Search Results (57)

Vineyard soils are frequently contaminated with copper due to the use of Cu fungicides to prevent downy mildew. This study investigated the effects of an aerated compost tea (ACT) made from grape pomace and animal manure on the downward transfer of Cu and on the accumulation of Cu in plants in a sandy loam vineyard soil. Crimson clover and pot marigold were grown in a 40 cm soil column with Cu supplied to the surface at loadings representative of those applied in European vineyards, plus additions of ACT. A source of Cu enriched in the stable isotope ⁶⁵Cu was used to distinguish freshly added Cu (fresh Cu) from Cu already present in the soil (aged Cu). ACT increased the concentration of soluble humic substances (SHS) in pore water in the top 7.5 cm of the column, and increased the concentration of Cu, Al, and Fe in pore water in proportion to the concentration of SHS. The transfer of fresh Cu to deeper soil was limited to the top 5 cm, even after the addition of ACT, although fresh Cu reacted slightly more to ACT than aged Cu. ACT had no effect on Cu phytoextraction but increased the concentration of Cu in roots by almost twofold. Relatively more fresh Cu was transferred to plants than aged Cu, primarily due to its preferential accumulation on the surface. The risk associated with the use of ACT on vineyard soils is not that of promoting the downward transfer of Cu, but rather of increasing Cu availability to plants and likely to other living organisms in the topsoil. Full article

Floodplains with fluvisols in Poland are crucial areas for both agriculture and environmental relevance. The largest areas of fluvisols are located in the floodplains of the Vistula River and have been identified as significant reservoirs of organic carbon. Humic substances were determined using the following procedure: C_dec—carbon after decalcification, C_HA+C_FA—carbon of humic and fulvic acids (extracted with 0.5 M NaOH solution), C_FA—carbon of fulvic acids (extracted with 2 M HCl solution), C_Humin—proportion of carbon in humins. The extraction of soluble organic matter (DOC and DON) was also determined. In the surface layer of grasslands, significantly higher mean contents of total organic carbon (TOC) and total nitrogen (Nt) were found compared with arable soils. In fluvisols used as grasslands, compared to the arable soils, significantly higher contents of C_dec, C_HA, C_FA, C_humin, DOC, DON, and C-stock were observed. The study results indicate that the agricultural use of environmentally valuable lands, such as floodplains, affected the stock of organic carbon and the properties of the humic substances. Grasslands stored significantly more SOC (10.9 kg m⁻²) than arable soils (6.7 kg m⁻²), emphasizing their role as organic carbon resevoirs. Agricultural practices such as limiting plowing and introducing grasslands can support carbon sequestration. Therefore, the role of fluvisols in floodplains in carbon sequestration should be emphasized in climate change mitigation strategies. Full article

The presence of silver nanoparticles (AgNPs) in water bodies has emerged as a new environmental concern and the efficient separation of these nanoparticles remains a critical challenge. Here, we developed novel magnetic nanoflocculants for the recovery of AgNPs from water. Alternating layers of biopolymers, in particular, chitosan, alginate, and polymeric bio-based soluble substances (BBS) derived from urban waste, were coated on magnetic nanoparticles via the layer-by-layer technique to prepare reusable magnetic nanoflocculants (MNFs). The MNFs obtained were characterized with diverse physicochemical techniques. Surface response methodology, based on the Doehlert matrix, has shown to be a useful tool to determine the effect of pH (in the range 5–9), concentration of AgNPs (7–20 mg L⁻¹), and MNFs (50–1000 mg L⁻¹) on the performance of AgNPs removal. The model predicts a high AgNPs removal percentage at low pH values and high MNF concentration. In particular, for the most efficient MNFs, 90% of AgNPs removal was obtained at pH 5 and 600 mg L⁻¹ MNF concentration. Additionally, the effects of AgNPs size, ionic strength, the presence of humic acids, and two types of surfactants (LAS anionic and TWEEN 20 nonionic) on the AgNPs removal were evaluated. Finally, recovery and reuse experiments showed that MNF made of Chitosan-BBS can be reused in ten cycles, losing only 30% of the initial removal capacity. Therefore, magnetic flocculation could represent a sustainable alternative for AgNPs separation with potential applications in water treatment and remediation of nanoparticle contamination. 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

