Objective To examine the association between exposure to airborne iron and pleural disease among Minnesota taconite mining workers.

Methods The goal of this study is to assess the association between exposure to airborne iron concentrations and pleural abnormalities in 1176 current and former workers employed in various operations in mining and processing of taconite (a low grade iron ore). Pleural abnormality, consistent with pneumoconiosis, was identified by consensus of two certified B-readers based on a single radiograph of the taconite workers.

The workers’ cumulative exposure to airborne iron was estimated using 679 present-day and 17,083 historical exposure measurements along with area measurements that were combined with the workers’ employment histories. Cumulative exposures to respirable silica (RS) and elongated mineral particles (EMP) were also estimated using present-day and historical measurements.

Logistic regression was used to estimate associations between iron exposure and pleural abnormalities adjusting for possible confounders (EMP exposure, smoking status).

Results Of the 1,176 participants 197 had pleural abnormalities. The averaged cumulative exposures to iron, RS, and EMP in the pleural abnormalities group were significantly higher than those in pleural normal group (Iron: 2.02 (mg/m³) × year vs 1.71 (mg/m³) × year; RS: 1.21 (mg/m³) × year vs 1.08 (mg/m³) × year; EMP: 3.9 (EMP/cc) × year vs 2.8 (EMP/cc) × year). The crude OR for Iron exposure was 1.21 (95% CI: 1.07 to 1.36) and 1.12 (95% CI: 0.98 to 1.27) after adjusting for EMP exposure, age and BMI.

Conclusions This study provides modest evidence that Iron exposure may play a role in the development of the pleural disease among taconite workers. Given the correlated multiple exposures in the taconite mine, the joint effect of Iron and EMP exposure warrants future investigation.