Seasonal studies of aquatic humic substances from Amazon rivers: characterization and interaction with Cu (II), Fe (II), and Al (III) using EEM-PARAFAC and 2D FTIR correlation analyses.

Aquatic humic substances (AHS) are defined as an important components of organic matter, being composed as small molecules in a supramolecular structure and can interact with metallic ions, thereby altering the bioavailability of these species. To better understand this behavior, AHS were extracted and characterized from Negro River, located near Manaus city and Carú River, that is situated in Itacoatiara city, an area experiencing increasing anthropogenic actions; both were characterized as blackwater rivers. The AHS were characterized by 13C nuclear magnetic ressonance and thermochemolysis GC-MS to obtain structural characteristics. Interaction studies with Cu (II), Al (III), and Fe (III) were investigated using fluorescence spectroscopy applied to parallel factor analysis (PARAFAC) and two-dimensional correlation spectroscopy with Fourier transform infrared spectroscopy (2D-COS FTIR). The AHS from dry season had more aromatic fractions not derived from lignin and had higher content of alkyls moities from microbial sources and vegetal tissues of autochthonous origin, while AHS isolated in the rainy season showed more metals in its molecular architecture, lignin units, and polysacharide structures. The study showed that AHS composition from rainy season were able to interact with Al (III), Fe (III), and Cu (II). Two fluorescent components were identified as responsible for interaction: C1 (blue-shifted) and C2 (red-shifted). C1 showed higher complexation capacities but with lower complexation stability constants (KML ranged from 0.3 to 7.9 × 105) than C2 (KML ranged from 3.1 to 10.0 × 105). 2D-COS FTIR showed that the COO- and C-O in phenolic were the most important functional groups for interaction with studied metallic ions.

Anoxic nitrification with carbon-based materials as terminal electron acceptors.

This study investigates the potential of humic substances (HS) and graphene oxide (GO), as extracellular electron acceptors (EEA) for nitrification, aiming to explore alternatives to sustain this process in wastewater treatment systems. Experimental results demonstrate the conversion of ammonium to nitrate (up to 87 % of conversion) coupled to the reduction of either HS or GO by anaerobic consortia. Electron balance confirmed the contribution of HS and GO to ammonium oxidation. Tracer analysis in incubations performed with 15NH4+ demonstrated 15NO3- as the main product with a minor fraction ending as 29N2. Phylogenetic analysis identified Firmicutes, Euryarchaeota, and Chloroflexi as the microbial lineages potentially involved in anoxic nitrification linked to HS reduction. This study introduces a new avenue for research in which carbon-based materials with electron-accepting capacity may support the anoxic oxidation of ammonium, for instance in bioelectrochemical systems in which carbon-based anodes could support this novel process.

Humic Acid Derived from Agricultural Biomass Mitigates Alveolar Bone Loss and Modulates Systemic Inflammatory Cytokines in Rats with Periodontitis.

BACKGROUND: Humic acid (HA) is a bioproduct that can be extracted from different sources and has anti-inflammatory properties that have been little explored in the treatment and prevention of Periodontal Disease (PD). Thus, we aimed to investigate the effects of oral administration of HA on the progression of PD in rats. METHODS: Twenty-four male Wistar rats were distributed into three experimental groups (Control/ Sham, PD, and PD + HA). HA was administered by gavage (80 mg/kg/day) for 28 days, and PD was induced 14 days after the beginning of treatment. Bone loss, bone topography, and surface elemental composition were analyzed. Circulating IL1-beta, TNF-alpha, and IL-10 levels were evaluated through Enzyme-Linked Immunosorbent Assay (ELISA). RESULTS: The animals treated with HA showed lower bone loss (p < 0.05). Calcium and phosphorus levels on the alveolar bone surface were lower in the PD group (p < 0.05) compared to the control group, whereas the animals treated with HA exhibited attenuation in this loss (p < 0.05). The animals treated with HA showed reduced TNF-alpha, IL1-beta, IL-10, and the TNF-alpha/IL-10 ratio compared to those with PD (p < 0.05). CONCLUSION: Treatment with HA attenuated the parameters of alveolar bone loss and modulated systemic inflammatory parameters in rats with ligature-induced PD.

