Fulvic Fractions Research Articles

Characterisation of humic materials of different origin: a multivariate approach for quantifying the latent properties of dissolved organic matter.

The inherent chemical properties of eight different dissolved organic matters (DOMs) originating from soil, surface and groundwater have been analysed. The samples consist of isolated fulvic acids (FA), humic acids (HA), and humic substances (HS), i.e. natural mixtures containing a humic and a fulvic fraction. The humic substances have been characterised by elemental analysis, size exclusion chromatography, E2/E3 and E4/E6 UV absorption ratios, and liquid-state 13C-NMR spectroscopy. The information contents of the different analytical methods have been investigated by pattern recognition, i.e. cluster analysis and principal component analysis (PCA). A comparative study of the information contents of DOM descriptors derived from different analytical methods is presented. Through extraction of information content of the individual analytical methods the inherent properties of DOM are quantified. Pattern recognition revealed significant quantitative differences in the inherent properties of DOM of different origin and type. PCA based on the NMR descriptors showed highest explained variance. However, all models showed low robustness due to the limited number of samples. The supervised pattern recognition, i.e. PCA, indicates a classification of DOMs into groups of similar properties by an increase in the number of samples. Furthermore that the number of groups may be higher and more continuously distributed than the conventional classification into fulvic acids, humic acids or humic substances.

Flocculation—cross-flow microfiltration hybrid system for natural organic matter (NOM) removal using hematite as a flocculent

This study investigates the performance of CFMF process with flocculation pretreatment for NOM removal using hematite as a flocculent. Spiral flocculator consists of rapid mixing and slow mixing units. The presence of rapid mixing prior to slow mixing enhances removal performance of the treatment system. The maximum dissolved organic carbon (DOC) removal of 60% was achieved using hematite in membrane hybrid system. CFMF with spiral flocculator pretreatment was able to reduce internal clogging of the membrane, thereby improving the removal performances. The effluent turbidity was found to be less than 1 NTU for the membrane hybrid system. Smaller membrane pore size (0.1 μm) lead to higher DOC and turbidity removal compared to larger pore size (0.65 μm) studied. For the same amount of coagulant concentration and membrane pore size humic acids were easier to be removed compared to fulvic fraction.

Binding of atrazine to humic substances from soil, peat and coal related to their structure.

Partition coefficients for the binding affinities of atrazine to 16 different humic materials were determined by the ultrafiltration HPLC technique. Sources included humic acids (HA), fulvic acids (FA), and combined humic and fulvic fractions (HF) from soil, peat, and coal humic acid. Each of the humic materials was characterized by elemental composition, molecular weight, and composition of main structural fragments determined by 13C solution-state NMR. The magnitude of K(OC) values varied from 87 to 575 L/kg of C, demonstrating relatively low binding affinity of humic substances (HS) for atrazine. On the basis of the measured K(OC) values, the humic materials can be arranged in the following order: coal HA approximately = gray wooded soil HA > chernozemic soil HA and HF > sod-podzolic soil HA approximately = peat HF > sod-podzolic soil FA >> peat dissolved organic matter. The magnitude of the K(OC) values correlated strongly with the percentage of aromatic carbon in HS samples (r = 0.91). The hydrophobic binding was hypothesized as the key interaction underlying the binding of atrazine to HS.

Comparison of two soil organic matter extractants and determination of the “Walkley–Black” correction factors for organic fractions from a volcanic soil

Two extractants (0.1 M NaOH and a mixture 0.1 M NaOH–0.1 M Na4P2O7) were used separately to recover organic matter from a volcanic soil under Corsican pine (Pinus nigra Arn. ssp. laricio Maire). The presence of pyrophosphate did not considerably improve the recovery; on the contrary, in the topsoil, the aqueous NaOH was even slightly more efficient than the mixture. A comparison between dry combustion and dichromate oxidation (Walkley–Black method) to measure the organic carbon (C) in the extracted (fulvic and humic) fractions and in the soil residue was accomplished. Dichromate oxidation did not allow the detection of the entire (dry-burnt) C in the extracted fractions. The correction factor to account for undetected C varied according to horizon, organic fraction, and extractant. An apparent complete oxidation with the Walkley–Black method occurred for the soil residues, but it could be due to magnetite interference.

