Characterization of humus-protease complexes extracted from soil

Pyrophosphate (140 mM, pH 7.1) extracts of two arable soils and one pasture soil were ultrafiltrated separating the extracted material into three fractions: A_I with nominal molecular weight (nmw) > 100 kD, A_II with nmw between 10 kD and 100 kD and R with nmw < 10 kD. Protease activity was determined in the fractions by using three different substrates: N-benzoyl-l-argininamide (BAA), specific for trypsin; N-benzyloxy-carbonyl-l-phenylalanyl l-leucine (ZPL), specific for carboxypeptidases; and casein, essentially a non-specific substrate. The derivative fractions were also analysed for their amino acid N and humic (HA) and fulvic (FA) acid contents. The organic matter of extracts and derivative fractions obtained from the pasture soil was analysed by isoelectric focusing (IEF) and that of fractions analysed by pyrolysis gas chromatography (Py-GC). Activities of the extract were monitored for their thermal stability and those of the extract and derivative fractions for their optimal pH.Due to the mechanical disintegrating action of sodium pyrophosphate over the humic substances during the fractionation process the amount of total organic C and FA in the fractions was ranked as R > A_II > A_I. The lowest amino acid N/organic C was found in the R fraction, whereas A_II fraction was rich in humic acids, carbohydrates and amino acid N and A_I fraction showed the lowest carbohydrate content. At least 70% of the total BAA- and ZPL-hydrolysing activity was associated to particles with nmw higher than 10 kD and at least 30% of these activities were present in particles with nmw higher 100 kD. Casein-hydrolysing activity was quite evenly distributed among the three fractions (A_I, A_II and R). The extracted protease-organic complexes were resistant to thermal denaturation and some of them showed optimal activity at pH values higher than 10 as a result of the polyanionic characteristics of the humic material surrounding enzyme molecules and of the presence of alkaline protease. Comparison of data obtained in Py-GC analyses and in protease activity suggests that BAA-hydrolysing activity was associated to a highly condensed humic matter and ZPL-hydrolysing activity to less resistant humic substances, while at least some of the extracted casein-hydrolysing activity was present as glyco-proteins not associated to humus. BAA-hydrolysing activity was probably inhibited by fresh organic matter of carbohydrate origin whereas lignin derived organic matter probably inhibited ZPL- and casein-hydrolysing activity.     

Fractionation of hydrolase-humus complexes by gel chromatography

Summary Purification of soil phosphatase-, urease-, casein- and benzoylarginamide-hydrolysing proteases was obtained by exhaustively ultrafiltering a soil extract using 0.1M pyrophosphate solution at pH 7.1, separating the retained material into fractions of molecular weight higher (A_I) and lower (A_II) than 10⁵ and eluting the fractions on gel chromatography.Three peaks of phosphatase and urease activity were obtained after gel chromatography of fraction A_I on Sephadex G200 using 0.1M pyrophosphate solution as eluant. Only one distinct activity peak was observed when casein- and benzoylarginamide-hydrolysing proteases were assayed in the eluted fractions. Elution diagrams obtained by gel chromatography of fraction A_II on Sephadex G100, using a water as eluant, were characterized by one peak each of phosphatase-, casein- and benzoylarginamide-hydrolysing activity and by two peaks of urease activity.Gel chromatography of both A_I and A_II, generally, but not always, increased specific activity on a C and N basis of derivative fractions. Both proteases showed the highest increase in specific activity due to a marked decrease in organic C and N and an increase in total activity.     

Fractionation of humus-urease complexes

Some techniques commonly used for enzyme purification were unsuitable to purify urease extracted by pyrophosphate from soil. An all-or-none behaviour seemed to be a prominent feature of such experiments but in some instances slight increases of specific activity were observed.The most effective purification of soil urease was achieved by exhaustively ultrafiltrating the soil extract against 0.1 m pyrophosphate at pH 7.1, separating the retained material into fractions of mol. wt. higher (A_I) and lower (A_II) than 10⁵, followed by gel chromatography.Increases in total activities were observed both after ultrafiltration and gel chromatography. Ultra-filtration increased the total activity of the extracted urease by about 8%. The specific activity of fraction A_I increased four fold, that of fraction A_II by more than three fold. Fractions obtained by gel chromatography accounted in toto for only 13.5% of the organic-C of the soil extract. Total urease activity increased by 45.6%. Specific activities increased to 6.9–18 times that of the soil extract.     

