Humic Substances

Linking the humification of organic amendments with size aggregate distribution: Insights into molecular composition using FT-ICR-MS

Soil organic matter (SOM) plays a pivotal role in enhancing physical and biological characteristics of soil. Humic substances constitute a substantial proportion of SOM and their increase can improve crop yields and promote agricultural sustainability. While previous research has primarily assessed the influence that humic acids (HAs) derived from natural water have on soil structure, our study focuses on the impact of HAs on soil aggregation under different fertilizer regimes. During the summer cropping season, maize was cultivated under organic and synthetic fertilizer treatments. The organic fertilizer treatment utilized barley (Hordeum vulgare L.) and hairy vetch (Vicia villosa R.) as an organic amendment five days prior to maize planting. The synthetic treatment included a synthetic fertilizer (NPK) applied at South Korea's recommended rates. The organic treatment resulted in significant improvements in the soil aggregates and stability (mean weight diameter, MWD; p < 0.05) compared to the synthetic fertilizer application. These improvements could be primarily attributed to the increased quantity and quality of HAs in the soil derived from the organic amendment. The amount of extracted HAs in the organic treatment was nearly twice that of the synthetic treatment. Additionally, the organic treatment had a 140 % larger MWD and a 40 % increase in total phenolic content compared to the synthetic treatment. The organic treatment also had an increased macronutrient uptake (p < 0.001), an 11 % increase in aboveground maize biomass, and a 21 % increase in grain yield relative to the synthetic treatment. Thus, the enhancement of HA properties through the incorporation of fresh organic manure can both directly and indirectly increase crop productivity.

Hazardous or Advantageous: Uncovering the Roles of Heavy Metals and Humic Substances in Shilajit (Phyto-mineral) with Emphasis on Heavy Metals Toxicity and Their Detoxification Mechanisms

Shilajit is a phyto-mineral diffusion and semi-solid matter used as traditional medicine with extraordinary health benefits. This study provides a comprehensive data on Shilajit with emphasis on heavy metal profile, associated toxicities, and metal detoxification mechanisms by humic substances present in Shilajit. Data was searched across papers and traditional books using Google Scholar, PubMed, Science Direct, Medline, SciELO, Web of Science, and Scopus as key scientific databases. Findings showed that Shilajit is distributed in almost 20 regions of the world with uses against 20 health problems as traditional medicine. With various humic substances, almost 11 biological activities were reported in Shilajit. This phyto-mineral diffusion possesses around 65 heavy metals including the toxic heavy metals like Cu, Al, Pb, As, Cd, and Hg. However, humic substances in Shilajit actively detoxify around 12 heavy metals. The recommended levels of heavy metals by WHO and FDA in herbal drugs is 0.20 and 0.30 ppm for Cd, 1 ppm for Hg, 10.00 ppm for As and Pb, 20 ppm for Cu, and 50 ppm for Zn. The levels of reported metals in Shilajit were found to be lower than the permissible limits set by WHO and FDA, except in few studies where exceeded levels were reported. Shilajit consumption without knowing permissible levels of metals is not safe and could pose serious health problems. Although the humic substances and few metals in Shilajit are beneficial in terms of chelating toxic heavy metals, the data on metal detoxification still needs to be clarified.

Coupling between chromophoric dissolved organic matter and dissolved inorganic carbon in Indian estuaries

This study investigates the coupling between Chromophoric Dissolved Organic Matter (CDOM) and Dissolved Inorganic Carbon (DIC) in eighteen Indian estuaries across salinity gradient of the east and west coasts during the monsoon season, characterized by significant river discharge. The hypothesis that humic acids (HA) and fulvic acids (FA), prominent in estuarine CDOM, closely correspond to the 'organic alkalinity' (Aorg) component of total alkalinity is examined. In most estuaries, specifically those along the northeast coast (NE) and southwest coast (SW), a significant linear relationship exists between DIC, CDOM abundance, and pH level. Notably, minor estuaries along the southeast coast (SE) and northwest coast (NW) exhibit elevated DIC levels beyond what this relationship predicts. These estuaries also reveal heightened ammonium levels, increased δ15N values, and decreased δ13C values, indicative of anthropogenic influence. CDOM properties, such as spectral slope (S300-500) and spectral slope ratio (SR, S275-295:S350-400), align with these findings, with SE and NW estuaries displaying higher values. On average, CDOM contributes 110.5 μM (6.8 %) to DIC in NE, 390.7 μM (11 %) in SE, 24.4 μM (4.8 %) in SW, and 122.2 μM (4 %) in NW estuaries. The relationship between total alkalinity minus DIC (TA-DIC) and pH25 suggests that CDOM, mediated by HA/FA, buffers the inorganic carbon system in estuaries. This buffering capacity weakens at elevated DIC levels, and this condition is marked by anomalous SR values compared to the baseline salinity-SR linear regression. This Study suggests that estuarine CDOM could largely represent "organic alkalinity" and could help monitor acidification in estuaries.

