Pahokee Peat Fulvic Acid Research Articles

Products from Photolysis Reactions of Tetracycline Mediated by Clay and Humic Substance Induce Contrasting Expressions of Target Resistance Genes.

Phototransformation is a key process affecting the fate of many antibiotics in the environment, but little is known about whether their photoproducts exert selective pressure on bacteria by inducing antibiotic resistance genes (ARGs). Here, we examined the expression of tetracycline resistance gene tet(M) of a fluorescent Escherichia coli whole-cell bioreporter influenced by the phototransformation of tetracycline. The presence of suspended smectite clay (montmorillonite or hectorite, 1.75 g/L) or dissolved humic substance (Pahokee Peat humic acid or Pahokee peat fulvic acid, 10 mg C/L) in aqueous solutions markedly facilitated the transformation of tetracycline (initially at 400 μg/L) with half-life shortened by 1.4-2.6 times. Despite the similar phototransformation ratios (80-90%) of the total loaded tetracycline after 60 min irradiation, the decreased ratios of cell fluorescence intensity (which was proportional to the expression amount of ARG tet(M)) were much higher with the two clays (94 and 93%) than with the two humic substances (44 and 69%) when compared to the respective dark controls. As illustrated by mass spectroscopic and chemical analyses, tetracycline was proposed to be mainly transformed to amide (ineffective in inducing ARGs) with the presence of clays by reaction with self-photosensitized singlet oxygen (1O2), while the humic substances might catalyze the production of another two demethylated and/or deaminated compounds (still effective in inducing ARGs) in addition to the amide compound via reaction with triplet excited state dissolved organic matter (3DOM*). As clay minerals and humic substances are important soil constituents and ubiquitously present in surface environments, the observed clay and humic-dependent photooxidation pathways of tetracycline and the differing selective pressures of the associated products highlight the need for monitoring the transformation compounds of antibiotics and provide critical insight into the development of antibiotic treatment protocols.

Spectroscopic Characteristics and Speciation Distribution of Fe(III) Binding to Molecular Weight-Dependent Standard Pahokee Peat Fulvic Acid.

Peat-derived organic matter, as powerful chelators, is of great significance for the transport of Fe to the ocean and the enhancement of dissolved Fe. However, the iron binding capacity of molecular weight (MW)-fractionated dissolved organic matter is variable, due to its structure and composition heterogeneity. In this work, we used the standard Pahokee Peat fulvic acid (PPFA) as an example, and investigated the spectroscopy properties and Fe(III) binding ability of PPFA and different molecular weight fractions by UV–Vis absorbance and fluorescence spectroscopy and the Donnan Membrane Technique (DMT). The results showed binding sites for Fe(III) at the 263 nm and >320 nm regions in differential absorbance spectra. Upon increasing the iron concentration to 18.00 μmol·L−1, the critical binding capacity was exceeded, which resulted in a decrease in absorbance. Fe(III) was found to prefer to bind to humic-like components, and ultraviolet humic-like fluorophores displayed stronger binding strength. High molecular weight PPFA fractions (>10 kDa) possessed more aromatic and hydrophobic components, displayed a higher degree of humification, and exhibited higher metal binding potential. Furthermore, the speciation analysis and stability constant (cK) were calculated using Donnan membrane equilibrium. The correlation between cK values and PPFA spectral properties demonstrated that aromaticity, hydrophobicity, molecular weight and humification degree were crucial indices of PPFA–Fe(III) affinity. Significantly, the humification degree, represented by HIX, showed the strongest correlation (r = 0.929, p = 0.003), which could be used to estimate the binding strength. This study provides further understanding of the complexation mechanism of iron and DOM in the peat environment and identifies the considerable effect of molecular weight.

Effects of fulvic acids on the electrochemical reactions and mass transfer properties of organic cation toluidine blue: Results of measurements by the method of rotating ring-disc electrode

