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Sulfate-reducing bacteria (SRB) often exist as cell aggregates and in biofilms surrounded by a matrix of extracellular polymeric substances (EPSs). The chemical composition of EPSs may facilitate hydrophobic substrate biodegradation and promote microbial influenced corrosion (MIC). Although EPSs from non-hydrocarbon-degrading SRB have been studied; the chemical composition of EPSs from hydrocarbon-degrading SRBs has not been reported. The isolated EPSs from the sulfate-reducing alkane-degrading bacterium Desulfoglaeba alkanexedens ALDC was characterized with scanning and fluorescent microscopy, nuclear magnetic resonance spectroscopy (NMR), and by colorimetric chemical assays. Specific fluorescent staining and 1 H NMR spectroscopy revealed that the fundamental chemical structure of the EPS produced by D . alkanexedens is composed of pyranose polysaccharide and cyclopentanone in a 2:1 ratio. NMR analyses indicated that the pyranose ring structure is bonded by 1,4 connections with the cyclopentanone directly bonded to one pyranose ring. The presence of cyclopentanone presumably increases the hydrophobicity of the EPS that may facilitate the accessibility of hydrocarbon substrates to aggregating cells or cells in a biofilm. Weight loss and iron dissolution experiments demonstrated that the EPS did not contribute to the corrosivity of D. alkanexedens cells.

"Clostridium ragsdalei" is an acetogen that ferments synthesis gas (syngas, predominantly H2:CO2:CO) to ethanol, acetate, and cell mass. Previous research showed that C. ragsdalei could also convert propionic acid to 1-propanol and butyric acid to 1-butanol at conversion efficiencies of 72.3 and 21.0 percent, respectively. Our research showed that C. ragsdalei can also reduce pentanoic and hexanoic acid to the corresponding primary alcohols. This reduction occurred independently of growth in an optimized medium with headspace gas exchange (vented and gassed with CO) every 48 h. Under these conditions, conversion efficiencies increased to 97 and 100 % for propionic and butyric acid, respectively. The conversion efficiencies for pentanoic and hexanoic acid to 1-pentanol and 1-hexanol, respectively, were 82 and 62 %. C. ragsdalei also reduced acetone to 2-propanol at a conversion efficiency of 100 %. Further, we showed that C. ragsdalei uses an aldehyde oxidoreductase-like enzyme to reduce n-fatty acids to the aldehyde intermediates in a reaction that requires ferredoxin and exogenous CO.

This study examines the design and evaluation strategies for a year-long teacher learning and development experience, including their effectiveness, efficiency and recommendations for strategic redesign. Design characteristics include programmatic features and outcomes: cognitive, affective and motivational processes; interpersonal and social development; and performance activities. Program participants were secondary math and science teachers, partnered with engineering faculty mentors, in a research university-based education and support program. Data from multiple sources demonstrated strengths and weaknesses in design of the program's learning environment, including: face-to-face and via digital tools; on-site and distance community interactions; and strategic evaluation tools and systems. Implications are considered for the strategic design and evaluation of similar grant-funded research experiences intended to support teacher learning, development and transfer., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

Microbially mediated anaerobic oxidation of methane (AOM) is an important sink in the global methane cycle, but the mechanism and microorganisms responsible for this oxidation are not fully known. Using quantum chemical calculations, fumarate addition to methane was examined to determine if it could be an energetically feasible mechanism for AOM. A potential energy surface (PES) for the initial reaction was created and the results suggest the reaction is exothermic, with a calculated overall energy change between -9.8 and -11.2 kcal/mol. The addition of methane to fumarate is calculated to be the highest point on the surface, 25.0-25.3 kcal/mol above the reactants. Of the three possible molecular configurations of fumarate considered, the one that presents the least steric obstacles to the addition reaction with methane yields the greatest energy gain. While 11.2 kcal/mol may support growth under energy limited conditions it is unknown if enzymes can mediate an energetic barrier of 25 kcal/mol. These calculated energies provide values for what could be one of the least reactive substrates to undergo fumarate addition, making methane a model substrate in defining the limits of energy barriers and minimal energy requirements for growth in reactions activated by glycyl radical-containing enzymes.

