Search Results (143)

This study evaluated birch and oak ash extracts as alternative extractants for isolating humic substances (HSs) from peat and lignite. The effects of ultrasound intensity, extraction time, and temperature were optimized using a Box–Behnken design and validated statistically. The highest HSs yields were obtained from peat with oak ash extract (pH 13.18), compared to birch ash extract (pH 12.09). Optimal process parameters varied by variant, falling within 309–391 mW∙cm⁻², 116–142 min, and 67–79 °C. HSs extracted under optimal conditions were fractionated into humic acids (HAs) and fulvic acids (FAs), and then analyzed by elemental analysis, Fourier Transform Infrared Spectroscopy (FTIR), and Cross-Polarization Magic Angle Spinning Carbon-13 Nuclear Magnetic Resonance Spectroscopy (CP/MAS ¹³C NMR). The main differences in HSs quality were influenced by raw material and fraction type. However, the use of birch ash extract consistently resulted in a higher proportion of carboxylic structures across all fractions. Overall, wood ash extract, especially from oak, offers a sustainable and effective alternative to conventional extractants, particularly for HSs isolation from lignite. Notably, HSs yield from lignite with oak ash extract (29.13%) was only slightly lower than that achieved with 0.5 M NaOH (31.02%), highlighting its practical potential in environmentally friendly extraction technologies. Full article

Stable isotope analysis is a powerful tool for inferring and quantifying transformation processes, but its effectiveness relies on understanding the magnitude and variability of isotopic fractionation associated with specific reactions. Potassium permanganate (KMnO₄) is widely used as an efficient oxidant for the degradation of trichloroethylene (TCE); however, the influence of environmental factors on the isotope fractionation during this process remains unclear. In this study, compound-specific isotope analysis (CSIA) was conducted to investigate the variability in carbon isotope effects during the KMnO₄-mediated degradation of TCE under varying conditions, including initial concentrations of KMnO₄ and TCE, the presence of humic acid (HA), pH levels, and inorganic ions. The results showed that the overall carbon isotope enrichment factors (ε) of TCE ranged from −26.5 ± 0.5‰ to −22.8 ± 0.9‰, indicating relatively small variations across conditions. At low KMnO₄/TCE molar ratio (n(KMnO₄)/n(TCE)), incomplete oxidation and/or MnO₂-mediated oxidation of TCE likely resulted in smaller ε. For dense, non-aqueous phase liquid (DNAPL) TCE, which represents extremely high concentrations, the ε value was −13.0 ± 1.7‰ during KMnO₄ oxidation. This may be attributed to the slow dissolution of isotopically light TCE from the DNAPL phase, altering the δ¹³C signature of the reacted TCE and resulting in a significantly larger ε value than observed for dissolved-phase TCE oxidation. The ε values increased with rising pH, probably due to the decrease in oxidation potential (E₀) of KMnO₄ from pH ~2 to ~12, as well as the emergence of different degradation pathways and intermediates under varying pH conditions. Both SO₄²⁻ and NO₃⁻ slightly influenced the ε values, potentially due to the formation of H₂SO₄ and HNO₃ at lower pH, which may act as auxiliary oxidants and contribute to TCE degradation. A high concentration (50 mM) of HA led to a decrease in ε values, likely due to competitive interactions between HA and TCE for KMnO₄, which reduced the effective oxidation of TCE. Overall, the carbon isotope enrichment factors for KMnO₄-mediated TCE degradation are relatively stable, although certain environmental conditions can exert minor influences. These findings highlight the need for caution when applying quantitative assessment based on CSIA for KMnO₄ oxidation of TCE. Full article

The purpose of this research was to determine the properties of humic acids isolated from soil samples taken from a 40-year static experiment—the experimental factors were fertilization with manure (30 t ha⁻¹; FYM) and nitrogen at rates of 40, 60 and 120 t ha⁻¹. From the soil samples (Luvisol), humic acids (HAs) were extracted and the following were determined: elemental composition, hydrophilic and hydrophobic properties and spectrometric properties in the UV–VIS and IR range. The HAs of the soil fertilized with manure and N compared to the HAs of the soil fertilized with N (without manure) were characterized by a higher degree of aliphaticity and, consequently, a higher share of hydrophilic fractions and lower values of internal oxidation. Based on the spectrometric parameters, it was indicated that the HA particles of the manure-fertilized soil are characterized by a higher share of undecomposed lignin fragments, a lower degree of humification and at the same time, a higher susceptibility to oxidation. The obtained relationships showed that the aromaticity and hydrophobicity of the HA molecules of the manure-fertilized soil can be increased at certain N doses (60 and 120 t ha⁻¹), which is particularly important in terms of the role that humic substances play in carbon sequestration. Full article