Role of the molecular structure of humified organic matter in rice plant response to environmental lead pollution.

Humified organic matter has been shown to decrease Pb toxicity in plants. However, there are still gaps in our understanding of the mechanism by which this phenomenon occurs. In this study, we aimed to assess the ability of humic substances (HSs), humic acids (HAs), and fulvic acids (FAs) to enhance defense mechanisms in rice plants under lead (Pb)-stressed conditions. HS fractions were isolated from vermicompost using the chemical fractionation methodology established by the International Humic Substances Society. These fractions were characterized by solid-state NMR and FTIR. Chemometric analysis was used to compare humic structures and correlate them with bioactivity. Three treatments were tested to evaluate the protective effect of humic fractions on rice plants. The first experiment involved the application of humic fractions along with Pb. The second comprised pretreatment with humic fractions followed by subsequent exposure to Pb stress. The third experiment involved Pb stress and subsequent treatment with humic fractions. The root morphology and components of the antioxidative defense system were evaluated and quantified. The results showed that HS + Pb, HA + Pb, and FA + Pb treatment preserved root growth and reduced the levels of O2- and malondialdehyde (MDA) in the roots by up to 5% and 2%, respectively. Pretreatment of the plants with humic fractions promoted the maintenance of root growth and reduced the contents of O2-, H2O2, and MDA by up to 48%, 22%, and 20%, respectively. Combined application of humic fractions and Pb reduced the Pb content in plant tissues by up to 60%, while pretreatment reduced it by up to 80%. The protective capacity of humic fractions is related to the presence of peptides, lignin, and carbohydrate fragments in their molecular structures. These results suggest that products could be developed that can mitigate the adverse effects of heavy metals on agricultural crops.

Selective sorption and desorption of DOM in Podzol horizons - DOC and aluminium contents of leachates from a column experiment.

Complexation of dissolved organic matter (DOM) with cations and minerals contributes to the stabilization of carbon in soils, and can enable the transport of metals in the environment. Hence, a proper understanding of mechanisms that control DOM binding properties in the soil is important for major environmental challenges, such as climate change and stream pollution. However, the role of DOM source in those mechanisms remains understudied. Here, we consider poorly drained tropical Podzols as a model environment to isolate effects of aluminium and DOM on sorption and desorption processes in podzolisation. We collected E- and Bh-horizons from a Brazilian coastal Podzol under tropical rainforest to conduct a column experiment, and percolated the columns with DOM collected from a stream (Stream), peat water (Peat), litter (Litter) and charred litter (Char). To quantify sorption and desorption from the columns, leachates were analysed for DOC content, aluminium content, pH, and the amount of fulvic acid relative to humic acid. The results showed large differences in DOC retention between DOM-types, which were consistent over all columns. Retention of DOC in the column varied between 25 % and 92 % for DOM-type Stream, between 33 % and 63 % for DOM-type Peat, between 22 % and 47 % for DOM-type Litter, and between 8 % and 49 % for DOM-type Char. Similarly, desorption from columns with B-horizon material highly differed between DOM-types. Percolation with DOM-types Stream and Peat caused a release of native DOC from B columns that was higher than in those percolated with water only. On the other hand, percolation of B columns with DOM-types Litter and Char caused a net DOC retention. These differences reflect that certain DOM-types hindered desorption, while other DOM-types caused active desorption. The large differences in sorption/desorption between DOM-types implies that changes in environmental conditions may highly influence the fate of soil carbon in Podzols.

Effect of the Addition of Humic Substances on Morphometric Analysis and Number of Goblet Cells in the Intestinal Mucosa of Broiler Chickens.