Samples of three humic acids and one fulvic acid with 1% loading of benzene-d(6) in sealed glass tubes have been studied with solid-state deuterium quadrupole-echo nuclear magnetic resonance spectroscopy. Calculated spectra combining three motional models, two isotropic models and a third more restricted small-angle wobble (SAW) motional model, are fit to the experimental spectra. One isotropic motion (ISO(v)) is assigned to vaporous benzene-d(6) due to the small line width, short T(1), and the loss of this component by about -25 °C when the temperature is lowered. The remaining two motional components, ISO(s) and SAW, are sorbed by the humic or fulvic acid. Benzene-d(6) slowly interacts with the humic substances, progressively filling SAW sites as ISO(s) motion diminishes. Both the sorption and increase in percentage of SAW motion are for the most part complete within 200 days but continue to a lesser extent over a period of a few years. For the SAW motion there are at least two and most likely a series of T(1) values, indicating more than one adsorption environment. Enthalpies of sorption, obtained from application of the van't Hoff equation to the percentages of the different motional models derived from a series of variable temperature spectra, are comparable in magnitude to the enthalpy of vaporization of benzene. In Leonardite humic acid, ΔH and ΔS for the ISO(s) to SAW transition change from positive to negative values with age, implying a transition in the driving force from an entropic effect associated with expansion and deformation in the molecular structure of the humic substance to accommodate benzene-d(6) to an enthalpic effect of strong benzene-d(6)-humic substance interactions. In contrast, at advanced ages, Suwannee River humic and fulvic acids have small positive or near zero ΔH and positive ΔS for the ISO(s) to SAW transition.

Polarizability ((alpha) and spin density (SD) of benzyl radical intermediates calculated using Gaussian O3 were correlated with the extent of anaerobic biodegradation for 17 C1 to C4 parent alkylbenzenes. The percent anaerobic biodegradation of the hydrocarbon series was determined in a previous study using an inoculum from a gas condensate-contaminated aquifer incubated under sulfate-reducing conditions. Many of the parent compounds are known to be biodegraded in the absence of oxygen by fumarate addition reactions. Percent biodegradation over a 100 day incubation (predicted) = -1.044 + 908.271SD - 586.197 (R2 = 0.839; all p-values < or = 0.058). This correlation suggests that compounds forming more stable alkylbenzyl radical intermediates biodegrade by fumarate addition more slowly than their counterparts forming less stable radicals. More highly substituted molecules including isopropylbenzene, 1-ethyl-2,6-dimethylbenzene and 1-ethyl-3,4-dimethylbenzene did not fit the model. The assumption of biodegradation by fumarate addition reaction was independently verified with several substrates. These findings help form a basis for predicting the relative rate of alkylbenzene metabolism in anaerobic environments.

