Permanganate oxidation of methylated fulvic and humic acids in chloroform

Methylated fulvic and humic acids were oxidized by permanganate in chloroform in the presence of a cyclic polyether, 18-crown-6. The total amount of oxidation products identified was 6.5% for fulvic acid and 6.7% for humic acid. About 46% of the oxidation products found from both fractions were dicarboxylic acids (15 compounds), the rest were benzenecarboxylic acids and their methoxyl derivatives (15 compounds). Alkanes and fatty acids were also found.Nonandioic acid and 3,4-dimethoxy-benzenecarboxylic acid are found in almost equal amounts. Each accounts for 1.3% of the starting material, and together they represent 40% of the oxidation products. 3,4-Dimethoxy-benzoic acid and 4-methoxy-benzoic acid are believed to result from the oxidation of terminal groups in the humic polymer.Proton resonance spectra show that about 25% of the aliphatic protons are part of methylene chains. The most prominent chain lengths consist of 6–8 methylene groups as shown by the dicarboxylic acids formed by oxidation.     

The persulfate oxidation of fulvic acids

Persulfate oxidation of two fulvic acids from different soils was accomplished. This is a new mild chemical degradative method which differentiates between fulvic acids isolated from soils developed under widely differing environments. A fulvic acid isolated from an Humic Haplorthod gives as major oxidation products phenolic acids, whereas a fulvic acid from an Andic Hapludult yields benzenecarboxylic acids as most abundant compounds. The possibility to differentiate between fulvic acids from different soils, as chemical degradation with persulfate does, offers interesting prospects to the characterization of humic materials.     

The role of free radicals in the oxidation and reduction of fulvic acid

The effects over a wide pH range of oxidation, reduction and irradiation on free radical concentrations of fulvic acid (FA) solutions and the reversibility of these reactions were investigated by i.r. and visible spectrophotometry and by e.s.r. spectrometry. Oxidizing agents used were H₂O₂, Ag₂O and NaIO₄ while NaBH₄, SnCl₂ and Na₂S₂O₄ were employed as reducing agents. Molar oxidant or reductant to fulvic acid ratios ranged from 1:1 to 10:1. Reaction conditions employed were relatively mild, because i.r. and visible spectra of oxidized, reduced and untreated FA solutions were practically identical. Two types of free radicals were detected in FA by e.s.r. spectrometry: (a) permanent ones, having long life spans and (b) transient ones, not sufficiently long-lived under oxidative conditions to be detected but sufficiently stable under reducing conditions and after irradiation. The oxidation-reduction reactions were reversible and proceeded by two one-electron steps via free radicals only. Because of their ability to act either as electron donors or electron acceptors, depending on environmental conditions, FA and other humic substances can actively participate in oxidation-reduction reactions with transition metal ions and biological systems in terrestrial and aquatic environments.     

Characterization of lignin in forest humus layers by high-performance liquid chromatography of cupric oxide oxidation products

A rapid method is described to prepare samples, separate and quantify phenolic lignin degradation products obtained from the alkaline cupric oxide oxidation of forest humus layers. The whole sample is treated with CuO-NaOH at 170°C to produce simple lignin-derived phenols, which are extracted with a commercially-available disposable column system. The extracted phenolic compounds are separated by reverse-phase high-performance liquid chromatography, based on the differential polarity of benzoic acids, aldehydes and cinnamic acids. Results from the oxidation of gymnosperm and angiosperm litter are presented.     

