Peat Humic Acid Research Articles

Influence of Electrochemical Processing on the Dispersed Composition of Humic Compounds

A preparation of peat humic acids modified by electrochemical treatment in an alkaline medium on iron electrodes was obtained. The effect of the electrochemical treatment on the dispersed composition of the particles of humic substances was determined using dynamic light scattering (quantum correlation spectroscopy). It was found that humic compounds in solution predominantly occur in the form of agglomerates (130–6000 nm), the dispersed composition of which becomes more homogeneous upon electrochemical treatment, and the ability for associative interactions decreases.

Is the traditional alkali extraction method valid in isolating chemically distinct humic acid?

The validity of traditional humic acid (HA) extraction methods and the existence of distinct chemical structures of HA have been recently intensively debated because some researchers believe that HA only forms (humification) due to secondary synthesis during the extraction process. In this study, HAs were synthesized through abiotic humification of a polyphenol and an amino acid with and without MnO2 as the catalyst. The synthesized HAs were first analyzed by Fourier-transform infrared spectroscopy and matrix-assisted laser desorption/ionization-time of flight mass spectrometry, and the results showed that the basic functional groups and molecular weight distribution of the synthesized HAs are similar to those of a standard peat HA from the International Humic Substance Society (IHSS). The products of homogenous abiotic humification (without MnO2) both before and after alkali extraction were then examined by 1D 1H and 2D 13C-1H nuclear magnetic resonance. Interestingly, the dominant features in the NMR spectra of the HAs before and after alkali extraction were largely comparable and no new structural signals were observed after the extraction, indicating that major structural features were not altered. This finding refuted the notion that the extraction method caused secondary synthesis and validated the extraction method of HA.

Solution-state NMR evaluation of molecular interaction between monoaromatic carboxylic acids and dissolved humic acid.

Understanding the nature of interactions between the aromatic organic pollutants with dissolved humic acid (HA) is fundamental for the prediction of their environmental fate and subsequent development of efficient remediation methods. The present study employs solution-state 1H/19F NMR methods to investigate the non-covalent interaction between aqueous peat humic acid (Aldrich HA) and monoaromatic carboxylic acids (CA), viz., 2, 6 diflourobenzoic acid (DFBA) and its non-fluorinated analog, benzoic acid (BA). NMR self-diffusion measurement of HA protons confirmed micellar nature indicating possibility of encapsulation of small molecules through host-guest interaction. 19F-1H and 1H-1H saturation transfer difference (STD) experiments reveal the mode of insertion of CA into HA superstructure. The strength of interaction has been evaluated by analyzing T1/T2 relaxation times and self-diffusion coefficients of CA as a function of HA concentration. Association constants extracted for CA-HA complexes from NMR diffusion experiments reflected that the association between DFBA-HA (2.34 mM-1) is significantly higher than that of BA-HA (0.97 mM-1). The experimental outcome reiterated that substitution of -H with halogen atoms (-F in specific) to aromatic ring plays a dominant role in modulating the strength of association and mode of insertion of organic pollutants into HA superstructure. The present study emphasizes that AHA can be a potential remediating agent for organic contaminants due to its superior binding affinity compared to less humified extracted HA (EHA) from Karwar, Rajasthan, India.

Effect of Humic Acids from Lowland Peat on Endurance of Rats in Forced Swim Test in Relation to Serum Lactate and Corticosterone.

The study substantiated the possibility of using peat humic acids for improving endurance during extreme physical exertion. The mature outbred Wistar rats weighing 200-250 g (n=40) were subjected to forced swim test until complete exhaustion. The humic acids (1%) were administered intragastrically (0.5 ml/100 g body weight) 30 min prior to the test. Chronic administration of peat humic acids for 5 days increased physical capacity and endurance of rats in exhaustive forced swim test without the changes in serum lactate and corticosterone.

