Complementary multianalytical approach to study the distinctive structural features of the main humic fractions in solution: gray humic acid, brown humic acid, and fulvic acid

Fulvic acid alleviates the stress of low nitrogen on maize by promoting root development and nitrogen metabolism

The potential of fulvic acid (FA) to improve plant growth has been acknowledged, but its effect on plant growth and nutrient uptake under nutrient stress remains unclear. This study investigated the effects of different FA application rates on maize growth and nitrogen utilization under low nitrogen stress. The results showed that under low nitrogen stress, FA significantly stimulated maize growth, particularly root development, biomass, and nitrogen content. The enhanced activity levels of key enzymes in nitrogen metabolism were observed, along with differential gene expression in maize, which enriched nitrogen metabolism, amino acid metabolism and plant hormone metabolism. The application of FA regulated the hormones' level, reduced abscisic acid content in leaves and Me-JA content in roots, and increased auxin and zeatin ribose content in leaves. This study concludes that, by promoting root development, nitrogen metabolism, and hormone metabolism, an appropriate concentration of FA can enhance plant tolerance to low nitrogen conditions and improve nitrogen use efficiency.

Accumulation of Ag(0) Single Atoms at Water/Mineral Interfaces during Sunlight-Induced Reduction of Ionic Ag by Phenolic DOM

Silver (Ag) undergoes a complex and dynamic Ag+/Ag0 cycle under environmental conditions. The Ag+ → Ag nanoparticles (AgNPs) transformation due to the combined actions of sunlight, O2, and dissolved organic matter has been a well-known environmental phenomenon. In this study, we indicate that this process may be accompanied by a pronounced accumulation of Ag(0) single atoms (Ag-SAs) on the minerals' surfaces. According to spherical aberration-corrected scanning transmission electron microscopy and high-energy-resolution X-ray adsorption fine structure analyses, humic acid (HA) and phenol (PhOH) can induce Ag-SAs accumulation, whereas oxalic acid causes only AgNPs deposition. Ag-SAs account for more than 20 wt % of total Ag(0) on the γ-Al2O3 surfaces during HA- and PhOH-mediated photolysis processes. HA also causes Ag-SAs to accumulate on two other prevalent soil minerals, SiO2 and Fe2O3, and the fractions of Ag-SAs are about 15 wt %. Our mechanism studies suggest that a phenolic molecule acts as a reducing agent of Ag+ and a stabilizer of Ag-SAs, protecting Ag-SAs against autocatalytic nucleation.

Pyrolysis of municipal solid waste compost: Pilot plant evaluation as a sustainable practise of waste management

To evaluate the potential of compost based on municipal solid waste (MSW) and 20% legume pruning under a pyrolysis process, generated products, including solids (biochar), liquids (bio-oil), and gases (non-condensable gases), through experimentation in a pilot plant with a fluidized bed reactor at 450°C and gas chromatography/mass spectrometry have been analysed. In addition, the compost kinetic behaviour by thermogravimetric analysis (TGA), using the Flynn-Wall-Ozawa (FWO) method, has been investigated. Four different reaction zones, associated with lignocellulosic materials (hemicellulose, cellulose, and lignin) with a first step for water evaporation, in TGA curve have been observed. A biochar with low stability and aromaticity, considering high and low O/C and H/C ratios, respectively, has been obtained. The obtained pyrolytic liquids contain a high concentration of phenolic compounds because of a significant presence of lignins and other high molecular weight compounds in the original material. Moreover, the generated non-condensable gases consist mainly of short-chain compounds, such as alcohols, aldehydes, and alkenes produced from hemicellulose, cellulose, and proteins.

Hydrothermal synthesis of similar mineral-sourced humic acid from food waste and the role of protein

Food waste is a challenging biomass resource due to its high moisture content, low calorific value, and complex composition. Natural humification of animal and plant residues is highly related to microorganism activity, but natural hydrothermal conditions are also speculated to play a significant role. In this work, a novel method for the conversion of food waste into artificial humic acid (HA_a) under hydrothermal conditions is proposed. The results revealed that an optimum HA_a yield of 43.5% from food waste was successfully obtained at 215 °C for only 1 h. Detailed analyses, including elemental analysis (EA), X-ray photoelectron spectroscopy (XPS), nuclear magnetic resonance (NMR), and Fourier transform infrared (FT-IR) spectroscopy, showed that the produced HA_a had similar structures and compositions with natural HA extracted from minerals. Moreover, the proteins contained in the food waste significantly promoted HA formation through the reaction of saccharides with amino acids, in which Maillard-like reactions were the key steps. These results not only provide experimental evidence for verifying the role of hydrothermal reactions in transforming food waste into humic acid but also provide insight into effective resource utilization of food waste.

