Robert G Arnold

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• Arnold, R. G., Saez, A. E., Snyder, S. A., Abrell, L. M., Dong, B., Kahl, A., Wickramasekara, S., Cheng, L., Vo, H., Ruehl, S., Zhang, T., & Quanrud, D. (2015). Fate of Trace Organics in an Effluent Dependent Stream. Science of the Total Environment, 518-19, 479-90.
• Noel-Brune, M., Goldizen, F. C., Neira, M., van, M., Lewis, N., King, M., Suk, W. A., Carpenter, D. O., Arnold, R. G., & Sly, P. D. (2013). Health effects of exposure to e-waste. The Lancet Global Health, 1(2), e70.
• Wickramasekara, S., Hernández-Ruiz, S., Abrell, L., Arnold, R., & Chorover, J. (2012). Natural dissolved organic matter affects electrospray ionization during analysis of emerging contaminants by mass spectrometry. Analytica Chimica Acta, 717, 77-84.
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  PMID: 22304818;Abstract: Dissolved organic matter (DOM), present in many forms in water, can interfere with analysis of organic contaminants by atmospheric pressure ionization-mass spectrometry. A quantitative analysis of this interference, or matrix effect, on organic contaminant target analyte measurements was carried out using un-fractionated and fractionated dissolved natural organic matter from the Suwannee River, GA (SROM), a standard reference material, that was directly infused into the tandem mass spectrometer during multiple reaction monitoring (MRM) of a suite of endocrine disrupting compounds-pharmaceuticals and personal care products (EDC/PPCPs). Most target analytes suffered signal suppression in the presence of both fractionated and un-fractionated SROM, however greater interferences were measured with fractionated relative to bulk SROM. This finding is consistent with the view of organic matter as a supramolecular association of low molecular mass components having separate charged and structural features revealed only after dissociation. © 2012 Elsevier B.V.
• Gavidia, T., Brune, M., McCarty, K. M., Pronczuk, J., Etzel, R., Neira, M., Carpenter, D. O., Suk, W. A., Arnold, R. G., Ha, E. H., & Sly, P. D. (2011). Children's environmental health - From knowledge to action. The Lancet, 377(9772), 1134-1136.
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  PMID: 20667587;
• Santamaría, J., De, M., Lemond, L., Arnold, R. G., Quanrud, D., Gerba, C., & Brusseau, M. L. (2011). Transport of Cryptosporidium parvum oocysts in sandy soil: Impact of length scale. Journal of Environmental Monitoring, 13(12), 3481-3484.
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  PMID: 22027739;Abstract: The objective of this study was to investigate the impact of length scale (travel distance) on the retention and transport of Cryptosporidium oocysts in a sandy soil. Long columns (1 and 2 meters) and an in situ lysimeter (4 m) were used to allow investigation of larger-scale transport under controlled conditions. Significant retention of oocysts was observed, with the magnitude of removal from solution ranging between 2 to 5 logs. While the removal was greater for longer travel distances (or residence times), the increase was not log-linear. This observation indicates that oocyst transport was not consistent with standard colloid filtration theory. The observed behavior is speculated to arise, at least in part, from intrapopulation variability in oocyst properties. The results of this study indicate that while Cryptosporidium oocysts may be expected to experience significant retention and removal during transport in sandy soil, the magnitude of retention may be less than that which would be predicted by applying standard colloid filtration theory to the results of typical short-column experiments. Thus, a fraction of the oocysts may be more mobile than anticipated and thereby pose a greater than expected risk to groundwater. © 2011 The Royal Society of Chemistry.
• Sly, P. D., Arnold, R. G., & Carpente, D. O. (2011). Environmental exposures in the era of climate change. Reviews on Environmental Health, 26(1), 3-5.
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  PMID: 21714375;
• Teske, S. S., & Arnold, R. G. (2008). Removal of natural and xeno-estrogens during conventional wastewater treatment. Reviews in Environmental Science and Biotechnology, 7(2), 107-124.
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  Abstract: The ecological impacts of natural estrogens and xenoestrogens in treated wastewater include altered sexual development and sex ratios among continuously exposed organisms. The primary sources of estrogenic activity in wastewater are natural estrogens such as estrone, 17β-estradiol and estriol and synthetic compounds like 17α-ethinylestradiol, alkylphenols and alklphenol ethoxylates. Precursors in raw wastewater can yield estrogenic intermediates during wastewater treatment. All these compounds can be destroyed by biochemical processes, albeit at significantly different rates or under different conditions. That is, estrogenic compounds can be, but are not always, destroyed by conventional wastewater treatment processes, suggesting that conventional processes can be optimized for removal of estrogenic activity from wastewater. Sorption to sludges derived from wastewater treatment affects the fates of hydrophobic xenoestrogens such as nonylphenol, in part because the biodegradability of sorbed contaminants is limited. It may also be possible to tailor sludge stabilization processes to remove trace contaminants, including estrogens. For example, there are significant differences in the efficiencies of aerobic and anaerobic digestion for destruction of alkylphenols and probably other estrogenic compounds with aromatic moieties. Because advanced wastewater treatment is not economically feasible for most communities, there is ample incentive to develop accurate relationships between operational parameters and removal of estrogenic compounds during secondary wastewater treatment. © 2008 Springer Science+Business Media B.V.
• Arnold, R. G., Carpenter, D. O., Kirk, D., Koh, D., Armour, M., Cebrian, M., Cifuentes, L., Khwaja, M., Ling, B., Makalinao, I., Paz-Y-Miño, C., Peralta, G., Prasad, R., Singh, K., Sly, P., Tohyama, C., Woodward, A., Zheng, B., & Maiden, T. (2007). Meeting report: threats to human health and environmental sustainability in the pacific basin.. Environmental health perspectives, 115(12), 1770-1775.
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  PMID: 18087598;PMCID: PMC2137106;Abstract: The coastal zone of the Pacific Rim is home for about one-third of the world's population. Disproportionate growth of Far Eastern economies has produced a disproportionate share of related environmental difficulties. As the region searches for acceptable compromises between growth and environmental quality, its influence on global environmental health is certain to increase. Consequences of global environmental change such as habitat alteration, storms, and sea level rise will be particularly acute among Pacific Rim nations. Adverse health effects from arsenic exposure in Pacific Rim nations have been used to justify drinking water standards in the United States and elsewhere. As global manufacturing in the Pacific Rim increases, the centroid of global air quality and waste management issues will shift further toward Far Eastern nations. The Eleventh International Conference of the Pacific Basin Consortium (PBC) was held in September 2005 in Honolulu, Hawaii. The purpose of the conference was to bring together individuals to discuss regional challenges to sustainable growth. The historic emphasis of the conference on hazardous wastes in relation to human health makes the PBC an ideal forum for discussing technical aspects of sustainable economic growth in the Pacific region. That role is reflected in the 2005 PBC conference themes, which included management of arsenic in potable waters, air quality, climate change, pesticides, mercury, and electronics industry waste-each with emphasis on relationships to human health. Arsenic management exemplifies the manner in which the PBC can focus interdisciplinary discussion in a single technical area. The conference program provided talks on arsenic toxicology, treatment technologies, management of arsenic-bearing residuals from water treatment, and the probable societal costs and benefits of arsenic management.
• Arnold, R., Conroy, O., Sáez, A. E., Quanrud, D., Ela, W., & Arnold, R. G. (2007). Changes in estrogen/anti-estrogen activities in ponded secondary effluent. The Science of the total environment, 382(2-3).
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  Total estrogenic activity, measured using the yeast estrogen screen reporter gene bioassay, decreased from 60 pM (equivalent 17alpha-ethinylestradiol concentration) to an estimated 1.4 pM during a 24-hour period in which secondary effluent was held in a shallow infiltration basin. Over the same period, anti-estrogenic activity, measured as an equivalent concentration of tamoxifen, increased from 35 to 260 nM, suggesting that antagonists produced during secondary effluent storage played a role in the apparent loss of estrogenic activity. Androgenic activity, measured over the same 24-hour period using the yeast androgen screen, was near or below the method detection limit (0.7 pM as testosterone). However, the same pond samples were clearly anti-androgenic. When whole-sample extracts were separated via adsorption and stepwise elution in alcohol/water solutions consisting of 20, 40 and 100% ethanol, the sum of estrogenic activities in derived fractions was always lower than the measured estrogenic activity in the whole-sample extracts. Summed anti-estrogenic activities in the same fractions, however, always exceeded values for corresponding whole-sample extracts. Results reinforce the importance of sample preparation steps (concentration of organics followed by estrogen/anti-estrogen separation) when measuring endocrine-related activities in chemically complex samples such as wastewater effluent. The potential complexity of relationships among estrogens, anti-estrogens and matrix organics suggests that additive models are of questionable validity for estimating whole-sample estrogenic activity from measurements involving sample fractions.
• Littlehat Jr., P., Arnold, R. G., Bahl, J. J., Quanrud, D., Morkin, E., & Adamson, C. (2007). Thyroid receptor-mediated transcriptional activity in environmentally relevant wastewater. Restoring Our Natural Habitat - Proceedings of the 2007 World Environmental and Water Resources Congress.