Association of fallout-derived [formula omitted] and [formula omitted] with natural organic substances in soils

Activity concentrations and associations of fallout-derived Cs, Sr and Pu in soils were investigated. The activity concentrations of 137 Cs, 90 Sr and 239,240 Pu in volcanic ash soil were much higher than those in granite soil. They decreased with increasing depth in the soil. The activity ratios of 239,240 Pu/ 137 Cs and 90 Sr/ 137 Cs tended to increase slightly with increasing soil depth. Alkali extraction experiments with 0.1 M NaOH solution showed that the percentage activities of the fallout radionuclides found in the organic acid fractions were in the order 239,240 Pu> 90 Sr> 137 Cs . The concentrations of 137 Cs and 239,240 Pu reacted with humic fractions were higher than those with fulvic fractions. In contrast to 137 Cs and 239,240 Pu, 90 Sr reacted more with fulvic fractions than with humic fractions. These results provide information about the effects of organic substances on the retention and migration of 137 Cs, 90 Sr and 239,240 Pu in soils under natural conditions.

Relationships between Structure and Binding Affinity of Humic Substances for Polycyclic Aromatic Hydrocarbons: Relevance of Molecular Descriptors

Partition coefficients for the binding affinities of pyrene, fluoranthene, and anthracene to 26 different humic materials were determined by fluorescence quenching. Sources included isolated humic acids, fulvic acids, and combined humic and fulvic fractions from soil, peat, and freshwater as well as Aldrich humic acid. Each of the humic materials was characterized by elemental composition, ultraviolet absorbance at 280 nm, molecular weight, and for 19 samples, composition of main structural fragments determined by 13C solution-state NMR. The magnitude of the Koc values correlated strongly with the independent descriptors of aromaticity of humic materials, including atomic H/C ratio, absorptivity at 280 nm, and three interdependent 13C NMR descriptors (CAr-H,R, ΣCAr, ΣCAr/ΣCAlk). Statistical comparison of humic sources grouped by the origin revealed that binding affinities were best predicted by the 13C NMR descriptors, with a slight prevalence of ΣCAr/ΣCAlk ratio, while molecular weight was the poorest predictor. The latter produced either direct or inverse significant correlation with the Koc values depending upon the origin and/or fractional composition of the grouped humic materials.

ASSOCIATION BETWEEN COLLOIDAL IRON, ALUMINUM, PHOSPHORUS, AND HUMIC ACIDS

In temperate regions a distinct part of phosphorus (P) in soils is associated with organic matter. Organic macromolecules can desorb from the soil matrix and, consequently, act as carriers for P in environments where it would otherwise be immobile. However, not all organic forms of P in soils have yet been characterized, and there is much debate about the involvement of Fe and Al in the association between organic matter and P. We studied the association between P, dissolved organic carbon (DOC), Al, and Fe in alkaline and aqueous extracts of an agricultural sandy soil. In these extracts, the high molecular weight fraction of the DOC was precipitated by adding CaCl2 or HCl. This selective precipitation of the humic fraction of the DOC resulted in the complete removal of Al and Fe from solution, whereas the removal of total P was only partial. The molar ratio for organic carbon (C) over (Al + Fe) in the precipitate was ∼1. This low ratio makes it highly unlikely that most of the Al and Fe are covalently bound to the humic material; rather, it suggests that Al and Fe oxides are, in colloidal form, associated with the humic macromolecules. Another important conclusion was that Al and Fe and a large fraction (more than 50%) of total P were associated with the humic and not the fulvic fraction of the DOC. The different chemical and physical characteristics of these two DOC fractions give them different transport behavior in soils, and this difference is expected to affect the behavior of at least a part of the "organic" P in the soil environment.

