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1.
《Organic Geochemistry》1999,30(8):901-909
Deuterium nuclear magnetic resonance spectroscopy (2H-NMR) spin–lattice relaxation (T1) experiments were used to measure noncovalent interactions between deuterated monoaromatic compounds (phenol-d5, pyridine-d5, benzene-d6) and fulvic acids isolated from the Suwannee River and Big Soda Lake. Noncovalent interactions, in aqueous solution, were examined as a function of monoaromatic hydrocarbon functional groups, fulvic acid concentration and identity, and solution pH. Phenol did not exhibit noncovalent interactions with either fulvic acid at any pH. Pyridine, in a pH range from 3 to 8, interacted with Suwannee River fulvic acid, forming a bond involving the lone pair of electrons on nitrogen. Conversely, no interactions were observed between pyridine and Big Soda Lake fulvic acid; the difference in noncovalent interactions is attributed to the structural and chemical differences of the two fulvic acids. The translational and rotational molecular motion of benzene increased in the presence of both fulvic acids, indicating that in aqueous solution, fulvic acids solubilize benzene rather than forming discrete bonds as with pyridine. The results of this study demonstrate that monoaromatic functional groups, solution pH, and identity and concentration of fulvic acid can influence the type and degree of noncovalent interactions with dissolved organic matter.  相似文献   

2.
The molecular weights of aquatic fulvic acids extracted from five rivers were determined by vapor pressure osmometry with water and tetrahydrofuran as solvents. The values obtained ranged from 500 to 950 dallons, indicating that the molecular weights of aquatic fulvic acids are not as great as has been suggested in some other molecular weight studies. The samples were shown to be relatively monodisperse from radii of gyration measurements determined by small angle x-ray scattering. THF affords greater precision and accuracy than H2O in VPO measurements, and was found to be a suitable solvent for the determination of molecular weight of aquatic fulvic acid because it obviates the dissociation problem. An inverse correlation was observed with these samples between the concentration of Ca++ and Mg++ in the river water and the radii of gyration and molecular weights of the corresponding fulvic acid samples.  相似文献   

3.
Algal humic-like substances were oxidized with KMnO4. The oxidation products were analyzed by GC-MS. Normal and branched fatty acids, dicarboxylic and benzene carboxylic acids were identified. Aliphatic acids were by far the most prominent compounds. Similarities between humic and fulvic acids of both Fucus and Laminaria algae were apparent. Fucus humic acids, however, showed a more aromatic structure than their Laminaria counterpart. The contribution of algae to marine sedimentary humus is discussed.  相似文献   

4.
Sources of sedimentary humic substances: vascular plant debris   总被引：1，自引：0，他引：1  
A modern Washington continental shelf sediment was fractionated densimetrically using either an organic solvent, CBrCl3, or aqueous ZnCl2. The resulting low density materials (<2.06 g/ml) account for only 1% of the sediment mass but contain 25% of the sedimentary organic carbon and 53% of the lignin. The C/N ratios (30–40) and lignin phenol yields (Λ = 8) and compositions indicate that the low density materials are essentially pure vascular plant debris which is slightly enriched in woody (versus nonwoody) tissues compared to the bulk sediment. The low density materials yield approximately one-third of their organic carbon as humic substances and contribute 23% and 14% of the total sedimentary humic and fulvic acids, respectively. Assuming that the lignin remaining in the sedimentary fraction is also contained in plant fragments that yield similar levels of humic substances, then 50% and 30% of the total humic and fulvic acids, respectively, arise directly from plant debris.Base-extraction of fresh and naturally degraded vascular plant materials reveals that significant levels of humic and fulvic acids are obtained using classical extraction techniques. Approximately 1–2% of the carbon from fresh woods and 10–25% from leaves and bark were isolated as humic acids and 2–4 times those levels as fulvic acids. A highly degraded hardwood yielded up to 44% of its carbon as humic and fulvic acids. The humic acids from fresh plants are generally enriched in lignin components relative to carbohydrates and recognizable biochemicals account for up to 50% of the total carbon. Humic and fulvic acids extracted directly from sedimentary plant debris could be responsible for a major fraction of the biochemical component of humic substances.  相似文献   

