Carbon-13 cross polarized magic-angle samples spinning nuclear magnetic resonance of melanoidins

Melanoidins synthesized from amino-acids and sugars in various ratios and humic substances from Hula Basin (Israel) have been investigated by ¹³C-CP/MAS NMR spectroscopy. Most spectra indicated a significant similarity between melanoidins and humics. It is suggested that the Maillard reaction plays a more significant role in the formation of humic substances than the “traditional” theory based on a lignin source. Several heterocyclic and heteroaromatic moieties (mainly furanoid, hydroxy-alkyl-furanone and hydroxy-alkyl-cyclopentenone) have been considered as major “building blocks” of humic substances and melanoidins.Aromaticities calculated from NMR spectral data of SM (“sugar” enriched melanoidins) and AAM (amino acid enriched melanoidins) coincide remarkably with the aromaticities of terrestrial and marine humics, respectively.     

Effects of heat treatment on fluorescence properties of humic substances from sandy soil in arid land and their Hg(II) binding behaviors

The topsoil temperature in arid areas of Xinjiang, China can be up to about 80°C in summer. This may significantly affect the chemical properties of soil humic substances. However, the effects of high temperature on characteristics of soil humic substances and their complexation with toxic metals are still poorly known. In the present study, binding of Hg(II) to unheated soil humic substances and heated soil humic substances from sandy soils was comparatively investigated using three-dimensional excitation?Cemission matrix (EEM) fluorescence spectroscopy. Two fluorescent peaks (peak I at Ex/Em?=?365?C370/470?C474?nm; peak II at Ex/Em?=?270?C275/468?C472?nm) identified as humic-like fluorescence were observed in the EEM spectra of humic substances. Both peaks were clearly quenched by Hg(II), indicating the strong interaction of humic-like substances with Hg(II), and showed blue shifts after heat treatment. Heat treatment caused an increase of the fraction of accessible fluorophore (f _a), binding sites number (n) and effective quenching constants (logK _a), indicating that more binding sites in humic substances could bind Hg(II) and form more stable humic substances?CHg(II) complexes after heat treatment. However, a decrease of binding constants (logK _b) suggested that heat treatment would reduce the binding capacity of each binding site of humic substances to Hg(II). This study implies the transport of Hg(II) may be affected by high temperature in the arid zone due to the modification of the physicochemical properties of humic substances in soil.     

Chemistry and transport of soluble humic substances in forested watersheds of the Adirondack Park,New York

Studies were conducted in conjunction with the Integrated Lake-Watershed Acidification Study (ILWAS) to examine the chemistry and leaching patterns of soluble humic substances in forested watersheds of the Adirondack region. During the summer growing season, mean dissolved organic carbon (DOC) concentrations in the ILWAS watersheds ranged from 21–32 mg C l^?1 in O/A horizon leachates, from 5–7 mg C l^?1 in B horizon leachates, from 2–4 mg C l^?1 in groundwater solutions, from 6–8 mg C l^?1 in first order streams, from 3–8 mg C l^?1 in lake inlets, and from 2–7 mg C l^?1 in lake outlets. During the winter, mean DOC concentrations dropped significantly in the upper soil profile. Soil solutions from mixed and coniferous stands contained as much as twice the DOC concentration of lysimeter samples from hardwood stands. Results of DOC fractionation analysis showed that hydrophobia and hydrophilic acids dominate the organic solute composition of natural waters in these watersheds. Charge balance and titration results indicated that the general acid-base characteristics of the dissolved humic mixture in these natural waters can be accounted for by a model organic acid having an average_pK_a of 3.85, an average charge density of 4–5 μeq mg^?1 C at ambient pH, and a total of 6–7 meq COOH per gram carbon.     

