Fish have made this heavy metal quite famous, and restricted intake of fish has been recommended by a wide variety of public health organizations due to risk of mercury contamination. But do you know your mercury-and-fish limits? Canned tuna is the most likely source of mercury exposure for U.S. consumers who eat fish. Just how much can you eat each week and still stay safe?

FULL STORY:

Like all environmental toxins, mercury can be found in great variety of locations and amounts. Some oceans are lined with ores that contain natural mercury deposits. The Mediterranean Sea, for example, contains cinnabar (mercury sulfide) deposits that can leech into the water and find their way into Mediterranean fish. Tuna from the Mediterranean tends to be higher in mercury than tuna from the Atlantic or the Pacific for this reason.

Human activities, however, can be an equally significant source of mercury contamination. Over 100 tons of mercury are released annually into the air by U.S. industries – primarily coal-fired power plants, municipal waste combustion facilities, and incinerators that handle medical waste. Mercury also finds it way into landfills across the country in the form of fluorescent light bulbs, thermostats, and electrical components (including components still used in automobiles).

Once deposited in the soil or in the air, mercury can be transported by natural ecological forces to groundwater, rivers, and oceans. This movement of toxins through our environment (along pathways called “transfer vectors”) can bring mercury into the natural habitat of fish thousands of miles away from the original site of contamination.

When it comes to canned light tuna, a good ballpark guideline for safe mercury intake can be based on body weight alone. For every 10 pounds of weight, allow yourself just under one ounce (technically, 0.95 ounces) of canned light tuna per week. If you weigh 150 lbs., for example, limit yourself to 14 ounces (or approximately 2 cans) of tuna. For canned albacore tuna, however, this restriction becomes much greater, because canned albacore averages substantially more mercury than canned light. With albacore, for every 10 pounds of weight, allow yourself only 1/3rd of an ounce per week. In this case, if you weigh 150 pounds, restrict yourself to 5 ounces (less than one can) per week.

While body weight can give you an initial ballpark estimate for restricting your canned fish intake, it’s important to note that your body and your lifestyle are unique. You may have other important sources of mercury exposure, and you may have unique metabolic needs when it comes to detoxification of mercury inside your cells. For these reasons, a truly personalized assessment of your mercury exposure and mercury risk can be helpful for planning your fish intake (and other dietary decisions as well).

Several health organizations, including the U.S. Environmental Protection Agency (EPA), have issued advisories cautioning pregnant women (and women considering pregnancy) against excess consumption of mercury-containing fish. For the latest EPA advisory, click here.

References:

1. Adams DH. (2004). Total mercury levels in tunas from offshore waters of the Florida Atlantic coast. Mar Pollut Bulletin 49(7-8):659-63.
2. Hood, E. (2003). A diet rich in fish. High-end consumers face more mercury risks. Environ Health Perspect 111(4):A233.
3. Kraepiel AM, Keller K, Chin HB et al. (2003). Sources and variations of mercury in tuna. Environ Sci Technol 37(24):5551-8.
4. Schober SE, Sinks TH, Jones RL, et al. (2003). Blood mercury levels in US children and women of childbearing age, 1999- 2000. JAMA 289(13):1667-74.
5. Storelli MM, Stuffler RG, and Marcotrigiano GO. (2002). Total and methylmercury residues in tuna-fish from the Mediterranean sea.
6. Food Addit Contam 19(8):715-20.
7. Sunderland EM. (2007). Mercury exposure from domestic and imported estuarine and marine fish in the U.S. seafood market. Environ Health Perspect 115:235-242.

Related Topics:

• WebMD Video: Mercury and Seafood
• Canned Tuna: Avoid if Pregnant?

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