Effects of urease and nitrification inhibitors on the efficient use of urea for pastoral systems

Abstract

The humic substances contained in an animal organic waste were extracted and the total extract separated into three humic fractions with different molecular weights (low, F₁ <10³; medium, F₂, with molecular weights ranging from 10³ to 10⁴; and high, F₃ >10⁴). The C content was highest in F₂, the same fraction also showing the lowest N content. The molecular weight of the humic fractions influenced the electrical conductivity, the highest molecular weight resulting in the lowest degree of electrical conductivity. Membrane-controlled ultrafiltra-tion (the method used to separate the various fractions from the whole extract) was also suitable for purifying such enzymes as phosphatase and β-glucosidase: the total activity obtained from the three fractions was considerably greater than that determined in the whole extract, Pyrolysis-gas chromatography (Py-GC) applied to the whole extract and humic fractions showed that in the F₃ fraction (highest molecular weight) benzene was the major fragment while furfural was the major fragment of F₁ (lowest molecular weight). For this reason, the humification index benzene/toluene indicates that the fraction with the highest molecular weight was the most humified while the furfural/pyrrole ratio indicates that the fraction with the lowest molecular weight was the most degradable. The whole extract and the fraction F₁ had a negative effect on seed germination when the concentration was equivalent to 100 mg kg^?1 of C, while the germination index was higher than that of the control when only 10 mg kg^?1 were used. The F₂ fraction had a positive effect on germination regardless of the concentration used. When 10 mg kg^?1 of C of the humic substances studied were added to the nutrient solution for growth experiments with maize plants, F₃ led to increases in root weight and F₂ led to increases in shoot weight. An inhibitor effect was observed for fraction F₁.     

Isoelectric focusing of soil humic substances in the presence of 8M urea

Summary The isoelectric focusing (IEF) of different-molecular-size humic fractions, either separately or recombined, was carried out in the presence and absence of 8M urea. In the presence of urea, the fractions were recognizable from both their characteristic microheterogeneity and ranges of focalization. Urea caused a slight shift of the bands towards lower pH values. The refocusing of characteristic band of one fraction produced a slight discrepancy in the isoelectric points (0.2–0.3 pH units). However, the maintenance of the banding in 8M urea and the homogeneity of the band under refocusing demonstrated the reliability of the IEF in fractionating structurally different humic substances. Such experiments should provide useful information on the association/dissociation properties of soil organic matter under controlled conditions.Joint program of C.N.R. (Italy) and C.S.I.C. (Spain), no. 7     

美国8种土壤的活性腐植酸和难溶性钙质腐植酸盐中碳官能团的特性分析

Solid state13C nuclear magnetic resonance(NMR)spectroscopy is a common tool to study the structure of soil humic fractions;however,knowledge regarding carbon structural relationships in humic fractions is limited.In this study,mobile humic acid(MHA)and recalcitrant calcium humate(CaHA)fractions were extracted from eight soils collected from six US states and representing a variety of soils and ecoregions,characterized by this spectroscopic technique and analyzed for statistical significance at P≤0.05.We found that the abundances of COO and N–C=O functional groups in the MHA fractions were negatively correlated to soil sand content,but were positively correlated to silt,total N and soil organic carbon contents.In contrast,the abundances of the COO and N–C=O functional groups were only positively correlated to the content of clay in the CaHA fractions,indicating that the two humic fractions were associated with diferent soil components.The two13C NMR peaks representing alkyls and OCH3/NCH were negatively correlated to the peaks representing aromatics,aromatic C–O and N–C=O/COO.Comparison of the sets of data from13C NMR spectroscopy and ultrahigh resolution mass spectrometry revealed that the aromatic components identified by the two methods were highly consistent.The comparison further revealed that protein in MHA was associated with,or bound to,the nonpolar alkyl groups,but a component competitively against(or complementary to)aromatic groups in the MHA composition.These observations provided insight on the internal correlations of the functional groups of soil humic fractions.     

