Environmental Exposure to Manganese and Motor Function in Adults

Abstract

BACKGROUND AND AIM: Santander, the capital of Cantabria, Spain (172,000 inhabitants) is 7 km from an industrial emission source of Mn (IES) located in a 10,000 inhabitants town (Maliaño) (annual arithmetic air Mn mean=231.8 ng/m3; reference WHO guideline=150 ng/m3). Our objective was to compare the motor function of adult healthy volunteers living in both places. METHODS: Cross-sectional study analyzing 130 consecutive participants: 95 women and 35 males, mean age 41.72; SD=14.0 years. Motor function was assessed by the Grooved Pegboard (GP) (the more seconds, the worse function) and by the Finger Tapping Test (FTT) (the less tappings, the worse function). Distance from the IES was categorized into “=1.5 km” versus “1.5 to 10 km from the IES”. For personal samplers (PS) and biomarkers assessment, exposures were dichotomous categorized according to medians (blood, hair and fingernails medians=9.58 µg/L; 185.31 and 555.28 ng/g respectively). RESULTS:Regarding GP, overall mean time to complete the test was 59.31 and 65.26 seconds (SD=10.11 and 11.69) for dominant and non-dominant hands respectively. Statistically significant higher times (indicating worse function) were observed when living near the IES in both hands (p = 0.024 and 0.014 respectively). Regarding Mn levels in their PS (in both bioaccessible and non-bioaccessible coarse&fine fractions) higher times were computed in participants with higher levels, but yielding statistical significance only for the bioaccessible-fine fraction. Regarding FTT, the mean number of finger tappings per 10 seconds was 68.27 and 60.25 seconds (SD=11.32 and 11.72) respectively. No statistically significant differences were found for exposure indices. Regarding biomarkers, statistically significant higher times in GP and lower tappings in the FTT were observed in participants with higher Mn Fingernails levels. CONCLUSIONS:Our results support poorer motor function as assessed by GP test according to exposure indices, especially in terms of proximity to IES and Mn Fingernails levels. KEYWORDS: Heavy metals, Neurodevelopmental outcomes, Neurodegenerative outcomes, Particulate matter, Biomarkers of exposure