Effects of Surfactants on the Bioavailability and Biodegradation of Contaminants in Soils
W.P. Inskeep and J.M. Wraith, Montana State University; C.G. Johnston, Mycotech Corporation
Goal: This project is designed to improve understanding of fundamental relationships between surfactant chemistry, contaminant solubilization, and subsequent biodegradation rates in soils, while developing novel methods which may be useful in the bioremediation of nonpolar organic compounds in soils.
Rationale: During the past decade, much discussion has centered on the unavailability of sorbed compounds to soil microorganisms; it is generally now assumed that desorption and diffusion of bound contaminants to the aqueous phase is required for microbial degradation. Furthermore, with aging, many nonpolar contaminants form irreversibly bound residues which are difficult to extract with nonpolar solvents and are essentially unavailable to indigenous microbial communities or to those added as an inoculum to stimulate biodegradation. In a recent workshop convened to discuss major research needs in bioremediation, the bioavailability of soil bound contaminants was consistently identified as a fundamental limitation in enhancing rates of contaminant biodegradation in soils. One of the strategies for enhancing desorption rates and subsequent biodegradation rates of nonpolar contaminants in soils is the use of surfactants.
Approach: A series of contaminant partitioning studies using a wide range of surfactants with varying structures will be performed. Functional relationships between surfactant concentration, surfactant structure, and extent of contaminant solubilized will be established using batch and column studies. Effects of surfactants on subsequent biodegradation rates of phenanthrene, PCP, DDT, and PCB will be studied under batch and transport conditions using two representative bioremediation strategies: indigenous microbial populations and addition of white-rot fungi. Degradation rates will be determined under batch and transport conditions in previously unconates fate of heavy metals in a vegetated soil and to use the model to develop a protocol for determining the most effective vegetative planting strategies for immobilizing heavy metals in contaminated soil.
Rationale: Abandoned sites associated with old heavy metal mining and smelting activities often have a large proportion of their area without vegetative cover. This allows erosional forces to proceed at a maximum rate, and materials with high heavy metal concentrations are dispersed by wintaminated soils with and without contaminant aging. In addition, contaminant degradation in soil samples from several field sites contaminated with PCP and polyaromatic hydrocarbons will be compared to controlled laboratory experiments.
Status: Collection of eight contaminated soils has been completed for use in surfactant experiments. These soils represent a range in creosote/hydrocarbon contamination. All soils are currently being characterized for chemical content, microbiological activity, and microbial community analysis. Development of laboratory methods for growing white-rot fungi in soil columns for use in surfactant experiments has been conducted. A preliminary screening experiment designed to determine the potential toxicity of biosurfactants on white-rot fungi has been performed. To date, white-rot fungi appear to grow well in the presence of biosurfactants. Several column transport experiments showing enhanced transport of DDT in the presence of micelle and nonmicelle forming surfactants have been conducted. Batch degradation experiments of phenanthrene in the presence of model soil organic matter phases have been performed. These experiments are designed to determine the extent of bioavailability of sorbed phenanthrene to various substrates. This project is in its first year.
Clients/Users: This research will be of interest to members of industry and to the U.S. Department of Defense.
Key words: surfactants, bioavailability, biodegradation, nonpolar organic compounds.
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