Transformations of 2-hydroxybenzoate and fluorobenzoate isomers were investigated in the strictly anaerobic Syntrophus aciditrophicus to gain insight into the initial steps of the metabolism of aromatic acids. 2-Hydroxybenzoate was metabolized to methane and acetate by S. aciditrophicus and Methanospirillum hungatei cocultures and reduced to cyclohexane carboxylate by pure cultures of S. aciditrophicus when grown in the presence of crotonate. Under both conditions, transient accumulation of benzoate but not phenol was observed, indicating that dehydroxylation occurred prior to ring reduction. Pure cultures of S. aciditrophicus reductively dehalogenated 3-fluorobenzoate with the stoichiometric accumulation of benzoate and fluorine. 3-Fluorobenzoate-degrading cultures produced a metabolite that had a fragmentation pattern almost identical to that of the trimethylsilyl (TMS) derivative of 3-fluorobenzoate but with a mass increase of 2 units. When cells were incubated with deuterated water, this metabolite had a mass increase of 3 or 4 units relative to the TMS derivative of 3-fluorobenzoate. (19)F nuclear magnetic resonance spectroscopy ((19)F NMR) detected a metabolite in fluorobenzoate-degrading cultures with two double bonds, either 1-carboxyl-3-fluoro-2,6-cyclohexadiene or 1-carboxyl-3-fluoro-3,6-cyclohexadiene. The mass spectral and NMR data are consistent with the addition of two hydrogen or deuterium atoms to 3-fluorobenzoate, forming a 3-fluorocyclohexadiene metabolite. The production of a diene metabolite provides evidence that S. aciditrophicus contains dearomatizing reductase that uses two electrons to dearomatize the aromatic ring.

In methanogenic environments, the main fate of benzoate is its oxidization to acetate, H(2) and CO(2) by syntrophic associations of hydrogen-producing benzoate degraders and hydrogen-using methanogens. Here, we report the use of benzoate as an electron acceptor. Pure cultures of S. aciditrophicus simultaneously degraded crotonate and benzoate when both substrates were present. The growth rate was 0.007 h(-1) with crotonate and benzoate present compared with 0.025 h(-1) with crotonate alone. After 8 days of incubation, 4.12 +/- 0.50 mM of cyclohexane carboxylate and 8.40 +/- 0.61 mM of acetate were formed and 4.0 +/- 0.04 mM of benzoate and 4.8 +/- 0.5 mM of crotonate were consumed. The molar growth yield was 22.7 +/- 2.1 g (dry wt) of cells per mol of crotonate compared with about 14.0 +/- 0.1 g (dry wt) of cells per mol of crotonate when S. aciditrophicus was grown with crotonate alone. Cultures grown with [ring-(13)C]-benzoate and unlabelled crotonate initially formed [ring-(13)C]-labelled cyclohexane carboxylate. No (13)C-labelled acetate was detected. In addition to cyclohexane carboxylate, (13)C-labelled cyclohex-1-ene carboxylate was detected as an intermediate. Once almost all of the benzoate was gone, carbon isotopic analyses showed that cyclohexane carboxylate was formed from both labelled and non-labelled metabolites. Glutarate and pimelate were also detected at this time and carbon isotopic analyses showed that each was made from a mixture labelled and non-labelled metabolites. The increase in molar growth yield with crotonate and benzoate and the formation of [ring-(13)C]-cyclohexane carboxylate from [ring-(13)C]-benzoate in the presence of crotonate are consistent with benzoate serving as an electron acceptor.

The influence of cations (Na(+), Ca(2+) and Mg(2+)) on noncovalent interactions between 6-propionyl-2-dimethylaminonaphthalene (PRODAN) and dissolved fulvic acids (FAs) (Norman landfill leachate fulvic acid (NLFA) and Suwannee River fulvic acid (SRFA)) and dissolved humic acids (HAs) (Suwannee River humic acid (SRHA) and Leonardite humic acid (LHA)) was examined using steady-state fluorescence spectroscopy at pH 4, 7 and 10 as a function of cation concentration (up to 25-100mM). Regardless of pH and cation concentration, PRODAN quenching by FA was unaffected by cations. However, interactions between PRODAN and HA decreased in the presence of cations at pH 7 and 10. Cation concentrations below the HA charge density resulted in the greatest decrease of PRODAN quenching, while very little additional decrease in PRODAN quenching occurred at cation concentrations above the HA charge density. This suggests that as the HA carboxylic acid functional groups form inner sphere complexes with divalent cations, intramolecular interactions result in a contraction of the HA molecular structure, thereby preventing PRODAN from associating with the condensed aromatic, electron accepting moieties inherent within HA molecules and responsible for PRODAN quenching. However, once the HA carboxylic acid functional groups are fully titrated with divalent cations, PRODAN quenching is no longer significantly influenced by the further addition of cations, even though these additional cations facilitate intermolecular interactions between the HA molecules to form supramolecular HA aggregates that can continue to increase in size. Regardless of FA and HA type, pH, cation type and concentration, the lack of blue-shifted fluorescence emission spectra indicated that micelle-like hydrophobic regions, amenable to PRODAN partitioning, were not formed by intra- and intermolecular interactions of FA and HA.