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  Abstract: Wastewater reclamation and reuse is imperative in water-starved areas such as the southwestern United States. In the Tucson Active Management Area, a geographic region defined for the purpose of groundwater management, the total demand for water already exceeds the available water supply, which consists of renewable ground water and the regional entitlement to Central Arizona Project water. Thus, the regional demand cannot be satisfied without resorting to groundwater mining unless water is reclaimed for local beneficial use. Less certain are the acceptable uses for reclaimed water and the nature of use-dependent treatments or water quality requirements that will protect human and ecological health. Disruption of thyroid-mediated actions is among the possible risks from chronic exposure to environmental contaminants. Although numerous pharmaceuticals and personal care products have been detected in surface waters of the United States that are influenced by wastewater effluent, only a few such compounds are present at concentrations that produce recognizable adverse effects in the environment. Endocrine disrupting compounds (EDCs) are generally of greater concern in this context than other trace contaminants because of the very low concentrations at which hormones induce physiological responses. Anthropogenic chemicals can disrupt nuclear thyroid hormone signaling without affecting circulating levels of thyroid hormone. Accordingly, we sought to develop a sensitive nuclear-based assay system in order to evaluate environmental samples. The use of a Luciferase-based reporter assay is commonly used to detect transcriptional activity. We evaluated a luciferase-reporter construct and the human thyroid receptor β (TR-β) construct for sensitivity in the human hepatoma cell line, (Hep G2). The transfected cells were exposed to T3 at concentrations in the range 10-6 to 10-1 1M in order to establish a lower thyroid hormone detection limit and EC50 for the new bioassay procedure. The assay was then applied to environmental samples containing organics concentrated from final effluent derived from a conventional secondary wastewater treatment plant. The effluent samples activated thyroid receptor-mediated transcription. © 2007 ASCE.
• Arnold, R., Otakuye, C., Quanrud, D. M., Ela, W. P., Wicke, D., Lansey, K. E., & Arnold, R. G. (2005). Fate of wastewater effluent hER-agonists and hER-antagonists during soil aquifer treatment. Environmental science & technology, 39(7).
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  Estrogen activity was measured in wastewater effluent before and after polishing via soil-aquifer treatment (SAT) using both a (hER-beta) competitive binding assay and a transcriptional activation (yeast estrogen screen, YES) assay. From the competitive binding assay, the equivalent 17alpha-ethinylestradiol (EE2) concentration in secondary effluent was 4.7 nM but decreased to 0.22 nM following SAT. The YES assay indicated that the equivalent EE2 concentration in the same effluent sample was below the method-detection limit (
• Arnold, R., Quanrud, D. M., Karpiscak, M. M., Lansey, K. E., & Arnold, R. G. (2004). Transformation of effluent organic matter during subsurface wetland treatment in the Sonoran Desert. Chemosphere, 54(6).
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  The fate of dissolved organic matter (DOM) during subsurface wetland treatment of wastewater effluent in a hot, semi-arid environment was examined. The study objectives were to (1) discern changes in the character of dissolved organics as consequence of wetland treatment (2) establish the nature of wetland-derived organic matter, and (3) investigate the impact of wetland treatment on the formation potential of trihalomethanes (THMs). Subsurface wetland treatment produced little change in DOM polarity (hydrophobic-hydrophilic) distribution. Biodegradation of labile effluent organic matter (EfOM) and internal loading of wetland-derived natural organic matter (NOM) together produced only minor changes in the distribution of carbon moieties in hydrophobic acid (HPO-A) and transphilic acid (TPI-A) isolates of wetland effluent. Aliphatic carbon decreased as a percentage of total carbon during wetland treatment. The ratio of atomic C:N in wetland-derived NOM suggests that its character is determined by microbial activity. Formation of THMs upon chlorination of HPO-A and TPI-A isolates increased as a consequence of wetland treatment. Wetland-derived NOM was more reactive in forming THMs and less biodegradable than EfOM. For both HPO-A and TPI-A fractions, relationships between biodegradability and THM formation potential were similar among EfOM and NOM isolates; the less biodegradable isolates exhibited greater THM formation potential.
• Arnold, R., Quanrud, D. M., Carroll, S. M., Gerba, C. P., & Arnold, R. G. (2003). Virus removal during simulated soil-aquifer treatment. Water research, 37(4).
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  Removals of indigenous coliphage and seeded poliovirus type 1 during simulated soil-aquifer treatment were evaluated during transport of secondary effluent under unsaturated flow conditions in 1-m soil columns. Independent variables included soil type (river sand or sandy loam) and infiltration rate. Removal of coliphage was in all cases less than removal of poliovirus type 1 (strain LSc-2ab), supporting contentions that indigenous coliphage can act as a conservative indicator of groundwater contamination by viral pathogens of human origin. Coliphage retention was significantly more efficient (p
• Arnold, R., Quanrud, D. M., Hafer, J., Karpiscak, M. M., Zhang, J., Lansey, K. E., & Arnold, R. G. (2003). Fate of organics during soil-aquifer treatment: sustainability of removals in the field. Water research, 37(14).
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  A 5-year program of study was conducted at the Sweetwater Recharge Facilities (SRF) to assess the performance of surface spreading operations for organics attenuation during field-scale soil-aquifer treatment (SAT) of municipal wastewater. Studies were conducted utilizing both mature (approximately 10 yr old) and new infiltration basins. Removals of dissolved organic carbon (DOC) were robust, averaging >90 percent during percolation through the local 37-m vadose zone. The hydrophilic (most polar) fraction of DOC was preferentially removed during SAT; removals were attributed primarily to biodegradation. Reductions in trihalomethane formation potential (THMFP) averaged 91 percent across the vadose zone profile. The reactivity (specific THMFP) of post-SAT organic residuals with chlorine decreased slightly from pre-SAT levels (60 vs. 72 microg THM per mg DOC, respectively). Variations in the duration of wetting/drying periods did not significantly impact organic removal efficiencies.
• Quanrud, D. M., Carroll, S. M., Gerba, C. P., & Arnold, R. G. (2003). Virus removal during simulated soil-aquifer treatment. Water Research, 37(4), 753-762.
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  PMID: 12531257;Abstract: Removals of indigenous coliphage and seeded poliovirus type 1 during simulated soil-aquifer treatment were evaluated during transport of secondary effluent under unsaturated flow conditions in 1-m soil columns. Independent variables included soil type (river sand or sandy loam) and infiltration rate. Removal of coliphage was in all cases less than removal of poliovirus type 1 (strain LSc-2ab), supporting contentions that indigenous coliphage can act as a conservative indicator of groundwater contamination by viral pathogens of human origin. Coliphage retention was significantly more efficient (p
• Arnold, R. G., Turney, K. D., & Scholz, M. (2001). In vitro measurement of chemical toxicity in complex mixtures. ACS Division of Environmental Chemistry, Preprints, 41(1), 1008-1010.
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  Abstract: Pressure on water resources has forced planners to consider use of less desirable water supply alternatives. A study on the development and/or application of two types of in vitro biochemical tests for the measurement of chemical toxicity in water was carried out. Microarray technologies that may be used to anticipate whole-organism or tissue-specific responses to low-dose chemical exposure were examined. About 30 cDNA sequences were selected for inclusion in a microarray based on their previously observed up or down regulation in embryonic rat hearts exposed to TCE. The gene expression products cross reacted with other genes with sufficient sequence homology. Such non-specific hybridizations would have to be eliminated or minimized before the technology can be widely applied. This is an abstract of a paper presented at the 221st ACS National Meeting (San Diego, CA 4/1-5/2001).
• Huling, S. G., Arnold, R. G., Sierka, R. A., & Miller, M. R. (2001). Influence of Peat on Fenton Oxidation. Water Research, 35(7), 1687-1694.
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  PMID: 11329670;Abstract: A diagnostic probe was used to estimate the activity of Fenton-derived hydroxyl radicals (·OH), reaction kinetics, and oxidation efficiency in batch suspensions comprised of silica sand, crushed goethite (α-FeOOH) ore, peat, and H2O2 (0.13mM). A simple method of kinetic analysis is presented and used to estimate the rate of ·OH production (POH) and scavenging term (kS), which were used to establish the influence of organic matter (Pahokee peat) in Fenton systems. POH was greater in the peat-amended systems than in the unamended control, and kS was approximately the same. Any increase in scavenging of ·OH that resulted from the addition of peat was insignificant in comparison to radical scavenging by reaction with H2O2. Also, treatment efficiency, defined as the ratio of probe conversion to H2O2 consumption over the same period was greater in the peat-amended system. Results suggest that ·OH production is enhanced in the presence of peat by one or more peat-dependent mechanisms. Fe concentration and availability in the peat, reduction of Fe(III) to Fe(II) by the organic matter, and reduction of organic-complexed Fe(III) to Fe(II) are discussed in the context of the Fenton mechanism. Copyright © 2001 Elsevier Science Ltd.
• Liu, Z., Arnold, R. G., Betterton, E. A., & Smotkin, E. (2001). Reductive dehalogenation of gas-phase chlorinated solvents using a modified fuel cell. Environmental Science and Technology, 35(21), 4320-4326.
