Reconstructing Historical Exposures to Respirable Dust and Respirable Silica in the Taconite Mining Industry for 1956-2010

摘要

As part of ongoing epidemiological studies for assessing the association between exposure to taconite dusts and the development of respiratory diseases, the goal of our study is to reconstruct the historical silica (RS) and respirable dust (RD) exposures of workers in Minnesota taconite industry from 1955-2010 by developing a job exposure matrix (JEM) that uses 9,128 RS and 19,408 RD industrial hygiene monitoring data. Historical RS and RD data were obtained for seven taconite mines from three sources:(1) the Mine Safety and Health Administration (MSHA) has online database records for all inspection results since 1978 for 13 MSHA Mine IDs with 4,303 RD monitoring records;(2) the mining companies' internal monitoring reports provided 14,417 RD records, most of which date from the late 1970s.(3) University of Minnesota in 2010 conducted 688 pairs of RS and RD measurements covering six active mines. Unlike RD data which can be directly read from IH reports, many historical RS data have to be calculated using RD and silica percentage information. 8,840 RS data were calculated using available silica percentage information. After data treatment, all these data were grouped into 7 mines and then into 8 departments. Within each department, we applied a two-level random-intercept model which assumes that the natural log of Y (RD or RS) changes over time at a constant rate. Among the 56 mine-department combinations, 13 combinations show a significant (p-value<0.05) decreasing RS and RD trend with the maximum rate of decrease of 3.3% per year; 12 combinations show a significant increasing trend with the maximum annual increase rate of 8.7%. The estimated percent silica varies by department, with the maximum value usually occurring in the crushing department (8.5%-27.6%) and the minimum value occurring in the pelletizing department (2.6%-8.5%).The result of this study is a JEM by mine, department, and year for RD and RS that will form the basis for future epidemiological studies.