New artificial network model to estimate biological activity of peat humic acids

PurposeThis article focuses on new method to estimate biological activity of peat humic acids (HAs) using artificial neural network (ANN) to process spectroscopic measurements in infrared and visible ranges. Conventional approaches generally rely on biological models and direct detection of chemical substances related to bioactivity. These methods proved to be accurate and reliable, but at the expense of speed and simplicity. Materials and methodsRecently, a conception of quantitative structure-activity relationship (QSAR) has been introduced and successfully implemented to predict effects of HAs on toxicity of polycyclic aromatic hydrocarbons. Our research stems from this conception, but employs multilayer perceptron (MLP) model to improve overall performance. The developed MLP model allowed us to estimate biological activity of the complete vertical peat cores collected from oligotrophic peat bog, located in southern taiga zone of West Siberia (north-eastern spurs of the Great Vasyugan Mire, 56°58′ N 82о36’ E). In total, 42 samples taken from the cores were collected. The protocol included spectroscopy (in infrared and visible ranges) and biological model with peritoneal activated macrophages as a reference method to directly measure biological activity of HAs. Resultsand discussion. Numerical experiments confirmed consistency of the measured and estimated bioactivity, coefficient of determination R2 = 0.97. These experiments also showed that the MLP model significantly outperforms conventional linear multiple regression models, mainly due to essential nonlinearity of structure-activity relationships. ConclusionsOur research demonstrates that biological activity of HAs extracted from peat samples can be estimated using an artificial neural network model trained on infrared and visible spectra.

Full wave analysis of stripping chronopotentiometry at scanned deposition potential (SSCP): Obtaining binding curves in labile heterogeneous macromolecular systems for any metal-to-ligand ratio

Abstract The different deposition potentials applied in Scanned Stripping ChronoPotentiometry (SSCP) probe different values of the free metal and complex concentrations at the electrode surface. The knowledge of these concentrations gives access to a relevant window of the binding curve of a metal to a homogeneous or heterogeneous ligand. Here, a suitable mathematical treatment for the determination of these surface concentrations, when using a mercury thin film rotating disk electrode, is reported. The proposed procedure does not require ligand excess conditions and takes advantage of the knowledge of the free metal ion concentration in the bulk solution provided by the technique AGNES (Absence of Gradients and Nernstian Equilibrium Stripping). It is experimentally shown that the information derived from the SSCP points (i.e. at different deposition potentials in a unique solution) is consistent with the speciation results yielded by the technique AGNES in pertinent solutions prepared within a range of metal-to-ligand ratios. Successful examples with polystyrene sulfonate, Laurentian Fulvic acid and a peat humic acid are reported. It is concluded that, by running consecutively SSCP and AGNES in a single solution, speciation information corresponding to different compositions (i.e. those locally generated at the electrode surface by the end of the deposition step) can be retrieved, this enabling an easy determination of the binding curve.

A significant correlation between kinetics of nitrobenzene reduction by sulfide and electron transfer capacity of mediating dissolved humic substances

Dissolved humic substances (DHS) are ubiquitous in surface and subsurface aquatic environments and greatly affect the redox transformation of organic contaminants as reactants and/or electron transfer mediators. However, little is known about the quantitative relationship between the mediation efficiency of DHS and the physicochemical properties of DHS. Using sulfide-induced nitrobenzene reduction as a model system, we measured the reduction rate of nitrobenzene in the presence of 12 different DHS (20 mgC·L−1), including 4 commercial humic substances (Suwannee River humic and fulvic acids and Pahokee Peat humic and fulvic acids) and 8 soil humic substances collected as leachates from a wide variety of soils. In addition to the UV–vis absorption and fluorescence spectra, the electron donating/accepting capacities (EDC/EAC) of the tested DHS were measured using an electrochemical approach. A significant linear correlation (r = 0.99, P < .0001) was observed between the observed pseudo-first-order rate constant (kobs) of nitrobenzene reduction and the sum of EDC and EAC which is defined as electron transfer capacity (ETC) of DHS. A relatively good positive correlation (r = 0.69, P < .2) was shown between the kobs and the specific UV-absorbance at 254 nm (SUVA254), whereas no good correlation was shown between the kobs and the fluorescence of the C1-C4 components identified by the excitation emission matrices and parallel factor (EEM-PARAFAC) analysis. This study provides a new framework for accurate prediction of the capability of DHS in mediating the redox transformation of organic contaminants. CapsuleA significant linear correlation exists between the kinetics of nitrobenzene reduction by sulfide and electron transfer capacity of mediating dissolved humic substances.

