Humic Acid Components Research Articles

Phase transitions and hygroscopic growth of aerosol particles containing humic acid and mixtures of humic acid and ammonium sulphate

Abstract. The phase transitions and hygroscopic growth of two humic acid aerosols (Aldrich sodium salt and Leonardite Standard (IHSS)) and their mixtures with ammonium sulphate have been investigated using a combination of two techniques, Fourier transform infra-red (FTIR) spectroscopy and tandem differential mobility analysis (TDMA). A growth factor of 1.16 at 85% relative humidity (RH) was found for the Aldrich humic acid which can be regarded as an upper limit for growth factors of humic-like substances (HULIS) found in atmospheric aerosol and is significantly smaller than that of typical atmospheric inorganics. We find that the humic acid aerosols exhibit water uptake over all relative humidities with no apparent phase changes, suggesting that these aerosols readily form supersaturated droplets. In the mixed particles, the humic acid component decreases the deliquescence relative humidity (DRH) and increases the efflorescence relative humidity (ERH) of the ammonium sulphate component, and there is some degree of water uptake prior to ammonium sulphate deliquescence. In addition, at low RH, the FTIR spectra show that the ammonium is present in a different chemical environment in the mixed aerosols than in crystalline ammonium sulphate, perhaps existing as a complex with the humic materials. The growth factors of the mixed aerosols are intermediate between those of the single-component aerosols and can be predicted assuming that the inorganic and organic fractions take up water independently.

Reactive Uptake of N2O5 by Aerosol Particles Containing Mixtures of Humic Acid and Ammonium Sulfate

The kinetics of reactive uptake of N2O5 on submicron aerosol particles containing humic acid and ammonium sulfate has been investigated as a function of relative humidity (RH) and aerosol composition using a laminar flow reactor coupled with a differential mobility analyzer (DMA) to characterize the aerosol. For single-component humic acid aerosol the uptake coefficient, gamma, was found to increase from 2 to 9 x 10(-4) over the range 25-75% RH. These values are 1-2 orders of magnitude below those typically observed for single-component sulfate aerosols (Phys. Chem. Chem. Phys. 2003, 5, 3453-3463;(1) Atmos. Environ. 2000, 34, 2131-2159(2)). For the mixed aerosols, gamma was found to decrease with increasing humic acid mass fraction and increase with increasing RH. For aerosols containing only 6% humic acid by dry mass, a decrease in reactivity of more than a factor of 2 was observed compared with the case for single-component ammonium sulfate. The concentration of liquid water in the aerosol droplets was calculated using the aerosol inorganic model (for the ammonium sulfate component) and a new combined FTIR-DMA system (for the humic acid component). Analysis of the uptake coefficients using the water concentration data shows that the change in reactivity cannot be explained by the change in water content alone. We suggest that, due to its surfactant properties, the main effect of the humic acid is to reduce the mass accommodation coefficient for N2O5 at the aerosol particle surface. This has implications for the use of particle hygroscopicity data for predictions of the rate of N2O5 hydrolysis.

Digestion of peptidic residues in humic substances by an alkali-stable and humic-acid-tolerant proteolytic activity in the gut of soil-feeding termites

Previous feeding experiments have shown that soil-feeding termites (Termitidae: Termitinae) preferentially mineralize the peptidic component of synthetic humic acids, but nothing was known about the mechanism involved in digestion. Here, we studied the hydrolysis of humus-stabilized peptides in gut extracts of Cubitermes orthognathus by measuring the release of radiolabel from 14C-peptide-labeled synthetic humic acids. Gut extracts exhibited proteolytic activity over a wide pH range (from 4 to 12) with a maximum at about pH 8. The highest activity was located in the gut section containing the midgut and the extremely alkaline (up to pH 12) mixed segment. Chemical hydrolysis at in situ pH (up to pH 12) was negligible. Proteolytic activity in the hindgut fluid was generally relatively low, but alkaline proteases dominated in the anterior hindgut. When compared to other alkaline proteases, the proteolytic activity of gut extracts had a higher alkali-stability and tolerance to humic acids than subtilisin and an alkaline protease of Streptomyces griseus. Gut extracts also hydrolyzed the peptidic component of synthetic humic acids more efficiently than the commercial enzymes. Together with previous results, this study strongly supports the hypothesis that soil-feeding termites mobilize and digest the peptidic component of organic nitrogen in soil humic substances by a combination of proteolytic activities and extreme alkalinity in their intestinal tract.

