Historical and exposure reconstruction in the Taconite mining industry – Study design

We will present the design of the exposure assessment for an epidemiological study of the relationship between exposures to components of taconite dust and adverse health effects, specifically mesothelioma and silicosis. The goal of this study is to assess historical and current exposures of workers to asbestos and non-asbestos fibers, respirable dust, and respirable silica in the taconite industry between 1955 and 2008. Exposure histories will be evaluated for a cohort of workers selected from three large mining companies in north-eastern Minnesota. Historical exposure data are available from the Mine Safety and Health Administration, the Mineral Resources Health Assessment Plan database, and internal databases from each of the mining companies. They include impinger, personal gravimetric, and area gravimetric measurements. The exposure data matrix will have dimensions of year, job title, task, job location, duration of shift, and type of process. We expect that monitoring data will be missing for substantial portions of the matrix. To fill in these missing data, we plan to use information on historical exposure determinants such as ventilation and generation rates using various exposure models. Interviews with veteran workers will help provide information on historical working conditions. Several statistical imputation methods will also be used. A comprehensive assessment of current exposures including personal measurements of asbestos and silica exposures and particle size distributions based on cascade impactor data will be used to provide a benchmark from which past exposures can be extrapolated. A Bayesian framework will be used to combine available monitoring data with modeling predictions and expert judgments.