This study investigated the TiO2 photocatalytic degradation of aqueous ammonia (NH4+/NH3) in the presence of surfactants and monosaccharides at pH approximately 10.1. Initial rates of NH4+/NH3 photocatalytic degradation decreased by approximately 50-90% in the presence of anionic, cationic, and nonionic surfactants and monosaccharides. Through correlation analysis, we concluded that scavenging of hydroxyl radical (.OH) by the products of surfactant/monosaccharide photocatalytic degradation, including carbonate and formate, could explain approximately 80% of the variance in initial rates of NH4+/NH3 removal in our system. Addition of a supplemental .OH source (H2O2) enhanced the rate of NH4+/NH3 degradation in the presence of the surfactant Brij 23 lauryl ether (Brij 35), further supporting the idea that .OH scavenging is the mechanism by which surfactants and monosaccharides decreased initial rates of NH4+/NH3 photocatalytic degradation. Despite slowed rates of NH4+/NH3 degradation, both surfactants/monosaccharides and NH4+/NH3 were removed by TiO2 photocatalysis, indicating that this process can effectively remove both carbonaceous and nitrogenous biochemical oxygen demand from gray water.

Cyclic oxidation and reduction reactions using oxygen and palladium with H2, respectively, of dissolved humic and fulvic acids (HA and FA) and model quinone compounds were used to structurally characterize and quantify the electron-carrying capacity (ECC) of reversible redox sites present in humic substances. This technique was used to examine 8 quinone compounds and 14 HA and FA samples and identified 3 redox sites as a function of their stability against the Pd-catalyzed hydrogenolysis process. Six highly aliphatic HA and FA isolated from landfill leachate did not contain redox sites under any conditions; however, the other HA and FA demonstrated reversible redox properties characterized by a combination of three redox sites. On the basis of the model compound results, it is proposed that one site consists of a non-quinone structure (NQ) and the other two sites have quinone structures. The two quinone sites differ in that one group (Q1) has electron-withdrawing groups adjacent to the quinone functional group while the second group (Q2) contains either no substituents near the quinone or has nearby electron-donating groups with additional substitutents hindering hydrogenolysis through steric interactions. The reversible ECC of NQ sites ranged from 25 to 265 microequiv e- transferred/g HA or FA, representing 21-56% of the total ECC of the HA and FA when measured with the mildest reducing method (pH 8.0, pure Pd). Q1 redox sites resistant to hydrogenolysis at pH 8.0 using Pd/Al2O3 accounted for 13-58% of the total ECC and ranged from 40 to 120 microequiv e-/ g HA or FA. The most sensitive O2 reversible redox sites accounted for 8-50% of the total ECC (20-220 microequiv e-/ g HA or FA). These results directly demonstrate that HA and FA are capable of acting as reversible electron-transfer agents using different functional groups, some of which may not be quinones.