Selective digestion of the peptide and polysaccharide components of synthetic humic acids by the humivorous larva of Pachnoda ephippiata (Coleoptera: Scarabaeidae)

In order to identify the potential nutrient and energy sources of humivorous beetle larvae, we carried out feeding trials with soil supplemented with specifically 14C-labeled model humic acids synthesized by peroxidase-initiated radical polymerization, using the cetoniid beetle Pachnoda ephippiata (Coleoptera: Scarabaeidae) as a model organism. Ingestion of soil by the larvae significantly increased the mineralization of humic acids labeled in their peptide (HA-*peptide) or polysaccharide components (HA-*peptidoglycan and HA-*chitin), whereas the mineralization of humic acids labeled in the aromatic components (HA-*catechol) did not increase significantly. Mineralization was accompanied by a reduction of residual radiolabel in the acid-soluble fraction and an increase in the humic acid and humin fractions of the fecal pellets. During the gut passage, the residual label in peptide or polysaccharide components was transformed into acid-soluble products, especially in the alkaline midgut. High-performance gel-permeation chromatography demonstrated that the changes in solubility were accompanied by large changes in the molecular weight of the residual material. The amount of radiolabel derived from the peptide and polysaccharide components recovered from the larval body and hemolymph was significantly higher than that derived from the aromatic component, which supports the hypothesis that humivorous beetle larvae selectively digest the peptide and polysaccharide components of humic substances, whereas the aromatic components of humic substances are not an important source of nutrients and energy. This is also the first experimental evidence that also chitin and peptidoglycan, the major structural polymers in fungal and bacterial biomass, can be protected from microbial degradation in soil by a copolymerization with phenols and might contribute substantially to the refractory nitrogen pool in soil organic matter.

Contact-time-dependent atrazine residue formation in surface soils

The formation of nonextractable atrazine residues was evaluated in sterilized agricultural and woodland soils pre-loaded with (14)C-atrazine for contact periods of 1 h (0.046 days), and 1, 7, 14, 28, 56, and 84 days. Extractability of the pre-loaded atrazine and nonextractable residue formation were determined by subjecting the soils to sequential fill-and-draw extractions with water, ethylacetate/water, and alkali. Nonextractable atrazine residues associated with the fulvic acid (FA), humic acid (HA) and humin/mineral (HM) components of soil were determined by separating FA and HA from the soils and measuring the (14)C-activity associated with each fraction. Longer herbicide-soil contact times resulted in attenuated water extractability and enhanced nonextractable residue formation. At the longest contact periods, residues recovered in the FA, HA and HM components of soil accounted for 35-50% of the pre-loaded herbicide. The woodland soil contained significantly larger amounts of HA and humin than the agricultural soil, and appeared to have contributed significantly to nonextractable residue formation. Results from this study indicate that physicochemical processes occurring at intra-mineral and intra-organic matter sites continue to influence the fate of organic pesticides long after their application on soils.

Identification of black carbon derived structures in a volcanic ash soil humic acid by Fourier transform ion cyclotron resonance mass spectrometry.

Electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), coupled with cross-polarization magic angle spinning 13C nuclear magnetic resonance (NMR) spectroscopy and Kendrick mass defect analysis, was used to study the molecular composition of an aromatic carbon-rich humic acid extracted from a dark black soil from Iwata, Japan. Black carbon, produced by the incomplete combustion of fossil fuels and organic matter, has been suggested as a major component of humic acids having intense peaks in the aromatic and carboxyl regions of the 13C NMR spectrum. Taking advantage of the high resolving power of FT-ICR MS to make precise formula assignments, three different types of highly carboxylated polycyclic aromatic compounds were identified in the sample: linearly fused aromatic structures, aromatic structures linked by carbon-carbon single bonds, and highly condensed aromatic structures. These carboxylated aromatic structures have a low mass defect in their mass spectra due to their abundance of oxygen and deficiency of hydrogen. This mass defect is observed in the vast majority of peaks present in the entire mass spectrum, differentiating them from structures that are hydrogen-rich (e.g., fatty acids, proteins, carbohydrates). Thus, we conclude that the bulk of the sample analyzed is comprised of these heavily carboxylated, hydrogen-deficient, condensed aromatic structures, features believed to be characteristic of black carbon-like material.

