Noninvasive biomarkers of manganese exposure and neuropsychological effects in environmentally exposed adults in Brazil

Abstract

Manganese (Mn), an essential element to humans, in excess can cause neurotoxic damage. So far, Mn exposure assessment has no ideal biomarker. This study aims to investigate the association between Mn exposure, using noninvasive biomarkers, and neuropsychological effects in environmentally exposed adults. The residents of two communities near to a ferromanganese refinery in Bahia, Brazil were evaluated. Volunteers aged 15–55 of both sexes provided scalp hair, axillary hair, fingernail and saliva specimens for Mn determination by electrothermal absorption spectrometry. Several neuropsychological tests were used to evaluate cognitive, attention, memory, motor and executive functions. Significant correlations were observed between Mn in hair (MnH, median 8.95 μg/g), axillary hair (MnAxH,18.49 μg/g) and fingernail (MnFN, 6.91 μg/g) with the performances in several neuropsychological tests. No association was observed between manganese levels in saliva (MnSal, 4.2 μg/L) and any neuropsychological function. Multiple regression analysis detected an inverse association between Log MnH and IQ (β = –4.76 [CI 95% –9.17 to –0.36]) and between Log MnFN and visual working memory (β = –3.33 [CI 95% –6.15 to –0.52]). Direct association was observed between Log MnFN and time of completion in the cognitive flexibility task (β = 56.29 [CI 95% 2.41–110.18]). The Mn biomonitoring using noninvasive biomarkers was able to detect high exposure levels, which were associated with detrimental neuropsychological effects in adults exposed to industrial emissions.