NEWS SCIENCE Mercury increases DNA damage from radiation Does pollution increase the risk of genetic damage caused by radioactivity? Researchers with the University of Georgia's Savannah River Ecology Laboratory (Aiken, SC) report that DNA damage in adult largemouth bass significantly increased when they were exposed to mercury and low levels of radioactive 137Cs. Radiation is known to cause DNA damage, but the added effect of mercury is a surprise. The study will be published this spring in the Journal of Environmental Toxicology and Chemistry. The increased damage, in the form of DNA strand breaks, is believed to be the result of mercury impairing DNA repair enzymes. These repair enzymes protect organisms by fixing potentially lifethreatening damage to DNA in chromosomes from a host of naturally occurring agents. "Most organisms are good at repairing normal breaks in DNA s strands," said Derrick Sugg of the Ecology Laboratory. However, in a
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Savannah River Ecology Laboratory research technician Janet Brooks prepares a sample for analysis for DNA strand breaks.
random sampling of bass from four lakes at the Department of Energy's Savannah River Site contaminated with various levels of 137 Cs and mercury, Sugg and his co-workers observed that mercury increased DNA damage. In fact, said Sugg, the fish in the contaminated waters appeared "skinny" and distressed, although
there were no observable tumors. Mercury levels were on the order of 1 to 3 ppm in affected fish. [The Food and Drug Administration's action level for mercury in fish is 1 ppm (wet weight).] "There is a threshold for seeing an appreciable number of DNA breaks [from radiation]," Sugg said. "Mercury in fish seems to lower that threshold." Other research has shown that mercury binds to proteins, which leads the group to speculate that the heavy metal is interfering with the repair enzymes. The researchers are also investigating the binding of mercury to DNA as an alternative explanation. Researchers from the Ecology Laboratory are looking for similar connections between radiation and increased damage caused by pollutants at sites including lakes in the Chernobyl region of the former Soviet Union where radiation levels are significantly higher and lead is present. —ALAN NEWMAN
Plant enzymes set for bioremediation field study Phytoremediation, a nascent technology in which plants are used as biological remediators of contaminated sites, is being developed quickly with interagency support. Even as researchers identify candidate plants for cleaning up pollutants, a $1.2 million field study of enzymes to break down TNT begins this spring. The field study will be conducted at a Childersburg, AL, site contaminated with TNT from a now-closed Army munitions plant. Engineers plan to investigate pollutant transport into plants, mechanisms and kinetics for transforming pollutants, and effects of growing conditions on phytoremediation. The study is supported by the Strategic Environmental Research and Development Program, an effort that unites EPA and the departments of Energy and Defense. The study will be conducted by EPA's Haz-
ardous Substances Research Center/South and Southwest. In an earlier pilot study run by Auburn University at the Childersburg site, the aquatic plant parrot feather was added to a large open tank of water containing TNT-contaminated soil. Within a week, aqueous TNT concentrations dropped from the saturation level of 128 ppm to approximately 10 ppm. The flooded soil, which originally was so toxic that it was sterile, supported the growth of tadpoles and snails. According to the discoverer of the process, Lee Wolfe of EPA's Environmental Research Laboratory (Athens, GA), laboratory tests show an even faster breakdown rate, about a 1-h half-life for TNT under optimum conditions. The key is a nitroreductase enzyme that reduces TNT to triaminotoluene. Parrot feather and other plants also contain another en-
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zyme, laccase, which oxidizes the triaminotoluene and incorporates the products into the plant. To accelerate the application of this new technology, the Athens laboratory has formed a science-engineering team. Investigations of natural processes have led to the discovery of several other plant-produced enzymes that can be "engineered," including a dehalogenase enzyme that might be used for cleaning up chlorinated organics, says Chief EPA Project Engineer Steve McCutcheon. Phytoremediation has received a boost because most states have stopped permitting incineration of TNT-contaminated soils. Moreover, plants, unlike microbes, can control metal concentrations and pH, thus ecologically engineering their surroundings and optimizing pollutant degradation. —ALAN NEWMAN
