Search Results (35)

The presence of pharmaceuticals in the environment can result in potentially dangerous situations. In soils and sediments, pharmaceuticals can be partially immobilized by interactions with humic substances. Interactions, thus, can strongly affect their mobility and bioavailability. An investigation of the thermodynamic aspects of the interactions is largely missing. Thermodynamic parameters are usually calculated on the basis of sorption experiments. Our study is focused on the direct measurements of the heat effect of interactions between fulvic acids and chosen drugs. Well-characterized fulvic sample standards provided by the International Humic Substances Society were used. Ibuprofen, diclofenac, and sulphapyridine were chosen as drugs. Isothermal titration calorimetry provided a complete set of thermodynamic characteristics of underlying processes—interaction enthalpy, entropy, and Gibbs energy. All studied interactions were found to be exothermic with heat liberation between −496 and −9938 J/mol. The lowest enthalpies were obtained for sulphapyridine and the highest ones for ibuprofen (on average). Changes in Gibbs energy were very similar for all studied interactions (20–28 kJ/mol). The highest change in entropy was determined for ibuprofen (73 J/mol·K); values obtained for diclofenac and sulphapyridine were comparable (57 and 56 J/mol·K, respectively). Full article

Phosphate (P) is the plant macronutrient with, by far, the lowest solubility in soil. In soils with low P availability, the soil solution concentrations are low, often below 2 [µmol P/L]. Under these conditions, the diffusive P flux, the dominant P transport mechanism to plant roots, is severely restricted. Phosphate is sorbed into various soil solids, Fe/Al oxides, clay minerals and, sometimes overlooked, humic Fe/Al surfaces. The immobilization of P in soil is often the result of the diffusion of P into the internal surfaces of oxides or humic substances. This slow reaction between soil and P further reduces the availability of P in soil, leading to P fixation. The solubilization of soil P by root-released carboxylates is a promising way to increase the acquisition and uptake of P from P-fixing soils. Citrate and, sometimes, oxalate are effective with respect to additional P solubilization or P mobilization, which may help increase the diffusive P flux into the roots by increasing the P solution concentrations in the rhizosphere. The mobilization of humic-associated P by carboxylates may be an effective way to improve soil P solubility. Not only orthophosphate anions are mobilized by root-released carboxylates, but also higher phosphorylated inositol phosphates, as the main part of P esters in soil are mobilized by carboxylates. Because of the rather strong bonding of higher phosphorylated inositol phosphates to the soil solid phase, the mobilization step by carboxylates appears to be essential for plants to acquire inositol-P. The ecological relevance of P mobilization by carboxylates and its effect on the uptake of P by crops and grassland species are, at best, partially understood. Plant species which form cluster roots such as white lupin (Lupinus albus L.) or yellow lupin (Lupinus luteus L.) release high rates of carboxylates, mainly citrate from these root clusters. These plant species acquire fixed or low available P which is accessible to plants at rates which do not satisfy their P demand without P mobilization. And white lupin and yellow lupin make soil P available to other plants in mixed cropping systems or for subsequent plant species in crop rotations. The mobilization of P by carboxylates is probably also important for legume/grass mixtures for forage production. Species such as alfalfa, red clover or white clover release carboxylates. The extent of P mobilization and P uptake from mobilized P by legume/grass mixtures deserves further research. In particular, which plant species mostly benefit from P mobilization by legume-released carboxylates is unknown. Organic farming systems require such legume/grass mixtures for the introduction of nitrogen (N) by forage legumes into their farming system. For this agricultural system, the mobilization of soil P by carboxylates and its impact on P uptake of the mixtures are an important research task. 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