Roles of organic matter transformation in the bioavailability of Cu and Zn during sepiolite-amended pig manure composting

The application of clay minerals facilitates the bioavailability of heavy metals and the humification in livestock manure composting. However, whether the humification plays a critical role in the bioavailability of heavy metals is still unclear. Here, with the addition of sepiolite (SEP), the fractions of Cu and Zn, and the spectral characteristics of humic acids (HAs) during aerobic pig manure composting were investigated. The SEP-amended composting had a decreased peak temperature and an increased electrical conductivity, regardless of the SEP dosage. The seed germination index increased by 15.9 ± 0.5% (p < 0.05) with the appropriate dosage of SEP (6%), indicating a higher maturity and a lower phytotoxicity of the SEP-amended compost. The addition of SEP reduced the water-extractable organic matter (WEOM) content and increased the percentage of HAs by 2.8-10.7%. More interestingly, during SEP-amended composting, the reducible fraction of heavy metals was transformed into the oxidizable fraction, and the bioavailability of Cu and Zn decreased by 11.0-15.9% and 15.4-26.5%, respectively. Ultraviolet-visible (UV-vis) spectra and fluorescence spectra analyses showed that the SUVA₂₅₄ and complex fluorescent components of HAs in the SEP-amended composting increased by 4.4-15.8% and 1.2-9.0%, respectively. Nuclear magnetic resonance (NMR) further confirmed that the addition of SEP increased the aromatic index and percentage of carbonyl-carboxyl C of HAs by 3.4-8.3% and 4.6-5.7%, respectively. The redundancy analyses (RDA) described the SUVA₂₅₄, aromatic index and carbonyl-carboxyl C of HAs had a strong positive correlation with the oxidizable fraction of heavy metals, which was further confirmed by variance partitioning analysis (VPA). Overall, this work suggested that the HAs structure play an important role in the bioavailability of Cu and Zn during SEP-amended composting, potentially providing safe organic fertilizer.

Effect of Operating Parameters on the Performance Evaluation of Benthic Microbial Fuel Cells Using Sediments from the Bay of Campeche, Mexico

Benthic microbial fuel cells (BMFC) are devices that remove organic matter (OM) and generate energy from sediments rich in organic nutrients. They are composed of electrodes with adequate different distances and floating air cathodes in an aqueous medium with saturated oxygen. In this study we proposed to design, build, analyze and evaluate a set of BMFCs with floating air cathodes to test the optimal distance between the electrodes, using sediment from the Bay of Campeche as a substrate. For the analysis of OM removal, COD tests, volatile solids (VS), E4/E6 study and FTIR analysis were performed. Power generation was evaluated through polarization curves, cyclic voltammetry and electrochemical impedance spectroscopy (EIS). We achieved a current density and power density at 10 cm depth of 929.7 ± 9.5 mA/m2 and 109.6 ± 7.5 mW/m2 respectively, with 54% removal of OM from the sediment, obtaining formation of aliphatic structures. BMFCs are proposed as adequate systems for bioremediation and power generation. The system at 10 cm depth and 100 cm distance between sediment and the floating air cathode had a good performance and therefore the potential for possible scaling.

Sorption of Fluorotelomer Sulfonates, Fluorotelomer Sulfonamido Betaines, and a Fluorotelomer Sulfonamido Amine in National Foam Aqueous Film-Forming Foam to Soil

During fire-fighter training, equipment testing, and emergency responses with aqueous film-forming foams (AFFFs), milligrams per liter concentrations of anionic, zwitterionic, and cationic per- and polyfluoroalkyl substances (PFASs) enter the environment. Because the behavior of zwitterionic and cationic PFASs in the subsurface is unknown, batch sorption experiments were conducted using National Foam AFFF, which contains anionic fluorotelomer sulfonates (FtSs), zwitterionic fluorotelomer sulfonamido betaines (FtSaBs), and cationic 6:2 fluorotelomer sulfonamido amine (FtSaAm). Sorption of the FtSs, FtSaBs, and 6:2 FtSaAm to six soils with varying organic carbon, effective cation-exchange capacity, and anion-exchange capacity was evaluated to determine sorption mechanisms. Due to the poor recovery of the FtSaBs and 6:2 FtSaAm with published PFAS soil extraction methods, a new soil extraction method was developed to achieve good (90-100%) recoveries. The 6:2 FtSaAm was depleted from the aqueous phase in all but one soil, which is attributed to electrostatic and hydrophobic interactions. Sorption of the FtSs was driven by hydrophobic interactions, while the FtSaBs behave more like cations that strongly associate with the solid phase relative to groundwater. Thus, the sorption mechanisms of the FtSs, FtSaBs, and 6:2 FtSaAm are more complex than expected and cannot be predicted by bulk soil properties.

