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PubMed2001

Two-dimensional NMR studies of size fractionated Suwannee River fulvic and humic acid reference.

Two-dimensional phase sensitive 13C,1H correlation spectra were applied to the investigation of substructures in size fractions obtained by tangential flow multistage ultrafiltration (MST-UF) of humic substances (HS) Suwannee River Fulvic Acid Reference (HS SR FA) and Suwannee River Humic Acid Reference (HS SR HA), purchased from the International Humic Substances Society (IHSS). After size fractionation with MST-UF the HS samples give well resolved two-dimensional 13C,1H-correlated NMR spectra which offer a great potential for substructure elucidation and even quantification. It is shown that low molecular size lignin moieties undergo demethylation of the methoxy groups, accompanied by removal of the phenylpropane side chains and subsequent reaggregation of the aromatic rings. These findings provide insight into the processes of lignin degradation. Only the fraction >100 kDa contains macromolecules that have spin-spin relaxation times too short for investigations employing NMR multipulse sequences.

Benzopyrans↗

PubMedDate not supplied

Elemental quantitation of natural organic matter by CPMAS 13C NMR spectroscopy.

Cross-polarized magic-angle-spinning NMR (CPMAS-NMR) techniques are assumed to be only semi-quantitative in the assessment of carbon distribution in humic substances or natural organic matter, due to a number of interferences such as spinning side bands (SSB) in spectra, paramagnetic species in samples, and low or remote protonation of aromatic carbons. Fast rotor spin rates or direct polarization NMR techniques are normally applied to improve quantitative signal detectability. Variable contact time pulse sequences were used here to obtain CPMAS-NMR spectra of organic compounds of known structure and different humic substances. Integration of spectral areas, previously subtracted of SSB, and relative stoichiometric factors were used for mathematical elaboration to calculate the elemental content in samples. These values did not significantly differ from those obtained by direct determination of elemental content with quantitative elemental analysis. Our results showed that the carbon observed CPMAS-NMR provides a quantitative representation of the whole carbon content in humic substances.

Magnetic Resonance Spectroscopy↗

PubMed2006

Removal of low-molecular weight DBPs and inorganic ions for characterization of high-molecular weight DBPs in drinking water.

High-molecular weight (MW) halogenated disinfection byproducts (DBPs) may cause adverse health effects. In this work several issues related to the better separation and characterization of the high MW halogenated DBPs (MW>500Da) were studied. Ultra-filtration (UF) coupled with a nominal 500-Da membrane was employed to flush out low MW DBPs and inorganic ions. Two procedures, intermittent UF and continuous UF, were used and compared. The results demonstrate that haloacetic acids, chloride and sodium ions could be effectively flushed out, and most of phosphate ions could be flushed out for a given dilution number or sufficient Milli-Q water. The size exclusion chromatograms indicate that haloacetic acids and trihalomethanes were not bound to Suwannee River fulvic acid (SRFA); 2,4,6-trichlorophenol might form some binding with SRFA, but it appeared to be very weak and readily broken up when passing along the size exclusion column. The octanol-water partition coefficients of low MW DBPs and the properties of humic substances seem to play key roles in determining the formation of possible bindings between low MW DBPs and humic substances.

Chromatography, Gel↗

PubMed2002

Formation of bound residues of 8-hydroxybentazon by oxidoreductive catalysts in soil.

This study was performed to determine which oxidoreductive catalysts were most efficient in catalyzing the binding of 8-hydroxybentazon to soil humic substances. 8-Hydroxybentazon was completely transformed by an oxidoreductive enzyme, laccase of Myceliophthora thermophila, at pH 3.0-7.0 within 30 min. When abiotic catalysts, manganese(IV), iron(III), and aluminum oxides were used in the same pH range, 8-hydroxybentazon was completely transformed only by manganese(IV) oxide (delta-MnO2), but a relatively small amount of 8-hydroxybentazon was transformed by iron(III) oxide and aluminum oxide. The adsorption of 8-hydroxybentazon in the soil showed an H-type and coincided well with the Langmuir isotherm. To better understand the factors involved in the rapid and strong binding of 8-hydroxybentazon with soil humic substances, 8-hydroxybentazon transformation by oxidoreductive catalysts was studied in various soil conditions: air-dried, preincubated, sterilized, and iron(III) oxide and manganese(IV) oxide free. 8-Hydroxybentazon was completely transformed within 24 h in the decreasing order of preincubated, air-dried, and sterilized soils. However, little transformation was observed in the iron(III) oxide and manganese(IV) oxide free soils. These results suggest that the major catalyst responsible for the rapid and strong binding of 8-hydroxybentazon to soil humic substances is a metal oxide, manganese(IV) oxide, not a soil oxidoreductive enzyme.