Marine microbial aggregating macromolecules: Potential mediators of coastal carbon flux

Microbial aggregation‐adhesion enhancing macromolecules (AAEM) in high molecular weight materials (HMWM) recovered from coastal seawater, suspended particulates and sediments were isolated using immunoaffinity chromatography. The quantity of AAEM recovered was an order of magnitude higher in suspended particulates compared to seawater and sediments. However, the AAEM/HMWM ratio remained constant in samples from all three sources. The fulvic acid component of suspended particulates had 91% of the AAEM, compared to 59% in the sediments. This change in AAEM distribution was directly correlated with decreased amounts of the predominant AAEM molecular size present in the sediment samples. Spectroscopic (FTIR) analyses revealed that the reduction in the relative quantities of fulvic acid AAEM in the sediment was most likely due to oxidative degradation of these residues. While significant adhesion enhancement activity was detected in both fulvic and humic acid AAEM fractions in sediments, the fulvic acid AAEM was significantly more active than the humic acid component. Fulvic and humic acid AAEM activity was strongly conserved in sediments despite reductions in quantity and oxidative degradation, indicating that these materials may play an important role in microbial organic carbon flux in this tropical coastal marine environment.

Capillary isoelectric focusing (CIEF) for the characterization of humic substances

Preparative solution isoelectric focusing was used to fractionate 50 mg of a soil fulvic acid (FA); the harvested fractions were characterized with UV-Vis spectroscopy, gel permeation chromatography and capillary zone electrophoresis (CZE) and showed a distribution in the created pH gradient of the focused fulvic fractions as a function of their molecular weight. Borate complexation was used in CZE to compare the relative acidities of the harvested fractions. Only 32% of the total FA did not interact with the used ampholytes (precipitation), and this FA fraction was mainly composed of low-molecular-weight compounds as shown with CZE. A capillary-free solution isoelectric focusing (CIEF) method was then adapted to the analysis of the same FA, and parallelisms were found in the repartition of the focused fulvic fractions. The potential of capillary electrophoresis in the isoeletric focusing mode (CIEF) is the rapidity of the analysis (40 min) and the use of samples in the microliters range; CIEF was used to characterize humic substances from different natural environments.

Evaluation of the stabilization level of pig organic waste: Influence of humic‐like compounds

Abstract The evolution of the organic matter during the maturation of solid samples of pig sludges and pig manure composted with straw was followed. A sample of pig sludge about 15 years old also was characterized for comparison. The organic matter of the composts and sludges was extracted and the humic (HA) and fulvic acids (FA) were separated. The organic carbon in the total extract (TEC) in the fulvic fraction and in the humic fraction was determined in order to evaluate the stabilization level of the organic matter using some humification parameters. The nature of the organic extract also was evaluated by characterization with analytical isoelectric focusing (IEF). The results confirm that the degree of humification (DH) decreases during the first period of maturation of the organic matter, because of the degradation of humic and fulvic‐like compounds contained into the raw organic materials, while then it increases progressively for all the maturation period. The data collected in this study confirm that the FA fraction could be the main cause of the lack of regularity in the trend of increasing DH as maturation progresses. The FA/TEC ratio infact decreases progressively for all the maturation period, while the HA/TEC ratio increases. The results obtained in the IEF characterization confirm the validity of this analytical technique. Moreover, the results do not appear to be affected by the presence of the humic‐like compounds. The presence of the bands focused at the higher pH values appear to be directly related to the stabilization of the organic material.

THE INFLUENCE OF PH ON THE DESORPTION AND SPECIATION OF COPPER IN A SANDY SOIL

The effect of pH on copper desorption from a sandy soil and on complexation by dissolved organic fractions was studied, using a soil, with pH ranging from 4.3 to 5.6, that had been polluted with copper a decade ago. For the desorption of exchangeable copper we used an unbuffered electrolyte solution (0.0033MCa(NO3)2; ionic strength 0.01M). Free copper was determined using an ion exchange resinmethod. Copper bound by dissolved organic matter was divided into a humic and a fulvic fraction using ultrafiltration. The Cu desorption isotherms were nonlinear and dependent on pH. The (desorbed) exchangeable copper was less than 3% of the total copper in the soil. About 1% of exchangeable copper was complexed with nitrate, and free copper varied from 2% (pH 5.7, 0.3 mmol/kg total Cu) to 9% (pH 4.4, 3 mmol/kg total Cu). The remainder of exchangeable Cu was bound by dissolved organic matter. The amount of Cu bound by solid organic carbon (CuSOC) was almost equal to Cu bound by dissolved organic carbon (CuDOC) when both are expressed in mmol/g C, although there was a pH dependency. At low pH (4.4) Cu was predominantly bound by fulvic fraction, and at pH 5.7 most was bound by humic fraction. Desorption of copper from soil and copper binding by humic and fulvic fraction (all different pH dependent) could be described adequately with the Two Species Freundlich (TSF) equation. With this equation the competition between soil, fulvic fraction, and humic fraction for free copper (Cu2+) was shown.

