Methylmercury in Seafood

Response to FDA Advisories

Whole Foods Market consistently offers the highest quality seafood gathered from the best sources around the world. We also pride ourselves on keeping our customers informed of the latest health and environmental issues. In reference to advice concerning mercury in fish and shellfish, as provided by the U.S. Food and Drug Administration (FDA) and the U.S. Environmental Protection Agency, here are some frequently asked questions about methylmercury in seafood.

What is methylmercury and what is the concern?

Methylmercury is a form of mercury that can be harmful to the developing brains of unborn babies and young children, affecting cognitive, motor, and sensory functions. The more methylmercury that accumulate into a person's bloodstream, the longer the exposure time, and the younger in age of the person consuming the fish, the more severe the effects may be.

If you are a pregnant woman, a woman of childbearing age who may become pregnant, a nursing mother, or a child the FDA and EPA advise against eating fish that might contain high levels of mercury. Since effects from too much mercury can also occur in men and in women not of childbearing age, their consumption of fish that may contain high levels of mercury should be limited to occasional use.

How does methylmercury accumulate in fish?

Although mercury occurs naturally in the environment, the primary source of methylmercury in fish is industrial pollution. Through rain, snow, and runoff, mercury can accumulate in streams, oceans, rivers, and lakes where, aided by bacteria, it undergoes a chemical transformation into methyl mercury, which can be toxic. Fish absorb methyl mercury from water as they feed on aquatic organisms. Larger, longer living fish feed on other fish throughout their lives, thereby accumulating the highest levels of methylmercury. Cooking preparation and heat does not reduce mercury levels.

As stated within the results of their study Toxicological Effects of Methylmercury (2000), the National Academy of Sciences stated: "Because of the beneficial effects of fish consumption, the long term goal needs to be a reduction in the concentrations of mercury in fish rather than the replacement of fish in the diet by other foods. In the interim, the best method of maintaining fish consumption and minimizing mercury exposure is the consumption of fish known to have lower methylmercury concentrations."

Which commercially available fish might contain high levels of methylmercury?

King Mackerel, Shark, Swordfish, Tilefish

What about tuna?

Since canned light tuna is processed from smaller varieties of tuna, it will have less mercury than either canned albacore ("white") tuna or tuna steaks/fillets. Accordingly, the FDA and EPA advise limiting intake of both albacore tuna and tuna steaks/fillets to up to 6 ounces (one average meal) of tuna steak eaten per week.

What about other fish?

You can reduce your exposure to mercury by eating a variety of fish known to have low mercury levels. While individuals outside of the more vulnerable, sensitive population groups may enjoy low mercury fish more frequently, the FDA and EPA recommend that women who are or may become pregnant, and nursing mothers eat up to 12 ounces (2 average meals) per week of a variety of fish and shellfish that are lower in mercury. Young children should be served smaller portions.

Which fish are considered low in mercury?

In general, smaller fish have less mercury than larger fish as the older and larger the fish, the greater the potential for high mercury levels in their bodies. Commercially available fish lower in mercury include:

  • Catfish

  • Cod

  • Crab

  • Flounder/Sole

  • Haddock

  • Herring

  • Lobster

  • Ocean Perch

  • Oysters

  • Rainbow Trout

  • Farmed Salmon

  • Wild Salmon

  • Sardines

  • Scallops

  • Shrimp

  • Spiny Lobster

  • Tilapia

  • Trout (farmed)

Besides fish, what other foods provide the omega-3 essential fatty acids that are found in significant quantities in fish?

As an alternative to eating fish, purified (often called "molecularly distilled") fish oil supplements offer omega-3 fatty acids with lower levels of contaminants. Omega-3-enriched eggs offer another alternative source of essential fatty acids, and micro-algae based omega-3 supplements, available in our Whole Body department, are a vegetarian alternative to fish-and egg-based forms.