Adsorption↗

PubMed2003

The volatilisation and sorption of (129)I in coniferous forest, grassland and frozen soils.

129I is a potentially important radionuclide in safety assessments of proposed deep geological radioactive waste repositories due to its radiotoxicity, high mobility and long physical half-life (15.7 million years). In soils, iodine is present both in an inorganic form and in organohalide complexes, some of which are volatile under natural environmental conditions. This study has examined volatilisation, sorption and the effect of freezing on sorption and loss of (125)I (physical half-life 60.2 days), as a surrogate for (129)I, within coniferous forest and grassland soils. The results do not suggest that volatilisation from these soils is a significant pathway for the transport of (129)I. Strong and specific sorption of iodine to humic substances has been demonstrated, which is reduced at freezing temperatures. It is hypothesised that rapid sorption to soil humic substances can significantly reduce volatilisation rates. The effect of freezing conditions on iodine extractability from soils suggests a microbially mediated sorption process.

Ecosystem↗

PubMed2003

Nitrilotriacetate stimulation of anaerobic Fe(III) respiration by mobilization of humic materials in soil.

An enrichment culture capable of naphthalene mineralization reduced Fe(III) oxides without direct contact in anaerobic soil microcosms when the Fe(III) was placed in dialysis membranes or entrapped within alginate beads. Both techniques demonstrated that a component in soil, possibly humic materials, facilitated Fe(III) reduction when direct contact between cells and Fe(III) was not possible. The addition of the synthetic Fe(III) chelator, nitrilotriacetic acid (NTA), to soil enhanced Fe(III) reduction across the dialysis membrane and alginate beads, with the medium changing from clear to a dark brown color. An NTA-soil extract was more effective in Fe(III) reduction than the extracted soil itself. Characteristics of the NTA extract were consistent with that of humic substances. The results indicate that NTA improved Fe(III) reduction not by Fe(III) solubilization but by extraction of humic substances from soil into the aqueous medium. This is the first study in which stimulation of Fe(III) reduction through the addition of chemical chelators is shown to be due to the extraction of electron-shuttling compounds from the soil and not to solubilization of the Fe(III) and indicates that mobilization of humic materials could be an important component of anaerobic biostimulation.

Anaerobiosis↗

PubMed2006

Binding of Pb(II) in the system humic acid/goethite at acidic pH.

The study of Pb(II) binding to the system humic acid/goethite in acidic medium is reported in the present paper. From a macroscopic point of view, we have constructed the experimental sorption isotherms (using atomic absorption spectroscopy) and compared them with the prediction of the additivity rule. It is found that this system presents positive deviations, that is, the amount sorbed is about an order of magnitude higher than predicted. Apart from this, microscopic and structural aspects have also been studied using in situ and ex situ infrared spectroscopy. These results suggest that the presence of Pb(II) increases the amount of humic acid bound to the oxide. It is proposed that proton displacement due to the interaction between humic substances and the oxide, along with the formation of ternary complexes with the Pb(II) cation bridging the oxide and the humic substances (Type A complexes), cause the deviation from additivity.

Humic Substances↗

PubMed2002

Humic acids isolated from earthworm compost enhance root elongation, lateral root emergence, and plasma membrane H+-ATPase activity in maize roots.

Earthworms (Eisenia foetida) produce humic substances that can influence plant growth by mechanisms that are not yet clear. In this work, we investigated the effects of humic acids (HAs) isolated from cattle manure earthworm compost on the earliest stages of lateral root development and on the plasma membrane H(+)-ATPase activity. These HAs enhance the root growth of maize (Zea mays) seedlings in conjunction with a marked proliferation of sites of lateral root emergence. They also stimulate the plasma membrane H(+)-ATPase activity, apparently associated with an ability to promote expression of this enzyme. In addition, structural analysis reveals the presence of exchangeable auxin groups in the macrostructure of the earthworm compost HA. These results may shed light on the hormonal activity that has been postulated for these humic substances.

Animals↗

PubMed1998

Oxidative stress induced by humic acid solvent extraction fraction in cultured rabbit articular chondrocytes.

