Functional Groups Of Humic Substances Research Articles

Impact of Humic Substances on Alleviation of Soil Salinity and the Enhancement of Plant Productivity: a review

Humic substances (HS) are a major component of organic matter in soil, and they have long been recognized for their ability to promote plant growth in a sustainable manner. Recently, there has been a lot of effort put into using multiple approaches to study the connection between the chemical structure of HS compounds and their effect on plant biological processes. Positive physiological responses at the local and systemic levels have been linked to the presence of specific functional groups in HS. Hormone-like signaling pathways are responsible for eliciting these reactions. This review was written with one goal in mind: to help readers gain a firm grasp on the research surrounding the application of HSs. The spatial arrangement of hydrophilic and hydrophobic regions, as well as the dosage, source, molecular size, degree of hydrophobicity, and aromaticity, all contribute significantly to HS's biological efficacy. Therefore, our hypothesis explains the beneficial effect of HS in salt-affected rhizospheres, likely attributed to both direct and indirect influences on plant metabolism, soil microorganism metabolism, soil nutrient uptake dynamics, and soil physical conditions. Keywords: Humic substance, germination, salinity, plant growth

HUMIC SUBSTANCES OF PEAT. PROPERTIES AND BIOLOGICAL ACTIVITY

Humic substances (HS) are a specific group of high-molecular biopolymers that are formed during the decomposition of plant and animal tissue. It has been established that humic substances have a wide range of biological properties, in addition, humic substances are quickly included in the processes of plant metabolism, which accelerates the development of the root system, increases resistance to adverse environmental factors. But to date, the nature of this phenomenon has not been studied enough. To deepen our understanding of the biological and growth-stimulating activity of humic substances, the influence of prepared solutions with different concentrations of humic substances on seed germination is considered. It has been shown that solutions of humic substances have a beneficial effect on seeds even in small concentrations.
 This research work is devoted to the study of the main functional groups of humic substances, such as carboxylic, phenolic, quinoid. Various physico-chemical methods were used in the work to determine the functional and elemental composition of peat HS.
 It has been established that peat HS have a stimulating effect and high physiological activity on the growth and biometric indicators of plants, which in the future can determine the increase in yield and quality of agricultural plants.

Chemical Structure and Biological Activity of Humic Substances Define Their Role as Plant Growth Promoters.

Humic substances (HS) are dominant components of soil organic matter and are recognized as natural, effective growth promoters to be used in sustainable agriculture. In recent years, many efforts have been made to get insights on the relationship between HS chemical structure and their biological activity in plants using combinatory approaches. Relevant results highlight the existence of key functional groups in HS that might trigger positive local and systemic physiological responses via a complex network of hormone-like signaling pathways. The biological activity of HS finely relies on their dosage, origin, molecular size, degree of hydrophobicity and aromaticity, and spatial distribution of hydrophilic and hydrophobic domains. The molecular size of HS also impacts their mode of action in plants, as low molecular size HS can enter the root cells and directly elicit intracellular signals, while high molecular size HS bind to external cell receptors to induce molecular responses. Main targets of HS in plants are nutrient transporters, plasma membrane H+-ATPases, hormone routes, genes/enzymes involved in nitrogen assimilation, cell division, and development. This review aims to give a detailed survey of the mechanisms associated to the growth regulatory functions of HS in view of their use in sustainable technologies.

Humic Substances Mediate Anaerobic Methane Oxidation Linked to Nitrous Oxide Reduction in Wetland Sediments.

Humic substances are redox-active organic molecules, which play pivotal roles in several biogeochemical cycles due to their electron-transferring capacity involving multiple abiotic and microbial transformations. Based on the redox properties of humic substances, and the metabolic capabilities of microorganisms to reduce and oxidize them, we hypothesized that they could mediate the anaerobic oxidation of methane (AOM) coupled to the reduction of nitrous oxide (N2O) in wetland sediments. This study provides several lines of evidence indicating the coupling between AOM and the reduction of N2O through an extracellular electron transfer mechanism mediated by the redox active functional groups in humic substances (e.g., quinones). We found that the microbiota of a sediment collected from the Sisal wetland (Yucatán Peninsula, southeastern Mexico) was able to reduce N2O (4.6 ± 0.5 μmol N2O g sed.–1 day–1) when reduced humic substances were provided as electron donor in a close stoichiometric relationship. Furthermore, a microbial enrichment derived from the wetland sediment achieved simultaneous 13CH4 oxidation (1.3 ± 0.1 μmol 13CO2 g sed.–1 day–1) and N2O reduction (25.2 ± 0.5 μmol N2O g sed.–1 day–1), which was significantly dependent on the presence of humic substances as an extracellular electron shuttle. Taxonomic characterization based on 16S rRNA gene sequencing revealed Acinetobacter (a ɣ-proteobacterium), the Rice Cluster I from the Methanocellaceae and an uncultured archaeon from the Methanomicrobiaceae family as the microbes potentially involved in AOM linked to N2O reduction mediated by humic substances. The findings reported here suggest that humic substances might play an important role to prevent the emission of greenhouse gases (CH4 and N2O) from wetland sediments. Further efforts to evaluate the feasibility of this novel mechanism under the natural conditions prevailing in ecosystems must be considered in future studies.