Pyrolysis gas chromatography atomic emission detection method for determination of N-containing components of humic and fulvic acids

In this study, a pyrolysis gas chromatography/atomic emission detector (pyrolysis GC/AED) analytical system was established and then investigated for its utility in the chemical characterization of the N-containing components of humic and fulvic acids. Our results show that: (1) the optimal sample pyrolysis temperatures, for observing the characteristic profiles of N-containing components in soil organic matter constituents such as humic and fulvic acids, are from 300 to 500 °C; (2) the main N-containing pyrolysis products of humic and fulvic acids are acetonitrile, hydrogen cyanide, ammonia, pyridine, pyrrole and acetamide; (3) except for pyridine, each of the main N-containing fragments had more than one dominant N-containing source, with source structures being different for humic acid and fulvic acid; and (4) pyrolysis GC/AED with high selectivity and sensitivity may be a useful tool for tracking quantitatively the changes of SOM N-containing components during their decomposition in soils.

Phenanthrene Sorption to Structurally Modified Humic Acids

Several studies emphasize the importance of soil organic matter characteristics in hydrophobic contaminant sorption and outline the strong dependence of sorption on organic matter aromaticity. In this study, the role of organic matter aromaticity in phenanthrene sorption was investigated using humic acids (HAs) from compost, peat, and soil that were structurally modified by bleaching, hydrolysis, oximation, and subcritical water extraction. The HAs were characterized with cross polarization magic angle spinning carbon-13 nuclear magnetic resonance (CPMAS 13C NMR) spectroscopy and used in batch equilibrations with phenanthrene. Bleaching substantially reduced the aromaticity of the samples whereas the other treatments increased the relative aromaticity. Phenanthrene sorption increased, even though there was a substantial reduction in sorbent aromaticity with some samples. The HAs that exhibited comparable CPMAS 13C NMR spectra and aromaticity did not behave similarly with respect to phenanthrene sorption. When the sorption data (K(oc) values) were correlated to sample aromaticity, the correlation coefficients (r2) did not exceed 0.39. Comparisons with the atomic H to C ratio provided slightly better r2 values (up to 0.54). This study demonstrates that macroscopic sorbent characteristics could not explain the observed phenanthrene sorption coefficients, aliphatic structural components of HAs can contribute appreciably to phenanthrene sorption, and organic matter physical conformation may regulate access to organic matter structures. Therefore, the use of only macroscopic sorbent properties, such as aromaticity, to predict and rationalize sorption values cannot solely be used to explain the behavior of organic contaminants in soil environments.

Glomalin, a newly discovered component of soil organic matter: Part —Environmental significance

Soil organic matter (SOM) is a key component of soil that greatly influences its structure and productivity, as well as aggregate stability. High soil aggregate stability translates to less soil erosion and hence lessens the likelihood of non-point-source water pollution. Repeated evidences of arbuscular mycorrhizal fungi increasing soil aggregate stability led to the rather accidental discovery of a soil protein called glomalin produced in abundance by the hyphae of these fungi. In the course of time, glomalin detaches from the hyphae, moves into the soil, and becomes a distinct component of the SOM. Although the structure of glomalin remains unknown to date, research has revealed that it may comprise as much as 2% of soil by weight and 30% of soil carbon. Compared to glomalin, the traditional components of SOM, humic and fulvic acids, typically average 0.1% by soil weight and 510% of soil carbon. Glomalin is uncommonly tough and acts as a glue to hold the soil particles together. Studies on soils from differing locations and management practices have demonstrated the overall abundance and uncommonly high stability of glomalin, as well as an overwhelming positive correlation between glomalin content and soil aggregation. Research has also identified the potential for glomalin in the role of carbon sequestration. Despite the significant amount of research that has been performed on glomalin in soils since its discovery in 1996, there is still a world of unknowns about this unique soil protein. Determining the structure of glomalin, as well as those environmental conditions that drive its presence in soils, will govern the future direction of glomalin research.