Interactions between montmorillonite and fulvic acid

The isotherms at 20°C for the adsorption of ¹⁴C-labelled fulvic acid from aqueous solutions by montmorillonite containing different exchangeable cations, have been determined. Below a concentration of 0.45 mg/ml and at near neutral pH, all samples give linear isotherms, the slope of which increases in the order Ba²⁺ < Ca²⁺ < Zn²⁺ < La³⁺ < Al³⁺ <Cu²⁺ < Fe³⁺. In the absence of interlayer expansion, the shape of the isotherms is interpreted in terms of solute entry into intercrystalline pores within a clay domain. The affinity of fulvic acid for the clay surface is related to the ionic potential or polarising power of the exchangeable cation. It is inferred that fulvic acid adsorbs by hydrogen bonding between an anionic group of the acid and a water molecule in the primary hydration shell of the saturating cation. Comparison of the data with those for the humic acid extracted from the same organic matter source, indicates that secondary interactions between adsorbed molecules or directly with the montmorillonite surface, contribute to the overall affinity. With samples saturated with Al³⁺, Fe³⁺, and Cu²⁺ ions, part of the adsorbed fulvic acid may also be attached to the clay by a complexation reaction involving the metals as such, or when they exist as polyhydroxy compounds at the mineral surface.     

The dissolution of micas by fulvic acid

Three micas commonly occurring in soils, that is, biotite, phlogopite and muscovite, were shaken with 0.2% (W/V) aqueous fulvic acid (FA) solution for 710 h at room temperature. Proportions of major constituent elements extracted (Fe, Al, Mg, K and Si from biotite, Al, Mg, K and Si from phlogopite and Al, K and Si from muscovite) were determined.Depending on the type of mineral and its Fe content, substantial amounts of Fe, Al, Mg, K and Si were brought into aqueous solution by the FA under mild conditions. The ease with which the micas were attacked by the FA decreased in the following order: biotite > phlogopite > muscovite. IR and ESR analyses indicated the formation of metal—FA complexes as a major reaction mechanism by which the minerals were dissolved. Our data show that aqueous FA solution can dissolve from micas relatively large amounts of metals and Si, which may then become more available to plant roots and microbes, active in soil genesis processes, as well as participants in the synthesis of new minerals.     

Reactions of fulvic acid with metal ions

Fulvic acid is a water-soluble humic material that occurs widely in soils and waters and that tends to form water-soluble and water-insoluble complexes with a variety of metal ions, some of which are toxic. This paper presents information on the conditions under which the different types of FA-metal complexes are formed. The solubility in water, separately and after mixing, of FA (2 to 30 mg/100 ml) and eleven metal ions (Fe(III), Al, Cr(III), Pb, Cu, Hg(II), Zn, Ni, Co, Cd and Mn; 1 × 10^?5 moles of each metal ion) was investigated over the pH range 4 to 9. After mixing, the solubility of the components was significantly affected by pH only when less than 20 mg of FA was present. As the systems became richer in FA (22 to 30 mg), most of the metal ions remained in the aqueous phase, likely due to the formation of FA-metal complexes, inhibiting the formation of metal hydroxides. The order in which the eleven metal ions tended to form water-insoluble FA-metal complexes depended on the pH. At pH 6 it was: Fe = Cr = Al > Pb = Cu > Hg > Zn = Ni = Co = Cd = Mn. This order appeared to correlate with the valence, 1st hydrolysis constants and effective hydrated ionic diameters of the metal ions. In general, FA/metals weight ratios of > 2 favored the formation of water-soluble FA-metal complexes; at lower ratios, water-insoluble complexes, which could accumulate in soils and sediments, were formed.     

A comparison of the structural characteristics of polymaleic acid and a soil fulvic acid

The purpose of this investigation was to compare structural characteristics of PMA with those of FA in order to assess the suitability of PMA to serve as a model for FA. Chemical (elemental analyses, CO₂H group determinations, increases in OCH₃ after methylation, oxidative degradation) and spectroscopic (visible, UV, fluorescence, IR, ¹³CNMR, and ESR) methods were used for this purpose. While PMA was found to resemble FA in a number of characteristics (water solubility, rich in CO₂H groups, dark brown colour), it significantly differed from FA in a number of respects (UV, fluorescence, ¹³CNMR spectra as well in oxidation products). Compared to FA, PMA appeared to be better organized and more homogeneous at the molecular level, richer in olefinic structures and less aromatic. But the chemical structures of both PMA and FA remain largely unknown.     