Carboxymethylation of Peat Humic Acids by a Mechanochemical Method

The effect of the conditions of carboxymethylation of peat humic acids with sodium monochloroacetate in the presence of sodium hydroxide by a mechanochemical method on the concentration of bound carboxymethyl groups and the water solubility of the resulting products was studied. Highly substituted O‑alkylation products containing to 13.3% bound carboxymethyl groups and soluble in water to 95% were obtained.

Interaction of Ag+ with soil organic matter: Elucidating the formation of silver nanoparticles.

Naturally silver nanoparticles (AgNPs) have been widely observed in ore deposits, coal, natural water and soil environment. Identifying the source of these naturally AgNPs could be helpful for the elucidation of the geochemical cycle of Ag+ and AgNPs. This paper presents the formation of AgNPs by reducing Ag+ in the presence of soil organic matter (SOM) under various environmentally relevant conditions. The formation of AgNPs associated with various SOM (peat humic acid (PHA), peat fulvic acid (PFA), and commercial humic acids (HA-1 and HA-2)) was determined and compared. The physicochemical properties of the tested SOM were studied by electron paramagnetic resonance (EPR) and attenuated total reflection-infrared (ATR-FTIR) techniques. The formation of AgNPs depended on reductive reactions mediated by SOM. Other influential parameters that influenced the formation of AgNPs included concentrations of Ag+ and SOM and the reaction temperature on AgNPs. The produced AgNPs were characterized by transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The mean hydrodynamic diameters of AgNPs associated with PHA and PFA were in range from 2.5 to 15nm, which were smaller than that produced from HA-1 and HA-2 in the range from 20 to 120nm. Two different Ag states, i.e., Ag2O and Ag0 species, were observed by XPS technique. The results indicated that the formation of AgNPs depends largely on the types and the properties of natural organic matter. These findings have important implications for the fate of AgNPs under the soil environment.

Differential absorbance study of interactions between europium, soil and aquatic NOM and model compounds

This study compared the binding of europium by soil and aquatic natural organic matter (NOM) exemplified by Pahokee Peat humic acid (PPHA) and Northern Reservoir NOM, respectively. NOM/Eu3+ interactions were measured based on the differential absorbance approach. The experimental results show that the binding of Eu3+ by humic acid isolated from agricultural soil results in several features of the differential spectra that are distinct from those observed for aquatic NOM. These features may be associated with the presence in soil NOM of functional groups similar to gallic acid. The binding of Eu3+ by NOM was modeled using a phenomenological approach that accounted for the involvement of dissimilar metal-binding functionalities. This study also introduced the concept of integrated differential absorbance; the use of that parameter allowed achieving a close fit between the experimental and model data. This study presents an alternative approach to ascertain mechanisms of, and differences in the interactions of europium with model compounds and natural organic matter with the provenance from soil and surface water.

Sorption of pentachlorophenol and phenanthrene by humic acid-coated hematite nanoparticles

Hematite nanoparticles (NPs) exist naturally and ubiquitously in soil, and they are always associated with soil organic matter by forming organic-inorganic complexes. In this work, hematite NPs coated with peat humic acid (HApeat) and soil humic acid (HAsoil) were chosen as sorbents for hydrophobic organic contaminants (HOCs) to simulate the sorption processes in soil. Ionizable pentachlorophenol (PCP) and non-ionizable phenanthrene (PHE) were selected as representative HOCs. Compared with sorption isotherms of uncoated hematite NPs, the coating of HA onto the surface of hematite NPs substantially increased its sorption affinity for PCP and PHE by about 1-2 orders of magnitude, and the increasing degree was positively correlated to the HA content. These phenomena emphasized the dominant role of HA in the sorption process. The reduced polarity and the introduction of functional groups contributed to the enhanced sorption of HOCs on HA-coated hematite NPs. Furthermore, HApeat-hematite NPs showed higher sorption affinity for both PCP and PHE than HAsoil-hematite NPs, which was mainly due to the lower polarity and higher hydrophobicity of HApeat-hematite NPs. The sorption of PCP and PHE on HA-coated hematite NPs was inhibited obviously with increasing pH values and the pH effect on PCP sorption was more significant than that of PHE, due to the deprotonation of functional groups within adsorbed HA, the loose structure of adsorbed HA and the dissociation of PCP. Our findings elucidated the mechanisms involved in HOCs sorption processes by HA-hematite NPs and provided a theoretical basis for environmental remediation with natural NPs (e.g., hematite NPs).

