Study finds fish remain focus of concern for high blood mercury levels

By Elizabeth Weise, USA TODAY

The good news is that most young children and women of childbearing age in the USA have blood mercury levels that are below levels of concern, according to a study in today's Journal of the American Medical Association.

The bad news is that 8% of women have concentrations above the Environmental Protection Agency's recommended levels. What's worse is that they're most likely exposed to the mercury by doing something we think of as healthy: eating fish.

"The average blood mercury levels were fourfold higher among women who ate three or more servings of fish in the past 30 days," says Susan Schober of the Centers for Disease Control, the lead author.

That's 1.94 micrograms per liter of blood compared with 0.51 micrograms in women who ate no fish in that period. The 8% with the highest concentrations were even higher than that, exceeding the EPA's recommended safety level of 5.8 micrograms per liter of blood, below which adverse effects are not expected.

Schober and her colleagues examined blood mercury levels in U.S. children and women of childbearing age by testing people who responded to a 1999-2000 national nutrition survey. The study focused on those groups because mercury causes neurological problems and is particularly harmful to the developing fetus. The group plans to expand its measurements to men and other age groups.

Symptoms of mercury poisoning can include fatigue, headache, memory loss and trouble concentrating. Mercury enters the environment primarily through the burning of fossil fuels. Eventually it ends up in lakes, streams and oceans.

"Mercury concentrates as it goes up the food chain. So fish that are long-lived, large and predatory have the largest concentrations," Schober says. Those also happen to be some of the tastiest and trendiest fish around, including shark, swordfish, king mackerel and tilefish, sometimes sold as golden snapper or golden bass.

The Food and Drug Administration now advises women who are pregnant, who might be pregnant or who are nursing not to eat those fish. It further says that children shouldn't eat them, either. Ten states also warn against women and children consuming fish high in mercury.

But Americans shouldn't give up the health benefits of including fish and shellfish in their diets, Schober says. "There's a wide variation in mercury content in fish."

Though all species of fish and shellfish show at least traces of mercury, the amounts in species such as haddock, tilapia, salmon, cod, pollock and sole, and most shellfish, are relatively low and can be an important part of a healthy diet.

But Jane Hightower, the San Francisco physician whose research into mercury poisoning set off shock waves last November, says there should be warning labels on fish in supermarkets.

"When you get a fishing license for non-commercial fish, you're given a booklet on the mercury content of fish," Hightower says. "But when you go to the grocery store, there are fish there that have higher mercury contents than anything you'd find in a stream but you don't know about it."