Neurological outcomes associated with low-level manganese exposure in an inception cohort of asymptomatic welding trainees.
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 follow-up we could identify a T1 threshold of toxicity at which clinical symptoms begin to manifest.
Department of Environmental and Occupational Health Sciences, 4225 Roosevelt Way NE, Suite 100, Seattle, WA 98105, USA. bakermg@uw.edu.
Marissa G
MG
Baker
Susan R
SR
Criswell
Brad A
BA
Racette
Christopher D
CD
Simpson
Lianne
L
Sheppard
Harvey
H
Checkoway
Noah S
NS
Seixas
D000293:Adolescent; D000328:Adult; D000395:Air Pollutants, Occupational / Q000009:adverse effects; D015415:Biomarkers; D015331:Cohort Studies; D005260:Female; D006801:Humans; D019570:Inhalation Exposure / Q000009:adverse effects; D008137:Longitudinal Studies; D008279:Magnetic Resonance Imaging / Q000379:methods; D008297:Male; D008345:Manganese / Q000009:adverse effects* / Q000032:analysis; D008875:Middle Aged; D009422:Nervous System Diseases / Q000139:chemically induced* / Q000175:diagnosis; D009784:Occupational Diseases / Q000139:chemically induced* / Q000175:diagnosis; D016273:Occupational Exposure / Q000009:adverse effects* / Q000032:analysis; D014202:Tremor / Q000175:diagnosis; D014896:Welding; D055815:Young Adult
D000395:Air Pollutants, Occupational; D015415:Biomarkers; D008345:Manganese