The mechanisms of action of humic substances (HS) as growth promoters in poultry are unknown. In this study, the productive performance, histology, and number of goblet cells (GC) in the intestinal villi of broilers under steady-state digestive conditions and under abrupt changes in diet with the addition of HS was evaluated. Broilers housed individually were offered three treatments from 14−28 days: 1 = diet with white corn/soybean meal, without growth promoter antibiotics (nonGPA); 2 = with GPA (GPA); and 3 = with 0.3% HS. At day 28, two diets were suddenly introduced: (A) white corn/soybean meal plus dried distillers' grains with solubles (DDGS); and (B) white/blue corn/soybean meal/DDGS, keeping the three original treatments. Diets A and B were also exchanged on day 37. FCR was lower with GPA and HS compared to nonGPA from 14−38 days (p < 0.05); at day 28, under steady-state digestive conditions, HS had a similar effect to GPA on the histology and GC number in the jejunum villi. The number of GC in the jejunum of HS-fed broilers on days 29 and 38, after diet changes, behaves similarly to that of AGP-fed broilers (p > 0.05). HS appears to strengthen the mucosal protection of the epithelium of the intestine.

Macronutrients, iron and humic substances summer cycling over the extended continental shelf of the South Brazil Bight.

We surveyed macronutrients and dissolved iron (DFe) concentrations and speciation in a transect over the shelf of the South Brazil Bight (SBB) at Santa Marta Grande Cape (SE Brazil) during a coastal downwelling episode. Driven by dominant NE winds, coastal downwelling is a common feature during the austral summer and force after water convergence, with contribution of internal wave breaking at the shelf edge, upwelling of macronutrients into the nutrient-depleted waters of the southbound Brazil Current at ~100 km from the coastline. As a result, we found a plume of high turbidity that reached the euphotic layer, a deepening of the silicate, nitrate, and phosphate isolines over the shelf and a bulging of the nitrate and phosphate isolines over the shelf edge and the slope. Our first measurements of DFe concentration and speciation in the area revealed that against prior findings in other coastal areas, macronutrients, DFe, and iron ligand cycles were disentangled. Higher DFe concentrations were often found at the surface indicating aerial deposition. Secondary DFe maxima over the sediment-water interface and in the upwelled plume indicated DFe fluxes from the sediment and from resuspended instable colloids. Iron ligand concentrations were higher than DFe concentrations in most stations with a clear land-to-ocean gradient. Subtraction of HS iron ligands revealed that except in upwelled water, the bulk of surface ligands was the result of local biological processes. The analysis of the concentrations of Fe-HS complexes showed that the contribution of HS to DFe was dominant in upwelled waters, significant in waters close to the coast, but nearly negligible in the rest of the studied area. We hypothesize that the injection of iron-humic complexes into the euphotic layer during summer upwelling episodes is the key to understanding the persistent high chlorophyll meanders found over the shelf edge of the SBB coast.

Effect of the application of vermicompost and millicompost humic acids about the soybean microbiome under water restriction conditions.

Humic substances (HSs) are constituent fractions of organic matter and are highly complex and biologically active. These substances include humic acids (HA), fulvic acids (FA), and humin. HS are known to stimulate the root system and plant growth and to mitigate stress damage, including hydric stress. Humic acids have already been reported to increase microbial growth, affecting their beneficial effect on plants. However, there is scarce information on whether HA from vermicompost and millicompost, along with Bradyrhizobium, improves the tolerance of soybean to water restriction. This study aimed to evaluate the responses of soybean plants to the application of vermicompost HA (HA-V) and millicompost (HA-M) along with Bradyrhizobium sp. under water restriction. The experiment was carried out in a greenhouse, and the treatments received Bradyrhizobium sp. inoculation with or without the application of HA from vermicompost and millicompost with or without water restriction. The results showed that HA provided greater soybean growth and nodulation than the control. The application of HA-M stimulated an increase in the richness of bacterial species in roots compared to the other treatments. After the application of water stress, the difference between the treatments disappeared. Microbial taxa were differentially abundant in plants, with the fungal fraction most affected by HA application in stressed roots. HA-V appears to be more prominent in inducing taxa under stress conditions. Although the results showed slight differences between HA from vermicompost and millicompost regarding plant growth, both humic acids promoted an increase in plant development compared to the control.

