Nuclear magnetic resonance and diffuse-reflectance infrared Fourier transform spectroscopy of biosolids-derived biocolloidal organic matter

We extracted the acid-soluble portion of municipal biosolids, fractionated it by both molecular weight (MW) and hydrophobicity, and used various solid-state nuclear magnetic resonance (NMR) methods and diffuse-reflectance infrared Fourier transform (DRIFT) spectroscopy to characterize the fractions. Spectroscopic characterization of the MW components of the biosolids-derived organic matter fractions revealed the presence of functionally distinct groups of compounds. Quantitative 13C NMR, CH spectral editing, and several two-dimensional NMR experiments show that the high-MW hydrophilic fraction in particular is structurally simple, consisting predominantly of N-acetylated polysaccharides, perhaps derived from bacterial peptidoglycans. In the high-MW hydrophobic fraction, aromatic compounds were present in addition to the N-acetylated polysaccharides. Infrared spectroscopy confirmed that hydrophilic fractions were dominated by carbohydrates and indicated that the lower-MW fractions lacked amide moieties. Complementary interpretations of the DRIFT and NMR spectra improved our knowledge of the components separated by this fractionation scheme, allowing better characterization of biosolids organic matter. Moreover, fractionation based on both MW and hydrophobicity may prove useful in detailed characterization of the structure of biosolids-derived organic matter and other similarly heterogeneous natural organic matter in soils and sediments.     

Characterization of water-soluble organic carbon in urban atmospheric aerosols using solid-state 13C NMR spectroscopy

Solid-state 13C nuclear magnetic resonance (NMR) spectroscopy has been used to investigate the distribution of carbon functional groups in urban Atlanta aerosol fine (PM2.5) particles. Carbonaceous aerosol particles comprise a significant fraction of the ambient particle mass and are environmentally significant as they may influence radiative and cloud-nucleating properties and can also produce adverse health effects upon inhalation. The water-soluble organic carbon (WSOC) fraction was extracted from multiple 24 h integrated high-volume quartz filter samples and further separated into recovered hydrophobic and hydrophilic fractions using an approach similar to that used to extract humic and fulvic acids from aqueous samples. Solid-state 13C NMR results indicate that WSOC in urban atmospheric aerosol particles is mostly aliphatic in nature (approximately 95% by C mass) with major contributions from alkyl and oxygenated alkyls (approximately 80%), carboxylic acid (approximately 10%), and aromatic functional groups (approximately 4%). The aromatic C is associated with the recovered hydrophobic fraction of WSOC. These spectra have been compared to the 13C NMR results obtained from Suwannee River humic acid and a fractionated biomass burning sample. WSOC, and more importantly, its recovered hydrophobic fraction, is found to be only qualitatively similar to aqueous humic material. The biomass burning sample is significantly different from urban Atlanta WSOC and is composed of substantial amounts of sugar derivatives and phenolic compounds, as expected. The NMR results demonstrate the potential of this technique to investigate aerosol WSOC composition and to study its variations with changes in parameters such aerosol sources.     

Comprehensive characterization of atmospheric organic matter in Fresno, California fog water

Fogwater collected during winter in Fresno (CA) was characterized by isolating several distinct fractions and characterizing them by infrared and nuclear magnetic resonance (NMR) spectroscopy. More than 80% of the organic matter in the fogwater was recovered and characterized. The most abundant isolated fractions were those comprised of volatile acids (24% of isolated carbon) and hydrophilic acids plus neutrals (28%). Volatile acids, including formic and acetic acid, have been previously identified as among the most abundant individual species in fogwater. Recovered hydrophobic acids exhibited some properties similar to aquatic fulvic acids. An insoluble particulate organic matter fraction contained a substantial amount of biological material, while hydrophilic and transphilic fractions also contained material suggestive of biotic origin. Together, these fractions illustrate the important contribution biological sources make to organic matter in atmospheric fog droplets. The fogwater also was notable for containing a large amount of organic nitrogen present in a variety of species, including amines, nitrate esters, peptides, and nitroso compounds.     

