FOR RELEASE JULY 18, 1996
Jane M. Sanders
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Plants and animals show promise as bioremediators and biomonitors
AIKEN, S.C. -- One of the world's most powerful X-ray machines is revealing information about the types and amounts of contaminants in plants that could be used to bioremediate a site and in turtle shell fragments that could be used as indicators of the effectiveness of remediation projects.
"There has been a lot of interest in using indigenous organisms for bioremediating contaminated sites and as biomonitors to evaluate the extent of contamination and the efficacy of environmental remediation and restoration activities," said Dr. Paul Bertsch, a senior researcher on the project at the Savannah River Ecology Laboratory near Aiken, S.C. "We are pleased that our analyses are showing promise for these cleanup and monitoring strategies, which we believe will save the taxpayers some money."
Researchers have found that several species of native aquatic plants hyperaccumulate contaminants in their tissue at rates up to 1,000 times higher than the concentrations in their watery habitats. Furthermore, these tiny plants contain a detoxification mechanism that allows them to transform the metal contaminant chromium from a highly toxic and mobile form to one that is relatively benign, Dr. Bertsch said.
In a study using the same X-ray analysis technique, the researchers determined a contaminant exposure history from shell fragments of turtles living in a stream and former farm pond system. "The waterway was highly contaminated with uranium and nickel from nuclear materials operations. The exposure history, which showed daily deposition of contaminants, indicated a high level of nickel, but not uranium, bioaccumulation in the shell materials. This information will be useful in developing an assessment of the need for remediation and for biological monitoring of a cleanup project once it has begun at the contaminated site," Dr. Bertsch said.
Both studies examined environmental samples from two different locations on the 310-square-mile Savannah River Site (SRS), a U.S. Department of Energy (DOE) nuclear weapons materials processing complex near Aiken, S.C. The researchers examined the chemical contaminant forms and concentrations using a high-powered X-ray machine called the National Synchrotron Light Source at Brookhaven National Laboratory on Long Island, N.Y. The Synchrotron allows scientists to examine contaminants at minute levels undetectable by other techniques.
Dr. Bertsch will present an invited lecture of the research findings at an Aug. 26-30 scientific meeting titled "The 9th International Conference on X-ray Absorption Fine Structure" in Grenoble, France. Dr. Bertsch's collaborators on the study are Drs. Doug Hunter and Sue Clark of the Ecology Laboratory and Dr. Ken Kenmer of the U.S. Naval Research Laboratory in Washington, D.C.
In the plant study, researchers examined samples from a wetland receiving outfall from coal combustion ash basins on the SRS. "The wetland was contaminated with chromium, selenium and arsenic, among other metals. Synchrotron studies showed where the plants transported the contaminants within their cells, the concentrations of the contaminant and its chemical form," Dr. Bertsch said.
"Studies have shown that these native aquatic plants, such as duckweed, could be planted and harvested as a bioremediation, or in this case, phytoremediation method," Dr. Bertsch said. "The harvested plants would be treated as a hazardous waste, probably incinerated. This is much easier to deal with than tons of contaminated sediment that would have to be removed, and this method doesn't destroy the ecosystem."
In the study of turtle shell fragments, researchers examined samples from Tims Branch and the former Steed Pond on the SRS, as well as the fly ash outfall from coal combustion ash basins. The Tims Branch system received about 44,000 kilograms (48.4 tons) of uranium from fuel fabrication operations from the early 1950s to late 1960s. About 70 percent of these discharges remains in the stream and pond sediments, researchers said.
"Some of the sediments in the area surrounding the former pond, which drained when the dam broke in 1984, are among the most heavily contaminated sediments at the SRS," Dr. Bertsch said. "Also, the ecosystem represents one of the most widely contaminated areas in the entire DOE complex," he added. "Remediation of this system will likely be required by federal regulations in the future given the precedence at other DOE sites, including the former Feed Materials Production Center at the Fernald Site near Cincinnati, Ohio," Dr. Bertsch said.
Synchrotron analyses by Dr. Bertsch and his colleagues found that turtle shell fragments are very sensitive biomonitors of uranium and nickel contamination in the Tims Branch system, and selenium and arsenic in the ash basins, the scientists said. In addition, researchers analyzed contaminant bioaccumulation in deformed tadpoles from the coal ash basins. Synchrotron analyses showed a high concentration of selenium and a significant level of arsenic in the tadpoles, as well as an incorporation of the selenium in the animals? key structural proteins.
"Both findings indicate that we can use these biota to chronicle contaminant exposure for purposes of environmental risk assessment and also determine the efficacy of remediation projects later on," Dr. Bertsch said.
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