Effect of soil depth on acid properties of humic substances extracted from an ombrotrophic peat bog in northwest Spain

The most southerly ombrotrophic peat bogs in Europe are in Galicia (northwest Spain). The humic matter in them originates from chemical processes in anaerobic conditions. We studied the acid properties of fulvic acids and humic acids isolated from two peat horizons of an ombrotrophic peat bog by potentiometric titration. Solutions containing 25, 50 and 100 mg l⁻¹ of each humic substance were titrated at ionic strengths 0.005 m , 0.01 m and 0.1 m (with KNO₃ as the inert electrolyte). Charge curves were analysed with a Donnan model to determine the intrinsic proton binding parameters. The concentration of the humic substance affected the charge curves more significantly at pH exceeding 6, and tended to disappear at greater concentrations. The proton binding conditional constants decreased with increasing ionic strength, this effect being more significant in the carboxylic groups with less affinity for protons. The proton binding constant of the carboxyl groups in a fulvic acid was one order of magnitude less than the value for the corresponding humic acid, whereas for the phenolic groups the values for both fractions were similar. The total content of acid groups was approximately 2 mol kg⁻¹ greater in the fulvic fraction than in the humic fraction. Both humic fractions from the lower horizon contained more acid groups than those from the upper horizon, mainly because the content of carboxyl groups increases with soil depth. Therefore, the humic substances in the lower horizon of the peat will be more negatively charged, which will affect their solubility and the binding of metal ions.     

Influence of organic matter on the sorption of aromatic hydrocarbons by peat and chernozem

The interaction of water-soluble monoaromatic hydrocarbons with an organic matrix of chernozem and peat was studied. As a result of high levels of soil pollution by monoaromatic hydrocarbons, soil organic matter with the high sorption capacity actively adsorbs aromatic hydrocarbons. The hydrophobic properties of aromatic compounds determine the strength of the interactions between themselves and the soil organic matrix. The presence of lipids in the organic matter of chernozem decreases the sorption of aromatic hydrocarbons because of the blocking of hydrophobic centers of the soil humic substances.     

Sorption and desorption of cobalt by soils and soil components

The sorption of Co by individual soil components was studied at solution Co concentrations that were within the range found in natural soil solutions. Soil-derived oxide materials sorbed by far the greatest amounts of Co although substantial amounts were also sorbed by organic materials (humic and fulvic acids). Clay minerals and non-pedogenic iron and manganese oxides sorbed relatively little Co. It is considered that clay minerals are unlikely to have a significant influence on the sorption of Co by whole soils. Cobalt sorbed by soil oxide material was not readily desorbed back into solution and, in addition, rapidly became non-isotopically exchangeable with solution Co. In contrast, Co was relatively easily desorbed from humic acid and a large proportion of the Co sorbed by humic acid remained isotopically exchangeable. Cobalt sorbed by montmorillonite was more easily desorbed than that sorbed by soil oxide but less easily than that sorbed by humic acid. Cobalt sorption isotherms for whole soils at low site coverage were essentially linear and the gradients of isotherms increased with pH. A comparison of isotherm gradients for whole soils and individual soil components supported the suggestion that Co sorption in whole soils is largely controlled by soil oxide materials.     

The distribution of the stable carbon isotope (13C/12C) in fractions of soil organic matter

The carbon-isotopic composition of fulvic and humic acid from the A horizons of eight soil types, developed under a wide variety of climatological conditions, was measured. The fulvic acid is always enriched in ¹³C as compared with the humic acid from the same soil by a rather constant factor of 0.9?. The fulvic acids are isotopically closer to the plant source of the organic matter and thus represent an intermediate stage in the formation of humic substances. Depth sections of peat soil showed that carbon isotopes can be used to evaluate the dynamic nature of the fulvic-acid fraction. With depth, a transfer of carbon groups from polysaccharides to fulvic acid is seen. Based on isotopic evidence it is shown that in addition to formation of β-humus, part of the fulvic acid is condensed with depth to a stable humic fraction — humin.     