5.
Two fractions of soil fulvic acid (FA) were separated by gel filtration chromatography. An observed increase in volume of the heavier fraction (FA I) with increasing pH was attributed to aggregation, intramolecular negative charge repulsions and the rupture of hydrogen bonds, which control molecular conformation. Optical absorption properties and elemental analyses of both fractions were determined. The stability constants and stoichiometries of FA complexes with vanadyl, VO2+, at pH 5.0 and ionic strength of 0.04 M were measured by electron paramagnetic resonance (EPR) spectroscopy. EPR spectra of model VO2+ complexes with phthalic and salicylic acids, which are the probable functional groups present in FA, are identical to those of the VO2+-FA complexes. Aggregation of FA I occurs in the presence of VO2+ to form a complex that can be approximated as ‘(VO)2(FA I)6’. The average site distance between vanadyl ions in this complex is shown to be greater than 1.2 nm. EPR parameters for FA I suggest binding by carboxylate groups. These parameters are compared with those of other vanadyl complexes with fulvic and humic acids reported by others. Reduction of VO3? to VO2+ by these materials is discussed.  相似文献   

6.
The naturally abundant nitrogen in soil and aquatic NOM samples from the International Humic Substances Society has been characterized by solid state CP/MAS 15N NMR. Soil samples include humic and fulvic acids from the Elliot soil, Minnesota Waskish peat and Florida Pahokee peat, as well as the Summit Hill soil humic acid and the Leonardite humic acid. Aquatic samples include Suwannee River humic, fulvic and reverse osmosis isolates, Nordic humic and fulvic acids and Pony Lake fulvic acid. Additionally, Nordic and Suwannee River XAD-4 acids and Suwannee River hydrophobic neutral fractions were analyzed. Similar to literature reports, amide/aminoquinone nitrogens comprised the major peaks in the solid state spectra of the soil humic and fulvic acids, along with heterocyclic and amino sugar/terminal amino acid nitrogens. Spectra of aquatic samples, including the XAD-4 acids, contain resolved heterocyclic nitrogen peaks in addition to the amide nitrogens. The spectrum of the nitrogen enriched, microbially derived Pony Lake, Antarctica fulvic acid, appeared to contain resonances in the region of pyrazine, imine and/or pyridine nitrogens, which have not been observed previously in soil or aquatic humic substances by 15N NMR. Liquid state 15N NMR experiments were also recorded on the Elliot soil humic acid and Pony Lake fulvic acid, both to examine the feasibility of the techniques, and to determine whether improvements in resolution over the solid state could be realized. For both samples, polarization transfer (DEPT) and indirect detection (1H–15N gHSQC) spectra revealed greater resolution among nitrogens directly bonded to protons. The amide/aminoquinone nitrogens could also be observed by direct detection experiments.  相似文献   