Susceptibility of humic acids from soils with various contents of metals to microbial utilization and transformation

Humic acids (HAs) from a pseudogley soil with various metal contents were added as supplemental sources of nutrients, or as the sole sources of carbon or nitrogen, to aerobic cultures of complex microbial populations indigenous to the same individual soils. Depending on nutrient conditions in the individual cultures and origin of HAs, between 44% and 67% of the added HAs were utilized. The lowest utilization rate was obtained for HAs from soil heavily contaminated with Mg. The overall carbon mineralization in the microbial cultures was significantly reduced in the presence of HAs. Simultaneously, the formation of microbial biomass was enhanced up to 261%. Variovorax (Alcaligenes) paradoxus, Pseudomonas fluorescens, and a yeast Cryptococcus sp. have been identified as the dominant microbial species utilizing HAs. The individual HA preparations re-isolated from the microbial cultures exhibited distinct changes in elemental and structural characteristics. Diminished contents of ash and alterations in infra-red absorptions indicated a splitting of organic and mineral components in HAs exposed to microbial activities.

Structural Components of Humic Acids as Determined by Chemical Modifications and Carbon‐13 NMR, Pyrolysis‐, and Thermochemolysis‐Gas Chromatography/Mass Spectrometry

The chemical structure of humic acids (HAs) extracted from a grassland surface soil and peat were studied using bleaching (NaClO2 oxidation) and acid hydrolysis (6 M HCl) in combination with advanced analytical techniques: solid‐state 13C nuclear magnetic resonance (NMR), pyrolysis‐gas chromatography/mass spectrometry (GC/MS), and tetramethylammonium hydroxide (TMAH) thermochemolysis‐GC/MS. The purpose of the chemical treatments was to remove known structural fragments from the HA to study the building blocks and components of the macromolecule. Bleaching the peat HA resulted in an attack on the lignin structures leading to a significant reduction in the C‐substituted and O‐substituted aromatic C peaks (128 and 150 ppm) in the 13C NMR spectrum. However, the bleached soil HA still contained residual aromatic C, suggesting that part of its aromaticity had originated from aromatic structures resistant to bleaching, possibly black C (charcoal). The pyrolysates of the bleached HAs contained mainly alkanes and alkenes (C8 to C29), whereas TMAH thermochemolysis yielded a homologous series of long‐chain fatty acid methyl esters (FAMEs) (C8 to C32) and dicarboxylic acid dimethyl esters (DAMES). The data are comparable with those obtained from pyrolysis and thermochemolysis of plant cuticular materials, and therefore suggest that cuticular residues are an integral part of the HA macromolecule. The acid hydrolysis treatment removed esters, amides, carbohydrates, and some of the N‐containing compounds from the HAs. This study demonstrates the effectiveness of bleaching and hydrolysis treatments together with advanced analytical techniques for characterization of aliphatic, lignin‐derived (LG) and nonhydrolyzable N‐containing structures associated with the HA macromolecule.

Preferential adsorption of fluorescing fulvic and humic acid components on activated carbon using flow field-flow fractionation analysis.

Activated carbon treatment of drinking water is used to remove natural organic matter (NOM) precursors that lead to the formation of disinfection byproducts. The innate hydrophobic nature and macromolecular size of NOM render it amenable to sorption by activated carbon. Batch equilibrium and minicolumn breakthrough adsorption studies were performed using granular activated carbon to treat NOM-contaminated water. Ultraviolet (UV) absorption spectroscopy and flow field-flow fractionation analysis using tandem diode-array and fluorescence detectors were used to monitor the activated carbon sorption of NOM. Using these techniques, it was possible to study activated carbon adsorption properties of UV absorbing, fluorescing and nonfluorescing, polyelectrolytic macromolecules fractionated from the total macromolecular and nonmacromolecular composition of NOM. Adsorption isotherms were constructed at pH 6 and pH 9. Data were described by the traditional and modified Freundlich models. Activated carbon capacity and adsorbability were compared among fractionated molecular subsets of fulvic and humic acids. Preferential adsorption (or adsorptive fractionation) of polyelectrolytic, fluorescing fulvic and humic macromolecules on activated carbon was observed. The significance of observing preferential adsorption on activated carbon of fluorescing macromolecular components relative to nonfluorescing components is that this phenomenon changes the composition of dissolved organic matter remaining in equilibrium in the aqueous phase relative to the composition that existed in the aqueous phase prior to adsorption. Likewise, it changes the composition of dissolved organic matter remaining in equilibrium in the aqueous phase relative to the adsorbed phase. This research increases our understanding of NOM interactions with activated carbon which may lead to improved methods of potable water production.