IRON HUMATE AS A SOURCE OF IRON FOR CITRUS IN HIGH-pH SOILS

Availability of iron (Fe) to plants is dependent on the stability of chelate to bind Fe. In soils with pH greater than 7.5, only EDDHA (Ethylenediamine di-o-hydroxyphenyl acetic acid) is the stable chelate to complex Fe. However, Fe EDDHA is an expensive material. Iron humate (IH) is a by-product of drinking water treatment, wherein, Fe is complexed with humic and fulvic fractions of the river water. Field experiments using Hamlin orange and Flame grapefruit on Swingle citrumelo rootstock conducted in two locations with high pH soils (> 7.5) have shown a significant increase in leaf Fe concentrations when IH was applied to the soil. Since the solubility of Fe from IH is lower than that of Fe EDDHA, the long-term effects of IH on growth and mineral nutrition of citrus are under investigation.

Structural characteristics and geochemical significance of humic acids isolated from three Spanish lignite deposits

Three Spanish lignites of similar low maturity level taken from different deposits and their humic acid (HA) fractions have been characterized by chemical and spectroscopic methods. Some remarkable differences were found in the HA contents, as well as in the distribution of humic and fulvic fractions among the parent lignites. These differences, however, are not reflected by spectral or chemical distinguishing features. The results suggest that lignin-derived materials contributed to the formation of the lignite deposits.

Chemical characterization of size-fractionated humic and fulvic materials in aqueous samples

Humic and fulvic acids have been shown to be potentially important transport agents for inorganic and organic contaminants, including radionuclides, in surface and groundwaters. In this work, the possibility of characterizing humic and fulvic materials in the colloidal and macromolecular size ranges (i.e., between 3000 molecular weight (1 nm) and 0.45 μm) after size fractionation and collection with hollow-fiber ultrafilters has been investigated. Three surface waters have been examined as test cases. Using ultrafiltration, sized samples of humic and fulvic acids were chemically characterized with 13C-nuclear magnetic resonance spectroscopy (NMR), Fourier transform infrared spectroscopy (FTIR) using diffuse reflectance, and pyrolysis/gas chromatography (GC). These test cases demonstrate that sufficient material can be obtained by ultrafiltration with minimal or no alteration to the materials. In addition, inorganic analyses performed on the size fractions show that ultrafiltration can also allow the binding capacity of the humic materials in each fraction to be measured. Substantial variability among the different humic and fulvic fractions demonstrates the importance of sizing submicron materials in attempts to understand the mechanisms of pollutant transport by natural humic materials.

Humic Substances Formed during the Composting of Organic Matter

AbstractHumic substances (HS) were extracted from separated cattle‐manure compost (CSM) at various stages of decomposition. Carbon‐13 nuclear magnetic resonance (13C‐NMR) and Fourier‐transform infrared (FTIR) spectroscopy measurements were performed on the purified humic acids (HA) as well as crude fiber and chemical analyses. Levels of HS extracted from the CSM samples doubled during the composting (from 377 to 710 g kg−1 organic matter [OM]). The HS were divided into: (i) HA, which increased from 184 to 457 g kg−1 OM; and (ii) a fulvic fraction (FF). The FF was separated on XAD‐8 resin to: (i) fulvic acid (FA), which maintained an unchanged level during composting (80–100 g kg−1); and (ii) a nonhumic fraction (NHF), which increased from 107 to 170 g kg−1 OM during the process. The ratios between the concentrations of these fractions were tested as humification indexes. These indexes changed significantly during the process and were found to correlate exponentially with the composting time, C/N ratio, or both. Quantities of low‐molecular‐weight components (FF and NHF) rapidly increased during the first 40 d of composting and were nearly constant thereafter. The HA and HS contents reached nearly constant values after ∼90 d. Only slight compositional and structural changes in CSM HA were detected with cross‐polarization magic‐angle spinning (CPMAS) 13C‐NMR, FTIR spectra, and chemical analyses. The elemental composition and functional groups of CSM HA resembled those reported for HA of plant residues, peats, and incompletely humified materials. The CPMAS 13C‐NMR spectra of the CSM HA resembled that of lignin. The aromaticity of the HA was about 40% and the lignin content was approximately 60%. The NMR data correlated well with results obtained by FTIR spectroscopy, both indicating that the CSM HA are composed of partially degraded constituents of plant tissue, which still retain to some extent their chemical structures. The major plant components identified in the HA were lignin, carbohydrates, and long‐chain aliphatic structural groups.

