the Food and Drug Administration's National Center for Toxicological Research (NCTR), who is coordinating development of a government research plan to evaluate the prevalence of low-dose effects. A committee of scientists with various affiliations is currently developing a research program to assess the prevalence of these effects as recommended by EDSTAC, Sheehan said. "We do not expect that every hormoneresponsive system will provide identical dose-response curves," he said. The development will be assisted by data from current NCTR studies designed with a large number of endpoints on five different chemical with hormonal activity. Toxicologists begin tests by
using high doses and work their way down to a dose with no observed adverse effect level. If researchers were to do this with something that has an inverted U dose-response curve, they could miss the most significant effect. If this sort of behavior were common and undetected, it would mean that instead of being protective, the screening and testing program could give a false sense of protection, said Timm. Until recently vom Saal's group was alone in reporting these effects, but research findings presented at a National Institute of Environmental Health Sciences workshop in May found a similar U-shaped response (4). Indeed, so important is the work on bisphenol A that the committee's first task, according to Timm, is to
initiate a project to reproduce it. Once the committee puts together a proposal, it will try to raise money to fund a program to assess the prevalence of low-dose effects, Sheehan said. —R.R.
References (1) Sheehan, D. M.; vom Saal, F. S.; Lamb, J. Point-Counterpoint in Risk Policy Report, September 19, 1997, pp. 31-39. (2) vom Saal, F. S.; Timms, B. G.; Montano, M. M.; Palanza, P.; Thayer, K. A.; Nagel, S. C; Dhar, M. D.; Ganjam, V K.; Parmigiani, S.; and Welshons, W. V. Proc. Natl. Acad. Sci. 1997, 94, 20562061. (3) vom Saal, F. S.; Cooke, E S.; Buchanan, D. L.; Palanza, P.; Thayer, K. A.; Nagel, S. C; Parmigiani, S.; Welshons, W. V Toxicol. Ind. Health 1998, 14 (1/2), 239-260. (4) Characterizing the Effects of Endocrine Disrupters on Human Health at Environmental Exposure Levels, May 11-13 1998, NIEHS, Research Triangle Park, N.C.
DNA fingerprinting holds promise for identifying nonpoint sources of pollution This September, Virginia joined a handful of states using DNA fingerprinting to track down sources of bacterial water pollution. These states have been able to avoid months of laborious detective work by using the technique to identify sources of fecal bacteria contamination. Experts predict that the method will help water quality officials respond more effectively to new government initiatives to control nonpoint source pollution. When the Virginia scientists announced their plan to clean up 14 polluted sections of streams across the state, they indicated that they would use DNA fingerprints to match the genetic characteristics of bacteria in water to bacteria in chickens, cows, and other animals to identify pollution sources. Fecal bacteria are responsible for impairment of half of the nation's streams, according to Don Waye, senior water resources planner for the Northern Virginia Planning District Commission Only in the past 10 years has the practice of using DNA fingerprinting been used to identify water pollution problems. Mansour Samadpour, environmental
health professor at the University of Washington, explained that each animal species hosts unique strains of the bacterium Escherichia coli that are adapted to the intestinal environment of the host. Samadpour samples bacteria from different hosts, breaks the DNA into fragments, and separates the fragments by applying an electric field to a gel substrate. The resulting pattern of fragments on the gel creates a fingerprint for each species. The technique, known as microbial source tracking, was employed this summer to clean up Juanita Beach on Lake Washington near Seattle, said John Frodge, county limnologist. When high bacterial counts closed the beach, the county hired Samadpour to identify whether the source originated from a sewage pipe leak, failed septic systems, or pet and goose droppings. Samadpour took samples from all the suspected sources to create a DNA library of known bacterial strains. He then made DNA fingerprints of bacteria sampled from the water and compared them to his library. Nearly all the bacteria samples matched the fingerprints of bacteria from wild
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geese. Through improved maintenance, and keeping geese off the beach with specially trained dogs, the county has since been able to hold fecal bacteria counts below the standard. "Microbial source tracking made it a lot easier for us to reach consensus on stringent goose population controls," Frodge said. However, microbial source tracking "takes a long time and is expensive to do," Frodge said. After collecting water samples, getting results can take anywhere from two weeks to a month, and costs start at $10,000 for small projects, he said. "If the cost and time could be reduced, this would be a really valuable tool for cleaning up nonpoint source pollution " Frodge noted. "But for the amount and quality of information you get, it's cheap," countered Waye. With traditional fecal bacterial counts, "all you find out is that your stream has a problem, nothing more," he said. Microbial source tracking not only identifies the pollution source, it helps water quality planners target the problem and formulate a mitigation strategy, Waye said.
