NMRD mortality was clearly associated with exposure to Libby vermiculite, with SMRs of 3.36 for 10–19 years and 5.30 for more than 20 years since first employment. found an elevated overall standardized mortality ratio (SMR) of 2.55 for NMRD among mine workers employed for at least 1 year. In a study commissioned by the mine owners, McDonald et al. The results of several studies have shown excessive mortality attributed to nonmalignant respiratory disease (NMRD) among sub-cohorts of Libby mine and mill workers. This review will focus on the main nonmalignant and malignant respiratory outcomes associated with exposure to Libby vermiculite, with emphasis on recent findings. Benign pleural effusions were identified among 12 workers in a vermiculite processing plant in Marysville, Ohio, which received most of its vermiculite from Libby. Interestingly, the first identification by public health authorities of pulmonary abnormalities associated with Libby vermiculite concerned exposures outside of Libby. Moreover, Libby vermiculite was shipped throughout the US to more than 200 domestic processing and receiving facilities. In addition, the fact that a very large estimated number of homes were insulated with Libby vermiculite represents an ongoing potential hazard. This resulted in widespread contamination of the Libby community with asbestos. Not only were workers at the mine and mill exposed, but the vermiculite was used in Libby for covering ball fields and outdoor athletic tracks, as loose-fill insulation in buildings, and in gardening activities. Vermiculite from other sources is not known to be associated with any substantial adverse health effects however, the vermiculite ore mined in Libby contained elongate mineral particles identified as a mixture of asbestiform amphiboles, including winchite, richterite, and tremolite asbestos. It expands when heated, and has been employed in many applications, such as loose-fill attic insulation, soil additive, and carrier for various chemicals, including herbicides, insecticides, and fertilizers. Vermiculite is a naturally occurring laminar aluminum-iron-magnesium silicate. A vermiculite mine and mill located near Libby, Montana, operated from the early 1920s until 1990.
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