Noncovalent interactions between the fluorescent probe 6-propionyl-2-dimethylaminonaphthalene (PRODAN) and dissolved Norman Landfill leachate fulvic acid, Suwannee River fulvic acid, Suwannee River humic acid, and Leonardite humic acid were examined as a function of pH, fulvic and humic acid (FA and HA) concentration, and solvent polarity using steady-state fluorescence spectroscopy. Static quenching processes, as indicated by linear Stern-Volmer plots and high K(d) values, were positively correlated with the % aromaticity of the FA and HAs, as well as with solution pH. Results illustrate that for FA molecules with relatively low % aromaticity values, solvophobic interactions between PRODAN and FA are the primary interaction mode. For HA molecules with higher % aromaticity, PRODAN engages in both solvophobic interactions and pi-pi interactions, in particular electron donor-acceptor interactions, via condensed aromatic, electron-accepting moieties inherent within HA molecules. Experiments modifying solvent polarity demonstrated that protonation of carboxylic acid functional groups at low pH ( approximately 4) increased the hydrophobicity of the dissolved FA and HA molecules, thereby enhancing noncovalent interactions with PRODAN through increased solvophobic forces.

Dynamic information is generally extracted from deuterium quadrupole echo spectra by matching a spectrum calculated for a particular motional model to the experimental spectrum. In this work, a set of computer programs has been written to facilitate fitting of calculated spectra to experimental spectra that represent from one to five motional models. The fitting program requires pre-calculated libraries of spectra for the models of interest, and accomplishes the fitting either by a systematic method or by simulated annealing. The systematic method is convenient for fitting with one or two motional models, but the simulated annealing method is faster for two or more models, if the libraries are made up of hundreds of spectra. The parameter Q, with the standard deviation of the spectral points estimated as the standard deviation of the baseline noise, provides a stringent measure of goodness of fit. Acceptable fits of experimental data as judged by this criterion have not been found, even in the case of ring flip motion in phenylalanine-d(5) in which the fit may be judged acceptable by eye. An example of fitting with isotropic and methyl rotation motional models of alanine-d(3), which have distinct spectral patterns, shows that it is possible to obtain reasonably accurate estimates of the relative amounts of deuterium representing the different models, even from poorly fitted spectra.

The anaerobic, syntrophic bacterium Syntrophus aciditrophicus grown in pure culture produced 1.4 +/- 0.24 mol of acetate and 0.16 +/- 0.02 mol of cyclohexane carboxylate per mole of crotonate metabolized. [U-13C]crotonate was metabolized to [1,2-(13)C]acetate and [1,2,3,4,5,7-(13)C]cyclohexane carboxylate. Cultures grown with unlabeled crotonate and [13C]sodium bicarbonate formed [6-(13)C]cyclohexane carboxylate. Trimethylsilyl (TMS) derivatives of cyclohexane carboxylate, cyclohex-1-ene carboxylate, benzoate, pimelate, glutarate, 3-hydroxybutyrate, and acetoacetate were detected as intermediates by comparison of retention times and mass spectral profiles to authentic standards. With [U-(13)C]crotonate, the m/z-15 ion of TMS-derivatized glutarate, 3-hydroxybutyrate, and acetoacetate each increased by +4 mass units, and the m/z-15 ion of TMS-derivatized pimelate, cyclohex-1-ene carboxylate, benzoate, and cyclohexane carboxylate each increased by +6 mass units. With [13C]sodium bicarbonate and unlabeled crotonate, the m/z-15 ion of TMS derivatives of glutarate, pimelate, cyclohex-1-ene carboxylate, benzoate, and cyclohexane carboxylate each increased by +1 mass unit, suggesting that carboxylation occurred after the synthesis of a four-carbon intermediate. With [1,2-(13)C]acetate and unlabeled crotonate, the m/z-15 ion of TMS-derivatized 3-hydroxybutyrate, acetoacetate, and glutarate each increased by +0, +2, and +4 mass units, respectively, and the m/z-15 ion of TMS-derivatized pimelate, cyclohex-1-ene carboxylate, benzoate, cyclohexane carboxylate, and 2-hydroxycyclohexane carboxylate each increased by +0, +2, +4, and +6 mass units. The data are consistent with a pathway for cyclohexane carboxylate formation involving the condensation of two-carbon units derived from crotonate degradation with CO2 addition, rather than the use of the intact four-carbon skeleton of crotonate.