Turnover of14C-labelled oat residues and small molecular organic compounds in two soils under different levels of mineral nutrition

Mineralization and redistribution of carbon from14C-labelled oat shoots and [14C(U)] labelled glucose, leucine, acetate and phenylacetate were studied in light loamy sand and medium clay loam under different levels of mineral nutrition. Losses of mineralized14C as CO2 were greater in the sandy soil than in the clay soil. NPK and NPK+Ca fertilization increased the rates of decay of the introduced plant organic matter. Among the small molecular organic compounds glucose was degraded fastest and phenylacetate slowest. Incorporation of radioactive carbon into humus fractions varied and depended on the nature of the compound introduced and on the soil type. Carbon of glucose, phenylacetate and acetate was mainly incorporated into fulvic acids, whereas14C of leucine was almost evenly distributed between humic and fulvic acids and14C of oat residues in fulvic acids and humin fractions. There was significantly higher incorporation of14C into humic acids and lower incorporation into humins in the sandy soil compared to the clay soil. NPK+Ca decreased the conversion of14C from phenylacetate and acetate to bitumens and increased its content in humic acids, particularly in the clay soil. The incorporation of14C from phenylacetate to humins benefitted from mineral fertilization during the first 30 days of the experiment in both soils.

Speciation of Pb-210/Po-210 in aquatic systems and their deposits

Lead-210 speciation was carried out on previously examined aquatic deposits of known ages and geochemical histories. The main separated fractions were fulvic, humic, humin and mineral-bonded humics. these organic components were wet-oxidized and their 210Po was extracted by coprecipitation with Fe 3+, distillation at 450°C and self-deposition on silver-discs. The 210Po activities were determined by isotope dilution and alpha spectrometry techniques. Nineteen samples from three lakes and one ombrotrophic peat-hummock in southern Sweden; and three fjords of Skagerrak, North Sea, were investigated. Humic materials proved to trap and preserve aquatic unsupported 210Pb, especially in lakes and peats. Fulvic compounds, on the other hand, seem to enhance the mobility of unsupported 210Pb particularly under acidic conditions. However, the fulvic fraction of marine sediments showed higher amounts of unsupported 210Pb. Our results show that the supported 210Pb is incorporated with the organo-mineral complexes, the NaOH-insoluble fraction. The 210Pb activity of this fraction was found to converge to the expected supported 210Pb of sediment samples older than 100 years or so. Some younger sediments may also show the last mentioned observation. This might serve as an alternative for evaluating the supported 210Pb in 210Pb dating.

Low molecular weight species in humic and fulvic fractions

Fourier transform solution 1H nuclear magnetic resonance (NMR) spectrometry with homogated water peak irradiation is a useful method for detecting low molecular weight substances in humic extracts. Succinate, acetate, methanol, formate, lactate and some aryl methoxyl compounds have been detected in extracts from a wide range of sources. In view of the controversy over whether low molecular weight substances are contaminants in humic extracts introduced by the concentration procedure, we report that some of these materials are not contaminants since 1H-NMR can be used to follow their formation from higher molecular weight species.

Analytical problems in determining peptide nitrogen in the humic fractions of three Italian soils

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.

Humic Substances in Ground Waters

AbstractThe humic materials isolated from ground waters of a borehole in Fjällveden (Sweden) were characterized by elemental and functional group analyses. Spectroscopic properties, molecular weight distributions as well as acid-base properties of the fulvic and humic fractions were also studied. The ground water humic substances were found to be quite similar in many respects (but not identical) to the Swedish surface water humics concentrated from the Gτ(b, A)öta River but appeared to be quite different from the American ground water humics from Biscayne Florida Aquifer or Laramie Fox-Hills in Colorado. The physico-chemical properties of the isolated humic materials are discussed.