Dispersion and transport of microplastics in three water-saturated coastal soils

The coastal area is one of the key zones for transport and fate of microplastics (MPs). This study investigated the transport behaviors of different sized MPs in three water-saturated coastal soils, with the aim to explore effects of properties of three different coastal soils on the dispersion and migration of three-sized MPs (0.3, 0.5, and 1 µm). All three-sized MPs had the strongest dispersion in Soil 3 solution, followed by that in Soil 1 solution and then that in Soil 2 solution. The strongest dispersion of MPs in Soil 3 solution was attributed to the lowest ionic strength. Such a high dispersion favored MPs movement in soil solution but readily be sorbed and fixed by rich Fe and Al oxides in Soil 3 solid through strong electrostatic attraction, leading to the lowest transport rate (20.5-41.2%). The high ionic strength in the Soil 1 solution decreased the dispersion of MPs, but the presence of high content of humic acid enhanced the electrostatic repulsion and steric hindrance between MPs and soil particles, resulting in the highest transport ability of MPs in Soil 1 (39.4-72.5%). The large amount of dissolved Ca²⁺ and Mg²⁺ in Soil 2 solution favored MPs bridged with fulvic acid, resulting in the highest aggregation of MPs and relatively lower transport ability (34.1-49.6%). Large-sized MPs had higher electrostatic repulsion between the particles, thus increasing the dispersion and transport capacity of MPs in soil. Modeling showed the experiment-consistent results that Soil 3 had the lowest MPs transport after 600 mm of heavy rainfall, with the maximum migration distance of 7.50-10.5 cm, which was smaller than that in Soil 2 (8.10-12.0 cm) and that in Soil 1 (9.00-18.3 cm). These results indicated that MPs transport in coastal soil is significant and soil solution and solid composition plays an important role in the dispersion and transport of MPs, respectively. These findings afforded a great basis for the assessment of the fate and risk of MPs in coastal areas.

Effect of Organic Substances on Nutrients Recovery by Struvite Electrochemical Precipitation from Synthetic Anaerobically Treated Swine Wastewater

Anaerobically treated swine wastewater contains large amounts of orthophosphate phosphorus, ammonium nitrogen and organic substances with potential nutrients recovery via struvite electrochemical precipitation post-treatment. Lab-scale batch experiments were systematically conducted in this study to investigate the effects of initial pH, current density, organic substances upon nutrients removal, and precipitates quality (characterized by X-ray diffraction, scanning electron microscopy and element analysis via acid dissolution method) during the struvite electrochemical precipitation process. The optimal conditions for the initial pH of 7.0 and current density of 4 mA/cm² favoured nutrients removal and precipitates quality (struvite purity of up to 94.2%) in the absence of organic substances. By contrast, a more adverse effect on nutrients removal, morphology and purity of precipitates was found by humic acid than by sodium alginate and bovine albumin in the individual presence of organic substances. Low concentration combination of bovine albumin, sodium alginate, and humic acid showed antagonistic inhibition effects, whereas a high concentration combination showed the accelerating inhibition effects. Initial pH adjustment from 7 to 8 could effectively mitigate the adverse effects on struvite electrochemical precipitation under high concentration combined with organic substances (500 mg/L bovine albumin, 500 mg/L sodium alginate, and 1500 mg/L humic acid); this may help improve struvite electrochemical precipitation technology in practical application for nutrients recovery from anaerobically treated swine wastewater.

