Environmental Science
Top Paper: Foundations of mercury in the environment
“Complexation of Mercury(II) in Soil Organic Matter: EXAFS Evidence for Linear Two-Coordination with Reduced Sulfur Groups” by Ulf Skyllberg and Jin Qian, Department of Forest Ecology, Swedish University of Agricultural Sciences; Paul R. Bloom and Chung-Min Lin, Department of Soil, Water and Climate, University of Minnesota, St. Paul; and William F. Bleam, Department of Soil Science, University of Wisconsin, Madison, 2006, 40 (13), 4174–4180.
Ulf Skyllberg says it felt as though he did not sleep during the entire week that he and his colleagues collected the initial data that eventually became the basis for their ES&T paper. Their results, which show how mercury binds to natural organic matter (NOM), have the potential to trickle through the entire mercury community.
Ensconced at the Brookhaven National Laboratory in 1999, Skyllberg spent days tending to the extended X-ray absorption fine structure (EXAFS) synchrotron machinery, which the team used to analyze samples from forest peatlands in Minnesota. Skyllberg had worked in Paul Bloom’s lab at the University of Minnesota, St. Paul, as a postdoctoral fellow in 1995–1996. He made the temporary move from Sweden with the intention to study aluminum in soils. Instead, Bloom persuaded him that mercury would be much more interesting.
Bloom had a hunch that the binding of mercury to thiol ligands in organic matter would control the chemistry. He recalls saying at the time, “It’s gotta be reduced sulfur sites. Nobody is thinking that way; we gotta correct this!”
After talking to Will Bleam of the University of Wisconsin, Madison, about some ideas, the group settled on synchrotron measurements. “There was not a lot of foresight in the beginning,” Bloom says. “Things just kind of fell together.”
Their collaboration ultimately resulted in images of mercury interacting with NOM at the most fundamental structural level, showing that sulfur is the key to binding, says Laura Sigg of Eawag (Switzerland). That information could help in determining how much mercury is available to microbes for methylation of the toxic metal.
But the sleepless week in Brookhaven was not enough to confirm what the team was seeing. Skyllberg eventually traveled to Grenoble, France, to take advantage of a more powerful synchrotron, which allowed him to get more spectroscopic data. “I think we were very lucky,” he says. “The beam line has to be optimized; it varies from one day to another.” Meanwhile, several years passed and other work encroached, Skyllberg says.
That time also gave Skyllberg the experience he needed to interpret the data, Bloom says. The additional measurements from Grenoble allowed Skyllberg “to explain some peaks we couldn’t explain” with only the Brookhaven data, he continues. “It made everything fall together, and we got some really good data.”
“I think it’s very difficult to work with natural organic matter in general” because of its heterogeneity, Sigg says. Applying EXAFS is “really quite new” and “technically difficult,” she adds. In addition to the expense and resources necessary for EXAFS, Sigg says, the “interpretation is also quite tricky. It requires quite a lot of insight to properly interpret these spectra. It seems this group has the expertise to do that.”
Skyllberg says that this is the first time any researchers have been able to examine mercury at this scale of environmentally relevant concentrations. Previous work at relatively high concentrations was published in ES&T, from his group and another.
Skyllberg says that his group continues its research linking mercury geochemistry to ecological effects. But he will always remember that first week of measurements: “For some reason, you work hard, you are excited—everything is running around in your head,” he says. That state of mind contributed to his fruitful, sleepless nights that week, many years ago.