Fluorescence excitation-emission matrix regional integration to quantify spectra for dissolved organic matter

Excitation-emission matrix (EEM) fluorescence spectroscopy has been widely used to characterize dissolved organic matter (DOM) in water and soil. However, interpreting the > 10,000 wavelength-dependent fluorescence intensity data points represented in EEMs has posed a significant challenge. Fluorescence regional integration, a quantitative technique that integrates the volume beneath an EEM, was developed to analyze EEMs. EEMs were delineated into five excitation-emission regions based on fluorescence of model compounds, DOM fractions, and marine waters or freshwaters. Volumetric integration under the EEM within each region, normalized to the projected excitation-emission area within that region and dissolved organic carbon concentration, resulted in a normalized region-specific EEM volume (phi(i,n)). Solid-state carbon nuclear magnetic resonance (13C NMR), Fourier transform infrared (FTIR) analysis, ultraviolet-visible absorption spectra, and EEMs were obtained for standard Suwannee River fulvic acid and 15 hydrophobic or hydrophilic acid, neutral, and base DOM fractions plus nonfractionated DOM from wastewater effluents and rivers in the southwestern United States. DOM fractions fluoresced in one or more EEM regions. The highest cumulative EEM volume (phi(T,n) = sigma phi(i,n)) was observed for hydrophobic neutral DOM fractions, followed by lower phi(T,n) values for hydrophobic acid, base, and hydrophilic acid DOM fractions, respectively. An extracted wastewater biomass DOM sample contained aromatic protein- and humic-like material and was characteristic of bacterial-soluble microbial products. Aromatic carbon and the presence of specific aromatic compounds (as indicated by solid-state 13C NMR and FTIR data) resulted in EEMs that aided in differentiating wastewater effluent DOM from drinking water DOM.     

Fractionation of UV and VUV pretreated natural organic matter from drinking water

Recent studies have examined the potential of ultraviolet (UV, 254 nm) and vacuum ultraviolet (VUV, 185 nm + 254 nm) irradiation as either a pretreatment for a biological process or as a sole treatment for the removal of natural organic matter as dissolved organic carbon from drinking water. To understand the potential of UV and VUV irradiation followed by subsequent biological treatment, treated water was fractionated into four components: very hydrophobic acid (VHA), slightly hydrophobic acid (SHA), hydrophilic charged (CHA), and hydrophilic neutral (NEU). The VHA fraction was found to be very susceptible to both UV and VUV irradiation, and the fragmentation products of the high molecular weight VHA and SHA molecules contributed to the CHA and NEU fractions to form a pool of biodegradable, non-UV-absorbing, low molecular weight moieties. The NEU fraction was the most difficult to remove, as most of the components in this fraction were refractory to both the biological and photo-oxidative processes. Therefore, enhanced removal of the NEU fraction is required to increase the effectiveness and potential of the treatment process.     

Relating carbon monoxide photoproduction to dissolved organic matter functionality

Aqueous solutions of humic substances (HSs) and pure monomeric aromatics were irradiated to investigate the chemical controls upon carbon monoxide (CO) photoproduction from dissolved organic matter (DOM). HSs were isolated from lakes, rivers, marsh, and ocean. Inclusion of humic, fulvic, hydrophobic organic, and hydrophilic organic acid fractions from these environments provided samples diverse in source and isolation protocol. In spite of these major differences, HS absorption coefficients (a) and photoreactivities (a bleaching and CO production) were strongly dependent upon HS aromaticity (r2 > 0.90; n = 11), implying aromatic moieties are the principal chromophores and photoreactants within HSs, and by extension, DOM. Carbonyl carbon and CO photoproduction were not correlated, implying that carbonyl moieties are not quantitatively important in CO photoproduction. CO photoproduction efficiency of aqueous solutions of monomeric aromatic compounds that are common constituents of organic matter varied with the nature of ring substituents. Specifically, electron donating groups increased, while electron withdrawing groups decreased CO photoproductivity, supporting our conclusion that carbonyl substituents are not quantitatively important in CO photoproduction. Significantly, aromatic CO photoproduction efficiency spanned 3 orders of magnitude, indicating that variations in the CO apparent quantum yields of natural DOM may be related to variations in aromatic DOM substituent group chemistry.     