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  PMID: 11718349;Abstract: The reductive dehalogenation of gas-phase chlorinated alkanes (CCl 4, CHCl 3, and 1,1,1-trichloroethane) and alkenes (perchloroethene (PCE) and trichloroethene (TCE)) was conducted in a modified fuel cell. The fuel-cell performance was a function of cathode material, electric potential, temperature, target compound identity and gas-phase concentration, partial pressure of O 2 in the cathode chamber, and cathode condition (time in service). TCE conversion was approximately first order in TCE concentration with half-lives of fractions of a second. Under the same reactor conditions, CCl 4 transformation was faster than CHCl 3, and TCE reduction was faster than PCE. Rates of both CCl 4 and PCE transformation increased substantially with temperature in the range of 30-70 °C. At 70 °C and a potential (potential of the cathode minus that of the anode) of -0.4 V, single-pass CCl 4 conversions were approximately 90%. Mean residence time for gases in the porous cathode was much less than 1 s. The presence of even 5% O 2(g) in the influent to the cathode chamber had a deleterious effect on reactor performance. Performance also deteriorated with time in service, perhaps due to the accumulation of HCl on the cathode surface. Conversion efficiency was restored, however, by temporarily eliminating the halogenated target(s) from the influent stream or by briefly reversing fuel-cell polarity.
• Betterton, E. A., Hollan, N., Arnold, R. G., Gogosha, S., Mckim, K., & Liu, Z. (2000). Acetone-photosensitized reduction of carbon tetrachloride by 2-propanol in aqueous solution. Environmental Science and Technology, 34(7), 1229-1233.
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  Abstract: Simple carbonyl chromophores can be used to facilitate the solar- promoted reductive dehalogenation of halo-organics. Here we describe the kinetics and mechanism of the reductive dehalogenation of carbon tetrachloride (CT) to chloroform (CF) in the presence of aqueous acetone and 2-propanol, which is added as a hydrogen donor. The reaction is rapid in sunlight, stoichiometrically converting 3 mM CT to CF in approximately 2 min. Under typical conditions (0.69 M acetone, 5.7 M 2-propanol, 3 mM CT) using a 75 W Xe lamp, the observed zero-order reaction occurs at a rate of 2.7 x 10-6 M s-1. The mechanism appears to become first order in CT near the end of the reaction. The zero-order reaction rate increased with both acetone- and 2-propanol concentration and also with absorbed light intensity. Other combinations of carbonyls, alcohols, and halogenated organics are also effective.
• Huling, S. G., Arnold, R. G., Jones, P. K., & Sierka, R. A. (2000). Predicting Fenton-driven degradation using contaminant analog. Journal of Environmental Engineering, 126(4), 348-353.
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  Abstract: The hydroxyl radicals generated by the reaction between hydrogen peroxide and Fe(II), also known as Fenton's reaction, can prove useful for the oxidation of contaminants contained in soils and aquifers. A number of factors can act to limit the impacts of chemical oxidation processes in such environments are considered, including reactions involving hydrogen peroxide that do not produce -OH, -OH reactions with nontargeted chemicals, and insufficient iron in the soil or aquifer. Site-specific analyses may be needed to assess the feasibility of chemical oxidation using hydrogen peroxide. Estimates of -OH concentrations were generated based on findings from tests investigating the degradation of a contaminant analog, α-(4-pyridyl-1-oxide) N-tert-butylnitrone. The development of a kinetic model is described.
• Huling, S. G., Arnold, R. G., Sierka, R. A., Jones, P. K., & Fine, D. D. (2000). Contaminant adsorption and oxidation via Fenton reaction. Journal of Environmental Engineering, 126(7), 595-600.
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  Abstract: A ground-water treatment process is described in which contaminants are adsorbed onto granulated activated carbon (GAC) containing fixed iron oxide. Hydrogen peroxide (H2O2) is amended to the GAC suspension and reacts with the iron, forming hydroxyl radicals (.OH). The radicals react with and oxidize sorbed and soluble contaminants regenerating the carbon surface. Laboratory results are presented in which 2-chlorophenol (2CP) was first adsorbed to GAC and subsequently oxidized via the Fenton-driven mechanism. Transformation of 2CP was indicated by the formation of carboxylic acids and Cl-release. The treatment efficiency of 2CP, defined as the molar ratio of Cl-released to H2O2 consumed, increased with increasing amounts of iron oxide and 2CP on the GAC. The extent of 2CP oxidation increased with H2O2 concentration. Lower treatment efficiency was evident at the highest H2O2 concentration utilized (2.1 M) and was attributed to increased .OH scavenging by H2O2. Aggressive oxidation procedures used in sequential adsorption/oxidation cycles did not alter the GAC surface to a degree that significantly interfered with subsequent 2CP adsorption reactions. Although process feasibility has not yet been established beyond bench-scale, experimental results illustrate the potential utility of the adsorption/oxidation process in aboveground systems or permeable reactive barriers for the treatment of contaminated ground water.
• Liu, Z., Betterton, E. A., & Arnold, R. G. (2000). Electrolytic reduction of low molecular weight chlorinated aliphatic compounds: Structural and thermodynamic effects on process kinetics. Environmental Science and Technology, 34(5), 804-811.
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  Abstract: A series of chlorinated low molecular weight alkanes and alkenes was transformed electrolytically using a porous nickel cathode at potentials from -0.3 to -1.4 V (versus standard hydrogen electrode). Kinetics were first- order with respect to the concentration of the halogenated targets. The dependence of the first-order rate constants on cathode potential followed thee Butler-Volmer equation, modified to account for mass transfer resistance to reaction. The masstransfer-limited rate constant for reaction of all species was about 1.55 L m-2 min-1. Log-transformed reaction rate constants for reduction of chlorinated alkanes, derived via experiments at the same cathode potential (E(c) = -1.0 or -1.2 V vs SHE), were linearly related to carbon-halogen bond enthalpies, as expected based on a physical model that was developed from transition state theory. The chlorinated ethenes reacted much faster than predicted from bond enthalpy calculations and the alkane-based correlation, suggesting that alkenes are not transformed via the same mechanism as the chlorinated alkanes. Dihaloelimination was the predominant pathway for reduction of vicinal polychlorinated alkanes. For chlorinated alkenes and geminal chlorinated alkanes, sequential hydrogenolysis was the major reaction pathway.
• Chen, G., Betterton, E. A., & Arnold, R. G. (1999). Electrolytic oxidation of trichloroethylene using a ceramic anode. Journal of Applied Electrochemistry, 29(8), 961-970.
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  Abstract: Trichloroethylene (TCE) was transformed to CO2, CO, Cl- and ClO3- at the anode of a two-chambered electrolytic cell. The working electrode was constructed from Ebonex, an electrically conductive ceramic (Ti4O7). Under our experimental conditions (anode potential Ea = 2.5 to 4.3 V vs SSCE), the disappearance of TCE was first order in TCE concentration. The transformation rate was independent of pH in the range 1.6
• Jewett, D. G., Logan, B. E., Arnold, R. G., & Bales, R. C. (1999). Transport of Pseudomonas fluorescens strain P17 through quartz sand columns as a function of water content. Journal of Contaminant Hydrology, 36(1-2), 73-89.
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  Abstract: Porous media column experiments were used to investigate Pseudomonas fluorescens strain P17 transport as a function of water content and the influences of the solid-liquid and gas-liquid interfaces. Retention of radiolabeled P17 in washed quartz sand was evaluated at 100, 84, and 46% water saturation. At the completion of each experiment, the porous medium was extruded and sampled directly for cell retention on the basis of a radiolabel mass balance. Maximum cell retention occurred in the top centimeter of porous media at all three water contents and decreased with depth in the column. The total fraction of cells retained (R(t)) was inversely proportional to water content, with nearly twice the cell retention at 46% saturation (R(t)=0.95) compared to retention in 100% water-saturated experiments (R(t)=0.50). Total retained cells were further divided into strongly and weakly attached fractions by settling a sample of the porous medium through groundwater to dislodge loosely adhering cells. Cells that became suspended in the solution represented the fraction retained at the gas-liquid interface or weakly attached to the solid-liquid interface (R(g)). Those that remained attached to the porous medium were defined as cells strongly attached to the solid-liquid interface (R(s)). Values of R(g)/R(t) were inversely related to water content, while R(s)/R(t) decreased with decreasing saturation. Bacteria thus preferentially accumulated at the gas-liquid interface with total cell removal inversely proportional to water content. The increased retention of bacteria at the gas-liquid interface indicates the presence of the interface is an important factor in limiting pathogen migration, evaluating biocolloid-facilitated transport of pollutants, and developing bioremediation strategies for unsaturated porous media. Copyright (C) 1999 Elsevier Science B.V.
• Liu, Z., Arnold, R. G., Betterton, E. A., & Festa, K. D. (1999). Electrolytic reduction of CCl₄-Effects of cathode material and potential on kinetics, selectivity, and product stoichiometry. Environmental Engineering Science, 16(1), 1-13.
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  Abstract: Carbon tetrachloride (CCl4) was reductively transformed via electrolysis at metal cathodes consisting of pure Ag, Al, Au, Cu, Fe, Ni, Pd, and Zn. Primary products included CHCl3, CH2Cl2 and CH4. Traces of CH3Cl, C2H4, C2H6, C3H8, and other unidentified products were also observed in headspace samples. CHCl3 was reduced to CH2Cl2 and CH4 under the same experimental conditions, although at a slower rate. CH2Cl2 was essentially stable during the course of these experiments (k(s) < 0.05 L/m2 · min). CCl4 reduction was first order in the bulk liquid phase concentration. Pseudo-first-order rate constants were a function of cathode material, pH, and applied cathode potential (E(c)) in the range -1.4 V ≤ E(c) ≤ -0.4 V vs. SHE. At all electrodes, reaction rates conformed to Butler-Volmer kinetics, modified to account for mass transfer limitations. Under comparable conditions, the kinetics of Cl4 electrolysis at Ni and Cu electrodes were superior to those of transformation using any other metal tested. At E(c) = -0.6 and -0.8 V, rate constants for CCl4 reduction at a Cu electrode decreased with increasing pH in the range 2 < pH < 6. At E(c) ≤ - 1.2 V, reduction was limited by mass transfer to the electrode surface and was independent of cathode material and pH. Electrode efficiency (ratio of dehalogenation rate to total electrolytic current) for CCl4 reduction was inversely related to the material-dependent exchange current density for hydrogen gas generation, suggesting that production of H2 (g) is the most significant competitive reaction under the conditions of the experiments. Based on efficiency considerations, the electrode materials were ordered Zn > Cu > Fe > Ni.
