Step 1 in curbing mercury emissions: Find their source.
Unique ‘fingerprints’ of coal beds will help scientists track airborne toxin – and agree on controls.
Some amount of the element mercury, which scientists say is toxic to humans and animals, occurs naturally on earth’s surface. Since the Industrial Revolution began in 1750, the rate at which mercury is deposited into the environment has tripled.Skip to next paragraph
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The government gives it third-place priority in its list of 275 hazardous substances, right after arsenic and lead. Forty-four states have one or more mercury advisories on fish. And the US Centers for Disease Control says that 5.6 percent of women of child-bearing age have mercury levels nearing those deemed dangerous by the Environmental Protection Agency (EPA).
“It’s a real problem in the US,” says Russ Flegal, a professor of environmental toxicology at the University of California, Santa Cruz. “And it’s becoming increasingly problematic because we’re continuing to add mercury to the environment.”
Coal-fired power plants are the greatest single source of airborne mercury in the US. But mercury emissions from power plants remain unregulated. One reason: A debate on where this highly reactive and far-traveling metal originates has delayed what many consider long-overdue controls. One camp says mercury pollution is a global problem: Tamping down emissions in the United States won’t help much if the mercury deposited here originates outside the country.
The opposing camp says that while the mercury problem certainly is global, it’s also clearly regional and local. Areas nearest to mercury emitters are disproportionately contaminated. And if emissions from nearby sources are controlled, mercury in the nearby food chain also diminishes measurably.
Now, a team of scientists is developing a way to trace mercury in the environment back to its origin by identifying a unique chemical signature and matching it to a known source. The technique promises to change – and perhaps end – the debate over how to control mercury.
“It’s very important to be able to identify the source.… That’s probably the kind of direct evidence that is needed to implement change,” says Celia Chen, a research professor at Dartmouth College in Hanover, N.H. “If it’s just this global pool, nobody has to be held accountable for it.”
The new method relies on the ratio of mercury isotopes – mercury atoms with differing numbers of neutrons – to find where the mercury originates. Scientists gather coal from fields around the world, burn it, capture the escaping mercury, and determine its unique isotopic “fingerprint,” says Joel Blum, a professor of geological sciences at the University of Michigan, Ann Arbor, and co-author of a paper explaining the technique in the journal Environmental Science & Technology in October. Scientists can then assemble a library of these mercury signatures from coal. When that fingerprint is again detected in the environment, it can be easily matched to coal beds in the US, China, Kazakhstan, and elsewhere. The method is maybe five years from full deployment, says Blum.
Scientists currently infer mercury’s origin by measuring other elements nearby, and by using computer models. For example, the presence of iron or magnesium implicates an iron or steel mill, says Matthew Landis, an EPA research scientist in Research Triangle Park, N.C. But the new technique lets scientists determine precisely where the mercury came from, geologically speaking.
“It would give us essentially a one-and-only tool to look at global-scale source apportionment,” says Dr. Landis.