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. According to Consumers Union, pregnant women should avoid tuna and younger women and kids should limit their consumption.

“Canned tuna, especially white, tends to be high in mercury, and younger women and children should limit how much they eat. As a precaution, pregnant women should avoid tuna entirely,” said Dr. Urvashi Rangan, Director of Technical Policy, at Consumers Union, nonprofit publisher of Consumer Reports.

The Food and Drug Administration (FDA) and the Environmental Protection Agency (EPA) advise that 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.

Consumers Union’s fish-safety experts continue to suggest a more cautious approach, advising pregnant women, as a precaution, to avoid eating tuna because of its potential effects on fetal development. Consumers Union further advises that children who weigh more than 45 pounds limit their weekly intake from 4 to 12.5 ounces of light tuna or from 1.5 to 4 ounces of white tuna, depending on their weight; and children who weigh less than 45 pounds limit their weekly intake from 0 to 4 ounces of light tuna or from 0 to 1.5 ounces of white tuna, depending on their 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 (ppm). 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 [PDF] the results of the FDA’s tests in 2002 to 2004 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 Consumer Reports found that as much as six 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 by Consumers Union, an FDA spokesman indicated to the group that the agency had already taken the spikes into account when formulating its mercury advice.

“The FDA should strengthen its current guidance and advise pregnant women to avoid tuna altogether, especially given the uncertainties about the impact of occasional fetal exposure to high mercury levels,” said Jean Halloran, Director of Food Policy Initiatives at Consumers Union. “The FDA should also continue to test for mercury across the spectrum of fish and seafood in the marketplace in order to provide consumers with adequate information on the mercury levels of all fish.”