Kashin-Beck disease (KBD), an endemic, chronic osteoarthritic disorder with necrosis of chondrocytes, commonly occurs in China. The humic substance present in the drinking water of endemic areas has been proposed as one of the causative factors. In this study an in vitro cell culture system was used to investigate the damaging effects of humic acid (HA), a constituent of humic substance, on cultured rabbit articular chondrocytes. The commercial Aldrich humic acid (AHA) was fractionated with a series of organic solvents including n-hexane, benzene, ethyl acetate, and methanol. Among the several fractions of AHA, the ethyl acetate fraction (AHA-[EA]) displayed the most potent inhibitory effect on the survival of chondrocytes in clonogenic assays. Cellular injury induced by AHA-[EA] was evaluated by measuring cell viability with methylthiazol tetrazolium (MTT) and by determining the release of intracellular lactate dehydrogenase (LDH). Incubation of chondrocytes with AHA-[EA] (100-500 microg/ml) for 12 h produced a concentration-dependent decrease in cell viability and increase in LDH release. In addition, AHA-[EA] triggered lipid peroxidation manifested by elevated malondialdehyde (MDA) formation. In chemiluminescence assay, AHA-[EA] at the concentrations of 150-600 microg/ml caused 6- to 15-fold increases of luminol-amplified chemiluminescence responses, which are considered to reflect the production of hydrogen peroxide (H2O2). Moreover, pretreating the cells with 500-750 U/ml of catalase significantly prevented the loss of cell viability, while superoxide dismutase (SOD) enhanced the adverse effect of 300 microg/ml AHA-[EA]. Data suggest that the injury to chondrocytes induced by AHA-[EA] may be first through O2.- production, which is then converted into H2O2, thus initiating lipid peroxidation and leading to chondronecrosis observed in KBD.

Animals↗

PubMed1989

Lignin degradation and humus formation in alluvial soils and sediments.

The contribution of lignin to the formation of humic compounds was examined in different environments of the terrestrial-aquatic interface in the Garonne River valley in southwestern France. Alluvial soils and submerged or nonsubmerged river and pond sediments containing alder, poplar, or willow [C-lignin]ligno-celluloses were incubated. After a 49-day incubation period, 10 to 15% of labeled lignins in alluvial soils was recovered as evolved CO(2). In nonsubmerged sediments, 10% of the applied activity was released as CO(2), and in submerged sediments, only 5% was released after 60 days of incubation. In the different alluvial soils and sediments, the bulk of residual activity (70 to 85%) remained in the two coarsest-grain fractions (2,000 to 100 and 100 to 50 mum). Only 2 to 6% of the residual activity of these two coarse fractions was recovered as humic and fulvic acids, except in the case of alder [C-lignin]lignocellulose, which had decomposed in a soil collected beneath alders. In this one 55% of the residual activity was extracted as humic substances from the 2,000- to 100-mum fraction. Humic and fulvic acids represented from 6 to 50% of the residual activity in the finest-grain fractions (50 to 20 and 20 to 0 mum). The highest percentages were obtained in soil collected beneath alders and in submerged pond sediment. The contribution of different groups of microorganisms, as well as nutrients and clay content, may influence humic-substance formation in such environments. Physical stability also may be an important factor for complex microbial activity involved in this process.

Journal Article↗

PubMed2002

Interaction of 2,4,6-trinitrotoluene (TNT) and 4-amino-2,6-dinitrotoluene with humic monomers in the presence of oxidative enzymes.

Oxidative coupling of nitroaromatic compounds involving soil organic matter was examined as a means of soil remediation. Humic monomers, serving as model compounds for soil humic substances, were used as cosubstrates, applying phenoloxidases (laccase from Trametes villosa and peroxidase from horseradish) as oxidative biocatalysts. Without the addition of a cosubstrate, only 30% of 4-amino-2,6-dinitrotoluene (4ADNT) and no 2,4,6-trinitrotoluene (TNT) were transformed in the presence of the laccase. Adding various phenolic monomers produced differing effects on the enzyme-mediated transformation, which indicated that xenobiotics are preferentially bound to quinoid and phenolic moieties of soil humic substances. In the presence of the humic monomer catechol and the enzyme, up to 100% of 4ADNT and up to 80% of TNT were transformed. Enzymatic transformation of 4ADNT in the presence of catechol reached a maximum at pH 6.8. TNT transformation, however, further increased at pH values above 6.8, even in the absence of the enzyme, due to chemical polymerization of catechol. We postulate a two-step reaction mechanism. The humic monomer is initially oxidized to a semi-quinone radical by a phenoloxidase. Subsequent oxidative coupling involves reactions with additional humic monomers or anilinic products derived from TNT, forming an anilinoquinone via nucleophilic addition or a benzoquinone-imine through condensation.

Aniline Compounds↗

PubMed2005

Influence of the composition of natural organic matter on Pb bioavailability to microalgae.

