Children whose drinking water contains high concentrations of manganese perform worse on IQ tests than children with less exposure to the metallic element, according to a new study.
Manganese, a trace mineral, is necessary for all living things, but can be toxic in mammals when ingested in high amounts, possibly causing irreversible brain damage.
The neurotoxic effects of manganese exposure in the workplace are well known, but this study, led by scientists from the Universite du Quebec at Montreal, the Universite de Montreal and the Ecole Polytechnique de Montreal, is the first to examine the effects of manganese in drinking water in North America.
For the study, researchers observed 362 Quebec children from 251 families, ages six to 13, living in homes supplied with naturally-occurring, high-concentrations of manganese in the groundwater.
In several regions of Quebec and Canada and in other parts of the world, the groundwater contains naturally high levels of manganese due to leaching from rocks and minerals.
All of the children in the study had been living in their current homes for at least three months, and 85 percent had been living in the same home for at least 12 months.
Factors such as family income, maternal education, maternal intelligence, the presence of other metals in the water, and the levels of manganese in food were taken into account.
Next, scientists measured the tap water concentrations of manganese, iron, zinc, magnesium, calcium, copper, lead and arsenic in each child’s home.
The children were then given a series of tests to determine their general cognitive skills, including their visual-spacial, verbal, and concept-formation abilities.
The study found that the average IQ of children whose tap water was in the top 20 percent of manganese concentration was six points below children whose water contained little or no manganese. This finding was very strong even after adjusting for socioeconomic status and other metals present in water.
Researchers took repeated water samples from the same homes, and the results showed little variation in manganese concentrations throughout the year. This suggests that the negative effects on children’s cognition were from long-term exposure.
Interestingly, only manganese intake from drinking water—not from the child’s diet—was significantly associated with elevated manganese concentration in the children’s hair. In fact, manganese intake from drinking water was relatively small when compared to the amount found in their diets.
These findings show that manganese from drinking water is metabolized differently in the child’s body than when it is ingested from food, where absorption is decreased during the digestive process.
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.
Based on these results, however, the Quebec researchers suggest that Canadian regulations on manganese in drinking water should be updated to protect children.
In some of the municipalities where the study was conducted, new filtration systems that remove manganese from the water have already been installed.
This study can be found in the journal Environmental Health Perspectives.
Source: Universite du Quebec at Montreal