This study aimed to evaluate the effect of soluble humic substances and plant-growth-promoting bacteria on the vegetative growth of Mombaça grass. A greenhouse experiment was conducted to study the effects of foliar applications of humic substances (0, 12, 24, 48, and 96 mg C L⁻¹) on the growth of Mombaça fifteen days after germination. After determining the optimal concentration range, a field trial was carried out in which humic substances at the best concentration were applied simultaneously with Herbaspirillum seropedicae strain UENF-H19 fifteen days after germination in three replicates. The best growth of Mombaça in the greenhouse was obtained with 48 mg C of the humic substance L⁻¹, which promoted a shoot fresh weight 80% higher than in the control treatment. The increase was almost identical to that observed during the 50-week field experiment in plots treated with humic substances combined with H. seropedicae. The treated plants produced an 81% higher shoot fresh weight than the control, with no dry mass, nitrogen content, or crude protein change during the one-year evaluation period. Despite the efficiency of the selected microbial inoculants under controlled-environment experiments, the agronomical significance under field conditions remains a subject of debate and improvement. The present study demonstrates that combining Herbaspirillum seropedicae with humic substances (plural) could significantly increase pasture production under field conditions. Full article

Agroecosystems play a crucial role in carbon sequestration and reducing atmospheric CO₂ emissions by storing organic carbon in soil. Soil fertility and productivity are essential for global crop demands and depend on soil organic matter, particularly humic substances (HS). HS is crucial for soil health and carbon sequestration as it involves the carbon cycle, supplies nutrients for plants, and reduces the emission of pollutants through microbial processes for the enhancement of CO₂ sequestration. Humification is a natural process of organic matter stabilization, playing a crucial role in maintaining soil organic content and carbon storage. Laccase is used to polymerize monomeric compounds such as phenols and their derivatives into highly polymerized HS. We screened five cellulose-degrading isolates, among which three strains demonstrate lignin-degrading capabilities. WSC-7 exhibited the highest laccase activity and showed a high similarity [99.51%] to Arthrobacter defluvii based on 16S rDNA analysis. Strain LiPK-078-5 in nutrient broth medium and WSC-7 in Difco Sporulation Medium exhibited optimal catalytic activity for catechol, indicating their efficiency for aromatic polymerization of soluble organic carbon. The addition of rice husk biochar with strains LiPK-078-5, WSC-6, and WSC-7 increased organic carbon content effectively. The synthesis of humic substances in soil through microbial processes increases soil carbon sequestration and reduces greenhouse gas emissions in the environment. 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

In this work, PM_2.5 was sampled at Dunkerque, a medium-sized city located in northern France. The mean concentration of PM_2.5 during the sampling period was 12.6 ± 9.5 μg·m⁻³. Samples were analyzed for elemental and organic carbon (EC/OC), water-soluble organic carbon (WSOC), humic-like substances (HULIS-C), water-soluble inorganic ions, and major and trace elements. The origin and the variations of species concentrations were examined using elemental enrichment factors, bivariate polar plot representations, and diagnostic concentration ratios. Secondary inorganic ions were the most abundant species (36% of PM_2.5), followed by OC (12.5% of PM_2.5). Secondary organic carbon (SOC) concentrations were estimated to account for 52% of OC. A good correlation between SOC and WSOC indicated that secondary formation processes significantly contribute to the WSOC concentrations. HULIS-C also represents almost 50% of WSOC. The determination of diagnostic ratios revealed the influence of anthropogenic emission sources such as integrated steelworks and fuel oil combustion. The clustering of 72 h air masses backward trajectories data evidenced that higher concentrations of PM_2.5, OC, and secondary inorganic aerosols were recorded when air masses came from north-eastern Europe and the French continental sector, showing the considerable impact of long-range transport on the air quality in northern France. Full article