Characterization of groundwater humic substances: influence of sedimentary organic carbon

A total of 35 groundwaters from 4 different aquifer systems in Germany are investigated for their physico-chemical properties, dissolved organic C (DOC) and humic and fulvic acids. Humic substances are isolated and characterized for their elemental composition, UV/Vis and fluorescence spectroscopic properties, size distribution by gel permeation chromatography (GPC) and ¹⁴C content. For isolation of sufficient quantities of humic substances a mobile sampling system is developed based on a combination of reverse osmosis (RO) and XAD–8 adsorption chromatography. One of the aquifer systems (Gorleben) covers a wide range of hydrogeochemical conditions, whereas the other 3 aquifer systems (Munich, Franconian Albvorland and Fuhrberg) have less diverse properties. One specific feature of the Gorleben aquifer system is the presence of a very high DOC, which, in contrast to other aquifer systems, contains considerable amounts of aquatic humic acid. This is attributed to the release of aquatic humic substances originating from sedimentary organic C (SOC) that is abundant in Gorleben sediments. The results show that aquatic humic substances from different aquifer systems have dissimilar properties which differ from one another. Systematic differences are found among humic substances from different regions of the Gorleben aquifer system. Such differences are considered to be caused by the mixing of humic substances from the SOC. However, exact quantification of such mixing appears difficult because overlapping effects of different geochemical processes feigning a dissolution of SOC cannot be excluded.     

Adsorption of diclofenac on activated carbon and its hypochlorination in the presence of dissolved organic matter

The nonsteroidal anti-inflammatory drug “diclofenac” is the pharmaceutically active ingredient of several medicines. Since the compound is used in many of its water-soluble salt forms, it is one of the most frequently found pollutants in different parts of the water cycle. Its reaction with sodium hypochlorite was investigated in the presence of humic substances and sandy soil extract at neutral pH at 25 and 250 mg/L initial concentrations. In the lower concentration, the reaction follows a pseudo-first-order kinetics, while at the higher concentration, it is described as the sum of two first-order reactions. These kinetic results, together with the organic chlorine content of the residues, indicated that both chlorination and oxidation took place. The chlorination is significantly faster. The colloids present catalyze the reactions: The clay minerals of soil extract accelerated the chlorination, while the humic acids could work as photocatalysts in the oxidation, while these compounds themselves were chlorinated. The adsorption of diclofenac on activated carbon was enhanced by humic substances, and every isotherm had a breaking point near to 3 mg/L equilibrium concentration (c _e) resulting in two steps. According to the measurements of the zeta potential, the system proved to be relatively stable at this c _e value, but at higher diclofenac concentrations the stability retained only in the presence of the hydrophilic fulvic acid. The results supported the adsorption hypothesis that in the first step the charge transfer interaction while in the second step hydrogen bond formation plays the key role.     

Characterization of humic substances by advanced solid state NMR spectroscopy: Demonstration of a systematic approach

Characterization of humic substances is challenging due to their structural complexity and heterogeneity. Solid state nuclear magnetic resonance (NMR) is regarded as one of the best tools for elucidating structures of humic substances. The primary solid state NMR technique that has been used so far is the routine ¹³C cross polarization-magic angle spinning (CP-MAS) technique. Although this technique has markedly advanced our understanding of humic substances, the full potential of NMR for characterizing humic substances has yet to be realized. Recent technical developments and applications of advanced solid state NMR have revealed the promise to provide deeper insights into structures of humic substances. In this paper, we summarized and demonstrated the systematic solid state NMR protocol for characterization of humic substances using a humic acid as an example. This protocol included (1) identification of specific functional groups using spectral editing techniques, occasionally assisted by ¹H¹³C two-dimensional heteronuclear correlation (2D HETCOR) NMR, (2) quantification of specific functional groups based on direct polarization-magic angle spinning (DP-MAS) and DP-MAS with recoupled dipolar dephasing, combined with spectral editing techniques, (3) determination of connectivities and proximities of specific functional groups by ¹H¹³C 2D HETCOR or 2D HETCOR combined with spectral editing techniques, and (4) examination of domains and heterogeneities by ¹H¹³C 2D HETCOR with ¹H spin diffusion. We used a soil humic acid as an example to demonstrate how this protocol was applied to the characterization of humic substances step by step. Afterwards, based on typical ¹³C NMR spectra of humic substances we described how we could combine different NMR techniques to identify specific functional groups band by band from downfield to upfield. Finally, we briefly mentioned the potential new NMR techniques that could be developed to enrich the current systematic protocol. This systematic protocol is not only applicable to humic substances but also to other natural organic matter samples.     

Use of solid-state 13C NMR in structural studies of humic acids and humin from Holocene sediments

¹³C NMR spectra of solid humic substances in Holocene sediments have been obtained using cross polarization with magic-angle sample spinning techniques. The results demonstrate that this technique holds great promise for structural characterizations of complex macromolecular substances such as humin and humic acids. Quantifiable distinctions can be made between structural features of aquatic and terrestrial humic substances. The aliphatic carbons of the humic substances are dominant components suggestive of input from lipid-like materials. An interesting resemblance is also noted between terrestrial humic acid and humin spectra.     

