High mercury levels in fish and shellfish are an ingestible manifestation of air pollution: Coal-burning power plants and other industrial processes release mercury into the atmosphere, where it then enters streams, lakes, and the ocean (and thereby fish flesh) as a carbon-bound form called methylmercury. Depending on the kind of aquatic creature, the mercury level varies. It’s found in the highest concentrations in large fish near the top of the food chain.
There’s more mercury in a shark than in a sardine, more in tilefish than tilapia. We humans are at the tippy-top of the food chain, which is why we need to be cautious. Too much mercury can cause neurological problems in fetuses and young children. Methylmercury has also been linked with problems—cardiovascular, neurological, and reproductive—in adults. Mercury is a toxin, but the question is how much does it take to cause these problems, and are we ingesting enough of it to offset the health benefits of having seafood in our diet?
Because, of course, seafood contains omega-3 fatty acids, those storied “good” fats that appear to prevent cardiac disease and encourage young nervous systems to develop. Some scientists, including Dr. Dariush Mozaffarian, a cardiologist at Harvard Medical School, are concerned that the public will be scared away from seafood because of a fear of mercury. “You have inconclusive evidence [of the dangers of the relatively small amounts of mercury in seafood] compared with very strong evidence of the cardiovascular benefits,” says Dr. Mozaffarian.
The federal government recommends that we continue eating seafood, up to 12 ounces per week. The feds also tell those in the sensitive population to avoid four fish altogether: shark, swordfish, king mackerel, and tilefish. Perhaps because it knows it’s serving a city of adventurous eaters, the New York City Department of Health has a broader list of fish it deems “too high in mercury.” It warns pregnant and breast-feeding women, women planning to become pregnant, and children to also steer clear of fresh tuna, marlin, grouper, orange roughy, Chilean sea bass, and my personal favorite at the sushi bar, Spanish mackerel.
There is a convenient correspondence between fish that are being stressed by overfishing—like the so-called Chilean sea bass, bluefin tuna, and tilefish—and those species that have higher levels of mercury. In comparison to smaller, lower-mercury fish, the bigger, steakier fish we crave so much don’t breed or mature as quickly. And slower growth means more time to accumulate mercury.
You’ll want to get to know those lower-mercury seafood options. While no one has yet managed to get me excited about pollack (which is often the mystery fish in a fish stick), lots of low-mercury seafood is great stuff (think clams, salmon, sardines, and shrimp). To find out where other fish fall on the mercury scale, check out the resources in the box below and pester your favorite seafood merchant to keep mercury info on hand.
And how about that can of tuna? Canned albacore tuna is singled out in the FDA-EPA advisory, which suggests we eat no more than six ounces per week. Chunk light tuna is generally regarded as the better low-mercury option for canned tuna, since it is made with smaller fish—usually skipjack. And albacore from smaller-scale hook-and-line fisheries in the colder Pacific waters, like American Tuna or Dave’s Gourmet Albacore, also tend to have relatively lower mercury levels than other canned albacore.
As for the rest of the general population, there is no government advisory for mercury in seafood: What to choose comes down to common sense and balance. If you eat a lot of sushi and you always include several orders of tuna-heavy dragon rolls, you should probably shake up your selection. Doctors agree that variety is essential for maximizing the health benefits of seafood. In other words, if you are part of the normal population of adults and you eat a variety of seafood once or twice a week, “you don’t need to worry about this stuff,” says Dr. Mozaffarian. With lots of sources of seafood in your diet, “you’re never going to just eat the low-omega-3 fish; you’re never going to just eat the higher-mercury fish.”
As Michael Pollan says, “Don’t overlook those oily little fish.” If you’re cooking fish at home, branch out from your normal routine. Learn new fish habits by going to the most reputable fishmonger in your city, a well-stocked specialty grocery store, or—if you’re lucky, as we are in Seattle—to the farmers’ market, where shellfish farmers and fishermen sell their products directly to customers. Not only will you get a better variety of seafood options, but you can ask the fish seller for recipes and techniques, too.
I have a series of assignments to help you incorporate new fish, especially the lower-mercury options, into your home cooking. (1) Learn how to slow-roast a salmon fillet in a really cool oven (225°F or so); unlike high-heat cooking methods, it’s hard to screw up. (2) Try grilling a whole fish. You pick the kind of fish: striped bass, sardines, branzino, you name it. You’ll be surprised at how easy it is to cook fish on the bone and in its skin, and how moist the results are. (3) Get over any fear of cooking shellfish. Ask your fish seller how to clean and cook them. Clams are the easiest, followed by mussels. (4) For extra credit, learn a quick pickling method for the oilier omega-3-rich fish like sardines or salmon. Call it escabèche or court bouillon—it really just means a brief poaching in a vinegary broth. If you don’t feel like experimenting, get a solid seafood cookbook like David Pasternack’s The Young Man and the Sea, Mark Bittman’s Fish, or Paul Johnson’s Fish Forever.
Fishing for More? If you’re pregnant or nursing or if you have young children, check out the NYC health department’s brochure Eat Fish, Choose Wisely, Protect Against Mercury (available at nyc.gov/health. Find out the mercury levels for 66 types of fish and shellfish atcfsan.fda.gov. If you’re at the seafood counter or reading a restaurant menu, learn immediately if the fish you’re considering has unhealthful levels of mercury by texting FishPhone (learn how at blueocean.org).
Why Mercury Levels In Food Matter.