The interactions between dissolved organic matter (DOM) and agrochemicals (e.g., neonicotinoid insecticides, NIs) govern the distribution, migration, and potential environmental risks of agrochemicals. However, the long-term effects of agricultural management on the DOM components and structure, as well as their further influences on the interactions between DOM and agrochemicals, remain unclear. Here, spectroscopic techniques, including Fourier transform infrared spectroscopy, two-dimensional correlation spectroscopy, and three-dimensional excitation–emission matrix fluorescence spectroscopy were employed to delve into the interaction mechanism between the DOM from citrus orchards with distinct cultivation ages (10, 30, and 50 years) and imidacloprid, which is a type of pesticide widely used in agricultural production. The findings revealed that the composition and structure of soil DOM significantly change with increasing cultivation age, characterized by an increase in humic substances and the emergence of new organic components, indicating complex biodegradation and chemical transformation processes of soil organic matter. Imidacloprid primarily interacts with fulvic acid-like fractions of DOM, and its binding affinity decreases with increasing cultivation age. Additionally, the interactions of protein-like fractions with imidacloprid occur after humic-like fractions, suggesting differential binding behaviors among DOM fractions. These results demonstrate that cultivation age significantly influences the composition and structural characteristics of soil DOM in citrus orchards, subsequently affecting its sorption capacity to imidacloprid. This study enhances the understanding of imidacloprid’s environmental behavior and provides theoretical support for the environmental risk management of neonicotinoid pesticides. Full article

Road-deposited sediments (RDS) from 28 sites in Beijing were studied and analyzed for eight heavy metals. In RDS, the levels of Cr, Ni, Cu, Zn, As, Cd, Pb and V were 2.76, 1.11, 2.40, 1.65, 1.09, 6.52, 4.13 and 0.06 times the background values, respectively. The levels were rated in accordance with the geoaccumulation index (Igeo) as follows: Cd>Pb>Zn>Cu>Cr>Ni>As>V. In the four functional zones, the potential ecological risk index method showed that most of the heavy metals have environmental risk index values (${\mathrm{E}}_{\mathrm{r}}^{\mathrm{i}}$) of less than 40, but the multifactor environmental risk value (RI) for Pb in the transportation area exceeded 150. Four functional areas had Cd values greater than 160, exhibiting the highest risk. The human health risk assessment revealed that exposure pathways followed this decreasing order: ingestion > dermal > inhalation. Three DOM fractions were resolved in the sediments of the four functional zones, including terrestrial fulvic-acid-like fractions (C1), humic-acid-like fractions (C2), and tryptophan-like fractions (C3), and the DOM fractions were affected by both exogenous and endogenous sources. A positive correlation existed between DOM and Ni and Cu in the transportation zone, and the correlation between DOM and heavy metals in other zones was not apparent. In conclusion, heavy metals in different functional zones affected the concentration and characteristics of DOM, and there was a strong correlation between heavy metals and DOM concentration and features. Full article

The aim of this study was to evaluate the influence of innovative mineral–organic mixtures containing zeolite composites produced from fly ashes and lignite or leonardite on the fractional composition of soil organic matter in sandy loam soil under two-year pot experiments with maize. The fractional composition of soil organic matter (SOM) was analyzed and changes in the functional properties of soil groups were identified using the ATR-FTIR method. Changes in the content of phenolic compounds were assessed, and the potential impact of fertilizer mixtures on soil carbon stocks was investigated. The addition of these mixtures improved the stability of SOM. The application of mineral–organic mixtures significantly increased the total organic carbon (TOC) by 18% after the 2nd year of the experiment. The maximum TOC content in the soil was observed by 33% with the addition of MC3%Leo3% amendment. Nitrogen content in soil was increased by 62% with MV9%Leo6% additive, indicating increased soil fertility. The study highlighted an increase in fulvic acid carbon relative to humic acid carbon, signaling positive changes in organic matter quality. The new mineral–organic mixtures influence changes in specific functional groups (ATR-FTIR) present in the soil matrix, compared to mineral fertilization alone. The additive mixtures also contributed to an increase in soil carbon stocks, highlighting their potential for long-term improvement of soil fertility and carbon sequestration. Full article