7.
The acid-base properties of 14 standard and reference materials from the International Humic Substances Society (IHSS) were investigated by potentiometric titration. Titrations were conducted in 0.1 M NaCl under a nitrogen atmosphere, averaging 30 min from start to finish. Concentrations of carboxyl groups and phenolic groups were estimated directly from titration curves. Titration data were also fit to a modified Henderson-Hasselbalch model for two classes of proton-binding sites to obtain “best fit” parameters that describe proton-binding curves for the samples. The model was chosen for its simplicity, its ease of implementation in computer spreadsheets, and its excellent ability to describe the shapes of the titration curves. The carboxyl contents of the IHSS samples are in the general order: terrestrial fulvic acids > aquatic fulvic acids > Suwannee River natural organic matter (NOM) > aquatic humic acids > terrestrial humic acids. Overall, fulvic acids and humic acids have similar phenolic contents; however, all of the aquatically derived samples have higher phenolic contents than the terrestrially derived samples. The acid-base properties of reference Suwannee River NOM are surprisingly similar to those of standard Suwannee River humic acid. Results from titrations in this study were compared with other published results from both direct and indirect titrations. Typically, carboxyl contents for the IHSS samples were in agreement with the results from both methods of titration. Phenolic contents for the IHSS samples were comparable to those determined by direct titrations, but were significantly less than estimates of phenolic content that were based on indirect titrations with Ba(OH)2 and Ca(OAc)2. The average phenolic-to-carboxylic ratio of the IHSS samples is approximately 1:4. Models that assume a 1:2 ratio of phenolic-to-carboxylic groups may overestimate the relative contribution of phenolic groups to the acid-base chemistry of humic substances.  相似文献   

8.
Peptides were released from organic matter fractions of three Italian soils (humin, humic and fulvic acids), when the samples were hydrolyzed in Ba(ON)2-saturated solution at 105°C for 2 hr. The peptides obtained were separated using electrophoresis and paper chromatography. The presence of polypeptides in the soil organic matter was indicated by: (1) their hydrolysis by pronase; (2) the amino acids released by 6 N HCl hydrolysis; (3) The comparison of i.r. spectra of humic fractions before and after hydrolysis with 6 N HCl.Attempts at isolating the native proteinaceous compounds using electrophoresis in polyacrylamide gel failed; additionally, our attempts to hydrolyze proteinaceous components enzymatically in unfractionated soil organic matter, as well as in its fractions, before and after methylation, with pepsin, papain and pronase, were unsuccessful. Pronase demonstrated a weak proteolytic activity only at very low substrate-enzyme ratios (20 : 1) in humic and fulvic fractions and in whole phyrophosphate extract. Deproteinated substrates treated with pronase also released free amino acids, suggesting autodigestion.In humin, humic and fulvic fractions we found a total amino acid content of 40–45%, 12–24% or 1–85, respectively. Amino acid recovery from single fractions was about 70–80% of the total content in the unfractionated soil.  相似文献   

9.
《Applied Geochemistry》2004,19(4):611-622
Subsurface aeration is the in situ oxidation of Fe from groundwater that is used to make drinking water potable. When subsurface aeration is applied to an anaerobic groundwater system with pH>7, Fe(II) is oxidised heterogeneously. The heterogeneous oxidation of Fe(II) can result in the in situ formation of Fe colloids. To study this, the effect of substances commonly found in groundwater (e.g. PO4, Mn, silicate and fulvic acid) on the heterogeneous oxidation process was measured. The heterogeneous oxidation of Fe(II) becomes retarded when PO4, Mn, silicate or fulvic acid is present in the groundwater in addition to Fe(II). Phosphate and fulvic acid retarded the oxidation process most. The heterogeneous oxidation was described using a model with a homogeneous (k1) and an autocatalytic oxidation rate constant (k′2). From the modelling it followed that the homogeneous oxidation rate constant was not affected or even slightly elevated whereas the autocatalytic oxidation rate constant decreased remarkably by the addition of PO4, Mn, silicate or fulvic acid. From speciation calculations it followed that the decreased availability of the Fe(II) species can only explain a small part of the retarded autocatalytic oxidation process. Therefore exploratory calculations were performed to gain insight into whether the adsorption of PO4 or fulvic acid could explain the retarded autocatalytic oxidation. These calculations showed that the adsorption of fulvic acid could explain the retarded autocatalytic oxidation process. In contrast the adsorption of PO4 only partly explained the retarded autocatalytic oxidation process. In terms of colloid formation this study shows that the heterogeneous oxidation of Fe(II) in presence of PO4, Mn, silicate or fulvic acid leads to the formation of Fe colloids.  相似文献   