• Huling, S. G., Arnold, R. G., Sierka, R. A., & Miller, M. R. (1998). Measurement of hydroxyl radical activity in a soil slurry using the spin trap α-(4-pyridyl-1-oxide)-N-tert-butylnitrone. Environmental Science and Technology, 32(21), 3436-3441.
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  Abstract: The spin trap-compound α-(4-pyridy-M-oxide)N-tert-butylnitrone (4- POBN) served as a probe to estimate the activity of Fenton-derived hydroxyl radicals (·OH) in a batch suspension comprised of silica sand and crushed goethite ore. The rate of probe disappearance was used to analyze system kinetics and oxidation efficiency under heterogeneous, Fenton-driven conditions. The ·OH-(4-POBN) adduct produced by the reaction of 4-POBN with ·OH was observed via electron paramagnetic resonance to confirm the mechanism of 4-POBN transformation. The disappearance of 4-POBN with ·OH in the sand/goethite slurry amended with H2O2 (150 mM) was first-order in 4- POBN. Under the conditions of this experiments, the effective steady-state ·OH concentration ([·OH](ss)) was estimated at 1.2 x 10-15 and 6.5 x 10-16 M, when 4-POBN was initially present at 700 and 144 μM, respectively. Observed kinetics were in qualitative agreement with a conceptual model in which H2O2 is consumed in both Fenton and non-Fenton reactions and 4-POBN competes with other slurry constituents for ·OH. Reaction of H2O2 with ·OH was an appreciable sink for ·OH, but the reaction did not contribute significantly to H2O2 depletion. Nonproductive reactions involving H2O2 (those that did not contribute to ·OH production) represented a significant source of overall reaction inefficiency, as defined.
• Amy, G., Debroux, J. -., Arnold, R., & Wilson, L. -. (1996). Preozonation for enhancing the biodegradability of wastewater effluent in a potable-recovery soil aquifer treatment (SAT) system. Revue des Sciences de l'Eau, 9(3), 365-380.
• Martin, M. J., Logan, B. E., Johnson, W. P., Jewett, D. G., & Arnold, R. G. (1996). Scaling bacterial filtration rates in different sized porous media. Journal of Environmental Engineering, 122(5), 407-415.
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  Abstract: Aquifer sediments contain a wide distribution of particle sizes, but only a single collector diameter (d) can be used in a filtration equation. To establish a method for selecting a characteristic d when media are composed of different sized particles, we measured bacterial retention in columns packed with either crushed quartz sand (separated into three different size ranges) or borosilicate glass beads. The best methods for choosing d were those that produced nearly constant collision efficiencies (αs). Characteristic diameters included: d10(10% of all particles were smaller), d90(90% of all particles were smaller), da (arithmetic mean), and dg (geometric mean), where all diameters were calculated using number, area, and volume size distributions. Bacteria αs decreased in proportion to the distance traveled in the packed bed, and were scaled by the number of bacteria-sediment collisions using a dimensionless collision number (ε). These comparisons indicated that characteristic diameters based on the smaller particles (da and dg using number distributions, and d10 using a volume distribution) most accurately described bacterial transport in the different-sized porous media.
• Quanrud, D. M., Arnold, R. G., Wilson, L. G., & Conklin, M. H. (1996). Effect of soil type on water quality improvement during soil aquifer treatment. Water Science and Technology, 33(10-11), 419-431.
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  Abstract: Bench-scale soil column experiments were performed at The University of Arizona to examine the effects of soil type and infiltration rate on the removal of wastewater organics during soil aquifer treatment (SAT). The suitability of such waters for potable uses following a combination of above-ground treatments and SAT polishing was under investigation, SAT was simulated in 1-meter soil columns containing repacked homogenized soils ranging from poorly graded sands to silty sands. Soils were obtained from existing and potential effluent recharge sites in Arizona. All columns received chlorinated/dechlorinated secondary effluent, ponded to a 25-cm depth above the soil surface, under alternating wet/dry conditions. Treatment efficiencies in biologically active and inhibited columns were compared to determine the mechanism(s) of water quality improvements and the sustainability of SAT. Water quality parameters included: (i) non-purgable dissolved organic carbon and (ii) UV absorbance at 254 nm (used as a measure of disinfection-by-product precursors). Differences in through-column removal of non-purgable dissolved organic carbon were significant for columns containing sandy loam (56%), sand (48%) and silty sand (44%). Removal of UV-absorbing organics was not significantly different for columns containing sand and sandy loam (22 and 20%, respectively). There was no significant correlation between infiltration rate and removal efficiency of either organic parameter for both soils.
• Quanrud, D. M., Arnold, R. G., Wilson, L. G., Gordon, H. J., Graham, D. W., & Amy, G. L. (1996). Fate of organics during column studies of soil aquifer treatment. Journal of Environmental Engineering, 122(4), 314-321.
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  Abstract: Soil column experiments were performed to differentiate between abiotic and biological mechanisms for removal of residual organics from chlorinated municipal effluent during soil aquifer treatment (SAT) and to relate SAT efficiency to degree of wastewater treatment. Three water-quality parameters were examined: dissolved organic carbon (DOC), ultraviolet (UV) absorbance at 254 nm (UVA254), and adsorbable organic halide (AOX). Secondary and tertiary-treated effluents were applied to 1-m unsaturated columns containing soils from the Sweetwater Underground Storage and Recovery Facility, Tucson, Ariz. DOC was removed primarily by biological activity during SAT. Through-column removal using chlorinated secondary effluent averaged 48%. UVA254 reductions were dependent on biological and abiotic removal mechanisms. Aerobic biological activity did not contribute significantly to AOX removal. Through-column reductions for UVA254 and AOX from secondary effluent averaged 30% and 17%, respectively. Forty-four percent of the through-column DOC removal and 57% of UVA254 attenuation occurred in the top 8 cm of soil. The post-SAT organic quality of secondary and tertiary (dual-media filtered) effluents was essentially equivalent. ©ASCE.
• Betterton, E. A., Arnold, R. G., Kuhler, R. J., & Santo, G. A. (1995). Reductive dehalogenation of bromoform in aqueous solution. Environmental Health Perspectives, 103(SUPPL. 5), 89-91.
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  PMID: 8565919;PMCID: PMC1519304;Abstract: The hybrid semiconducter-macrocycle catalyst TiO2-cobalt phthalocyanine promotes the solar photolysis of aqueous bromoform under anaerobic conditions. The major decomposition products are dibromoethane and HBr. Bromomethane and methane were produced only after prolonged photolysis (30 hr). Acetone, derived from added 2-propanol, was the only observed oxidation product. Preliminary experiments showed that electrolytic reduction of aqueous carbon tetrachloride at a vitamin B12-modified silver electrode produced the expected lower homologues but with surprisingly high yields of methane.
• Debroux, J., Amy, G., Arnold, R., & Wilson, L. (1995). Effluent pretreatment and its effects on water quality during soil aquifer treatment. International Symposium on Artificial Recharge of Ground Water - Proceedings, 512-518.
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  Abstract: Soil Aquifer Treatment (SAT) was simulated at the bench scale by exposing wastewater effluent to bacteria in 5-day aerobic recirculating batch reactors. Ozonation, at two doses, was utilized to enhance the biodegradability of the effluent organic matter. Biodegradable dissolved organic carbon (BDOC) increased with the application of ozone, and again with a higher transferred ozone dose. Disinfection by-product formation potential (DBPFP) decreased after biotreatment, with the application of ozone and without.
• Gross, M. J., Albinger, O., Jewett, D. G., Logan, B. E., Bales, R. C., & Arnold, R. G. (1995). Measurement of bacterial collision efficiencies in porous media. Water Research, 29(4), 1151-1158.
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  Abstract: A new method, utilizing radiolabeled (3H-leucine) cells and 1-cm columns packed with 40-μm borosilicate glass beads was used to estimate bacterial collision efficiency by directly measuring the retention of cells in porous media. At a fractional retention of 0.051 (n = 3), the coefficient of variation was 0.037, permitting meaningful estimation of collision efficiencies as low as 3 × 10-5. Collision efficiency was a function of the ionic strength and pecies identity; α increased from 1.6 × 10-3 to 1.4 × 10-2 for A. paradoxus in 10-5 and 10-3 M NaCl solutions, respectively, and from 8.9 × 10-3 to 6.2 × 10-2 for P. fluorescens in the same solutions. Results were not sensitive to test parameters such as velocity, volume filtered and rinse volume. The new procedure provides a convenient, reliable, accurate method for estimating low-end biocolloid collision efficiencies in porous media. In the range α < 0.01, the method is economical, significantly faster, and much more reliable than other published procedures. Its application may accelerate efforts to establish functional relationships between biocolloid collision efficiency and governing physical-chemical variables. © 1995.
