SEARCH · PubMed Health

Results for “Humic Substances”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 325 records · Page 18Linked to original sources

PubMed2002

Fulvic acid oxidation state detection using fluorescence spectroscopy.

Humic substances are a heterogeneous class of moderate molecular weight, yellow-colored biomolecules present in all soils, sediments, and natural waters. Although humic substances are generally resistant to microbial degradation under anaerobic conditions, some microorganisms in soils and sediments can use quinone moieties in humic substances as electron acceptors. Laboratory experiments have shown that humic substances can act as electron shuttles in the microbial reduction of ferric iron. Field studies of electron shuttling processes have been constrained by the lack of methods to characterize the oxidation state of quinone moieties in humic substances at natural concentrations. All humic substances have fluorescent properties, and fluorescence spectroscopy can indicate differences in precursor organic source of humic substances. Here we show that the quinone moieties responsible for electron transfer reactions contribute significantly to the fluorescence of humic substances. Further we use fluorescence spectroscopy to elucidate the oxidation state of quinone moieties in humic substances at natural concentrations found in sediment interstitial waters.

Benzopyrans↗

PubMed2005

The effects of combined ozonation and filtration on disinfection by-product formation.

The effects of combined ozonation and membrane filtration on the removal of the natural organic matter (NOM) and the formation of disinfection by-products (DBPs) were investigated. Ozonation/filtration resulted in a reduction of up to 50% in the dissolved organic carbon (DOC) concentration. Furthermore, humic substances were converted to non-humic substances, with changes in the humic and non-humic substance concentrations of up to -50% and +20%, respectively. Ozonation/filtration resulted in the formation of partially oxidized compounds from NOM that were less reactive with chlorine, decreasing the concentration of simulated distribution system total trihalomethanes (SDS TTHMs) and simulated distribution system halo acetic acids (SDS HAAs) by up to 80% and 65%, respectively. Reducing the molecular weight cut-off (MWCO) of the membranes resulted in reductions in the concentrations of SDS TTHMs and SDS HAAs. Using a membrane with a 5 kD MWCO, the minimum gaseous ozone concentration required to bring about effective NOM degradation and meet regulatory requirements for chlorinated DBPs was 2.5 g/m(3).

Acetates↗

PubMed1998

Recovery of humic-reducing bacteria from a diversity of environments.

To evaluate which microorganisms might be responsible for microbial reduction of humic substances in sedimentary environments, humic-reducing bacteria were isolated from a variety of sediment types. These included lake sediments, pristine and contaminated wetland sediments, and marine sediments. In each of the sediment types, all of the humic reducers recovered with acetate as the electron donor and the humic substance analog, 2,6-anthraquinone disulfonate (AQDS), as the electron acceptor were members of the family Geobacteraceae. This was true whether the AQDS-reducing bacteria were enriched prior to isolation on solid media or were recovered from the highest positive dilutions of sediments in liquid media. All of the isolates tested not only conserved energy to support growth from acetate oxidation coupled to AQDS reduction but also could oxidize acetate with highly purified soil humic acids as the sole electron acceptor. All of the isolates tested were also able to grow with Fe(III) serving as the sole electron acceptor. This is consistent with previous studies that have suggested that the capacity for Fe(III) reduction is a common feature of all members of the Geobacteraceae. These studies demonstrate that the potential for microbial humic substance reduction can be found in a wide variety of sediment types and suggest that Geobacteraceae species might be important humic-reducing organisms in sediments.

Acetic Acid↗

PubMed2005

Selenite reduction in Boom clay: Effect of FeS(2), clay minerals and dissolved organic matter.

Several experiments were set up to study Se speciation and solubility in the reducing Boom clay environment, starting from oxidized Se species which were added in oversaturation with respect to the thermodynamic solubility of reduced Se solid phases. Upon introduction of SeO3(2-) to FeS(2)-containing samples, adsorption of SeO3(2-) occurred at the FeS2 surface, and led to a reduction and precipitation of a Se0 solid phase with a solubility of 3x10(-9) M (after 60 days). In the presence of humic substances, an association of Se with these humic substances was observed and the 3x10(-9) M solubility limit was not reached in the same time delay. Upon introduction of SeO3(2-) to Boom clay suspensions (equilibration up to 9 months), the initial adsorption of SeO3(2-) on the solid phase was increased with respect to systems containing only FeS2, due to the presence of (illite) clay minerals. This competing adsorption process, and the presence of humic substances, again decreased the kinetics of reduction with respect to FeS2 samples. Also, an association of Se with Boom clay humic substances was observed, and amounted up to approximately 10(-7) M in some samples after 9 months equilibration.