Factors influencing the formation and relative distribution of haloacetic acids and trihalomethanes in drinking water

Various water quality and treatment characteristics were evaluated under controlled chlorination conditions to determine their influences on the formation and distribution of nine haloacetic acids and four trihalomethanes in drinking water. Raw waters were sampled from five water utilities and were coagulated with alum and fractionated with XAD-8 resin. The resulting four fractions--raw and coagulated water and the hydrophobic and hydrophilic extracts--were then chlorinated at pH 6 and 8 and held at 20 degrees C for various contact times. The results show that increasing pH from 6 to 8 increased trihalomethane formation but decreased trihaloacetic acid formation, with little effect on dihaloacetic acid formation. More trihalomethanes were formed than haloacetic acids at pH 8, while the reverse was true at pH 6. Hydrophobic fractions always gave higher haloacetic acid and trihalomethane formation potentials than their corresponding hydrophilic fractions, but hydrophilic carbon also played an important role in disinfection byproduct formation for waters with low humic content. The bromine-containing species comprised a higher molar proportion of the trihalomethanes than of the haloacetic acids. The hydrophilic fractions were more reactive with bromine than their corresponding hydrophobic fractions. Coagulation generally removed more haloacetic acid precursors than trihalomethane precursors. Waters with higher specific ultraviolet absorbance values were more amenable to removal of organic material by coagulation than waters with low specific ultraviolet absorbance values. Experimental evidence suggests that haloacetic acid precursors have a higher aromatic content than trihalomethane precursors.     

Characterization of disinfection byproduct precursors based on hydrophobicity and molecular size

Natural organic matter (NOM) from five water sources was fractionated using XAD resins and ultrafiltration membranes into different groups based on hydrophobicity and molecular weight (MW), respectively. The disinfection byproduct formation from each fraction during chlorination and chloramination was studied. In tests using chlorination, hydrophobic and high MW (e.g., >0.5 kDa) precursors produced more unknown total organic halogen (UTOX) than corresponding hydrophilic and low MW (e.g., <0.5 kDa) precursors. Trihaloacetic acid (THAA) precursors were more hydrophobic than trihalomethane (THM) precursors. The formation of THM and THAA was similar among different fractions for a water with low humic content. Hydrophilic and low MW (<0.5 kDa) NOM fractions gave the highest dihaloacetic acid (DHAA) yields. No significant difference was found for DHAA formation among different NOM fractions during chloramination. Increasing pH from 6 to 9 led to lower TOX formation for hydrophobic and high MW NOM fractions but had little impact on TOX yields from hydrophilic and low MW fractions. Bromine and iodine were more reactive with hydrophilic and low MW precursors as measured by THM or HAA formation than their corresponding hydrophobic and high MW precursors. However, hydrophobic and high MW precursors produced more UTOX when reacting with bromine and iodine.     

Ultrafiltration of nonionic surfactants and dissolved organic matter

A brownwater sample with a high content of humic substances (HS) was fractionated by multistage ultrafiltration (mst-UF) into five fractions with nominal molecular weights ranging from >30 to <1 kDa. Fractions were characterized with respect to molecular size distribution and structure. Size exclusion chromatography with online DOC detection revealed that mst-UF yielded fractions with decreasing Mp (molecular weight at peak maximum) and polydispersities from nominally large to small mst-UF fractions. 13C MAS NMR analysis showed that the content of carbohydrate structures decreased from the original sample toward smaller molecular weight (MW) fractions, which in turn contained more carboxylic groups and branched aliphatic structures. Specific UV absorbances (SUVA254) were highest in the >30 kDa fraction and decreased with decreasing MW. To evaluate whether separation mechanisms other than size exclusion were of importance during the fractionation, the behavior of low molecular weight model compounds (MC) with a range of polarities was studied. Recoveries decreased with increasing hydrophobicity of the MC. For selected nonylphenol ethoxylates and 4-nonylphenol the recovery correlated well with the hydrophile-lipophile balance value. The presence of dissolved organic matter (DOM) caused an additional loss of hydrophobic MC, possibly because of sorption of the compounds onto DOM fouling layers. The hydrophilic MC caffeine was recovered almost completely (85-86%) regardless of the DOM content of the model solution. It was concluded that size exclusion was the dominant fractionation mechanism for caffeine, whereas hydrophobic interactions played a major role during the mst-UF fractionation of nonpolar contaminants. For a better understanding of the behavior of polyfunctional molecules such as HS, the effect of other physicochemical properties needs to be investigated in further studies.     