This paper characterizes the composition of extracellular polymeric substances (EPSs) in different types of activated sludge (AS) processes and analyzes the biosorption of soluble organics when waste AS (WAS) is mixed with raw wastewater for primary carbon diversion. The fraction of AS organics identified as EPSs was 26% in a membrane bioreactor (MBR), 54% in conventional AS (CAS), and 51% in a trickling filter/solids contact (TF/SC) process. EPSs were found to be approximately 15% carbohydrates, 40% proteins, 40% humics, and 5% uronics in CAS and MBR AS. Biosorption was not correlated to the organic portion (VSS) of the WAS; however, statistically significant correlations were found for the total amount of EPSs (for TF/SC and CAS) and the protein fraction (for TF/SC and MBR) in the VSS. EPSs from different types of AS biosorbed the same amount of soluble organics, removing 1.43 ± 0.15 (n = 16) mg of soluble chemical oxygen demand (sCOD), and 1.20 ± 0.18 (n = 16) mg of truly soluble COD (ffCOD), per mg of cation exchange resin (CER) total extracted EPSs. Utilizing multiple extraction methods in series (CER–base–sulfide) increased EPS extraction yields by nearly 100% relative to CER alone and indicated different EPS fractionization for CAS (a smaller fraction of carbohydrates and a larger fraction of humics). Full article

Soil erosion results in dissolved organic matter (DOM) loss and is one of the main paths of soil carbon loss. Bacteria affect the generation and transformation of DOM. However, the effect of bacteria on the composition and slope distribution of DOM has rarely been investigated under field conditions. Based on a long-term experiment of three gradients (3°, 5°, 8°) in a black soil erosion area of Northeast China, the content, composition, and source of DOM were studied. The results showed that the DOM of the 3° and 5° slope was enriched midslope, and the DOM of the 8° slope was enriched downslope. Parallel factor (PARAFAC) analysis indicated that the main substances in DOM were fulvic-like acid, humic-like acid, tryptophan-like protein, and soluble microbial metabolites. The upslope and downslope soils of 3° and 5° slopes showed high DOM bioavailability, while the downslope soil of the 8° slope showed high DOM bioavailability. The content of new DOM in downslope soil increased with the gradient. Bacteria played an important role in the synthesis and transformation of DOM and affected its composition and slope distribution. Verrucomicrobiota, Firmicutes, Planctomycetota, and Gemmatimonadota were the main factors affecting soil DOM. The results could be helpful in understanding the loss mechanism of DOM in eroded black soil and provide support for soil carbon sequestration. Full article

The effluent discharged from wastewater treatment facilities frequently enters the ocean, posing a considerable threat to the health of marine life and humans. In this paper, an alkali lignin-based biochar-loaded modified Fe–Cu catalyst (FeCu@BC) was prepared to remove soluble microbial products (SMP) from secondary effluent as disinfection by-products precursors at ambient temperature and pressure. The humic acid (HA) was taken as the representative substance of SMP. The results showed that the maximum removal efficiency of HA reached 93.2% when the FeCu@BC dosage, pH, initial HA concentration, and dissolved oxygen concentration were 5.0 g/L, 7, 100 mg/L, and 1.75 mg/L, respectively. After three cycles, the removal efficiency of HA could be maintained at more than 70%. The quenching experiments and electron spin resonance (EPR) results showed that •OH and ¹O₂ were involved in the degradation of HA in the FeCu@BC catalyst reaction system, with ¹O₂ playing a dominant role. Theoretical calculations confirmed that •OH and ¹O₂ were more prone to attack the C=O bond of the side chain of HA. After processing by the FeCu@BC catalyst, the yield of chlorinated disinfection by-products from secondary effluent had decreased in an obvious manner. This study provides a new solution to efficiently solve the problem of chlorinated disinfection by-products from HA. Full article

