Parkinsonian symptoms can develop in welders, and with longer and greater exposure to manganese—a chemical found in welding fumes—become worse over time, according to study results published online December 28, 2016, in Neurology. Worsening symptoms included upper limb bradykinesia, limb rigidity, and speech and facial expression impairment, noted researchers.
“These welders are developing parkinsonian symptoms even though their exposure to manganese is below the current regulatory limits,” said study author Brad A. Racette, MD, executive vice chair and professor, department of neurology, Washington University School of Medicine, St. Louis, MO.
“This study suggests that we need more stringent workplace monitoring of manganese exposure, greater use of protective equipment and monitoring, and systematic assessment of workers to prevent this disabling disease,” added Dr. Racette, who is also a fellow of the American Academy of Neurology.
In this trade union-based, longitudinal study, Dr. Racette and fellow researchers studied 866 Midwestern workers employed by two shipyards and a heavy machinery fabrication shop, who underwent 1,492 neurological assessments by a movement disorders specialist at baseline. Of these subjects, 398 completed up to 10 years of follow-up, and were tested for Parkinson’s symptoms.
Linear mixed modeling was used, with cumulative manganese exposure as the independent variable and annual change in Unified Parkinson Disease Rating Scale motor subsection part 3 (UPDRS3) as the primary outcome. UPDRS3 subcategories comprised the secondary outcomes. The primary exposure metric was cumulative manganese exposure in mg Mn/m3-year, as assessed via a questionnaire about job type and length of time on the job.
In all, 135 of workers (15%) had parkinsonism, scoring at least 15 on a scale of zero to 108 points. Dr. Racette and colleagues found that cumulative manganese exposure was associated with a yearly increase in scores on a movement test. Each mg Mn/m3-year of exposure added an estimated 0.24 points on the scale of movement problems (95% CI: 0.10-0.38).
“For example, a worker who had been a welder for 20 years before the first examination had an estimated 2.8 milligrams manganese per cubic meter years exposure and would be predicted to have nearly a seven-point increase on the movement test related to that welding fume exposure,” said Dr. Racette.
Even after adjusting for factors that could affect the risk of movement disorders, including smoking, alcohol consumption, and pesticide exposure, results remained the same. Cumulative manganese exposure caused progression of upper limb bradykinesia, upper and lower limb rigidity, and impairment of speech and reductions in facial expressions.
This association between welding exposure and increased symptoms was particularly strong in welders who engaged in flux core arc welding in confined spaces. This welding process is known to generate the greatest levels of particulate matter.
Workers in whom the first exam was conducted within 5 years after initiating welding showed a strong relationship between exposure to welding and increased symptoms as well. Researchers hypothesized that this may be due to the absence of workers with higher exposure who may develop parkinsonism and then drop out of the workforce.
Dr. Racette noted that the effects of other metals present in welding fumes and other exposures to paint and degreasing solvents could not be ruled out.
This study was supported by the National Institute for Environmental Health Sciences, Michael J. Fox Foundation for Parkinson’s Research, National Institute of Neurological Disorders and Stroke, National Center for Research Resources, and National Institutes of Health Roadmap for Medical Research.