Effect of short-term pig slurry amendment of soil on humified organic matter and its relationship with the dynamics of heavy metals and metals uptake by plants.

The impact of pig slurry (PS) application on the structural dynamics of humic substances (HS) and on the mobility of Cu, Zn, Ni, and Pb in a dystrophic Red Nitosol planted with winter forage grasses was evaluated. After four PS applications, the humic acids (HA) and fulvic acids (FA) were characterized by spectroscopy techniques allied to chemometrics methods. The metals contents in soil, in HS and in the tissues of plant were quantified. PS application increases the total organic carbon, especially the nonhumic carbon, which contribute to increase FA content. The carbon in FA and HA increases with the highest PS dose applied, especially aliphatic structures in FA and aromatic structures in HA. The amount of Pb and Cu in FA and HA increases respectively, as well as Cu, Zn, Ni, and Pb bioavailable. PS applications increase the biomass production in grasses and the metals content accumulated in the tissues. Our study shows that the PS application modifies the structure of SOM, incorporating fragments, and modifying its dynamics, which regulates the dynamics and the accumulation of metals in soils and plants. The association of metals with soluble structures seems to inactivate their toxicity and does not affect plant growth.

Spectroscopic-chemometric modeling of 80 humic acids confirms the structural pattern identity of humified organic matter despite different formation environments.

The structure of humic substances (HSs) and the humification process are critical topics for understanding the dynamics of carbon on the planet. This study aimed to assess the structural patterns of 80 humic acid (HA) samples isolated from different soils, namely, Histosols, Ferralsols, Cambisols, Mollisols, Planosols and vermicompost, by spectroscopic characterization using solid-state 13C nuclear magnetic resonance cross-polarization/magic angle spinning combined with chemometric techniques. All 80 HAs had a similar structural pattern, regardless of their source of origin, but they had different relative quantities of organic C species. The different structural amounts of the various organic C fractions generated different properties in each of the HAs. This explains why there were similarities in the HS functions but why the intensities of these functions varied among the samples from the different soil types and environments, confirming that HSs are a group of compounds with a structural identity distinct from the molecules that give rise to them. There appears to be no single definition for the humification process; therefore, for the soils from each source of origin, a specific humification process occurs that depends on the characteristics of the local environment. Humification can be understood as a process that is similar to a chemical reaction, where the key factor that determines the formation of the products is the structural characteristics of the reactants (organic substrates deposited in the soil). The degree to which the reaction progresses is governed by the reaction conditions (chemical, physical, and biological properties of the soil). The structural patterns for HSs obtained in this study justify the existence of HSs structured as self-assembled, hydrophilic and hydrophobic domains that, under certain conditions, can undergo transformations, altering the balance of organic carbon in the environment.

Hatching under brownification: DOC-mediated changes in physical, but not chemical properties of water affect hatching patterns of Cladocera resting eggs.

Dissolved organic carbon (DOC) is often related to the brownification of water in continental aquatic systems and to changes in the physiology of zooplankton organisms. Zooplankton resting eggs are particularly sensitive to changes in light and chemical characteristics of water, but the physical and chemical effects associated to DOC on dormant stages have never been tested before. Herein, we tested how DOC affects hatching rates and time to hatching of Cladocera (Diaphanosoma birgei) resting eggs. In order to analyze the chemical (i.e., toxic) and physical (i.e., light attenuation) effects of DOC on hatching patterns, resting eggs were exposed to different concentrations of DOC (0, 50, and 100 mg L-1) in an experimental design which isolated chemical from physical effects. When evaluating the physical effects of DOC, hatching was more than 150% less in 100 than 50 mg L-1 DOC and time to hatching was 66% lesser in 50 mg L-1 DOC than control. Hatchling numbers and time to hatching were not affected by DOC chemical effects. We conclude DOC effects on hatching mainly relied on light attenuation, while chemical effects were likely of minor importance. DOC may change Cladocera emergence patterns mainly through light attenuation in the water column.