Thermogravimetry Applicability in Compost and Composting Research: A Review

Composting could be a suitable solution to the correct treatment and hygienization of several organic waste, producing compost that can be used in agriculture. The evolution and maturity of this process has been studied using a variety of techniques. One very promising technique for these studies is thermogravimetric analysis. On the other hand, the compost can be used for a variety of purposes different to the agricultural one, such as direct energy by combustion or energy and products by pyrolysis and its suitability can be measured by thermogravimetric techniques. With these goals, a bibliographic analysis has been done, applying Preferred Reporting Items for Systematic Reviews and Meta-Analyses PRISMA methodology, to the use of thermogravimetric equipment applied to the study of composting and compost uses. According to the methodology for PRISMA systematic reviews, the following databases have been searched Google Scholar, Web of Science, Mendeley, Microsoft Academic, World Wide Science, Science Direct, IEEE Xplore, Springer Link, Scopus, and PubMed by using the terms “thermogravimetry AND (compost OR composting) AND NOT plastic”.

New insights into interactions of organic substances in poultry slurry with struvite formation: An overestimated concern?

The high content of organic substances in strength agro-industrial wastewater has been documented to be among the major barriers hampering nutrient recovery efficiency of struvite precipitation. However, our results in this study show that the previously reported negative impacts of organic substances in high-strength agricultural wastewater on struvite precipitation might be overestimated. This study is the first to test the influence of three forms of organic substances from real high-strength wastewater that contains a complex of particulate, colloidal and soluble organic substances, on nutrient recovery efficiency and product quality through struvite precipitation at varying pH conditions. Our results demonstrated that the inhibition of organic substances on struvite formation only happens at the pH levels of <9.0 with recovery reduction of PO₄^3- (5-15%) and NH₄⁺ (6-13%). The inhibitory effect of the organic substances at the optimal pH range (9.5-10) reported from the literature review is only ≤5%. Moreover, the transformation in the contents of humic- and protein-like substances with an increment in pH was characterized and may contribute to mitigate the inhibition of nutrient recovery. Even though the particulate and colloidal organic substances slowed the precipitation reaction, they substantially increased the particle size (i.e., 70% and 40%, respectively) of the formed struvite. The presence of organic substances in all tested forms does not significantly influence the purity and crystalline structure of struvite which can still be used as a slow-releasing fertilizer. Regarding the relocation process of organic substances during struvite precipitation under varying pH conditions, understanding the interaction between organics and heavy metals which in turn affect the dynamics of heavy metals in solution and precipitates remains limited; thus, additional research is needed.

Extraction of Fulvic Acid from Lignite and Characterization of Its Functional Groups

Fulvic acid (FA) is a complex organic mixture composed of small molecules. The structure and composition of FA vary greatly because of the different raw materials used for preparing FA. In this work, FA was extracted from shallow low-rank lignite by hydrogen peroxide (H2O2) in a microwave field, and the functional groups of FA were characterized. The optimal extraction process was determined, with the H2O2 concentration being the key factor affecting the yield of FA. Thermogravimetric analysis showed that FA was mainly composed of low molecular weight and readily pyrolyzed compounds. As shown by Fourier transform infrared spectroscopy, in the process of FA extraction by H2O2 oxidation of lignite, the content of -COOH increased, long-chain aliphatic compounds decreased, stretching vibrations of aromatic ring skeletons disappeared, and aromatic ring substitution became mainly tri- or disubstitution. Fluorescence spectroscopy indicated that FA had a low degree of aromaticity. X-ray photoelectron spectroscopy qualitatively and quantitatively revealed that the main modes of carbon-oxygen bonding in FA were C-O-, COO-, and C=O. Thus, this study not only lays a foundation for studying the composition and structure of coal-based FA but also opens a new avenue for a clean and efficient utilization of lignite.

