Goal
The objective of this element is to understand the mechanisms of microbially mediated transformation of metals and radionuclides in subsurface environments, leading to in situ immobilization and long-term stability. Physiological studies of the transformation of metals and radionuclides by key subsurface microorganisms and microbial consortia will provide the knowledge base needed to understand intrinsic bioremediation and to stimulate in situ biotransformation.

R&D Challenges

DOE subsurface sites encompass a wide range of redox environments where contaminants such as uranium are present. The first challenge is to understand the impact of these environments on microbial physiological processes involved in the transformation of radionuclides and metals to an immobilized form. The second challenge is to accelerate the rates of these physiological processes in situ, in complex “real world” environments where multiple contaminants are common.

R&D Initiatives: Current Status

The focus of the current research in this element is on the effects of dominant redox processes on microbial transformation of metals and radionuclides. Microcosm studies, utilizing consortia of naturally occurring microbial communities from subsurface environments, serve as laboratory-scale models of intrinsic bioremediation and biostimulation. These studies include the examination of a range of terminal electron acceptors such as oxygen, nitrate, iron, manganese, sulfate, chlorate, and humics. Model subsurface organisms such as Shewanella, Geobacter, and Desulfovibrio are being utilized to study in detail the physiological processes of metal reduction and immobilization. Microbe-metal or microbe-radionuclide interactions, including microscopic and submicroscopic characterization of the cellular microenvironment, are being studied using state-of-the-art tools such as the advanced light sources at DOE laboratories (see Figure 2). The biotransformation of organic-metal/radionuclide complexes also is being studied, because transport of radionuclides and metals is profoundly affected by complexing agents and chelators that commonly occur at DOE sites.

R&D Initiative: 3 Year Targets

Within three years, physiological processes studied at the laboratory scale will begin to be scaled to the field. Biotransformation researchers will take advantage of the FRC as a key resource, both for field-scale hypothesis testing and for obtaining DOE-relevant sample material. Quantitation of in situ biotransformation kinetics will be a strong emphasis. Potential in situ inhibitors of microbial biotransformation of metals and radionuclides at the FRC will be identified. The in situ production of extracellular polymers for immobilization of metals and radionuclides will be examined.

R&D Initiatives: 7-10 Year Targets

Within seven to ten years, biostimulation strategies to accelerate intrinsic processes for immobilization of metals and radionuclides will be developed and tested in the field. Opportunities for combining biostimulation approaches developed in NABIR with existing chemical approaches for in situ immobilization will be explored. Mechanistic understanding of in situ biotransformation will be incorporated into numerical models (along with biogeochemical data) for predicting rates of immobilization and long-term stability.