Levels of mercury higher than the federal limit have been found in many imported cans of tuna, according to a study released Tuesday by the not-for-profit environmental group Defenders of Wildlife, the AP/Philadelphia Inquirer reports (Quaid, AP/Philadelphia Inquirer, 7/12). High levels of mercury -- which accumulates in the environment, as well as in the flesh of fish and the bodies of those who eat fish -- have been shown to contribute to birth defects and other health problems, and several studies have demonstrated a subtle loss of mental acuity in the offspring of women who consume fish during pregnancy. FDA and the Environmental Protection Agency in 2005 issued warnings that advise young children, pregnant women, nursing women and women of childbearing age to avoid consuming swordfish, king mackerel, shark and tilefish because of high mercury levels. The warning also recommends that those groups eat no more than 12 ounces of fish weekly and eat no more than six ounces of canned albacore tuna weekly (Kaiser Daily Women's Health Policy Report, 6/7). Researchers at New Age/Landmark Laboratory in Benton Harbor, Mich., for Defenders of Wildlife tested 164 cans of tuna -- purchased in California, the District of Columbia and five other states -- that originated from Costa Rica, Ecuador, Malaysia, Mexico, the Philippines, Thailand and the U.S., the AP/Inquirer reports (AP/Philadelphia Inquirer, 7/12). Of these, six types of tuna -- from Costa Rica, Ecuador and Mexico -- exceeded the government limit of one part per million, according to the San Diego Union-Tribune (Green, San Diego Union-Tribune, 7/12). The study also finds that tuna from Asia had the lowest levels of mercury; tuna from Latin America had the highest mercury levels; and the average mercury level in U.S. tuna was generally lower than imported tuna. The study also finds higher levels of mercury in light tuna, which FDA considers to be low in mercury levels (AP/Philadelphia Inquirer, 7/12). The U.S. Tuna Foundation, which represents American canners, in a statement said that the study is "statistically insignificant," adding that it stands by the safety, quality and nutritional benefits of its products. "We urge consumers to ... review the real science, which demonstrates that canned tuna is one of the healthiest foods for Americans of any age," the statement says (San Diego Union-Tribune, 7/12).