A novel humic acid extraction procedure from Tunisian lignite

The present study investigates the efficient extraction of humic acid (HA) from Tunisian lignite (TL). The extraction method was optimized using the full factorial design (FFD) based on the interactive effects of sodium hydroxide (NaOH) and sodium pyrophosphate (Na4P2O7) concentrations, extraction temperature, and agitation time as input factors. The output response was the absorbance ratio at 465 and 665 nm (E465/E665) of HA. Fourier-transformed infrared (FT-IR), was used for the characterization of TL-HA. Under optimized conditions (NaOH of 0.8 mol l−1, Na4P2O7 of 0.06 mol l−1, a temperature of 85 °C and an agitation time of 6 h), the obtained lignite-based fertilizer contains a high HA’s aromaticity degree as evidenced by the lower ratio (E465/E665) with a value equal to 1.34. The TL-HA characterization shows the predominance of OH, COOH, CH, C=C and COO groups, which are typical functional groups in humic substances. The effects of this new humic acid (HA) source on wheat germination and root elongation were investigated. The results showed that the wheat seeds germinated in HA fertilizer diluted 20 times produced high germination percentage. Indeed, the addition, of diluted HA, increased the elongation rate of the wheat roots up to 120% compared to the controls. The results of the present study might be useful for practical and commercial applications of this fertilizer based on its humification parameters and its conformity to Tunisian legislation. To investigate the limits of this alkali exaction method, large-scale processes experiments are still necessary.

Interaction between the bituminous and humic components of peat

It was established that an increase in the bituminosity of peat with the degree of decomposition can be explained by an exchange interaction between the π electrons of the molecular polyconjugation systems of humic acids and the quasi-polyconjugation systems of bitumens (the presence of the latter is caused by a synergistic effect of the interaction of separated aromatic rings and the hydrogen bonds of functional groups). This interaction leads to the formation of unique associates, and this fact explains an increase in the concentration of humic substances in a composition with bitumens with increasing the degree of decomposition. The concept of associates is confirmed by a considerable increase in the EPR signal observed upon the removal of a low bitumen content, which was accompanied by changes in its parameters in a number of cases. The formation of these associates occurs under different geoclimatic conditions of peat deposit formation. The lower bituminosity of lowland peats is caused by steric hindrances created by the Ca2+ ions bound to the functional groups of humic substances for the access of hydrocarbon molecules.

Characteristics of Soil Humic Substances as Determined by Conventional and Synchrotron Fourier Transform Infrared Spectroscopy

Humic substances (HS) play an important role in soil fertility and carbon sequestration in soil. The structural characteristics of soil HS, extracted from two natural soils and a laboratory-incubated soil, were investigated by conventional beamline-based Fourier transform infrared radiation (CB-FTIR), a common FTIR technique based on a conventional thermal source, and synchrotron radiation-based (SR-FTIR) spectroscopy. The relative area of absorbance peaks that appeared at 2930, 2860, 1711, and 1635 cm –1 were calculated to make a comparison of the absorbance intensities. The absorption of aromatic functional groups of HS was stronger in SR-FTIR spectroscopy than in CB-FTIR spectroscopy. Compared with humic acid extracted with a 0.1 mol/l Na4P2O7 solution, the level of aliphaticity in humic acid extracted with a 0.1 mol/l NaOH solution was higher. The aliphaticity of humin associated with clay (HMc) was higher than that of humin associated with iron (HMi). These results suggest that SR-FTIR spectroscopy is a useful and nondestructive technique to study the structural characteristics of soil humic substances. Sequential extraction of soil humic substances with NaOH and Na4P2O7 solutions may be helpful in providing additional information in cases where differences in the material obtained from different extraction solutions occur. The aliphaticity and complexity of HMc were higher than those of HMi.

