July 2006, Vol. 18, No.7
Bacteria Aid in Cleanup of Uranium Contamination
Contamination from the radioactive element uranium could be controlled by bacteria, according to a news release issued by the Georgia Institute of Technology (Georgia Tech; Atlanta).
Based on laboratory studies, Georgia Tech researchers report that some bacteria found in the soil and subsurface can release phosphate that converts uranium contamination into an insoluble and immobile form. Uranium contamination is a concern at U.S. Department of Energy sites because it can migrate to groundwater in surrounding areas, noted Georgia Tech assistant professor of earth and atmospheric sciences Martial Taillefert, co-director of the research.
Researchers conducted preliminary screenings of many bacterial isolates and found several candidate strains that released inorganic phosphate after hydrolyzing an organophosphate source the researchers provided. The bioremediation research project is in its early stages, the news release notes.
“These organisms release phosphate into the medium, but the precipitation (of uranium phosphate) occurs chemically,” Taillefert explained.
The process begins when the bacteria — from the genera Rhanella, Bacillus and possibly Arthrobacter — degrade an organophosphate compound, such as glycerol-3-phosphate or phytic acid, which can be present in subsurface soils.
“During their growth, the organisms liberate phosphate they derive from the organophosphate compound,” said project co-director Patricia Sobecky, an associate professor of biology. “The free phosphate is released to the surrounding media, which is a solution in the lab. Then we conduct assays to see how much uranium is mineralized by the phosphate released by the bacteria.”
The bacteria’s role is crucial in this process because uranium cannot dissociate the organo-phosphate compound chemically, Taillefert explained. So uranium in the presence of organophosphate alone does not result in significant uranium precipitation.
As researchers work toward a bioremediation strategy that will work in the field, they have to design a mechanism to deal with competing organisms in the soil that might isolate the free phosphate, Sobecky noted.
“At this point, we know the organisms we’re studying are active in precipitating uranium phosphate,” she said. “Now we need to determine how chemically stable it is.”
Researchers also have learned that when the bacteria are releasing phosphate from glyceraldehyde-3-phosphate, the bacteria can tolerate the toxic uranium and can continue to grow once the uranium is precipitated by the released phosphate.
“Our challenge now is fine-tuning the conditions around the bacterium so eventually it can thrive and work chemically in a natural setting,” Taillefert said.
What White Perch Can Reveal About River Contaminants
Scientists in the Chesapeake Bay region are studying white perch to determine how pollutants, such as PCBs, contaminate fish and shellfish. In the Chesapeake Bay watershed, the bay states have issued fish consumption advisories throughout the bay and its rivers to protect the health of people who dine on the water’s fish and shellfish.
According to an article by the Chesapeake Bay Program (Annapolis, Md.) — a regional partnership including local states, the U.S. Environmental Protection Agency, and citizen advisory groups — PCB concentrations in white perch provide an indication as to whether other chemical contaminants are present in an area. The majority of white perch remain in the local waters of the bay throughout their lives, noted the Chesapeake Bay Program, making the species a good indicator of toxic contaminant concentrations in the Bay’s waters.
Data gathered from Maryland and Virginia suggests that PCB concentrations are higher among white perch in the upper than in the lower bay, according to a fact sheet issued by the Chesapeake Bay Program. Similarly, there is a trend in fish tissue where fish on the eastern shore have lower concentrations of PCBs than their counterparts on the western shore.
A common characteristic among the areas of the bay where white perch have higher PCB concentrations is related to land development; the bay’s western shore is more developed than its eastern shore, and white perch from the western shore have higher PCB concentrations than their counterparts on the eastern shore, the fact sheet says. Additionally, white perch sampled from the Patapsco River had particularly high PCB concentrations, which can be attributed to the level and type of industrialization in the Baltimore area.
Without sufficient data to determine a trend in PCB concentrations in white perch in the bay, Chesapeake Bay Program scientists cannot say for sure what to expect regarding the future of those toxic contaminants in white perch in the bay. However, PCBs were banned more than 25 years ago, so scientists expect to see a natural decrease in their concentration in white perch over time.
Contact the Chesapeake Bay Program at (800) YOUR-BAY or see www.chesapeakebay.net. Read more about the white perch study at www.chesapeakebay.net/newswhiteperchhealth021006.htm.