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PubMed2001

Relating ion binding by fulvic and humic acids to chemical composition and molecular size. 1. Proton binding.

Proton binding by a soil fulvic acid, humic acid, and a set of size fractions of the humic acid was studied as a function of pH and ionic strength by potentiometric titrations. The negative charge of the humic substances resulting from deprotonation of acidic functional groups generally increased with increasing pH and increasing ionic strength. At any given pH and ionic strength, the fulvic acid fraction exhibited much higher negative charge than the humic acid fraction. For the size-fractionated humic acids, negative charge decreased steadily with increasing apparent molecular weight, as determined by size exclusion chromatography. Observed differences in proton binding by the various humic substances corresponded well to differences in functional group composition, which has been extensively characterized in a previous study using a combination of analytical techniques. The proton binding behavior of the humic substances was described very well by the consistent NICA-Donnan model. However, when all adjustable model parameters were determined using a least-squares minimization technique without introducing parameter constraints, the values of some parameters turned out physically and chemically unreasonable. Therefore, we propose to derive some model parameters from chemical characterization results obtained by size exclusion chromatography and solid-state 13C NMR spectroscopy. Using this approach, we obtained excellent descriptions of all titration data, and the model parameter values were more consistent and chemically reasonable. Our results demonstrate that characterization results of humic substances can be used in NICA-Donnan modeling to reduce the number of free fitting parameters without arbitrary constraints and, thereby, obtaining a more reliable database for environmental modeling.

Benzopyrans↗

PubMed2005

Modeling salt-dependent proton binding by organic soils with the NICA-Donnan and Stockholm humic models.

Models are available for simulations of proton dissociation and cation binding by natural organic matter; two examples are the NICA-Donnan and Stockholm Humic (SHM) models. To model proton and metal binding, it is necessary to properly account for the ionic strength dependence of proton dissociation. In previous applications of the models for soils itwas assumed that the electrostatic interactions for solid-phase humic substances were the same as in solution; this assumption was recently challenged. Therefore, we reanalyzed previously published acid-base titrations of acid-washed Sphagnum peat, and we produced additional data sets for two Sphagnum peats and two Spodosol Oe horizons. For the soil suspensions, the original NICA-Donnan and SHM models, which were developed for dissolved humic substances, underestimated the observed salt dependence considerably. When a fixed Donnan volume of 1 L kg(-1) for humic substances in the solid phase was used, the NICA-Donnan model fits were much improved. Also for SHM, slight changes produced improved model fits. The models also produced acceptable simulations of the dissolved Ca, Mg, and Cd concentrations, provided that cation selectivitywas introduced. In conclusion, the proposed extensions to the NICA-Donnan and SHM models were shown to predict the salt dependence of solid-phase humic substances more satisfactorily than earlier model versions.

Humic Substances↗

PubMed2003

Hygroscopic properties of two model humic-like substances and their mixtures with inorganics of atmospheric importance.

Water-soluble macromolecular polyacids can play a potentially important role in the hygroscopic properties of atmospheric aerosols. These acids have molecular structures similar to natural fulvic acids (FA) (or humic acids) and are referred to as humic-like substances (HULIS). In this study, the hygroscopicity of HULIS and the mixture of HULIS and sodium chloride (NaCl) and that of HULIS and ammonium sulfate (AS) aerosols at a mass ratio of 1:1 are studied using two natural FA: the Nordic Aquatic Fulvic Acid (NAFA) and the Suwannee River Fulvic Acid (SRFA) as model compounds in an electrodynamic balance. NAFA and SRFA both absorbed and desorbed water reversibly without crystallization and retained water at a relative humidity (RH) < 10%. NAFA and SRFA have a mass growth ratio of 1.25 and 1.45 from RH = 10% to RH = 90%, respectively. However, these results are different from those of another natural FA (the Nordic River Fulvic Acid Reference) in the literature. The differences are possibly due to the differences in the chemical composition of the natural FA, which depends on their sources and the isolation methods. These results suggest that a standardization of the isolation methods of HULIS is needed for better understanding of their atmospheric properties and environmental impacts. In general, the deliquescence and crystallization RH of FA-inorganic mixtures are comparable with those of their respective pure inorganic species. Since FA are less hygroscopic than NaCl and AS, all mixtures absorb less water compared to their respective pure inorganic species of equal particle mass. The FA-AS mixtures have a larger water uptake than the sum of those of the FA and AS individually following a simple additivity rule as noninteracting species at RH = 90%. This enhancement effect increases as the RH decreases. There is no such enhancement effect for the FA-NaCl mixtures until RH is below 90%. These results reveal that the effect of the interactions between FA and inorganic species on the water uptake of the mixtures, in general, is a function of RH.

