The Quebec researchers who conducted the study suggest that Canadian regulations on manganese in drinking water should be updated to protect children.
"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 Maryse Bouchard, the study's lead author.
Manganese in drinking water lowers children's intelligence quotient (Photo credit unknown)
Dr. Bouchard is an adjunct professor at the Center for Interdisciplinary Research in Biology, Health, Environment and Society, CINBIOSE, at the Universite du Quebec at Montreal and a researcher at Sainte-Justine University Hospital.
"This is a very marked effect," said study co-author Donna Mergler, professor emerita in the Department of Biological Sciences at the Universite du Quebec at Montreal. "Few environmental contaminants have shown such a strong correlation with intellectual ability."
The study, carried out by researchers at the Universite du Quebec at Montreal, the Universite de Montreal and the Ecole Polytechnique de Montreal, examined 362 Quebec children, between the ages of six and 13, living in homes supplied by with groundwater from either individual wells or public wells with naturally occurring high manganese concentrations in water.
For each child, the researchers measured the concentration of manganese in tap water in his or her home, as well as the concentrations of 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.
The average IQ of children whose tap water was in the upper 20 percent of manganese concentration was six points below children whose water contained little or no manganese.
Manganese ore (Photo courtesy B.N. Minerals)
The analyses of the association between manganese in tap water and children's IQ took into account factors such as family income, maternal intelligence, maternal education, and the presence of other metals in the water.
The authors say that the amount of manganese present in food showed no relationship to the children's IQ.
Their results are published in the current issue of the scientific journal "Environmental Health Perspectives," issued by the U.S. National Institute of Environmental Health Sciences in an article entitled "Intellectual Impairment in School-Age Children Exposed to Manganese from Drinking Water."
Manganese is a required trace mineral for all known living organisms, but in larger amounts, the metal can cause a poisoning syndrome in mammals, with neurological damage that can be irreversible.
Manganese is essential to iron and steel production and is a key component of low-cost stainless steel formulations. The neurotoxic effects of manganese exposure in the workplace are well known, but this is the first study of the effects of manganese in drinking water in North America.
This metal is naturally occurring in soil and in several regions of Quebec and Canada and in other parts of the world, the groundwater contains naturally high levels of manganese.
Dr. Maryse Bouchard (Photo courtesy Harvard School of Public Health)
"Although elevated manganese levels are fairly common in ground water, the concentration of manganese in drinking water is not regulated in most countries," said Bouchard.
"The World Health Organization set a guideline for manganese in drinking water at 400 micrograms per liter, but the safety of this guideline was questioned because of the lack of data appropriate for risk analysis," she said.
Some of the municipalities where the study was conducted have already installed a filtration system that removes manganese from the water.
"A viable alternative solution is home use of filtering pitchers that contain a mixture of resins and activated carbon. Such devices can reduce the concentration of manganese by 60 percent to 100 percent depending on filter use and the characteristics of the water," said study co-author Benoit Barbeau, Natural Sciences and Engineering Research Council of Canada Industrial Chair in Drinking Water at the Ecole Polytechnique de Montreal.
In Quebec, where the study was conducted, manganese is not on the list of inorganic substances regulated by the Ministry of Sustainable Development, Environment and Parks Regulation.
The authors conclude, "Because of the common occurrence of this metal in drinking water and the observed effects at low concentrations, we believe that national and international guidelines for safe manganese in water should be revisited."
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