This study examined effects of aquatic and soil natural organic matter (NOM) exemplified by standard Suwannee River fulvic acid (SRFA) and Pahokee Peat fulvic acid (PPFA), respectively, on the electrochemical (EC) reactivity and mass transfer properties of the cationic organic probe toluidine blue (TB) that forms complexes with NOM. EC measurements that were carried out using the method of rotating ring-disc electrode (RRDE) showed that for disc potentials below −0.4 V vs. the standard Ag/AgCl reference electrode, TB molecules undergo EC reduction accompanied by the formation of EC-active products that undergo oxidation at the ring electrode. EC reactions of TB in the range of potentials −0.2 to −0.4 V were determined to involve free TB+ cations and TB species adsorbed on the electrode surface. The EC reduction of TB species at the disc potentials < −0.4 V was controlled by the mass transfer of the free TB+ cations and TB/NOM complexes to the electrode surface. Formation of TB/NOM complexes caused the mass transfer-controlled TB currents to undergo a consistent decrease. The observed changes were correlated with the extent of TB/NOM complexation and decreases of the diffusion coefficients of TB/NOM complexes that have higher molecular weights (MW) than the free cations. Properties of the intermediates formed upon the reduction of TB+ cations were also affected by NOM. These results demonstrate that RRDE measurements of EC reactions of TB or possibly other EC active probes allow probing the complexation of EC-active organic species with NOM and mass transfer properties of NOM complexes and ultimately NOM itself.

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.

Determination of the speciation and bioavailability of samarium to Chlamydomonas reinhardtii in the presence of natural organic matter.

As technological interest and environmental emissions of the rare earth elements increase, it is becoming more important to assess their potential environmental impact. Samarium (Sm) is a lanthanide of intermediate molar mass that is used in numerous high-technology applications including wind turbines, solar panels, and electric vehicles. The present study relates the speciation of Sm determined in the presence of natural organic matter (NOM) to its bioavailability to the unicellular green alga Chlamydomonas reinhardtii. The free ion concentration was determined using a cation exchange resin (ion exchange technique) in dynamic mode and compared with thermodynamic modeling. Short-term biouptake experiments were performed in the presence of 4 types of NOM: Suwannee River fulvic acids, Pahokee Peat fulvic acids, Suwannee River humic acids, and a Luther Marsh dissolved organic matter isolate (90-95% humic acids). It was clearly shown that even a small amount of NOM (0.5 mg C L-1 ) resulted in a significant decrease (10 times) in the Sm internalization fluxes. Furthermore, complexation with humic acids (and the corresponding reduction in Sm bioavailability) was stronger than that with fulvic acids. The results showed that the experimentally measured (free) Sm was a better predictor of Sm internalization than either the total concentrations or the free ion concentrations obtained using thermodynamic modeling. Environ Toxicol Chem 2018;37:1623-1631. © 2018 SETAC.

Electron transfer at microbe-humic substances interfaces: Electrochemical, microscopic and bacterial community characterizations

Soluble and colloidal humic substances (HSs) involved in microbial extracellular electron transfer (EET) have been extensively investigated. However, little is known regarding EET at HS adlayers that are bound or complexed to the surface of natural solids. Here, we investigated EET process on seven types of HS adlayers by forming electroactive biofilms (EABs) and monitoring the biocurrent generation. The HS immobilized surfaces were carried out by firstly modifying glassy carbon surfaces via electrochemical reduction of aryl diazonium salts to create amino-functionalized surfaces, and then various HSs were covalently bonded to these amino groups via linkage molecules. The results showed that the HS adlayers formed from Leonardite, Elliott Soil and Pahokee Peat humic acids (HAs) facilitated EET by forming more active EABs, whereas the Suwannee River and Aldrich HAs, Suwannee River and Pahokee Peat fulvic acids (FAs) hindered EET. The EET positively correlated with electron accepting capacity and wettability of the HSs, and negatively correlated with the polarity of the HSs, and only weakly correlated with electron donating capacity and zeta potential of the HSs. Microscopic images showed that the thickness and viability of the biofilms varied based on the HS properties. A microbial community structure analysis showed that all of the biofilms were dominated by Proteobacteria and selectively enriched in Firmicutes and Bacteroidetes. Our study indicated that the HS adlayers significantly affected microbial EET, and these results provide a more comprehensive understanding of the HSs involved biogeochemical and biotransformation processes.

Nitrosation and Nitration of Fulvic Acid, Peat and Coal with Nitric Acid.