Batch experiments were conducted to study the effects of titanium dioxide (TiO2) concentration and pH on the initial rates of photocatalytic oxidation of aqueous ammonium/ ammonia (NH4+/NH3) and nitrite (NO2-) in UV-illuminated TiO2 suspensions. While no simple kinetic model could fit the data at lower TiO2 concentrations, at TiO2 concentrations > or = 1 g/L, the experimental data were consistent with a model assuming consecutive first-order transformation of NH4+/NH3 to NO2- and NO2- to nitrate (NO3-). For TiO2 concentrations > or = 1 g/L, the rate constants for NO2 photocatalytic oxidation to NO3 were far more dependent on TiO2 concentration than were those for NH4+/NH3 oxidation to NO2-, suggesting that, without sufficient TiO2, complete oxidation of NH4+/NH3 to NO3- will not occur. Initial NH4+/NH3 photocatalytic oxidation rates were proportional to the initial concentrations of neutral NH3 and not total NH3(i.e., [NH4+] + [NH3]). Thus, the pH-dependent equilibrium between NH4+ and NH3, and not the pH-dependent electrostatic attraction between NH4+ and the TiO2 surface, is responsible for the increase in rates of NH4+/NH3 photocatalytic oxidation with increasing pH. Electrostatic adsorption, however, can partly explain the pH dependence of the initial rates of NO2- photocatalytic oxidation. Initial rates of NO2- photocatalytic oxidation were 1 order of magnitude higher for NO2- versus NH4+/NH3, indicating thatthe rate of NH4+/NH3 photocatalytic oxidation to NO3- was limited by NH4+/NH3 oxidation to NO2- under our experimental conditions.

Newsprint samples collected from 12-16 ft (top layer (TNP)), 20-24 ft (middle layer (MNP)), and 32-36 ft (bottom layer (BNP)) below the surface of the Norman Landfill (NLF) were characterized by infrared (IR) spectroscopy, cross-polarization, magic-angle spinning 13C nuclear magnetic resonance (CP-MAS 13C NMR) spectroscopy, and tetramethylammonium hydroxide (TMAH) thermochemolysis gas chromatography/mass spectrometry (GC/MS). The extent of NLF newsprint degradation was evaluated by comparing the chemical composition of NLF newsprint to that of fresh newsprint (FNP) and newsprint degraded in the laboratory under methanogenic conditions (DNP). The O-alkyl/alkyl, cellulose/lignin, and lignin/resin acid ratios showed that BNP was the most degraded, and that all three NLF newsprint samples were more degraded than DNP. 13C NMR and TMAH thermochemolysis data demonstrated selective enrichment of lignin over cellulose, and TMAH thermochemolysis further exhibited selective enrichment of resin acids over lignin. In addition, the crystallinity of cellulose in NLF newsprint samples was significantly lower relative to that of FNP and DNP as shown by 13C NMR spectra. The yield of lignin monomers from TMAH thermochemolysis suggested that hydroxyl groups were removed from the propyl side chain of lignin during the anaerobic decomposition of newsprint in the NLF. Moreover, the vanillyl acid/aldehyde ratio, which successfully describes aerobic lignin degradation, was not a good indicator of the anaerobic degradation of lignin on the basis of the TMAH data. The toluene sorption capacity increased as the degree of newsprint degradation increased or as the O-alkyl/alkyl ratio of newsprint decreased. The results of this study further verified that the sorbent O-alkyl/ alkyl ratio is useful for predicting sorption capacities of natural organic materials for hydrophobic organic contaminants.