Reactivity and transport mapping of Cu(II) ions in humic hydrogels

Purpose Reactivity and transport properties of metal ions are important both for evaluating and understanding role of humic substances in natural systems and human-driven applications as solving their structural questions. This paper focuses on metal ions diffusion and immobilization in humic hydrogels with various contents of reactive functional groups of humic substances in order to study an effect of their selective blocking on the mobility and immobilization of Cu(II) ions.

In situ study of binding of copper by fulvic acid: Comparison of differential absorbance data and model predictions

This study examined the binding of copper(II) by Suwannee River fulvic acid (SRFA) using the method of differential absorbance that was used at environmentally-relevant concentrations of copper and SRFA. The pH- and metal-differential spectra were processed via numeric deconvolution to establish commonalities seen in the changes of absorbance caused by deprotonation of SRFA and its interactions with copper(II) ions. Six Gaussian bands were determined to be present in both the pH- and Cu-differential spectra. Their maxima were located, in the order of increasing wavelengths at 208 nm, 242 nm, 276 nm, 314 nm, 378 nm and 551 nm. The bands with these maxima were denoted as A0, A1, A2, A3, A4 and A5, respectively. Properties of these bands were compared with those existing in the spectra of model compounds such as sulfosalicylic acid (SSA), tannic acid (TA), and polystyrenesulfonic acid-co-maleic acid (PSMA). While none of the features observed in differential spectra of the model compound were identical to those present in the case of SRFA, Gaussian bands A1, A3 and possibly A2 were concluded to be largely attributable to a combination of responses of salicylic- and polyhydroxyphenolic groups. In contrast, bands A4 and A5 were detected in the differential spectra of SRFA only. Their nature remains to be elucidated. To examine correlations between the amount of copper(II) bound by SRFA and changes of its absorbance, differential absorbances measured at indicative wavelengths 250 nm and 400 nm were compared with the total amount of SRFA-bound copper estimated based on Visual MINTEQ calculations. This examination showed that the differential absorbances of SRFA in a wide range of pH values and copper concentrations were strongly correlated with the concentration of SRFA-bound copper. The approach presented in this study can be used to generate in situ information concerning the nature of functional groups in humic substances engaged in interactions with metals ions. This information can be useful for further elaboration and development of detailed theoretic models that describe the complexation of metals in the environment.

Uranyl(VI) Complexation by Sulfonate Ligands: A Relativistic Density Functional and Time‐Resolved Laser‐Induced Fluorescence Spectroscopy Study

AbstractTo study the role of sulfonate functional groups of humic substances in uranyl(VI) complexation, all‐electron density functional calculations and time‐resolved laser‐induced fluorescence spectroscopy (TRLFS) were applied using small sulfonate ligands as models. A thiolate ligand was explored for comparison. As in an earlier experiment, 4‐hydroxybenzenesulfonic acid (HBSA) and benzenesulfonic acid (BSA) were examined and compared to methylsulfonic acid (MSA). Structural parameters as well as energetic aspects of uranyl complexes by BSA and HBSA ligands were determined to be rather similar, in contrast to earlier experimental findings. The present TRLFS measurements show complexation of uranyl by both ligands, which is in agreement with the computational results. Overall, the combined computational and experimental results also indicate that sulfonate groups play only a minor role in uranyl complexation of humic substances because of the rather low stability constants.

Implications of organic matter on arsenic mobilization into groundwater: Evidence from northwestern (Chapai-Nawabganj), central (Manikganj) and southeastern (Chandpur) Bangladesh