An electron microscopic examination of fulvic acid

An electron microscopic examination of fulvic acid shows that the crystallinity, shapes, dimensions and extent of aggregation vary with pH. At pH 2.5, three types of particles can be observed: small spheroids (15–20 Å in diameter), aggregates of spheroids (200–300 Å in diameter) and an amorphous material of low contrast, perforated by voids, 500–1,100 Å in diameter. spheroidal aggregates tend to form elongated, irregularly shaped structures, 20,000–30,000 Å long.At pH 3.5, which is the natural pH of a dilute fulvic acid solution, electron micrographs show a sponge-like structure of variable thickness (100–300 Å), punctured by voids, 200–1,000 Å in diameter.At pH 4.5 and higher, electron micrographs show flat sheet-like lamellae of very low contrast, perforated by voids, 200–2,000 Å in diameter.Electron diffraction patterns show crystallinity in fulvic acid aggregates formed at pH 2.5 only but not in those formed at pH 3.5. The electron microscopic data are in harmony with X-ray, chemical and spectroscopic data on the same fulvic acid, and point to a relatively “openlrd structure, perforated by voids of varying dimensions which can trap or fix organic and inorganic compounds that fit into the voids, provided that the charges are complementary.     

Permanganate oxidation of methylated and non-methylated aquatic humus in Norway

The chemical composition of aquatic humus was investigated by permanganate oxidation. Both methylated and non-methylated samples were investigated and the results compared with those of different soil humic fractions investigated earlier.The total amount of oxidation products identified from the methylated sample was 2%, and from the non-methylated sample 0.9%. The composition of the oxidation products from methylated aquatic humus was 42% benzenecarboxylic acid methyl esters (8 different compounds), 43% methoxy-benzenecarboxylic acid methyl esters (12 compounds), 10% dimethoxy-benzenecarboxylic acid methyl esters (4 compounds), and 5% of 1, 2, 3-propanetricarboxylic acid trimethyl ester. The unmethylated aquatic humus yielded 84% benzenecarboxylic acid methyl ester (7 compounds), 7% methoxy-benzenecarboxylic acid methyl esters (2 compounds), and 9% of 1, 2, 3-propanetricarboxylic acid trimethyl ester. Three diazines isolated from methylated material were believed to be artefacts from diazomethane treatment. Two of the diazines have earlier been found by oxidation of methylated soil samples, the third, C₁₀H₁₂N₂O₆, is an oxidation product of methylated aquatic humus only.Oxidation of aquatic humus yielded more benzenecarboxylic acids and methoxy-benzenecarboxylic acids than soil humic fractions, and less dimethoxy-benzenecarboxylic acids. No aliphatic dicarboxylic acids were detected among the oxidation products of the aquatic humus.The compounds identified are mainly the same as those found by oxidation of different soil humic fractions, although their yields clearly demonstrated that the aquatic humus differed in composition from the soil fractions.     

Biological oxidation of nitric oxide in a humisol

Consumption of nitric oxide (NO) in a humisol was studied at 0.1–2 ppmv NO, a range representative of NO concentrations in ammonium-fertilized soil. Denitrification was not a major sink for NO. The principal NO-consuming reaction was a biological oxidation, leading ultimately to nitrate (NO₃ ^–). Nitrogen dioxide (NO₂) and nitrite (NO₂ ^–) may have been intermediates in this pathway. An abiological reaction accounted for about 25% of the NO-consuming activity in soil at 90% H₂O (d.w.) and 25^oC, but contributed relatively more to total NO consumption at higher temperatures. Biological NO-consuming activity was highest at 25^oC, while the abiological activity increased exponentially with temperature. The product of the abiological reaction was neither NO₃ ^–, NO₂ ^–, nor nitrous oxide (N₂O), and the reaction did not require O₂. Received: 12 March 1996     