Organic onion growth, yield and storage improved by foliar sprays of microalgae and fulvic acid as a natural biofertilizer

The use of microalgae as natural biofertilizer in horticulture has recently been reported, while the use of humic substances is widespread. However, the combined use of microalgae with humic substances applied to plant leaves is still unexploited. Thus, the objective of this work was to combine fulvic acid (FA) with the Scenedesmus subspicatus microalga biomass (SC) as a natural biofertilizer applied via leaf in two onion cultivars in organic system. Four experiments were conducted: i) bioassays to verify the bioactive effect of FA, SC and combinations using the Vigna radiata model plant; ii) greenhouse pot experiment with foliar applications of FA, SC and combination in two onion cultivars; iii) field experiment in organic system with foliar applications of FA, SC and combination in two onion cultivars; and iv) onion bulb storage experiment. The bioactive effect of SC, FA and their combinations was identified by promoting changes in root growth of V. radiata. In pots, treatments containing FA, SC and combination promoted increase in fresh and dry leaf mass. The foliar application of FA, SC and combination promoted an increase in field bulb productivity, reduced mass loss in stored bulbs and increased carbohydrate, amino acid and protein contents in onion bulbs.

Biochar increases soil carbon pools: Evidence from a global meta-analysis.

Biochar is a carbon-rich material that increases soil C sequestration and mitigates climate change. However, due to the variability of experimental conditions, types of biochar and soil, the influence of biochar on the accumulation of different soil carbon fractions remains unclear. Therefore, a meta-analysis was performed that included 586 paired comparisons obtained from 169 studies conducted in various countries around the globe. The data set average showed significant relative increases of 64.3, 84.3, 20.1, 22.9 and 42.1% for total C, organic C, microbial biomass C, labile C and fulvic acid, respectively. The dissolved organic C, humic acid and humin fractions showed no significant variations. The relative increase in TC was favored by increasing biochar rates applied to fine-textured soils with low C content in temperate climate regions seen through short-term experiments conducted under controlled conditions. This behavior was different for each soil C fraction. Therefore, variations between experimental conditions, types of biochar and soil show that it is necessary to consider multiple factors when choosing the conditions of biochar use to maximize C sequestration in the soil and/or the increase of labile C fractions in the soil.

Comparison between Aliivibrio fischeri and activated sludge microorganisms in the evaluation of the toxic pollutants of leachates from Brazilian landfills.

Ecotoxicological assessment of landfill leachate has become a priority to determine its impacts on the ecosystem. Toxicity assays with microorganisms stand out due to their quick response, low cost and ease of testing. In this context, the present study evaluated the acute toxic effects of leachates from two landfills of different ages and modes of operation to bacterium Aliivibrio fischeri and activated sludge microorganisms and the ammonia nitrogen and humic substances (HS) sensitivity to these organisms. Reductions greater than 30% in leachate toxicity were observed after ammonia removal for A. fischeri and activated sludge microorganisms. After 97% removal of HS, the greater reductions in toxicity (44.28 to 79.82%) were verified for microbial species studied, indicating that the organic compounds (measured as chemical oxygen demand, total organic carbon and humic substances) were the primary pollutants responsible for the toxicity of the leachates. Concerning the organisms studied, A. fischeri showed greater sensitivity to the leachates' pollutants compared to the activated sludge microorganisms. Nevertheless, a strong correlation was observed between A. fischeri and activated sludge microorganisms' toxicity responses, suggesting that respirometry assay can be used to determine leachate toxicity.

Growth Performance and Tibia Mineralization of Broiler Chickens Supplemented with a Liquid Extract of Humic Substances