Interaction of heavy metals with the organic matter of an ordinary chernozem

Lead, copper, and zinc interacted with the soil organic matter when applied to an ordinary chernozem in a pot experiment. Two years after the treatment, an appreciable part of the metals applied was found in the organic substances, predominantly in a loosely bound state. These organic substances were supposed to be organomineral complexes, the formation of which resulted in the partial destruction of humic acid molecules. These processes increased the content of aliphatic structures and the share of fulvic acids and decreased the content of humic acids in the organic matter of the chernozem.     

Chromatographische Unterscheidung von Huminstoffen und Nichthuminstoffen aus Schwarzerdehumus

Chromatographic distinction of humic and non humic substances in chernozem-humus Fulvic acids, brown humic acids and grey humic acids from a chernozem from the Austrian Marchfeld were analyzed chromatographically on controlled pore glass with pore diameters of 177 and 259 Å. Concentration of coloured material and concentration of carbon were recorded in the chromatogramms. Specific extinctions at 400 nm were calculated for unit of C and maximal values were taken as constants specific for “pure” humic substances. These were 445,6 ± 10,5,388,7 ± 19,3 and 128,9 ± 0,8 for “pure” grey humic acids, brown humic acids and fulvic acids, respectively. With the aid of these constants, “pure” humic substances could be distinguished from accompanying non humic substances. “Pure” humic substances amounted to 63%, non humic substances to 37% of extractable organic C. 53%, 22% and 25% of the carbon of “pure” humic substances were from grey humic acids, brown humic acids and fulvic acids, respectively.     

对硝基氯苯在土壤和腐殖酸上的长期吸附与多步解吸的研究

采用批量平衡实验法研究了对硝基氯苯（p-NCB）在土壤和腐殖酸上的长期吸附和多步解吸,比较了连续的多步解吸与一步解吸的差异。结果表明,随着吸附时间的增加吸附量均会有所增加,随吸附时间增加吸附等温线的非线性增强。p-NCB在液相和固相上的初始浓度对吸附速率有一定影响,低浓度比高浓度时达到平衡的速率要低。对于两种受试土壤,两次解吸得到的等温线均无法与吸附等温线重合,表现出很强的吸附不可逆性。而尽管p-NCB在腐殖酸上表现出明显的非线性吸附（n = 0.794）,但4次解吸后所得到的平衡位点与吸附所得的平衡位点基本落在同一条直线上,对数坐标下进行线性拟合的相关系数（R2）可达0.988,说明吸附过程是完全可逆的。     

ADSORPTION ON HYDROUS OXIDES. III. FULVIC ACID AND HUMIC ACID ON GOETHITE, GIBBSITE AND IMOGOLITE

Adsorption isotherms were obtained for fulvic and humic acids on synthetic gibbsite and goethite and on a natural imogolite. The results were interpreted with the help of spectra of the adsorption complexes, and measurements of hydroxyl displaced. The mechanism of adsorption involved ligand exchange with the surface hydroxyl groups and hydrogen bonding. The hydroxyl groups displaced included singly coordinated species on the (100) face of goethite and on the edge faces of gibbsite. The doubly coordinated hydroxyl groups on the (001) face of gibbsite were not replaced, and this face adsorbed only un-ionized fulvic acid probably by a hydrogen bonding mechanism. Imogolite adsorbed most fulvic acid because of its high porosity. Only isolated places on its surface reacted with fulvic acid to form carboxylate groups.     

Depolymerization and degradation of humic acids with sodium perborate

Two humic acids of different origin (peat and soil) were degraded with a 5% sodium perborate solution (140°C). This degradation process consists mainly of a stoichiometric production of hydrogen peroxide while the perborate is reacting with carboxyl groups of the oxidized polymers. A single perborate treatment degraded more than 40% of the humic acids to soluble products, but a 5-step oxidation was necessary for total degradation, the sample being transformed into soluble oligomers with properties similar to those of fulvic acids. The oligomeric fractions with lowest molecular weights, including individual molecules (soluble in ethyl acetate), were purified by adsorption chromatography and studied by GC-MS after methylation. The higher molecular weight fractions of oligomers were recovered over polyvinylpyrrolidone, eluted by alkali, and purified by ion-exchange chromatography (47% peat HA; 25% soil HA).Degradation products included alkanes, fatty acids and dicarboxylic acids. Aromatic compounds (mainly phenolic, benzenecarboxylic and cinnamic acids), amounted to 24–50% of the total volatile degradation products. There were striking differences between peat and soil humic acids, the former yielding typical lignin degradation products. Independently checked, the perborate degradation products were not the same as those obtained by mild treatment with hydrogen peroxide under alkaline conditions.     