• Jewett, D. G., Hilbert, T. A., Logan, B. E., Arnold, R. G., & Bales, R. C. (1995). Bacterial transport in laboratory columns and filters: Influence of ionic strength and pH on collision efficiency. Water Research, 29(7), 1673-1680.
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  Abstract: The influence of ionic strength and pH on the transport of Pseudomonas fluorescens P17 in porous media was investigated using continuous-flow laboratory columns and a rapid screening technique in which radiolabeled cells were applied to large-pore, glass-fiber filters. Colloid-filtration theory was used to interpret P17 transport results in the two systems. Bacterial retention was directly related to the ionic strength of the carrying solution. Decreasing the ionic strength from 10-1 to 10-5 M caused the bacterial collision efficiency, α, to decrease nearly 90% (from 0.18 to 0.026 in screening experiments and from 0.12 to 0.015 in column experiments). This change in α is qualitatively consistent with double-layer theory, but suggests that very large changes in ionic strength are needed to influence transport. Bacterial transport was unaffected by changes in pH in the range of 5.5 < pH < 7.0 in both systems. This suggests that changes in surface properties of the bacteria and the silica collectors over the pH range that is commonly encountered in soil and ground water are not sufficient to influence cell attachment. The screening technique provided a rapid alternative to column experiments. Even though estimated α's were different in the two systems, the responses to changes in ionic strength and pH were similar. © 1995.
• Johnson, W. P., Blue, K. A., Logan, B. E., & Arnold, R. G. (1995). Modeling bacterial detachment during transport through porous media as a residence-time-dependent process. Water Resources Research, 31(11), 2649-2658.
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  Abstract: Bacterial transport through porous media was modeled using detachment functions that incorporate the dependence of detachment rate on bacterial residence time on the collector. Model parameters and the relative merit of alternative forms for the detachment function were evaluated on the basis of comparisons between model simulations and experimentally derived bacterial breakthrough and elution curves. Only detachment functions that provided an initial period into which bacteria were rapidly released, followed by slow bacterial detachment, were able to reproduce the elution portion of the breakthrough curves. It is concluded that both a time-dependent detachment function and a degree of sorption site heterogeneity are required to describe bacterial attachment and detachment during transport as observed in our laboratory. -from Authors
• Logan, B. E., Jewett, D. G., Arnold, R. G., Bouwer, E. J., & O'Melia, C. (1995). Clarification of clean-bed filtration models. Journal of Environmental Engineering, 121(12), 869-873.
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  Abstract: Clean-bed filtration models are frequently used to make engineering calculations on aquasol removal in filters. They consist of a filtration equation, derived from a mass balance around a collector, a single-collector collision efficiency, and an empirically derived sticking coefficient. In order to be correctly applied and referenced, the two most commonly used models, the Yao model and the Rajagopalan and Tien (RT) model, require additional clarification. The filtration equation used in the Yao model has a different form than that of an aerosol counterpart due to assumptions made in choosing a reference velocity in the system. The RT model, as originally published, had variables hidden within constants and contained typographic errors. In this paper we identify the differences in the Yao and aerosol filtration model derivations, correctly present the RT model, and compare model predictions with particle removals reported in laboratory columns.
• McCaulou, D. R., Bales, R. C., & Arnold, R. G. (1995). Effect of temperature controlled motillity on transport of bacteria and microspheres through saturated sediment. Water Resources Research, 31(2), 271-280.
• Padival, N. A., Weiss, J. S., & Arnold, R. G. (1995). Control of Thiobacillus by means of microbial competition: Implications for corrosion of concrete sewers. Water Environment Research, 67(2), 201-205.
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  Abstract: Corrosion of concrete sewers is associated with the biological oxidation of hydrogen sulfide to sulfuric acid by bacteria of the genus Thiobacillus. Inhibition of acid production by these organisms, was investigated by challenging established cultures with a heterotrophic competitor under controlled conditions. Two-organism competition experiments (T. thiooxidans or T. neapolitanus versus the heterotrophic competitor) were conducted in a bench-scale, continuous-flow, constantly stirred tank reactor. Results were sensitive to the influent nitrogen:carbon ratio. Under conditions designed to produce nitrogen-limited growth, the numbers of thiobacilli were reduced 60- to 1 200-fold after introduction of the competitor. Effluent sulfate concentrations, an indicator of acid production, dropped by 85%. Under carbon-limited conditions, modest reductions in thiobacilli cell density and effluent sulfate concentration were observed. Microbial competition reduced acid production under the conditions of the experiment. The results suggest that strategies based on competitive displacement of thiobacilli to inhibit corrosion of concrete sewers may be feasible.
• Picardal, F., Arnold, R. G., & Huey, B. B. (1995). Effects of electron donor and acceptor conditions on reductive dehalogenation of tetrachloromethane by Shewanella putrefaciens 200. Applied and Environmental Microbiology, 61(1), 8-12.
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  PMID: 7887629;PMCID: PMC167256;Abstract: Shewanella putrefaciens 200 is a nonfermentative bacterium that is capable of dehalogenating tetrachloromethane to chloroform and other, unidentified products under anaerobic conditions. Since S. putrefaciens 200 can respire anaerobically by using a variety of terminal electron acceptors, including NO3-, NO2-, and Fe(III), it provides a unique opportunity to study the competitive effects of different electron acceptors on dehalogenation in a single organism. The results of batch studies showed that dehalogenation of CT by S. putrefaciens 200 was inhibited by O2, 10 mM NO3-, and 3 mM NO2- , but not by 15 mM Fe(III), 15 mM fumarate, or 15 mM trimethylamine oxide. Using measured O2, Fe(III), NO2-, and NO3-, reduction rates, we developed a speculative model of electron transport to explain inhibition patterns on the basis of (i) the kinetics of electron transfer at branch points in the electron transport chain, and (ii) possible direct inhibition by nitrogen oxides. In additional experiments in which we used 20 mM lactate, 20 mM glucose, 20 mM glycerol, 20 mM pyruvate, or 20 mM formate as the electron donor, dehalogenation rates were independent of the electron donor used. The results of other experiments suggested that sufficient quantities of endogenous substrates were present to support transformation of tetrachloromethane even in the absence of an exogenous electron donor. Our results should be significant for evaluating (i) the bioremediation potential at sites contaminated with both halogenated organic compounds and nitrogen oxides, and (ii) the bioremediation potential of iron-reducing bacteria at contaminated locations containing significant amounts of iron-bearing minerals.
• Rusin, P., Cassells, J., Quintana, L., Arnold, R., & Chrisman, N. (1995). Elimination of toxic factors in leachate to enhance biooxidation of sulfide ores. Mining Engineering, 47(2), 173-177.
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  Abstract: Toxic substances in On solutions can retard biological leaching of sulfide dump ores. On solutions were analyzed for metals, organics and chloride and showed inhibitory concentrations of aluminum, manganese and chloride. Inhibition of bacterial activity by the solid fraction of On solution, with and without the organic constituents, was evaluated. Bacterial toxicity was evaluated by monitoring bacterial numbers, pH, Eh, and rates of iron oxidation. The On solution solids were toxic at 50% to 60% of their field concentration. Most of the toxicity of the On solution was due to the organic fraction. Different solvent extraction (SX) reagents show varying degrees of inhibition of T.ferrooxidans. Bacterial inhibitory effects of carriers and lixiviants used in the SX plant should be determined so that entrained SX reagents do not retard biological dump leach systems. The reagents used should be the most cost-effective and the least toxic.
• Warren, K. D., Arnold, R. G., Bishop, T. L., Lindholm, L. C., & Betterton, E. A. (1995). Kinetics and mechanism of reductive dehalogenation of carbon tetrachloride using zero-valence metals. Journal of Hazardous Materials, 41(2-3), 217-227.
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  Abstract: Elemental iron and zinc reduced part-per-thousand levels of aqueous-phase carbon tetrachloride to chloroform in a few hours. Free metal ions, chloride ion and hydrogen gas were produced in the reaction; protons were consumed. Process kinetics were dependent on solution pH, surface area of the elemental metal, carbon tetrachloride concentration, buffer selection and solvent composition (volume fraction 2-propanol). Reaction rate was first-order with respect to carbon tetrachloride at concentrations less than 7.5 mM. This class of reactions offers promise as a means for initiating the destruction of heavily halogenated organic compounds. © 1995.
• Wilson, L. G., Quanrud, D., Arnold, R., Amy, G., Gordon, H., & Conroy, A. D. (1995). Field and laboratory observations on the fate of organics in sewage effluent during soil aquifer treatment. International Symposium on Artificial Recharge of Ground Water - Proceedings, 529-538.
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  Abstract: This paper reviews field- and laboratory-scale studies to determine the fate of dissolved organic carbon (DOC) and total organic halide (TOX) in sewage effluent during soil aquifer treatment (SAT). Field-scale studies, conducted at Tucson Water's Sweetwater Underground Storage and Recovery (US&R) Facility, showed DOC and TOX removals averaging about 90% and 80%, respectively, as tertiary effluent percolated through the 37-m vadose zone. Based on the results of laboratory column experiments, DOC is reduced primarily by biodegradation during SAT while sorption dominates in reducing TOX levels.
• Albinger, O., Biesemeyer, B. K., Arnold, R. G., & Logan, B. E. (1994). Effect of bacterial heterogeneity on adhesion to uniform collectors by monoclonal populations. FEMS Microbiology Letters, 124(3), 321-326.
