Children exposed to high levels of manganese in their drinking water fare worse on intelligence tests compared to their peers, according to Environmental Health Perspectives.
Manganese is an essential micronutrient for life. As a component of active enzymes, it is involved in the metabolism of amino acids, proteins and fats. However, in excess, it can be toxic to nervous tissue.
Previous research has shown that exposure to manganese dust in the workplace and in the environment is associated with neurological problems in children and adults.
This metal also occurs naturally in soil and can, under certain conditions, enter groundwater. In some parts of the world, such as Quebec in Canada, groundwater contains particularly high levels of manganese.
Since the concentration of this element in the body is kept in balance, mainly due to low absorption and early elimination in the liver, it is believed that manganese entering the body via the alimentary route should not have toxic effects. Besides, so far manganese ingested with water has been neglected, because – compared to food, it is a very small source of it.
Researchers from the University of Quebec in Montreal and two other Canadian universities studied 362 children between the ages of 6 and 13 who lived in homes supplied with groundwater from a private or public source.
All homes have measured levels of various elements in the tap water – including manganese, iron, copper, lead, zinc, arsenic, magnesium and calcium. The consumption of manganese by children with tap water and with food was assessed on the basis of a diet questionnaire. The level of this element in the hair of children was also measured. Finally, all children underwent a set of tests to assess intellectual, motor and behavioral abilities.
The analysis took into account various factors that may affect the children’s intelligence quotient (IQ), such as family income, mother’s intelligence level and education, and the presence of other metals in the water.
We observed that children exposed to higher levels of manganese in drinking water had a significantly lower IQ, comments Dr Maryse Bouchard, who leads the study.
The mean IQ of children whose water at home contained the highest concentration of manganese (an average of 216 micrograms per liter) was six points lower than the average IQ of peers who had water at home with little or no manganese.
This is a very clear effect; few environmental pollutants have such a strong relationship with intellectual potential, comments co-author Donna Mergler.
In the European Union countries, the aim is to ensure that the manganese content in water from water supply systems does not exceed 50 micrograms per liter.
It also turned out that the manganese content in children’s hair was closely related to its concentration in drinking water at home. On the other hand, the amounts of manganese from the diet – although much higher than from water – did not translate into its concentration in hair and IQ. According to scientists, this means that manganese entering the body with water can be processed differently in the body than in food.
Some of the municipalities in Quebec where the research has been carried out have meanwhile installed a filter system that removes manganese from drinking water. But, according to co-author Benoit Barbetu of the Montreal University of Technology, an alternative solution may be to use water filter jugs that contain a resin composition and activated carbon at home. Such devices can reduce the concentration of manganese by 60-100 percent, depending on the type of filter and the chemical composition of the water, the researcher explains. (PAP)