Nonoccupational Environmental Exposure to Manganese is Linked to Deficits in Peripheral and Central Olfactory Function

Abstract

Manganese is of growing concern as a toxic air pollutant. It is readily transported from the olfactory epithelium to the olfactory bulb, and unlike other metals, it is transported transynaptically to structures deep within the brain. However, little is known regarding the possible effect of nonoccupational exposure to manganese on olfactory function. Using the Sniffin' Sticks test battery, we compared the olfactory performance of subjects from a manganese mining district living <1 km from a manganese processing plant, with nonexposed subjects living 50 km from the closest source of exposure (N = 30/group). Groups were matched for age, sex, and schooling, and none had ever worked in mining-related activities. Concentrations of manganese in hair were measured as a biomarker of exposure; exposed subjects had significantly higher concentrations than nonexposed subjects. They were also significantly outperformed by the nonexposed subjects on all olfactory measures (threshold, discrimination, and identification), indicating adverse effects of manganese exposure on a range of olfactory functions, including those involving higher order cognitive processes. This contrasts with previous findings showing adverse peripheral but not central effects on olfactory function of big city air pollution, which mostly consists of toxicants known to affect the olfactory epithelium but with lower transynaptic transport capacity compared with manganese. We conclude that nonoccupational exposure to airborne manganese is associated with decrements in both peripheral and central olfactory function.

What Makes a Better Smeller?

“…They found people from the Cook Islands had the lowest detection thresholds, followed by the Tsimane' and then Polish people, as predicted. Although this study does not provide causal evidence for a link between environmental pollution and olfactory sensitivity, it dovetails with other data showing everyday pollution negatively affects olfactory perception (e.g., Guarneros et al, 2009;Guarneros, Ortiz-Romo, Alcaraz-Zubeldia, Drucker-Colı´n, & Hudson, 2013;Hudson, Arriola, Martinez-Gomez, & Distel, 2006), and intensive exposure to airborne smoke and dust can deteriorate odor detection, discrimination, and identification (e.g., Altman et al, 2011;Dalton et al, 2010). Conversely, then, we can conclude that unpolluted environments have a positive effect on olfactory perception and cognition.…”

Neurofunctional dopaminergic impairment in elderly after lifetime exposure to manganese

“…The alteration of the Luria Nebraska motor coordination subtest, as well as the odor identification Sniffin Sticks test, were observed also in adolescents (Lucchini et al, 2012) and ferromanganese workers (Lucchini et al, 1999) from the same geographical area. Alteration of both olfactory discrimination and sensitivity, as examined with the complete Sniffin Stick test battery, was seen in 30 adults residing in the Mn mining district of Molango, Mexico, compared to controls (Guarneros et al, 2013). Notably, cognitive functions were also related to Mn exposure, further supporting the hypothesis that a common mechanism of neurotoxicity of Mn underlying many of the observed neurological deficits is dopaminergic system dysregulation (Guilarte, 2013).…”

Olfactory dysfunction revisited: a reappraisal of work-related olfactory dysfunction caused by chemicals

“…In the two studies conducted on workers in the metals industry [58, 59], in which only the sensory test method was employed, the results were either not significant [58] or, surprisingly, revealed a significantly increased olfaction perception among the workers in measurements of the sensory olfactory threshold [59]. By comparison, use of the olfactory identification test employing Sniffin’ Sticks on welders or the inhabitants of an area with elevated background manganese values revealed significantly poorer values [60–62, 64–66]. In further magnetic or functional resonance imaging studies, elevated manganese deposition in the olfactory bulb was measured on welders [63] and a reduction in activity in relevant olfactory brain regions was measured in young people living in a region exhibiting elevated manganese values [66].…”

“…Guarneros et al (2013) conducted a Sniffin’ Sticks olfactory test series encompassing threshold, discrimination and identification tests on persons living in proximity to a manganese plant and exhibiting an elevated manganese concentration (mean 9.73 μg/g vs. 1.01 μg/g) in their hair [64]. Significant differences between the subjects were observed.…”