Overview of the Research Program
The aim of the ORNL remediation SFA is to gain a fundamental understanding of the mechanisms that govern contaminant transformation and behavior in the environment in order to predict and mitigate their adverse impact. This is a key goal set by DOE’s Subsurface Biogeochemical Research program. Over the next 5 to 10 year period, this SFA will address significant knowledge gaps regarding mercury transformation at the water-sediment interface that are characterized by steep chemical gradients. The principal research components in the SFA are: (1) Site Biogeochemical Processes and Microcosm Studies; (2) Fundamental Mechanisms and Transformations; (3) Microbial Transformations and Genetics; (4) Biomolecular Structure, Dynamics, and Simulation.
Scientific Issues Addressed
The ORNL biogeochemical research SFA will examine (1) how abiotic reactions affect Hg speciation and complexation, (2) what products or forms of Hg are bioavailable for microbial methylation, (3) what levels of Hg to initiate microbial demethylation and how this process can be tuned to favor demethylation, (4) what are the dominant microbes that participate in methylation or demethylation and how do geochemical conditions affect these transformations, and (5) how catalyzed chemical and photochemical reactions influence Hg speciation and transformations in water.
Anticipated Impacts of the ORNL SFA
By emphasizing fundamental mechanisms of mercury transformation at water-sediment interface, the ORNL SFA research program will generate significant contributions to the science-based understanding. This understanding is required for the development and implementation of alternative strategies for controlling methyl mercury production at Hg contaminated sites at the Oak Ridge Reservation as well as other contaminated DOE sites (e.g., Paducah Gaseous Diffusion Plant, Savannah River Plant). The DOE Oak Ridge Operations office is considering its final clean up strategy and mercury problem is the top priority at the site. The major scientific impacts of the SFA are:
- Elucidation of the mechanisms by which inorganic Hg is transformed into methyl mercury at the sediment-water interface and, particularly, the coupled abiotic and microbiologic processes that control Hg speciation, transformation, and methyl mercury production. Such knowledge is essential for the design of effective alternative strategies to decrease methyl mercury production.
- Quantification of the relative rates of methylation and demethylation. The research will provide an improved understanding of the basic mechanisms by which Hg is speciated, and bioavailable for microbial methylation and demethylation.
- Support of enhanced bioremediation by genetic controls. Advanced models to understand in details the biochemical and biophysical mechanisms of subcellular transformation between major Hg species and methyl mercury, which may lead to genetic transcription to enhance demethylation.