Studies on the humus forms of forest soils

Samples described in the previous paper were analyzed for humus composition by the method of Kumada el al,, elementary composition of humic acids, nitrogen distribution among humic acid, fulvic acid, and humin, and organic matter composition by the modified Waksman method. The samples obtained by physical fractionation from each horizon of Higashiyama soil were as follows: f₁ and f₂ from the L layer, f₁, f₂ and f₃ from the F layer, f₁ f₂, sand, silt, and clay fractions from the H-A and A horizons.

With the progress of decomposition, the following tendencies were rather clearly observed.

The extraction ratio of soluble humus, amounts of humic acid and fulvic acid, and PQ, value tended to increase with some exceptions. The degree of humification of humic acid proceeded. Most humic acids belonged to the Rp type, but those of the clay fractions belonged to the B type.

As for the elementary composition of humic acid, transitional changes from the Lf₁ to the clay fraction of the A horizon were observed. But differences in elementary composition among humic acids were far less, compared with those among whole fractions.

Nitrogen contents in humic, fulvic, and humin fractions increased with the progress of decomposition and humiliation, and the largest relative increase was found in fulvic acid nitrogen.

According to the modified Waksman's method, the amounts of residues and protein increased, while the total amounts of each extract, except for the HCl extract, and the amounts of sugars and starch, phenolic substances, hemicelluloses and pectin, and cellulose decreased. Sugars and starch comprised only a small portion of the hot water extract, and polyphenols substances comparable to sugars and starch were also found in the extract. Hemicelluloses and pectin accounted for only about one-half of the HCl extract. Several characteristic differences in the elementary composition of extracts and residues were found.

Pheopigments existed in benzene-ethanol extracts and their amounts seemed to decrease from Lf₁ to Ff₂.     

Etude des diphenol oxydases extraites d'une litiere de foret

Study of diphenol oxidases extracted from beech litter. Lyophilized neutral sterile extract from the fermentation (F) layer of beech litter (NALF Extract) exhibited the chemical characteristics of humic acids. It possessed diphenol oxidase activities. The specific activities (sp. act.), given in parentheses, are expressed in nmoles O₂ absorbed mg C^?1 min^?1: p-crcsol (19.5); catechol (0.6); dl-3(3,4-dihydroxyphenyl)alanine (5.7); d(+) catechine (4.8) and p-phenylenediamine (7.1). The NALF Extract was polydispersed by G100 Sephadex column chromatography. The firsi peak kd ~ 0.05 (fraction I), the intermediate band (fractions II + III) and the second peak k_d ~ 1.02 and 1.38 (fractions IV + V). Diphenol oxidases were localized in fractions I, II and III. Electrophoretic studies have shown that the fractions I, II and III are heterogeneous. Chromatography on DEAE cellulose of fraction I permitted the separation of 30 per cent of the laccase activity in a form which is free from humic material.     

Quantitative solid-state 13C NMR spectroscopy of organic matter fractions in lowland rice soils

Spin counting on solid‐state ¹³C cross‐polarization (CP) nuclear magnetic resonance (NMR) spectra of two humic fractions isolated from tropical lowland soils showed that only 32–81% of potential ¹³C NMR signal was detected. The observability of ¹³C NMR signal (C_obs) was higher in the mobile humic acid (MHA) than in the calcium humate (CaHA) fraction, and increased with increasing intensity of irrigated rice cropping. NMR observability appeared to be related to the nature of the organic carbon, with phenol‐ and methoxyl‐rich samples having the higher values of C_obs. The Bloch decay (BD) technique provided more quantitatively reliable ¹³C NMR spectra, as evidenced by values of C_obs in the range 91–100% for seven of the eight humic fractions studied. The BD spectra contained considerably more aryl and carbonyl signal, and less O–alkyl and alkyl signal, with the greatest differences between CP and BD spectra observed for the samples with low C_obs(CP). The causes of low CP observability were investigated using the spectral editing technique RESTORE ( RE storation of S pectra via T _CH and T O ne R ho (T_1ρH) E diting). Rapid T_1ρH relaxation was found to be primarily responsible for the under‐representation of carbonyl carbon, whereas inefficient cross‐polarization was primarily responsible for the under‐representation of aryl carbon in CP spectra. Proton NMR relaxation rates T_1H and T_1ρH were found to correlate with other NMR properties and also with cropping management. Non‐uniform rates of T_1H relaxation in two of the CaHA fractions enabled the generation of proton spin relaxation editing subspectra.     

