Making Sense Out of Mercury in Fish

by Allison Aubrey
NPR Morning Edition, January 31, 2008.

Recent nationwide studies have raised new worries about the level of mercury in fish. Government health officials say that there's no need for most consumers to worry. But they say the new findings reinforce earlier advice on limiting consumption of certain types of fish by pregnant women and young children.

One of the recent studies was conducted by Oceana, a marine conservation group. Researchers tested 94 samples of tuna and other forms of sushi purchased from grocery stores and restaurants in 23 cities. The fish was shipped to an independent certified lab in Michigan for testing.

"We found very high levels of mercury in nearly half the samples," says Kimberly Warner, a marine scientist with Oceana.

One sample of sushi tuna had a mercury content of 2.2 parts per million, which is more than twice the "action level" established by the Food and Drug Administration. That's the point at which the FDA can take food off the market.

In 2004, the FDA, together with the Environmental Protection Agency, issued a joint advisory aimed at protecting pregnant women, women considering becoming pregnant, nursing mothers and young children. The advisory recommends that these populations avoid four types of large predator fish - swordfish, shark, tilefish from the Gulf of Mexico and king mackerel.

Larger fish tend to be older, so they have more time to accumulate toxins like mercury. The agencies advise these groups to avoid eating these fish altogether because they contain average levels of mercury at or above the "action point."

At high enough levels, mercury can harm a developing fetus and cause problems with brain development.

Tuna Being Debated

Tuna is not included on the advisory's do-not-eat list, but pregnant women are advised to limit consumption.

For lower mercury varieties, such as canned light tuna, pregnant women are advised to eat no more than 12 ounces (two average meals) per week. Canned light tuna is usually skipjack tuna, which is a smaller fish and therefore lower in mercury.

For a higher mercury variety, such as albacore, pregnant women are advised to eat no more than 6 ounces (one average meal) per week.

Oceana is calling on the FDA to add certain types of fresh tuna to the restricted list, if further tests confirm higher mercury concentrations.

For instance, yellowfin tuna, which is used commonly in grocery-store sushi and sold as tuna steaks, is one of the species on Oceana's list.

"We've heard people say these have higher levels" says Mike Bolger, a chief toxicologist with the FDA. But FDA tests don't confirm this, he says.

It's possible that the limited number of tests by Oceana and other independent testers may not be providing a representative picture of mercury contamination in fish.

In 2006, for example, the FDA tested only 87 samples of yellowfin. Oceana and other testers have sampled even fewer. Moreover, mercury concentrations vary from species to species, and even fish to fish, so a larger sample size may be needed.

The FDA says that it has not evaluated the findings from Oceana and other independent tests. But the FDA's Bolger says that if these independent tests do show a pattern of higher mercury concentrations, the FDA could take more action.

"Probably a minimal effort step would be to go out and get more samples of yellowfin," he says.

He also says that the FDA hasn't evaluated another tuna, bluefin. It's a prized and expensive species mostly served in high-end sushi restaurants.

"It's such a minor species," says Bolger.

Sales of bluefin account for less than 1 percent of seafood sales. But it's clear that some Americans are eating the high-end tuna. A recent New York Times investigation found high levels of mercury in bluefin tuna sold in several New York City restaurants.

The National Marine Fisheries Database shows about $19 million worth of bluefin was imported by the United States between January 2006 and November 2007.

Scaring People Away from Fish

Some nutritionists, as well as the seafood industry, worry that the concern over mercury will turn people off eating fish.

"The general public should be encouraged to continue eating a variety of fish," says Gavin Gibbons of the National Fisheries Institute. "Seafood is a very safe part of a healthy American diet."

Nutrition researchers have documented the benefits of consuming omega-3 fatty acids found in fish. These include improved cardiovascular health and possibly beneficial effects on childhood development. Seafood is also a good source of protein, rich in vitamins and minerals.

To limit the risk and maximize the benefit, experts recommend low-mercury options such as tilapia or mackerel (saba), which is a good sushi option.

According to Oceana, the sushi mackerel sold in the U.S. is either horse, Atlantic, Pacific or chubb mackerel, as opposed to king mackerel, which is on the FDA's "do not eat" list.