Investigation of the role of structural domains identified in sedimentary organic matter in the sorption of hydrophobic organic compounds

The role of composition and structure of sedimentary organic matter (SOM) in the sorption of hydrophobic organic compounds (HOCs) was investigated by spiking 13C-labeled phenanthrene onto six estuarine sediments known to vary in SOM content and character. After equilibration and HF treatment, 13C NMR cross polarization and stable carbon isotope analyses indicated that the amount of desorption-resistant phenanthrene was related to aromatic carbon content. Application of the 13C NMR spectral editing technique proton spin relaxation editing (PSRE) demonstrated that all samples consisted of a rapidly relaxing and a slowly relaxing component, further evidence that SOM can be described as a structurally heterogeneous sorbent. Further, comparison of corresponding control and spiked PSRE subspectra revealed that, for each of the six sediments, desorption-resistant phenanthrene had become associated almost exclusively with the rapidly relaxing component. In only two of the sediments were there even small amounts of phenanthrene discernible in the slowly relaxing component, which is signficant as it was not always true that aromatic carbon was concentrated exclusively in the rapidly relaxing phase. The implication of these findings is that not all aromatic fractions have the same affinity for phenanthrene and that some fractions may indeed have little affinity at all. These results were interpreted as indicative that rapidly relaxing aromatic carbon associated with either sediment-associated charcoal or diagenetic organic matter plays a controlling role in the sorption of HOCs. However, the exact manner in which this rapidly relaxing aromatic phase relates to models presented elsewhere remains unclear.     

Impact of vegetation on sedimentary organic matter composition and polycyclic aromatic hydrocarbon attenuation

Results from natural and engineered phytoremediation systems provide strong evidencethatvegetated soils mitigate polycyclic aromatic hydrocarbon (PAH) contamination. However, the mechanisms by which PAH mitigation occurs and the impact of plant organic matter on PAH attenuation remain unclear. This study assessed the impact of plant organic matter on PAH attenuation in labile and refractory sediments fractions from a petroleum distillate waste pit that has naturally revegetated. Samples were collected in distinct zones of barren and vegetated areas to assess changes to organic matter composition and PAH content as vegetation colonized and became established in the waste pit. Sediments were fractionated into bulk sediment and humin fractions and analyzed for organic matter composition by isotope ratio mass spectrometry (delta (13)C), 13C nuclear magnetic resonance (13C NMR), delta 14C AMS (accelerator mass spectrometry), and percent organic carbon (%TOC). Gas chromatography mass spectrometry (GC/ MS) of lipid extracts of SOM fractions provided data for PAH distribution histograms, compound weathering ratios, and alkylated and nonalkylated PAH concentrations. Inputs of biogenic plant carbon, PAH weathering, and declines in PAH concentrations are most evidentfor vegetated SOM fractions, particularly humin fractions. Sequestered PAH metabolites were also observed in vegetated humin. These results show that plant organic matter does impact PAH attenuation in both labile and refractory fractions of petroleum distillate waste.     

