Occupational exposure to total and hexavalent chromium in welders: an integrated environmental and biological monitoring study

Introduction: Chromium (Cr), and particularly its hexavalent form is classified as a Group 1 human carcinogen and represents a major occupational hazard, particularly in stainless-steel welding. This exploratory study integrated environmental and biological monitoring to characterize welders' exposure and assessed how analytical methods influence exposure estimates. Methods: Twenty-two welders from two Northern Italian companies and 10 administrative controls were enrolled (May-June 2025) and monitored during full 8 h shifts. Personal respirable particulate samples were analyzed for total Cr (CrTOT) and Cr(VI) using NIOSH 7,600 and a speciation-preserving modified ISO 17075 protocol. Biological monitoring included pre-/post-shift urinary Cr (U-Cr, creatinine-adjusted) and post-shift exhaled breath condensate Cr (EBC-Cr). Results: All airborne CrTOT and Cr(VI) concentrations were below their respective Occupational Exposure Limit Values (500 and 5 μg/m3, respectively), though welders consistently showed higher exposure than controls. MMA welding produced the highest CrTOT and Cr(VI) levels. NIOSH 7600 yielded higher Cr(VI) values than the modified ISO method, a pattern consistent with a possible positive bias related to species interconversion during extraction. U-Cr was significantly elevated in welders at both sampling times [geometric mean (GM): 0.34, 0.36, and 0.05 μg/g creatinine in pre-, post-shift exposed workers and controls, respectively], whereas EBC-Cr did not differ between groups (GM: 0.08 μg/L in all samples). Biomarker levels showed minimal variation across demographic and occupational subgroups. Correlations between airborne Cr and biological indicators were weak, yet U-Cr values in welders exceeded population reference ranges, indicating a clear occupational contribution despite low absolute exposure. Discussion: Integrated monitoring confirmed Cr absorption in welders despite regulatory compliance. Within the limits of this study, U-Cr appeared to be the most informative biomarker, whereas EBC-Cr showed limited sensitivity. Although exposures remained below biological limit values, welders exhibited an upward shift in U-Cr relative to background populations, supporting continued exposure minimization-especially for high-emission processes such as MMA-consistent with As Low As Reasonably Achievable principles.