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  Abstract: Transport of bacteria over significant distances through aquifer sediments occurs primarily among bacteria with low affinity for sediment materials. Bacterial affinity for a uniform collector surface has been represented quantitatively by a collision efficiency (α), defined as the fraction of colliding cells that adhere to the collector surface. Using a new method for estimating α during advective transport of monoclonal bacterial populations through a uniform bed of 40-μm borosilicate glass spheres, we found that α decreased 10-fold over a bed depth of only 1 cm. Depth-dependent differences in α were not related to variation in bacterial size or intra-strain genetic variation. Intra-population heterogeneity in biocolloid-collector affinity may be important determinant of subsurface bacterial transport characteristics, with critical implications for pathogen transport and dispersal of bacteria for the remediation of hazardous waste. © 1994.
• Neilson, J. W., Josephson, K. L., Pepper, I. L., Arnold, R. B., Giovanni, G. D., & Sinclair, N. A. (1994). Frequency of horizontal gene transfer of a large catabolic plasmid (pJP4) in soil. Applied and Environmental Microbiology, 60(11), 4053-4058.
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  PMID: 7993092;PMCID: PMC201935;Abstract: Limited work has been done to assess the bioremediation potential of transfer of plasmid-borne degradative genes from introduced to indigenous organisms in the environment. Here we demonstrate the transfer by conjugation of the catabolic plasmid pJP4, using a model system with donor and recipient organisms. The donor organism was Alcaligenes eutrophus JMP134 and the recipient organism was Variovorax paradoxus isolated from a toxic waste site. Plasmid pJP4 contains genes for mercury resistance and 2,4- dichlorophenoxyacetic (2,4-D) acid degradation. A transfer frequency of approximately 1/103 donor and recipient cells (parent cells) was observed on solid agar media, decreasing to 1/105 parent cells in sterile soil and finally 1/106 parent cells in 2,4-D-amended, nonsterile soil. Presumptive transconjugants were confirmed to be resistant to Hg, to be capable of degrading 2,4-D, and to contain a plasmid of size comparable to that of pJP4. In addition, we confirmed the transfer through PCR amplifications of the tfdB gene. Although transfer of pJP4 did occur at a high frequency in pure culture, the rate was significantly decreased by the introduction of abiotic (sterile soil) and biotic (nonsterile soil) stresses. An evaluation of the data from this model system implies that the reliance on plasmid transfer from a donor organism as a remediative strategy has limited potential.
• Fitch, M. W., Graham, D. W., Arnold, R. G., Agarwal, S. K., Phelps, P., Speitel Jr., G. E., & Georgiou, G. (1993). Phenotypic characterization of copper-resistant mutants of Methylosinus trichosporium OB3b. Applied and Environmental Microbiology, 59(9), 2771-2776.
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  PMID: 8215352;PMCID: PMC182364;Abstract: Cultures of Methylosinus trichosporium OB3b grown in the presence of very low concentrations of copper synthesize a soluble methane monooxygenase (sMMO) that efficiently catalyzes the oxidation of trichloroethylene and other organic pollutants. Recently, we isolated five M. trichosporium OB3b mutants that express sMMO activity when grown in the presence of elevated copper concentrations (P. A. Phelps, S. K. Agarwal, G. E. Speitel, Jr., and G. Georgiou, Appl. Environ. Microbiol. 58:3701-3708, 1992). Here we show that, in contrast to the results for the wild-type cells, the addition of copper to mutant cultures grown on methane and nitrate as the nitrogen source has no noticeable effect on the growth rate and sMMO expression. In vitro experiments indicated that the copper-resistant phenotype does not arise from an increased stability of sMMO to copper deactivation. Furthermore, the mutant cultures exhibit altered speciation of copper in the extracellular fluid and have substantially decreased levels of cell-associated copper. On the basis of these results, we propose that the mutant phenotype arises from defects in copper uptake and metabolism rather than from changes in sMMO expression or enzyme stability.
• Graham, D. W., Chaudhary, J. A., Hanson, R. S., & Arnold, R. G. (1993). Factors affecting competition between type I and type II methanotrophs in two-organism, continuous-flow reactors. Microbial Ecology, 25(1), 1-17.
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  PMID: 24189703;Abstract: Competition experiments were performed in a continuous-flow reactor using Methylosinus trichosporium OB3b, a type II methanotroph, and Methylomonas albus BG8, a type I methanotroph. The experiments were designed to establish conditions under which type II methanotrophs, which have significant cometabolic potential, prevail over type I strains. The primary determinants of species selection were dissolved methane, copper, and nitrate concentrations. Dissolved oxygen and methanol concentrations played secondary roles. M. trichosporium OB3b proved dominant under copper and nitratelimited conditions. The ratio of M. trichosporium to M. albus in the reactor increased ten-fold in less than 100 hours following the removal of copper from the reactor feed. Numbers of M. albus declined to levels that were below detection limits (
• Jewett, D. G., Bales, R. C., Logan, B. E., & Arnold, R. G. (1993). Comment on "application of clean-bed filtration theory to bacterial deposition in porous media". Environmental Science and Technology, 27(5), 984-986.
• Kuhler, R. J., Santo, G. A., Caudill, T. R., Betterton, E. A., & Arnold, R. G. (1993). Photoreductive dehalogenation of bromoform with titanium dioxide-cobalt macrocycle hybrid catalysts. Environmental Science and Technology, 27(10), 2104-2111.
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  Abstract: The hybrid semiconductor-macrocycle catalyst, TiO2-Co-tetrasulfophthalocyanine, (TiO2-CoTSP) effectively enhances the solar-promoted reductive dehalogenation of bromoform (CHBr3) under anaerobic conditions. Reaction rates are 4-10 times faster than those obtained using silanized TiO2, unmodified TiO2, or direct (uncatalyzed) solar photolysis under the same conditions. CHBr3 is reduced to its lower homologues, dibromomethane (CH2-Br2), and bromomethane (CH3Br). HBr is also produced. No other major dehalogenation products are observed, although methane is found in trace amounts after prolonged photolysis. 2-Propanol, the sacrificial electron donor, is oxidized stoichiometrically to acetone. The catalyst is stable in sunlight for at least 30 h without loss of activity. The reaction mechanism is postulated to involve nucleophilic attack of Co(I)TSP, generated by the semiconductor, on CHBr3. The organometallic complex that is formed, TiO2-CoTSP-CHBr2, is postulated to subsequently undergo photolysis via homolytic Co-C bond cleavage to regenerate the catalyst. 2-Propanol is oxidized by valence band holes. © 1993 American Chemical Society.
• Logan, B. E., Hilbert, T. A., & Arnold, R. G. (1993). Removal of bacteria in laboratory filters: Models and experiments. Water Research, 27(6), 955-962.
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  Abstract: Five filtration models were used to predict the effect of particle size on removal in several types of laboratory filters (nylon, cellulose and glass fiber). All models predicted similar trends in removal with particle size, although the capillary-pore model predicted substantially lower removals than the other four fibrous filtration models. These models indicated that bacterium-size (~ 1 μm) particles are removed in filters primarily through the filtration mechanism of particle interception. Based on advertised pore sizes, removal of bacterium-size particles was a function of filter material in the order cellulose > nylon > glass fiber. The percent of bacteria removed in a nylon filter (5 μm pore diameter) was similar to removal in GF/C filters (1.2 μm pore diameter) as a result of a higher sticking coefficient of bacteria with nylon than with glass. The average sticking coefficients of three bacteria, Pseudomonas sp. JS6, Pseudomonas fluorescens P17 and Bacillus pumilus, in glass fiber (GF/C) filters, were 0.01, 0.24 and 0.20, respectively. These results indicate that filtration models can be used to describe particle removal during laboratory filtration of water and wastewater samples, and that bacteria have relatively high sticking coefficients for filter materials.
• Picardal, F. W., Arnold, R. G., Couch, H., Little, A. M., & Smith, M. E. (1993). Involvement of cytochromes in the anaerobic biotransformation of tetrachloromethane by Shewanella putrefaciens 200. Applied and Environmental Microbiology, 59(11), 3763-3770.
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  PMID: 8285682;PMCID: PMC182529;Abstract: Shewanella putrefaciens 200 is an obligate respiratory bacterium that can utilize a variety of terminal electron acceptors, e.g., NO3-, NO2-, Fe(III), and trimethylamine N-oxide, in the absence of O2. The bacterium catalyzed the reductive transformation of tetrachloromethane (CT) under anaerobic conditions. The only identified product was trichloromethane (CF), but CF production was not stoichiometric. No dichloromethane, chloromethane, or methane was produced. A chloride mass balance indicated that fully dechlorinated products were not formed. Studies with [14C]CT suggested that a portion of the transformed CT reacted with biomass to form unidentified soluble and insoluble products. Intermediate production of a trichloromethyl radical can explain observed product distribution without significant CO2 formation. Evidence suggests that respiratory c-type cytochromes are responsible for the dehalogenation ability of S. putrefaciens 200. Previous growth under microaerobic conditions ([O2],
• Rusin, P. A., Sharp, J. E., Oden, K. L., Arnold, R. G., & Sinclair, N. A. (1993). Isolation and physiology of a manganese-reducing Bacillus polymyxa from an Oligocene silver-bearing ore and sediment with reference to Precambrian biogeochemistry. Precambrian Research, 61(3-4), 231-240.
