Respiratory effects of exposure to dust in taconite mining and processing.

Taconite is a low-grade iron ore consisting of iron, quartz, and numerous silicates. Taconite from the eastern tip of the Mesabi Iron Range contains the amphibole silicate cummingtonite-grunerite, which is a mineral relative of amosite asbestos. In the present study, data were collected from 249 men with 20 or more years of exposure to taconite dust and 86 men without history of intimate exposure to taconite dust. Bronchitic symptoms and impairment of expiratory flow correlated significantly with history of cigarette smoking, but not with exposure to dust. Chest radiographs revealed three cases of possible silicosis. No case of definite interstitial fibrosis, ill-defined diaphragm, pleural calcification, or mesothelioma was found. We conclude that (1) cigarette smoking is significantly correlated with bronchitic symptoms and impairment of expiratory flow; (2) taconite workers are at risk of silicosis; (3) if dust containing cummingtonite-grunerite has biologic activity comparable to that of dust from asbestos, it is not evident after 20 years of low-level exposure.