Bone meal has been used as economic and effective additive for heavy metals (HMs) pollution remediation due to the distinct components and structures that enable their favorable properties, such as its low cost, high adsorption capacity, acid-base adjustability, and ion-exchange capability. However, no attempt has been made to establish whether cow bone could promote the passivation of HMs and the removal of metal resistance genes (MRGs) and antibiotics resistance genes (ARGs) during the composting process. Two sizes of cow bone (meal (T2) and granule (T3)) were added to investigate their effects on humification, HMs passivation and the abundance of ARGs and MRGs during swine manure composting. Excitation-emission matrix (EEM)-parallel factor analysis showed that the percentage of maximum fluorescence intensity of humic-like substances were higher in T2 (91.82%) than in T3 (88.46%), implying that T2 could promote the humification process compared to T3. In comparison with control (T1), the addition of T2 and T3 could promote the change of exchangeable Cu and reducible Cu into oxidizable Cu, thus reducing the mobility factors (MF) of Cu in T2 and T3 treatments by 10.48% and 6.98%, respectively. In addition, T2 and T3 could increase exchangeable Zn into reducible Zn and oxidizable Zn, thereby reducing the MF of Zn in T2 and T3 treatments by 18.80% and 2.0%, respectively. Quantitative Real-time PCR (qPCR) analysis revealed that the total abundances of MRGs were decreased by 100% in T2 and T3 treatments, and T2 decreased the total relative abundance of ARGs. Furthermore, the relative abundance of ARGs and MRGs had significantly correlated with intI1 and bio-available of Cu and Zn, which was triggered by selective pressure of HMs and horizontal gene transfer. The present study suggested that cow bone meal as additives can be a feasible approach to promote the passivation of HMs and enhance the removal of MGRs and ARGs by decreasing horizontal gene transfer and selective pressure by bioavailable HMs. Full article

Diversifying crop rotations by incorporating legumes is recommended to enhance the resilience of agricultural systems against environmental stresses and optimize nitrogen utilization. Nonetheless, ploughing forage legumes or grass-legumes poses a significant risk of nitrate leaching. The study aimed to assess the impact of strip tillage intercropping management on soil mineral nitrogen, water-extractable organic carbon, mobile humic substances content, and winter wheat (Triticum aestivum L.) grain yield compared to forage legume and winter wheat monocropping with conventional tillage. In the intercropping systems, the following bicrops were used: black medick (Medicago lupulina L.) with winter wheat, white clover (Trifolium repens L.) with winter wheat, and Egyptian clover (Trifolium alexandrinum L.) with winter wheat. Research was conducted in two experiments. The results indicated that after implementing strip tillage and winter wheat intercropping, the soil mineral nitrogen content was similar to or lower than that observed in conventional tillage and winter wheat sowing after forage legumes. Winter wheat grain yield in intercrops decreased compared to the legumes monocultures that were ploughed before winter wheat sowing. The highest amount of water- extractable organic carbon was in intercropping growing white clover and winter wheat bicrops or in all fields (except Egyptian clover and winter wheat bicrops) after applying strip tillage. During the research period, the quantities of mobile humic substances and mobile humic acids exhibited similar changes. Their content increased substantially in fields with white clover and Egyptian clover, regardless of whether the legumes were ploughed or grown with winter wheat. Full article

Phosphorus (P) retention in soils in the presence of organic matter (OM) has been, for years, a topic with no clear conclusions. Considering the important ecological functions of peatlands, the objective of this study is to examine the role of OM transformation in relation to P status in Histosols in the Oder Valley (Poland). Basic physical and chemical properties and the following P forms were determined in the organic horizons of 5 soil profiles from two habitats (eutrophic and dystrophic): total (Pt) and organic P (P_o), available P (P_M3), easily soluble P (P_CaCl2), water-soluble P (P_W), and fraction of P_o in humic (P_o_HA) and fulvic (P_o_FA) acids after extraction with 0.5 mol L⁻¹ NaOH. The results were statistically verified in both examined habitat groups separately. The higher values of mobile P forms were found in the upper organic horizons released from OM constituents as a result of their decomposition. The role of OM in P retention was strongly related to the activity of humic substances (HS): a higher P_o percentage (6.9–99.4% of P_o) was observed in dystrophic, whereas a lower (9.3–28.6% of P_o) was observed in eutrophic Histosols. Humic acids played a dominant role in P retention compared to fulvic acids in most peat horizons, especially at pH < 5. The role of HA and FA in P retention was clearly dependent on forms found only in eutrophic Histosols. The important role of FA in P retention during OM transformation was confirmed by negative correlations between P_o_FA and macronutrient ratios in both soil groups. The results confirm the variable role of OM in P retention, depending on soil environmental conditions and OM type (peat and moorsh). This may have important applications not only in areas of natural importance, for which the release of mobile P forms may be a threat, but also in agricultural areas where, for a change, we struggle to increase P availability. Full article