Biodegradability of fractions of dissolved organic carbon leached from decomposing leaf litter

Dissolved organic matter leached from decomposing organic matter is important in the leaching of nutrients from the root zone of ecosystems, eluviation of metals, and transport of hydrophobic pollutants. The objective of this study was to compare microbial mineralization rates in intact soil cores of various fractions of water-soluble dissolved organic matter. Uniformly 14C-labeled Populus fremontii leaf litter that had decomposed for 1 year was extracted in water and this extract was fractionated into phenolic, humic acid, fulvic acid, hydrophilic acid, and hydrophilic neutral fractions. Fulvic acid comprised 42.1% of C in dissolved organic carbon (DOC) extracted from the litter. These fractions were added to intact cores of soil or sand, and respired 14CO2 was collected. The percentage of labeled substrate C mineralized in soil at the end of 1 year was, in order from least to greatest, hydrophilic acid (30.5), fulvic acid (33.8), humic acid (39.0), whole, unfractionated DOC (43.5), unseparated hydrophilic acid and neutral (44.7), phenolic (63.3), glucose (66.4), and hydrophilic neutral (70.2). In acid-washed nutrient-amended sand that was inoculated with soil microbes, mineralization rates of fulvic acid and glucose were lower. The fractionation appeared to separate the DOC into components with widely different rates of mineralization. Results also supported the ideas that the dissolved humic substance and hydrophilic acid fractions are inherently difficult for microbes to mineralize, and this property can contribute to movement of refractory C in soil and into aquatic ecosystems.     

Linking phosphorus sequestration to carbon humification in wetland soils by 31P and 13C NMR spectroscopy

Phosphorus sequestration in wetland soils is a prerequisite for long-term maintenance of water quality in downstream aquatic systems, but can be compromised if phosphorus is released following changes in nutrient status or hydrological regimen. The association of phosphorus with relatively refractory natural organic matter (e.g., humic substances) might protect soil phosphorus from such changes. Here we used hydrofluoric acid (HF) pretreatment to remove phosphorus associated with metals or anionic sorption sites, allowing us to isolate a pool of phosphorus associated with the soil organic fraction. Solution (31)P and solid state (13)C NMR spectra for wetland soils were acquired before and after hydrofluoric acid pretreatment to assess quantitatively and qualitatively the changes in phosphorus and carbon functional groups. Organic phosphorus was largely unaffected by HF treatment in soils dominated by refractory alkyl and aromatic carbon groups, indicating association of organic phosphorus with stable, humified soil organic matter. Conversely, a considerable decrease in organic phosphorus following HF pretreatment was detected in soils where O-alkyl groups represented the major fraction of the soil carbon. These correlations suggest that HF treatment can be used as a method to distinguish phosphorus fractions that are bound to the inorganic soil components from those fractions that are stabilized by incorporation into soil organic matter.     

Comparison of sorption domains in molecular weight fractions of a soil humic acid using solid-state 19F NMR

Humic acid was fractionated into eight different molecular size components using ultrafiltration. Solid-state CPMAS 13C NMR demonstrated that fractions larger than 100,000 Daltons were primarily aliphatic in character, while fractions smaller than 30,000 Daltons were predominantly aromatic in character. Solid-state 19F NMR examination of the sorptive uptake of hexafluorobenzene (HFB) by HA and each of the fractions gave spectroscopic evidence for the existence of at least three sorption sites in the smaller molecular size fractions, while two predominant sorption sites could be established in the larger molecular size fractions. Sorbed HFB displayed higher mobility in the smaller, more aromatic fractions while HFB in the larger, more aliphatic fractions displayed lower mobility. The relative mobilities of HFB in each sorption domain suggest that the rigid domain may be composed of aliphatic carbon rather than aromatic carbon moieties. In larger size fractions, this domain may be the result of rigid, glassy regions composed of aliphatic molecules or side chains.     

Accurate quantification of aromaticity and nonprotonated aromatic carbon fraction in natural organic matter by 13C solid-state nuclear magnetic resonance

An improved approach for accurately determining the aromatic carbon fraction (fa) and nonprotonated aromatic carbon fraction (faN) in natural organic matter by solid-state 13C NMR is described. Quantitative peak areas are obtained from direct polarization 13C nuclear magnetic resonance (NMR) under high-speed magic angle spinning (MAS). The problem of overlap between aromatic and alkyl carbon resonances around 90-120 ppm in 13C NMR spectra is solved by a 13C chemical shift anisotropy (CSA) filter technique. After correction for residual spinning sidebands, an accurate value of the aromaticity fa is obtained. To obtain a quantitative faN fraction, dipolar dephasing was adapted for high-speed MAS 13C NMR; the separation of the signals of nonprotonated alkyl and aromatic carbons was achieved by CSA filtering plus dipolar dephasing. The method is demonstrated on a peat humic acid, yielding fa = 45 +/- 2% and faN = (0.64 +/- 0.07) x 45%.     