Speciation of iodine in soils

In order to analyze the behavior and phytoxicity of iodine in soil, the chemical forms of soil iodine must be identified. Therefore, a method for quantitative speciation of iodine in soil was proposed. Iodine extracted from soil samples with tetrametBPyIammonium hydroxide (TMAH) was separated into humic and fnalvic acid fractions at pH4 1.5 after the addition of ascorbic acid into the TMAH extract to reduce iodate into iodide. Since the iodide in the TMAH extract was recovered in the fdvic acid fraction by this procedure, iodine contained in the haamic acid fraction was considered to be organically bound. Podine in the fulvic acid fraction was separated into organic iodine bound to fnlvic acids and the total inorganic iodine. Furthermore, iodine soluble from soil in 0.1 mol L^-1 potassium chloride was assumed to correspond to the amount of total iodide in soil, and from the difference in the concentration of total inorganic iodine and soluble iodide, the amount of iodate was calculated. By the application of this method, iodine in soil was separated into four fractions: organic iodine bound to humic acids, organic iodine bound to fulvic acids, iodate, and iodide. This speciation method was applied to two soils. It was found that s Barge proportion of iodine in soil occurred in an organicalPy bound form.     

THE ACCUMULATION OF SOIL ORGANIC MATTER AND ITS CARBON ISOTOPE CONTENT IN A CHRONOSEQUENCE OF SOILS DEVELOPED ON AEOLIAN SAND IN NEW ZEALAND

Soil organic matter was extracted by a mixture of O.IM Na₄P₂O: O.IM NaOH from a chronosequence of weakly weathered soils developed on aeolian sand, and fractionated into humin (non-extractable), humic acid, and fulvic acid. The mass of total organic carbon in the profiles, the ¹⁴C content and the ¹³C/12C ratios were also determined. The weight of total carbon increased rapidly at first and then gradually without attaining a steady state. This trend was also shown by the humin and fulvic acid fractions, but the humic acid fraction appeared to have reached a maximum after about 3000 years. The order of total weights of the organic fractions was humin > fulvic acid > humic acid. The evidence suggests that the proportions of the humic fractions formed by decomposition are related to soil differences but not to vegetation. The greater part of the plant material found in the soils appears in the humin and fulvic acid fractions.     

Effect of earthworm humic substances on esterase and peroxidase activity during growth of leaf explants of Nicotiana plumbaginifolia

Summary Leaf explants of Nicotiana plumbaginifolia were compared in cultures supplemented with hormones or humic substances (extracted from faeces of Allolobophora caliginosa) of various molecular complexity and concentration. The results showed that the humic substances (F₁, F₂, and T) at the concentration of 1 mg C l^-1 produced greater leaf explants than those grown in the control. Furthermore, humic fractions like gibberellic alone induced a rhizogenic activity in leaf explants. Quantitative differences were also observed in the peroxidase activity induced in Nicotiana plumbaginifolia by humic matter (F₂, F₂, and T). In addition, the Nicotiana sp. tissue treated with humic fractions revealed, in the esterase enzyme pattern, the appearance of the 2a band, which was attributable to indoleacetic acid, since its profile was consistent with those obtained from tissues treated with indoleacetic acid. These differences demonstrate that humic substances exhibited a hormone-like behaviour, but no evidence of a relationship between biological activities and chemical characteristics of humus substances was found.     

