Scientists at the Idaho National Engineering and Environmental Laboratory are developing a chemical tracer technique to map the underground abundance of iron oxide-rust-that provides the ideal home for pollution-eating bacteria.
Their technique represents an important step toward better harnessing the bacteria to clean up heavy metals, organic chemicals, and radioactive contaminants polluting soils and aquifers and threatening water supplies.
Biogeochemist Robert W. Smith has been awarded a three-year $600,000 grant by the Department of Energy's Natural and Accelerated Bioremediation Research (NABIR) Program to develop a method to determine subterranean surface areas available to feed and house microbes. This mapping method will also enable researchers to track how bacteria move through the earth.
Harnessing the activity of microbes in contaminant clean-up is the basis for bioremediation. Bacteria can immobilize or destroy hazardous chemicals in polluted environments. To use microbes effectively, researchers need a greater understanding of how they interact with their environment.
Measuring available surface area will allow researchers to assess the bioactivity and movement of the microbes. "If you take organisms that do specialized bioremediation activities and inject them into the ground," Smith said, "how do they move to the places you want them to?"
The key to measuring surface area for microbes is measuring iron oxide, a common mineral found layered in soil everywhere. Iron oxide not only provides a surface for the microbes, but contaminants and bacterial nutrients interact with it in various ways. Microbes that travel through the ground--and potentially remediate soil contamination--stick to iron oxide, and certain kinds of bacteria use iron oxide like we use oxygen, said Smith.
Currently, researchers use averaged information about the extent of iron oxide layers derived from core samples, he said. The core samples are removed from the field and the information they provide is applied to the whole area. This is like pulling several pages at random from a book and trying to understand the story. At most, the reader gets the general gist of the book. To get the details of the plot, the reader needs to know what words are there.
Smith believes he can get the details. He and his INEEL colleagues plan to send a tracer molecule that interacts with iron oxide, such as fluoride, through 4-inch wells dug several feet deep into sandy ground in Oyster, Virginia. By monitoring how fast tracers migrate to surrounding wells, they can deduce how much iron oxide the tracer traveled over. Taking measurements at different depths will give them a three-dimensional view of the subsurface.
A cross-section of the Virginian soil reveals orange streaks of iron oxide layered between light-colored sand. Smith said they chose Oyster because "the ground is very, very simple there. If we can't do it at a simple site, we can't do it at a more complex one."
But trips out to Virginia's eastern shore won't happen soon. Smith said, "It's a new concept. This hasn't been done on a field scale and we have a lot of lab experiments to do first." Early experiments will be done on core samples from Oyster to determine how such the tracers flow vertically and horizontally.
Smith and his colleagues, computer modeler Annette Shafer and hydrologist Bob Starr, are contributing surface area information to a larger research effort involving other universities, including Princeton and Old Dominion, and other national labs who are all using the Oyster site to study microbial behavior below the ground surface.
Established last year, NABIR http://www.lbl.gov/NABIR/ supports basic research into how biological systems can be used to remediate hazardous and radioactive contaminants in soils and groundwater. What NABIR researchers learn will be applicable to other bioremediation needs, including contamination due to mining, manufacturing processes and even agriculture.
The Idaho National Engineering and Environmental Laboratory is operated for the U.S. Department of Energy by Lockheed Martin Idaho Technologies Company.