Absorption↗

PubMed2005

Phenanthrene sorption to sequentially extracted soil humic acids and humins.

Humic substances strongly influence the environmental fate of hydrophobic organic chemicals in soils and sediments. In this study, the sorption of phenanthrene by humic acids (HAs) and humins was examined. HAs were obtained from progressively extracting a soil, eight times with 0.1 M Na4P207 and two times with 0.1 M NaOH solution, and then the residue was separated into two humin fractions by their organic carbon contents. The chemical and structural heterogeneity of the HAs and humins were characterized by elemental analysis, ultraviolet-visible spectroscopy, diffuse reflectance infrared Fourier transform spectroscopy, and solid-state 13C NMR. There were significant chemical and structural differences among the HA fractions and humins; the later extracted HAs had relatively high aliphatic carbons content. All sorption data were fitted to a Freundlich equation, S = K(F)C(N), where S and C are the sorbed and solution-phase concentrations, respectively, and K(F) and N are constants. All of the phenanthrene sorptions were nonlinear, and the nonlinearity decreased with further extractions from 0.90 (first extracted HA) to 0.96 (ninth HA) and was the lowest (0.88) for the higher organic carbon content humin. Phenanthrene sorption coefficient by HAs significantly increased with progressive extractions, being the highest for the humins. For HAs isotherms, a positive trend was observed between the sorption coefficient and the aliphaticity, but a negative relation was shown between the nonlinearity and the aliphaticity and between the sorption capacity and polarity of HAs. Phenanthrene sorption was greatly affected by chemical structure and composition of humic substances, even from a same soil. In addition, polarity of humic substances seems to mainly regulate the magnitude of phenanthrene sorption rather than structure.

Adsorption↗

PubMed1994

Complexation of iron by humic-like substances in lung tissue: role in coal workers' pneumoconiosis.

Deposition of coal dust in the lungs during the mining of this energy resource can cause an inappropriate fibrosis. Those characteristics of the coal responsible for lung injury are not known. The hypothesis was tested that 1) humic-like substances (HLS) in coal complex iron cations, which subsequently catalyze oxidant generation; and 2) the accumulation of this metal in the lungs of coal miners is associated with collagen deposition. In vitro measurements of ionizable ferric ion concentration ([Fe3+]) and oxidant generation by 10 standard coal dusts increased with the concentration of HLS. Dust mass, nonheme [Fe3+], and hydroxyproline concentrations in lung tissue were significantly higher in the lungs of coal miners, relative to matched controls. Although hydroxyproline concentrations increased with both dust mass and tissue nonheme [Fe3+], the association with the latter appeared greater. HLS in coal dusts sequestered in human lungs may be associated with injury as a result of their capacity to complex metals, which catalyze oxidant generation.

Coal↗

PubMed2006

[Inoculating microbes on municipal solid wastes composting affects organic acids and maturity].

Inoculating microbes (Meishang compound microbes, MS; Zhongjia fermentation microbes, ZJ) on municipal solid wastes composting which adopted industrialized technology was studied. The dynamic changes of low molecule weight organic acid and high molecule weight humic substance were discussed. The results show that inoculating microbes on municipal solid wastes composting could increase the content of organic acid at initial stage of composting, and decrease that at final stage. But humic substance and humic acid decline at the initial stage, then increase at the final stage of composting. The dynamic changes of organic acid and humification index indicate that inoculating microbes on municipal solid wastes can obviously increase the maturity of composting, and order as follow: MS+ ZJ>ZJ > MS>CK.

Acids↗

PubMed2004

UV spectroscopy: a tool for monitoring humification and for proposing an index of the maturity of compost.

Composting organic matter is an interesting way to valorize waste. Compost is a product obtained after a humification process. The humification of organic matter during composting was studied by the quantification and monitoring of the evolution of humic substances. The final objective was to be able to evaluate the state of humification based on a spectrum of total humic substances using the method of UV spectral deconvolution. This study presented a new index obtained by UV spectroscopy using the deconvolution of an unknown spectrum of compost with 3 reference spectra. This index was compared to the maturity indices usually used, such as total extraction of humic substances (rate of extraction), IP (index of polymerization) or the humic acid to fulvic acid ratio. This new parameter, which was easy and quick to determine, gave precise information about the quality of the compost. It made it possible to disregard the values of aberrant concentrations caused by the classical protocol of extraction. Compared to the humic acid to fulvic acid ratio, the new index obtained by UV spectral deconvolution showed more representative results: the humic acid to fulvic acid ratio for an apparently non-mature compost was abnormally high, suggesting that the compost was mature, whereas the UV index proposed showed that the compost was really young and not yet humified.