It is important to ensure the ratio of stable and labile soil organic carbon (SOC) compounds in the soil as this influences ecosystem functions and the sustainability of soil management. The aim of this investigation was to determine the changes in SOC compounds and soil quality improvement in Arenosol soil after the conversion of arable land to natural and agricultural land use. The land use types included pine afforestation (PA), uncultivated abandoned land (UAL), unfertilised and fertilised cropland (CLunf, CLf), and unfertilised and fertilised grassland (GRunf, GRf). To assess the lability of organic carbon (OC) compounds, levels of mobile humic substances (MHSs), mobile humic acids (MHAs), mobile fulvic acids (MFAs), active C pool (POXC), and water-soluble C (WEOC) compounds were determined. It was found that faster OC accumulation occurs in PA soil than in CLf, and is somewhat slower in grassland uses (GRf and UAL). As the amount of SOC increased, more MHS formed. A significant increase in their quantity was found in PA (+92.2%) and CRf and UAL (+51.5–52.7%). The application of mineral fertilisers promoted the formation of MHSs in CLf and GRf. PA, GRunf, and GRf soils had more suitable conditions for MHA formation (MHA/MFA > 1.3), whereas CLunf soil contained more MFAs. The POXC pool was insensitive to land-use changes in the Arenosol. After land-use conversion, POXC amounts were significantly (p < 0.05) higher in natural ecosystems (UAL and PA) and fertiliser perennial grasses than in CL. The amount of WEOC increased the most in UAL, PA, and GRf (7.4–71.1%). The sequence of decrease in land use was GRf, UAL, and PA > CLunf, CLf, and GRunf. The decreasing order of the carbon management index (CMI) of different land uses (PA > UAL > GRf > GRunf > Clunf) confirms that faster OC accumulation in Arenosol soil occurred in PA and grassland land uses (GRf and UAL). The values of the carbon lability index (CLI) variation (CLunf > GRunf GRf > UAL > PA) show that in PA, UAL, and GRf land uses, mobile organic matter (OM) forms are relatively less formed, which stabilises OC accumulation in the soil. The CMI showed that UAL and GRf were the most suitable soil uses for Arenosol soils. Full article

The production of sugar beet in the Republic of Kazakhstan is insufficient to meet the domestic sugar needs of the population. This shortfall is attributed to the natural and climatic conditions, the high cost of production, and the low use of mineral fertilizers. The objective of the study is to investigate the impact of the organic humic fertilizer “Tumat” on the growth, development, yield, and sugar content of sugar beet in the conditions of irrigated light chestnut soils in Southeast Kazakhstan. Scientific research confirms the effectiveness of using the organic humic fertilizer Tumat for cultivating sugar beets. This fertilizer is highly bioavailable and contains a balanced mix of essential macronutrients and micronutrients, polyunsaturated fatty acids, and other biologically active substances. Foliar feeding of sugar beets enriches the soil with exchangeable potassium, mobile phosphorus, and easily hydrolyzable nitrogen during the plant’s vegetative period. Using the Tumat fertilizer enhances plant germination rates by 6.0–16.0%, stimulates growth and development, accelerates the ripening of sugar beets, and increases the yield of tubers by 10.5–15.2%, sugar content by 0.4–0.7%, and sugar output by 13.6–20.8%. An organic humic fertilizer, is recommended as an environmentally safe and effective agricultural product that boosts the productivity and quality of sugar beets, as well as soil fertility. Full article

With the wide application of graphene oxide nanoparticles (GONPs), a great amount of GONP waste is discarded and concentrated in landfills. It has been proven that GONPs have strong toxicity and could gather toxic substances due to their high adsorption capacity. GONPs will seriously pollute the surrounding environment if they leak through the geosynthetic clay liner (GCL) in landfills. To investigate various factors (temperature, ionic strength (IS) and humic acid (HA)) on the transport and retention of GONPs in the GCL, a self-designed apparatus was created and column tests were carried out. The experimental results show that GONPs could be transported through the GCL. The mobility and sorption ratio of GONPs in GCL decreased with an increase in temperature and IS, and increased with an increase in HA. The temperature had little effect on the deposition ratio of GONPs in the GCL. The deposition ratio of GONPs in the GCL increased with IS, and decreased with an increase in HA. The transport of GONPs in GCL, glass beads and quartz sand was compared, and the results show that the retention ability of the GCL is much better than other porous materials. The experimental results could provide significant references for the pollution treatment in landfills. Full article

