inhibiting AsV sorption to sediments. The measured concentrations of ferrihydrite sorbed AsV, PV and H4SiO4 for the Waikato River suspended sediment allow for the informed selection of appropriate model parameters for applying the Diffuse Layer Model to the system. In this way it was possible to quantify the effect of the individual components in the river water on AsV sorption. This study provides an explanation for the observation that the proportion of sorbed As in the Waikato River is generally significantly lower than that observed in rivers closer to the world average concentrations. More generally the study provides a method to quantify the role of individual water chemistry components on AsV distribution in natural systems.

Stratification of Phosphorus Forms from Long-Term Conservation Tillage and Poultry Litter Application

Phosphorus stratification leaves high P concentrations at the soil surface, which are vulnerable to loss in runoff. Understanding P forms at the soil surface may help control P loss, but little information is available on how P forms stratify in soils. We used 31P nuclear magnetic resonance (NMR) spectroscopy and chemical analysis to characterize P forms and the elements controlling P cycling in Cecil soil (a fine, kaolinitic, thermic Typic Kanhapludult) that became P stratified after 11 yr of cropping management conducted under combinations of tillage (conventional and no-till, CT and NT, respectively) and inorganic chemical (CF) and poultry litter (PL) fertilization. Samples from three soil depths (0–2.5, 2.5–5, and 5–15 cm) were sequentially extracted in NaOH–ethylenediaminetetraacetic acid (EDTA) and HCl before 31P-NMR spectroscopy. The NaOH–EDTA extraction recovered 63 to 83% of the total P in a range of P forms, and HCl recovered 2 to 16% of the total P, mainly orthophosphate. Phosphorus forms and concentrations were evenly distributed in soil layers only in the CT treatment with CF. Stratification of orthophosphate and phytate occurred in NT samples fertilized with PL and CF, with the highest concentrations in the top 2.5 cm. Increased orthophosphate and phytate concentrations were detected at the soil surface for CT–PL samples, indicating that PL is not as well mixed by tillage as CF. These results suggest that P fertilizers should be placed below the soil surface under NT to avoid stratification and thus reduce potential P loss in surface runoff.

Ex situ remediation technology for heavy metals in contaminated sediment

The importance of metal mobile fractions rather than total contents in environmental matrices is increasing in the risk assessment evaluation of contaminated sites. Ethylenediaminetetraacetic acid (EDTA), aimed at the measurements of metals mobile fractions, was used to extract the metals from the contaminated dredged sediments based on chemical extraction technology. This work examined the influences of contact time and EDTA concentration on the extraction efficiency for metals from polluted dredged sediment. In addition, the sequential extraction method was carried out to show the change in distribution pattern of metals in sediment before and after EDTA extraction. The dredged sediment from Helwan area (H) was mainly polluted by Pb (685 mg/kg), and the dredged sediment from Talkha area (T) was significantly polluted by Cd (236 mg/kg), Cu (229 mg/kg), and Zn (2,888 mg/kg). For sediment (H), the maximum lead removal of 72.54% was achieved using EDTA under the optimum conditions. While For sediment (T), the maximum cadmium removal of 53.58% was achieved under the same conditions. Finally, EDTA can be used as washing solution for contaminated sediment as well as single-step extraction to identify non-residual metal content (the anthropogenic fraction) and to evaluate the potential bioavailability of metal.

Phytotoxicity of trace metals in spiked and field-contaminated soils: Linking soil-extractable metals with toxicity.

Soil tests have been widely developed to predict trace metal uptake by plants. The prediction of metal toxicity, however, has rarely been tested. The present study was set up to compare 8 established soil tests for diagnosing phytotoxicity in contaminated soils. Nine soils contaminated with Zn or Cu by metal mining, smelting, or processing were collected. Uncontaminated reference soils with similar soil properties were sampled, and series of increasing contamination were created by mixing each with the corresponding soil. In addition, each reference soil was spiked with either ZnCl2 or CuCl2 at several concentrations. Total metal toxicity to barley seedling growth in the field-contaminated soils was up to 30 times lower than that in corresponding spiked soils. Total metal (aqua regia-soluble) toxicity thresholds of 50% effective concentrations (EC50) varied by factors up to 260 (Zn) or 6 (Cu) among soils. For Zn, variations in EC50 thresholds decreased as aqua regia > 0.43 M HNO3 > 0.05 M ethylenediamine tetraacetic acid (EDTA) > 1 M NH4 NO3 > cobaltihexamine > diffusive gradients in thin films (DGT) > 0.001 M CaCl2 , suggesting that the last extraction is the most robust phytotoxicity index for Zn. The EDTA extraction was the most robust for Cu-contaminated soils. The isotopically exchangeable fraction of the total soil metal in the field-contaminated soils markedly explained the lower toxicity compared with spiked soils. The isotope exchange method can be used to translate soil metal limits derived from soils spiked with metal salts to site-specific soil metal limits.

Effects of remediation train sequence on decontamination of heavy metal-contaminated soil containing mercury

When a contaminated site contains pollutants including both nonvolatile metals and Hg, one single remediation technology may not satisfactorily remove all contaminants. Therefore, in this study, chemical extraction and thermal treatment were combined as a remediation train to remove heavy metals, including Hg, from contaminated soil. A 0.2 M solution of ethylenediamine tetraacetic acid (EDTA) was shown to be the most effective reagent for extraction of considerable amounts of Cu, Pb, and Zn (>50%). Hg removal was ineffective using 0.2 M EDTA, but thermogravimetric analysis suggested that heating to 550°C with a heating rate of 5°C/min for a duration of 1 hr appeared to be an effective approach for Hg removal. With the employment of thermal treatment, up to 99% of Hg could be removed. However, executing thermal treatment prior to chemical extraction reduced the effectiveness of the subsequent EDTA extraction because nonvolatile heavy metals were immobilized in soil aggregates after the 550°C treatment. The remediation train of chemical extraction followed by thermal treatment appears to remediate soils that have been contaminated by many nonvolatile heavy metals and Hg.ImplicationsA remediation train conjoining two or more techniques has been initialized to remove multiple metals. Better understandings of the impacts of treatment sequences, namely, which technique should be employed first on the soil properties and the decontamination efficiency, are in high demand. This study provides a strategy to remove multiple heavy metals including Hg from a contaminated soil. The interactions between thermal treatment and chemical extraction on repartitioning of heavy metals was revealed. The obtained results could offer an integrating strategy to remediate the soil contaminated with both heavy metals and volatile contaminants.