Benzopyrans↗

PubMed2003

Fluorescence spectroscopic studies of natural organic matter fractions.

Because of the well-known molecular complexity and heterogeneity of natural organic matter (NOM), an aquatic bulk NOM was fractionated into well-defined polyphenolic-rich and carbohydrate-rich subfractions. These fractions were systematically characterized by fluorescence emission, three dimensional excitation-emission matrices, and synchronous-scan excitation spectroscopy in comparison with those of the reference International Humic Substances Society soil humic acid and Suwannee River fulvic acid. Results indicate that fluorescence spectroscopy can be useful to qualitatively differentiate not only NOM compounds from varying origins but also NOM subcomponents with varying compositions and functional properties. The polyphenolic-rich NOM-PP fraction exhibited a much more intense fluorescence and a red shift of peak position in comparison with the carbohydrate-rich NOM-CH fraction. Results also indicate that synchronous excitation spectra were able to provide improved peak resolution and structural signatures such as peak positioning, shift, and intensity among various NOM components as compared with those of the emission and excitation spectra. In particular, the synchronous spectral peak intensity and its red shift in the region of about 450-480 nm may be used to indicate the presence or absence of high molecular weight and polycondensed humic organic components, or the multicomponent nature of NOM or NOM subcomponents.

Chemical Fractionation↗

PubMed2002

Charge effects in the fractionation of natural organics using ultrafiltration.

Comparison of two commonly used techniques for molecular weight determination of natural organics, ultrafiltration (UF) fractionation and high-performance size exclusion chromatography (SEC), shows that neither technique gives absolute measures of molecular weight. Investigations of International Humic Substances Society standard humic and fulvic acids as well as natural organic matter concentrated from surface freshwaters show that charge effects and solution conditions are important in both SEC and UF fractionation with various components of the natural organics being affected differently. Membranes with a smaller molecular weight cutoff (MWCO) produce permeates with a lower UV/DOC ratio, suggesting that the more aromatic components of natural organics are removed by the lower molecular weight cutoff membranes. Variation in ionic strength has little effect on the rejection of humic acid fractions but does significantly influence the rejection of low molecular weight acids. pH and organic concentration do not affect DOC rejection significantly over the pH range of 4.5-10 and the DOC concentration range of 15-60 mgL(-1). These results indicate that UF should not be applied for quantitative "size" analysis unless performed under well-defined conditions. If performed under conditions appropriate to water treatment, UF fractionation can give information of direct applicability to treatment such as the MWCO required to achieve significant organics removal.

Benzopyrans↗

PubMed2005

Acid-base properties of humic and fulvic acids formed during composting.

The soil acid-base buffering capacity and the biological availability, mobilization, and transport of macro- and micronutrients, toxic metal ions, and xenobiotic organic cations in soil are strongly influenced by the acid-base properties of humic substances, of which humic and fulvic acids are the major fractions. For these reasons, the proton binding behavior of the humic acid-like (HA) and fulvic acid-like (FA) fractions contained in a compost are believed to be instrumental in its successful performance in soil. In this work, the acid-base properties of the HAs and FAs isolated from a mixture of the sludge residue obtained from olive oil mill wastewater (OMW) evaporated in an open-air pond and tree cuttings (TC) at different stages of composting were investigated by a current potentiometric titration method and the nonideal competitive adsorption (NICA)-Donnan model. The NICA-Donnan model provided an excellent description of the acid-base titration data, and pointed out substantial differences in site density and proton-binding affinity between the HAs and FAs examined. With respect to FAs, HAs were characterized by a smaller content of carboxylic- and phenolic-type groups and their larger affinities for proton binding. Further, HAs featured a greater heterogeneity in carboxylic-type groups than FAs. The composting process increased the content and decreased the proton affinity of carboxylic- and phenolic-type groups of HAs and FAs, and increased the heterogeneity of phenolic-type groups of HAs. As a whole, these effects indicated that the composting process could produce HA and FA fractions with greater cation binding capacities. These results suggest that composting of organic materials improves their agronomic and environmental value by increasing their potential to retain and exchange macro- and micronutrients, and to reduce the bioavailability of organic and inorganic pollutants.

Adsorption↗

PubMed2005

Carbon-specific analysis of humic-like substances in atmospheric aerosol and precipitation samples.

