Lower IQ levels linked to mercury exposure in the womb costs the United States $8.7 billion a year in lost earnings potential, according to a study released Monday by researchers at a New York hospital.
The Mount Sinai Center for Children's Health and the Environment combined a number of previous studies to determine hundreds of thousands of babies are born every year with lower IQ associated with mercury exposure.
Using work examining the effects of lead exposure on IQ, researchers determined that even a 1.6 point drop in IQ could cost a person $31,800 in lifetime earnings because of missed educational opportunities or jobs.
Peter McCaffery, a scientist at the University of Massachusetts Medical School who studies the brain, said the Mount Sinai researchers did a reasonable job piecing together a wide range of possible reactions to mercury exposure.
"Some people are not going to be affected by mercury, and some people are, just based on their genetic disposition," McCaffery said.
The journal Environmental Health Perspectives published the Mount Sinai study.
The findings are derived in part from statistics from the Centers for Disease Control, which studied the frequency of high mercury levels in women of childbearing age.
The Food and Drug Administration has warned that high levels of mercury in albacore tuna and some other fish can pose a hazard for pregnant women. The Environmental Protection Agency estimates that about 8 percent of American women of childbearing age have enough mercury in their blood to put a fetus at risk.
Mount Sinai pediatrician and lead researcher Leonardo Trasande estimated that between 316,588 and 637,233 children are born each year with umbilical cord blood mercury levels linked to IQ loss.
The research found the IQ losses linked to mercury range from one-fifth of an IQ point to as much as 24 points.
As an example, Trasande said about 4 percent of babies, or about 180,000, are born each year with blood mercury levels between 7.13 and 15 micrograms per liter. That level of mercury, the group concluded, causes a loss of 1.6 IQ points.
Mercury levels, Trasande said, are probably lower generally than they were in years before limits were placed on emissions from medical waste and municipal incinerators.
"We've made great progress in reducing mercury emissions over the past decade, and this is likely to have reduced the number of affected children and to have reduced costs by a similar amount," Trasande said.
Leonard Levin, a scientist at the Electric Power Research Institute, said no group has yet to produce solid data defining the impact of mercury on intelligence.
Mount Sinai released its findings in hopes of influencing the debate over legislation before Congress, known as Clear Skies, that would change how the government regulates emissions from power plants and other sources.
The study was supported by a grant from the National Institute of Environmental Health Sciences, and with financial support from the Jennifer Altman Foundation, Physicians for Social Responsibility, and the Rena Shulsky Foundation.
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