To avoid mercury in fish, go deep
By Laura Reiley, Times Food Critic
Published January 30, 2008
Last week, conservation group Oceana released a study that revealed much higher levels of mercury in tuna than the Food and Drug Administration had previously estimated. A study conducted by the New York Times revealed similar findings. For fish eaters, the news is alarming and confusing.
Though we've heard for years that canned tuna may be unhealthy, now it's our beloved ahi tuna sushi that's suspect.
For tuna lovers seeking guidance, here's the skinny.
How does mercury get in fish?
Mercury pollution comes from numerous sources like coal-fired power plants and incinerators, and mining. Some of the contamination is runoff but some comes from airborne mercury vapor, which is returned to the oceans via rainwater and watersheds. A small amount of mercury occurs naturally.
According to the Monterey Bay Aquarium's Seafood Watch in California, bacteria in water transform mercury into methylmercury. Smaller bottom-feeding fish absorb the methylmercury, which they then pass up the food chain in higher concentrations. Top-level carnivores like tuna and swordfish have the highest likelihood of containing harmful amounts of chemicals, stored in their muscles and fatty tissue. These larger, longer-living species have more time to accumulate mercury.
Mercury is the second most toxic substance known to man after uranium.
What does methylmercury do?
According to the FDA, exposure to high levels can harm a fetus' developing nervous system brain and spinal cord. Those exposed to high doses of mercury while in the womb or at a young age are at risk for limited attention span, poor language, visual-spatial, memory and coordination skills, and lower IQ. But adults are at risk as well. Mercury poisoning victims have experienced nervous system effects such as loss of coordination, blurred vision or blindness, and hearing and speech impairment.
Who should be concerned about mercury?
In 2004, the Environmental Protection Agency and the FDA formally advised women of childbearing age and young children that they could safely eat up to 12 ounces of low-mercury seafood per week. But other groups are at risk, says Dr. Rashid Buttar, head of the Center for Advanced Medicine and Clinical Research in Charlotte, N.C., and chairman of the American Board of Clinical Metal Toxicology. He says some diabetics, transplant and cancer patients, people with HIV and anyone older than 70 and younger than 7 should avoid high-mercury fish.
Then which kinds of fish are okay?
Buttar suggests avoiding all large game fish (tuna, swordfish, marlin). He recommends deep-ocean, midsized fish (cod, for instance) and smaller to mid-sized farm-raised fish like tilapia, trout or striped bass. "Fish from the Gulf of Mexico is more worrisome than fish from the open ocean. In the gulf there's more drainage from land masses."
Buttar avoids shellfish: "I try not to eat shellfish because they're bottom feeders, they are the first line of absorption for eating these metals." The Monterey Bay Aquarium's Seafood Watch, however, thinks farm-raised bivalves and crustaceans are safe to eat. (Read more about the aquarium's seafood recommendations at www.mbayaq.org.)
For people eager to maximize the benefits of omega-3 fatty acids but minimize mercury risk, he suggests wild salmon from Alaska. Domesticated farm-raised salmon has less omega-3.
But what if I only eat a little - is it safe to eat ahi once a week?
"How much high-mercury fish is safe? None, as far as I'm concerned," says Buttar. "There's no safe level of mercury. Mercury levels should be aggressively monitored and documented by the FDA."
Laura Reiley can be reached at lreiley@sptimes.com or (727) 892-2293. Her dining blog can be found at blogs.tampabay.com/dining.