Patricia J.S. Colberg

Carbon isotope systematics of monoaromatic hydrocarbons: vaporization and adsorption experiments

Abstract This study investigates the carbon isotope systematics of benzene, toluene, ethylbenzene, and xylene monoaromatic hydrocarbons (BTEX) with regard to an improved understanding of the behavior of these compounds in the subsurface, particularly during remediation processes. We found that fractionation effects due to vaporization are small and positive for all compounds studied (Δ 13 C vapor–liquid ≌+0.2‰), and that fractionation effects due to soil adsorption are also likely to be small ( 13 C-labeled compounds cannot be resolved from unlabeled compounds by HPLC). We also evaluated use of the isotopic composition of contaminants as tracers of source and migration in the subsurface by performing a survey of the bulk isotopic composition of commercially available sources of BTEX. The results indicate that a wide range of δ 13 C values exist (e.g., benzene, −23.87‰ to −29.40‰). Our work suggests that stable C isotope analysis has great potential for qualifying, and possibly quantifying, the subsurface processes affecting contaminant concentrations. In particular, stable isotope analysis may be especially beneficial for monitoring the efficacy of abiological and biological remediation efforts.

Precipitation of arsenic during bacterial sulfate reduction

Contaminated sediments from the Milltown Reservoir in western Montana release arsenic and various heavy metals (e.g., Cu, Cd, Pb, Zn, Mn) into an underlying alluvial aquifer as redox conditions in the sediments change with seasonally fluctuating water levels. Porewater analyses indicate that sulfate is depleted with depth. In this study, the feasibility of inducing As(III) precipitation through bacterial reduction of sulfate was evaluated in laboratory microcosms established under strictly anaerobic conditions. As(lII), Fe(II), and sulfate concentrations were routinely monitored in the aqueous phase as sulfate was reduced to sulfide. Both As(III) and Fe(II) concentrations in the sediment microcosms decreased as sulfide was made available. Energy‐dispersive x‐ray (EDS) analysis indicated that some of the arsenic was precipitated as an iron‐arsenic‐sulfide solid phase. The precipitation of arsenic observed in this laboratory study suggests that bacterial sulfate reduction may be a process by which heavy met...

Toxicity of heavy metals (Ni, Zn) to desulfovibrio desulfuricans

This study is the first to address systematically five important factors necessary to quantify the toxicity of heavy metals to sulfate‐reducing bacteria: metal precipitation due to reaction with components in the media; metal adsorption onto solid phases; precipitation of metal sulfides due to reaction with sulfide initially present in an active microcosm; quantification of initial metal concentrations; and aqueous metal complexing, which reduces metal bioavailability. The toxicity of Ni and Zn to pure cultures of Desulfovibrio desulfuricans was quantified using a chemically defined medium at pH 7.2. Free heavy metal ion activity was calculated using MINTEQA2 and an amended database. A total activity of NP*(aq) + Zn2*(aq) greater than approximately 2.5 X 10‐5 molal is toxic to D. desulfuricans. The results indicate that attempts to remediate Ni and/or Zn contamination by bacterial sulfate reduction are likely to be successful only if total Ni + Zn activity is below this level in order to prevent heavy met...

Does the Segregation of Evolution in Biology Textbooks and Introductory Courses Reinforce Students’ Faulty Mental Models of Biology and Evolution?

The well-established finding that substantial confusion and misconceptions about evolution and natural selection persist after college instruction suggests that these courses neither foster accurate mental models of evolution’s mechanisms nor instill an appreciation of evolution’s centrality to an understanding of the living world. Our essay explores the roles that introductory biology courses and textbooks may play in reinforcing undergraduates’ pre-existing, faulty mental models of the place of evolution in the biological sciences. Our content analyses of the three best-selling introductory biology textbooks for majors revealed the conceptual segregation of evolutionary information. The vast majority of the evolutionary terms and concepts in each book were isolated in sections about evolution and diversity, while remarkably few were employed in other sections of the books. Standardizing the data by number of pages per unit did not alter this pattern. Students may fail to grasp that evolution is the unifying theme of biology because introductory courses and textbooks reinforce such isolation. Two goals are central to resolving this problem: the desegregation of evolution as separate “units” or chapters and the active integration of evolutionary concepts at all levels and across all domains of introductory biology.

In situ immobilization of heavy metals associated with uranium leach mines by bacterial sulfate reduction

Abstract Laboratory experiments with mixed populations of sulfate-reducing bactreria were shown to mediate the removal of milligrams/liter concentrations of uranium, selenium, arsenic and vanadium from aqueous solution via reduction, precipitation and adsorption. Results of laboratory experiments with active sulfidogenic biomass suggest that injection of sulfate and a source of carbon could enhance anaerobic microbial activity in and around uranium leach mines leading to in situ immobilization contaminating metals.