Isoelectric focusing of β-glucosidase humic-bound activity in semi-arid Mediterranean soils under management practices

Changes in β-glucosidase enzyme–humic complexes and conventional parameters (pH, total organic C, total N, water-soluble C, and bulk density) were studied in an almond-cropped soil prone to erosion under a rehabilitation practice. The experimental plan included three soil slopes (0%, 2%, and 6%) and two type of fertilization (organic and mineral), with sampling of rhizosphere and inter-row soils. The enzyme humic complexes were extracted by pyrophosphate, purified by ultrafiltration of the organic extracts on molecular mass exclusion membranes (mol wt > 10⁴) and fractionated by isoelectric focusing technique (IEF). The IEF on polyacrylamide rod gels with a restricted pH gradient ranging between 6.0 and 4.0 gave five humic bands on the basis of the little differences of their electric charges (pI). Under both organic and mineral fertilization, β-glucosidase activity bound to the fractionated humic substances, especially in the pH range 4.5–4.2 of the rhizosphere soil, was higher than that of the inter-row soil. This also occurred in 6% slope where the enzyme activity was lower than in soil with lower slopes. The higher number of the β-glucosidase active humic bands in rhizosphere than inter-row soil, particularly for the 0% slope, may be due to the presence of humic molecules capable of preserving the enzyme molecules in the active form, other than to the higher microbial activity synthesizing and releasing the tested enzymes.     

Characterization of the organic fraction of an uncomposted and composted sewage sludge by isoelectric focusing and gel filtration

Summary Isoelectric focusing was used to characterize the organic matter of composted and uncomposted sewage sludge. The technique was applied to organic matter extracts and to three fractions, obtained by ultrafiltration, with different molecular weights (<10³, 10³–10⁴, >10⁴). The elution curves of the extracts through Sephadex G-50 revealed a loss in the proportion of organic matter of low molecular weight as composting progressed, together with an enrichment of the high-molecular-weight proportion. Separation into fractions by controlled ultrafiltration proved to be valid, as deduced from the chromatograms obtained by Sephadex G-50 filtration. The extracts of uncomposted sludge showed a greater number of bands with a low isoelectric point than the composted extract, because there were more acidic molecules in the samples that had not undergone humification. The spectrum corresponding to the extract of the 210-day compost showed greater homogeneity with a lower number of bands. A great part of the organic matter extracted with 0.1 M Na₄P₂O₇ at pH 7.1 corresponded to an intermediate molecular weight. The ampholytes at pH 4–6 gave better resolution than those at pH 3.5–10, in the focusing of fractions with the lowest and the greatest molecular weight. A more homogeneous spectrum was observed for the high-molecular-weight fractions from extracts of the 210-day composted sample; in addition, the bands were displaced towards higher isoelectric points, which indicated that the molecules were more condensed, with a minor content of negatively charged groups and a spectrum similar to that of relative fractions of true humic acids.     

THE HUMIC ACIDS EXTRACTED BY VARIOUS REAGENTS FROM A SOIL

Solutions of o.5N NaOH, o.1M pyrophosphate (pH 7), and o.5N Na(CO^2?₃/HCO^?₃) [2:1] extract humic acid and organic matter from a soil with decreasing effectiveness. Pre-treating the soil with o.1N HC1 increased the yield of humic acid obtained with the alkaline extractants. An additional pre-treatment with a mixture, which was normal with respect to HC1 and HF, gave a slight reduction in yield. Increasing the temperature of extraction increased the yield of humic acid. The total C extracted was usually in excess of the humic acid recovered. The difference was obtained as ‘humins’. The sum of the Fe₂O₃, SiO₂, and A1₂O₃ contents of the humic acids was always less than 2 per cent. Where the extraction was carried out at room temperatures the SiO₂/Al₂O₃ ratio suggested that they might be present as clay mineral. When extraction was carried out at an elevated temperature this ratio was altered. Humic acids of low ash content (0.1–0.5 per cent) could be obtained by the use of hot reagents. Of all the extractants used at room temperature, pyrophosphate produced the humic acid of lowest ash content (～ 0.2 per cent). The Fe₂O₃ content of the humic acids was not correlated with their SiO₂ or A1₂O₃ content. The N-content of the humic acids was substantially independent of the method of extraction. The cation-exchange capacities (C.E.C.), average pK values and range of pK values, have been determined from the titration curves of the humic acids. These quantities vary with the method of extraction. There are good correlations between cation exchange capacity and both average pK values and the range of pK values. The within-molecule variation of pK values appears to be greater than the between-molecule variation. No correlation exists between C.E.C. and Fe, Al, Si, and N content of the humic acids.     