Regularization of peat humic acids functional composition

Humic acids are perspective complicated natural objects for different purposes. The problem of humic acids functional composition regularization is very important. The effect of heat treatment on peat humic acids group composition alteration was evaluated to solve this problem. The projection study by principal component analysis of IR-spectra data is presented. The possibility of peat humic acids functional composition regularization by temperature treatment and subsequent storage was found.

Abiotic reduction of Cr(VI) by humic acids derived from peat and lignite: kinetics and removal mechanism

Hexavalent chromium contamination of groundwater is a worldwide problem caused by anthropogenic and natural processes. We report the rate of Cr(VI) removal by two humic acids (extracted from Miocene age lignite and younger peat soil) in aqueous suspensions across a pH range likely to be encountered in terrestrial environments. Cr(VI) was reduced to Cr(III) in a first-order reaction with respect Cr(VI) concentration, but exhibited a partial order (~ 0.5) with respect to [H+]. This reaction was more rapid with the peat humic acid, where Cr(VI) reduction was observed at all pH values investigated (3.7 ≤ pH ≤ 10.5). 13C NMR and pyrolysis GC-MS spectroscopy indicate that the reaction results in loss of substituted phenolic moieties and hydroxyl groups from the humic acids. X-ray absorption spectroscopy indicated that at all pH values the resulting Cr(III) was associated with the partially degraded humic acid in an inner-sphere adsorption complex. The reaction mechanism is likely to be controlled by ester formation between Cr(VI) and phenolic/hydroxyl moieties, as this initial step is rapid in acidic systems but far less favourable in alkaline conditions. Our findings highlight the potential of humic acid to reduce and remove Cr(VI) from solution in a range of environmental conditions.

Optical Properties of Humic Material Standards: Solution Phase and Aerosol Measurements

Aerosols generated from aqueous samples of readily obtainable humic material standards are often used as proxies for organic particulates found in the atmosphere in various investigations, such as consideration of radiative forcing effects. Here, we present results for the retrieved complex index of refraction, m = n + ik, at a wavelength of 403 nm for aerosols prepared from six humic material standards using a calibrated cavity ring-down spectrometer: a humic acid sodium salt, Pahokee peat humic and fulvic acids, Elliott soil humic and fulvic acids, and Suwannee river fulvic acid. In addition, we have conducted UV–vis spectrometric studies to measure the mass absorption coefficients, molar absorptivities, and absorption Angstrom exponents of bulk aqueous solutions of the humic materials. We find clear differences between the humic acid (HA) and fulvic acid (FA) samples with the HA having larger values for the imaginary part of the refractive index, k. The mean value for the HA samples is k = 0.170 while ...

Fungistatic Activity of Multiorigin Humic Acids in Relation to Their Chemical Structure.

Humic acid (HA) has an inhibitory effect on phytopathogenic fungi, but the structure-activity relationship remains unclear. HAs were extracted from 14 different materials, and their fungistatic activities and elemental C, N, S, and O contents were measured. Cross-polarization magic-angle spinning 13C nuclear magnetic resonance (CPMAS 13C NMR) was used to measure the organic carbon composition. The results showed that all HAs suppressed phytopathogenic fungi growth, with Yunnan lignite HAs showing the highest inhibition (85.3%) against Physalospora piricola. The soil and compost HA aromaticity (ARO) was <50%, except for black soil HAs, while the ARO of all coal HAs was >60%. The ARO of meadow and moss peat HAs was <50%, while the ARO of woody peat HAs was 50.61%. Mantel test and redundancy analysis (RDA) were applied to evaluate the structure-activity relationship. The Mantel test revealed that the N, S, O, N/O, carbonyl C, aromatic C-O, and anomeric C contents were significantly correlated with fungistatic activity. The RDA analysis showed that the S content was positively correlated with fungistatic activity, while the O content was negatively correlated. The carbonyl C content had a positive correlation with fungistatic activity, while the anomeric C and aromatic C-O content had a negative correlation. A high S content and an active composition (carbonyl C) in HAs would lead to a high degree of fungistatic activity. Phytotoxicity test indicated all HAs were beneficial to plant growth. This work identified the basic properties of HAs from various raw materials that control their fungistatic activities.