The objective of the study was to evaluate the productive, carcass, and tibia mineralization responses in broiler chickens supplemented with a liquid extract of humic substances (HS) in the drinking water. Chicks were housed in holding cages from 8-42 days of age and were randomly assigned to one of five increasing HS levels in the drinking water (0, 161, 322, 483, and 644 µg/L). At 21 and 42 days, to obtain carcass and tibia measurements half of the broilers were slaughtered. ANOVA and linear regression were used to analyze the data. The HS chemical composition and flat structures were estimated. At 21 days, increasing levels of HS in the drinking water resulted in a cubic response on breast weight (p<0.05), tibia ashes percentage (p<0.05) and tibia Ca percentage, as well as a linear increasing response (p<0.05) on P percentage. HS elicited a quadratic response on the tibia DM percentage (p<0.05), Ca content (p<0.01), and P content (p<0.05) at 42 days. The optimal HS supplementation level to achieve the highest tibia DM percentage, Ca and P content were 345.00, 322.46, and 347.75 µg/L, respectively. Increasing HS levels also resulted in a cubic response in tibia Ca (p<0.05) and P percentage (p<0.01). In conclusions, HS supplementation in drinking water improved bone mineralization in broiler chickens at 21 and 42 days of age.(AU)

Responses of Broiler Chickens Fed Low or High Non-Starch Polysaccharide Diets and the Addition of Humic Substances from a Worm Compost

The objective was to evaluate the productivity, microbiology and histopathology of the jejunum, ceca and liver in broilers fed a control or a high non-starch polysaccharide (HNSPs) diet added with an extract of humic substances (EHS). 240 broilers individually allocated, from 21-42 d of age were assigned to a factorial arrangement of 2 types of diets: 1) A corn/soybean meal diet (Control) and 2) As Control plus 7% distillers dried grain with solubles and 12% of wheat bran (HNSPs), and 3 growth promoters: 1) Antibiotic growth promoters (AGP); 2) without AGP (NAGP) and C) with 0.5% of EHS. At the end of the trial, the breast and carcass were weighed and samples of the intestine, ceca and liver were taken for microbial and histopathology analysis. Results were subjected to ANOVA. EHS-fed broilers had lower feed conversion ratio (FCR) and total aerobic bacterial (TAB) counts in the liver and higher ashes digestibility with the Control diet, but negative responses were seen with the HNSPs diet (Type of diet and growth promoter interaction, p≤0.05). The lesion scores in the jejunum were lower in EHS-fed broilers with the Control and HNSPs diet (p≤0.05). The TAB and E. coli were lower in the jejunum and ceca of AGP-fed broilers (p<0.01) compared to NAGP and EHS groups. EHS-fed broilers showed improved FCR and ileal ashes digestibility and lower TAB in the liver with the Control diet and had lower lesion score in the jejunum and similar weight gain compared to the AGP-fed broilers.(AU)

Addition of Different Levels of Humic Substances Extracted from Worm Compost in Broiler Feeds.

Different sources and inclusion levels of humic substances (HS) have been tested in broiler rations as an alternative to the addition of growth promoter antibiotics (GPA) with promising results. The current study was carried out to assess the influence of HS extracted from worm compost on broiler production parameters, carcass yield, tibia characteristics, lactic acid bacteria (LAB) counts, excretion of Eimeria oocysts, and antioxidant status of breast meat. A total of 1200 broilers were used, housed in groups of 30 per pen, and assigned to five treatments: 1 = basal diet with GPA (positive control), 2 = basal diet without GPA (negative control), 3-5 = basal diet with 0.15, 0.30, and 0.45% HS, respectively. The data was subjected to a variance analysis and orthogonal contrasts. The FI decreased linearly (p < 0.05) from 1-14, 29-42, and 1-42 days as the inclusion of HS in the feed increased. The FCR had quadratic responses (p < 0.01) from 29-42 and 1-42 days concerning the HS inclusion levels. Lactic acid bacteria was higher (p ˂ 0.05) in ten-day-old chicks with 0.45% HS in the diet. The 1,1-diphenyl-2-picrylhydrazyl radical scavenging activity antioxidant potential decreased linearly (p < 0.05) concerning increasing HS in the feed. The results indicate that HS can be used as growth promoters in broiler feeds.

Environmental implications of the organic matter structure for white-rot fungus Pleurotus eryngii growth in a tropical climate.

