PULLMAN, Wash. — A team of researchers from Washington State University, Montana State University, and Battelle Pacific Northwest National Laboratory began work in June to help stop the movement of toxic metals in groundwater.
The project targets two of the most common radioactive and metallic contaminants found in soil and groundwater at U.S. Department of Energy facilities — uranium and lead. Both are prevalent in the DOE soils throughout the country as a result of years of weapons production.
The research team is led by Brent Peyton, assistant professor of chemical engineering at WSU and its Center for Multiphase Environmental Research. Other teammates are Gill Geesey, microbiology professor from Montana State University’s NSF Center for Biofilm Engineering; and James Amonette, senior research geochemist at PNNL’s Environmental Molecular Science Laboratory. The group of microbiologists, geochemists and engineers will work for three years under a grant of $1,027,000 from the Natural and Accelerated Bioremediation Research program of the Department of Energy.
In laboratory tests lasting three to four weeks, researchers used bacteria found naturally in most soils to reduce high concentrations of toxic metals to concentrations that are below drinking water standards. In the presence of common substances, such as vinegar or ethanol, the bacteria can use sulfate in a way similar to the way humans use oxygen in the air. Sulfate is a common non-toxic mineral compound found as a major component of Epsom salts, plaster of Paris, and in drywall found in nearly every home.
Sulfate-reducing bacteria can convert sulfate to sulfide, which then reacts with the toxic metals to form small insoluble crystals, thus reducing further migration of the contaminants, Peyton said. In addition to treating lead and uranium, the process has the potential to treat soils contaminated with other metals such as copper, nickel, cadmium, mercury, zinc and selenium.
The goal of the research is to understand the fundamental microbiology and chemistry that control the formation and stability of uranium and lead solids that result when sulfate-reducing bacteria are active. This knowledge can help abate movement of toxic metals in groundwater systems to prevent further contamination of creeks, rivers or wells, he said.
While microbial treatment does not remove the lead or uranium from soils, it can reduce their further journey. The bacteria also could be used to create a protective underground wall that would remove heavy metals as contaminated groundwater comes in contact with the barrier. In this way, property boundaries could be protected from unwanted metal contaminants migrating in from contaminated sites, according to Peyton.
The question for this team is not if this stabilization can occur, or even how fast. The real question is how many years the immobilized metals will stay stable and what microbial and geochemical variables control this status. The team will observe contaminant behavior at the microscopic level using optical and x-ray techniques and in the lab’s soil columns to determine what controls the stability of metals “captured” by sulfate-reducing conditions.
They also will try to quantify the dependency of remobilization rates on the types of mineral surfaces present in the aquifer. Because of the widespread distribution of soils and geologic regions affected by lead and uranium contamination, the research group is looking at the effects of various classes of minerals on metal immobilization and remobilization.