Aluminum Silicates↗

PubMed2002

The effect of thermodynamic data on computer model predictions of uranium speciation in natural water systems.

Computer models have found widespread application in order to help elucidate and predict changes in environmental systems. One such application is the prediction of trace metal speciation in aqueous systems. This is achieved by solving a set of non-linear equations involving equilibrium constants for all the components in the system, within mass and charge balance constraints. In this study a comparison of the predicted uranium speciation from two computer programs, WHAM and PHREEQCI, is used to illustrate the effect variations in thermodynamic data can have on the models produced. Using the original thermodynamic data provided with the models, WHAM predicted the UO2(2+) ion as the major species (84%) while PHREEQCI predicted UO2(HPO4)2(2-) as the major species (86%). Substituting uranium data from the Nuclear Energy Agency Thermochemical Database project (NEA-TDB) into both programs produced similar results from each program, with UO2F+ predicted to dominate (68%) in a groundwater sample. Natural water samples often contain humic substances. The possible interaction of such substances with uranium was also modelled. The WHAM program includes a discreet site electrostatic humic substance model, however in order to use the PHREEQCI program to model humic substance interactions, a 'model fulvic acid' dataset was added to the program. These models predicted 85 to 98% uranium-humic substance species at neutral pH. This indicates that humic substances do need to be taken into account when modelling uranium speciation in natural water samples.

Computer Simulation↗

PubMed2006

Electrocoagulation of synthetically prepared waters containing high concentration of NOM using iron cast electrodes.

The aim of this investigation is to evaluate the treatability of synthetically prepared water with high concentration of humic substances by electrocoagulation in batch mode using iron cast electrodes. Effects of applied potential, initial humic substance concentration and supporting electrolyte type on humic substance removal efficiency were investigated. NaNO3, Na2SO4 and NaCl were used as supporting electrolyte. Among these supporting electrolytes, Na2SO4 and NaCl have provided high removal efficiencies, whereas in the experiments using NaNO3 as supporting electrolyte have been observed no flock formation. The highest removal rate is obtainable with NaCl as supporting electrolyte. Removal efficiencies for initial humic substance concentration of 500 mg L-1 with NaCl and Na2SO4 equal to 97.95% for 35 min and 92.69% for 70 min, respectively. This behavior of the system has been derived from oxidation products, available in the bulk solution, of chloride ions. When NaCl is used as supporting electrolyte, there is an advantage of providing the disinfection of water, but humic substances and chloride ions are available in the bulk solution with risk of formation undesirable organo-chlorine compounds, so the Na2SO4 is the most favorable supporting electrolyte.

Biological Products↗

PubMed1999

Role of humic-bound iron as an electron transfer agent in dissimilatory Fe(III) reduction.

The dissimilatory Fe(III) reducer Geobacter metallireducens reduced Fe(III) bound in humic substances, but the concentrations of Fe(III) in a wide range of highly purified humic substances were too low to account for a significant portion of the electron-accepting capacities of the humic substances. Furthermore, once reduced, the iron in humic substances could not transfer electrons to Fe(III) oxide. These results suggest that other electron-accepting moieties in humic substances, such as quinones, are the important electron-accepting and shuttling agents under Fe(III)-reducing conditions.

Deltaproteobacteria↗

PubMed2005

Humic substance-enhanced ultrafiltration for removal of cobalt.

It is well known that the membrane separation process combined with surfactant micelle (micellar-enhanced ultrafiltration) or polyelectrolyte (polyelectrolyte-enhanced ultrafiltration) can remove heavy metal ions or radionuclides effectively. However, the complexing agent, surfactant or polyelectrolyte remained in effluent is a serious disadvantage of these methods. In this study, humic substances (HS) were used as complexing agents instead of synthetic chemicals. The HS are sorts of natural organic matters and their functional groups such as carboxyl and phenyl groups can bind with the cation and form complexes. The effects of HS concentration and pH on the removal of cobalt were investigated. At the HS concentration of 3g/L and pH of 6, over 95% of cobalt was removed by regenerated cellulose membrane with molecular weight cut-off (MWCO) of 3000. As the HS concentration increased, the removal of cobalt was also enhanced because of the increase in binding sites (functional groups). The removal of cobalt increased from 72.5% to 97.5% as pH increased from 4 to 8 at the HS concentration of 3g/L. It resulted from the more deprotonation of functional groups in humic acid at higher pH.

