Steven G. Gilbert, PhD, DABT
Director and Founder of the Institute of Neurotoxicology and Neurological Disorders
We have heard a lot about the adverse effects of lead, even at very low levels of exposure, on the intellectual development of children, and now there is further evidence that manganese exposure from drinking water causes similar harm to children. A new study by Maryse Bouchard and co-authors1 describes the adverse effects of manganese exposure from drinking water on childhood IQ. Manganese is a very interesting metal, widely distributed and occurring naturally in food and drinking water. It is a well-established neurotoxicant. Unlike lead, which has no known biological function, manganese is an essential nutrient and in trace amounts is necessary for growth and development. In industry, manganese is used to harden steel, and manganese fumes during welding are a work place hazard.
The unique aspect of the present study is the documentation of decrements in IQ associated with drinking water and hair manganese levels. The study assessed IQ in 362 children ages 6 to 13 years along with naturally occurring manganese in groundwater. The median manganese home drinking water was 34 μg/L (range: 1–2700 μg/L). The authors found that elevated levels of manganese in water and manganese in hair were significantly associated with lower IQ scores. It is important to note that manganese in home water “was not associated with socioeconomic or other family characteristics, such as family income, family structure, home stimulation score, nonverbal maternal intelligence, and maternal education.” The estimated dietary intake of manganese was a median of 2335 μg/kg/month, which was much high than the estimated water intake of a 1.6 μg/kg/month. When children were sorted by manganese levels in drinking water there was a 6.2-IQ point difference between children in the lowest and highest groups. The authors concluded: “The findings from the present study support the hypothesis that low level, chronic exposure to manganese from drinking water is associated with significant intellectual impairments in children.”
There is also an environmental justice component to these findings in that children lacking certain nutrients are more vulnerable to toxicants. For example, iron and/or calcium deficiency affects the absorption and toxicity of heavy metals such as lead and manganese.2 The role of nutrition in mitigating exposure to environmental agents is an important public health issue.
While manganese levels in water are not regulated, the US EPA advises that levels should not exceed 300 μg Mn/L. Approximately six percent of domestic household wells exceed this level. The FDA has established that the manganese concentration in bottled drinking water should not exceed 50 μgMn/L. The World Health Organization advisory is 400 μgMn/L for drinking water. There are also work place levels in air established by OSHA. See ATSDR for additional information.3 The results from this and other studies clearly indicate the manganese levels in drinking water should be carefully monitored and appropriate advice given to consumers. In addition, the current recommendations for safe levels of manganese in drinking water should be reviewed and revised.
Finally, we have yet to address the complex issue of multiple chemical exposures. What would be the consequences of elevated lead exposure along with excess manganese in the drinking water? We need to strive for an environment in which our children can reach and maintain their full potential free from the adverse effects of heavy metals.
1. Bouchard MF, Sauvé S, Barbeau B, Legrand M, Brodeur M-È, et al. 2010 Intellectual Impairment in School-Age Children Exposed to Manganese from Drinking Water. Environ Health Perspect doi:10.1289/ehp.1002321. (as pre print)
2. Scientific Consensus Statement on Environmental Agents Associated with Neurodevelopmental Disorders. Collaborative on Health and the Environment’s Learning and Developmental Disabilities Initiative.