The efficient characterization of compost quality is essential for optimizing its application in agriculture and soil improvement. In this study, a correlation-based approach was employed to evaluate relationships between physicochemical properties, structural features, and reactivity indicators of compost extracts—fulvic acid-like (FA-L), humic acid-like (HA-L), and dissolved organic matter (DOM)—and their respective bulk composts. The goal was to identify key compost parameters that can serve as reliable predictors of humic substance composition and bioactivity, thereby reducing reliance on labor-intensive humic substance extractions. A comprehensive set of elemental, spectroscopic (UV-vis, ATR-FTIR, ¹H-NMR), and thermal (TGA-DSC) analyses were conducted to assess the composition and stability of the extracts. Strong correlations were found between compost oxidation state (C_oxi/C), cation exchange capacity (CEC), thermal stability, and the structural characteristics of humic substances-like (HS-L) fractions, suggesting that direct compost characterization can effectively predict humic substance reactivity and agronomic potential. The findings also align with a previously developed Compost Quality Index (CQI), reinforcing the functional role of humic substances in soil fertility and nutrient retention. By establishing a simplified yet robust compost assessment framework, this study advances the potential for efficient, cost-effective evaluation methodologies for compost quality. Full article

The influence of different mineral and organic fertiliser applications on the soil organic matter (SOM) content and quality was monitored in long-term field trials. We used long-term field experiments (27 years) with a crop rotation of potatoes, winter wheat, and spring barley on cambisol soil. The treatments were as follows: an unfertilised control (Cont), sewage sludge in normal and triple doses (SS1 and SS3, respectively), farmyard manure (F1) in a conventional dose, a half dose of farmyard manure with a half dose of mineral nitrogen (F1/2 + N1/2), straw with mineral nitrogen fertiliser (N + St), and mineral nitrogen without any organic fertiliser (N). This study focused on the ability of the total and easily extractable glomalin-related soil protein (T-GRSP and EE-GRSP, respectively) and the water stability of aggregates (WSA) as indicators of long-term SOM quality changes. The results were compared with the content of humic substance fractions and the carbon in humic substances (C_HS), humic acids (C_HA), and fulvic acids (C_FA). The lowest SOM content and quality were observed in the control treatment. The highest overall SOM quality, including the degree of polymerisation (HA) and the GRSP content, was found in the F1 treatment. The organic matter in sewage sludge contributed less to the formation of stable SOM than straw. A significant correlation was found between both the EE-GRSP and the T-GRSP and the content of the C_SOM, C_HS, C_HA, and HA, but not with the C_FA. The influence of fertiliser on the GRSP content was demonstrated. However, no relationship was observed between the WSA and SOM quality, the EE-GRSP, or the T-GRSP content. Full article

The aim of this study was to determine the effect of progressive pig slurry (PS) rates, applied over a 12-year period, on the molecular composition of soil organic matter in a calcareous soil. Annual organic matter rates of PS ranged from 1.0 to 4.8 Mg ha⁻¹. Humic acids (HAs) were extracted from field plots treated with PS, including a control (no PS applied). These HAs were analysed using pyrolysis–gas chromatography–mass spectrometry. The proportions of the 122 major compounds released from the soil HAs indicated that PS stimulated humification processes, with the degree of enhancement depending on the application rate. The applied PS contained a high proportion of aliphatic compounds, but only steroids and triterpenes accumulated in the HA soil fraction, and this was only observed at low PS rates. These results suggest that the application of PS leads to a dose-dependent increase in alkyl compounds, mainly alkanes and olefins. Aromatic compounds also showed a dose-dependent increase, but not in terms of the demethoxylated compounds typical of mature humic substances found in the original soil. Instead, the increase in aromatics was observed in the form of methoxyphenols, suggesting a recent incorporation of lignin derivatives from crop residues into the HA. Full article