Geogenic arsenic (As)-rich groundwater poses a significant environmental challenge worldwide, yet our understanding of the interplay between dissolved organic matter (DOM) transformation and arsenic mobilization during microbial sulfate reduction remains limited. This study involved microcosm experiments using As-rich aquifer sediments from the Singe Tsangpo River basin (STR) and Jianghan Plain (JHP), respectively. The findings revealed that microbial sulfate reduction remarkably increased arsenic mobilization in both STR and JHP sediments compared to that in unamended sediments. Moreover, the mobilization of As during microbial sulfate reduction coincided with increases in the fluorescence intensity of two humic-like substances, C2 and C3 (R = 0.87/0.87 and R = 0.73/0.66 in the STR and JHP sediments, respectively; p < 0.05), suggesting competitive desorption between DOM and As during incubation. Moreover, the transformations in the DOM molecular characteristics showed significant increases in CHOS molecular and low-O/C-value molecular intensities corresponding to the enhancement of microbial sulfate reduction and the possible occurrence of methanogenesis processes, which suggests a substantial bioproduction contribution to DOM components that is conducive to As mobilization during the microbial sulfate reduction. The present results thus provide new insights into the co-evolution between As mobilization and DOM transformations in alluvial aquifer systems under strong microbial sulfate reduction conditions. Full article

In the context of climate change, the questions of the sustainability of peat soil use are particularly relevant. The evaluation of changes in the properties of soils (including histosols) using chemical methods is expensive, thus, their application possibilities are limited. Analyzing the morphology of histosol profiles would provide effective spatial analysis opportunities for assessing the extent of their anthropogenic transformation and impact on climate change. The key diagnostic horizons and their sequences for the identification of the risk group are the main results of the study. The analysis included 12 soil profiles, whose morphological structure was characterized using the WRB 2022 system of master symbols and suffixes for soil profile horizon descriptions. The analyzed profiles were excavated in forested (relatively natural), agricultural (agrogenized) and peat mining (technogenized) areas. The insights of this article in the discussion are based on the chemical analyses (pH KCl, N, P and K, soil organic carbon, dissolved organic carbon, mobile humus substance, humic and fulvo acids, C:N ratio and humification degree) of three histosol profiles. The main discussion is based on the results of the morphological analysis of the profiles. The results of this research allowed for the identification of a different structure of the histosol profile. The upper part of the histosol profile, which consists of O–H(a,e,i) horizons, indicates its naturalness. The murshic horizon (Hap) is the classic top horizon of the agricultural histosol profile, which is most affected by mineralization. The technogenized histosols have a partially destroyed profile, which is represented by the Ahτ/Haτ or only Haτ horizons at the top. The morphology of the histosol profile and the identification of the relevant horizons (Hap, Haτ and Ahτ) indicate its risks and presuppose a usage optimization solution. The most dangerous in the context of sustainable land use principles and climate change is the murshic horizon (Hap), which is uncovered after removing the horizon O. The risks of sustainable use of histosol are caused by measures that promote its microbiological activity, which is the maintenance of a drained state and cultivation. In the context of GHG emissions and sustainable use, the most favorable means would be the formation of the horizon O by applying perennial plants. Rewetting should be applied to those histosols whose removal from the agricultural or mining balance would provide maximum ecological benefits. Full article

