Activity-based exposure assessments to Libby amphibole associated with public and occupational tasks in the Kootenai National Forest and weatherization of homes containing vermiculite attic insulation
Up to 80% of the world’s supply of vermiculite was produced from a mine near Libby, MT. A common use for expanded vermiculite was loose fill insulation in attics and walls. Unfortunately, vermiculite from the Libby mine was contaminated with amphibole asbestos minerals referred to as Libby amphibole, LA. Fifteen years after the closure of the vermiculite mine, substantial (14 - 110 million structures/cm2) LA contamination was discovered on the surface of tree bark in the forested areas surrounding the former mine. Research was conducted to evaluate the potential for LA exposure associated with tree bark and vermiculite attic insulation (VAI) sources. The potential for airborne LA exposure and clothing contamination to Libby residents who harvest firewood for home heating and to United States Department of Agriculture Forest Service (USDA FS) employees who work in the in the Kootenai National Forest was evaluated through activity-based exposure assessments. In addition, research was conducted to evaluate the impact of weatherization activities in homes with VAI and/or other asbestos containing materials (ACM). Personal breathing zone (PBZ), high volume air and surface sampling were conducted throughout the weatherization of 37 homes. Firewood harvest exposure assessments revealed a strong potential for exposure with LA detected in 100 % of the PBZ samples. The mean transmission electron microscopy (TEM) LA concentration for fibers > 5 μm was 0.07 structures per mL (s/mL). Outside of the restricted zone, the PBZ samples from the FS occupational study revealed detectable LA in 25 % of the PBZ TEM samples. In addition to airborne exposure, LA was detected on wipe samples from all activities related to the firewood harvest and occupational assessment. During the weatherization of homes containing VAI or other ACM, the majority (79% and 80% respectively) of high volume air and PBZ air samples did not reveal detectable concentrations of asbestos. However, airborne asbestos was detected in 76% of the homes. Airborne asbestos was detected during numerous weatherization measures, suggesting that weatherization practices as a whole, not single weatherization activities, may contribute to the disturbance and dispersal of asbestos fibers into the air. While substantial cleanup of homes, yards, etc., has been conducted in Libby, MT, through Superfund activities, additional potential sources of LA exposure in this area, such as tree bark, are important to consider when assessing public and occupational health risks. Outside of Lincoln County, MT the number of homes and other structures containing VAI is unknown. The exposure potential associated with VAI, especially associated activities that may disturb this insulation, warrant attention from a U.S. public health standpoint as well.
© Copyright 2013 Julie Faroni Hart