Hair manganese and hyperactive behaviors: pilot study of school-age children exposed through tap water

Abstract

Background: Neurotoxic effects are known to occur with inhalation of manganese particulates, but very few data are available on exposure to Mn in water. We undertook a pilot study in a community in Quebec (Canada) where naturally occurring high Mn levels were present in the public water system. Our objective was to test the hypothesis that greater exposure to Mn via drinking water would be reflected in higher Mn content in hair which, in turn, would be associated with increased level of hyperactive behaviors.

Methods: Forty-six children participated in the study, 24 boys and 22 girls, 6-15 years of age (median, 11 years). Their homes received water from one of two wells (W) with different Mn concentrations: WI: mean 610 microg/L; W2: mean 160 microg/L. The Revised Conners' Rating Scale for parents (CPRS-R) and for teachers (CTRS-R) were administered, providing T-scores on the following subscales: Oppositional, Hyperactivity, Cognitive Problems/Inattention, and ADHD Index.

Results: Children whose houses were supplied by WI had higher hair Mn (MnH) than those supplied by W2 (mean 6.2+/-4.7 microg/g vs. 3.3+/-3.0 microg/g, p = 0.025). MnH was significantly associated with T-scores on the CTRS-R Oppositional (p = 0.020) and Hyperactivity (p = 0.002) subscales, after adjustment for age, sex, and income. All children with Oppositional and Hyperactivity T-scores > 65 had MnH > 3.0 microg/g.

Conclusions: The findings of this pilot study are sufficiently compelling to warrant more extensive investigations into the risks of Mn exposure in drinking water.

Figure 1

Evolution of Mn concentration [mean and 95% confidence interval (μg/L)] in the water of the public aqueduct system for the two wells (W1 and W2).

Figure 2

Distribution of MnH concentrations with respect to wells. Dashed line represents the upper reference limit for MnH.

Figure 3

Adjusted T-scores (age, income) on the CTRS-R subscales as a function of levels of MnH (μg/g): (A) Oppositional (y = 49.0 + 0.937 × MnH, R² = 0.106, p = 0.031, n = 44); (B) Hyperactivity (y = 49.1 + 1.103 × MnH, R² = 0.156, p = 0.008, n = 44).