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  Abstract: Samples from an Oligocene silver-bearing manganese ore mining site in Saguochi country, Colorado were screened for bacteria which solubilize manganese in the refractory ore thus making the silver more amenable to standard extraction techniques. Over 300 bacterial isolates were tested. Manganese reduction was detected by growing the organisms in a mineral salts medium supplemented with the insoluble MnO2 (pyrolusite). Reduction of the black MnO2 resulted in the formation of colorless solubilized Mn2+. One of the most efficient manganese reducers was a Bacillus polymyxa strain D1. This bacterium was isolated from the ore heap and from a zone 5 cm below the sediment surface of the inlet which drained ore heap leachate into a holding pond. Isolate D1 has a unique mode of manganese reduction as shown by the following combination of characteristics: (1) anaerobiosis is absolutely necessary; (2) direct surface contact with the mineral particle is required; (3) facultative fermentation occurs concomitantly with manganese reduction; and (4) Mn4+ does not substitute for O2 at the end of the respiratory electron transport chain. Although the ore deposit is approximately 35-30 Ma old, D1 probably have first appeared at the site contemporaneous with mining activities as evidenced by its resistance to exogenous zinc used in the silver extractive process. If organisms such as D1 were present > 600 Ma ago they could have played a role in the Precambrian manganese cycle as they do in the Holocene. Encrustations of MnO2 have been found in Precambrian sediments which are thought to be biogenic in origin. Solubilized reduced Mn2+ must also have been present to serve as a substrate. Anaerobic conditions alone are insufficient for the reduction of manganese dioxide, therefore, it is likely that manganese reduction was due, in part, to microbial activity. Solubilization of manganese occurs via microbial dissimilatory reduction as seen with isolate D1. Precipitation results from oxidation of manganese coupled to ATP synthesis as described by Ehrlich (1976, 1983). © 1993.
• Graham, D. W., Korich, D. G., LeBlanc, R. P., Sinclair, N. A., & Arnold, R. G. (1992). Applications of a colorimetric plate assay for soluble methane monooxygenase activity. Applied and Environmental Microbiology, 58(7), 2231-2236.
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  PMID: 1637160;PMCID: PMC195760;Abstract: A straightforward method is described for screening methanotrophic colonies for soluble methane monooxygenase (sMMO) activity on solid media. Such activity results in the development of a colored complex between 1- naphthol, which is formed when sMMO reacts with naphthalene, and o- dianisidine (tetrazotized). Methanotrophic colonies expressing sMMO turned deep purple when exposed successively to naphthalene and o-dianisidine. The method was evaluated within the contexts of two potential applications. The first was for the enumeration of Methylosinus trichosporium OB3b in a methane-amended, unsaturated soil column dedicated to vinyl chloride treatment. The second application was for the isolation and enumeration of sMMO-bearing methanotrophs from sanitary landfill soils. The technique was effective in both applications.
• Graham, D. W., Korich, D. G., LeBlanc, R. P., Sinclair, N. A., & Arnold, R. G. (1992). Erratum: Applications of a colorimetric plate assay for soluble methane monooxygenase activity (Applied and Environmental Microbiology 58:7 (2235)). Applied and Environmental Microbiology, 58(10), 3441-.
• Rusin, P., Cassells, J., Sharp, J., Arnold, R., & Sinclair, N. A. (1992). Bioprocessing of refractory oxide ores by bioreduction: Extraction of silver, molybdenum, and copper. Minerals Engineering, 5(10-12), 1345-1354.
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  Abstract: Although much research has been conducted in the area of biooxidation of sulfide ores, few investigations in the bioreduction of oxide ores have been published. We report high recoveries of silver, molybdenum, and copper from refractory oxide ores through bioreduction. Metal-reducing Bacilli solubilize manganese and iron. Crystals of pyrolusite, goethite, and hematite are bacterially dissolved and entrapped target metal ions are released. Zinc and copper are solubilized by metabolic end products such as organic acids. Bioreductive leaching of oxide ores was more successful than chemical leaching. A 0.1% cyanide bottle roll on an Arizona manganiferous silver ore resulted in 13.7% silver extraction. Bioreductive leaching extracted 86% of the silver into the growth medium. Also, 99.8% of the manganese, >2;99% of the copper, and 91% of the zinc were solubilized. A cyanide bottle roll of the bioleached solids extracted an additional 8.5% of the silver for a total recovery of 94.5%. A 5% sulfuric acid bottle roll of a Nevada iron oxide molybdenum ore recovered 1.8% of the moly. Bioreduction solubilized 93% of the molybdenum into the growth medium. A follow-up acid bottle roll recovered no additional moly. Bioreductive leaching can be used to recover target metals from refractory oxide ores without the use of cyanide or sulfuric acid. © 1992.
• Kupillas, G. E., Pill, K. G., Picardal, F. W., & Arnold, R. G. (1991). A multiparameter chemical toxicity test using Salmonella typhimurium and Spirochaeta aurantia. Environmental Toxicology and Water Quality, 6(3), 293-307.
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  Abstract: A battery of measurements, including specific growth rate, intracellular ATP level, and respiration rate, was designed to measure the responses of Salmonella typhimurium and Spirochaeta aurantia to chemical toxicants. The test battery provided both a measure of relative toxicity and an indication of the biochemical mechanism of chemical toxicity. The utility of the battery was investigated using chemicals (cyanide, 2,4-dinitrophenol, chloramphenicol, and dicyclohexylcarbodiimide) for which toxic mechanisms have been clearly established. Test battery results provided a reproducible ''signature'' for each model compound, which was useful for differentiating among compounds whose primary mechanism of toxicity involves (a) inhibition of catabolic activity leading to oxidative phosphorylation, (b) disruption of membrane integrity, and (c) interference with biosynthetic activity. The responses of the two test organisms to model inhibitors were qualitatively identical and paralleled predictions based on theoretical grounds. In theory, the test battery can measure toxicity among classes of compounds that alternative, single-parameter microbial tests would classify as nontoxic. The microbial test battery described may eventually provide a theoretically superior and economically attractive alternative to established toxicity testing procedures.
• Morton, R. L., Yanko, W. A., Graham, D. W., & Arnold, R. G. (1991). Relationships between metal concentrations and crown corrosion in Los Angeles County sewers. Research Journal of the Water Pollution Control Federation, 63(5), 789-798.
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  Abstract: Sulfide generation and crown corrosion rates increased sharply in reinforced concrete trunk sewers in Los Angeles County during the years following implementation of categorical industrial waste pretreatment requirements. Measured rates of crown deterioration were several times larger than predictions developed using accepted engineering methods and many times faster than rates observed in the same sewers before 1990. To investigate the discontinuous record of crown corrosion in Los Angeles County sewers, relationships between sulfide generation and wastewater quality characteristics were examined for statistical significance. Wastewater concentrations of dissolved and/or total sulfide were correlated with concentrations of several transition metals, including Ni, Fe, Pb, Cd, and Cr. A series of experiments was then undertaken to examine directly the effect of transition metal supplements, alone and in combination on the activities of sulfate-reducing bacteria (SRB) in batch reactors and two types of continuous-flow reactors. None of the metals tested individually, at concentrations approaching those in Los Angeles County wastewater before implementation of federally mandated industrial waste pretreatment measures, inhibited sulfide generation. When added together at concentrations that approximated their 1971-1974 levels in county wastewater, Cr, Cu, Ni, Zn, and CN- inhibited SRB activity in each reactor configuration tested. Results suggest that wastewater quality was an important determinant of sulfide generation and crown corrosion rates in Los Angeles County sewerage.
• Padival, N. A., Arnold, R. G., & Weiss, J. (1991). Interruption of sewer crown corrosion. Ecological solutions. Environmental Engineering, 108-113.
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  Abstract: Competitive inhibition of acid production by thiobacilli was investigated by encouraging the growth of potential competitors. Two-organism competition experiments (Thiobacillus sp. vs. heterotrophic yeast) were conducted in a bench-scale, continuous-flow reactor. Results were sensitive to the influent ammonia/glucose ratio. Under NH4+-limiting conditions, the concentration of T. thiooxidans or T. neapolitanus and acid production rates were reduced by about two orders of magnitude. Under carbon-limiting conditions, only modest reductions in the thiobacilli cell density and effluent sulfate were observed. In general, encouragement of microbial competition can interrupt acid production by thiobacilli and may inhibit crown corrosion in concrete sewers.
• Pill, K. G., Kupillas, G. E., Picardal, F. W., & Arnold, R. G. (1991). Estimating the toxicity of chlorinated organic compounds using a multiparameter bacterial bioassay. Environmental Toxicology and Water Quality, 6(3), 271-291.