Humic complexes of diethyl phthalate: molecular modelling of the sorption process

The sorption mechanisms and complex formation between humic acid (HA) and a successively increasing number of diethyl phthalate (DEP) molecules have been studied theoretically using molecular mechanics, the number ( n) of DEP molecules being varied from 1 to 30. The energy components of the single HA· nDEP complexes have been used as explanatory variables in a principal component analysis for exploring the presence of similarities/dissimilarities in the energetic properties of the individual xenobiotic complexes. The sorption can be explained in terms of a two-step mechanism. Absorption takes place as long as the host humic acid structure offers (a) enough internal docking space and (b) favorable interactions (energy release) with the guest molecule. This takes place for up to 7 DEP molecules. Further increase in the number to 30 DEP molecules will, due to the lack of free available internal voids, lead to surface controlled adsorption. The two-step sorption process apparently results in (a) a linear increase in energy gain by DEP bonds, and similarly (b) a constant incremental rise in molecular properties of the complexes such as volume and surface area. Three outstanding observations emerge: (1) Structural features at the atomic level (nanochemistry), such as partial atomic charges and high aromaticity of the humic acid, are observed to be dominating the intermolecular interactions in the complexes at the specific sorption sites. (2) Torsional relief and favorable changes in bonding energy also prevail for the growing complex. The latter indicates both the structural flexibility of the HA host and the stabilizing effect of DEP on the complex, by filling of the voids within the HA molecule. (3) The intermolecular forces are described mainly by hydrogen bonds (electrostatic energy) and interactions between dipole–dipole, such as carboxylic functions and uncharged moieties such as aromatic rings (van der Waals energy).

Stability of Reduced Organic Sulfur in Humic Acid as Affected by Aeration and pH

Reduced S groups in soil organic matter (OM) play an important role in the complexation of heavy metals. These complexation reactions are often studied using the humic acid component of OM. The objective of our study was to determine the effect of pH on humic acid yield and the effect of pH and exposure to O2 on the oxidation of reduced organic S. Humic acid was extracted at pH levels between 11.5 and 13.0 from a soil collected from a salt marsh. Also, aqueous samples of humic acid at different pH levels were aspirated with CO2‐free air for 4 or 44 h. X‐ray absorption near‐edge structure (XANES) spectroscopy was used to determine changes in S oxidation states for the various treatments. With increasing pH, the yield of humic acid increased from 1.3 to 4.6 g humic acid kg−1 soil, and the total S in these samples was 24 ± 1 g kg −1 humic acid. Linear‐combination fitting of XANES spectra showed that all of these humic acid samples contained ≈70% (mol/mol) reduced S (modeled as benzyl disulfide) and 30% (mol/mol) oxidized S (modeled as sulfonate and ester sulfate). For humic acid exposed to aeration for 4 h at pH levels between 11.5 and 13.0, reduced organic S was oxidized only at pH 13.0 (15% [mol/mol] of total S). Samples exposed to aeration for 44 h between pH 3.5 and 12.4 showed no detectable change in reduced organic S.

Noncovalent interactions between monoaromatic compounds and dissolved humic acids: a deuterium NMR T1 relaxation study.