The black soil in northeast China plays an important role in coping with global climate change. However, long-term predatory production methods and the excessive application of pesticides and fertilizers to respond to the growing demand resulted in a severe contamination of the black soil with Cd, leading to a decrease in the properties of black soil. In this study, we propose the preparation of bio-adsorbents including a natural bio-adsorbent (AW), a modified bio-adsorbent (AM), biochar cracking at 300, 500, and 700 °C (C300, C500, C700), modified biochar (CM), and a magnetic bio-adsorbent particle (MBP) using the waste of black soil autotrophic specialty crop multiplier onion (Allium cepa var. aggregatum) to investigate the adsorption and immobilization of Cd in contaminated soil. The results show that the application of bio-adsorbents resulted in a 17.29–35.67% and 18.24–30.76% decrease in effective and total Cd content in soil after dry–wet–freeze circulation. Exchangeable Cd in soil decreased and gradually transformed to more stable fractions, with a reduction in Cd bioavailability after remediation. Interestingly, an increase in plant uptake of Cd was observed in the biochar-treated group for a short period, causing a 93.72% increase in Cd concentration in plants after the application of C700, which can be applied concomitantly with hyperaccumulator plants harvested multiple times annually by encouraging higher Cd uptake by plants. Additionally, the rich content of humic acid (HA) in black soil was capable of promoting the immobilization of Cd in soil, enhancing the Cd resistance of black soil. Bio-adsorbents derived from Allium cepa var. aggregatum waste can be applied as a new type of green and effective material for the long-term remediation of Cd in the soil at a lower cost. Full article

The aim of this study was to examine the hepatoprotective activity of multicomponent mixtures of natural origin in the BALB/C mouse model, with subacute liver failure (SALF) induced by the administration of toxin carbon tetrachloride (CCl₄). The hepatoprotective activity of activated hydrolytic lignin (BP-Cx-1), humic acid peloids (HA), and isoflavones from kudzu Pueraria lobata roots (IFL) was evaluated using mass spectrometry (MS)-based omics technologies. Our MS-based approach revealed new insights into the molecular mechanisms of the hepatoprotective activity of multicomponent mixtures of natural origin. Significant differences were observed in the proteome and metabolome profiles of the urine and liver of BALB/c mice with SALF between a control group with CCl₄ administration, intact controls, and groups receiving potential hepatoprotectors of natural origin (BP-Cx-1, HA, IFL). Proteomic and metabolomics analyses demonstrated that among the hepatoprotectors, IFL possessed the highest hepatoprotective potential, which correlated well with the relative effectiveness of the drugs recorded during in vitro studies. These results correlate with the relative effectiveness of the drugs recorded in previous in vitro and in vivo studies. The leading IFL activity may be attributed to a higher content of active polyphenolic components compared to heterogeneous HA and BP-Cx-1. Enrichment with active components by fractionation is a direction that can be explored for developing hepatoprotective agents based on natural complex polyphenols. Full article

In recent decades, there has been a significant decrease in humus resources in the terrestrial environment, including in agriculturally used soils, due to increased mineralisation of soil organic matter (SOM). Using composting as a method for recycling lignin-cellulosic biomass, the application of innovative microbial stimulation seems reasonable for obtaining the most useful product. The aim of this study was the qualitative and quantitative analysis of humic acids during the composting of exogenous organic matter (EOM) of energy willow biomass (WBC) and biodegradable municipal waste (MSWC). Samples were collected at different maturity stages, and the following determinations were performed: total organic carbon (TOC) and total nitrogen (TN), carbon of fulvic (CFA) and humic (CHA) acids, carbon of residual fraction (CR), the elemental composition of humic acids, humification index (HR₁), and ω (oxidation) ratios. Results indicated the direction and intensity of biotransformation processes were determined by the availability of nitrogen compounds. The innovative use of microbial preparation has resulted in a more useful final product. Inoculation of lignocellulosic substrates stimulated the synthesis of humic acids, and the decomposition of the CR fraction, as well as HR₁ and ω ratios, may be used to assess the recycling efficiency. Full article