13C NMR analyses of hydrophobic dissolved organic matter (DOM) fractions isolated from a landfill leachate contaminated groundwater near Norman, OK; the Colorado River aqueduct near Los Angeles, CA; Anaheim Lake, an infiltration basin for the Santa Ana River in Orange County, CA; and groundwater from the Tomago Sand Beds, near Sydney, Australia, found branched methyl groups and quaternary aliphatic carbon structures that are indicative of terpenoid hydrocarbon precursors. Significant amounts of lignin precursors, commonly postulated to be the major source of DOM, were found only in trace quantities by thermochemolysis/gas chromatography/mass spectrometry of the Norman Landfill and Tomago Sand Bed hydrophobic DOM fractions. Electrospray/tandem mass spectrometry of the Tomago Sand Bed hydrophobic acid DOM found an ion series differing by 14 daltons, which is indicative of aliphatic and aryl-aliphatic polycarboxylic acids. The product obtained from ozonation of the resin acid, abietic acid, gave a similar ion series. Terpenoid precursors of DOM are postulated to be derived from resin acid paper sizing agents in the Norman Landfill, algal and bacterial terpenoids in the Colorado River and Anaheim Lake, and terrestrial plant terpenoids in the Tomago Sand Beds.

The acid-precipitated (AP) and acid-soluble (AS) fractions of the combined hydrophobic neutral and hydrophobic acid dissolved organic carbon (DOC) were isolated from leachate collected from three municipal landfills of different age and redox conditions. The AP and the AS combined hydrophobic neutral and hydrophobic acid DOC comprised 6-15% and 51-66%, respectively, of the leachate nonpurgable organic carbon. Elemental analysis, infra-red spectroscopy, 13C CP-MAS nuclear magnetic resonance spectroscopy and dipolar dephasing experiments, and thermochemolysis gas chromatography/mass spectrometry results showed that the AP and AS fractions of hydrophobic neutral and hydrophobic acid DOC are highly aliphatic, with linear and branching moieties, and less oxidized than most terrestrial and aquatic humic substances. Very little, if any, polysaccharide or cellulose, lignin, or cutin components comprise these fractions. It is hypothesized that a majority of the organic carbon in these fractions originates highly branched, cyclic aliphatic organic compounds.

The sorption of toluene and o-xylene to individual municipal solid waste (MSW) constituents [office paper, newsprint, model food and yard waste, high density polyethylene, and poly(vinyl chloride) (PVC)] was evaluated. Effects of sorbent decomposition and solvent composition on alkylbenzene sorption were studied by evaluating biodegradable sorbents in both fresh and anaerobically decomposed form and by complementing single-solute isotherm tests with experiments conducted in acidogenic and methanogenic leachate. Alkylbenzene sorption to plastics was greaterthan to biopolymer composites, and differences in sorbate/sorbent solubility parameter compatibility explained this observation. Alkylbenzene sorption to biopolymer composites yielded linear isotherms, and sorption capacities [log(Koc/Kow)] decreased linearly with increasing sorbent polarity as expressed by the O-alkyl/alkyl ratio. Leachate composition had little effect on alkylbenzene sorption with one exception; volatile fatty acids in acidogenic leachate appeared to convert PVC from a glassy to a rubbery polymer. The results of this study showed that sorbent organic matter affinity for hydrophobic organic contaminants (HOCs) increases with increasing extent of MSW decomposition because of the recalcitrance of plastics and the preferential degradation of polar biopolymers. Furthermore, the plasticizing effect of volatile fatty acids in acidogenic leachate may enhance the bioavailability of HOCs sorbed to glassy organic matter in MSW or in soils contaminated with acidogenic leachate.