Molecular composition of humic substances in tundra soils (13C-NMR spectroscopic study)

Functional groups and molecular fragments of humic substances (HSs) from cryohydromorphic peat gley tundra and surface-gley tundra soils have been identified by ¹³C-NMR spectroscopy. The analysis of HS preparations has shown that the molecules of humic acids (HAs) are enriched with aromatic fragments compared to fulvic acids (FAs). Aliphatic chains, carbohydrate- and amino acid-type structures prevail in the carbon skeleton of the FAs. An integrated parameter of the HS hydrophobicity has been proposed. The parameter represents the total portion of unoxidized carbon atoms and allows indirectly assessing the amphiphilic properties of HSs.     

Evaluation of different fractions of the organic matter of peat on tetracycline retention in environmental conditions: in vitro studies

Purpose

Due to the modernization of the agro-industrial sector, compounds with different toxicity and effects on human health and animal have been used and consequently affecting the environment. Among them, tetracycline (TC) stands out as one of the antibiotics most commonly used worldwide. This study evaluated the TC interaction with different fractions of peat in natura and humic substances, humic acid, fulvic acid, and humin.

Materials and methods

The different fractions of the organic matter were characterized by organic matter content, elemental analysis, spectroscopic analysis (E₄/E₆), and nuclear magnetic resonance of carbon 13 (NMR ¹³C), and the interaction between TC and different fractions of organic matter was made by fluorescence spectrometry. We used the tangential ultra-filtration system for determining the complexation capability of humic substances (HSs), fulvic acids (FA), humic acids (HA), and humin (HUM) from peat with TC. Finally, we evaluated sorption kinetic experiments between TC and peat in natura.

Results and discussion

The peat samples, humic substances, FAs, HAs, and HUM were characterized by organic matter (OM), atomic ratio (H/C and C/O) calculated from elemental analysis data, functional groups quantified by NMR ¹³C data, and E₄/E₆ ratio, and the results show significant differences in the structural characteristics of the fractions of OM influenced by the type of microorganisms and environmental factors associated with this decomposition. Data analysis revealed the strongest interaction between HUM and TC (59.19 mg g^?1), followed by interaction between HS and TC (43.36 mg g^?1 HS). In the sorption studies, these conditions showed the best model to describe the system under consideration using the Freundlich model.

Conclusions

The results showed that the different fractions of the OM extracted from peat show different contributions that affect the bioavailability of contaminants to the environment.

     

Acid pyrophosphate extraction of soil fulvic acids

A simple three step method is described for isolation of soil fulvic acids in high yield. The complexing agent H₂P₂O₇^2? (at pH 2) is used to release soil-bound fulvic acids. Extraction of humic acids is minimal. Selective separation of the protonated fulvic acids from the ionic extractant is achieved on a non-ionic polyacrylate resin (Amberlite XAD-7); after washing the resin, fulvic acids were retrieved in >98% yield by adjusting the pH to 6.5. Two problems associated with the classical alkali extraction method are avoided: possible alkaline oxidation of phenolic components, and their oxidation by Fe³⁺ under the acidic conditions employed to precipitate humic acids. The product typically has an ash weight of <0.6% after one XAD treatment. The method has been applied to three soils and one IHSS peat sample.     

Dissolved organic matter in lysimetric water of mountain forest soils in the southern Sikhote Alin

The fractional composition of dissolved organic matter and the chemical nature of humic and fulvic acids were studied in lysimetric waters from forest soils of different altitudinal zones in the Sikhote Alin Range. The elemental composition, infrared absorption spectra, concentrations of acid functional groups, and pK spectra of humic and fulvic acids were determined. Fulvic acids predominated in the upper soil horizons, and fraction of nonspecific dissolved organic substances predominated in the lower mineral horizons. The portion of humic acids in the humus horizons markedly decreased from the low-mountain soils to the high-mountain soils; the nitrogen content of humic and fulvic acids decreased in the same direction. Three classes of carboxyl and phenolic groups were determined in pK-spectra of humic and fulvic acids. The soils of high-mountain zones had stronger acidic properties of humic and fulvic acids in comparison with the soils of low-mountain zones. The determined characteristics of the composition of dissolved organic matter and the trends of their changes contribute to our knowledge of pedogenetic processes in the altitudinal sequence of forest landscapes of the Sikhote Alin Range.     