Boreholes (50 m depth) and piezometers (50 m depth) were drilled and installed for collecting As-rich sediments and groundwater in the Ganges, Brahmaputra, and Meghna flood plains for geochemical analyses. Forty-one groundwater samples were collected from the three areas for the analyses of cations (Ca 2+, Mg 2+, K +, Na +), anions (Cl −, NO 3 −, SO 4 2−), total organic carbon (TOC), and trace elements (As, Mn, Fe, Sr, Se, Ni, Co, Cu, Mo, Sb, Pb). X-ray powder diffraction (XRD) and X-ray fluorescence (XRF) were performed to characterize the major mineral and chemical contents of aquifer sediments. In all three study areas, results of XRF analysis clearly show that fine-grained sediments contain higher amounts of trace element because of their high surface area for adsorption. Relative fluorescent intensity of humic substances in groundwater samples ranges from 30 to 102 (mean 58 ± 20, n = 20), 54–195 (mean 105 ± 48, n = 10), and 27–243 (mean 79 ± 71, n = 11) in the Ganges, Brahmaputra and Meghna flood plains, respectively. Arsenic concentration in groundwater (20–50 m of depth) ranges from 3 to 315 μg/L (mean 62.4 ± 93.1 μg/L, n = 20), 16.4–73.7 μg/L (mean 28.5 ± 22.4 μg/L, n = 10) and 4.6–215.4 μg/L (mean 30.7 ± 62.1 μg/L, n = 11) in the Ganges, Brahmaputra and Meghna flood plains, respectively. Specific ultra violet adsorption (SUVA) values (less than 3 m −1 mg −1 L) indicate that the groundwater in the Ganges flood plain has relatively low percentage of aromatic organic carbon compared to those in the Brahmaputra and Meghna flood plains. Arsenic content in sediments ranges from 1 to 11 mg/kg (mean 3.5 ± 2.7 mg/kg, n = 17) in the three flood plains. Total organic carbon content is 0.5–3.7 g/kg (mean 1.9 ± 1.1 g/kg) in the Ganges flood plain, 0.5–2.1 g/kg (mean: 1.1 ± 0.7 g/kg) in the Brahmaputra flood plain and 0.3–4.4 g/kg (mean 1.9 ± 1.9 g/kg) in the Meghna flood plain. Arsenic is positively correlated with TOC ( R 2 = 0.50, 0.87, and 0.85) in sediments from the three areas. Fourier transform infrared (FT-IR) analysis of the sediments revealed that the functional groups of humic substances in three areas include amines, phenol, alkanes, and aromatic carbon. Arsenic and Fe speciation in sediments were determined using XANES and the results imply that As(V) and Fe(III) are the dominant species in most sediments. The results also imply that As (V) and Fe (III) in most of the sediment samples of the three areas are the dominant species. X-ray absorption fine structure (EXAFS) analysis shows that FeOOH is the main carrier of As in the sediments of three areas. In sediments, As is well correlated with Fe and Mn. However, there is no such correlation observed between As and Fe as well as As and Mn in groundwater, implying that mobilizations of Fe, Mn, and As are decoupled or their concentrations in groundwater have been affected by other geochemical processes following reductive dissolution of Fe or Mn-hydroxides. For example, dissolved Fe and Mn levels may be affected by precipitation of Fe- and Mn-carbonate minerals such as siderite, while liberated As remains in groundwater. The groundwaters of the Brahmaputra and Meghna flood plains contain higher humic substances in relative fluorescence intensity (or fluorescence index) and lower redox potential compared to the groundwater of Ganges flood plain. This leads to the release of arsenic and iron to groundwater of these three plains in considerable amounts, but their concentrations are distributed in spatial variations.

Analytical constraints on acidic functional groups in humic substances

Four standard fulvic acids and two standard humic acids from the International Humic Substances Society (IHSS) were analyzed to quantify the in situ generation of new acidity during direct titrations, as observed by hysteresis between tandem forward and reverse titration curves. The resulting concentrations of carboxyl and phenolic groups were then corroborated by analytical constraints imposed by elemental data and 13C NMR data. Collectively, carboxyl groups in the IHSS samples, as determined by rapid forward direct titrations, consistently accounted for 69% (±6) of the maximum possible carboxyl-like structures that were estimated by 13C NMR spectra. The concentrations of carboxyl groups in the samples increased for two separate reverse titrations initiated at 30 min and 24 h after the completion of the forward titrations, representing 73% (±7) and 84% (±8) of the maximum carboxyl-like groups, respectively. Conversely, the concentrations of phenolic groups were invariant between forward and reverse titrations. Elemental constraints coupled with titration data predicted that the IHSS samples have, on average, one acidic hydroxyl group per every two phenyl rings, as constrained by 13C NMR estimates of aromatic carbon.

Interaction of uranium(VI) with various modified and unmodified natural and synthetic humic substances studied by EXAFS and FTIR spectroscopy

