20/20: Health Risks of Mercury in Fish

— -- Pregnant women and women who may become pregnant should not eat shark, swordfish, king mackerel and tile fish because they could contain levels of mercury that could lead to brain damage in a developing fetus according to a Food and Drug Administration advisory.

The advisory came on the heels of an extensive report issued by the National Academy of Sciences, which estimates that each year 60,000 children may be born in the United States with neurological problems as a result of exposure to methylmercury in the womb.

According to the NAS report, "humans are exposed to methylmercury primarily through the consumption of contaminated fish, particularly large predatory fish species such as tuna, swordfish, shark and whale."

The FDA rejected calls to put tuna on the do-not-eat list because it does not consider tuna a health risk. Vermont Sen. Patrick Leahy, who helped commission the NAS study, calls the FDA's announcement "a step in the right direction," but the FDA's warning comes amid criticism that the agency has not been aggressive in informing the public about the risks of high-mercury fish.

The FDA stopped testing fish for mercury in 1998 and has since relied on the fish industry to police itself. National Fisheries Institute president Dick Gutting says that, overall, the industry’s tests show that mercury is not a problem.

Last summer, 20/20 conducted its own tests. 20/20 bought 40 samples of fresh tuna, swordfish and shark in three major U.S. cities and sent the fish to Battelle Marine Science Labs, a facility that performs food tests for the FDA and the EPA.

20/20 discovered that while the tuna samples averaged well below the FDA limit of 1 part per million (ppm), the shark and swordfish did not fare as well. Two out of four shark samples and 14 out of 18 swordfish samples had mercury levels greater than 1 part per million. Two of the swordfish samples tested had mercury levels triple the FDA’s limit.

When 20/20 presented its findings to Gutting, he could not explain the results but said that "the fact that one particular meal is over one part per million is not significant." Gutting stressed that the average level of mercury in commercially sold fish is well below the FDA limit. Both the fish industry and the FDA say that there is a ten-fold safety factor built in to the 1 ppm limit.