Effect of fulvic acid on the crystallization of aluminum hydroxides

Effects of addition of increasing amounts of fulvic acid (FA) on the crystallization of aluminum hydroxides from AlCl₃, solution, neutralized to different degrees, were investigated. All systems were allowed to age at 30°C for 70 days.In the absence of FA, gibbsite was formed at pH 6, a mixture of nordstrandite and bayerite at pH 8, and bayerite crystallized at pH 10. At pH 6 and 8, the addition of increasing amounts of FA (up to 10 mg/l or $\text{FA/Al molar ratio}\text{? 10}{}^{\mathrm{?2}}$) first delayed and then inhibited the crystallization of these aluminum-hydroxide polymorphs but tended to favor the crystallization of pseudoboehmite, an aluminum oxyhydroxide. At pH 10, the addition of FA totally inhibited crystallization and precipitation.Our data suggest that FA so strongly complexes Al that it prevents its full hydroxylation to Al(OH)₃. Another explanation is that the action of FA on the crystallization of aluminum hydroxides resembles that of salts in that FA appears to favor the formation of Al-O-Al (oxo) over that of

(ol) linkages. Either reaction mechanism throws new light on the genesis of some bauxites, which consist of submicroscopic boehmite-like particles which are very similar to pseudoboehmite.     

Pyrolysis of a soil humic acid and of their hydrolyzed and methylated products

Pyrolysis of soil humic acid yields a variety of products arising from heterogeneous materials associated to the humic structure and from this self. After acid hydrolysis most of the compounds related to proteins, polysaccharides and lignin dissappear. Adsorbed compounds such as fatty and dicarboxylic acids are released after methylation and subsequent pyrolysis. In addition pyrolysis produces aromatic and substituted aromatic hydrocarbons. All the identified pyrolysis products have also been isolated by different complex and time-consuming chemical degradations and solvent extraction procedures. Pyrolysis provide some evidence of the humic acid structure.     

Effects of a fulvic acid on the speciation and mobility of mercury in aqueous solutions

The presence of humic substances in aqueous systems generally has a large impact on speciation as well as on mobility of metal ions at trace levels. At pH<pH_zpc, the humic substances tend to adsorb and enhance the uptake of trace metals from the solution phase. At pH>pH_zpc, the reverse effect is expected. Experimental data on the adsorption of Hg on an oxide (alumina) in the presence of a fulvic acid (FA; 0 to 25 mg L⁻¹) is reported in the present work. Generally the presence of the FA enhances the Hg adsorption in the whole pH-range studied (2.5 to 9.5). A Hg-FA complex is the dominant species already in the presence of 1 mg L⁻¹ FA in the solution phase. Chloride increases the adsorption at pH<pHZpc possibly related to the formation of the negatively charged HgCl₃ ⁻ species. The Hg adsorption is compared with Zn and Cd in the corresponding systems. The mobility of these bivalent metals in the aqueous environment is discussed.     

土壤胡敏酸与富里酸热力学稳定性及其驱动因素初步研究

从过程考虑,腐殖质的形成和转化主要是微生物主导的生物化学过程,但就其始态和终态的能量水平变化而言,是热力学稳定性问题。在土壤中,影响腐殖质的形成转化的因素很多,如黏粒含量和类型,植被和微生物状况,土壤湿度、温度和空气组成,土壤溶液的化学组成、浓度、酸度和氧化还原状况等。但从热力学角度,为了计算反应平衡常数(logKR)和吉普斯生成自由能(ΔGfθ),如果将温度设为25℃,我们可以将土壤条件诸多因素简化为水活度([H2O])、氧分压(PO2)和二氧化碳分压(PCO2)这3个参数。之所以简化为这3个参数,因为任何有机成分均是由含有这3种元素的物质形成的,最终又均可以分解为含有这3种元素的H2O和CO2。本文按照上述新思路,以黑土为例探讨了胡敏酸(HA)、富里酸(FA)形成转化的驱动因素和热力学稳定性的研究方法,用元素组成-土壤条件参数法计算HA、FA的logKR和ΔGfθ及热力学稳定性范围。同时通过土壤添加有机物料的模拟培养实验研究了氧气和二氧化碳等单因素对HA和FA数量积累的影响。结果表明,黑土HA和FA的元素组成分子式分别为nC21H21O9N和nC24H33O17N。FA在缺氧、多水和高浓度二氧化碳条件下较稳定;HA则相反。培养实验中,高二氧化碳和低氧气浓度处理使FA与HA的相对比例增加。这一研究方法和结果将有助于解释和推测土壤腐殖质组成的空间变异规律,指导土壤肥力、土壤固碳的调控实践。     