Deuterium nuclear magnetic resonance spectroscopy (2H NMR) spin-lattice relaxation (T1) experiments were used to examine solution-phase, noncovalent interactions between deuterated monoaromatic compounds (phenol-d5, pyridine-d5, benzene-d6) and Suwannee River, soil, and peat humic acids. Noncovalent interactions, in aqueous solution, were examined as a function of solution pH, monoaromatic hydrocarbon functional groups, and humic acid identity. Benzene interacted with dissolved humic acids at all pH values; however, these interactions increased with decreasing pH and generally were proportional with the humic acid percent aromaticity. Pyridine behaved similarly as benzene; however, two modes of interaction between pyridine and humic acids were detected as a function of pH and humic acid type: bonding with the lone pair of electrons of pyridine's nitrogen and pi-pi interactions between the aromatic ring of pyridine and aromatic components of humic acid. The latter interaction was favored by increasing humic acid percent aromaticity and decreasing solution pH. On the other hand, because of its strong capacity for hydrogen bonding, phenol interacted preferentially with water, except at pH values 5 or lower and with humic acids with 45% or greater aromaticity. Under these conditions, strong interactions between phenol and humic acids were observed. These results demonstrate that solution-phase, noncovalent interactions between monoaromatic compounds and humic acids are a function of solution pH, percent aromaticity, and the monoaromatic functional group.

Transformation and mineralization of synthetic 14C-labeled humic model compounds by soil-feeding termites

The majority of termite species are considered to be humivorous, but the exact nature of their carbon and energy source, the mechanisms involved in digestion and the impact of this feeding habit on the humification of soil organic matter are largely obscure. We performed feeding trials with soil-feeding termites (Termitidae: Termitinae), using 14C-labeled humic model compounds as substrates. In the case of Cubitermes orthognathus, the components of chemically identical synthetic humic acids (HA), labeled either in their proteinaceous or aromatic building blocks, and synthetic fulvic acids (FA), labeled in the aromatic building blocks, all had similarly low mineralization rates (2.5, 2.2 and 2.7%, respectively) when incubated in soil for 10 days in the absence of termites. When termites were present, the mineralization rate of the aromatic component of HA and FA increased only slightly but significantly (2.4 and 3.1%, respectively; P < 0.05), whereas that of the proteinaceous component increased more than 10-fold (30.8%). Similar results were obtained when the protein was peptonized prior to polymerization (9.7 vs. 27.4% mineralization). Mineralization of HA was accompanied by a transformation of the residual peptide label to FA, whereas the aromatic label of HA and FA was partly transformed to humin during gut passage. High-performance gel permeation chromatography showed a strong shift in the size-class distribution of peptide label towards low-molecular-weight products, especially of the material ingested by the termites; the smallest molecules were recovered from the termite bodies. Similar results were obtained in feeding trials with Cubitermes umbratus and Thoracotermes macrothorax. Together with previous findings, the current results provide strong evidence that during gut passage, the combined action of extreme alkalinity in the anterior hindgut, autoxidative processes, and probably also proteolytic activities, renders a large reservoir of potential substrates accessible. While peptidic components of humic substances are selectively digested, aromatic components are apparently not an important food source for soil-feeding termites. These findings have important implications for the mobilization of organic nitrogen in tropical soils.

L3C NMR spectra and elemental composition of fractions with different particle sizes from an andosol humic acid

Elemental composition and solution 13C NMR spectra for six humic acid fractions with different particle sizes (i.e. 3K, 10K, 30K, l00K, 300K, and 500K) which were prepared from a humic acid in an Umbric Andosol by successive gel permeation chromatography were determined. Elemental composition of the particle size fractions clearly differed from one another. Contents of nitrogen and hydrogen increased with the increase of the particle size. Small and middle particle size fractions (3K to l00K) showed low contents of hydrogen and nitrogen corresponding to those in typical Andosol humic acids, while the contents in the large fractions (300K and 500K) were distributed in the ranges of those in the other humic acids. As the particle size increased, the HIC ratio increased whereas the O/H decreased. In the HIC versus OIC diagram, the large particle size fractions (300K and 500K) were observed in the area around humic acids with a low humification degree. Variation of the chemical structural properties with particle size differences was assumed, based on the analysis of the HIC versus OIH and HIC versus OIC diagrams. The changes of the carbon species with particle size differences were examined based on the 13C NMR spectra. As the particle size increased, the aliphatic C content increased whereas the carboxylic and aromatic C content decreased and, therefore, the aromaticity decreased. In addition, a negative correlation (r= -0.977) was found to be significant at 0.1% level between the HIC ratios and aromaticity. The peak strength around 30 ppm assigned to chains of methylene group increased remarkably with the increase of the particle size. It was suggested that the changes of the content of the aliphatic carbon with the decrease of the particle size may depend on the changes of the aliphatic chain length. In conclusion, these findings suggest that the Andosol humic acid molecule may be composed of humic acid components with long chains of aliphatic groups for the larger particle size fractions, and of their homologous series through the reduction of the length of the aliphatic long chain for the smaller particle size fractions. These assumptions were compatible with those made in a series of studies previously reported.