Cobalt↗

PubMed2002

Reactivity of partially reduced arylhydroxylamine and nitrosoarene metabolites of 2,4,6-trinitrotoluene (TNT) toward biomass and humic acids.

Sequential anaerobic/aerobic treatment of 2,4,6-trinitrotoluene (TNT) generally results in the incorporation of residues into biomass and natural organic matter fractions of a system. To better understand the potential contribution of hydroxylamine and nitroso moieties in these reactions, studies were conducted using model systems taking advantage of the biocatalytic-activity of Clostridium acetobutylicum that does not produce aminated TNT derivatives. To evaluate binding to biomass only, systems containing cell-free extracts of C. acetobutylicum and molecular hydrogen as a reductant were employed. At the end of treatment, mass balance studies showed that 10% of the total 14C was associated with an insoluble protein-containing precipitate that could not be extracted with organic solvents. Model reactions were conducted between a mixture of 2,4-dihydroxylamino-6-nitrotoluene (DHA6NT) and 4-hydroxylamino-2,6-dinitrotoluene (4HADNT) and 1-thioglycerol to test the involvement of the nitroso-thiol reaction in binding to biomass. It was demonstrated that DHA6NT formed a new and relatively polar product with 1-thioglycerol only in the presence of oxygen. The oxygen requirement confirmed that the nitroso functionality was responsible for the binding reaction. The reactivity of arylhydroxylamino and nitrosoarene functionalities toward International Humic Substance Society (IHSS) peat humic acid was evaluated under anaerobic and aerobic conditions, respectively. 4HADNT showed no appreciable reactivity toward peat humic acid. Conversely, the nitrosoarene compound, nitrosobenzene, showed rapid reactivity with peat humic acid (50% removal in 48 h). When tested with two other humic acids (selected on the basis of their protein content), it became apparent that the proteinaceous fraction was responsible at least in part for the nitrosoarene's removal from solution. Furthermore, the pretreatment of the humic acids with a selective thiol derivatizing agent had a considerable effect on their ability to react with nitrosobenzene. Finally, molecular modeling tools were used to compare the electrophilic characteristics of potential nitroso intermediates forming from the oxidation of arylhydroxylamino metabolites of TNT. Molecular modeling analysis demonstrated that the more reduced TNT derivative containing nitroso groups were more likely to react with nucleophiles in humic substances than the less reduced nitroso intermediates.

Bacteria, Aerobic↗

PubMed2000

Electrochemical degradation of humic acid.

The treatment of natural water for drinking water production goes through the degradation of humic substances. In this study, humic acid, extracted from a peat area located at the margins of the Mogi Guaçu River at São Paulo State, Brazil, was used to perform electro-oxidation essays in order to evaluate the possibilities of electrochemical methods in the degradation of humic substances. The working electrodes were dimensionally stable anodes (DSA) type with the following compositions: Ti/Ir0.3Ti0.7O2; Ti/Ru0.3Ti0.7O2; and Ti/Ir0.2Ru0.2Ti0.6O2. The electrolyses were performed by using a solution composed of an electrolyte support (0.1 mol l(-1) KCL) and 30 mg l-1 of the humic acid. Samples were taken during the electrolyses and analysed by the pH, transmittance, UV-vis spectra and chromatography. The results show that the Ti/Ru0.3Ti0.7O2 electrode presents the best performance considering the elimination of most of the electro-oxidation products after approximately 2 h of electrolysis at 40 mA cm(-2).

Electrochemistry↗

PubMed1998

Characterization of Metal Complexation in Multiligand Systems with Lanthanide Luminescence.

The effectiveness of an Eu3+ luminescence technique to describe metal complexation reactions in humic substances was evaluated. The molecular uncertainties intrinsic to humic substances were circumvented by using polyacrylic acid (PAA) and polyvinylsulfonic acid (PVS) as probes. An adequate determination of the Eu3+-citrate affinity constant suggested that this technique could potentially be used to characterize metal binding reactions in polyelectrolytes. Various mixtures of PAA and PVS were then evaluated. The commonly adopted assumption of a single metal binding environment in those systems proved ineffective and resulted in a misleading representation of the Eu-PAA binding isotherm. Our evidence indicates that prior knowledge about the number of binding environments, as well as their relative contribution to the overall sorption, is needed to describe metal binding on humic substances appropriately through this approach. The effect of metal competition on Eu3+ binding by a mixed polymer system (1:1 PAA:PVS) was also ascertained. The affinity series obtained (Cu2+ > Pb2+ >> Cd2+ >/= Co2+ congruent with Mg2+ congruent with Ni2+ > Ca2+) was similar to that frequently observed in humic substances, which reinforces the utility of these polymers as their surrogates in metal sorption studies. Copyright 1998 Academic Press.