A new approach for the carbon-specific determination of humic-like substances (HULIS) in atmospheric aerosols is presented. The method is based on a two-step isolation procedure of HULIS and the determination of HULIS carbon with a dissolved organic carbon analyzer. In the first step, a C18 solid-phase extraction is performed to separate HULIS from inorganic and hydrophilic organic sample constituents in aqueous sample solutions. The second isolation step is conducted on a strong anion exchanger to separate HULIS from remaining carbonaceous compounds. This ion chromatographic separation step including the subsequent on-line detection of HULIS carbon was performed fully automated to avoid the risk of sample contamination and to enhance the reproducibility of the method. With a 5-mL sample volume, a limit of detection of 1.0 mg C/L was obtained; this corresponds to an absolute amount of 5 microg of HULIS carbon. The reproducibility of the method given as the relative standard deviation was 4.3% (n = 10). The method was applied for the determination of water-soluble HULIS in airborne particulate matter. PM10 concentrations at an urban site in Vienna, Austria, ranged from around 0.1 to 1.8 microg of C/m(3) (n = 49); the fraction of water-soluble HULIS in OC was 12.1 +/- 7.2% (n = 49).

Journal Article↗

PubMed1999

Oxidative injury induced by synthetic humic acid polymer and monomer in cultured rabbit articular chondrocytes.

Humic substance has been proposed as one of the causative factors of Kashin-Beck disease (KBD), an endemic osteoarthritic disorder with necrosis of chondrocytes widely prevalent in some regions of China. In order to exclude the complications of natural humic substance, here we prepared phenolic polymers of synthetic humic acid (SHA) by oxidation of phenolic monomer, the protocatechuic acid (PCA). The biological effects of SHA and PCA on primary culture of rabbit articular chondrocytes were investigated. We found that not only SHA but also PCA caused chondrocyte injury, as evidenced by the loss of cell viability measured with methylthiazol tetrazolium (MTT) assay and the increased release of intracellular lactate dehydrogenase (LDH). Both SHA and PCA could result in lipid peroxidation and glutathione (GSH) depletion in chondrocytes, indicating that oxidative stress may be involved in chondrocyte injury. Furthermore, a marked increase in intracellular calcium level ([Ca2+]i) occurred after chondrocytes treated with SHA or PCA. These results suggest that chondrocyte injury elicited by SHA or PCA may be mediated through the occurrence of oxidative stress and the disruption of intracellular Ca2+ homeostasis. Data also suggest that the monomeric phenolic acid may be considered one of the causative factors of KBD in addition to humic substance.

Animals↗

PubMed2006

Sorption kinetics of toluene in humic acid: a computational approach.

Molecular dynamics, a computational technique aiming to describe the time-dependent movement of molecules, has been applied to study the sorption kinetics of volatile organic contaminants in soil organic matter. The molecular dynamics simulation results obtain reasonably accurate estimates of diffusion rates and activation energy of the penetration of a volatile organic compound molecule into a model humic substance. The sorption rate of toluene to humic acid decreases with the density of the humic acid matrix and increases with temperature. All the present results indicate that the sorption of toluene into humic acid is mainly diffusion controlled. Finally, the present studies have shown that molecular dynamics of volatile organic compounds in humic substances yields meaningful results, which help in the understanding of diffusion at the molecular level and which facilitate the problem-solving capability for removing the contaminants from the soils.

Adsorption↗

PubMed1994

Humic-like substances in cigarette smoke condensate and lung tissue of smokers.

Deposition of pigmented matter in the lower respiratory tract correlates with the extent of emphysema in smokers as well as with free radical generation and iron accumulation. Pulmonary emphysema is postulated to be mediated by free radical generation which is either directly or indirectly associated with cigarette smoke exposure. The hypothesis was tested that 1) incomplete combustion of tobacco yields humic-like substances (HLS) which 2) deposit in the lung as pigmented particulates, 3) complex iron cations in vitro and in vivo, and 4) have a capacity to catalyze oxidant formation. HLS, isolated by alkali extraction of cigarette smoke condensate (CSC) (Tobacco Health Research Institute, University of Kentucky), demonstrated a high carbon and low carboxylate content on elemental and functional group analyses, respectively, compared with values for HLS sequestered from soils. The HLS isolated from CSC had a capacity to complex iron in vitro and accumulated the metal in vivo after intratracheal instillation in an animal model. Both HLS and its iron complex generated free radicals, and some portion of this oxidant generation was metal dependent. Lung tissue collected at autopsy from smokers contained HLS with an infrared spectrum almost identical to that of the material isolated from CSC. Associations between particulate deposition, metal accumulation, and free radical generation suggest a possible role of HLS in the induction of lung disease following cigarette exposure.