To clarify the contribution of the bridging effect from three metal cations (K⁺, Mn²⁺, and Fe³⁺) on the humification of lignin-rich Tilia wood shavings and further enrich the theory of lignin humification, an indoor incubation method with constant temperature and humidity was adopted. K⁺, Mn²⁺, and Fe³⁺ served as additives, with CK as the control for studying the differential influence of metal cations with different valences on the humus composition of dark-brown soil mixed with Tilia wood shavings. The change in the C contents of water-soluble substance (C_WSS), humic-extracted acid (C_HE) and humin (C_Hu), ∆logK value of HE, atomic ratio and FTIR spectra of humic acid (HA), and the ratio of C content of humic acid to fulvic acid (C_HA/C_FA) of dark-brown soil mixed with Tilia wood shavings were analyzed after 0, 30, 80, and 150 days of incubation, and the following conclusions were reached: (1) The addition of metal cations, regardless of their valence, could effectively improve the microbial utilization and consumption of WSS, and the effect was as follows: Fe³⁺ > Mn²⁺ > K⁺. The addition of three metal cations could effectively inhibit mineralization and reduce the loss of TOC, and the effect could be seen as follows: Fe³⁺ > Mn²⁺ > K⁺. (2) Although the C_HE content first decreased and then increased with incubation, the addition of Fe³⁺ and Mn²⁺ ions increased the C_HE content, showing that Fe³⁺ > Mn²⁺, and K⁺ ions had no significant effect. Throughout the incubation, the structure of HE molecules changed first via a complex process and then through a simple process. Comparing the change before and after the incubation, the overall structure of HE molecules tended to be simpler with the CK control, and HE became more complicated with the addition of Fe³⁺ and Mn²⁺; however, the addition of K⁺ had little effect on the structure of HE molecules. (3) At the end of the incubation, the addition of Fe³⁺, Mn²⁺, and K⁺ ions strengthened the molecular condensation of HA and its aromatization degree, while the CK control without any added metal cations caused HA molecules to decompose and obtain a greater aliphatic degree. In addition, the number of O-containing functional groups and N-containing compounds in HA molecules increased to varying degrees regardless of which metal cation was added. The decomposition of Tilia wood chips led to a partial entry of the decomposition products into the HA component, which was then reconsumed by continuous mineralization. After incubation, the polysaccharides in HA molecules were consumed only with the addition of Mn²⁺ ions. Fe³⁺ and Mn²⁺ ions had greater advantages in increasing the C_HA/C_FA ratio and improving the humus quality than K⁺ ions. (4) The addition of metal cations could effectively inhibit the mineralization and decomposition of the Hu component, among which Fe³⁺ ions had the most significant effect, followed by Mn²⁺ ions. Compared to monovalent cations (K⁺), polyvalent cations (Fe³⁺ and Mn²⁺) had the advantage of a bridging effect, and their addition promoted the microbial utilization of WSS, effectively reduced the loss of TOC, increased the C_HE content, complicated its molecular structure, improved the humus quality, and inhibited the decomposition of Hu. Regardless of which metal cation was added, the degree of molecular polycondensation and aromatization of HA was enhanced, and the number of O-functional groups and N-containing compounds in HA molecules increased. Full article

Composting is an interesting option to recycle big quantities of organic waste because it helps to mitigate different environmental problems. Complementary characteristics of rice straw (RS) and sewage sludge (SS) create a suitable mixture to be used in a composting process. This work studies industrial-scale RS and SS composting to assess both its viability and optimization. Windrow composting was conducted during two seasons. The complete characterisation (moisture, pH, electrical conductivity, total, oxidisable and water-soluble organic carbon, humic substances, organic and mineral nitrogen, macronutrients, micronutrients, heavy metals) of starting materials, samples taken periodically and final composts were carried out. During the first season, an RS:SS ratio of 1:8 (w:w fresh weight) was used, which led to a process with adequate temperatures for biodegradation, but not for ensuring materials’ sanitation. During the second season, the RS:SS ratio was increased (1:6) to enhance the energy process and, thus, temperatures. Although this increase took place, degradation slowed down as oxidisable organic carbon and water-soluble organic carbon indicated. During both seasons, final composts presented adequate pH, high N-richness, and interesting macro- and micronutrient values. Notwithstanding, they also presented certain salinity and high ammonium contents, which must be considered for their field application. The obtained composts have interesting agronomic characteristics, which suggest their potential as an alternative to conventional fertilisers. 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