Excess amounts of manganese - a hard, brittle metal found in some drinking water around the world - may have adverse effects on children's smarts, Canadian scientists said Monday.
A team of researchers at the University of Quebec in Montreal discovered that children exposed to high concentrations of manganese in drinking water performed worse on tests of intellectual functioning than children with lower exposures.
The results, published in the scientific journal Environmental Health Perspectives, prompted the researchers to urge a review of national and international guidelines for safe levels of manganese in drinking water, and home use of water filtering pitchers to reduce concentrations where it is high.
The study examined 362 children between the ages of six and 13, living in Quebec homes supplied by groundwater. For each child, the researchers measured the concentration of manganese in tap water from their home, as well as iron, copper, lead, zinc, arsenic, magnesium and calcium.
The amount of manganese from both tap water and food was estimated from a questionnaire. Finally, each child was assessed with a battery of tests assessing cognition, motor skills and behavior.
"We found significant deficits in the intelligence quotient (IQ) of children exposed to higher concentration of manganese in drinking water. Yet, manganese concentrations were well below current guidelines," said lead author Maryse Bouchard.
The average IQ of children whose tap water contained the highest manganese concentrations was six points below children whose water contained little or no manganese. Presence of manganese in food had no impact.
"This is a very marked effect," said study co-author Donna Mergler. "Few environmental contaminants have shown such a strong correlation with intellectual ability."
Manganese is naturally occurring in soil and air, and in certain conditions is present in groundwater in naturally high levels. It is also used in stainless steel, alkaline batteries, unleaded gasoline and coins.