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  Abstract: A battery of microbial tests that included comtemporary measurement of specific growth rate, intracellular ATP level, and respiration rate proved capable of distinguishing among toxicants that acted primarily as (a) catabolic inhibitors, (b) uncouplers, and (c) inhibitors of biosynthetic processes. The concentration of chlorinated phenols and ethanes that produced a 50% reduction in specific growth rate (ECk50) provided the most useful single-parameter indication of relative chemical toxicity generated within the test battery. Among the chlorinated ethanes tested, toxicity resulted from nonspecific chemical interactions with bacterial membranes, as indicated by correlation between toxicity (ECk50) and measures of lipophilicity. The ECk50 value for 1,2-dichloroethane was 8.5 x 10-3M as compared to 1.7 x 10-4M for the more hydrophobic pentachloroethane. Intermediate ECk50 values were obtained for 1,1,1-trichloroethane and 1,1,2,2-tetrachloroethane. For a comparable degree of lipophilicity, the chlorinated phenols were about an order of magnitude more toxic than chlorinated ethanes. ECk50 values for Spirochaeta aurantia at pH 7 ranged from 1.3 x 10-3M for 2-chlorophenol to 9.4 x 10-6M for pentachlorophenol. There was indirect evidence that the toxicity of chlorinated phenols arises from both specific and nonspecific chemical interactions with bacterial membranes. The test battery proved capable of distinguishing among the relative toxicities of the chemicals tested at least as well as other bioassay procedures including Microtox and Daphnia-based tests. However, ECk50 was less sensitive than parameteric measures of chemical toxicity generated via other procedures.
• Rusin, P. A., Quintana, L., Sinclair, N. A., Arnold, R. G., & Oden, K. L. (1991). Physiology and kinetics of manganese-reducing Bacillus polymyxa strain D1 isolated from manganiferous silver ore. Geomicrobiology Journal, 9(1), 13-25.
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  Abstract: Manganese-reducing bacteria were isolated from a manganiferous silver ore mining site using enrichment procedures. The most rapid Mn(IV) reducer was identified as Bacillus polymyxa and was designated as strain D1. Stain D1 is capable of liberating silver via the reductive dissolution of refractory manganiferous ores. -from Authors
• Arnold, R. G., Hoffmann, M. R., DiChristina, T. J., & Picardal, F. W. (1990). Regulation of dissimilatory Fe(III) reduction activity in Shewanella putrefaciens. Applied and Environmental Microbiology, 56(9), 2811-2817.
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  PMID: 16348289;PMCID: PMC184848;Abstract: Under anaerobic conditions, Shewanella putrefaciens is capable of respiratory-chain-linked, high-rate dissimilatory iron reduction via both a constitutive and inducible Fe(III)-reducing system. In the presence of low levels of dissolved oxygen, however, iron reduction by this microorganism is extremely slow. Fe(II)-trapping experiments in which Fe(III) and O2 were presented simultaneously to batch cultures of S. putrefaciens indicated that autoxidation of Fe(II) was not responsible for the absence of Fe(III) reduction. Inhibition of cytochrome oxidase with CN- resulted in a high rate of Fe(III) reduction in the presence of dissolved O2, which suggested that respiratory control mechanisms did not involve inhibition of Fe(III) reductase activity or Fe(III) transport by molecular oxygen. Decreasing the intracellular ATP concentrations by using an uncoupler, 2,4-dinitrophenol, did not increase Fe(III) reduction, indicating that the reduction rate was not controlled by the energy status of the cell. Control of electron transport at branch points could account for the observed pattern of respiration in the presence of the competing electron acceptors Fe(III) and O2.
• Logan, B. E., Parker, D. S., & Arnold, R. G. (1990). O₂ limitations in CH₄ and NH₄⁺ utilizing biofilms. National Conference on Environmental Engineering, 31-38.
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  Abstract: Oxygen gradients can rapidly develop in fluid films covering biofilms in trickling filters. We use a computer model to calculate the maximum oxygen flux to a biofilm, and show that the maximum ammonia removal rate in nitrifying trickling filters (NTFs) is within the range expected from oxygen-limited transport. Based on our experience with NTFs, we discuss the implications of gas-transport limitations for methanotrophic biofilms in plastic media trickling filters.
• Logan, B. E., Steele, J. A., & Arnold, R. G. (1989). Computer simulation of DDT distribution in Palos Verdes shelf sediments. Journal of Environmental Engineering, 115(1), 221-238.
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  Abstract: Prior to the imposition of effective source-control measures in 1970, large quantities of DDT were discharged to the Los Angeles County municipal sewer system and, subsequently, to the Pacific Ocean. A fraction of this material accumulated among sediments of the Palos Verdes shelf. While the bulk of the DDT lies 10-40 cm below the sediment surface, its fate may be affected by future wastewater-treatment decisions at the Joint Water Pollution Control Plant (JWPCP), Los Angeles County's 385-mgd treatment plant. To assess the impact of impending JWPCP secondary treatment requirements on shelf sediment quality (processes that potentially affect the distribution of chemical tracers among those sediments, including background sedimentation rate), contributions from effluent-related solids, sediment mixing, and diffusive transport were incorporated in mathematical models. Model projections of surface-sediment quality at the most heavily contaminated sites are sensitive to projected effluent solids concentrations, and thus treatment-level decisions at JWPCP. Full secondary treatment projections of surface-sediment DDT concentration are 75% higher than those corresponding to continuation of present treatment practice.
• Arnold, R. G., DiChristina, T. J., & Hoffmann, M. R. (1988). Reductive dissolution of Fe(III) oxides by Pseudomonas sp. 200. Biotechnology and Bioengineering, 32(9), 1081-1096.
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  PMID: 18587827;Abstract: The kinetics and mechanism of reductive dissolution of Fe(III) oxides were examined in pure, batch cultures of Pseudomonas sp. 200. Primary factors controlling hematite dissolution kinetics were mineral surface area (or concentration of high-energy surface sites), ligand concentration, and cell number. In the presence of nitrilotriacetic acid (NTA), saturation kinetics were apparent in the relationship governing reductive dissolution of hematite. A kinetic expression was developed in which overall iron-reduction rate is functionally related to the concentrations of both NTA and Fe(III).
• DiChristina, T. J., Arnold, R. G., Lidstrom, M. E., & Hoffmann, M. R. (1988). Dissimilative iron reduction by the marine eubacterium Alteromonas putrefaciens strain 200. Water Science and Technology, 20(11-12), 69-79.
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  Abstract: The ability of microorganisms to mediate the transformation of iron coupled with the participation of iron as a reactive redox species in natural waters and sediments has prompted recent speculation that such bacteria play an important role in such activities as global iron cycling, biologically induced mineral formation, and localized competition for available organic substrates. Microaerophilic soil bacteria dominate the list of microorganisms capable of iron reduction. However, screening experiments have shown that the marine eubacterium Alteromonas putrefaciens strain 200 is one of the most efficient iron reducers yet isolated. Respiratory inhibitor studies have suggested that a branched respiratory chain and two ferri-reductases (one constitutive and one indiced by growth under microaerophilic conditions (2 μM O2)) are involved in iron reduction. Further complementary biochemical and genetic studies have concentrated on characterizing the components of the induced iron reduction system. Ethyl methane sulfonate (EMS) has been used to develop mutagenesis procedures for A. putrefaciens 200; under optimal conditions, the frequency of total auxotrophy for EMS-treated cultures is approximately 0.4%. Tests for specific auxotrophic requirements have indicated the presence of a complex distribution of loci required for biosynthetic pathways. Mutants in both high-rate and low-rate ferri-reductase activity have been identified via a newly developed technique for screening EMS-treated A. putrefaciens 200 cultures. Ferri-reductase-deficient mutants generated by these techniques have been shown to contain reduced cytochrome content. Preliminary results indicate that the broad host range cloning vector pVK100 (Inc P) is mobilizable into A. putrefaciens 200. Current work is aimed at construction of an A. putrefaciens 200 clone bank, and complementation of the ferri-reductase mutants.
• Arnold, R. G., DiChristina, T. J., & Hoffmann, M. R. (1986). Inhibitor studies of dissimilative Fe(III) reduction by Pseudomonas sp. strain 200 ('Pseudomonas ferrireductans'). Applied and Environmental Microbiology, 52(2), 281-289.
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  PMID: 2428308;PMCID: PMC203516;
• Arnold, R. G., Olson, T. M., & Hoffmann, M. R. (1986). KINETICS AND MECHANISM OF DISSIMILATIVE Fe(III) REDUCTION BY PSEUDOMONAS SP. 200.. Biotechnology and Bioengineering, 28(11), 1657-1671.
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  Abstract: The kinetics and mechanism of Fe(III) reduction to Fe(II) were studied in pure batch cultures of Pseudomonas sp. 200. The rate of iron reduction has been mechanistically related to aqueous phase iron speciation. Initial rates of microbial iron reduction were accelerated more than 20-fold by the addition of equimolar quantities of nitrilotriacetic acid (NTA) to media initially containing 1. 86 multiplied by 10** minus **3M total Fe(III). The results indicate that soluble ferric iron species are not equivalent in terms of their susceptibility to bacterial (dissimilative) iron reduction. The concentration of Fe-NTA complex correlated strongly with observed iron reduction rates. Ferrous iron species appeared to inhibit the reduction process.
• Brooks, N. H., Arnold, R. G., Koh, R. C., Jackson, G. A., & Faisst, W. K. (1982). DEEP OCEAN DISPOSAL OF SEWAGE SLUDGE OFF ORANGE COUNTY, CALIFORNIA: A RESEARCH PLAN.. EQL Report - California Institute of Technology, Environmental Quality Laboratory.
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  Abstract: A seven-year research program is recommended to study the environmental and possible health effects of a proposed ocean discharge of sewage sludge via a special pipeline to an unprecedented depth of about 1000 to 1300 feet (300-400 meters) off the coast of Orange County in southern California. Disposal of sludge presents difficult and costly problems for sewge treatment agencies throughout the United States. Although such a discharge is not now legal, the County Sanitation Districts of Orange County is seeking approval for a unique research and demonstration project to discharge sludge at that depth and to fully study its behavior and effects.