Stability of Nano-ZnO in simulated landfill leachate containing heavy metal ions

As the presence of nanosized zinc oxide particles (nano-ZnO) in landfill leachate increases, their interaction with coexisting heavy metal ions (HMs) also increases. The interface interaction between nano-ZnO and HMs will influence nano-ZnO stability and therefore affect its bioavailability and environmental impact. In the present study, we investigated the effects of Cu(II), Cr(III), and Cr(VI) ions on the aggregation, sedimentation, and dissolution of nano-ZnO using batch experiments with a view to better understanding their co-effect on the environment. Dynamic light scattering and UV-Vis spectroscopy results show enhanced aggregation of nano-ZnO in the presence of Cr(VI) ions under fresh landfill leachate conditions, in addition to distinct sedimentation of nano-ZnO in the presence of Cr(III) ions in both fresh and aged landfill leachate. In fresh leachate, Cu(II) ions improved the concentration of dissolved Zn from nano-ZnO. However, the effects of Cu(II), Cr(III), and Cr(VI) ions on the aggregation and dissolution of nano-ZnO were markedly reduced in aged landfill leachate. Both acetic and humic acids in landfill leachate significantly affected the stability of nano-ZnO in the presence of HMs. According to the ATR-FTIR results, Cr(III) ions reacted with hydroxyl groups on nano-ZnO to form ZnO-O bonds, which induced chains of nano-ZnO and Cr(III) complexes, and hence the increased of nano-ZnO aggregates. ATR-FTIR shows merely electrostatic adsorption effects between nano-ZnO and Cu(II) or Cr(VI) ions. In brief, the mode of interactions between HMs and nano-ZnO influenced the stability via adsorption and binding effects. The results of the present research provide insight into the potential effects of nano-ZnO on the environment in the presence of HMs in landfill leachate.

A comparative study on the structural features of humic acids extracted from lignites using comprehensive spectral analyses

The lignite reserves of Zhaotong and Mile in China are abundant and lignite utilizations are limited, however, humic acids (HAs) extracted from lignites play a significant role in many fields including agriculture, environmental protection and so on. Herein, the structures of HAs extracted from Zhaotong and Mile lignites (denoted as ZLHA and MLHA, respectively) were characterized and compared to each other using comprehensive spectral analyses. As a result, the UV-Vis spectrum analyses of HAs indicated that the molecular weight of MLHA is larger than that of ZLHA. Cross polarization magic angle spinning ¹³C NMR, which is rarely used to analyze the structures of HAs using fitting peaks, and FT-IR spectrum analyses indicated that both the aromaticity and the oxygen-containing group contents of ZLHA are higher than those of MLHA, and the HAs' aromaticity could be confirmed by the results of the X-ray diffraction patterns. Additionally, the main existing forms of the elements in the HAs were obtained from X-ray photoelectron spectrum analyses, which are not commonly used for HA analyses. In this work, the utilization of comprehensive spectral analyses was an effective method to study the structural features of ZLHA and MLHA and it could provide a basic reference for the applications of ZLHA and MLHA.

The structural features of humic acids extracted from Zhaotong and Mile lignites were analyzed using comprehensive spectral analyses including UV-vis, FTIR, CP/MAS ¹³C NMR, XRD and XPS.

Molecular Composition of Size-Fractionated Fulvic Acid-Like Substances Extracted from Spent Cooking Liquor and Its Relationship with Biological Activity

The treatment of spent cooking liquor is critical for clean production of pulp and paper industry. There is a compelling need to develop a cost-effective and green technology for reuse of organic matter in spent cooking liquor to mitigate the negative impacts on the environment. The objective of this study is to examine the chemical structure of fulvic acid-like substances extracted from spent cooking liquor (PFA) and their relationship with bioactivity in plant growth. Compared with the benchmark Pahokee peat fulvic acid (PPFA), PFA has less aromatic structure, but higher content of lignin, carbohydrates, and amino acid. After fractionation, protein/amino proportion decreased with increasing molecular weight, but the aromaticity increased. Under salt stress, rice seedling growth was promoted by PFA with low molecular weight (<5 kDa), but inhibited by fraction with high molecular weight (>10 kDa). Principal component analysis suggested that promoted growth was more related with chemical structure (O- and N-alkyl moieties) than with molecular weight. This study provided the theoretical basis for development of an innovative green technology of sustainable reuse of spent cooking liquor in agriculture.

Characterization of Fulvic Acid Beverages by Mineral Profile and Antioxidant Capacity

The main purpose of the study was to investigate the quality of fulvic acid-based food products. The concentrations of Ca, K, Mg, Na, Cu, Fe, Mn, and Zn, and antioxidant capacities of fulvic acid concentrates and ready-to drink beverages available on the global market were determined. The concentrations of minerals were determined using microwave plasma-atomic emission spectrometry. Antioxidant capacity was expressed as total polyphenol (TP) and flavonoid (TF) contents, the trolox equivalent antioxidant capacity (TEAC) and ferric reducing ability of plasma (FRAP) values. The daily portion of eight out of 14 products realized 45–135% of recommended daily allowance (RDA) for Fe. One of ready-to-drink beverages was also a good source of Mg (about 40% of RDA), and another one of Mn (about 70% of RDA). The concentrations of TP and TF in ready-to-drink beverages varied from 6.5 to 187 µg/mL, whereas in concentrates, from 5886 to 19,844 µg/mL. Dietary supplements or food products with fulvic acids may be a good source of antioxidant polyphenolic compounds and some minerals.

