Imaging of Mn Washout in the Individual Welder Brain After Wearing Powered Air-Purifying Respirators (PAPRs)

Details

• Personal Author:
  Hsu, C. ; Monsivais, H. ; Mizimakoski, C. ; Lee, C. ; Park, J. ; Dydak, U.
• Description:
  Background and Purpose: Chronic exposure to welding fumes increases manganese (Mn) deposition in the brain, leading to adverse neurobehavioral health effects. Since the signs of metal-induced toxicity are neurological, understanding the spatio-temporal dynamics of accumulated Mn in the human brain is essential. To date, no data exist on the spatial distribution of Mn accumulation in the individual brains of welders, nor has the washout of Mn been measured in the human brain following cessation of exposure. Due to Mn's paramagnetic properties, magnetic resonance imaging (MRI) is the only imaging modality capable of non-invasive, in-vivo assessment of Mn accumulation. Specifically, the longitudinal relaxation time (T1) decreases with increased Mn deposition in the brain. While hyperintensities in T1-weighted MRI images are typically visible only in cases of severe exposure, this study developed a whole-brain Mn-mapping approach to detect subtle but significant increases in Mn deposition in individual welders compared to a normative map from non-welding factory controls. This method enables the first investigation of the spatio-temporal dynamics of brain Mn deposition in response to changes in occupational exposure. In this pilot study, changes in brain Mn accumulation were monitored before and after welders began using powered air-purifying respirators (PAPRs), which significantly reduce exposure to airborne metal particle levels. Methods: As part of a larger imaging study on welders, four welders who had recently started using a PAPR and 31 non-welding factory controls were recruited from a U.S. truck manufacturer. All participants provided written informed consent to participate in the study. Personal air sampling was conducted over one work shift to measure respirable Mn concentrations in each subject's breathing zone. MRI scans were performed once for controls and twice for welders - one prior to and the other 1-2 months after initiating PAPR use. Whole-brain T1 relaxometry maps were acquired using a 3T Siemens Prisma MRI. A normative T1 atlas was created by modeling the relaxation time variability within the control cohort using a linear regression model that accounted for the impact of age at each voxel position. Individual z-score maps were then calculated against this atlas to quantify deviations specific to each subject. A threshold of z-scores < -6 and a minimum cluster size of 100 voxels was applied to reduce false positives. The total number of voxels exceeding the threshold was determined, and whole-brain z-score maps, indicating individual Mn deposition, were visualized to assess brain changes before and after PAPR use among welders. Results: Respirable Mn concentrations in welders' breathing zones, sampled outside of PAPRs, ranged from 63-321 µg/m³, compared to the controls' mean Mn concentrations of 0.005 µg/m³. The total number of thresholded voxels, indicating above-average Mn deposition, decreased by over 60% in 3 of the 4 welders after using the PAPR, with no significant changes observed in one welder. For the 3 welders with significant changes, z-score maps acquired before PAPR use showed widespread significant z-scores of reduced T1 values compared to the control cohort, indicating excess Mn accumulation throughout much of the cerebral white matter and deep brain structures. However, the maps acquired two months after PAPR use showed a significant decrease in elevated Mn deposition. Specifically, Mn accumulation was visibly reduced in the bilateral globus pallidus, thalamus, and several white matter tracts, with minimal reduction observed in the brainstem. Conclusions: Mn accumulation significantly decreased in welders in several brain regions within just 1-2 months of using a PAPR, with varying reduction rates observed across brain regions. Upon investigating the one welder who did not show much change, it was found that he welds only part-time and wears the PAPR exclusively during welding. However, his workstation is located adjacent to a welding robot, leading to co-exposure even when he is not welding, which may explain the lack of observed changes. Future work will include a one-year follow-up of these four welders and an increase in the sample size. Overall, this study provides the first insight into the spatio-temporal dynamics of brain Mn washout in humans following reduced Mn exposure and highlights the impact of PAPR use. Description provided by NIOSH
• Subjects:
  • Manganese
  • Nervous System
  • Nervous System Diseases
  • Occupational Health
  • Respiratory Protective Devices
  • Safety
  • Welders
• Keywords:
  • Manganese; Welders; Welding fumes; Powered air purifying respirator; PAPR; Magnetic resonance imaging; MRI; Brain function
• Source:
  Toxicologist 2025 Mar; 204(S1):362-363
• ISSN:
  1096-6080
• Document Type:
  Text
• Funding:
  Grant
• Genre:
  Abstract or Summary
• Place as Subject:
  Chicago Region OSHA ; Dallas Region OSHA ; Indiana ; Texas
• CIO:
  National Institute for Occupational Safety and Health (NIOSH)
• Topic:
  Workplace Safety & Health
• Location:
  North America
• Pages in Document:
  3 pdf pages
• Volume:
  204
• NIOSHTIC Number:
  nn:20071595
• CAS Registry Number:
  • Manganese (CAS RN 7439-96-5)
• Federal Fiscal Year:
  2025
• Performing Organization:
  Purdue University, West Lafayette, Indiana
• Peer Reviewed:
  False
• Start Date:
  20010701
• End Date:
  20270630
• Download URL:
  https://stacks.cdc.gov/view/cdc/259370/cdc_259370_DS1.pdf
• File Type:
  [PDF - 280.45 KB]
• Collection(s):
  National Institute for Occupational Safety and Health
• Main Document Checksum:
  urn:sha-512:180a035150e793228e314e6c76b6d784128a2ed31b601d3a2bf95816f79dfb29f3def36b2c06955fba8129ff6c81a8f874bcb47f3db7b3694dad771066fc6b16