About 630,000 children are born each year at risk for lowered intelligence and learning problems caused by exposure to high levels of mercury in the womb, according to a new analysis by the Environmental Protection Agency.
That’s nearly double the previous EPA estimate of 320,000 babies a year.
The analysis prompted a call for government warnings about eating some kinds of fish with high levels of mercury and for a crackdown on mercury pollution.
The new estimate is based on data collected by the Centers for Diseases Control and Prevention and recent studies that show the level of mercury in the umbilical cord blood of newborns is 1.7 times higher than the mercury level in their mother’s blood.
According to the new estimate, one in every six women of childbearing age has enough mercury in her blood to pose a risk to her child, compared with previous estimates of one in every 12 women.
Blood samples taken by the CDC from 1,709 women found that 8 percent of women of childbearing age had mercury levels at or above 5.8 parts per billion, which is the EPA’s safety limit.
However, recent studies indicate that the developing fetus may have more difficulty excreting mercury than pregnant women, which would account for the higher mercury levels in cord blood versus maternal blood.
That means a mercury level of only 3.5 ppb in a mother’s blood would be enough for her fetus’ blood to cross the 5.8 ppb safety threshold, according to an analysis by Kathryn Mahaffey, a scientist with the EPA’s Office of Prevention, Pesticides and Toxic Substances.
Nearly 16 percent of women have mercury blood levels of 3.5 ppb or higher, Mahaffey calculated.
Blood mercury levels also were seven times higher in women who told the CDC they had eaten fish two or more times a week over the previous month compared with women who said they had not eaten fish in the previous month, Mahaffey reported.
While adults can be harmed by long-term exposure to small amounts of mercury, a powerful neurotoxin, the risk is much greater for fetuses and young children because their nervous systems are still developing.
The main source of human exposure to mercury is through eating fish, particularly larger species at the top of the food chain, such as shark, swordfish, and some species of tuna.
The new estimate is likely to add more fuel to the already heated debate over whether the government should be doing more to warn consumers of the health risks of eating fish with high levels of mercury, including such frequently consumed fish as canned albacore tuna.
“Over 600,000 children are born each year overexposed to mercury in seafood,” said Jane Houlihan, a scientist with the Environmental Working Group, an advocacy organization. “This increases the urgency for the Food and Drug Administration to correct the misinformation it is giving the public and for the Bush administration to crack down on mercury pollution from coal-fired power plants.”
However, Linda Candler, a spokeswoman for the National Fisheries Institute, a trade association for the commercial seafood industry, said that the consumption of seafood in the United States is generally so low that children are not at risk.
“It’s long been known that if you eat a lot of high-level mercury species, your mercury levels go up,” Candler said. “However, fish is so important to the diet and the developing fetus that mothers should not let these things scare them away from eating fish during pregnancy. They should of course follow the FDA’s advice to avoid those high-mercury species.”
The Washington state Department of Health already urges women of childbearing age and children to skip fish known to be high in mercury.
“We’re going to have a look at this (EPA) report, but it certainly wouldn’t change (our) message,” said Rob Duff, acting director of the Office of Environmental Health Assessment.
The department recommends limits on canned tuna consumption based on weight and age for women and children. Recent studies have found much higher levels of mercury in canned white albacore tuna up to three times more than in chunk or solid light tuna.
“Now we know there’s a difference,” said Duff. “You can reduce your amount of mercury exposure by choosing light over albacore white.”