The underlying mechanism of calcium peroxide pretreatment enhancing methane production from anaerobic digestion of waste activated sludge

Recent investigations verified that calcium peroxide (CaO₂) could be used to pretreat waste activated sludge to promote methane yield from anaerobic digestion. However, the underlying mechanism of how CaO₂ pretreatment promotes methane production is unclear. This work therefore aims to provide insights into such systems. Experimental results showed that with an increase of CaO₂ dosage from 0 to 0.14 g/g VSS (volatile suspended solids) the methane yield increased linearly from 146.3 to 215.9 mL/g VSS. Further increases of CaO₂ resulted in decreases in methane yield. CaO₂ pretreatment promoted the disintegration of sludge and the degradation of sludge recalcitrant organics (especially humus and lignocellulose), thereby providing more substrates for subsequent methane production. Ultraviolet absorption spectroscopy indicated that CaO₂ enhanced the cleavage of unsaturated conjugated bonds and reduced the aromaticity of humus and lignocellulose. Fourier transform infrared spectroscopy showed that CaO₂ changed the structures and functional groups of humus and lignocellulose, making them transform to be biodegradable. GC/MS analyses exhibited that the degradation products of humus and lignocellulose included several types of small molecular organics such as ester-like, acid-like, and alcohol-like substances. Further investigation demonstrated that substantial methane could be produced from these degradation products. It was also found that the presence of recalcitrant organics was detrimental to anaerobes relevant to anaerobic digestion, and the degradation of such recalcitrant organics mitigated their inhibitions to the anaerobes. Model-based analysis suggested that CaO₂ pretreatment increased the maximum methane yield and methane production rate, which were consistent with the analysis above.

Activation of fulvic acid-like in paper mill effluents using H2O2/TiO2 catalytic oxidation: Characterization and salt stress bioassays

Increasing environmental concerns about organic waste in paper mill effluents demand alternative wastewater management technology. We reported novel activation of fulvic acid-like in paper mill effluents using hydrogen peroxide (H₂O₂) as oxidizer and titanium oxide (TiO₂) as catalyst. Spectroscopic characteristics of fulvic acid-like in paper mill effluents before and after activation (PFA and PFA-Os, respectively) were compared with a benchmark fulvic acid extracted from leonardite (LFA). Results indicated that PFA-Os exhibited less lignin structures, more functional groups and lower molecular weight than PFA, sharing much similarity with LFA. Among PFA-Os with varying degrees of oxidation, PFA-O-3 activated with 1:2 vol ratio of paper mill effluent and 30% H₂O₂ for 20 min digestion at 90 °C stands out to be the optimal for further examination of its biological activity. Bioassays with rice seed/seedling indicated that applications of LFA at 2-5 mg-C/L and PFA-O-3 at 60-100 mg-C/L significantly increased rice seed germination rate and seedling growth under salt stress imposed with 100 mM NaCl. The mechanism was mainly through reduced oxidative damage via activation of antioxidative enzymes and lipid peroxidation. This study provides the needed technical basis of safer and cleaner technologies for innovative management of paper mill effluents.

Inhibition of urease activity by humic acid extracted from sludge fermentation liquid

This study achieved effective extraction of humic acid from sludge fermentation liquid, and the inhibition of urease activity by the extract were investigated in the urea decomposition. The addition of extract could remarkably inhibit urease activity and extend the releasing time of ammonia nitrogen. The interaction between the extract and urease took times, and the inhibition was irreversible. The results of fluorescence analysis revealed that the inhibition of urease activity was correlated to the amount of humic acid extracted. The mechanisms of inhibition were proposed that the functional groups of humic acid might interact with the thiol group of urease and formed a larger particle size of complex to inhibit the activity of urease. The extraction of humic acid from sludge fermentation liquid can not only recover the resource from the fermentation liquid, but also provide a potential urease inhibitor for the sustained-release effect of the soil organic nitrogen fertilizer.