The current work examines the effects of model allochtonous (humic substances) and autochtonous (microbial polysaccharides) natural organic matter (NOM) on Pb speciation and bioaccumulation. The results demonstrated that polysaccharides, in particular alginic acid, had complexing properties and effects on Pb bioaccumulation by the green alga Chlorella kesslerii that were similar to equivalent complexing capacity of humic substances. Pb uptake decreased in the presence of humic, alginic, and polygalacturonic acids with respect to noncomplexed Pb, but accumulated Pb was higher than predicted from measured Pb2+ concentrations or from previous results obtained in the presence of simple synthetic ligands. An improved fit between experimental observations and Pb speciation was obtained by taking into account the formation of a ternary complex at the algal surface. The contribution of the ternary complexes to Pb bioaccumulation was dependent on the relative binding constants of the Pb to the NOM and to the binding sites on the biological surface. In the presence of the humic acid, a decreased surface charge and increased membrane permeability were considered to be of secondary importance to explain the observation of increased Pb uptake with respect to that predicted on the basis of [Pb2+]. The environmental implications of the results are discussed with respect to the development of site-specific water quality criteria.

Biological Availability↗

PubMed2007

Effects of filtration and pH perturbation on freshwater organic matter fluorescence.

Fluorescence of organic matter from six contrasting freshwaters was analysed after filtration (1.2 microm and 0.2 microm filter sizes) and pH perturbation (+/-2 pH units from ambient conditions). Two fluorophores were compared in detail: tryptophan-like fluorescence, whose filtration and pH characteristics are relatively poorly understood, and humic-like fluorescence, which is better characterised. Although there was some variability in both fluorophores, the tryptophan-like fluorescence showed the most significant decrease in fluorescence intensity between raw and 1.2 microm filter samples, and a much smaller decrease between 1.2 and 0.2 microm, demonstrating a significant source associated with particulate material as well as a significant <0.2 microm fraction. In contrast, humic-like fluorescence shows little change with filtration, suggesting that the majority of this fluorescence is associated with truly dissolved material. The pH perturbation experiments demonstrate that tryptophan-like fluorescence is less impacted by pH than with filter fraction. For humic-like fluorescence, pH effects are weak and are not as consistent as those reported in the literature for extracted humic substances. pH perturbation of the freshwaters shows a wide range of sample specific pH responses, significantly more variable than that observed in experiments using extracted humic substances and tryptophan standards, demonstrating the natural variability of freshwater dissolved organic matter.

Filtration↗

PubMed2005

Characterization of non-extractable residues of the fungicide dithianon in soil using 13C/14C-labelling techniques.

The fate of the (14)C-labelled fungicide dithianon in soil is characterized by the formation of non-extractable, "bound" residues of approximately 63% of applied amount in 64 d. Humic acids containing these "bound" residues were isolated after conducting degradation studies of the active ingredient in an orthic luvisol under standardized conditions. In the same way, (13)C-labelled dithianon was incubated in an artificial soil which was produced by humification of (13)C-depleted straw in an incinerated soil. The "bound" residues of the (13)C-labelled dithianon in the humic acid fraction of the artificial soil were analyzed using (13)C-NMR techniques. There was no evidence of a covalent bonding of the residues to the humic substances. Results of polarity gradient high performance thin layer chromatography (AMD-HPTLC) of "bound" residues of the (14)C-labelled dithianon in the humic acid fraction indicate a sequestration process of metabolites into the humic substance as a possible binding mechanism.

Anthraquinones↗

PubMed2005

Enhancement of p,p'-DDT photodegradation on soil surfaces using TiO2 induced by UV-light.

Enhancement of p,p'-DDT photodegradation on soil surfaces using TiO2 induced by UV-light was mainly investigated in this work. After being spiked with p,p'-DDT, soil samples loaded with different doses of TiO2 (0%, 0.5%, 1%, 2%, and 3% wt) were exposed to UV-light irradiation for 24 h. The results indicated that the photodegradation of p,p'-DDT followed the pseudo-first-order kinetics. TiO2 accelerated the photodegradation of p,p'-DDT significantly as indicated by the half-life reduction from 23.3 h to 10.4 h, corresponding to the TiO2 content from 0% to 3% respectively. In addition, the effects of soil pH, photon flux and humic substances on p,p'-DDT degradation were investigated. The photodegradation rate increased with the increase of the soil pH and photon flux. The humic substances (2% wt) inhibited the p,p'-DDT photodegradation by reducing the amount of light available to excite the p,p'-DDT and TiO2 or by quenching radicals capable of oxidizing p,p'-DDT. p,p'-DDE, p,p'-DDD and DDMU were main degradation intermediates and they were further degraded in the presence of TiO2.

