Objective Welders are exposed via the inhalation route to respirable-sized (<4µm) metal fume particles, in particular the two main components of welding fume, manganese (Mn) and iron (Fe). Exposure to high levels of Mn and Fe have each been found to be associated with neurological dysfunction. In this study we investigated how the increased exposure to Mn and Fe in welding is reflected in toenail and brain levels of Mn and Fe in vivo.

Methods Our study on 30 typically exposed welders and 20 controls in the United States investigated the associations between occupational Mn and Fe exposure from respirable welding fume with magnetic resonance imaging (R1 and R2* mapping), indicative of brain Mn and Fe levels, and a biomarker (toenails). Multiple exposure measures including job tasks, cumulative airborne exposure based on personal respirable airborne concentrations, and metals concentrations determined in toenail samples were utilised to study the associations with regional brain Mn and Fe concentrations.

Results Welders were significantly more exposed to airborne respirable Mn and Fe than the control population (Mn: 0.11 vs. 0.007 mg/m³, P < 0.01; Fe: 1.05 vs. 0.11 mg/m³, P < 0.01). Welders were also found to have significantly elevated levels of Mn and Fe in their toenails as compared to controls (Mn: P < 0.01; Fe: P < 0.05). Significant deposition of Mn and Fe were found in several brain regions including globus pallidus (Mn & Fe: p < 0.01), substantia nigra (Fe: P < 0.05), and frontal cortex (P < 0.05). R2* was significantly (p < 0.05) correlated with cumulative exposure in the substantia nigra, whereas R1 was associated (p < 0.01) with exposure in motor cortex and basal ganglia regions

Conclusions Our findings suggest that typical U.S. welders are significantly exposed to Mn and Fe through welding fumes. Their exposure is associated with both increased deposition of Mn and Fe in toenails and the brain