Systematic studies on the binding of metal ions in aggregates of humic acid: Aggregation kinetics, spectroscopic analyses and MD simulations

The binding of metal ions with humic acid (HA) plays an important role in the aggregation of HA and the migration of metal ions in the environments. The effects of common cations (Na⁺, Mg²⁺, Ca²⁺ and Al³⁺) and heavy metal ions (Ag⁺, Cd²⁺, Cu²⁺, Cr³⁺ and Eu³⁺) on the aggregation of HA were investigated systematically by aggregation kinetics, spectroscopic techniques and molecular dynamic (MD) simulations. The critical coagulation concentration (CCC) of mono-, di- and trivalent cations could be predicted by the Schulze-Hardy rule. The aggregation of HA in the presence of Na⁺ and Ag⁺ was mainly due to the reduction of repulsive force and the hydrogen bonds between HA molecules. While the complexation of di- and trivalent cations with carboxylic/phenolic groups, or the cation-π interactions enhanced the intra- or inter-molecular bridges in HA and then contributed greatly to the aggregation of HA. Heavy metal ions could easily pass through the electric double-layer of HA compared with common cations. MD simulations further signified the strong aggregation ability of HA molecules in solutions containing high valence metal ions. These findings are important for understanding not only how the influence of metal ions on the aggregation of HA, but also the conditions which ions more efficient for aggregation.

Separation of Benzoic and Unconjugated Acidic Components of Leonardite Humic Material Using Sequential Solid-Phase Extraction at Different pH Values as Revealed by Fourier Transform Ion Cyclotron Resonance Mass Spectrometry and Correlation Nuclear Magnetic Resonance Spectroscopy

Here, we report on sequential solid-phase extraction of leonardite hymatomelanic acid (CHM) on a non-ionic sorbent at four steadily lowered pH values: 7, 5, 3, and 2, yielding fractions with different acidic properties. Using nuclear magnetic resonance (NMR) spectroscopy and ultrahigh-resolution mass spectrometry, we revealed a gradual shift of dominating scaffolds in the fractions of CHM from reduced saturated to oxidized aromatic compounds. An increase on the average aromaticity of the CHM fractions was accompanied by a red shift in fluorescence spectra. These results were supported by heteronuclear single quantum coherence and heteronuclear multiple bond correlation NMR experiments. We have demonstrated that the CHM fraction isolated at pH 5 was dominated by aliphatic carboxyl carriers, while the pH 3 fraction was dominated by aromatic carboxyl acids. The developed fractionation technique will enable deeper insight on structure-property relationships and the design of the humic-based materials with tailored reactive properties.

Enhanced mechanical stability and sensitive swelling performance of chitosan/yeast hybrid hydrogel beads

Up to the present time, improving the mechanical stability of hydrogel beads is still a challenging task for future applications of chitosan hydrogels.

Effect of humic substances on phosphorus removal by struvite precipitation

Humic substances (HS) are a major fraction of dissolved organic matters in wastewater. The effect of HS on phosphorus removal by struvite precipitation was investigated using synthetic wastewater under different initial pH values, Mg/P molar ratios and HS concentrations. The composition, morphology and thermal properties of harvested precipitates were analyzed by X-ray diffraction (XRD), scanning electron microscope (SEM) and thermo-gravimetric analysis (TGA), respectively. It showed that inhibition effect of HS reached its maximum value of 48.9% at pH 8.0, and decreased to below 10% at pH>9.0. The increase of Mg/P ratio enhanced phosphorus removal efficiency, and thus reduced the influence of HS on struvite precipitation. At pH 9.0, the inhibitory effect of initial HS concentration matched the modified Monod model with half maximum inhibition concentration of 356mgL(-1), and 29% HS was removed in conjunction with struvite crystallisation. XRD analysis revealed that the crystal form of struvite precipitates was changed in the presence of HS. The morphology of harvested struvite was transformed from prismatic to pyramid owing to the coprecipitation of HS on crystal surface. TGA results revealed that the presence of HS could compromise struvite purity.

