by Dr. Frank M. Dunnivant, Professor of Chemistry, Whitman College
Most of the weather patterns arriving in the Pacific Northwest originate in Asia, and along with these air masses come many pollutants. While the actual concentrations are low, these near-detection limit amounts pose significant contributions to alpine lakes, especially given biomagnification in lake trout. We are investigating two sets of pollutants, chlorinated hydrocarbons and mercury.
Our first study
Our first investigation, begun four years ago, surveyed the presence of 31 chlorinated hydrocarbons in alpine lakes in the Eagle Cap Wilderness Area (northeast Oregon) and the Frank Church Wilderness Area (Big Horn Crags, central Idaho). Most published results measuring chlorinated hydrocarbons focus only on DDT and show that DDT has been observed in every environmental compartment investigated.
Our investigation was the first to study a broad range of chlorinated compounds. We used a combination of gas chromatography with electron capture detection (GC-ECD) and solid phase micro-extraction (SPME) that theoretically yields a detection limit of 1 part per quadrillion (ppq) (one millionth of a part per million) or less. In practice, the technique yielded a detection limit of 5 ppq for most analytes, and field blanks yielded no quantifiable GC-ECD peaks for the 31 analytes. Of the 31 chlorinated hydrocarbons,o,p’-DDT, p,p’-DDT, p,p’-DDE, o,p’-DDE, chlorthal-dimethyl, endosulfan I, gamma-HCH, heptachlor, and trans-nonachlor were routinely measured in the tens to hundreds of parts per quadrillion (nanograms/liter). All other analytes were below the detection limit.
This field research confirms the presence of not only DDT, as has been observed around the world, but several chlorinated analytes not previously documented. We plan to submit this work to a peer-reviewed publication early next year.
Current work – where does the mercury come from?
Our current project is an extension of both the work described above and a USGS publication about mercury deposition at high altitudes. If low level chlorinated hydrocarbons are being deposited in the Pacific Northwest from air masses originating in Asia, what about toxic elements from the thousands of coal-fired power plants in Asia, specifically mercury? Schuster, et al. (2002) of the USGS documented the historic deposition of total mercury in a western U.S. glacier (see Figure 1 below). But total mercury measurements alone cannot determine the source of mercury.
The key to our current project is that mercury has seven stable isotopes and a few publications indicate that mercury isotope ratios, specifically 198Hg to 202Hg, can be used to distinguish between Pacific Rim volcanoes and Asian coal-fired power plants. We are currently analyzing alpine lake water samples by ICP-MS with a detection limit of less than 0.1 ppq from Olympic National Park in Washington, Seattle’s watershed reservoirs, Eagle Cap Wilderness Area (Oregon), and the Big Horn Crags in the Frank Church Wilderness Area (Idaho). Preliminary results indicate that total mercury concentrations decrease from parts per trillion in the Olympic National Park lakes to parts per quadrillion in Idaho lakes. To determine the source of current mercury deposition in the Pacific Northwest, we are comparing our measurements to mercury isotope ratios from several “coal mercury free” sources. Our current comparison isotope sources include published Asian coal analyses, deep-sea Pacific fish tissue, and water from deep Pacific thermal vents. But preliminary results are not yet conclusive.
Help us with clean core samples
You can help! To distinguish conclusively between Pacific volcano and Asian coal-fired power plant mercury, we need core samples from a relatively clean Pacific Northwest lake or glacier dating back to the 1700s or earlier. This will be the key dataset to help us determine the current source of mercury to our pristine lakes. If you have or will soon have these samples, or know someone who does, please contact me at dunnivfm@whitman.edu. Thank you for reading.
Figure 1. Profile of historic concentrations of mercury in the Upper Fremont Glacier (USA). From, Atmospheric Mercury Deposition during the Last 270 Years: A Glacial Ice Core Record of Natural and Anthropogenic Sources. Paul F. Schuster,* David P. Krabbenhoft, David L. Naftz, L. Dewayne Cecil, Mark L. Olson, John F. Dewild, David D. Susong, Jaromy R. Green, and Micheal L. Abbott Environ. Sci. Technol., 2002, 36 (11), pp 2303–2310 (DOI: 10.1021/es0157503). Courtesy of USGS.