10.
A set of surface samples was created using purified laboratory grade sand treated with 0.05 μg/g Hg as the HgCl2 salt and various concentrations of purified humic and fulvic acids. Emissions of elemental Hg from these substrates to the atmosphere were inversely correlated with the organic content of the samples (99% confidence level). The greatest differences in Hg emissions were found between samples containing the lowest concentrations of humic matter (0% versus 0.01% humic, and 0.01% versus 0.1% humic), only small differences in Hg flux were found to exist for samples with higher concentrations of humic acid (1%, 5%, and 100%). This effect was independent of the type of humic substance used, with both humic and fulvic acids showing an inhibitory effect on surface Hg emissions.  相似文献   

11.
The sorption of Cu(II) and Pb(II) to kaolinite-fulvic acid colloids was investigated by potentiometric titrations. To assess the possible interactions between kaolinite and fulvic acid during metal sorption, experimental sorption isotherms were compared with predictions based on a linear additivity model (LAM). Suspensions of 5 g L−1 kaolinite and 0.03 g L−1 fulvic acid in 0.01 M NaNO3 were titrated with Cu and Pb solutions, respectively. The suspension pH was kept constant at pH 4, 6, or 8. The free ion activities of Cu2+ and Pb2+ were monitored in the titration vessel using ion selective electrodes. Total dissolved concentrations of metals (by ICP-MS) and fulvic acid (by UV-absorption) were determined in samples taken after each titration step. The amounts of metals sorbed to the solid phase, comprised of kaolinite plus surface-bound fulvic acid, were calculated by difference. Compared to pure kaolinite, addition of fulvic acid to the clay strongly increased metal sorption to the solid phase. This effect was more pronounced at pH 4 and 6 than at pH 8, because more fulvic acid was sorbed to the kaolinite surface under acidic conditions. Addition of Pb enhanced the sorption of fulvic acid onto kaolinite at pH 6 and 8, but not at pH 4. Addition of Cu had no effect on the sorption of fulvic acid onto kaolinite. In the LAM, metal sorption to the kaolinite surface was predicted by a two-site, 1-pK basic Stern model and metal sorption to the fulvic acid was calculated with the NICA-Donnan model, respectively. The LAM provided good predictions of Cu sorption to the kaolinite-fulvic acid colloids over the entire range in pH and free Cu2+ ion activity (10−12 to 10−5). The sorption of Pb was slightly underestimated by the LAM under most conditions. A fractionation of the fulvic acid during sorption to kaolinite was observed, but this could not explain the observed deviations of the LAM predictions from the experimental Pb sorption isotherms.  相似文献   

12.
《Applied Geochemistry》2000,15(2):133-139
The sorption of Yb3+, UO2+2, Zn2+, I− and SeO2−3 onto Al2O3, Fe2O3 and SiO2 were determined by a batch technique in the presence and absence of fulvic acids. The effects of fulvic acid on sorption were compared. The existing general consensus, that humic substances tend to enhance metal cation sorption at low pH, reduce metal cation sorption at high pH and reduce inorganic anion sorption between pH values 3 to 10, was generally shown to be true. However, in this work many exceptions to the general consensus were found. The study indicated that the effect of humic substances on sorption of inorganic cations or anions depends not only on pH, but also on the nature of the oxide, the nature of humic substance, fractionation of the humic substance by sorption, the relative strength of complexes of both soluble and sorbed humic substances, the extent of surface coverage by humic substance, the initial concentration of humic substance and the inorganic electrolyte composition.  相似文献   

