An FDA draft advisory on mercury levels in fish now recommends that women limit their consumption of tuna. See the mercury cycle.
How Mercury Gets into the Fish Supply
Mercury is a naturally occurring element in the environment and is also released into the air through industrial pollution. Mercury that falls from the air can accumulate in streams and oceans.
Bacteria in the water cause chemical changes that transform mercury into methylmercury, which can be toxic. Fish absorb the methylmercury as they feed in these waters.
Methylmercury builds up more in some fish than others depending on what they eat. High levels of methylmercury can damage a baby or child's developing nervous system.
The latest draft of a new government advisory on mercury in fish for the first time specifically mentions tuna. But the document doesn't tell pregnant women how much tuna they can eat safely, or offer them a list of alternatives.
For more than two years, the Food and Drug Administration has advised women of childbearing age to avoid four types of fish: shark, swordfish, king mackerel and tilefish. These fish are known to contain high levels of mercury, which can damage the brain of a developing fetus.
But new government studies show that other fish, including tuna, also may contain worrisome quantities of mercury. Taking this into consideration, the FDA teamed up with the Environmental Protection Agency to update its advisory and presented the latest draft Thursday in Washington, D.C. NPR's Jon Hamilton reports.
Excerpt from the FDA Draft Advisory:
Pregnant women, women who might become pregnant, and nursing mothers should follow three rules:
1. DON'T EAT shark, swordfish, king mackerel, or tilefish because they contain high levels of mercury.
2. Levels of mercury in other fish can vary. You can safely eat up to 12 ounces (two to three meals) of other purchased fish and shellfish a week. Mix up the types of fish and shellfish you eat and do not eat the same type of fish and shellfish more than once a week.
3. Check local advisories about the safety of fish caught by family and friends in your local rivers and streams. If no advice is available, you can safely eat up to 6 ounces (one meal per week of fish you catch from local waters, but don't consume any other fish during that week).
Follow the same rules when feeding fish and shellfish to a young child, but the serving sizes should be smaller.
New Addition to the Advisory, Regarding Tuna:
Tuna is one of the most frequently consumed fish in the United States. Mercury levels in tuna vary. Tuna steaks and canned albacore tuna generally contain higher levels of mercury than canned light tuna. You can safely include tuna as part of your weekly fish consumption.
What's New in the Advisory:
1. The recommendation to mix up the types of fish consumed.
2. The advice not to eat any other fish in the same week as locally caught fish are consumed.
3. The advisory for the first time addresses mercury levels in tuna.