EXPOSURE ASSESSMENT AMONG LIBBY COMMUNITY MEMBERS

Six miles northeast of the town of Libby, Montana lies an extensive vermiculite deposit which, from about 1920 to 1990, represented a major source of vermiculite ore for the United States and for the world. Co-located with the Libby vermiculite deposit is a deposit of amphibole asbestos (“Libby amphibole” or “LA”) which is composed of a number of related mineral types, most commonly winchite and richterite, but also tremolite, actinolite, and magnesioriebeckite. Open-pit mining, milling, and processing operations at the Libby mine resulted in the release of vermiculite and LA to the environment, which, coupled with multiple environmental transport pathways, has resulted in extensive non-occupational inhalation exposure to LA among the residents of Libby via a number of exposure pathways. Adverse health effects have been reported in Libby residents having no occupational exposure to LA-contaminated vermiculite. General non-occupational exposure pathways potentially contributing to the cumulative exposure of Libby residents include 1) disturbance of gross product or waste material, 2) outdoor ambient air, 3) outdoor air associated with the disturbance of contaminated soils or other contaminated media, and 4) indoor air. Early actions implemented by the US Environmental Protection Agency (EPA) targeted the removal of gross vermiculite product and waste materials, resulting in the elimination or significant reduction of related exposures. Subsequent EPA exposure pathway investigations have focused on quantification of remaining LA levels in outdoor ambient air, and, using activity-based sampling methods, quantification of LA levels in indoor air and outdoor air associated with the disturbance of contaminated soils. Data analysis reveals variable exposure levels associated with season and intensity of disturbance. Cumulative exposures vary depending on exposure parameters, but outdoor air associated with disturbance of contaminated soils consistently represents a major exposure pathway for Libby residents.