There have been very few studies of the possible neurotoxic impacts from chronic low level exposures, the kind of exposure to manganese that would occur from drinking water supplied from groundwater. The largest study (involving 362 children from 251 families) was performed in Canada using communities with a public water supply and private water supplies from groundwater with a natural manganese levels from the bedrock geology and not human activities. The tap water concentration of manganese ranged from 1 to 2,700 µg/L manganese. (MMT the gasoline additive containing manganese has been banned in Canada since 2004, but the highest concentrations of manganese found in that study seem very high. In New England, 45% of wells for public use have manganese concentrations greater than 30 µg/L. According to a 2009 report by the U.S. Geological Survey, about 5% of domestic household wells in the United States have manganese concentrations greater than 300 µg/L.)
The study, “Intellectual Impairment in School-Age Children Exposed to Manganese from Drinking Water,” was published in 2010 in Environmental Health Perspectives, the Canadian journal and is fully cited below examined possible neurotoxic effects from manganese at concentrations they claim are commonly found in North American aquifers. The scientists assessed the relationship between exposure to manganese from drinking water and IQ of school-age children living in communities relying on groundwater. In addition, they examined the relations between manganese concentration in hair follicles and estimated manganese intakes from water consumption and from the food.
Until recently, exposure to manganese from water consumption has been of little concern, because the intake of manganese from ingestion of water is small compared with that from foods, except in the case of infants. In the Canadian study they discovered though manganese consumption from water was very small compared with the amount ingested from foods (by more than two orders of magnitude), yet only consumption from water was significantly associated with manganese concentration in the hair follicles of the children. The mechanism of manganese uptake into hair is not well understood, but it has long been postulated that its affinity for melanin, a protein present in hair, skin, and the central nervous system, could be involved. Though the children had all lived at the same locations for at least 12 months, the duration of that level of exposure is not known.
The scientists found that IQ scores decreased steadily with increasing manganese concentrations in the drinking water. Children in the highest manganese concentration quintile (median, 216 µg/L) scored 6.2 IQ points below those in the lowest quintile (median, 1 µg/L). It is not known whether exposure during a critical developmental period is responsible for their observations. Interestingly enough, manganese concentrations in drinking water were was lower in houses with private wells than houses served from the public well (8 µg/L versus 55 µg/L ). Concentrations of manganese from food and ingestion was estimated.
|from Bouchard et al|
Maryse F. Bouchard, Sébastien Sauvé, Benoit Barbeau, Melissa Legrand, Marie-Ève Brodeur, Thérèse Bouffard, Elyse Limoges, David C. Bellinger, Donna Mergler. Intellectual Impairment in School-Age Children Exposed to Manganese from Drinking Water. Environmental Health Perspectives, 2010; DOI: 10.1289/ehp.1002321