Solvents such as trichloroethene (TCE) are common groundwater contaminants at Superfund sites. By manipulating subsurface conditions, we aim to enhance microbial degradation of chlorinated solvents such as TCE to nontoxic products (e.g., ethene or carbon dioxide) in the ground, thereby reducing the impact of these chemicals on human health and the environment.

Approximately 70 field experiments have been conducted at TCE-contaminated sites in Oregon, California, Washington, South Carolina, and Tennessee. An important result of this work is our demonstration that chemical tracers allow us to indirectly monitor microbial transformations of TCE in heavily contaminated environments, where direct monitoring of TCE is impractical. Based on this result we have developed a suite of tracers to probe each step in the TCE biodegradation pathway.

At many sites, biotransformation of TCE can result in the accumulation of the toxic intermediate, vinyl chloride, if the microbial community cannot further transform vinyl chloride to ethene. We have developed an assay for this transformation, and have demonstrated that degradation of TCE to nontoxic products is feasible under field conditions.

Tracers have also been used to compare the effectiveness of a non-microbial process (chemical reduction using iron) with microbial processes and to compare lactate and hydrogen as substrates to stimulate the growth and activity of biodegradation organisms. At one site, we found that iron treatment produced the greatest extent of chemical transformation, whereas lactate and hydrogen additions produced only incomplete transformations of TCE.

We are monitoring bioaugmentation strategies: the addition to the subsurface of microbial strains with special metabolic capabilities for TCE transformation. Microbial strains have been isolated from several field sites and grown in culture in preparation for field studies. We are also developing inhibitors of key metabolic processes so that we may distinguish between microbially mediated and abiotic TCE transformations in laboratory and field tests.

The technology being developed has generated international interest. Dr. Field was invited to participate, and spoke about her work at the U.S.-Vietnam Scientific Workshop on Dioxin Screening, Remediation Methodologies and Site Characterization, held Nov 2-5, 2003, in Hanoi, Vietnam.

This project addresses a critical need, because TCE is present at many Superfund sites and is the organic contaminant most frequently detected in groundwater. Collectively this work represents a major advance in our ability to understand and manipulate microbial processes to degrade TCE and similar contaminants. The tracers we have developed provide the ability to probe relevant microbial processes under actual field conditions and have a variety of applications to industry (e.g., to perform rapid feasibility assessments and pilot testing of remediation technologies).