Neurological Outcomes Associated with Low-level Manganese Exposure in an Inception Cohort of Asymptomatic Welding Trainees

• Published in: Scandinavian Journal of Work, Environment ＆ Health Vol. 41; no. 5; pp. xi+94 - 101
• Main Authors: Baker, Marissa G, Criswell, Susan R, Racette, Brad A, Simpson, Christopher D, Sheppard, Lianne, Checkoway, Harvey, Seixas, Noah S
• Format: Journal Article
• Language: English
• Published: Finland Scandinavian Journal of Work, Environment ＆ Health 01.01.2015; Nordic Association of Occupation Safety and Health; Scandinavian Journal of Work, Environment & Health; Nordic Association of Occupational Safety and Health (NOROSH)
• Subjects: Adolescent; Adult; Air Pollutants, Occupational - adverse effects; Asymptomatic; Basal ganglia; Biological markers; biomarker of effect; biomarker of exposure; Biomarkers; Central nervous system; Cohort analysis; Cohort Studies; effect; exposure; Female; grooved pegboard; Health outcomes; Humans; Imaging; Inhalation Exposure - adverse effects; learning effect; Longitudinal Studies; Magnetic resonance imaging; Magnetic Resonance Imaging - methods; Male; Manganese; Manganese - adverse effects; Manganese - analysis; manganese exposure; Metal workers; Middle Aged; mri; Nervous system; Nervous System Diseases - chemically induced; Nervous System Diseases - diagnosis; neurological outcome; Occupational Diseases - chemically induced; Occupational Diseases - diagnosis; Occupational exposure; Occupational Exposure - adverse effects; Occupational Exposure - analysis; Parkinson's disease; Putamen; Tremor - diagnosis; updrs3; welder; Welders; Welding; welding trainee; Young Adult; United States > US; welder; exposure; grooved pegboard; MRI; biomarker of effect; learning effect; effect; UPDRS3; biomarker of exposure
• ISSN: 0355-3140; 1795-990X; 1795-990X
• DOI: 10.5271/sjweh.3466

Objective Long-term, high-level exposure to manganese (Mn) is associated with impaired central nervous system (CNS) function. We quantitatively explored relations between low-level Mn exposure and selected neurological outcomes in a longitudinal inception cohort of asymptomatic welder trainees. Methods Welders with no previous occupational Mn exposure were observed approximately every three months over the course of the five-quarter traineeship. Fifty-six welders were assessed for motor function using the Unified Parkinson Disease Rating Scale motor subsection part 3 (UPDRS3) and Grooved Pegboard tests. A subset of 17 also had MRI scans to assess T1-weighted indices. Personal exposure to Mn in welding fume was quantitatively assessed during the study period using a mixed model to obtain estimates of subject-specific exposure level by welding type. These estimates were summed to estimate cumulative exposure at the time of each neurological outcome test. Results When adjusting for possible learning effects, there were no associations between cumulative exposure and UPDRS3 score or Grooved Pegboard time. T1-weighted indices of the basal ganglia (caudate, anterior putamen, posterior putamen, and combined basal ganglia, but not the pallidal index) exhibited statistically significant increases in signal intensity in relation to increased cumulative Mn exposure. Conclusions This study demonstrates that T1-weighted changes can be detected in the brain even at very low levels of exposure among humans before any clinically evident deficits. This suggests that with continued followup we could identify a T1 threshold of toxicity at which clinical symptoms begin to manifest.