Acid neutralizing processes in an alpine watershed front range, Colorado, U.S.A.—1: Buffering capacity of dissolved organic carbon in soil solutions

Soil interstitial waters in the Green Lakes Valley, Front Range, Colorado were studied to evaluate the capacity of the soil system to buffer acid deposition. In order to determine the contribution of humic substances to the buffering capacity of a given soil, dissolved organic carbon (DOC) and pH of the soil solutions were measured. The concentration of the organic anion, Ai⁻, derived from DOC at sample pH and the concentration of organic anion, Ax⁻ at the equivalence point were calculated using car☐yl contents from isolated and purified humic material from soil solutions. Subtracting Ax⁻ from Ai⁻ yields the contribution of humic substances to the buffering capacity (A_equiv.⁻). Using this method, one can evaluate the relative contribution of inorganic and organic constituents to the acid neutralizing capacity (ANC) of the soil solutions. The relative contribution of organic acids to the overall ANC was found to be extremely important in the alpine wetland (52%) and the forest-tundra ecotone (40%), and somewhat less important in the alpine tundra sites (20%). A failure to recognize the importance of organic acids in soil solutions to the ANC will result in erroneous estimates of the buffering capacity in the alpine environment of the Front Range, Colorado.     

Sources of sedimentary humic substances: vascular plant debris

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 ($\text{Λ = 8}$) 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.     

Uranium(VI) sorption to hematite in the presence of humic acid

A long-standing problem in aquatic geochemistry has been the incorporation of natural organic matter (NOM) into speciation models. The general effect of NOM on metal ion sorption by particles has been understood for some time, and significant progress has been made in elucidating some of the details of the role of NOM through the use of surrogate organic acids such as citric acid. However, a gap exists between the general observations that have been made of NOM behavior and the inclusion of NOM in surface chemical models for metal ion sorption. In this paper, we report on the results of a study on the sorption of U(VI) by hematite in the absence and presence of Suwannee river humic acid (HA) and over a range of other system conditions (e.g., pH, I). Essential HA characteristics (e.g., its acid/base, metal binding, and surface chemical properties) were “captured” by representing the HA as an assembly of monoprotic acids with assumed pK values and without explicit correction for electrostatic effects. The ternary system (hematite/HA/U(VI)) was simulated through the combination of the binary submodels (i.e., CO₃²⁻/hematite, U(VI)/HA, U(VI)/hematite, and HA/hematite) with model constants fixed at the values determined from simulations of the respective experimental systems. However, the “summed-binary” approach undersimulated experimental results, and the ternary system model required the postulation of two ternary surface (Type A) complexes composed of the uranyl ion, hematite surface sites, and the model ligands comprising the HA. Consideration of the HA in this manner permitted the simulation of HA effects on U(VI) sorption by hematite over a range of solution conditions using a general speciation model.     

The role of humic acids from Tasmanian podzolic soils in mineral degradation and metal mobilization

Humic acid extracted from a podzolic soil developed under Eucalyptus delegatensis and Pteridium aquilinum in northwestern Tasmania exhibits very strong solvent activity towards a number of minerals and metals. Aqueous solutions (0.1 per cent w/v) of this acid acting for 24 hours on mineral grains ranging in size from 297 to 590 μ, extracted varying amounts of metal. Chalcopyrite yielded 140 μg Cu whereas chalcocite released 15,000 μg Cu. Some correlation is found between relative bond strengths of sulphides and their degradation by humic acids. For example, galena is far less stable than sphalerite. Haematite and pyrolusite are quite vulnerable to humic acid attack and this may be a factor in the lack of development of extensive gossans over mineralization in western Tasmania during the current erosional cycle. Metals are particularly strongly attacked with a maximum release of 291,000 μg Pb in 24 hours. Contrary to earlier findings, Ag and Au were found to release 400 μg and 20 μg respectively of metal in a period of 6 weeks.Humic acid extracted from soils below other vegetation types in northwestern and western Tasmania are all active in mineral degradation. The variable effect of the acids is possibly the result of overall differences in complexing sites active under the conditions of experimentation and selective complexation. Several examples of minor soil organic compounds show no greater activity than humic acids and on the basis of their very low content in the soils studied, they are considered inferior to the latter as agents of weathering. Many metal humates display low solubility in water, but they are readily mobilized in the presence of humic acids. Humic acids developed under varying vegetation in a cool temperate climate are potentially very powerful solvents in the weathering cycle. Their ability to mobilize precipitated metal humates suggests that classical concepts of relative metal mobility may need modification in environments where appreciable concentrations of these substances are found.     