13.
The reactivity of iron(III) oxyhydroxides as reflected by their tendency to dissolve is of great importance in the redox cycling of iron and the bioavailability of iron to phytoplankton in natural waters. In this study, various iron(III) oxyhydroxides were produced by oxygenation of iron(II) in the presence of solutes, such as phosphate, sulfate, bicarbonate, valeric acid, TRIS, humic and fulvic acids, and in the presence of minerals, such as bentonite and δ-Al2O3 under conditions encountered in aquatic systems. The reactivity of the different iron(III) oxyhydroxides was subsequently assessed by means of a reductive dissolution using ascorbate and non-reductive dissolution using HQS (8-hydroxyquinoline-5-sulfonic acid) or oxalate. The experimental results show that the iron(III) oxyhydroxides with a low degree of polymerization exhibit higher reactivity than those with a high degree of polymerization or with high crystallinity. The quantity of active surface sites and the coordination arrangement of the functional groups at the surface of the iron(III) oxyhydroxides, especially the extent of the endstanding -OH groups per iron(III) ion determine the reactivity of iron(III) oxyhydroxides toward dissolution.Surfaces, such as clay and aluminum oxides, not only accelerate the oxygenation reaction of iron(II), but also induce the formation of iron(III) oxyhydroxides which are more active toward the dissolution reactions. Polymerization of iron(III) oxyhydroxides on the surfaces occurs predominantly in two dimensions rather than in three dimensions.In a laboratory experiment, the iron(III) oxyhydroxide formed in the presence of TRIS can be reduced by fulvic acid in a closed system under the following conditions: Fe(OH)3(s) 0.01 g/l, fulvic acid 5 mg/l, pH 7.5, 20°C. The kinetics of the reaction depend on the reactivity of iron(III) oxyhydroxide and reducing power of fulvic acid. Although reductants other than fulvic acid may be of importance in antural waters, this result provides the laboratory evidence that the >FeIII-OH/Fe(II) is able to act as an electron transfer mediator for the oxidation of natural organic substances, such as fulvic acid, by molecular oxygen either in the absence of microorganisms or as a supplement to microbial activity.  相似文献   

14.
Potentiometric titrations were used to measure conditional stability constants of UO22+-fulvic acid and UO22+-humic acid complexes. Both 2:1 and 1:1 COO-:UO22+ binding were observed. With decreasing metal concentration (2.5·10−4-6.25·10−5 M) increasing amounts of UO22+ were in the form of 1:1 humate complexes and 2:1 fulvate complexes. Despite the high nitrogen content and the low acidic OH group content, the successive stability constant values were similar to those determined for divalent cations associated with fulvic and humic compounds isolated from soils. Stability constant values increase simultaneously with increasing ionization of the humic (or fulvic) acid polyelectrolytes and with decreasing metal concentration.  相似文献   

15.
Monochloramine is interesting both as a selective oxidant of fulvic acid and as a drinking water disinfectant. In this study, the controlled reaction of aquatic fulvic acid with monochloramine did not result in products detectable by ether extraction-gas chromatography-flame ionization detection techniques. Evidence of a reaction was shown by bleaching of the fulvic acid solution (decreased absorbance at 465 nm) and chlorine substitution. Chlorine-containing products were quantified by the total carbon adsorbable organic halide (TOX) parameter. Bleaching and organic chlorine formation were much less extensive than in the reaction of free chlorine with fulvic acid. Monochloramine was shown to produce an organic chlorine fraction more hydrophilic and with higher molecular size than that produced by chlorine and fulvic acid. Results suggest that monochloramine may be useful tool for the investigation of certain humic functionalities because it reacts rather selectively and to a small extent with aquatic fulvic acid.  相似文献   

16.
Organic matter from an arable soil derived from base rich parent material was extracted by alkali and fractionated on the basis of solubility in 0.1 N HCl, hot water and hot 6 N HCl and by selective adsorption on charcoal. The distribution of associated metals was determined and Cu had the largest proportion, 15%, associated with the organic matter. Moderate proportions of the total Al, Co, Ni, and V (3–8%) but only small amounts (?1%) of the Mn, Fe, Ti, Cr, Ba and Sr were extracted from the soil by alkali. The Fe and Ti were concentrated mainly in the humic fraction whereas Mn and V were both found largely in the fulvic acid.Electron paramagnetic resonance spectra of the various fractions were examined and attempts made to relate the spectra to the forms of some of the metals present. In the humic acid fraction Cu was present partly as a copper porphyrin-type complex but in the fulvic acid it was in some other complexed form. VO2+ occurred in complexed forms in the fulvic acid which were more covalent than VO2+ humic acid complexes, whereas the Mn2+ components of the humic and fulvic acids all had a high degree of ionicity.  相似文献   