Nitrohumic acids, produced from base extraction of coals and peats oxidized with nitric acid, have received considerable attention as soil ammendments in agriculture. The nitration chemistry however is incompletely understood. Moreover, there is a need to understand the reaction of nitric acid with natural organic matter (NOM) in general, in the context of a variety of environmental and biogeochemical processes. Suwannee River NOM, Suwannee River fulvic acid, and Pahokee Peat fulvic acid were treated with 15N-labeled nitric acid at concentrations ranging from 15% to 22% and analyzed by liquid and solid state 15N NMR spectroscopy. Bulk Pahokee peat and Illinois #6 coal were also treated with nitric acid, at 29% and 40% respectively, and analyzed by solid state 15N NMR spectroscopy. In addition to nitro groups from nitration of aromatic carbon, the 15N NMR spectra of all five samples exhibited peaks attributable to nitrosation reactions. These include nitrosophenol peaks in the peat fulvic acid and Suwannee River samples, from nitrosation of phenolic rings, and N-nitroso groups in the peat samples, from nitrosation of secondary amides or amines, the latter consistent with the peat samples having the highest naturally abundant nitrogen contents. Peaks attributable to Beckmann and secondary reactions of the initially formed oximes were present in all spectra, including primary amide, secondary amide, lactam, and nitrile nitrogens. The degree of secondary reaction product formation resulting from nitrosation reactions appeared to correlate inversely with the 13C aromaticities of the samples. The nitrosation reactions are most plausibly effected by nitrous acid formed from the reduction of nitric acid by oxidizable substrates in the NOM and coal samples.

Character of Humic Substances as a Predictor for Goethite Nanoparticle Reactivity and Aggregation.

Natural organic matter (NOM) is ubiquitous in surface water and groundwater and interacts strongly with mineral surfaces. The details of these interactions, as well as their impacts on mineral surface reactivity, are not well understood. In this work, both the reactivity and aggregation of goethite (α-FeOOH) nanoparticles were quantified in the presence of well-characterized humic substances. Results from monitoring the kinetics of reductive degradation of 4-chloronitrobenzene (4-ClNB) by Fe(II) adsorbed onto the goethite nanoparticles with and without added humic substances demonstrates that, in all cases, humic substances suppressed Fe(II)-goethite reactivity. The ranking of the standards from the least to most inhibitive was Pahokee Peat humic acid, Elliot Soil humic acid, Suwannee River humic acid, Suwannee River NOM, Suwannee River fulvic acid I, Suwannee River fulvic acid II, and Pahokee Peat fulvic acid. Correlations between eight characteristics (molecular weight, carboxyl concentration, and carbon, oxygen, nitrogen, aliphatic, heteroaliphatic, and aromatic content) and 4-ClNB degradation rate constants were observed. Faster kinetic rates of reductive degradation were observed with increased molecular weight and nitrogen, carbon, and aromatic content, and slower rates were observed with increased carboxyl concentration and oxygen, heteroaliphatic, and aliphatic content. With these correlations, improved predictions of the reactivity of Fe(II)-goethite with pollutants based on properties of the humic substances are possible.

Interactions of Aqueous Ag+ with Fulvic Acids: Mechanisms of Silver Nanoparticle Formation and Investigation of Stability

This study investigated the possible natural formation of silver nanoparticles (AgNPs) in Ag(+)-fulvic acid (FA) solutions under various environmentally relevant conditions (temperature, pH, and UV light). Increase in temperature (24-90 °C) and pH (6.1-9.0) of Ag(+)-Suwannee River fulvic acid (SRFA) solutions accelerated the appearance of the characteristic surface plasmon resonance (SPR) of AgNPs. The rate of AgNP formation via reduction of Ag(+) in the presence of different FAs (SRFA, Pahokee Peat fulvic acid, PPFA, Nordic lake fulvic acid, NLFA) and Suwannee River humic acid (SRHA) followed the order NLFA > SRHA > PPFA > SRFA. This order was found to be related to the free radical content of the acids, which was consistent with the proposed mechanism. The same order of AgNP growth was seen upon UV light illumination of Ag(+)-FA and Ag(+)-HA mixtures in moderately hard reconstituted water (MHRW). Stability studies of AgNPs, formed from the interactions of Ag(+)-SRFA, over a period of several months showed that these AgNPs were highly stable with SPR peak reductions of only ~15%. Transmission electron microscopy (TEM) and dynamic light scattering (DLS) measurements revealed bimodal particle size distributions of aged AgNPs. The stable AgNPs formed through the reduction of Ag(+) by fulvic and humic acid fractions of natural organic matter in the environment may be transported over significant distances and might also influence the overall bioavailability and ecotoxicity of AgNPs.

