PULLMAN, Wash. — A team of researchers has tricked bacteria from contaminated soil into cleaning up the toxic heavy metal chromium. The Natural and Accelerated Bioremediation Research of the Department of Energy recently awarded them $767,000 to study the basic science behind this bacterial conversion. Eventually, the researchers hope to optimize the microbial action at contaminated sites simply by adding the appropriate nutrients.
James Petersen, chemical engineering professor and director of the Center for Multiphase Environmental Research at Washington State University, and William Apel, a scientific fellow at the Idaho National Engineering and Environmental Laboratory, received the three-year grant.
Chromium is a heavy metal naturally found in several different forms. Hexavalent chromium, also referred to as chromate, is toxic even at low concentrations. At high concentrations, it can cause cancer and damage DNA. Chromate found in the environment, most often left over from mining operations, agricultural procedures and oil refining, is generated almost exclusively by human activities. It is a contaminant in almost one-third of Superfund sites. Trivalent chromium, on the other hand, is a benign form of the metal that actually is an essential element for good nutrition.
In previous research funded by the INEEL University Research Consortium, Petersen and biochemistry colleagues at WSU, and Apel and other INEEL microbiologists, demonstrated that bacteria normally found in contaminated soils are capable of converting the hexavalent chromium to trivalent chromium by a microbial process called reduction.
However, a major component of this process is the microbe’s preference for reducing nitrate rather than chromate. Nitrate is in great supply in the microbe’s natural environment. Since the ultimate goal of this bioremediation is to induce resident bacteria to clean up toxic chromium, it may be necessary to stimulate appropriate microbial systems that allow chromate reduction. Therefore, the researchers needed to find conditions under which chromate is reduced in the presence of nitrate.
Bringing bacteria into the lab from several contaminated sites — including DOE’s Superfund-listed Hanford site in southeastern Washington state — the researchers found feeding conditions under which bacteria would reduce chromate to nearly undetectable levels.
“We’ve converted a carcinogenic, hazardous compound to a non-hazardous one,” said Petersen. “Now we’re trying to determine the best sugars and nutrients to reduce chromium, to determine what effect other contaminating species (such as uranium and technetium) have on chromium reduction, and what the relative concentrations of chromate and nitrate do to the amount of reduction.”
The team also will study the biochemical pathways that the bacteria use to convert hexavalent chromium to trivalent chromium. They will demonstrate the ability of resident microbes to decontaminate heavy metals using bacteria-containing soil obtained from contaminated DOE sites, including the Hanford site.
The three-year project started in September.