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Manganese Exposures May Worsen Parkinsonism in Welders

Brad A. Racette, M.D.
University of Washington
R01ES021488, K24ES017765, P42ES004696, K23ES021444

Welders exposed to manganese may develop Parkinson’s disease-like symptoms, and the symptoms may get worse the more they are exposed, according to NIEHS-funded researchers. A study of Midwestern workers over 10 years linked the progression of movement abnormalities seen in Parkinson's disease, or parkinsonism, to cumulative exposure, even at manganese levels below the regulatory limit.

Researchers examined 886 workers at two shipyards and a heavy machinery fabrication shop, looking for movement disorders associated with Parkinson’s disease. For up to 10 years after the initial assessments, 398 workers had follow-up examinations. Researchers estimated exposure to manganese through a questionnaire about the workers’ job types and length of time on the job. The team reported that the average exposure to manganese was equivalent to 0.14 milligrams of manganese per cubic meter. Throughout the study, approximately 15 percent of the workers received motor scores that indicated they had parkinsonism.

The researchers found that Parkinson’s disease-like symptoms got worse the more the welders were exposed over time. Symptoms included slowness of movement in the arms and hands, stiffness in arms and legs, speech problems, and reduced facial expressions. According to the authors, each additional year of manganese exposure might increase the risk of parkinsonism, even when concentrations of manganese were below regulatory levels.

Based on their findings, the researchers emphasized the need for more stringent workplace monitoring of manganese exposures, greater use of personal protective equipment and ventilation, and systematic worker assessment.

Citation: Racette BA, Searles Nielsen S, Criswell SR, Sheppard L, Seixas N, Warden MN, Checkoway H. 2016. Dose-dependent progression of parkinsonism in manganese-exposed welders. Neurology 88(4):344−351.