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Yellowstone Snowmobile Studies


    Well, we finally have the first in a series of reports on monitoring of snowmobile activity in Yellowstone National Park last winter. However, the data are built around such a small sample, and do not involve any sampling during "worst-case" scenarios, that I wonder how valid it is.
    In fact, the two researchers themselves caution against drawing any strong conclusions from their report.

    The Associated Press reported on the study earlier this week. The very first sentence in the AP story stated that, "The levels of air and noise pollution that Yellowstone National Park workers were exposed to declined after new limits on the number and type of snowmobiles in the park went into effect, a new study shows."
    While the writer then correctly pointed out that researchers say further study is needed before any strong conclusions can be made, the version of story I saw failed to note the seemingly small sampling pool and the fact that the researchers were unable to conduct monitoring under "worst-case" weather conditions.
    There's one other interesting tidbit that should be noted: On the days the monitoring took place, snowmobile traffic in the park was far, far below the 720 machines allowed daily under the current program. Snowmobile traffic at the West Entrance on the days of the studies ranged from a low of 109 to a high of 279.   
    The report on "Yellowstone Winter Use Personal Exposure Monitoring" was prepared by Terry Spear of Montana Tech and Dale Stephenson at Boise State University.
    Last winter, during the three-day Martin Luther King weekend and the three-day President's Day weekend, the two conducted monitoring at Yellowstone's West Entrance, the Madison Warming Hut, and at the Mammoth Hot Springs Maintenance Shop. The monitoring looked for a wide range of airborne pollutants, ranging from benzene and toluene to hydrocarbons, VOCs and carbon monoxide.
    "All employee exposure to the above air contaminants and noise were well below established Occupational Safety and Health Administration permissible exposure limits and other established recommended exposure limits," Spear and Stephenson noted.
    However, that conclusion was based on what seems to me to be very little data. For instance, they took just six samples to test for exposure to aldehydes; just ten for exposure to benzene, ethyl benzene, toluene and xylenes; just 11 for VOCs; 16 for elemental and organic carbon results; eight for nitrogen dioxide and nitric oxide; and 13 for suspended particulate matter.
    Furthermore, the testing was conducted on what the report's narrative indicates were pretty nice days. No testing was conducted on socked-in days that might hold the pollutants low to the ground where they can swirl about employees.
    "Due to the absence of inversions noted during the monitoring dates of the current study, worst-case data were not collected," Spear and Stephenson noted.
    Later in their report the two cautioned against making any strong conclusions from their data.
"There are many uncertainties associated with risk assessment. The exposure assessment in the current study involved a limited time period. Although this time period was thought to represent worst-case exposures, it cannot be construed to represent all possible exposure scenarios to snowmobile emissions and/or other toxic contaminants that park employees may encounter at work or during non-occupational activities," they wrote.
    "The current study focused on integrated shift exposures and did not evaluate short-term peak exposures for the gaseous/vapor contaminants," they added. "Exposure to high concentrations for short time periods presents uncertainties in assessing risk. Studies have indicated that short-term exposures at higher doses may increase cancer risk beyond that of an equivalent dose administered over a longer period of time."
    So, while it's nice to see some monitoring data, I don't think anyone -- snowmobile advocates or opponents -- can seize this report and say it justifies either allowing the machines in the park or banning them.

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