Abstract
Welding-generated metallic fumes contain a substantial amount of manganese (Mn), making welders susceptible to Mn toxicity. Although overt Mn toxicity manifests as a type of parkinsonism, the consequences of chronic, low-level Mn exposure are unknown. To explore region-specific Mn accumulation and its potential functional consequences at subclinical levels of Mn exposure, we studied seven welders without obvious neurological deficits and seven age- and gender-matched controls. Mn exposure for welders was estimated by an occupational questionnaire. High-resolution brain magnetic resonance imaging (MRI), Grooved Pegboard performance of both hands, Trail making, and olfactory function tests were obtained from all subjects. Compared with controls, the welders had a significantly higher T1 relaxation rate (R1) in the olfactory bulb (OB, p = 0.02), mean T1-weighted intensity at frontal white matter (FWM; p = 0.01), bilateral globus pallidus (GP; p = 0.03), and putamen (p = 0.03). The welders scored worse than the controls on the Grooved Pegboard test for both dominant (p = 0.06) and nondominant hand (p = 0.03). The dominant hand Grooved Pegboard scores correlated best with mean MRI intensity of FWM (R² = 0.51, p = 0.004), GP (R² = 0.51, p = 0.004), putamen (R² = 0.49, p= 0.006), and frontal gray matter (R² = 0.42, p = 0.01), whereas the nondominant hand scores correlated best with intensity of FWM (R² = 0.37, p = 0.02) and GP (R² = 0.28, p = 0.05). No statistical differences were observed in either the Trail-making test or the olfactory test between the two groups. This study suggests that Mn accumulates in OB and multiple other brain regions in "asymptomatic" welders and that MRI abnormalities correlate with fine motor but not cognitive deficits. Further investigations of subclinical Mn exposure are warranted.
Highlights
Welding fumes generated during the welding process are a well-known source of hazardous toxicants in the form of submicron metal particulates (OSHA, 2009)
Mn toxicity is manifested by a neurological syndrome called manganism that initially consists of reduced response speed, irritability, intellectual deficits, mood changes, and compulsive behaviors
Mn transport into the brain may occur via three pathways (Crossgrove and Zheng, 2004): (1) transport across the blood-brain barrier (BBB) by transporter-mediated kinetics, (2) transport across the blood-cerebrospinal fluid barrier of the choroid plexus, and (3) via the olfactory nerve bypassing the BBB
Summary
Welding fumes generated during the welding process are a well-known source of hazardous toxicants in the form of submicron metal particulates (OSHA, 2009). Welding fumes vary depending on the type of welding rod being used and the type of metal being welded, with iron (Fe) and manganese (Mn) being the two most common cations that are generated (Jenkins and Eagar, 2005; Sowards et al, 2010). Of these metals, Mn has been well documented as a neurotoxicant for over a 100 years (Couper, 1837) and has been studied extensively in the past (Guilarte, 2010; Meyer-Baron et al, 2009). The present study was designed to investigate the Mn accumulation in different brain regions and to explore their functional correlations
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