TENTATIVE EXPLANATORY VARIABLE OF LUNG DUST CONCENTRATION IN GOLD MINERS EXPOSED TO CRYSTALLINE SILICA

Introduction: The first objective of the study was to investigate the relationships between quantitative lung mineral dust burdens, dust exp osure history, and pathological fibrosis grading in silicotic workers. The second objective was to evaluate the association between particle size parameters, concentration of retained silica particles and the s everity of the silicosis. Sixty-seven paraffin-embedded lung tissue sa mples of silicotic patients were analyzed. The cases of silicosis incl uded 39 non-lung cancer patients and 28 patients with lung cancer. All of the cases were gold miners in the Province of Ontario, Canada. Mat erial and methods: Particles, both angular and fibrous, were extracted from lung parenchyma by a bleach digestion method, mounted on copper microscopic grids by a carbon replica technique, and analyzed by trans mission electron microscopy (TEM) and energy dispersive spectroscopy ( EDS). Quartz concentration was also determined by X-ray diffraction (X RD) on a silver membrane filter after the extraction from the lung par enchyma. Results: Total particles, silica, clay, and quartz also incre ase in concentration with increased age at death, although the trends are not statistically significant. Quartz concentration has a statisti cally significant correlation with the silicosis severity score (r = 0.45, p < 0.001), with the geometric mean concentration increasing fro m 2.24 mu g/mg in the group having silicosis severity score less than 1 to 4.80 mu g/mg in group with highest score. Quartz concentration is the only significant explanatory variable of the silicosis severity w ith a regression coefficient of +0.41 (p < 0.001). Conclusion: Among s everal dust exposure variables extracted from the work history of the miners, the calendar year of first exposure was the primary significan t determinant of lung retained total particles, silica, and clay miner als, except for quartz. A statistically significant linear relationshi p between lung quartz concentration and silicosis severity in the gold miners was observed (p < 0.001). Among the several types of lung part icles detected, quartz was the only significant determinant of the sil icosis severity in the gold miners in this study, and vice versa, alth ough it explained only 20% of the variation in the severity. This stud y suggested no significant linear relationship between the duration of dust exposure and the lung burden of any particle types in the sold m iners.