Journal Article↗

PubMed2001

Complexation, Stabilization, and UV Photolysis of Extracellular and Surface-Bound Glucosidase and Alkaline Phosphatase: Implications for Biofilm Microbiota.

Biofilm-produced and commercially-purified a- and b-glucosidase and alkaline phosphatase were subjected to different spectral portions of natural and artificial light and exposed to various humic substances to elucidate their impact on enzyme activities. Photochemical degradation of all enzymes occurred under different portions of the light spectrum. UVB irradiance produced the greatest overall photochemical degradation of enzymes, with significant rates occurring with UVA and PAR irradiance. The complexation of enzymes with humic substances resulted in inhibition, stabilization, and photochemical protection of the enzyme. Inhibition of enzyme activity occurred via reductions in overall enzyme activity in the presence of humic substances. However, humic-enzyme complexation also resulted in stabilization by restricting enzyme degradation while retaining high activities. Enzymes exposed to natural and artificial light sources had significantly lower reductions in enzyme activities in the presence of humic substances, which indicates that humic-enzyme complexes may protect enzymes from light-induced photochemical degradation. Bacterial surface-bound a- and b-glucosidase activities were significantly reduced in the presence of humic substances. Photosynthetically induced pH changes within biofilm communities can cause large reductions in a- and b-glucosidase activities while enhancing the hydrolytic activity of alkaline phosphatase.

Journal Article↗

PubMed2002

Characterisation of humic materials of different origin: a multivariate approach for quantifying the latent properties of dissolved organic matter.

The inherent chemical properties of eight different dissolved organic matters (DOMs) originating from soil, surface and groundwater have been analysed. The samples consist of isolated fulvic acids (FA), humic acids (HA), and humic substances (HS), i.e. natural mixtures containing a humic and a fulvic fraction. The humic substances have been characterised by elemental analysis, size exclusion chromatography, E2/E3 and E4/E6 UV absorption ratios, and liquid-state 13C-NMR spectroscopy. The information contents of the different analytical methods have been investigated by pattern recognition, i.e. cluster analysis and principal component analysis (PCA). A comparative study of the information contents of DOM descriptors derived from different analytical methods is presented. Through extraction of information content of the individual analytical methods the inherent properties of DOM are quantified. Pattern recognition revealed significant quantitative differences in the inherent properties of DOM of different origin and type. PCA based on the NMR descriptors showed highest explained variance. However, all models showed low robustness due to the limited number of samples. The supervised pattern recognition, i.e. PCA, indicates a classification of DOMs into groups of similar properties by an increase in the number of samples. Furthermore that the number of groups may be higher and more continuously distributed than the conventional classification into fulvic acids, humic acids or humic substances.

Chromatography, Gel↗

PubMed2005

Humic-like substances extracted from composts can promote the photodegradation of Irgarol 1051 in solar light.

Humic-like substances (HLS) were extracted from a mixture of sewage sludges and trimmings (70-30%, w/w) after different times of composting (0, 70 days and 130 days). HLS were analyzed by elemental analysis, UV-visible and fluorescence spectroscopy and also tested for their ability to photosensitize the degradation of Irgarol. The rate of Irgarol photodegradation in artificial solar light was found to be 2.5- to 4.3-fold higher in the presence of HLS than in buffered Milli-Q water. These results were confirmed by experiments in solar light that evidenced the photodegrading properties of HLS in a more striking way. Using 2-propanol as hydroxyl radical scavenger, we could show that hydroxyl radicals contributed to the photosensitized Irgarol degradation for about 25%. The photodegrading activity of HLS, their absorbance and their emissive properties were all found to increase between 0 and 70 days of composting and to remain quite constant between 70 and 130 days. The degree of humification varied in the same way, linking all these properties to the humification process.

2-Propanol↗

PubMed2002

Fluorescence diagnostics of oil pollution in coastal marine waters by use of artificial neural networks.