The complexation of uranium(VI) by humic acids (HAs) and fulvic acids (FAs) was studied to obtain information on the binding of uranium(VI) onto functional groups of humic substances. For this, various natural and synthetic HAs were chemically modified resulting in HAs with blocked phenolic OH groups. Both from the original and from the modified humic substances, solid uranyl humate complexes were prepared at pH 2. FTIR and extended X-ray absorption fine structure (EXAFS) spectroscopy were applied to study the chemical modification process of humic substances, to study the structure of uranyl humate complexes and to evaluate the effect of individual functional groups of humic substances (carboxylic and phenolic OH groups) on the complexation of uranyl ions. The results confirmed the predominant blocking of phenolic OH groups in the modified HAs. These modified HAs are suitable model substances to study the role of phenolic OH groups of HAs in dependence on pH. By EXAFS spectroscopy, identical structural parameters were determined for all uranyl humates. Axial UO bond distances of 1.78 Å were determined. In the equatorial plane approximately five oxygen atoms were found at a mean distance of 2.39 Å. The blocking of phenolic OH groups of HAs did not change the near-neighbor surrounding of uranium(VI) in uranyl humate complexes. Thus, the results confirmed that predominantly HA carboxylate groups are responsible for binding of uranyl ions and that the influence of phenolic OH groups is insignificant under the applied experimental conditions. The carboxylate groups are monodentate coordinated to uranyl ions.

Removal of organic polyelectrolytes and their metal complexes by adsorption onto xonotlite

Natural organic polyelectrolytes (humic and fulvic acids) and their metal complexes were removed by adsorption onto xonotlite. The removal percentages of humic and fulvic acids by xonotlite were ≈80% and 30%, respectively. Humic acid removal from solution by adsorption onto xonotlite took place more readily than fulvic acid removal. The molecular weight distributions of the humic substances remaining in solution after adsorption with the xonotlite were measured with size exclusion chromatography. A comparison of molecular weight distributions demonstrated conclusively that large molecular weight components were adsorbed preferentially, indicating that adsorption efficiency depends on the number of functional groups of humic substances. Furthermore, the surface topography of the adsorbent was observed before and after adsorption by scanning electron microscopy. The calculated heat of adsorption was of 330 kJ mol −1 which was evaluated from the Clapeyron–Clausius equation. Therefore, the adsorption type can be considered chemical. Since xonotlite can be easily synthesized and obtained at low cost, the adsorption method of humic and fulvic acids is superior to their precipitation.

Comment on “the interaction of humic substances with cationic polyelectrolytes”

Kam and Gregory (Water Research 35(2001) 3557– 3566) reported on the removal of humic substances (HS) in the coagulation and flocculation process using cationic polyelectrolytes. The investigation was devoted to the dominant mechanism of HS removal in the process. The HS elimination was compared in a Jar test performed with cationic polymers of different charge and molecular weight under constant pH of 7. The experimental results showed that charge neutralization was a significant factor for the removal of aquatic HS in the coagulation/flocculation process, monitored by the colloid titration and the streaming current procedures, and indicated that a bridging mechanism was unlikely to play a major role in this process. The authors concluded that the key mechanism of charge neutrality was applied to the HS removal in the coagulation process of metal coagulants used, as well as cationic polymers. However, the former is questionable. In coagulation using metal coagulants, three kinds of mechanisms were commonly referred for the HS removal: (1) charge neutralization, (2) complexation, and (3) adsorption [1,2]. A dominant mechanism depends on the pH of a solution. Gregor et al. [2] noted that cationic Al ions formed complexes combined with acidic functional groups (carboxylic and phenolic groups) of HS in the pH condition below 5.5, and that the function (defined as complexation) prevalently attributed to the HS reduction under the pH region. The complexation was differentiated from charge neutralization in that the complex would be precipitated due to size increase rather than charge neutrality [2]. On the other hand, Bell-Ajy et al. [3] recently reported that at low pH conditions insoluble complexes could be established through charge neutralization between negative HS and cationic metal hydrolysis products. It is likely that at low pH values the key mechanism of the HS removal is not clarified yet in the coagulation process. It was reported that the adsorption of humic substances to alum flocs played a major role in the HS removal under pH 6–7 favoring Al hydroxide precipitation [4,5]. The adsorption of HS to Al hydroxide occurs through surface complexation or ligand exchange [6]. Here, the surface complexation means interactions between functional groups of HS and surface hydroxyl on Al hydroxide [7,8]. Bose and Reckhow [9] also suggested that the adsorption of HS to Al hydroxide floc was a prevalent process in removing aquatic HS. In this paper, it was concluded that charge neutralization was the key mechanism in the coagulation process using cationic polymers, and the phenomenon extended to the HS removal in the coagulation of metal salts employed without experimental validation. However, it has been demonstrated that the dominant mechanism for the HS removal seriously varies depending on the pH of the solution in the coagulation/flocculation process when metal salts are used as coagulants. It is likely that a supplementary experiment is required to evaluate the HS removal mechanism in the coagulation using metal coagulants.

