Quicksilver Lining: High Levels of Mercury in Seafood Don’t Mean the End of Eating Fish

Consuming smaller species of fish is the key to avoiding mercury in seafood.

mercury in seafood

Don't fear mercury in seafood—just consider the size of the fish you're eating.(Photo: Ming Tang-Evans/Getty Images)

Clare Leschin-Hoar's stories on seafood and food politics have appeared in Scientific American, Eating Well and elsewhere.

Scientists looking into the high levels of mercury in seafood came back with shocking news this week.

Researchers targeted their testing to global hotspots—areas known or suspected to harbor high levels of mercury contamination—including countries like Japan, Thailand, Russia, Indonesia and elsewhere. What did they find? A shocking 84 percent of fish samples collected across the globe contained unsafe levels of mercury.

The U.S. Food and Drug Administration, along with Environmental Protection Agency guidelines, set a limit of one part per million (ppm) for mercury in seafood. Exposure to high levels of mercury can damage the brain and kidneys of fish.

“Findings demonstrate that 43-100 percent of the fish sampled exceeded the recommendation for consuming more than one fish meal per month. Mercury concentrations in fish from sites in Japan and Uruguay were so high that no consumption is recommended according to the USEPA [United States Environmental Protection Agency] guidelines,” says the report.

Fish species tested included albacore, Pacific bluefin, catfish, perch, swordfish, freshwater bream, snakehead and halibut.

The study was released as officials from 130 countries meet in Geneva to create the first legally binding treaty on reducing mercury emissions, after a report that mercury pollution in the oceans has doubled in the last century. While mercury is naturally occurring in our environment, it can also enter the ecosystem through the use of coal-fired powerplants, small-scale gold mining and other sources. Its primary means of entering our food chain is through fish.

Which circles us back to the all-important question: Should we stop eating seafood? The simple answer is no.

As we told you earlier this year, USDA guidelines recommend adults consume eight ounces of seafood per week, and up to 12 ounces for women who are pregnant or breastfeeding. But according to Jennifer McGuire, registered dietitian for the National Fisheries Institute, most Americans only eat a fraction of that—roughly 3.5 ounces a week, while pregnant women are nibbling an inadequate 1.89 ounces a week—in part because information about mercury in seafood can scare consumers away.

In a blog post about mercury and seafood consumption, ocean scientist Carl Safina writes about getting his hair tested for mercury containation and finding that it had levels of 1.3 ppm.

"As a lifelong avid fisherman, 30 years ago I started eating fish I caught instead of buying meat. It was a big part of my diet; I ate fish probably five or six nights a week. And because I caught a lot, I served large portions. As my fishing skills improved I sought bigger and bigger fish, until a very large proportion of my diet was tuna steaks and shark—some of the highest-mercury fish around," he writes. But with fish and mercury, size matters. "It makes a difference; the bigger the fish, the bigger the mercury dose. A big part of what I hope you get from all this is: it’s not about avoiding fish; it’s about avoiding mercury.”

Dr. Nicholas Fisher, a researcher studying mercury contamination in seafood at Stony Brook University, agrees that seafood lovers don't need to give up the healthy fish they adore, since different fish have different levels of mercury contamination.

“Upper-level predators like shark, some species of tuna (such as bluefin and albacore) have higher levels, as opposed to tilapia or salmon, which have much lower mercury levels. You can eat all the tilapia you want and show no signs of mercury contamination. That isn’t true for swordfish, bluefin, or marlin.”

What else gets the okay? Seafood like shrimp, mussels, clams, oysters, and flounder.

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