Canned tuna, Americans' favorite fish, is the most common source of mercury in our diet. Consumer Reports' latest tests of 42 samples from cans and pouches of tuna bought primarily in the New York metropolitan area and online confirm that white (albacore) tuna usually contains far more mercury than light tuna.
The Food and Drug Administration and the Environmental Protection Agency say women of childbearing age and young children may eat up to 12 ounces a week of light tuna or other "low in mercury" seafood, including, within that limit, up to 6 ounces per week of white tuna.
Fish-safety experts at Consumers Union, the nonprofit publisher of Consumer Reports, continue to suggest a more cautious approach. Because of its potential effects on fetal development, Consumers Union advises pregnant women, as a precaution, to avoid eating tuna. Consumers Union further advises that children who weigh less than 45 pounds limit their intake to 4 ounces or less of white (albacore) tuna, depending on the child's weight and that children who weigh 45 pounds or more limit their intake to about 4 to 12.5 ounces of light tuna or 1.5 to 4 ounces of white tuna, depending on the child's weight.
Consumer Reports' tests, conducted at an outside lab, found:
*Every sample contained measurable levels of mercury, ranging from 0.018 to 0.774 parts per million. The FDA can take legal action to pull products containing 1 ppm or more from the market. (It never has, according to an FDA spokesman.)
*Samples of white tuna had 0.217 to 0.774 ppm of mercury and averaged 0.427 ppm. By eating 2.5 ounces (about half a can) of any of the tested samples, a woman of childbearing age would exceed the daily mercury intake that EPA considers safe.
*Samples of light tuna had 0.018 to 0.176 ppm and averaged 0.071 ppm. At that average, a woman of childbearing age eating 2.5 ounces would get less than the EPA's limit, but for about half the tested samples, eating 5 ounces (about one can) would exceed the limit.
In 2006, Consumer Reports scrutinized the results of the FDA's tests in 2002-04 of mercury levels in hundreds of samples of canned tuna. The agency's white-tuna samples averaged 0.353 ppm; light tuna, 0.118 ppm. But the magazine found that as much as 6 percent of the FDA's light-tuna samples had at least as much mercury as the average in white tuna -- in some cases more than twice as much.
Given the uncertainties about the impact of occasional fetal exposure to such high levels, Consumer Reports urged the FDA to warn consumers about occasional spikes in mercury levels in canned light tuna. More than four years later, the FDA still hasn't issued such a warning. When asked why, an FDA spokesman indicated that the agency had already taken the spikes into account when formulating its mercury advice.
The heavy metal accumulates in tuna and other fish in an especially toxic form, methylmercury, which comes from mercury released by coal-fired power plants and other industrial or natural sources. Some studies have linked even low-level mercury exposure in pregnant women and young children to subtle impairments in hearing, hand-eye coordination and learning ability. Other evidence suggests that frequent consumption of high-mercury fish might affect adults' neurological, cardiovascular and immune systems.
Some popular seafood, including clams, Alaskan salmon, shrimp and tilapia, contain relatively little mercury and are better choices. Other lower-mercury choices include: oysters, pollock, sardines, Pacific flounder and sole, herring, mullet and scallops (with some limitations for women of childbearing age and children). Federal agencies advise children and women of childbearing age to avoid four high-mercury fish: king mackerel, shark, swordfish and tilefish.
Bottom line: Canned tuna, especially white, tends to be high in mercury, and younger women and children should limit how much they eat.
By the editors of Consumer Reports at www.consumerreports.org.