Adsorption of triazine derivatives with humic fraction-immobilized silica gel in hexane: a mechanistic consideration

A fraction of humic acid is collected under acidic conditions, then immobilized on silica gel and used as the adsorbent for various symmetrical triazine (s-triazine) derivatives in hexane. The enhanced hydrogen bonding between the analyte and humic fraction molecules, not the complexation interaction, is responsible for the adsorption observed in hexane, based on Fourier transform infrared (FTIR) spectroscopy results. The percentage of adsorption in hexane for all s-triazine derivatives reaches nearly 100% in 1 h, independent of the type, position, and size of the substituent on the aromatic nitrogen heterocyclic ring. Other factors leading to the variation of the percentage of adsorption include the type of liquid phase and the additive of acidic or basic origin present in the matrix.

Relationship between oxidation level and optical properties of secondary organic aerosol

Brown carbon (BrC), which may include secondary organic aerosol (SOA), can be a significant climate-forcing agent via its optical absorption properties. However, the overall contribution of SOA to BrC remains poorly understood. Here, correlations between oxidation level and optical properties of SOA are examined. SOA was generated in a flow reactor in the absence of NOx by OH oxidation of gas-phase precursors used as surrogates for anthropogenic (naphthalene, tricyclo[5.2.1.0(2,6)]decane), biomass burning (guaiacol), and biogenic (α-pinene) emissions. SOA chemical composition was characterized with a time-of-flight aerosol mass spectrometer. SOA mass-specific absorption cross sections (MAC) and refractive indices were calculated from real-time cavity ring-down photoacoustic spectrometry measurements at 405 and 532 nm and from UV-vis spectrometry measurements of methanol extracts of filter-collected particles (300 to 600 nm). At 405 nm, SOA MAC values and imaginary refractive indices increased with increasing oxidation level and decreased with increasing wavelength, leading to negligible absorption at 532 nm. Real refractive indices of SOA decreased with increasing oxidation level. Comparison with literature studies suggests that under typical polluted conditions the effect of NOx on SOA absorption is small. SOA may contribute significantly to atmospheric BrC, with the magnitude dependent on both precursor type and oxidation level.

Adsorption and desorption of plasticizers with humic-fraction-immobilized silica gel in hexane: a facile approach to pre-concentration

Humic fraction (HF) collected under acidic conditions and used as an adsorbent for various phosphate-based plasticizers in hexane is immobilized on silica gel. Most plasticizer analytes examined in this study under the same conditions achieved adsorption percentages above 90% in 1 h based on the difference in peak area. The Fourier transform infrared (FTIR) spectroscopy results indicate that the interaction leading to the adsorptions between the functional moieties of the analyte and HF (e.g., the carboxylate group of analyte against the carboxyl group of HF) is specific, reversible, and dipole-dipole-oriented. Moreover, it is significantly enhanced by hexane. However, the π−π interaction (even hydrogen bonding in all cases) was either not as significant or absent in hexane and, therefore, contributed little or nothing to the percentage of adsorption. The interaction is highly affected by the acidic or basic origin of the additive introduced to the liquid phase of the matrix, and it is subject to the steric hindrance effect caused by the bulky alkyl groups attached to ether linkages and the relative position of the two ether bonds on the aromatic moiety of the analyte. The pre-concentration of the analyte and, thus, the recycle of the adsorbent can be achieved by adsorbing and, subsequently, desorbing it in a different solvent, such as acetonitrile. Furthermore, the adsorption process is surface-oriented because of its dependence upon both time and the amount of adsorbent.

Adsorption of pesticidal compounds bearing a single carboxyl functional group and biogenic amines by humic fraction-immobilized silica gel

Fractions collected from humic acids under acidic and basic conditions were immobilized on silica gel and used as adsorbents for a variety of agricultural pesticide compounds bearing a single carboxyl functional group and biogenic amines in acetonitrile. Among these compounds examined under the same conditions, the percentage of adsorption varies considerably from 0 to almost 100%. The percentage is found to be highly related to the structure of the analyte and the type of functional group attached to it. The adsorption, better performed on adsorbent immobilized with the fraction collected under acidic conditions, is believed to result from the reversible interaction between the functional moieties of the analyte and humic acids (e.g., amino or carboxyl group of analyte vs carboxyl group of humic acids, etc.) as no adsorption is observed under the same conditions for analytes that are derivatives of alcohol, amide, and ester. Given the nature of the analyte, the time needed to reach the maximum percent of adsorption decreases as the amount of adsorbent is increased. Also, the longer the time that has elapsed, the higher the percentage of analyte adsorbed, thus indicating that the adsorption process is surface-oriented. Factors such as the acidic or basic origin of the additive in the liquid phase of the matrix also affect the percentage of analyte adsorbed.