Biodegradation, Environmental↗

PubMed2006

Indolacetic and humic acids induce lateral root development through a concerted plasmalemma and tonoplast H+ pumps activation.

Increasing evidences have indicated that humic substances can induce plant growth and productivity by functioning as an environmental source of auxinic activity. Here we comparatively evaluate the effects of indole-3-acetic acid (IAA) and humic acids (HA) isolated from two different soils (Inseptsol and Ultisol) and two different organic residues (vermicompost and sewage sludge) on root development and on activities of plasmalemma and tonoplast H(+ )pumps from maize roots. The data show that HA isolated from these different sources as well as low IAA concentrations (10(-10) and 10(-15) M) improve root growth through a markedly proliferation of lateral roots along with a differential activation not only of the plasmalemma but also of vacuolar H(+)-ATPases and H(+)-pyrophosphatase. Further, the vacuolar H(+)-ATPase had a peak of stimulation in a range from 10(-8) to 10(-10) M IAA, whereas the H(+)-pyrophosphatase was sensitive to a much broader range of IAA concentrations from 10(-3) to 10(-15) M. It is proposed a complementary view of the acid growth mechanism in which a concerted activation of the plasmalemma and tonoplast H(+ )pumps plays a key role in the root cell expansion process driven by environment-derived molecules endowed with auxinic activity, such as that of humic substances.

Chloroplast Proton-Translocating ATPases↗

PubMed2006

Specific antioxidant reactions to oxidative stress promoted by natural organic matter in two amphipod species from Lake Baikal.

Aquatic organisms are exposed to a variety of natural chemical stressors such as humic substances. The aim of this study was to investigate the mode of action of natural organic matter (NOM, roughly 80% of which is humic substances) on two freshwater amphipods from Lake Baikal, Eulimnogammarus verrucosus (Gerstf.) and Eulimnogammarus cyaneus (Dyb.), in order to assess the potential oxidative stress of NOM impact. Chosen as oxidative stress markers were lipid peroxidation and cell internal hydrogen peroxide level as well as peroxidase, catalase, and glutathione S-transferase activities. Exposure of amphipods to NOM caused a significant increase in lipid peroxidation but a concomitant decrease in hydrogen peroxide concentration, and peroxidase and (to a lesser degree) glutathione S-transferase activities. An interim increase of catalase activity was observed. A possible reason for the decrease in major antioxidant enzyme activity is exhaustion of the reservoir of reduced substrates in the first stage of the antioxidant defense reaction. Despite the inhibition of major antioxidant enzymes, the studied amphipods were able to successfully resist the NOM oxidative impact and, at low NOM concentrations, to combat lipid peroxidation processes.

Amphipoda↗

PubMed2002

Trace metal levels in uncontaminated groundwater of a coastal watershed: importance of colloidal forms.

Groundwater and surface water were collected using trace metal clean techniques from the upper glacial aquifer of West Neck Bay (Shelter Island) in eastern Long Island, NY, during the late spring and summer of 1999. The collection sites on Shelter Island are located in an area that is primarily residential and believed to have uncontaminated groundwater. Ultrafiltration was used to size-fractionate the dissolved (<0.45 microm) fraction into colloidal (1 kDa - 0.45 microm) and low molecular weight (<1 kDa) size pools. These fractions were analyzed for trace metals (Al, Ag, Cd, Cu, Mn, Pb, and Zn), organic carbon, and inorganic nutrients (NH4, NO3, PO4). The levels of metals and organic carbon in the groundwater were as low as those found in the open ocean, far removed from anthropogenic inputs. These findings corroborate the need to apply trace metal clean techniques in the determination of metal levels in uncontaminated groundwater. A significant fraction of dissolved metals (22-96%) and organic carbon (approximately 40%) in the groundwater and in surface waters of the Bay was found to be associated with colloids. The significance of the metal association with the colloidal fraction decreased in the order of Al > Cu > Ag > Zn = Cd = Mn and appeared to be dependent on the affinities of these metals for humic substances. In contrast, NO3 and NH4 were found to be almost entirely (approximately 98-99%) in the low molecular weight size fraction. Metal/aluminum and metal/carbon ratios measured in the colloids were similar to those reported for humic substances and significantly different from those of soils. This suggests that colloidal particles might originate from humic materials as opposed to purely inorganic minerals. These results indicate the need to consider the colloidal fraction in the fate and mobility of metals in groundwater and that, despite the low levels of organic matter (<50 microM of DOC) measured in groundwater, some groundwater colloids appear to be organic in nature.

Colloids↗