Effects of copper on sulfate reduction in bacterial consortia enriched from metal‐contaminated and uncontaminated sediments

The effects of copper amendments on bacterial sulfate reduction in enrichment cultures obtained from two types of freshwater sediment were examined. Sulfate-reducing bacterial (SRB) consortia were enriched from pond sediment with no known history of metal contamination (uncontaminated) and from reservoir sediment with a well-documented history of metal contamination (metal-contaminated). The rates and extent of sulfate reduction in each sediment type in the absence of added copper were indistinguishable. With amendments of 0.8 mg/L copper, no inhibitory effects on sulfate reduction were observed in either consortium type. At 8.0 mg/L copper, activity in uncontaminated SRB consortia was significantly inhibited, as evidenced by a delay in and decreased rate of sulfate reduction; sulfidogenesis in metal-contaminated consortia was apparently unaffected. When the dissolved copper concentration was 30.0 mg/L, sulfidogenic activity in pond sediment consortia was completely inhibited. The rate of sulfate reduction temporarily decreased in the metal-contaminated enrichments but recovered after a short time. In active microcosms, copper was precipitated as CuS. The results of this study suggest that SRB from metal-contaminated environments have a markedly higher metal tolerance than those enriched from uncontaminated environments. The most significant inference from this work is that metal sulfide formation alone does not explain observed differences in metal tolerance between SRB consortia enriched from uncontaminated sediments and those that are derived from metal-contaminated sediments.

Estimation of Koc values for deuterated benzene, toluene, and ethylbenzene, and application to ground water contamination studies

Sorption partition coefficients between water and organic carbon (Koc) for deuterated benzene, toluene, and ethylbenzene have been estimated by measuring values of the octanol-water partition coefficient (Kow) and HPLC retention factors (k1), which correlate closely to values of Koc. Measured values of log Kow for non-deuterated and deuterated toluene are 2.77 (+/- 0.02) and 2.78 (+/- 0.04), respectively, indicating that within experimental error, log Koc for deuterated and non-deuterated toluene are the same. The HPLC method provides greater precision, and yields values of delta log Koc (= log Koc [deuterated]-log Koc [non-deuterated]) of -0.021 (+/- 0.001) for benzene, -0.028 (+/- 0.002) for toluene, and -0.035 (+/- 0.003) for ethylbenzene. The small values of delta log Koc demonstrates that deuterated compounds are excellent tracers for the hydrologic behavior of ground water contaminants.

Benzene and toluene biodegradation down gradient of a zero-valent iron permeable reactive barrier

This study simulated benzene and toluene biodegradation down gradient of a zero-valent iron permeable reactive barrier (ZVI PRB) that reduces trichloroethylene (TCE). The effects of elevated pH (10.5) and the presence of a common TCE dechlorination by product [cis-1,2-dichloroethene (cis-1,2-DCE)] on benzene and toluene biodegradation were evaluated in batch experiments. The data suggest that alkaline pH (pH 10.5), often observed down gradient of ZVI PRBs, inhibits Fe(III)-mediated biotransformation of both benzene and toluene. Removal was reduced by 43% for benzene and 26% for toluene as compared to the controls. The effect of the addition of cis-1,2-DCE on benzene and toluene biodegradation was positive and resulted in removal that was greater than or equal to the controls. These results suggest that, at least for cis-1,2-DCE, its formation may not be toxic to iron-reducing benzene and toluene degrading bacteria; however, for microbial benzene and toluene removal down gradient of a ZVI PRB, it may be necessary to provide pH control, especially in the case of a biological PRB that is downstream from a ZVI PRB.

Role of sulfate in microbial transformations of environmental contaminants: chlorinated aromatic compounds.

Abstract Despite recent progress made in describing microbial transformations that occur under anaerobic conditions, our understanding of the role sulfate‐reducing bacteria may play in the remediation of environmental contaminants is still very limited. The objective of this mini‐review is to summarize what is currently known of the metabolism of chlorinated aromatic compounds in the presence of sulfate. Sulfidogenic processes are discussed with respect to the thermodynamics of haloaromatic oxidation and to their potential use in the in situ bioremediation of hazardous organic wastes. A comprehensive listing is made of anaerobic transformations that involve both halogenated and nonhalogenated monoaromatic substrates by denitrifiers, dissimilatory iron‐reducing bacteria, and methanogenic consortia. In contrast to other anaerobic processes, studies involving sulfate‐mediated metabolism of hazardous organic compounds have been neglected; however, the recent success in defining methanogenic transformations, i...

Characterization and treatment of dissolved organic matter from oilfield produced waters.

Dissolved organic matter (DOM) has been studied intensively in streams, lakes and oceans due to its role in the global carbon cycle and because it is a precursor of carcinogenic disinfection by-products in drinking water; however, relatively little research has been conducted on DOM in oilfield produced waters. In this study, recovery of DOM from two oilfield produced waters was relatively low (~34%), possibly due to the presence of high concentrations of volatile organic compounds (VOCs). A van Krevelen diagram of the extracted DOM suggested the presence of high concentrations of lipids, lignin, and proteins, but low concentrations of condensed hydrocarbons. Most of the compounds in the oilfield DOM contained sulfur in their structures. Fourier transform infrared (FTIR) spectra indicated the presence of methyl groups, amides, carboxylic acids, and aromatic compounds, which is in agreement with results of Fourier transform ion cyclotron resonance (FT-ICR) analysis. Qualitatively, DOM in oilfield produced waters is similar to that reported in oceans and freshwater, except that it contains much more sulfur and is less aromatic. Treatment studies conducted in a fluidized bed reactor suggested that volatilization of organics may be a more important mechanism of DOM removal than microbial degradation.