Elevated airborne manganese and low executive function in school-aged children in Brazil

Abstract

Exposure to airborne manganese (Mn) has been associated with neurotoxic effects, including motor and cognitive deficits. The main deficits related to excessive exposure to Mn are predominantly the dysfunction of fronto-striatal and dopaminergic circuits observed in animal experimental studies, which are involved in attention, working memory and motor function. The present study aims to assess the association between elevated Mn exposure and performance on executive function and attention neuropsychological tests in children living in two communities near a ferro-manganese alloy plant. Seventy children aged between 7 and 12 years with no history of neurologic disease and an estimated IQ >68 (Vocabulary and Block Design subtests) that had lived near the iron-Mn production alloy plant for at least 1.5 years were included. Participants were assessed for cognitive functioning with neuropsychological measures for sustained attention (Test of Visual Attention – TAVIS-3R), cognitive flexibility (WCST), and verbal and visual working memory (WISC-III Digit Span subtest and Corsi Block). Manganese hair (MnH) levels were used as a biomarker of exposure. Mean scores among study participants were lower than general population norms/averages for block design, digit span, reaction time and commission errors. The median MnH level was 11.48 (range 0.52–55.74) μg/g, and no difference between sexes was observed. Spearman's correlation analysis showed a significant inverse correlation between MnH levels and estimated IQ (rho = −0.448, p = 0.0001), Vocabulary (rho = −0.272, p = 0.02), Block Design (rho = −0.485, p = 0.00002) and Digit Span (rho = −0.410, p = 0.0004). Multiple regression analyses detected inverse associations between log MnH and scores on estimated IQ (β = −9.67; 95%CI = −16.97 to −2.37), Block Design (β = −2.50; 95%CI = −3.91 to −1.10) and Digit Span Total (β = −2.59; 95%CI = −4.13 to −1.05) standardized scores and the number of correct answers in forward and backward Digit Span methods, after adjusting for covariates (β = −1.32 = 95%CI = −2.23 to −0.40; β = −1.09 95%CI = −2.02 to −0.16, respectively). The results suggest that airborne Mn exposure may be associated with lower IQ and neuropsychological performance in tests of executive function of inhibition responses, strategic visual formation and verbal working memory. Executive function is dependent on the fronto-striatal circuit, which may be disrupted by Mn accumulation in the brain.