The metabolism of benzoate, cyclohex-1-ene carboxylate, and cyclohexane carboxylate by "Syntrophus aciditrophicus" in cocultures with hydrogen-using microorganisms was studied. Cyclohexane carboxylate, cyclohex-1-ene carboxylate, pimelate, and glutarate (or their coenzyme A [CoA] derivatives) transiently accumulated during growth with benzoate. Identification was based on comparison of retention times and mass spectra of trimethylsilyl derivatives to the retention times and mass spectra of authentic chemical standards. (13)C nuclear magnetic resonance spectroscopy confirmed that cyclohexane carboxylate and cyclohex-1-ene carboxylate were produced from [ring-(13)C(6)]benzoate. None of the metabolites mentioned above was detected in non-substrate-amended or heat-killed controls. Cyclohexane carboxylic acid accumulated to a concentration of 260 microM, accounting for about 18% of the initial benzoate added. This compound was not detected in culture extracts of Rhodopseudomonas palustris grown phototrophically or Thauera aromatica grown under nitrate-reducing conditions. Cocultures of "S. aciditrophicus" and Methanospirillum hungatei readily metabolized cyclohexane carboxylate and cyclohex-1-ene carboxylate at a rate slightly faster than the rate of benzoate metabolism. In addition to cyclohexane carboxylate, pimelate, and glutarate, 2-hydroxycyclohexane carboxylate was detected in trace amounts in cocultures grown with cyclohex-1-ene carboxylate. Cyclohex-1-ene carboxylate, pimelate, and glutarate were detected in cocultures grown with cyclohexane carboxylate at levels similar to those found in benzoate-grown cocultures. Cell extracts of "S. aciditrophicus" grown in a coculture with Desulfovibrio sp. strain G11 with benzoate or in a pure culture with crotonate contained the following enzyme activities: an ATP-dependent benzoyl-CoA ligase, cyclohex-1-ene carboxyl-CoA hydratase, and 2-hydroxycyclohexane carboxyl-CoA dehydrogenase, as well as pimelyl-CoA dehydrogenase, glutaryl-CoA dehydrogenase, and the enzymes required for conversion of crotonyl-CoA to acetate. 2-Ketocyclohexane carboxyl-CoA hydrolase activity was detected in cell extracts of "S. aciditrophicus"-Desulfovibrio sp. strain G11 benzoate-grown cocultures but not in crotonate-grown pure cultures of "S. aciditrophicus". These results are consistent with the hypothesis that ring reduction during syntrophic benzoate metabolism involves a four- or six-electron reduction step and that once cyclohex-1-ene carboxyl-CoA is made, it is metabolized in a manner similar to that in R. palustris.

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.

[1-13C]acenaphthene, a tracer compound with a nuclear magnetic resonance (NMR)-active nucleus at the C-1 position, has been employed in conjunction with a standard broad-band-decoupled 13C-NMR spectroscopy technique to study the biodegradation of acenaphthene by various bacterial cultures degrading aromatic hydrocarbons of creosote. Site-specific labeling at the benzylic position of acenaphthene allows 13C-NMR detection of chemical changes due to initial oxidations catalyzed by bacterial enzymes of aromatic hydrocarbon catabolism. Biodegradation of [1-13C]acenaphthene in the presence of naphthalene or creosote polycyclic aromatic compounds (PACs) was examined with an undefined mixed bacterial culture (established by enrichment on creosote PACs) and with isolates of individual naphthalene- and phenanthrene-degrading strains from this culture. From 13C-NMR spectra of extractable materials obtained in time course biodegradation experiments under optimized conditions, a number of signals were assigned to accumulated products such as 1-acenaphthenol, 1-acenaphthenone, acenaphthene-1,2-diol and naphthalene 1,8-dicarboxylic acid, formed by benzylic oxidation of acenaphthene and subsequent reactions. Limited degradation of acenaphthene could be attributed to its oxidation by naphthalene 1,2-dioxygenase or related dioxygenases, indicative of certain limitations of the undefined mixed culture with respect to acenaphthene catabolism. Coinoculation of the mixed culture with cells of acenaphthene-grown strain Pseudomonas sp. strain A2279 mitigated the accumulation of partial transformation products and resulted in more complete degradation of acenaphthene. This study demonstrates the value of the stable isotope labeling approach and its ability to reveal incomplete mineralization even when as little as 2 to 3% of the substrate is incompletely oxidized, yielding products of partial transformation. The approach outlined may prove useful in assessing bioremediation performance.