Are current biomarkers suitable for the assessment of manganese exposure in individual workers?

Background: Whole blood and urinary manganese have been measured in occupational and environmental studies for the assessment of exposure. The aim of this study was to assess the relationship between the airborne concentrations of manganese and these biological indicators. Methods: Environmental and biological monitoring was performed in a group of 94 employees in a ferroalloy production, who were exposed to manganese (Mn) oxides (MnO₂ and Mn₃O₄). The results were compared with those from a control group of 87 subjects not exposed to Mn. Results: Mn exposure levels ranged between 5 and 740 μg/m³, with arithmetic and geometric mean and median values being 202.6, 97.6, and 150 μg/m³, respectively. Arithmetic and geometric means for Mn in total blood (MnB) were, respectively, 10.3 ± 3.8 and 9.7 μg/L in the exposed and 5.9 μ 1.7 and 5.7 μg/L in the controls. For urinary Mn (MnU), arithmetic and geometric means were, respectively, 4.9 μ 3.6 and 3.8 μg/L in the exposed and 1.2±1.4 and 0.7μg/L in the controls. On a group comparison, a significant relationship was found between high and low exposed subgroups, identified according to Mn atmospheric concentrations (MnA), for both MnB (F value=38.0, P>0.0001) and MnU (F value=36.1, P>0.0001). On a linear relationship, a correlation was observed between MnA and MnB (r = 0.34; r² = 0.112; P=0.001), whereas no association was found between MnA and MnU. A significant relationship emerged also between MnB and MnU (r = 0.48, r² = 0.23, P< 0.0001). No association was observed between an index of cumulative exposure and the biological indicators of exposure. Conclusion: These results confirm that MnB and MnU can discriminate groups of occupationally exposed workers from groups of nonexposed subjects. MnB is also related to the intensity of external exposure on a linear relationship, but given a high variability, it is not suitable for individual biological monitoring. Therefore, further research should focus on more accurate biomarkers of Mn exposure.