Origin of heat-induced structural changes in dissolved organic matter

Humic substances play an important role in many environmental processes such as sequestration and transport of hydrophobic compounds. The supramolecular character of humic substances imparts high flexibility of the aggregates associated with their variable reactivity under different conditions. In this study, heat-induced transitions and character of the hydration shell of sodium salts of humic and fulvic acids originating from various sources were investigated using ultrasonic velocimetry in the temperature interval from 5 to 90°C. Results clearly showed differences in stability and characteristics of the hydrated states at concentrations above and below 1gL−1 with the exception of Pahokee peat fulvic acids. It has been concluded that predominantly the relaxation part of the adiabatic compressibility plays an important role below 1gL−1 in contrast to both relaxation and intrinsic parts of the compressibility being important at higher concentrations. Dilution brought several temperature induced transitions which were investigated with respect to composition of all investigated humic substances. Correlation analysis revealed that the transition around 17°C is associated with disruption of H-interactions whereas the transition around 42°C depends on the aromaticity. Comparison of cooling and heating records revealed hysteresis in the structural relaxation resembling the behavior of physically stabilized hydrogels. Results indicated a difference in the conformation and therefore reactivity of dissolved humic substances in the dependence on temperature and thermal history. It has been hypothesized that this may play an important role in the transport and sequestration of hydrophobic pollutants by dissolved organic matter.

Mobilization and deposition of iron nano and sub-micrometer particles in porous media: A glass micromodel study

Mobilization and deposition of iron nano and sub-micrometer particles (INSMP) in a porous medium were investigated using a water-saturated glass micromodel. The deposition and detachment of INSMP in the micromodel were visualized by taking serial images and experimentally verified by analysis of breakthrough curves. This first visualization study of INSMP fate showed that there were dense aggregations at the pores as the concentration of INSMP increased. The presence of dissolved humic substances (>1 ppm) significantly reduced deposition of suspended particles and enhanced detachment of the deposited particles. The mobility of INSMP in the presence of Pahokee peat fulvic acid standard II (PPFA) was higher than for Pahokee peat humic acid standard I (PPHA) due to the presence of more aromatic groups and the molecular weight in PPFA. Interfacial energy estimation based on the DLVO theory revealed that the adsorption of humic substances onto the INSMP increased the energy barrier and reduced the depth of secondary minimum between particles. The “affinity transition” in the initial deposition of INSMP within the micromodel was observed in the presence of Pahokee peat humic substances.

Distribution of barium and fulvic acid at the mica–solution interface using in-situ X-ray reflectivity

The interfacial structures of the basal surface of muscovite mica in solutions containing (1) 5 × 10 −3 m BaCl 2, (2) 500 ppm Elliott Soil Fulvic Acid I (ESFA I), (3) 100 ppm Elliott Soil Fulvic Acid II (ESFA II), (4) 100 ppm Pahokee Peat Fulvic Acid I (PPFA), and (5) 5 × 10 −3 m BaCl 2 and 100 ppm ESFA II were obtained with high resolution in-situ X-ray reflectivity. The derived electron-density profile in BaCl 2 shows two sharp peaks near the mica surface at 1.98(2) and 3.02(4) Å corresponding to the heights of a mixture of Ba 2+ ions and water molecules adsorbed in ditrigonal cavities and water molecules coordinated to the Ba 2+ ions, respectively. This pattern indicates that most Ba 2+ ions are adsorbed on the mica surface as inner-sphere complexes in a partially hydrated form. The amount of Ba 2+ ions in the ditrigonal cavities compensates more than 90% of the layer charge of the mica surface. The electron-density profiles of the fulvic acids (FAs) adsorbed on the mica surface, in the absence of Ba 2+, had overall thicknesses of 4.9–10.8 Å and consisted of one broad taller peak near the surface (likely hydrophobic and positively-charged groups) followed by a broad humped pattern (possibly containing negatively-charged functional groups). The total interfacial electron density and thickness of the FA layer increased as the solution FA concentration increased. The sorbed peat FA which has higher ash content showed a higher average electron density than the sorbed soil FA. When the muscovite reacted with a pre-mixed BaCl 2–ESFA II solution, the positions of the two peaks nearest the surface matched those in the BaCl 2 solution. However, the occupancy of the second peak decreased by about 30% implying that the hydration shell of surface-adsorbed Ba 2+ was partially substituted by FA. The two surface peaks were followed by a broad less electron-dense layer suggesting a sorption mechanism in which Ba 2+ acts dominantly as a bridging cation between the mica surface and FA. When the muscovite reacted first with FA and subsequently with BaCl 2, more Ba 2+ could be adsorbed on the FA-coated mica surface. The peak closest to the mica included Ba 2+ ions adsorbed directly on the mica in an amount similar to that in the BaCl 2 solution but more broadly distributed. A second peak observed within the FA layer suggests that the FA coating provides additional sites for Ba 2+ sorption. The results indicate that enhanced uptake of heavy metals can occur when an organic coating already exists on a mineral surface.