Mercury Environmental Fate and Transport
The Idaho National Laboratory (INL) and other research laboratories across the nation are conducting fundamental research on quantifying atmospheric mercury sources and environmental cycling to better understand why observed concentrations of this highly toxic air pollutant have been increasing globally. The INL project began in 2000 to assess transport and cycling of atmospheric mercury being released from high-level waste treatment operations (primarily calcining) at INL. Since then, the project has expanded its goals to fill important national data gaps on mercury cycling and develop improved techniques to assess the national and global buildup of this highly toxic air pollutant. The location of past mercury sources at INL in a relatively low background area has provided an ideal setting to study mercury source-receptor relationships. Read more about mercury in the environment.
Mercury concentrations in numerous environmental media, including air, precipitation (rain and snow), soil, surface water, and lake sediments have been measured on a regional basis to better understand multi-pathway environmental cycling. These results have provided new understanding of the relative impacts of past and present INL mercury releases and those from regional and global background sources (both natural and anthropogenic).
For instance, age-dated sediment cores taken from the Mud Lake area immediately downwind from INL (see poster [444kB PDF)] provide evidence that 36-years of mercury emissions from calcining operations at INL have not increased the buildup of mercury beyond that observed globally. In addition, a state-of-the-science Tekran mercury analyzer has been deployed in the field to provide continuous ultra-low measurements of mercury air concentrations downwind from the Idaho Nuclear Technology and Engineering Center. The system includes a portable meteorological station, which provides important information on the sources of mercury, and a self-contained field trailer that allows deployment of the system to any vehicle accessible location. (A PDF showing the Tekran system, and data, is available here [705kB].) A flux measurement system also is being developed using a dynamic flux chamber and the Tekran to measure re-emission of deposited mercury from the surface back to the atmosphere. This will help confirm whether low soil concentrations observed at INL are a result of lower than expected local fallout rates or soil volatilization of deposited mercury. When fully developed, the flux system may be used to help quantify non-assessed sources of mercury (e.g., Yellowstone geothermal areas), which is of interest to the U.S. Environmental Protection Agency (EPA) and the Electric Power Research Institute (EPRI).
Multivariate Receptor Methods to Assess Atmospheric Transport of Air Pollutants
Researchers are determining whether a unique combination of trace elements and common ions could be used as distinguishable "fingerprints" for contamination sources. The objectives of this 3-year research project are to develop new multivariate receptor methods to source-apportion fallout at regional-scale downwind distances (see 2001 project report [243kB PDF] and 2002 mid-year project update [97kB PDF]) to enhance INL’s capability to meet regulatory permitting requirements for existing and future environmental management waste treatment facilities. The approach uses multivariate correlations (principal component analysis and classical least squares regression modeling) of trace element/common ion measurements in snow (a good fallout scavenger) to 1) identify the major fallout sources in the region and 2) predict the relative contribution to total fallout at a sampling location from the different sources. In FY 2001, we collected more than 250 INL and regional snow samples and analyzed them in triplicate using inductively-coupled plasma mass spectrometry and ion chromatography. Thirty-nine trace elements and nine common ions were positively identified in most samples. The results were processed, plotted on regional maps, and plotted as bivariate element scatter plots. In FY 2002, we developed a new sampling strategy that used real-time meteorological data from the National Oceanic and Atmospheric Administration (NOAA) and the NOAA MDIFF trajectory model to identify optimum sampling sites. We collected 135 new snow samples after three precipitation events and are currently analyzing the data to characterize source area emission profiles. The final step will be source apportionment of medium-range downwind sampling data using the source area emission profiles and classical least squares regression.
Speciated Atmospheric Mercury: Gas/Particle Partitioning, Transformations, and Source Characterization
INL’s Michael Abbott will be collaborating with Jim Schauer, Ph.D., of the University of Wisconsin-Madison and Dave Krabbenhoft, Ph.D., US Geological Survey, on a recently funded EPA Science to Achieve Results (STAR) proposal. Total project funding is $900K. STAR grant funding is directed towards university researchers, although other agencies (Department of Energy and contractors) may participate. The project is considering including measurements to characterize gas/particle partitioning and chemical speciation near mercury sources at INL (downwind of the Idaho Nuclear Technology and Engineering Center). The principal investigators are interested in INL collaboration because of recent source-receptor mercury work by Mike Abbott, the existence of quantified mercury air emission sources at INL, and the recent deployment of a Tekran mercury vapor analyzer system at INL. This work will benefit the INL by opening up new external research opportunities, especially within the difficult-to-access EPA research and development area.