Consumer Challenge: Making Head or Tail of Fish and Mercury

"The crux of the matter is that you've got this neurotoxin," notes toxicologist Michael Bolger, head of the FDA's Chemical Hazard Assessment Team. "No one debates that. But where does it fit in the matrix of risks and benefits? What does it mean ultimately in seafood? That is the real issue here."

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How damaging mercury can be at high levels is illustrated by a Japanese chemical plant disaster in the 1950s. Tons of mercury compounds and other chemicals were dumped into Minamata Bay. Babies exposed prenatally to this chemical mix developed mental retardation, cerebral palsy, deafness, blindness and other severe effects. Not only were there deaths from eating contaminated fish, but hundreds of people suffered neurological damage.

In the early 1970s, there was another disaster, this time in Iraq: Scores died and 6,500 people were hospitalized after eating grain products treated with a fungicide containing methyl mercury.

Concerns that mercury from coal-fired power plants and other sources was contaminating seafood prompted the FDA to issue an advisory in 1995 for the general population to limit eating shark and swordfish (which are known to be high in mercury) to no more than once per week. Pregnant women were advised to eat no more than one such meal per month. That's because those larger fish are higher on the food chain. The bigger the fish, the more likely it is to accumulate methyl mercury.

Prompted by a National Academy of Sciences report on the toxicological effects of methyl mercury, the FDA reevaluated its advisory and withdrew the general warning about shark and swordfish in 2001. But the agency expanded its warning for pregnant women, adding tilefish and king mackerel to the list of fish to avoid.

In 2004, the FDA issued a third advisory, this time with the EPA. It addressed pregnant and breast-feeding women as well as women of childbearing age who wished to become pregnant. Young children were also included. Those groups were advised to eat no more than 12 ounces weekly of fish or seafood and to limit albacore tuna to six ounces per week.

Not surprisingly, the advisories appear to have cut fish consumption among women of childbearing age. Project Viva, a federally funded study of 2,000 pregnant women begun in 1999 by Emily Oken, an assistant professor at Harvard Medical School, found that average fish consumption was increasing. But after the 2001 advisory was issued, fish consumption dropped from an average of nearly 2 servings per week to a little more than 1 1/2 weekly among participants.

Because of this decline, some scientists and physicians worry that fears about methyl mercury contamination in some fish have been misinterpreted by the public to mean eat less fish of any sort.

"What we don't want people to do is to stop eating fish," says the FDA's Bolger, who helped to draft the advisories. "That is a big concern. Or that pregnant women would reduce their level of fish consumption during pregnancy. That is what we have always been concerned would happen with this advisory."

A more recent study of nearly 12,000 parents and children in the United Kingdom has underscored the benefits of eating 12 ounces a week of fish during pregnancy -- or even more. Earlier this year, the study's team of British and American scientists published their findings in the Lancet: Children of women who ate less than 12 ounces of fish a week during pregnancy had lower IQs and lower academic test scores at age 8, and more behavioral and social problems throughout early development, than youngsters whose mothers ate 12 or more ounces per week. That study was funded by the University of Bristol and the nonprofit Wellcome Trust.

Also, a 20-year longitudinal study in Seychelles, funded by the National Institute for Environmental Health Sciences and conducted jointly with Seychelles scientists and researchers at the University of Rochester, has not linked increased fish consumption with adverse affects. The Seychelles experience is especially relevant, since the seafood there contains nearly identical methyl mercury levels to that found in the United States. One difference: Residents of the Seychelles consume about 10 times as much fish as Americans.

Those worried about mercury's effects in pregnant women often point to a long-term study in the Faeroe Islands that found children born to mothers with the highest levels of mercury had a very slight but measurable decrease in some neurobehavioral measures. For example, children who are now in their teens have slight but persistent attention deficits and score lower on tests that measure motor skills and verbal ability. But the major source of mercury in the Faeroe Islanders' diet was not fish but pilot whales, which have very high concentrations of methyl mercury.

Unlike a lot of other seafood, pilot whales also happen to have low levels of the mineral selenium. One theory under investigation by Nicholas Ralston at the EPA's Energy and Environmental Research Center at the University of North Dakota is that selenium may help protect against mercury contamination. Selenium is present in deep-water seafood at five to 20 times the concentration of mercury.When the two chemicals bind, methyl mercury appears to be neutralized.

Until scientists sort out all the details, many think that the message to the public ought to be eat fish, just make it the fish lowest in methyl mercury, especially when pregnant. That means choosing salmon, sardines, tilapia, anchovies, shrimp and light tuna, not albacore. (See this chart for more options.)

"I think so far this has been a false controversy," says Kathryn Mahaffey, senior scientist in the EPA's Office of Pesticides and Toxics. When Mahaffey's daughter was pregnant, Mahaffey said, she encouraged her to eat fish that was lower in methyl mercury. "And now, I have two wonderful, healthy grandchildren," she says.

And Mahaffey notes that for vegetarians, vegans and those who don't like fish, there are foods naturally rich in omega-3s, such as flaxseed, and those fortified with them, including eggs and margarine. Fish oil supplements are another choice. Earlier this year, the European Commission recommended that pregnant and lactating women take fish oil supplements.

The messages about seafood have become needlessly confusing, says Solomon of the Natural Resources Defense Council. "Consumers can understand shades of gray," she says. "People can understand that fish is good for you but that there are some fish that are high in mercury levels and those should be avoided or eaten in moderation."