Acid properties of fulvic and humic acids isolated from two acid forest soils under different vegetation cover and soil depth

We studied the acid‐base properties of 16 fulvic acids and 16 humic acids isolated from the surface (3–15 cm) and subsurface (> 45 cm) horizons of two types of acid forest soils, derived respectively from amphibolite and granite rocks, under five different types of vegetation. The observed differences between the contents of humic substances in the two types of soils were related to the degree of Al‐saturation of the soil organic matter, as indicated by the molar ratio between pyrophosphate extractable Al and C. Humic fractions were characterized in terms of elemental composition, and CPMAS ¹³C NMR spectrometry. The contents of carboxylic and phenolic groups were estimated by potentiometric titrations conducted in 0.1 m KNO₃ in a nitrogen atmosphere. The fulvic acids contained more carboxylic groups but less phenolic groups than the humic acids: the ratio of phenolic to carboxylic groups in the humic acids was 0.48 ± 0.10 and in the fulvic acids 0.23 ± 0.05. The mean values of the protonation constants of each of the humic substance fractions can be used as generic parameters for describing the proton binding properties. The fulvic acids isolated from the subsurface horizon of the soil contained between 2.6 and 23% more carboxylic groups, and the humic acids between 8 and 43% more carboxylic groups than those isolated from the surface horizon of the same soil.     

新疆典型草原土壤腐殖酸组分的变化规律

以新疆典型草原黑钙土、栗钙土和棕漠土为对象,研究了3种土壤不同土层腐殖质矿物复合体组分及其垂直分布规律。结果表明:13种典型草原土壤腐殖质总碳量的顺序为黑钙土(35、46g/kg)、栗钙土(31.30g/kg)和棕漠土(0.68g/kg);23种草原土壤都是以胡敏素(HM)含量最高,黑钙土、栗钙土和棕漠土的含量分别为68.17%、65.47%和42.81%;3按照腐殖酸类型分析,黑钙土和栗钙土是以胡敏酸(HA)为主的富啡酸(FA)-胡敏酸(HA)型,CH/CF＞1;而棕漠土则相反,是胡敏酸-富啡酸型,CH/CF＜1;4黑钙土、栗钙土和棕漠土腐殖质组分中游离R₂O₃结合的胡敏酸分别为6.85%、5.65%和1.65%,而富啡酸分别为0.53%、0.84%和4.91%;5在3种草原土壤中,游离腐殖酸从0~20cm到40~60cm的垂直变化规律分别为:黑钙土中游离胡敏酸和富啡酸分别从5.74和2.33g/kg降到2.70和0.89g/kg;栗钙土中游离胡敏酸和富啡酸分别从1.88和1.03g/kg降到0.59和0.75g/kg;棕漠土中游离胡敏酸和富啡酸分别由2.10和2.90g/kg降到1.92和0.67g/kg。     

Free-radical condensation as a natural mechanism of the formation of humic acids

Recently suggested structural models of humic acids (Schulten, Schnitzer, etc.) do not agree with the existing notions on the biochemical origin of some fragmentary groups composing a significant part of the molecules of humic acids. It is hypothesized that free-radical reactions of the polycondensation of low-molecular organic compounds derived directly from soil biota, from primary products of its posthumous decomposition, and from fulvic acids represent an obligatory stage of natural humus formation. Calculations demonstrate that different natural sources of free hydroxyl radicals (forming in the troposphere and deposited with atmospheric precipitation, produced by soil prokaryotes, etc.) ensure the possibility of free-radical condensation of organic substances and the formation of humic acids in the pedosphere of the Earth; moreover, the actual supply of free hydroxyl radicals exceeds the necessary amount by several orders of magnitude. The development of this concept allows us to assume the existence of a general evolutionary scheme of transformation of organic residues of biological origin on the Earth with the formation of stable products (humic substances, peat, and coal).     