Marine microbial aggregating macromolecules: Potential mediators of coastal carbon flux

Microbial aggregation‐adhesion enhancing macromolecules (AAEM) in high molecular weight materials (HMWM) recovered from coastal seawater, suspended particulates and sediments were isolated using immunoaffinity chromatography. The quantity of AAEM recovered was an order of magnitude higher in suspended particulates compared to seawater and sediments. However, the AAEM/HMWM ratio remained constant in samples from all three sources. The fulvic acid component of suspended particulates had 91% of the AAEM, compared to 59% in the sediments. This change in AAEM distribution was directly correlated with decreased amounts of the predominant AAEM molecular size present in the sediment samples. Spectroscopic (FTIR) analyses revealed that the reduction in the relative quantities of fulvic acid AAEM in the sediment was most likely due to oxidative degradation of these residues. While significant adhesion enhancement activity was detected in both fulvic and humic acid AAEM fractions in sediments, the fulvic acid AAEM was significantly more active than the humic acid component. Fulvic and humic acid AAEM activity was strongly conserved in sediments despite reductions in quantity and oxidative degradation, indicating that these materials may play an important role in microbial organic carbon flux in this tropical coastal marine environment.

Influence of Structural Features on Sorption of NOM-Analogue Organic Acids to Goethite

A systematic study of the role of structural features of NOM-analogue organic acids in influencing mineral−organic acid interactions was performed. Goethite, a crystalline form of iron oxide important in geochemical systems, was employed as a model mineral. Sorption experiments with a series of small molecular weight, aromatic organic acids were performed to assess the effects of particular features of compound structure on sorption to goethite and to obtain insight into the kinds of surface reactions responsible for organic acid sorption. Important functional groups of the humic acid component of NOM were examined. Experiments were also performed with Aldrich humic acid to allow comparison between sorption behavior of simple organic acids and NOM and to determine suitable analogues for modeling NOM sorption. Sorption characteristics for most organic acids were typical for anionic sorbates, with high sorption at low pH and decreasing sorption as pH increased. Sorption of simple organic acids exhibited strong dependence on the number, type, and position of reactive functional groups, and compounds having particular structural features in common exhibited similar sorption behavior. The important structural characteristics governing sorption of simple aromatic organic acids appeared to be adjacent carboxylic groups, adjacent phenolic groups, phenolic groups in the ortho position relative to a carboxylic group, and overall acidity of the compound. Organic acid sorption also appeared to be influenced by hydrophobic interactions for some of the compounds. NOM sorption was best mimicked by 1,2,4,5-benzenetetracarboxylic acid (pyromellitic acid) and 2,3-dihydroxybenzoic acid. Compounds having a combination of the structural features present on these organic acids might better represent NOM sorption.

TCE adsorption by GAC preloaded with humic substances

Molecular weight makes a difference—lower‐molecular‐weight substances reduce TCE adsorption.Adsorption of trichloroethylene (TCE) by activated carbon preloaded with humic and fulvic acids was studied under several conditions in completely mixed batch systems. The authors investigated how molecular weight and molecular‐weight distribution of preloaded humic substances affected subsequent adsorption of TCE. The capacity of carbon to adsorb TCE was most greatly reduced in carbon that was preloaded with humic acid components having molecular weights less than about 1,400 g/mol as polystyrene sulfonate. The adsorption capacity was greatly reduced in carbon that was preloaded with whole humic mixtures in which lower molecular weights predominated. The energy distributions of adsorbent indicate that preloaded compounds preferentially occupy high‐energy sites, making them inaccessible to subsequently encountered TCE.