One of the challenges of microbial source tracking is developing a complete library of bacterial strains that is specific to each locale. George Simmons, professor at Virginia Tech, said that the geographic distribution of strains is unknown. For instance, "we don't know if bacterial strains from raccoons on Virginia's Eastern Shore are the same as strains from raccoons in North Carolina
or California," he noted. Samadpour concurred that the diversity of bacterial strains increases as the geographic range of the library is expanded. His library now contains more than 23,000 fingerprints. He hopes someday to make a source-specific database of 150,000-200,000 fingerprints generally available. Meanwhile, his work has caught the attention of the Amer-
ican Water Works Association Research Foundation, which is funding a bicoastal study of drinking water sources. The $150,000 project will "demonstrate the utility of the microbial source tracking method as a way to pinpoint [potential contaminant] sources and treat or prevent the problem," said Misha Hasan, project manager with the foundation. JANET PELLEY
Worldwide effort underway to reduce SF6 greenhouse gas emissions This October, EPA began promoting voluntary pollution prevention agreements to reduce sulfur hexafluoride (SF6) emissions from two key industries. The effort is part of a worldwide effort to decrease emissions of the compound, which is one of the six greenhouse gases on the negotiating table at last year's international climate change conference in Kyoto Japan. Although total emissions of SF6 are far lower than those of the other greenhouse gases discussed in Kyoto, its longevity makes it an important target for reductions. With a large global warming potential (GWP)—23,900 times greater than mat of C0 2 —and an atmospheric lifetime of 3200 years, it is "the most potent greenhouse gas known," according to researchers from Germany's Max-PlanckInstitute for Chemistry (Environ. Sci. Technol. 1998 32(20) 30773086). Their ES&T report correlates sales of SF with the observed global burden "The lifetime of this comDound is as long as civilizations " noted A R Ravishankara senior scientist at Oceanic spheric Administration's omy Lahnratory in Rnnlder Colo Because of its large GWP it is much easier for nations to reduce greenhouse gas emissions by decreasing their use of SF6, explained Manfred Maiss, coauthor of the ES&T paper. The fact that the compound's price more than tripled in 1995 has added to industry's impetus to reduce its use, said Philip Bolin, product manager at Mitsubishi Electric Power Products Inc. in Warrendale Pa. a manufacturer of equipment that uses die gas. "Sixty
to seventy percent of SF6 emissions could be abated cost efficientiy if a trade system for greenhouse gas emission rights existed," said Jochen Harnisch of the Massachusetts Institute of Technology's Joint Program on die Science and Policy of Global Change, in Cambridge, Mass. To aid scientists in using models to evaluate the effects of emissions reductions, scientists working on the Global Emission Inventory Activity hope to be releasing maps showing SF6 emissions on a 1 ° by 1 ° grid, said Jos Olivier, senior scientist at the National Institute of Public Health and the Environment in Bilthoven The Netherlands. The maps are being created as part of the International GeosphereBiosphere project. The reduction efforts that are being undertaken by EPA's Atmo-
Sales of sulfur hexafluoride have grown dramatically over the past 40 years and correlate strongly with its atmospheric burden, which has experienced a similar growth trend. Source: Environ. Sci. Technol. 1998, 32(20), 3077-3086.
spheric Pollution Prevention division target industries associated with some of the largest emissions of SF6: electric utilities, magnesium casters, and electronics manufacturers. Companies signing an EPA memorandum of understanding aimed at electric utilities would pledge to annually report their emissions of the compound, as well as commit to establish a corporate policy to properly handle it, explained Eric Dolin a program manager with the division It is estimated that electric utilities directly or indirectly purchase 80% of all SF6 produced, although the assumptions behind this estimate are debated, explained Eric Campbell, general manager for Dilo Company, a German business with U.S. headquarters in Odessa, Fla., which manufactures equipment for recycling SF6. Dolin said that EPA's goal was to convince each of die nation's 3000 utilities and cogeneration facilities that has equipment requiring the use of SF to join the partnership The SF6 used by electric utilities is encased inside switchgear, where it serves as an insulating gas. The compound is similarly encapsulated inside linear accelerators used in the semiconductor industry and some research facilities. Before the price of the gas skyrocketed, utilities found it more economic to simply release SFfi during routine maintenance said Bolin. Now it is only vented into the atmosphere unintentionally. Equipment like that made by Dilo allows SF6 to be recycled during maintenance by capturing
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