Variation in 15N natural abundance of soil, humic fractions and plant materials in a disturbed and an undisturbed grassland

The natural abundance of δ¹⁵N in disturbed and undisturbed pasture soils was examined. From the disturbed soil, the top 10 cm of the profile was examined and the soil split into fractions based on particle size. Plant shoot and root material contained similar low enrichments in ¹⁵N, whereas recently deposited shoot residues were highly enriched. Differences between the soil fractions in observed total N did not reflect similar ¹⁵N variation. However, the enrichment of humic material extracted from the largest soil fraction was considerably lower in ¹⁵N relative to that from the smaller fractions. The complexity of the humic material from the larger fractions was less according to the E ₄ /E ₆ ratio. Analysis of the profile from the undisturbed soil showed increasing ¹⁵N enrichment with depth which corresponded well with visible soil horizons and showed an inverse relationship with total soil N. This ¹⁵N enrichment was mirrored by the enrichment in humic materials down the profile and also corresponded with an increasing chemical complexity as shown by the E ₄ /E ₆ ratio. Received: 15 March 1996     

Sephadex-Gelfiltration von Huminsäuren und deren Gehalt an Aminosäuren

Gel filtration on Sephadex of humic acids and their content of amino acids

• 1 Brown humic substances from the A_h of an iron-humus podzol were separated on Sephadex G 25 into three fractions. The first fraction (Ve/Vo = 1.0–1.5) has the lowest value of Q 4/6 (5.0–8.0), the second the highest Q 4/6 (10.0–12.0) and the third a middle one (8.0–10.5). The adsorption effect may take place during separation.
• 2 The asymmetric form of the integral elution curves of the first fraction indicated that the humic substances are a set of particles with different size. The separation is influenced by diffusion into the pores of gel matrix.
• 3 In the first fraction were determined 16, in the second 13 and in the third 10 amino acids.
• 4 The titration curves of the first fraction (after separation on G 25) indicated that the rate of pH change with alkali added becomes its maximum at pH 6.5–7.5 at different ionic strengths.
• 5 Dialysed humic acids (H⁺ form) were fractionated on G 75. The alkali consumption up to pH 7.5 in the eluate shows that small amounts of mineral acids increase the conductivity of the solution. Their V_e is lower than that of the second fraction of humic acids. Therefore it is impossible to determine the alkali consumption by the second fraction and by the humic acids as a whole without their total desalting.

     

Relationship Between Extractable Metals in Acid Soils and Metals Taken Up by Tea Plants

Abstract

The accumulation of heavy metals in plants is related to concentrations andchemical fractions of the metals in soils. Understanding chemical fractions and availabilities of the metals in soils is necessary for management of the soils. In this study, the concentrations of copper (Cu), cadmium (Cd), lead (Pb), and zinc (Zn) in tea leaves were compared with the total and extractable contents of these heavy metals in 32 surface soil samples collected from different tea plantations in Zhejiang province, China. The five chemical fractions (exchangeable, carbonate‐bound, organic matter‐bound, oxides‐bound, and residual forms) of the metals in the soils were characterized. Five different extraction methods were also used to extract soil labile metals. Total heavy metal contents of the soils ranged from 17.0 to 84.0 mgCukg^?1, 0.03 to 1.09 mg Cd kg^?1, 3.43 to 31.2 mg Pb kg^?1, and 31.0 to 132.0 mg Zn kg^?1. The concentrations of exchangeable and carbonate‐bound fractions of the metals depended mainly on the pH, and those of organic matter‐bound, oxides‐bound, and residual forms of the metals were clearly controlled by their total concentrations in the soils. Extractable fractions may be preferable to total metal content as a predictor of bioconcentrations of the metals in both old and mature tea leaves. The metals in the tea leaves appeared to be mostly from the exchangeable fractions. The amount of available metals extracted by 0.01 mol L^?1 CaCl₂, NH₄OAc, and DTPA‐TEA is appropriate extractants for the prediction of metals uptake into tea plants. The results indicate that long‐term plantation of tea can cause sol acidification and elevated concentrations of bioavailable heavy metals in the soil and, hence, aggravate the risk of heavy metals to tea plants.     

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.