Dissolved organic matter (DOM) is widely present in soil environments and plays a crucial role in controlling the morphology, environmental behavior, and hazards of arsenic (As) in soil. In the Fe-rich red soil of tea plantations, the decomposition of tea tree litter complicates DOM properties, leading to more uncertain interactions between DOM, Fe, and As. This study focused on three tea plantations in Huangshan City to investigate the contents of DOM, Fe, and As in surface red soils (Ferralsols) and establish their correlations. Three-dimensional fluorescence spectroscopy and PARAFAC analysis methods were used to analyze the DOM components and fluorescence signatures. Additionally, the process and mechanism of the binding of DOM-Fe with As were explored through laboratory experiments on the morphological transformation of As by DOM-Fe. The results showed that the pH values of the soils in the three tea plantations ranged from 3.9 to 5.2, and the entire sample was strongly acidic. The DOM exhibited strong intrinsic properties and low humification, containing three types of humic acid components and one intermediate protein component. The DOC content in the Fe-rich red soil did not have a direct correlation with Fe and As, but the interaction of DOM fractions with Fe significantly influenced the As content. Specifically, the interaction of protein-like fractions with Fe had a more pronounced effect on the As content. The maximum sorption rate of As by DOM was 15.45%, and this rate increased by 49 to 75% with the participation of Fe. In the configuration of the metal electron bridge, Fe acts as a cation, forming a connecting channel between the negatively charged DOM and As, thus enhancing the DOM’s binding capacity to As. DOM-Fe compounds bind As through surface pores and functional groups. These findings provide deeper insights into the influence of DOM on As behavior in Fe-rich soil environments and offer theoretical support for controlling As pollution in red soil. Full article

The frequency and intensity of harmful cyanobacterial blooms have increased in the last decades, posing a risk to public health since conventional water treatments do not effectively remove extracellular cyanotoxins. Consequently, advanced technologies such as the Fenton process are required to ensure water safety. The cyanotoxin cylindrospermopsin (CYN) demands special attention, as it is abundant in the extracellular fraction and has a high toxicological potential. Hence, this study aimed to assess the application of the Fenton process for the oxidation of CYN spiked in natural water from Paranoá Lake (Brasília, Brazil). The H₂O₂/Fe(II) molar ratio was evaluated from 0.2 to 3.4, with an optimum molar ratio of 0.4, achieving a CYN degradation efficiency of 97.8% when using 100 µM of H₂O₂ and 250 µM of Fe(II). The CYN degradation efficiency, using 75 µM of H₂O₂ and 187.5 µM of Fe(II), decreased by increasing the initial pH (from 96.2% at pH 2 to 23.0% at pH 9) and the initial CYN concentration (from 93.7% at 0.05 µM of CYN to 85.0% at 0.2 µM of CYN). At the optimum H₂O₂/Fe(II) molar ratio of 0.4, the hydroxy radical scavengers tested (124.3 µM C of algogenic organic matter, 5 mg L⁻¹ of humic acid, and 513.3 µM of methanol) did not considerably affect the CYN degradation, reaching a maximum CYN degradation reduction from 98.3% to 82.2%. Full article

Our recent study demonstrated that fulvic and humic acids are the major contributors to the adsorption of phenoxyalkanoic acid herbicides in soils. At very low pH, the neutral forms of these herbicides are bound directly to fulvic and humic acids, whereas at higher pH, their anionic forms are adsorbed mainly via bridges created by Al³⁺ species. The number of active sorption sites associated with Al³⁺ species complexed with fulvic acids is pH-dependent, whereas the number of corresponding sites in humic acids is pH-independent. Based on the results of the FTIR analysis, research into adsorption thermodynamics, and molecular modeling, an attempt was made in the present study to explain the adsorption mechanisms of six phenoxyalkanoic herbicides used currently in the European Union on the surfaces of the above fractions of humic substances. The obtained values of standard enthalpy (${\Delta H}^0$) for the adsorption of the anionic forms of phenoxyalkanoic herbicides on fulvic or humic acids complexed with Al³⁺ were in the range of physical adsorption, i.e., from −8.4 kJ/mol to −2.9 kJ/mol for the former, and from −5.3 kJ/mol to −2.4 kJ/mol for the latter. The study demonstrated that the neutral forms of phenoxyalkanoic herbicides were bound to humic substances mainly via H-bonds, π-π stacking interactions, and hydrophobic interactions. Al³⁺ species were complexed with fulvic and humic acids to form outer-sphere complexes. Ternary outer-sphere complexes were also created between the anionic forms of phenoxyalkanoic acid herbicides and positively charged Al³⁺ species complexed with fulvic acids. The mechanisms of adsorption on humic acids involved a ligand exchange between a loosely bound hydroxyl group of hydrolyzed Al³⁺ complexed with this adsorbent and the anionic form of the herbicide. However, in this case, adsorption took place only in the presence of sufficiently strong hydrophobic and π-π stacking interactions supported by H-bonds. These findings elucidate why phenoxyalkanoic herbicides are mobile in the soil profile and are often rapidly degraded in soils. Full article