Animals↗

PubMed2006

Microbially mediated biodegradation of hexahydro-1,3,5-trinitro-1,3,5- triazine by extracellular electron shuttling compounds.

The potential for humic substances to stimulate the reduction of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) was investigated. This study describes a novel approach for the remediation of RDX-contaminated environments using microbially mediated electron shuttling. Incubations without cells demonstrated that reduced AQDS transfers electrons directly to RDX, which was reduced without significant accumulation of the nitroso intermediates. Three times as much reduced AQDS (molar basis) was needed to completely reduce RDX. The rate and extent of RDX reduction differed greatly among electron shuttle/acceptor amendments for resting cell suspensions of Geobacter metallireducens and G. sulfurreducens with acetate as the sole electron donor. AQDS and purified humic substances stimulated the fastest rate of RDX reduction. The nitroso metabolites did not significantly accumulate in the presence of AQDS or humic substances. RDX reduction in the presence of poorly crystalline Fe(III) was relatively slow and metabolites transiently accumulated. However, adding humic substances or AQDS to Fe(III)-containing incubations increased the reduction rates. Cells of G. metallireducens alone reduced RDX; however, the rate of RDX reduction was slow relative to AQDS-amended incubations. These data suggest that extracellular electron shuttle-mediated RDX transformation is not organism specific but rather is catalyzed by multiple Fe(III)- and humic-reducing species. Electron shuttle-mediated RDX reduction may eventually become a rapid and effective cleanup strategy in both Fe(III)-rich and Fe(III)-poor environments.

Anthraquinones↗

PubMed2003

The fate of estrogenic compounds in the aquatic environment: sorption onto organic colloids.

In this study, sorption of some estrogens and estrogenic compounds onto several organic colloids was examined using fluorescence quenching techniques. Selected organic colloids included humic substances of several sources, Aldrich humic acid (AHA), Suwannee River humic acid (SRHA), Suwannee River fulvic acid (SRFA), and Nordic fulvic acid (NFA). Polysaccharides, alginic acid (AA) and dextran (Dex), and tannic acid (TA) were also selected. 17beta-estradiol (E2), 17alpha-ethynylestradiol (EES), and estriol (E3) were selected as estrogens. Nonylphenol (NP), octylphenol (OP), and dibutylphthalate (DBP) were selected as estrogenic compounds. For most of the selected compounds, the sorption coefficients were in the order of TA > humic acids (SRHA or AHA) > fulvic acids (NFA or SRFA) > AA. The smallest or no significant sorption onto dextran was found for selected estrogens and estrogenic compounds. Comparing those compounds, neither a significant trend nor linear correlation with Log K(ow) was found. The resulting sorption coefficients for humic substances and TA suggested approximately 15 to 50% of the estrogens and estrogenic compounds were bound in typical natural water of 5 mg TOC/L and significant effects on the removal of them by water treatment processes, toxicity, or bioavailability were suggested.

Adsorption↗

PubMed2002

[Outflows of trihalomethane precursors from soils].

Outflows of trihalomethane formation potential (THMFPs) which was chosen as an index of the amount and reactivity with chlorine of THMs precursors from soils were studied with soil column experiment. The results indicated that factors influencing THMFP concentrations of leacheates were the physicochemical properties of soils, especially contents, composition and reactivities with chlorine of humic substances, the pH value of feed solution and cumulative leaching volume. The THMFP concentrations of leachates rose with increases in amounts of humic substances with high solubility as well as reactivity with chlorine. The effluents of soil samples contained the lowest THMFP concentrations under the feed solution of the lowest pH value (pH 3.0). THMFPs appeared to more easily flow out from soils with the feed solution of lower pH value, which was properly due to the increases in solubility of humic substances under the lower pH value conditions. In most cases, THMFP concentrations of leachates showed decline with the increase of cumulative leaching volumes of feed solution.

Halogens↗

PubMed2001

Impact of natural nanophases on heavy-metal retention in zeolite-supported reactive filtration facilities for urban run-off treatment.

The retention of lead in zeolite-supported sand-filter columns has been tested with focus on the effect of potentially mobile natural nanophases (natural colloids, humic substances). It could be shown that interaction of lead with natural nanophases enhanced the mobility of the contaminant. In the presence of iron oxide particles (goethite) a normal breakthrough of lead was observed. Humic substance can act as a carrier for lead itself and can enhance the mobility of lead bound to inorganic nanophases, because of the increased mobility of the nanophases in the presence of humic substances.

Chelating Agents↗