[1H] and [13C]NMR studies on the importance of aromatic structures in fulvic and humic acids

To obtain information on the contribution of aromatic fragments to the chemical structure of humic substances, we carried out a study on the [¹H]NMR and [¹³C]NMR spectra of humic and fulvic acids and their oxidative degradation products extracted from an Andosol soil.[¹H]NMR spectra of all organic fractions present considerable adsorption between 7.4 and 8.8 ppm, due to the presence of aromatic protons.The percentages of aromatic protons in respect to the total amount of protons are as follows: FA 20%, HA 19%, degraded FA < 12%, degraded HA 14%. The values indicate that the contribution of aromatic structures to the humic substances is significant, also considering that they are highly substituted.The degraded fractions contain smaller amounts of aromatic protons, because degradation causes the opening of the aromatic rings. Thus results obtained from the degradation do not seem to be reliable for defining the importance of aromatic structures in humic substances.Also the [¹³C]NMR spectra show signals in the aromatic region which derive from unsubstituted carbon atoms, while signals originating from tertiary carbon atoms merge with the noise. We believe that, at present, [¹H]NMR spectroscopy is more suited for studying the role played by aromatic compounds in organic soil fractions.     

Determination of the conditional interaction constant between colloidal technetium(IV) and Gorleben humic substances

Varying pertechnetate (Tc(VII)) doses were reduced to Tc(IV) in the presence and absence of Gorleben humic substances with the aid of magnetite, a reducing Fe(II)-containing surface. In absence of humic substances dissolved Tc(IV) concentrations are over-saturated with respect to the known TcO₂ · nH₂O solubility and increase with increasing Tc(VII) dose due to the formation of a range of mononuclear to colloidal Tc(IV) species. In presence of dissolved humic substances, the Tc solubility is enhanced due to the additional interaction of dissolved Tc(IV) species with humic substances. Both in the absence and the presence of dissolved humic substances a sorption mechanism controls the distribution of the range of mononuclear to colloidal Tc(IV) species between the solid and the liquid phase. The proposed reaction mechanism between Tc(IV) and HS is represented by Σ[TcO(OH)₂]_n+HS = [TcO(OH)₂]_n − HS in which Σ[TcO(OH)₂]_n stands for the sum of monomeric and polynuclear (colloidal) Tc(IV) species present in the equilibrium solution. A log K-value of 2.9 (±0.3) was quantified from a modified Schubert approach which is based on the competition of HS and magnetite for all dissolved Tc(IV) species and was found independent of Tc–HS loading, Tc–magnetite loading and pH.     

Iron(III) reduction and phosphorous solubilization in humid tropical forest soils

