In several regions of Quebec and Canada and in other parts of the world, groundwater contains naturally high levels of manganese. Maryse Bouchard, Université du Québec à Montréal, report that children exposed to high concentrations of Mn in drinking water performed worse on tests of intellectual functioning than children with lower exposures.

362 Quebec children, between the ages of 6 and 13 were studied. The concentration of Mn in tap water from their home was measured, as well as iron, copper, lead, zinc, arsenic, magnesium and calcium. Each child was assessed with tests measuring cognition, motor skills, and behavior.

The average IQ of children whose tap water was in the upper 20 % of Mn concentration was 6 points below children whose water contained little or no Mn.

• Intellectual Impairment in School-Age Children Exposed to Manganese from Drinking Water
  M. F. Bouchard, S. Sauvé, B. Barbeau, M. Legrand, M.-È. Brodeur, T. Bouffard, E. Limoges, D. C. Bellinger, D. Mergler,
  Environ. Health Perspect. 2010, 118.
  DOI: 10.1289/ehp.1002321