Abundant Nonprotonated Aromatic and Oxygen-Bonded Carbons Make Humic Substances Distinct from Biopolymers

The nature of humic substances (HSs) extracted from soil organic matter and their distinction from degrading plant material has recently been called into question. Quantitative solid-state 13C nuclear magnetic resonance (NMR) analyses, in good agreement with elemental analysis, show that HSs are distinct from common biopolymers, refuting claims to the contrary made based on 1H-detected NMR spectra of the same standard peat humic acid as studied here. Aromatic carbons not bonded to hydrogen or oxygen, which are rare (≤10%) in common biomolecules, constitute a large fraction (28%–33%) of prairie soil and peat humic acids. Oxygen-bonded nonprotonated carbons such as aryl ketones, nonprotonated alkyl C–O, and abundant COOH groups are also characteristic of humic and fulvic acids but not observed in plant biopolymers. These distinctive structural differences between HSs and biopolymers challenge the recent proposal that HSs are unremarkable intermediates in a continuum of degrading biomolecules.

Nuclear Magnetic Resonance Analysis of Changes in Dissolved Organic Matter Composition with Successive Layering on Clay Mineral Surfaces

Dissolved organic matter (DOM) chemistry and the potential for organic matter (OM) to self-associate with other OM components are important aspects of understanding the mechanisms of DOM sorption to clay surfaces. To investigate this further, we sorbed DOM isolated from peat humic acid onto either kaolinite, montmorillonite and gibbsite via ten sequential batch equilibration sorption experiments. Dissolved organic carbon (DOC) sorption to all minerals increased consistently, suggesting that sorption occurred via mineral-OM interactions at the beginning of the experiment. After six successive DOM loadings, the concentration of DOC sorbed by kaolinite and gibbsite began to plateau, likely due to the saturation of mineral surface sorption sites. Solution-state nuclear magnetic resonance (NMR) analysis of unbound DOM showed that kaolinite and montmorillonite sorbed aliphatic, protein and lignin components initially and primarily aliphatic and aromatic constituents in later sorption experiments, whereas gibbsite sorbed mostly aliphatic compounds during all DOM loadings. Analysis of the organo-clay complexes using 1H high resolution–magic angle spinning (HR-MAS) NMR confirmed the preferential sorption of aromatic and aliphatic components to all three minerals. Overall, these results suggest that OM-OM interactions may be important mechanisms of DOM sorption to clay mineral surfaces.

Studying of the interaction between peat humic acids and metazachlor using spectroscopy methods

PurposeThe analysis covered the interaction of humic acids (HA) isolated from peats with the metazachlor using spectroscopic methods.Materials and methodsFive peatlands have been selected for the study in the southern and northern parts of Poland. Extraction of humic acids (HA1, HA2, HA3, HA4, and HA5) was performed using a procedure recommended by the International Humic Substances Society. Metazachlor 500 SC with metazachlor as a biologically active substance [2-chloro-N-(pyrazol-1-ylmethyl)acet-2′,6′-xylidide] has been used. HA have been assessed on the basis of their elemental composition. Spectroscopic techniques have been used to study the HA structure and their interaction with metazachlor including: UV-visible spectroscopy, dynamic light scattering, and delayed luminescence (DL)Results and discussionBased on their morphological and chemical properties, the studied peat soils can be classified as follows: (1) Eutric Murshic Sapric Histosols, (2) Eutric Sapric Histosols, (3) Eutric Hemic Histosols, (4) Eutric Fibric Histosols, and (5) Dystric Dranic Hemic Histosols according to the WRB guidelines (2015). Results showed that the largest particle size, measured by E4/6 coefficient, was found in HA2 sample, while the smallest in HA3 sample. The addition of metazachlor to HA solutions reduced the values of E4/6 coefficient by 33 to 72%, while the values of hydrodynamic diameter by 4 to 32%. No significant changes were found between E4/6 after adding of metazachlor to HA solutions. The largest changes in DL intensity, excited both by blue and red light after herbicide addition, were observed in HA2 sample, which is characterized by the largest particle size, the highest oxygen content and CQ value as well as the lowest “aromatization rate” value.ConclusionsThe particle sizes of HA molecules measured by E4/6 coefficient do not impact on the particle sizes of HA-herbicide systems measured by the same ratio. The delayed luminescence may become valuable, because it is simple, fast, and sensitive. Additionally, the results show minor errors comparing with chemical methods. This method may provide information about structure and nature of humic acids, as well as their photoreactivity. The using of delayed luminescence in studies of HA-pesticides interaction may enable us to better understand the luminescence properties of HA.