17.
The oxidation of Fe(II) by H2O2 has been studied in the presence of Suwannee River fulvic acid, a standard form of natural organic matter, by adding inorganic Fe(II) to solutions containing both H2O2 and fulvic acid and monitoring the total Fe(II) concentration using a luminol chemiluminescence method. At pH 8.4 and in the absence of competing metals, Suwannee River fulvic acid significantly retards the rate of Fe(II) oxidation due to gradual formation of a species that is oxidized more slowly than inorganic Fe(II) by both O2 and H2O2. It is suggested that rapid formation of a weak Fe(II)-fulvic acid complex that is not readily oxidized by H2O2 is the cause of the reduction in the initial oxidation rate, and that the subsequent further reduction in oxidation rate is a result of the formation of a second type of Fe(II)-fulvic acid complex that is resistant to both O2 and H2O2 oxidation. A kinetic model has been developed that supports this conceptual model. The results demonstrate that, under certain conditions, natural organic matter may stabilize Fe(II) in the presence of elevated H2O2 concentrations, significantly increasing the lifetime of ferrous iron and reducing the flux of hydroxyl radicals produced through this oxidation pathway.  相似文献   

18.
Pb2+, like Cu2+, forms strong complexes with fulvic acids (Cd2+-fulvate complexes are much weaker), but Pb-fulvate precipitates at a much lower mole ratio of metal ion to fulvic acid than either Cu-fulvate or Cd-fulvate does. Physical association of Pb2+ with Pb-fulvate solids as well as complexation by sites still available in the precipitates probably causes the increased removal of free Pb2+ from solution after precipitation begins.  相似文献   

19.
A suite of well-characterized humic and fulvic acids of freshwater, soil and plant origin was subjected to pyrolysis-mass spectrometry and the resulting data were analyzed by pattern recognition and factor analysis. A factor analysis plot of the data shows that the humic acids and fulvic acids can be segregated into two distinct classes. Carbohydrate and phenolic components are more pronounced in the pyrolysis products of the fulvic acids, and saturated and unsaturated hydrocarbons contribute more to the humic acid pyrolysis products. A second factor analysis plot shows a separation which appears to be based primarily on whether the samples are of aquatic or soil origin.  相似文献   

20.
Thermodynamic modeling of equilibria in the system water–rock–organic acids was used to study the influence of organic acids on Ca and Mg redistribution between a solution and a solid phase in connection with the use of calcites of variable composition CaxMg1–xCO3 as indicators of paleoclimatic environments. In the thermodynamic model, high-molecular humic substances (fulvic + humic acids) were represented by a set of independent metal-binding centers. Therefore, their number was preset based on the given density of proton- or metal-binding sites. The numerical implementation of several geochemical situations involving the dissolution/deposition of calcites with different Mg contents showed that the main effect of fulvic and humic acids is the acidification of solutions and the reduction of carbonate stability. Although humic substances can play an important role in fixing Ca and Mg and removing them from solution, their actual concentrations in natural media (<<1 g/L) do not cause significant changes in the composition of CaxMg1–xCO3 phases. On the other hand, there is quantitative evidence that variations in the Mg/Ca ratio in a solution and a solid phase are significantly influenced by the evaporative concentration of Mg-oversaturated solutions, alkalization/acidification during their evolution, or CO2 content variations owing to changes in climate and lake activity.  相似文献   

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