Characterization and diagenesis of strong-acid carboxyl groups in humic substances

A small fraction of carboxylic acid functional groups in humic substances are exceptionally acidic with pKa values as low as 0.5. A review of acid-group theory eliminated most models and explanations for these exceptionally acidic carboxyl groups. These acidic carboxyl groups in Suwannee River fulvic acid were enriched by a 2-stage fractionation process and the fractions were characterized by elemental, molecular-weight, and titrimetric analyses, and by infrared and 13C- and 1H-nuclear magnetic resonance spectrometry. An average structural model of the most acidic fraction derived from the characterization data indicated a high density of carboxyl groups clustered on oxygen-heterocycle alicyclic rings. Intramolecular H-bonding between adjacent carboxyl groups in these ring structures enhanced stabilization of the carboxylate anion which results in low pKa1 values. The standard, tetrahydrofuran tetracarboxylic acid, was shown to have similar acidity characteristics to the highly acidic fulvic acid fraction. The end products of 3 known diagenetic pathways for the formation of humic substances were shown to result in carboxyl groups clustered on oxygen-heterocycle alicyclic rings.

金属イオンと錯形成する腐植物質官能基のATR-FTIR法による<i>in situ</i>分析

金属イオンと錯形成する腐植物質官能基のATR-FTIR法による<i>in situ</i>分析

Effect of functional groups of humic substances on uf performance

The role of different functional groups present in humic substances on the membrane flux is unclear. This study is undertaken to (1) separate the carboxyl and phenolic groups from a humic solution, and (2) evaluate the effect of each fractionated humic substances on the ultrafiltration (UF) performance. A weak-base amine resin was used for the adsorption (pH 7) and the subsequent desorption (pH 13) of the phenolic groups from a commercial humic solution. These fractions were evaluated qualitatively (via Fourier transform infrared spectroscopy) and quantitatively (titration); they were further subjected to the analyses of the trihalomethane formation potential (THMFP) and ultrafiltration performance. Although, a complete separation of the phenolic and carboxyl groups is not possible, the results nevertheless provide useful information about their effects on UF performance. The fraction with a higher content of the phenolic OH group exhibits the highest THMFP (190 μg/mg C), whereas the fraction with a higher content of the carboxyl groups exhibits more flux decline. The UF system evaluated is unable to remove a significant portion of THM precursors, resulting in high THMs in permeate. The use of powdered activated carbon for the pretreatment of these fractions fails to improve membrane fouling. The pore size of UF membrane does not appear to affect the membrane flux, and the switch from the hydrophobic to hydrophilic membrane only slight improves the permeate flux.

Covalent Binding of Aniline to Humic Substances. 2. 15N NMR Studies of Nucleophilic Addition Reactions

Aromatic amines are known to undergo covalent binding with humic substances in the environment. Although previous studies have examined reaction conditions and proposed mechanisms, there has been no direct spectroscopic evidence for the covalent binding of the amines to the functional groups in humic substances. In order to further elucidate the reaction mechanisms, the Suwannee River and IHSS soil fulvic and humic acids were reacted with 15N-labeled aniline at pH 6 and analyzed using 15N NMR spectrometry. Aniline underwent nucleophilic addition reactions with the quinone and other carbonyl groups in the samples and became incorporated in the form of anilinohydroquinone, anilinoquinone, anilide, imine, and heterocyclic nitrogen, the latter comprising 50% or more of the bound amine. The anilide and anilinohydroquinone nitrogens were determined to be susceptible to chemical exchange by ammonia. In the case of Suwannee River fulvic acid, reaction under anoxic conditions and pretreatment with sodium borohydri...

Direct Determination of Lead Speciation in Contaminated Soils by EXAFS Spectroscopy

Direct determination of the chemical form of trace metals in soils still remains a challenge for instrumental analytical techniques. This paper examines the potential of EXAFS spectroscopy to speciate and quantify the form of trace metals in the solid fraction of soil materials using lead as a case study. Three soils contaminated by different sorts of industrial activities, including the synthesis of lead organometallics for gasoline antiknocks, Pb−Zn smelting, and recycling of lead acid battery, were investigated. In soil contaminated by alkyl-tetravalent lead compounds, lead was found to be divalent and complexed to salicylate and catechol-type functional groups of humic substances. Lead sulfate and silica-bound lead are the predominant forms in the vicinity of the battery reclamation area. Near the smelter, lead was found to be divalent and coordinated to O,OH ligands. It is present in several chemical forms, which prevented them from being identified individually. The multiplicity of lead species in s...