Phosphorus is one of the nutrients most commonly limiting net primary production in soils of humid tropical forests, mainly because insoluble Al and Fe phosphates and strong sorption to Fe(III) (hydr)oxides remove P from the bioavailable pool. Recent field studies have suggested, however, that this loss may be balanced by organic P accumulation under a wet moisture regime (>3350 mm annual precipitation). It has been hypothesized that, as the moisture regime changes from dry to mesic to wet, periods of anoxic soil conditions increase in intensity and duration, depleting Fe(III) (hydr)oxides and releasing sorbed P, but also slowing organic matter turnover, thus shifting the repository of soil P from minerals to humus. Almost no quantitative information is available concerning the coupled biogeochemical behavior of Fe and P in highly weathered forest soils that would allow examination of this hypothesis. In this paper, we report a laboratory incubation study of the effects of biotic Fe(III) (hydr)oxide reduction on P solubilization in a humid tropical forest soil (Ultisol) under a wet moisture regime (3000-4000 mm annual rainfall). The objectives of our study were: (1) to quantify Fe(III) reduction and P solubilization processes in a highly weathered forest soil expected to typify the hypothesized mineral dissolution-organic matter accumulation balance; (2) to examine the influence of electron shuttling on these processes using anthraquinone-2,6-disulfonate (AQDS), a well-known surrogate for the semiquinone electron shuttles in humic substances, as an experimental probe; and (3) to characterize the chemical forms of Fe(II) and P produced under anoxic conditions, both with and without AQDS. Two series of short-term incubation experiments were carried out, one without AQDS and another with an initial AQDS concentration of 150 μM. We measured pH, pE, and the production of Fe(II), total Fe [Fe(II) + Fe(III)], inorganic P, total P (inorganic P + organic P), and biogenic gases (CO₂, H₂ and CH₄). The same positive correlation was found between soluble P release and soluble Fe(II) production throughout incubation, implying that reduction of Fe(III) solubilized P. The Fe(II) produced was mainly particulate, evidently due to the formation of Fe(II) solid phases. Thermodynamic calculations indicated that precipitation of siderite and, in the presence of AQDS, vivianite was favored under the anoxic conditions that developed rapidly in the soil suspensions. Inorganic soluble P released during incubation was very small, indicating that the soluble P produced was mainly in organic form, which is consistent with the hypothesis that P accumulates in soil humus. Our net CO₂ production, H₂ consumption, and Fe(II) production data all suggested that reductive dissolution of Fe(III) (hydr)oxides was a terminal electron-accepting process coupled both to H₂ consumption and organic C oxidation by the native population of microorganisms in the soil. Addition of AQDS accelerated the production of Fe(II) and the release of soluble P, while hastening the decline in H₂ gas levels and suppressing CH₄ production. However, throughout incubation, the same quantitative relationships between soluble Fe(II) and P, and between pE and pH, were found, irrespective of AQDS addition. Thus we conclude that, in our soil incubation experiments, added AQDS functioned with the native microbial population solely as an electron shuttle catalyzing Fe(III) reduction. Whether humic substances in the soil also can act as electron shuttles in this way is a matter for future investigation.     

Chemistry of metal–humic complexes contained in Megalopolis lignite and potential application in modern organomineral fertilization

Lignite samples from two deposits located in the Megalopolis Basin, Southern Greece, were evaluated for their potential applicability as raw materials for the production of organomineral fertilizers. Fundamental chemical analyses were carried out to demonstrate high humic substances and metal contents. To determine their relative distribution in the Megalopolis lignite extract, eight elements, namely Na, K, Cd, Mn, Mg, Pb, Zn, and Cu, were studied both in H₂O and in Na₄P₂O₇/NaOH solutions. The behavior of these metals showed significant variations; Zn, Pb, Cd, and Cu associate mostly to the humic substances and proved scarce in the water extract. Contrarily, K and Mg gave a significantly low total yield in the Na₄P₂O₇/NaOH solution, while Mn was classified among the least extracted elements. Further enrichment of Megalopolis humic substances in these metals was achieved; Pb and Mg proved the most and least retained metal, respectively. Decomplexation titration curves of humic matter saturated with these metal ions demonstrated that novel organomineral fertilizing materials may develop based on optimized metal ion and humate contents, which can retain metals in a soluble form within a wide pH range. Formation of complexes between humic substances and Zn, Cd, and Mg was clearly indicated.     

Carbonate equilibrium in the water of the Razdol’naya River

The paper suggests an accurate approach to studying carbonate equilibrium in the water of the Razdol’naya River. The approach involves measuring pH by Pitzer’s scale, using a cell without liquid junction; measuring the total alkalinity by Bruevich’s technique; and using apparent constants of carbonate equilibrium with regard for the organic alkalinity. The Pitzer technique was employed to calculate the apparent constants of carbonate equilibrium in solution that models the riverine water: Ca(HCO₃)₂–NaCl–H₂O within the range of alkalinity of 0–0.005 mol/kg and temperatures of 0–25°C. Carbonate equilibrium in the water of the Razdol’naya River was sampled for studying at eight sites during all four seasons. Although the contents of biogenic compounds in the water are high, they can merely insignificantly affect the acid–base equilibrium, which is controlled in the riverine water by carbonate equilibrium and the concentrations of humic substances, which play the greater role, the greater the discharge of the river. In addition to the production and destruction of organic matter, carbonate equilibrium in the river is also affected by the supply of humic substances with soil waters and total alkalinity with groundwaters. The fluxes of alkalinity and humic substances annually brought by the Razdol’naya River to Amur Bay are evaluated at 1.33 × 10⁹ mol and 9.9 × 10⁶ kgC, respectively. The carbon dioxide export with the Razdol’naya River is equal to the alkalinity flux and does not depend on the weathering mechanisms.     

