Manganese, arsenic and children's learning
An exploratory study led by David Bellinger, PhD, a Children's Hospital Boston neuropsychology researcher, raises intriguing questions about the cognitive effects of environmental exposure to heavy metals. The study took him to Miami, Okla., located near the Tar Creek Superfund site, where more than 75 million tons of mining waste had been left on the ground's surface. Bellinger and colleagues enrolled 32 fifth- and sixth-grade science students and took samples of their hair, testing the samples for manganese, arsenic and cadmium.
Children with higher manganese and arsenic levels in their hair samples had significantly lower IQ scores -- by an average of 10 points -- than children with low levels of both metals. They also scored worse on tests of verbal learning and memory, showing poorer recall of words and story lines. The higher the levels of manganese and arsenic in the children's hair, the more poorly they scored. "It was quite surprising to see such a significant statistical correlation in a study this small," Bellinger says.
Bellinger emphasizes that this was only a pilot study: the findings were adjusted for maternal education and hair levels of lead -- a metal whose neurotoxicity is established -- but not other factors like parental IQ. In addition, unlike lead or mercury, there are no national "norms" for arsenic and manganese exposure with which to compare the levels found in the children's hair. What's clear is that a larger, more in-depth study is needed, and Bellinger will apply for NIH funding to continue the work.
Coauthors on the study, published in the February issue of NeuroToxicology, included Robert Wright, MD, MPH, of Emergency Medicine, and Alan Woolf, MD, MPH, director of the Program of Environmental Medicine.