Soil fulvic acid properties as a means to assess the use of pig slurry amendment

Soil amendment with animal manures is a common practice for either increasing soil organic matter (SOM) and nutrient content or disposing of wastes from intensive animal industries. However, the application of organic amendments that are not sufficiently mature and stable may adversely affect soil properties, especially the content and quality of SOM pools. In this work, the effect of the consecutive annual additions of pig slurry (PS) at rates of 0 (control), 90 and 150 m³ ha⁻¹ per year over a 4-year period on the soil fulvic acid (FA) fraction of SOM was investigated in a field plot experiment conducted under semiarid conditions on a Calcic Luvisol in Toledo province, Spain. The FAs isolated from PS and control and amended soils were characterized for chemical, compositional, structural and functional properties by use of elemental and functional group analysis, and ultraviolet/visible, Fourier transform infrared (FT IR), fluorescence and electron spin resonance (ESR) spectroscopies. PS-FA was characterized by a prevalent aliphatic character, large contents of acidic functional groups, S- and N-containing groups and polysaccharide components, extended molecular heterogeneity, small organic free radical (OFR) contents and small degrees of aromatic ring polycondensation, polymerization and humification. With respect to the control soil FA, the PS-amended soil FAs were characterized by a smaller extraction yield, O and OFR contents and ratios of absorbances at 465 and 665 nm, and larger C, N, S, COOH and phenolic OH contents, C/N ratios and aliphaticity. Statistical analysis of experimental data showed that, with some exceptions, these effects generally increased with increasing cumulative amount of PS applied to soil over time. In conclusion, cumulative PS application to soil over time modifies the content and properties of the FA fraction of SOM. Thus, this material should not be considered as a mature organic amendment and should be treated appropriately before it is applied to soil, so as to increase the degree of humification and enhance its potential as a soil organic fertilizer.     

Computer simulation of metal ion—humic and fulvic acid interactions

The humate model, RANDOM, was investigated in combination with the general speciation program, PHREEQE. After an initial investigation of cobalt(II)–humic acid and copper(II)–fulvic acid interactions this coupled code approach was modified to include a sensitivity analysis which identified the ligands which were statistically significant in any one system. Subsequent speciation modelling with these significant ligands is shown to produce a reasonable agreement between experimental and modelled data. The systems chosen to demonstrate the advantages of this approach were uranyl–humate and nickel(II)–humate interactions. Although this technique is not fully developed, it shows great potential for improving the predictive qualities of the RANDOM model.     

溶解性富里酸对土壤中多环芳烃迁移的影响

多数多环芳烃（PAHs）因其水溶性低,且易被土壤有机质固持,曾经被认为其迁移能力十分微弱。但土壤中溶解性有机质可能影响PAHs的溶解、吸附等环境过程,进而影响其迁移性。本文旨在研究富里酸提取的溶解性有机质（FDOM）对PAHs在土－水间迁移的影响及其可能机制。溶液化学稳定性研究结果显示,FDOM在溶液pH 2.0～7.0、CaCl₂浓度0～1 500 mmol L^-1范围内均能保持较好的分散性,未发生絮凝沉淀。室内土柱淋溶试验结果表明,FDOM在土壤中具有较强的迁移能力,在FDOM持续淋溶条件下,菲、芘以及苯并[a]芘在淋出液中的浓度明显提高,并有少量二苯并[a, h]蒽淋出。FDOM淋溶处理的土柱表层土壤中菲、芘、苯并[a]芘和二苯并[a, h]蒽的淋失率分别为92.06%、92.07%、84.52%和23.27%,显著高于对照组（p<0.05）。以上研究结果表明,FDOM可作为载体提高PAHs在土壤中的迁移性,增加PAHs向深层土壤和地下水迁移的可能性。