Biodegradation of CO2, CH4 and volatile organic compounds (VOCs) in soil gas from the Vicano–Cimino hydrothermal system (central Italy)

We investigated the effect of microbial activity on the chemistry of hydrothermal fluids related to the Vicano–Cimino system, central Italy. The database included the composition and δ¹³C CO₂ and δ¹³C CH₄ values for soil gas from an area characterized by intense degassing of fluids having a deep origin. The δ¹³C CH₄ values along vertical profiles in the soil indicated that CH₄ was controlled by microbial oxidation occurring at shallow (< 50 cm) depth, where free O₂ was available. This was consistent with the vertical gradients of CH₄, H₂S and O₂ concentrations. The δ¹³C CO₂ values in soil gas, characterized by a composition similar to that of the hydrothermal fluids, were not significantly influenced by biodegradation. On the contrary, gas strongly affected by air contamination showed a significant δ¹³C CO₂ fractionation. Microbial activity caused strong consumption of hydrothermal alkanes, alkenes, cyclics and hydrogenated halocarbons, whereas benzene was recalcitrant. Oxygenated compounds from hydrocarbon degradation consisted of alcohols, with minor aldehydes, ketones and carboxylic acids. A predominance of alcohols at a high rate of degassing flux, corresponding to a short residence time of hydrothermal gas within the soil, indicated incomplete oxidation. N-bearing compounds were likely produced by humic substances in the soil and/or related to contamination by pesticides, whereas α-pinene traced air entering the soil. The study demonstrates that microbial communities in the soil play an important role for mitigating the release to the atmosphere of C-bearing gases, especially CH₄, through diffuse soil degassing, a mechanism that in central Italy significantly contributes to the discharge of CO₂-rich gas from deep sources.     

Geochemistry of magnetite and maghemite in soils in European Russia

A method is proposed for determining the proportions of soluble Fe oxides (magnetite, FeOFe₂O₃, and maghemite, γ-Fe₂O₃) based on the measured magnetic susceptibility before and after treatment of soil with the Tamm or Mehra-Jackson (DCB) reagents. The development of hydromorphism in steppe soils in Ciscausiaia is associated with an increase in the magnetite fraction and, consequently, the average magnetite: maghemite ratio increases from 0.8–0.9 to 1.1. In these soils, smectites facilitate magnetite oxidation to maghemite. Soddy-podzolic and dark humic soils in the Cis-Ural region are noted for low values of the magnetite: maghemite ratio (0.5 on average) due to maghemite predominance. Soils in the Cis-Ural region on cover red-earth clays inherit lithogenic Fe oxides: hematite and maghemite. Hydromorphism in humid environments in northern taiga is accompanied by a significant increase in the magnetite: maghemite ratio to 4–9. Some issues of Fe geochemistry in magnetite and maghemite are considered.     

Calculation of molecular weights of humic substances from colligative data: Application to aquatic humus and its molecular size fractions

A rigorous mathematical expression for the dependence of colligative properties on acid dissociation of water soluble humic substances is presented. New data for number average molecular weights of a river derived humic material and its gel permeation Chromatographic fractions are compared with $\text{M}\text{?}{}_{\mathrm{n}}$ values obtained by a reevaluation of previously published experimental observations on soil and water fulvic acids. The results reveal a remarkable similarity of fulvic acids from widely different sources with respect to number-average molecular weight.     

Spectroscopic characterization of fulvic acids extracted from the rock exudate Shilajit

The present work describes the extraction of fulvic acids (FA) from Shilajit and its spectroscopic and mass spectrometric characterization. The spectral features obtained from FT-IR and ¹HNMR were similar to those reported for humic substances from other sources. The molecular elemental composition analysis by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) in electrospray negative ion mode resulted in extraordinary high average O/C ratios (0.55) which might be caused by a significant contribution of carbohydrates in Shilajit. A very high average H/C ratio of 1.27 also points to dominant aliphatic or alicyclic structures and relatively low aromaticity. The average molecular formula of the nitrogen free elemental compositions measured by FT-ICR mass spectrometry is C_18.2H_23.0O_10.0.