The nation's first region-by-region analysis of mercury in women's blood shows vast differences based on where they live, with the highest levels found in the Northeast.
There, nearly one in five women of child-bearing age have eaten so much contaminated fish that the toxic metal in their blood would pose a risk to their fetuses, compared with one in 10 nationally, the federally financed study found.
Women in the Midwest generally had much less mercury in their bodies; less than 3 percent exceeded a safety level intended to protect the developing brain before birth.
The study also found that women who make more money tend to have higher mercury levels. That may be because they are better able to afford expensive seafood, such as swordfish or high-grade tuna, that often is more contaminated.
Within the otherwise troubling analysis there were some glimmers of welcome news. Nationally, the percentage of women with high mercury levels declined from 16 percent in 2000 to 10 percent four years later, the most recent data available. Levels of mercury also dropped most dramatically among the women with the most exposure--a decline that occurred, the authors noted, even though those women were eating the same amount of seafood.
That finding suggests consumer advisories about mercury in fish are starting to work, the researchers argue. The seafood industry and top officials with the Food and Drug Administration have insisted that advising women about high- and low-mercury species would scare women away from eating seafood altogether.
"Women are a lot smarter than they have assumed," said the study's lead author, Kathryn Mahaffey, who until this week was a top scientist at the U.S. Environmental Protection Agency. "They're eating fish, but they're choosing more wisely."
Medical experts agree that on balance, eating fish is good for most people. Seafood generally is a low-fat source of protein, and some fish, such as salmon and sardines, are rich in omega-3 fatty acids that are thought to help prevent heart disease and stimulate brain development.