Altered manganese and iron biomarkers in welders: a multi-element biomonitoring study across blood, serum and urine

Background: Interpreting biomonitoring data for welding fume exposure remains challenging due to complex metal mixtures and tight homeostatic regulation of essential elements. In gas metal arc welding (GMAW), manganese is of particular concern due to its neurotoxic potential upon overload. Iron, although being the dominant mass fraction of welding fumes, has received less attention despite possible disturbance of systemic metal homeostasis. Methods: Twelve GMAW welders and matched controls were investigated in this pilot study using a multi-matrix biomonitoring approach. Blood and serum samples were collected pre- and post-shift, and urine samples post-shift only. 17 metals were quantified by inductively coupled plasma tandem mass spectrometry (ICP-MS/MS). Iron-related biomarkers (ferritin, transferrin saturation, soluble transferrin receptor (sTfR)) were additionally assessed. Results: Urinary chromium, iron, manganese, antimony, and vanadium were elevated in welders compared with controls. Blood manganese, although still widely used in occupational biomonitoring, showed only minor differences between groups, consistent with well-known concerns about its limited sensitivity as a marker of internal exposure. In contrast, serum and urinary manganese demonstrated more distinct patterns between welders and controls. Descriptive subgroup analysis according to respiratory protection use suggested higher biomarker concentrations in welders without powered air-purifying respirators. Welders exhibited approximately threefold higher serum ferritin levels accompanied by reduced sTfR, unaltered serum iron, and increased urinary iron excretion. This biomarker pattern is compatible with alterations in systemic iron homeostasis affecting iron storage rather than circulating iron pools. Ferritin concentrations were positively associated with manganese in serum and urine. Conclusion: These findings highlight the complexity of biomonitoring in welding environments and suggest limitations of single-matrix approaches for assessing internal manganese and iron exposure under contemporary working conditions. Multi-matrix strategies and further studies integrating biological and exposure-related measurements are needed to improve occupational biomonitoring concepts for welders.