Effect of ammonia nitrogen and dissolved organic matter fractions on the genotoxicity of wastewater effluent during chlorine disinfection

Chlorine is a widely used disinfectant which prevents the spread of harmful pathogens when reusing wastewater, but harmful byproducts might be formed and cause adverse ecological and health effects. In this study, the potential effects of chlorination on the genotoxicity of different biologically treated wastewater samples were investigated using the umutest. For the firsttime, ammonia nitrogen (NH3-N) was found to significantly influence genotoxicity during wastewater chlorination. After chlorination, the genotoxicity decreased in wastewater with a low NH3-N concentration (<10-20 mg/L), but it increased notably in wastewater with a high NH3-N concentration (>10-20 mg/L). By fractionating the DOM (dissolved organic matter) in wastewater into different fractions, it was found that the hydrophilic substances (HIS) fraction of DOM was the key fraction involved in decreasing genotoxicity during the chlorination of wastewater with a low NH3-N concentration, while the hydrophobic acids (HOA) fraction of DOM was the key fraction involved in increasing genotoxicity during chlorination of wastewater with a high NH3-N concentration. Furthermore, fluorescence spectroscopy analysis on different fractions indicated that some free or combined aromatic amino acids might produce highly genotoxic byproducts during the chlorination of wastewater with a high NH3-N content, and this was then demonstrated through experiments on the chlorination of free aromatic amino acids.     

Distributed sequestration and release of PAHs in weathered sediment: the role of sediment structure and organic carbon properties

Polycyclic aromatic hydrocarbon (PAH) contaminated sediments from Piles Creek (PC) and Newtown Creek (NC) in the NY/NJ Harbor estuary were separated into size fractions and further separated into low (<1.7 g cm(-3)) and high (>1.7 g cm(-3)) density fractions. The fractionated sediments were characterized for carbon content pore structure, surface area, and PAH concentration. Most PAHs (50-80%) in both sediments were associated with the low-density fraction, which represents only 3-15% of total sediment mass, at levels greater than expected based on equilibrium partitioning. PC low-density sediment had 10 times greater organic carbon-normalized equilibrium partitioning coefficients (Koc) than the other size fractions and whole sediment. Characterization of the sediment organic matter suggested that the preferential sequestration observed in PC sediment was not correlated with soot carbon but was likely due to the presence of detrital plant debris, an important food source for benthic animals. Fractional PAH desorption from whole PC sediment was significantly higher than from NC sediment after 3 months. For both sediments, a smaller percentage of the total PAHs was desorbed from the low-density fraction. However, because PAH concentrations were greatly elevated in these fractions, more PAH mass was desorbed than from the corresponding bulk and high-density fractions. These results demonstrate that PAHs are preferentially sequestered in a separable, low-density fraction at levels not predictable by equilibrium partitioning theory. Further, the low-density fraction apparently controls whole-sediment PAH release. Although plant debris appears to be an important sorbent for PAHs, this material may readily release PAHs into the aqueous phase.     

Black carbon and kerogen in soils and sediments. 2. Their roles in equilibrium sorption of less-polar organic pollutants