Applications of the continuous-flow stirred-cell (CFSC) technique: II. The adsorption behaviour of Na, Cs, Sr, Cu, Ni and Pb on humic acids

The first part of this paper deals with the sorption of Na, Cs, Sr, Ni, Cu and Pb on two humic fractions derived from a soil. The sorption data for individual elements were obtained using the continuous-flow stirred-cell (CFSC) technique, in which the metal sorptive solution is pumped through a cell containing a known mass of the humic acid retained by a filter and the solution emerging from the cell was analysed by either atomic absorption spectrometry (Cu, Ni and Pb) or by the combined use of radioisotope dilution and gamma-ray spectroscopy (Na, Cs and Sr). Sorption isotherms were determined at two flow rates. It was found that, in general, the sorption isotherms for all the metals studied could be described by the Langmuir equation and parameters derived from the fitted line provided information on the metal-humate binding strengths and the maximum amount of metal sorbed per unit mass of humic acid. Caesium showed anomalous behaviour at certain flow rates in both its sorption and desorption behaviour. In the second part of the paper we discuss the sequential sorption and desorption of one metal by another on the same humic fraction, using Na, Cs, Zn and Cd. The aim was to elucidate the nature of the binding process when several metals were competing simultaneously for the functional groups on the humic acids. In addition, at the end of the experiment, the humic material was isolated and analysed by gamma-ray spectroscopy to determine the metals still bound in this fraction. Some tentative conclusions concerning the nature of the metal-humate complexes are made on the basis of these data.     

Infrared spectroscopic investigations of humic substances and their metal complexes

A study has been made on the infrared spectra of lowland peats and purified humic, hymatomelanic and fulvic acids, as well as their acetylated derivatives and metal complexes. Extraction and purification may modify humic acids of untreated peats only to a small extent. Acetylation of fulvic and humic acids with acetic acid anhydride resulted mainly in the reaction of phenolic hydroxyl and quinone groups. Similarities of the spectra of the individual humic substances point to similar structures, differing only in the number of functional groups and the degree of aggregation. Metals are bound by humic substances mainly in metalcarboxylate bonds. The degree to which these bonds are ionic or covalent can be determined by the antisymmetric carboxylate stretching frequencies.     

Phenanthrene sorption by compost humic acids

Nonlinear isotherms were observed for sorption of polycyclic aromatic hydrocarbons (PAHs) to humic materials, but the exact sorption mechanism is not clearly understood. This study aimed to investigate the sorption of PAHs by compost humic materials. Humic acids (HAs) were progressively extracted from two compost samples by a 0.1-M sodium pyrophosphate solution. Sorption of phenanthrene by the extracted HAs was studied with a batch equilibration technique. Competitive sorption between pyrene and phenanthrene in the HAs was also examined. Elemental analysis and solid-state ¹³C NMR were used to characterize HAs. All sorption isotherms were nonlinear although these samples contained little black carbons if any. Isotherm linearity increased with increasing number of extractions. Isotherm nonlinearity was negatively related to HA aliphaticity. Addition of pyrene to the phenanthrene-HA system increased isotherm linearity. Competition between phenanthrene and pyrene sorption was more pronounced in the first fraction of HAs with a higher content of aromatic moieties. This study showed that humic materials alone could lead to nonideal sorption for PAHs.     

Quantification of Humic and Fulvic Acids,Macro- and MicroNutrients and C/N Ratio in Organic Fertilizers

Humic substances are the main responsible for soil conditioning and are one of the major components of the composting product. However, there is still little information about their composition and mechanisms of activity. This study aimed to evaluate quantitatively the humic and fulvic fraction by size-exclusion liquid chromatography and the metal content by atomic absorption spectrometry. The chromatographic method used was efficient for humic and fulvic acids quantitation. Levels of 1.73 ± 0.03 and 1.6 ± 0.5 g kg^?1 were found for chicken manure regarding humic and fulvic acids, respectively, and 5.1 ± 0.9 and 1.2 ± 0.1 g kg^?1 for peat. The metal contents indicated the need of a mineral enrichment, because only the levels of iron reached the minimum recommended by legislation. It was also observed that evaluated organic fertilizers were in accordance with the specifications established by legislation in relation to carbon and total nitrogen and the pathogen levels.