G. Nelson1, B. A. Racette2, W. W. Dlamini2, P. Prathibha2, J. R. Turner2, M. Ushe2, H. Checkoway3,

L. Sheppard2, S. Searles-Nielsen2

1University of the Witwatersrand, Johannesburg, South Africa

2Washington University, St Louis, USA

3University of California, San Diego, USA



Exposure to manganese (Mn) through occupations such as mining, smelting and welding, is associated with neurotoxic brain injury, manifesting primarily as parkinsonism. However, the neurological health effects of exposure to lower, environmental levels is unclear. The current occupational exposure limit may not protect workers from ill health effects.


We sampled residents older than 40 years, living near a large Mn smelter in South Africa and those living in an unexposed settlement, from 2016 to 2020. A movement disorders specialist examined all participants using the Unified Parkinson Disease Rating Scale motor subsection part 3 (UPDRS3). The 621 Mn-exposed and 95 unexposed participants completed accelerometry-based kinematic (ABK) and grooved pegboard tests. We compared performances between the two groups, using linear regression. We also measured airborne PM2.5-Mn in both settlements.


Mean PM2.5-Mn concentration at a long-term fixed site near the smelter was 203 ng/m3 in 2016-2017. The mean Mn concentration in the unexposed settlement was ~ 20 times lower. UPDRS3 scores were 6.6 (95% CI 5.2, 7.9) points higher in the exposed than the unexposed participants. Mean angular velocity for finger-tapping on the ABK test was slower in the exposed than the unexposed participants [dominant hand 74.9 (95% CI 48.7, 101.2) and non-dominant hand 82.6 (CI 55.2, 110.1) degrees/second slower]. Mn-exposed participants took longer to complete the grooved pegboard, especially for the non-dominant hand (6.9, CI -2.6, 16.3 seconds longer).


Environmental airborne Mn exposures at levels substantially lower than occupational exposures may be associated with clinical parkinsonism.


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