An environmental watchdog group say they have found that some canned tuna imported into the United States has mercury levels higher than the federal limit.
According to the Defenders of Wildlife, an analysis carried out by the New Age and Landmark laboratory, a Michigan, company that has been used by the federal government, high levels of mercury has been found in tuna from Ecuador and Mexico.
The group initiated tests on 164 cans of tuna labelled as being from Ecuador, Mexico, Costa Rica, Thailand, Malaysia, the Philippines and the United States.
Ecuador and Mexico had the record for the highest levels and according to the group's senior vice president for conservation, Bob Irvin, this is because they tend to catch larger, more mature fish, which tend to have higher levels of mercury as they are at the top of the food chain.
The group is a longtime advocate of dolphin-safe tuna.
The tests found that the average mercury content of U.S. tuna was generally lower than imported tuna, but tuna from Asia had the lowest average levels of mercury.
Tuna from Latin America had the highest mercury levels, with some exceeding the government limit of 1.0 parts per million and the laboratory found higher levels of mercury in light tuna, which the Food and Drug Administration considers to have lower levels.
The FDA says it's safe to eat two meals a week of fish and shellfish that are lower in mercury, such as canned light tuna, shrimp, salmon, pollock and catfish, but recommends a limit of white tuna to one meal per week because it contains higher levels of mercury.
Now the Defenders of Wildlife say people should limit light tuna to one meal each week and avoid any canned tuna that is from Latin America.
Irvin says the government needs to do a better job in monitoring mercury content in light canned tuna, which up to now has been advocated as a low-mercury source of protein.
The federal government advises pregnant women, nursing mothers and young children to avoid fish with high levels of mercury - shark, swordfish, king mackerel or tilefish.
Research has found that elevated mercury levels have been associated with learning disabilities and developmental delays in children and to heart, nervous system and kidney damage in adults.
Practically all fish and shellfish contain traces of mercury which builds up in fish and shellfish as they feed, and is more prevalent in some types of fish.
The American Heart Association advises people to eat fish at least twice a week as it is widely recognised that eating fish is beneficial to health.
Frequently Asked Questions about Mercury in Fish and Shellfish from the FDA:
"What is mercury and methylmercury?"
Mercury occurs naturally in the environment and can also be released into the air through industrial pollution. Mercury falls from the air and can accumulate in streams and oceans and is turned into methylmercury in the water. It is this type of mercury that can be harmful to your unborn baby and young child. Fish absorb the methylmercury as they feed in these waters and so it builds up in them. It builds up more in some types of fish and shellfish than others, depending on what the fish eat, which is why the levels vary.
"I'm a woman who could have children but I'm not pregnant - so why should I be concerned about methylmercury?"
If you regularly eat types of fish that are high in methylmercury, it can accumulate in your blood stream over time. Methylmercury is removed from the body naturally, but it may take over a year for the levels to drop significantly. Thus, it may be present in a woman even before she becomes pregnant. This is the reason why women who are trying to become pregnant should also avoid eating certain types of fish.
"Is there methylmercury in all fish and shellfish?"
Nearly all fish and shellfish contain traces of methylmercury. However, larger fish that have lived longer have the highest levels of methylmercury because they've had more time to accumulate it. These large fish (swordfish, shark, king mackerel and tilefish) pose the greatest risk. Other types of fish and shellfish may be eaten in the amounts recommended by FDA and EPA.
"I don't see the fish I eat in the advisory. What should I do?"
If you want more information about the levels in the various types of fish you eat, see the FDA food safety website www.cfsan.fda.gov/~frf/sea-mehg.html or the EPA website at www.epa.gov/ost/fish.
"What about fish sticks and fast food sandwiches?"
Fish sticks and "fast-food" sandwiches are commonly made from fish that are low in mercury.
"The advice about canned tuna is in the advisory, but what's the advice about tuna steaks?"
Because tuna steak generally contains higher levels of mercury than canned light tuna, when choosing your two meals of fish and shellfish, you may eat up to 6 ounces (one average meal) of tuna steak per week.
"What if I eat more than the recommended amount of fish and shellfish in a week?"
One week's consumption of fish does not change the level of methylmercury in the body much at all. If you eat a lot of fish one week, you can cut back for the next week or two. Just make sure you average the recommended amount per week.
"Where do I get information about the safety of fish caught recreationally by family or friends?"
Before you go fishing, check your Fishing Regulations Booklet for information about recreationally caught fish. You can also contact your local health department for information about local advisories. You need to check local advisories because some kinds of fish and shellfish caught in your local waters may have higher or much lower than average levels of mercury. This depends on the levels of mercury in the water in which the fish are caught. Those fish with much lower levels may be eaten more frequently and in larger amounts.