The first paper of this series reported that soil/sediment organic matter (SOM) can be fractionated into four fractions with a combined wet chemical procedure and that kerogen and black carbon (BC) are major SOM components in soil/sediment samples collected from the industrialized suburban areas of Guangzhou, China. The goal of this study was to determine the sorptive properties forthe four SOM fractions for organic contaminants. Sorption isotherms were measured with a batch technique using phenanthrene and naphthalene as the sorbates and four original and four Soxhlet-extracted soil/sediment samples, 15 isolated SOM fractions, and a char as the sorbents. The results showed that the sorption isotherms measured for all the sorbents were variously nonlinear. The isolated humic acid (HA) exhibited significantly nonlinear sorption, but its contribution to the overall isotherm nonlinearity and sorption capacity of the original soil was insignificant because of its low content in the tested soils and sediments. The particulate kerogen and black carbon (KB) fractions exhibited more nonlinear sorption with much higher organic carbon-normalized capacities for both sorbates. They dominate the observed overall sorption by the tested soils and sediments and are expected to be the most important soil components affecting bioavailability and ultimate fate of hydrophobic organic contaminants (HOCs). The fact that the isolated KB fractions exhibited much higher sorption capacities than when they were associated with soil/sediment matrixes suggested that a large fraction of the particulate kerogen and BC was not accessible to sorbing HOCs. Encapsulation within soil aggregates and surface coverage by inorganic and organic coatings may have caused large variations in the accessibility of fine kerogen and BC particles to HOCs and hence lowered the sorption capacity of the soil. This variability posts an ultimate challenge for precisely predicting HOC sorption by soils from the contents of different types of SOM.     

15N NMR investigation of the reduction and binding of TNT in an aerobic bench scale reactor simulating windrow composting

T15NT was added to a soil of low organic carbon content and composted for 20 days in an aerobic bench scale reactor. The finished whole compost and fulvic acid, humic acid, humin, and lignocellulose fractions extracted from the compost were analyzed by solid-state CP/MAS and DP/MAS 15N NMR. 15N NMR spectra provided direct spectroscopic evidence for reduction of TNT followed by covalent binding of the reduced metabolites to organic matter of the composted soil, with the majority of metabolite found in the lignocellulose fraction, by mass also the major fraction of the compost. In general, the types of bonds formed between soil organic matter and reduced TNT amines in controlled laboratory reactions were observed in the spectra of the whole compost and fractions, confirming that during composting TNT is reduced to amines that form covalent bonds with organic matter through aminohydroquinone, aminoquinone, heterocyclic, and imine linkages, among others. Concentrations of imine nitrogens in the compost spectra suggest that covalent binding by the diamines 2,4DANT and 2,6DANT is a significant process in the transformation of TNT into bound residues. Liquid-phase 15N NMR spectra of the fulvic acid and humin fractions provided possible evidence for involvement of phenoloxidase enzymes in covalent bond formation.     

Characterization and copper binding of humic and nonhumic organic matter isolated from the South Platte River: evidence for the presence of nitrogenous binding site

Humic substances typically constitute 40-60% of the dissolved organic matter (DOM) in surface waters. However, little information is available regarding the metal binding properties of the nonhumic hydrophilic portion of the DOM. In this study, humic and nonhumic DOM samples were isolated from the South Platte River (Colorado, DOC = 2.6 mg x L(-1), SUVA254 = 2.4 L/mg x m) using a two-column array of XAD-8 and XAD-4 resins. The three major isolated fractions of DOM, which accounted for 57% of the bulk DOM,were characterized using a variety of analytical tools. Proton and copper binding properties were studied for each fraction. The main objective of this work was to compare the structural and chemical characteristics of the isolated fractions and test models describing DOM reactivity toward metal ions. The characterization work showed significant structural differences between the three isolated fractions of DOM. The hydrophobic acid fraction (i.e., humic substances isolated from the XAD-8 resin) gave the largest C/H, C/O, and C/N ratios and aromatic carbon content among the three isolated fractions. The transphilic acid (TPHA) fraction ("transphilic" meaning fraction of intermediate polarity isolated from the XAD-4 resin) was found to incorporate the highest proportion of polysaccharides, whereas the transphilic neutral (TPHN) fraction was almost entirely proteinaceous. The gradual increase of the charge with pH for the three DOM fractions is most likely caused by a large distribution of proton affinity constants for the carboxylic groups, as well as a second type of group more generally considered to be phenolic. In the case of the DOM fraction enriched in proteinaceous material (i.e., TPHN fraction), the results showed that the amino groups are responsible for the charge reversal. For low copper concentrations, nitrogen-containing functional groups similar to those of amino acids are likely to be involved in complexation, in agreement with previously published data.