combustion to deposition in North America,” he cautions. Atmospheric scientist Steven Lindberg, an emeritus fellow at and Laure Laffont at the LaboraThe mercury that occurs in coal Oak Ridge National Laboratory toire des Me´canismes et Transdeposits from different parts of the who specializes in mercury speciferts en Ge´ologie (France), are world appears to have different raation, also urges caution. “The working on mercury fractionation. tios of stable isotopes, according to whole idea of comparing soils to Blum’s researchers analyzed a new study published in ES&T coal and concluding [that] soils stable-isotope ratios in 30 coal de(DOI 10.1021/es801444b). The premay show a coal combustion imposits from three of the world’s liminary results offer the tantalizing print seems to be a case of putgreat coal producers: the U.S., possibility that researchers could ting the cart well before eventually use stable-isothe horse,” he says. “Soils tope signatures to track may derive their [mercury] mercury emissions from isotope signatures from a coal-fired power plants, large range of influences, according to the authors. including [mercury] Mercury contamination chemical alterations after of fish is a worldwide deposition. Without an health threat. But atmoextensive analysis of all spheric transport distribpossible sources, one canutes mercury globally; not yet conclude much of thus, it is hard to differanything,” he adds. entiate local versus gloThe mercury-isotope bal sources or natural ratios may not provide versus anthropogenic enough data to unambiguones. Natural sources of ously identify the source mercurysmercury deposof the mercury, says Oak its, volcanoes, and the Ridge National Laboratooceansare estimated to ry’s Patrick Mulholland, contribute about 40% of Coal mining: burning coal for electricity is one of the biggest anthropogenic sources of mercury. who uses stable nitrogen worldwide mercury air isotopes and other isotoemissions. Anthropogenic pic tracers to study stream food China, and Kazakhstan. They resources account for the rest; webs. He notes that “to distinported that the mercury stable-isocoal-fired power plants are subguish among a given number of tope ratios of the coals can be used stantial contributors. The majordifferent sources, say, for exto identify the deposits by source. ity of such power-plant ample, five, you need to have five They also measured mercury-isoemissions currently come from minus one, or four, independent tope ratios in soils from remote China. Once mercury is released tracers. If there are many different parts of North America and found into the environment, it cycles sources of mercury, then the isothat the ratios fall in the range for in a complex and not entirely topic ratios wouldn’t be enough U.S. and Kazakhstan coals. understood way. to uniquely identify the source.” “We have a useful way of fingerStable-isotope ratios are a relaBlum accepts that the techprinting mercury from different tively new addition to scientists’ nique is still in its early days. combustion sources in the atmotool kit for tracking mercury in “This is an exciting and powerful sphere,” says Blum. “This is a work the environment. In 2003, Holger method. This paper demonstrates in progress. But it demonstrates the Hintelmann at Trent University that these fingerprints are really great potential of this method for (Canada) showed that mercury worth pursuing, but we still do distinguishing between different ores have different isotope ratios, not have all the answers,” he says. combustion sources,” he adds. which suggests that mass-depen“Their data definitely shows that dent fractionation occurs. Last —REBECCA RENNER different coal deposits vary with year Joel Blum at the University Note Added after ASAP Publication respect to their mercury-isotope of Michigan and colleagues reThe source of a quote was attributed fingerprint, which is an important ported that exposure to sunlight incorrectly in the version published on first step to track mercury from can cause mass-independent fracthe web October 8, 2008. The corrected sources to deposition sites,” Hinteltionation that affects only odd version was published October 11, 2008. mann says. “But we don’t know if isotopes. Several other groups, the mercury-isotope signature is including those led by Leroy conserved on its way from coal Odom at Florida State University ISTOCKPHOTO
Mercury isotopes may put the finger on coal
10.1021/es802623b
2008 American Chemical Society
Published on Web 10/08/2008
November 15, 2008 / ENVIRONMENTAL SCIENCE & TECHNOLOGY 9 8177