White-rot fungi (Pleurotus eryngii) are decomposers of lignocellulosic substrates. The relationship between the structure of humified organic matter and P. eryngii growth, is poorly understood. This study aimed to evaluate the relationship between the growth and development of white-rot fungi (P. eryngii) in two structurally different sources of humified organic matter. Fungus growth and development (mycelium diameter, fresh and dry mycelium mass, mycelium density, and biological yield) were evaluated in experiments with the application of humic substances (HS) extracted from vermicompost (VC) and peat. Both HS were characterized by CP/MAS 13C NMR spectroscopy associated with chemometrics analysis. The HS present different structural characteristics, with those extracted from VC having a predominance of functionalized C-aliphatics (carbohydrates), low hydrophobicity, and a 90% proportion of cellulose/hemicellulose carbon in the composition. HS extracted from peat have a predominance of C-aromatics (lignin fragments), higher hydrophobicity, and a proportion of lignin carbon of up to 80%. The results showed that P. eryngii growth is dependent on the C-cellulosic and C-lignin balance. HS extracted from lignin-rich peat regulates the fungus growth at initial times and sometimes inhibits the biological performance. The highly cellulosic HS from VC regulate the fungus growth at later times and its biological performance.

Influence of humic acid structure on the accumulation of oxyfluorfen in tropical soils of mountain agroecosystems.

Herbicide application is a practice commonly used in agricultural systems because it is an efficient method of weed control. An inherent characteristic of some herbicides used in mountain agriculture, such as oxyfluorfen, is high adsorption to soil organic matter (SOM). Thus, intensive management that changes the quantity and quality of SOM, such as soil tillage and the massive application of organic fertilizers such as poultry litter, may favor soil contamination by this herbicide and alter its dynamics in the environment. Therefore, this study aimed to characterize the structures of humic substances (HSs) in the soil of forest areas and areas with intensive production of vegetables, relating them to the accumulation of the herbicide oxyfluorfen in tropical mountain agroecosystems. Organic carbon content was quantified in HSs, humic acid (HAs) were structurally characterized by CP/MAS 13C-NMR spectroscopy, and the oxyfluorfen molecule was detected and quantified using the QuEChERS residue detection method with subsequent analysis by LC-MS/MS. Oxyfluorfen was not detected in the forest areas, but it was detected in the vegetable growing areas at points with the lowest slope and high contents of organic matter and clay, with values of up to 0.13 mg kg-1. The intensification in the SOM mineralization process, promoted by the intensive management adopted in the vegetable growing areas, resulted in a 16.46% reduction in COT, a 58.84% reduction in the carbon content in the form of SH and a reduction in the structures that give recalcitrance to the HA molecule (CAlkyl-H,R, CCOO-H,R, CAromatic-H,R, and CAromatic-O) when compared to those values in the forest area, presenting HAs with more aliphatic and labile properties. Thus, due to the structural characteristics of the HAs in the vegetable production areas, the herbicide oxyfluorfen showed a close relationship with the more aliphatic oxygenated structures, namely, CAlkyl-O,N, CAlkyl-O and CAlkyl-di-O.

Composting of swine production chain wastes with addition of crude glycerin: organic matter degradation kinetics, functional groups, and carboxylic acids.

Little is known about the effect of adding crude glycerin (CG) as a carbon source during the composting of agro-industrial residues, such as those generated in the swine production chain, especially concerning the impact on organic matter humification. Therefore, the aim of this work was to study the effect of adding crude glycerin during the composting of organic swine waste, using appropriate analyses to determine the degree of maturation of the organic material. The experiment was performed using composters constructed from pallets. The variables considered were temperature, mass, volume, organic matter, functional groups, carboxylic acids, pH, electrical conductivity, total organic carbon, total Kjeldahl nitrogen, total phosphorus, potassium, basal respiration, and germination index. For all the CG concentrations tested, thermophilic temperatures were reached, while higher amounts of CG (4.5 and 6.0%) maintained temperatures above 55 °C for longer periods (28 days). Fourier transform infrared spectroscopy analysis showed the presence of an aromatic stretching vibration signal at 1620 cm-1, confirming mineralization of the organic matter, while the decrease of carboxylic acids at the end of the composting period indicated stabilization. The organic composts presented high nutrient contents and absence of toxicity, indicating that they could be safely used in agriculture.