Impact of coal structural heterogeneity on the nonideal sorption of organic contaminants

Carbonaceous geosorbents (black carbon, coal, and humin/kerogen) play a primary role in the nonideal sorption (isotherm nonlinearity, hysteresis, and multiphasic kinetics) of hydrophobic organic chemicals by soils and sediments. The present study investigated the impact of coal structural heterogeneity on sorption/desorption of two model monoaromatic compounds (1,3-dichlorobenzene and 1,3-dinitrobenzene). Due to the higher degree of aromaticity and condensation, anthracite showed stronger sorption affinity and nonlinearity and slower sorption kinetics than lignite. Removal of humic substances by alkali extraction and/or mineral fraction by acidification did not much affect organic carbon-normalized sorption coefficient to the coal, suggesting nearly complete accessibility of adsorption sites on the condensed organic carbon. However, the treatments greatly increased sorption kinetics and meanwhile alleviated hysteresis of 1,3-dinitrobenzene, as compared with the original lignite. These observations were attributed to the enhanced exposure of high-energy adsorption sites on the condensed organic carbon after exfoliating the surface coverage by humic substances and minerals. An empirical biphasic pseudo-second-order model consisting of a fast sorption phase and a slow sorption phase adequately quantified the overall sorption kinetics for the coal sorbents. The results indicated that the condensed organic carbon, in combination with other structural components, controls the nonideal sorption of unburned coal.

Molecular breeding of polymerases for resistance to environmental inhibitors

Potent inhibitors limit the use of PCR assays in a wide spectrum of specimens. Here, we describe the engineering of polymerases with a broad resistance to complex environmental inhibitors using molecular breeding of eight different polymerase orthologues from the genus Thermus and directed evolution by CSR in the presence of inhibitors. Selecting for resistance to the inhibitory effects of Neomylodon bone powder, we isolated 2D9, a chimeric polymerase comprising sequence elements derived from DNA polymerases from Thermus aquaticus, Thermus oshimai, Thermus thermophilus and Thermus brockianus. 2D9 displayed a striking resistance to a broad spectrum of complex inhibitors of highly divergent composition including humic acid, bone dust, coprolite, peat extract, clay-rich soil, cave sediment and tar. The selected polymerase promises to have utility in PCR-based applications in a wide range of fields including palaeobiology, archaeology, conservation biology, forensic and historic medicine.

Pyrolysis-gas chromatography/mass spectrometry identification of distinctive structures providing humic character to organic materials

Flash pyrolysis-gas chromatography/mass spectrometry(Py-GC/MS) was used to study the structural transformations of humic fractions formed as a result of composting processes of diverse organic materials (solid wastes of wineries, solid olive-mill wastes, domestic wastes, ovine manures plus straw, and mixtures of animal manures). Sodium hydroxide-extracted total humic-like extracts (THE; humic plus fulvic acids) from the composted and the initial noncomposted wastes and several reference humic and fulvic acids from soils were analyzed. These results were compared with results from previous studies using 13C-cross polarization magic angle spinning-nuclear magnetic resonance (NMR), UV-visible, and fluorescence emission spectroscopies. Alkylbenzenes and alkylphenols predominate in the pyrograms of the soil humic acids, whereas the fulvic acids showed higher contents of phenolic and polysaccharide-derived compounds. The pyrolysates of THE from the composted samples showed an increase in aromatic and nitrogenated structures and a decrease in polysaccharide-derived compounds. The aromatic contents as determined by Py-GC/MS and 13C-NMR were well correlated in the reference humic substances and THE from composted materials (r = 0.99 and 0.94, respectively; P < 0.01) but not in the case of THE from noncomposted materials, probably due to an aliphatic enhancement in the pyrolysates of these samples and other secondary reactions. The content in alkylbenzenes was consistent with the variations found previously for several UV-visible and fluorescence indexes as a function of the degree of humification, suggesting their involvement in structures that are a characteristic feature of the formation and evolution of humic substances.