The bioavailability and mobility of copper (Cu) in soil play a crucial role in its toxicity and impact on soil organisms. Humic substances, with their abundant functional groups and unique pore structure, have demonstrated the ability to effectively mitigate the toxic effects of heavy metals in soil. This study explores the potential of a soluble humic substance (HS) derived from leonardite for Cu removal from contaminated soils. The effects of various washing conditions, such as concentration and washing cycles, on removal efficiency were assessed. The results showed that a single washing with HS solution achieved an optimal removal efficiency of 37.5% for Cu in soil, with a subsequent reuse achieving a removal efficiency of over 30.5%. To further enhance Cu removal efficiency, a two-step soil washing approach using a chemical reductant NH₂OH·HCl coupled with an HS solution (NH₂OH·HCl + HS) was employed, resulting in an increased removal efficiency to 53.0%. Furthermore, this approach significantly reduced the plant availability and bioaccessibility of Cu by 13.6% and 11.4%, respectively. Compared to a single washing with NH₂OH·HCl, both HS and NH₂OH·HCl + HS increased the soil pH and organic matter content. These findings suggest that the two-step soil-washing approach using NH₂OH·HCl + HS effectively removed Cu from polluted soil. This study demonstrates the potential of humic substances as environmentally friendly materials for remediating heavy metal-polluted soil, promoting green and sustainable applications in soil remediation practices. Full article

Dissolved organic matter (DOM) plays important roles in environmental ecosystems. While many studies have explored the characteristics of aged biochar, limited information is available about the properties of DOM derived from aged biochar. In this study, biochar obtained from maize stalk and soybean straw were aged using farmland or vegetable-soil solution, as well as soil solution containing hydrogen peroxide (H₂O₂). Chemical composition of the extracted DOM from the aged biochar was analyzed via excitation–emission matrix coupled with fluorescence regional integration (FRI) and parallel factor analysis (PARAFAC). Obtained results showed that biochar aged with H₂O₂-enriched soil solution had higher water-soluble organic carbon, ranging from 147.26–734.13% higher than the controls. FRI analysis revealed fulvic and humic-like organics as the key components, with a considerable increase of 57.48–235.96% in the humic-like component, especially in soybean-straw-aged biochar. PARAFAC identified four humic-like substance components. Concurrently, the aromaticity and humification of the aged-biochar-derived DOM increased, while the molecular weight decreased. These findings suggest that DOM derived from aged biochar, with a high content of humic-like organics, might impact the mobility and toxicity of pollutants in soil. Full article

One of the practices often mentioned to achieve climate change mitigation is the long-term cultivation of perennial plants. The objective of the study was to estimate changes in the accumulation of soil organic carbon (SOC) and its fractions in 0–10, 10–20, 20–30 cm, and within 0–30 cm soil layer of red fescue (Festuca rubra L.) swards that differ in age (5, 10 and 15 years) as well as to compare them with the arable field. Our results show that SOC accumulation at 5-year-old cultivation of red fescue is high, later this SOC increase slowed down from 71% in the 0–30 cm soil layer when land use was converted from arable field to 5-year-old sward to 1% from 10 to 15 years. The level of water extractable organic carbon (WEOC) in the 0–30 cm soil layer of swards was significantly higher compared to the arable field. The positive effect of these swards in the accumulation and stabilization of organic carbon during humification in the soil was also determined. The largest amounts of mobile humic substances (MHS) and mobile humic acids (MHA) accumulated in the 0–10 cm layer of sward soil (3.30–4.93 and 1.53–2.48 g kg⁻¹, respectively). In conclusion, the findings suggest that a conversion from arable to soil under permanent grass cover significantly improves carbon status. Full article

The dissolved organic matter (DOM) is one of the most sensitive indicators of changes in the soil environment, and it is the most mobile and active soil component that serves as an easily available source of nutrients and energy for microbes and other living organisms. In this paper, DOM structural characteristics and main properties were investigated by three-dimensional fluorescence spectroscopy (EEM) and UV–visible spectrum technology in the farmland soils around Urumqi of China, and its possible sources and pathways were analyzed by spectroscopic indices. The results showed that humic-like substances were the main composition of the soil DOM, and its autogenesis characteristics were not obvious. Main DOM properties such as aromatability, hydrophobicity, molecular weight, molecular size, and humification degree in the southern region of Urumqi were higher than those of the northern region of Urumqi and Fukang in China, and higher on the upper layers of the soil (0–0.1 and 0.2 m) than in the deeper layer (0.2–0.3 m).This may be because the tilled layer is more subjected to fertilization and conducive to microbial activities. The spectroscopic analysis showed that the source of DOM of these regions is mainly from microbial metabolites. These results provide basic scientific data for the further research on the environmental chemical behavior of pollutants and pollution control in this region. Full article