TORONTO -- Children whose drinking water contains high concentrations of manganese appear to have lower IQ scores on average than children not exposed to the metallic element, researchers have found.
In a study of more than 350 children in Quebec communities dependent on tap water from wells, researchers found a striking correlation between manganese in the water and IQ scores.
"It's pretty straight-up," said lead author Maryse Bouchard, a researcher in environmental health at the University of Montreal.
"We saw that the average IQ decreased with increasing tap water manganese concentration," Bouchard said from Montreal.
"And the difference between the least exposed and the most exposed was in the order of six IQ points, which is a very big difference."
The researchers, whose paper is published in Monday's issue of Environmental Health Perspectives, tested tap water used by 251 families living in eight communities in an area roughly between Montreal and Quebec City.
The area has no industrial source of manganese, which is used in batteries, plant fertilizer and in steel alloys. It is commonly found in groundwater due to leaching from minerals and rocks.
Neuropsychologists gave a battery of tests to 362 children aged six to 13 taking part in the study to determine their general cognitive abilities, including verbal, visual-spacial and concept-formation skills.
The researchers also estimated manganese intake from water ingestion as well as diet, using a food frequency questionnaire. Manganese is an essential nutrient and is found in a wide variety of fruits, vegetables and grains.
But it can be a potent neurotoxin in high concentrations, and occupational and environmental exposure to air-borne manganese has been linked to neurological deficits in both children and adults. Manganese is believed to interfere with neurotransmitters like dopamine and serotonin, which are "important for proper cognitive functioning," Bouchard said.
The amount of manganese in drinking water is not regulated in Canada or the United States, although health-based recommendations for maximum levels are set at 400 micrograms per litre by the World Health Organization and 300 mcg/l by the U.S. Environmental Protection Agency.
-- The Canadian Press