We discuss the problems with and the real possibilities of determining oil pollution in situ in coastal marine waters with fluorescence spectroscopy and of using artificial neural networks for data interpretation. In general, the fluorescence bands of oil and aquatic humic substance overlap. At oil concentrations in water from a few to tens of micrograms per liter, the intensity of oil fluorescence is considerably lower than that of humic substances at concentrations that typically are present in coastal waters. Therefore it is necessary to solve the problem of separating the small amount of oil fluorescence from the humic substance background in the spectrum. The problem is complicated because of possible interactions between the components and variations in the parameters of the fluorescence bands of humic substances and oil in water. Fluorescence spectra of seawater samples taken from coastal areas of the Black Sea, samples prepared in the laboratory, and numerically simulated spectra were processed with an artificial neural network. The results demonstrate the possibility of estimating oil concentrations with an accuracy of a few micrograms per liter in coastal waters also in cases in which the contribution from other organic compounds, primarily humic substances, to the fluorescence spectrum exceeds that of oil by 2 orders of magnitude and more.

Journal Article↗

PubMed2002

Immobilizing humic acid in a sol-gel matrix: a new tool to study humic-contaminants sorption interactions.

Humic substances originated from aquatic, soil, or sediment environments are mixtures of humic compounds with various characteristics. Sorption interactions with isolated, well defined humic fractions can be studied either in an aqueous phase ("dissolved humic substances"), or in a solid-phase, by coating mineral particles with the humic materials, or simply by working with humic acid particles (powder) at low pH to minimize dissolution. Each attitude, by definition, can be studied by different experimental techniques and has a different meaning for understanding natural environmental processes. In this study, a new tool for studying sorption interactions is presented. Sol-gel was used as an inert matrix to immobilize (entrap) various humic acids (HAs), and then used to study the interactions of several polycyclic aromatic hydrocarbons (PAHs) with the entrapped HA. Linear and nonlinear sorption coefficients were highly correlated with contaminant hydrophobicity. Sorption of pyrene to immobilized HA was in the order of soil HA > Aldrich HA approximately = peat HA. It was concluded that the entrapped HAs retained their original properties in the gel matrix and were accessible to the external contaminant through the pore network. Additionally, binding coefficients of pyreneto dissolved humic substances and to dissolved organic matter (DOM) were determined from the reduction in pyrene sorption to immobilized HA in the presence of dissolved humic material or DOM in solution. Binding coefficients of pyrene were in the order of the following: dissolved Aldrich HA > dissolved peat fulvic acid (FA) > DOM derived from mature compost > DOM derived from fresh compost.

Adsorption↗

PubMed2005

Study of the organic matter evolution during municipal solid waste composting aimed at identifying suitable parameters for the evaluation of compost maturity.

In this work the composting process of municipal solid wastes was studied in order to characterize the transformations of organic matter, particularly humic acid (HA). A composting process, lasting three months, was monitored by chemical methods; the following parameters were measured: water-soluble carbon concentration (WSC) and humic substances content (humic and fulvic acid (FA)). The effects of humification on the molecular structure of humic acid (HA) were also evaluated by Fourier transform infrared (FT-IR) and (13)C NMR spectroscopy. WSC concentration rapidly increased reaching a maximum at day-14 of the composting process and then declined. The humic and fulvic acid content (HA and FA, respectively) slightly increased during the process. The FT-IR and (13)C NMR spectra of HA indicate a high rate of change in structure during composting. The groups containing aromatic and carboxylic C increased, while polysaccharides and other aliphatic structures degraded during composting, resulting in HA structures of higher aromaticity. Therefore, spectrometric measurements could provide information significantly correlated to conventional chemical parameters of compost maturity.

Biodegradation, Environmental↗

PubMed1980

Determining the role of human substances in the fate of pesticides in the environment.

The data presented in this paper emphasize that the behavior and fate of pesticides in the environment is influenced by humic substances. Various methods most frequently used for the characterization of humic substances are discussed. Both humic acid and fulvic acid can solubilize in water certain organic compounds and are important carriers of some pesticides in soil. Humic substances have the potential for promoting the nonbiological degradation of many pesticides. Several methods of bleaching humus color from drinking water, including chlorination, ozonation, and UV-radiation, are described. Finally, the photochemical stability to UV-radiation of certain pesticides in aqueous fulvic acid solution is discussed.

Atrazine↗