Removal of organic matter and electricity generation of sediments from Progreso, Yucatan, Mexico, in a sediment microbial fuel cell

Sediment microbial fuel cells (SMFCs) are devices that generate electrical energy through sediments rich in organic matter (OM). The present study assessed the potential of sediments collected at two sites in Yucatan, Mexico, (the swamp of Progreso port and Yucalpetén dock) to be used in these electrochemical devices. Sediments were collected during the rainy and winter seasons and were monitored in the SMFC for 120 days through electrochemical and physicochemical characterization. OM removal in the SMFC ranged from 8.1-18.01%, generating a maximum current density of 232.46 mA/cm² and power density of 95.85 mW/cm². SUVA analysis indicated that with a young soil, the ratio E4/E6 presented evidence directly related to the degradation of aromatic and aliphatic compound formation, implying humification and, therefore, sediment enrichment.

Chitosan nanoparticles loaded the herbicide paraquat: the influence of the aquatic humic substances on the colloidal stability and toxicity

Polymeric nanoparticles have been developed for several applications, among them as carrier system of pesticides. However, few studies have investigated the fate of these materials in the environment in relation to colloidal stability and toxicity. In nature, humic substances are the main agents responsible for complexation with metals and organic compounds, as well as responsible for the dynamics of these nanoparticles in aquatic and terrestrial environments. In this context, the evaluation of the influence of aquatic humic substances (AHS) on the colloidal stability and toxicity of polymeric nanoparticles of chitosan/tripolyphosphate with or without paraquat was performed. In this study, the nanoparticles were prepared by the ionic gelation method and characterized by size distribution measurements (DLS and NTA), zeta potential, infrared and fluorescence spectroscopy. Allium cepa genotoxicity studies and ecotoxicity assays with the alga Pseudokirchneriella subcapitata were used to investigate the effect of aquatic humic substances (AHS) on the toxicity of this delivery system. No changes were observed in the physical-chemical stability of the nanoparticles due to the presence of AHS using DLS and NTA techniques. However some evidence of interaction between the nanoparticles and AHS was observed by infrared and fluorescence spectroscopies. The ecotoxicity and genotoxicity assays showed that humic substances can decrease the toxic effects of nanoparticles containing paraquat. These results are interesting because they are important for understanding the interaction of these nanostructured carrier systems with species present in aquatic ecosystems such as humic substances, and in this way, opening new perspectives for studies on the dynamics of these carrier systems in the ecosystem.

Pollutant toxicity and detoxification by humic substances: mechanisms and quantitative assessment via luminescent biomonitoring

The paper considers mechanisms of detoxification of pollutant solutions by water-soluble humic substances (HSs), natural detoxifying agents. The problems and perspectives of bioassay application for toxicity monitoring of complex solutions are discussed from ecological point of view. Bioluminescence assays based on marine bacteria and their enzymes are of special attention here; they were shown to be convenient tools to study the detoxifying effects on cellular and biochemical levels. The advantages of bioluminescent enzymatic assay for monitoring both integral and oxidative toxicities in complex solutions of model pollutants and HS were demonstrated. The efficiencies of detoxification of the solutions of organic oxidizers and salts of metals (including radioactive ones) by HS were analyzed. The dependencies of detoxification efficiency on time of exposure to HS and HS concentrations were demonstrated. Antioxidant properties of HS were considered in detail. The detoxifying effects of HS were shown to be complex and regarded as 'external' (binding and redox processes in solutions outside the organisms) and/or 'internal' organismal processes. The paper demonstrates that the HS can stimulate a protective response of bacterial cells as a result of (1) changes of rates of biochemical reactions and (2) stabilization of mucous layers outside the cell walls. Acceleration of auto-oxidation of NADH, endogenous reducer, by HS was suggested as a reason for toxicity increase in the presence of HS due to abatement of reduction ability of intracellular media.