Mercury in Seafood

 For many people who enjoy seafood, the conflicting health and safety messages of fish, omega-3 fats versus mercury contamination, may have caused some confusion. Here’s the bottom line: Fish and shellfish are an important part of a healthy diet because they are low in saturated fat and contain omega-3 fatty acids (heart-healthy fats). However, certain fish species should be avoided due to their high levels of mercury, a potent neurotoxin.
 
Mercury Contamination
Mercury contamination of seafood is a serious public health threat to children and women who are pregnant or plan to become pregnant. About 70% of mercury comes from human sources, the worst polluters being coal-burning electric plants and chlorine production plants.  Mercury accumulates in streams and oceans where it is converted to the neurotoxic form methylmercury, which is then absorbed by the fish that feed in those waters (1,2).
 
Human Health Concerns
Even at relatively low levels, mercury can accumulate in the human liver, kidney, brain, and blood and harm the nervous system. At higher levels, mercury can cause kidney failure, cardiovascular disease and genetic damage in both children and adults (1).
 
Women should be particularly cautious because mercury consumed before, during or after pregnancy can significantly affect a child’s development (particularly in the womb). Children exposed to mercury are at high risk for birth defects, impaired motor skills and other developmental disabilities. .
 
The U.S. Food and Drug Administration (FDA) and Environmental Protection Agency (EPA) recommend that women who are pregnant, nursing or planning to become pregnant should not consume any swordfish, shark, tilefish, or king mackerel because they contain the highest levels of methylmercury and are considered unsafe for consumption. Organizations such as the Environmental Working Group also recommend avoiding tuna (except light canned tuna) because of the mercury risk (3).    
 
Fish containing highest levels of mercury
 Fish
 Average mercury level
(in micrograms per gram)
 King mackerel
 0.73
 Swordfish
 0.97
 Shark
 0.99
 Tilefish (golden bass or golden snapper)
 1.45
Source: FDA (4)
 
Mercury and Fish Recommendations 
Not all agencies have provided the same advice about mercury in fish, so there has been some confusion as to how much mercury is considered safe. A reliable guideline is the EPA’s “reference dose,” which is a recommended limit on mercury consumption that’s based on your body weight. The EPA’s reference dose is 0.1 micrograms/kilogram body weight per day. So for a person who is 120 lbs (or 55 kg), the reference dose for methylmercury would be 5.5 micrograms per day.
 
What does this mean in terms of fish consumption? Based on the chart above, four ounces (or 113 grams) of swordfish contains 110 micrograms of mercury. For the person weighing 120 lbs, this is 20 times more methylmercury than is considered safe by the EPA.
 
To find out if your mercury consumption is above or below your recommended reference dose use the Mercury Calculator on GotMercury.org.   
 
Although the health risks of consuming mercury are serious, this does not mean everybody should avoid fish completely. Fish and shellfish are healthy sources of protein because they are low in saturated fat and contain omega-3 fatty acids, which may lower your risk for heart disease. As seen in the chart below, the most commonly consumed fish and shellfish in the U.S. are relatively low in mercury. 
 
Top 10 fish and shellfish consumed in the United States
Fish and shellfish
Average mercury level
(in micrograms per gram)
Omega-3 fatty acids
(in grams per 3 oz. serving)
Canned tuna (light)
0.12
0.26 - 0.73
Shrimp
not detectable
0.27
Pollock
0.06
0.46
Salmon
0.01
0.68 - 1.83
Cod
0.11
0.13 - 0.24
Catfish
0.05
0.15 - 0.2
Clams
not detectable
0.24
Flounder or sole
0.05
0.43
Crabs
0.06
0.34 - 0.4
Scallops
0.05
0.17
Source: American Heart Association (5)
 
According to the American Heart Association, the benefits and risks of consuming fish and shellfish depend on your stage of life. For children, women of reproductive age, pregnant and nursing women who have low heart disease risk, avoiding high levels of mercury is more important than consuming fish for the omega-3 fatty acids.  However, for middle-aged or older men and women after menopause, the health benefits of eating fish far outweigh the mercury risk (5). There is no set recommendation for omega-3 fatty acids but research shows that consuming 0.5 g to 2 g per day significantly reduces one’s risk for heart disease (6). Eating fatty fish like mackerel, lake trout, herring, sardines, albacore tuna and salmon at least twice a week is recommended to achieve this level (6).   
 
Mercury Awareness Campaign
Because the health and safety of our guests is our number one priority, Bon Appétit launched a Mercury Awareness Campaign in 2006.  Signage throughout our cafés directs our guests to www.GotMercury.org where they can calculate their mercury risk based on the type and amount of seafood consumed.  We believe that it is our responsibility to provide the necessary information for our diners to make educated choices about their seafood consumption.    
 
Sources:
1. Got Mercury? Sea Turtle Restoration Project. Accessed May 2007.
2. U.S. Food and Drug Administration.  What you need to know about mercury in fish and shellfishMarch 2004.  Accessed May 2007.
3. Environmental Working Group. Brain Food: What women should know about mercury contamination of fish. Washington, DC; 2001.
4. U.S. Food and Drug Administration. Mercury Levels in Commercial Fish and Shellfish. Accessed July 2007.
5. American Heart Association. Fish, Levels of Mercury and Omega-3 Fatty Acids. Accessed June 2007.
6. American Heart Association. Fish and Omega-3 Fatty Acids. Accessed July 2007.