Iron status in manganese alloy production workers.

The aim of this study was to investigate markers of iron status in production workers with current and long-term exposure to manganese (Mn) alloys. A total of 100 Mn-exposed male workers were compared with 100 male controls matched for age in a cross-sectional study. The geometric mean urinary Mn concentration in the exposed workers was 0.9 nmol mmol(-1) creatinine (range = 0.1-126.3), compared with 0.4 nmol mmol(-1) creatinine (range = 0.1-13.1) in the controls. The index group had been exposed to Mn for 20 years on average (range = 2.1-41.0). The geometric mean concentration of soluble transferrin receptor was lower in the exposed subjects than in the controls (2.2 vs 2.6 mg l(-1); P < 0.001) and the concentration was negatively associated with current exposure to "soluble" Mn in the inhalable aerosol fraction and with current smoking habits. An association was found between the concentration of serum soluble transferrin receptor and the concentration of Mn in whole blood (Pearson's r = 0.48; P < 0.001) in the controls. The results suggest that Mn-exposed workers have higher intracellular iron concentration in the erythrocyte precursors than the controls, resulting in a down-regulation of transferrin receptors on the surface of these cells. The concentrations of Mn in the blood of occupationally non-exposed individuals appear to be influenced by iron status, even at physiological iron levels.