THE CHARACTERISTIC FEATURES OF THE ELECTRONIC ABSORPTION SPECTRA AND ELEMENTAL COMPOSITION OF HUMIC ACIDS OF DIFFERENT TYPES AND TYPES OF PEAT KHANTY-MANSIYSK AUTONOMOUS OKRUG - YUGRA

The article reveals the results of studies of the humic acids electronic spectra for various types and kinds of peat in the middle-taiga zone of Western Siberia (Khanty-Mansiysk Autonomous Okrug - Yugra). It was found that the increase in optical density is observed in samples of humic acids which were extracted from the peat with a high degree of decomposition (40-65 %). At the first approximation the interpretation of received electronic spectra gives reason to range humic acids in the order with increasing proportion of aromatic structures share in macromolecules in the following order: 1) peat humic acids having a degree of expansion from 0 to 35 % with the content of a large number of peat-forming plants, where the extinction coefficients vary from 0.039 to 0.054 or sphagnum peat with the same degree of decomposition with the sphagnum containing 95-100 %, where the extinction coefficients have values between 0.030 and 0.042; 2) humic acids of all types and kinds of peat with a degree up to 35 %, where the extinction coefficients are from 0.042 to 0.068; 3) humic acid of peats of all examined types and species with a degree of decomposition from 40 % to 65 %, where the extinction coefficients vary from 0.059 to 0.087. Although the method of electron spectroscopy is an important tool in the study of humification processes in peat, it has a limited informative value due to unresolved spectra. Thus, peat humic acids with various botanical composition and various degree of decomposition are characterized by similar absorption spectra in the visible area in the form of a monotone increasing of absorption in short wavelength interval and differ from each other only by the absorption intensity. Based on the obtained values of the electronic absorption spectra of the GK and the magnitudes of their degree of benzoindole (α), which are calculated by the results of elemental analysis, the obtained information about the ratio of aromatic and aliphatic fragments in the molecules of humic acids, i.e. the information about the structural organization of the molecule . For the conditions of the Khanty-Mansi Autonomous Okrug - Yugra in all samples of peat humic acids did not reveal the dependence of their elemental composition from the types of source of peat, from the peculiarities of their species caused by the location and the specifics of peat formation.

Blackwater in South African estuaries with emphasis on the Mgobezeleni Estuary in northern KwaZulu-Natal

The blackwater Mgobezeleni Estuary is a small system below a peat swamp. From the air the estuary is completely black, but the water revealed only a light tea colouration with a Secchi reading of >1.7 m. The sediment is covered with black low-density fragments overlying light coloured sand. When the estuary is open the colouration of the sea is blacker than might be expected from the light tea-coloured estuary water. The results of X-ray spectroscopy showed the black fragments have a high carbon content that is most likely peat. The dissolved organic carbon content of the Mgobezeleni Estuary water is lower than that in Swartvlei in the South Western Cape, which has very dark water. The presence of very large deposits of peat at the head of the estuary together with spectroscopy data indicate that the colouration of the water emanates from leached leaves of swamp vegetation. The penetration of light through the water is not reflected from the light sand due to the peat covering, giving the appearance of very dark water. The literature suggests that the cause of blackwater is due to humic acids, peat and tannins leached from fallen leaves. The results of this study point to peat fragments not reflecting sunlight rather than peat extract and humic acids as the main cause. The slight colouration of the water is likely due to the small amount of fresh leaf litter in the catchment for the release of tannins that colour the Mgobezeleni Estuary water.