Environ. Sci. Technol. 2004, 38, 5656-5664
Cd and Proton Adsorption onto Bacterial Consortia Grown from Industrial Wastes and Contaminated Geologic Settings D A V I D M . B O R R O K , * ,† JEREMY B. FEIN,† AND CHARLES F. KULPA, JR.‡ Department of Civil Engineering and Geological Sciences, University of Notre Dame, 156 Fitzpatrick Hall, Notre Dame, Indiana 46556, and Department of Biological Sciences, University of Notre Dame, 107 Galvin Life Science Center, Notre Dame, Indiana 46556
To model the effects of bacterial metal adsorption in contaminated environments, results from metal adsorption experiments involving individual pure stains of bacteria must be extrapolated to systems in which potentially dozens of bacterial species are present. This extrapolation may be made easier because bacterial consortia from natural environments appear to exhibit similar metal binding properties. However, bacteria that thrive in highly perturbed contaminated environments may exhibit significantly different adsorptive behavior. Here we measure proton and Cd adsorption onto a range of bacterial consortia grown from heavily contaminated industrial wastes, groundwater, and soils. We model the results using a discrete site surface complexation approach to determine binding constants and site densities for each consortium. The results demonstrate that bacterial consortia from different contaminated environments exhibit a range of total site densities (approximately a 3-fold difference) and Cd-binding constants (approximately a 10-fold difference). These ranges for Cd binding constants may be small enough to suggest that bacteria-metal adsorption in contaminated environments can be described using relatively few “averaged” bacteria-metal binding constants (in conjunction with the necessary binding constants for competing surfaces and ligands). However, if additional precision is necessary, modeling parameters must be developed separately for each contaminated environment of interest.
Introduction Determining the speciation of metals in both natural and engineered settings is critical for predicting the mobility of the metals and their impact on the environment. Because metal cations readily adsorb to bacterial surfaces, bacteria have been recognized as important metal-complexing agents (1-4), and various models have been proposed to account for metal adsorption onto a number of individual bacterial species (5-8). It is unclear whether these models can be accurately applied to more realistic settings that can po* Corresponding author phone: (574)631-4307; fax: (574)631-9236; e-mail:
[email protected]. † Department of Civil Engineering and Geological Sciences. ‡ Department of Biological Sciences. 5656
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ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 38, NO. 21, 2004
tentially contain dozens of different bacterial species. If the cell wall functional group sites of each bacterial species exhibit unique adsorption properties, it would be necessary to determine site densities and binding constants for each site on each bacterial species of interest. This would be an impractical task because experimentation on dozens of different bacterial species (many of which cannot even be isolated in the laboratory) would be necessary. However, if bacterial species exhibit similar, or “universal”, adsorptive behavior, existing models and modeling parameters could be extrapolated more easily to describe complex systems. Recent observations by a number of researchers working with individual pure strains of bacteria (9-13), and artificial mixtures of pure strains of bacteria (14), suggest that to a first approximation, bacteria do exhibit universal adsorptive behavior. This universality of adsorptive behavior was tested by Borrok et al. (15) using consortia of bacteria grown from a range of uncontaminated soil and water environments. Borrok et al. (15) found that these consortia of bacterial species exhibit roughly similar affinities for protons and Cd, although the extents of adsorption were less than what had been measured in some previous studies using individual pure strains of bacteria. Other studies involving bacteria isolated from contaminated industrial wastes suggest that some bacterial species are capable of enhanced metal adsorption and that these bacteria can develop a specificity for adsorbing a given metal. For example, Wong et al. (16) and Malekzadeh et al. (17) show that specific bacteria isolated from metal-rich electroplating effluents are capable of adsorbing elevated quantities of Cu and U, respectively. Chang et al. (18) describe a bacterium isolated from hospital sewage that is capable of adsorbing large quantities of Hg and other metals, while Esposito et al. (19) identify a bacterium isolated from a water purification plant that shows “good performance in heavy metal removal”. These studies suggest that bacteria from contaminated sites may have evolved the capacity to adsorb unusually high metal concentrations and may exhibit site concentrations and/or binding constants that are significantly higher than for bacterial consortia from uncontaminated environments. In this study, we test whether consortia of bacteria isolated from a variety of industrial wastes and contaminated geologic systems adsorb protons and Cd to similar extents. We use a surface complexation modeling approach to constrain the values of the thermodynamic modeling parameters that best fit data collected in acid-base titrations and Cd adsorption experiments. The raw data and modeling results from this and previous studies are compared to determine whether a single set of modeling parameters are capable of describing all of the experimental data and whether “universal” bacteriametal adsorption behavior can be assumed in contaminated environments.
Materials and Methods Sample Descriptions. Soil samples were collected from a manufactured gas plant (MGP) site in Iowa, from dredged river sediments in Mississippi, and from a former explosives testing facility in New Jersey. The clay-rich soils from the MGP site were severely impacted by polycyclic aromatic hydrocarbons (PAHs) that had comingled with gasoline range hydrocarbons from a nearby leaky underground storage tank (LUST) site. The contamination is characterized by visible coal tar and concentrations of benzene, toluene, ethylbenzene, and xylene (BTEX), all in excess of remediation criteria. The soil sample collected from river sediment was impacted 10.1021/es049679n CCC: $27.50
2004 American Chemical Society Published on Web 10/01/2004
by dichlorodiphenyltrichloroethane (DDT) and its breakdown products, dichlorodiphenyldichloroethylene (DDE) and dichlorodiphenyldichloroethane (DDD). Concentrations of the composite material sampled ranged from 100 to 300 µg/ kg total DDT+DDE+DDD. Soil from the New Jersey site was heavily impacted by explosive residue, mainly 2,4,6-trinitrophenylmethylnitramine (tetryl). A composite sample of this material was collected from silty soils that ranged from about 1000 to 100 000 mg/kg tetryl. In addition to these soil samples, groundwater samples were collected from shallow (
