One of the major long term health risks in food, particularly in vulnerable populations like pregnant and nursing women and children, is mercury pollution from eating fish. But, some kinds of fish pose much more of a risk than other kinds of fish.
Very Low Risk Seafood 43% of market - 9.1% of mercury inputs
Medium Risk Seafood 49% of market - 41% of mercury inputs
Moderately High, High and Very High Risk Seafood 8% of market - 40% of mercury inputs
Very Low Mercury Risk Seafood
Oysters and Mussels
Ocean Perch and Mullet
Below Average Mercury Risk Seafood
Anchovies, Herring and Shad
Flounder, Sole and Paice
Above Average Mercury Risk Seafood
Pacific Mackerel (Chub)
Canned Light Tuna
Snapper, Porgy, Sheepshead
Haddock, Hake, Monkfish
Moderately High Mercury Risk Seafood
Carp and Buffalofish
Lingcod & Scorpionfish
High Mercury Risk Seafood
Canned Albacore Tuna
Very High Mercury Risk Seafood
Tuna Sushi/Bluefin Tuna
On average, mercury risks are highest in top of the food chain predator fish and are greatest in the largest types of those fish, because mercury accumulates and becomes more concentrated in fish as it works its way up the marine food chain.
Not All Tuna Poses The Same Risk
About 15% of bigeye, bluefin and yellowfin tunas served in sushi restaurants and a few percent supermarket sushi tuna has twice the U.S. Environmental Protection Agency action level for mercury, and the average is around the U.S. EPA action level. Restaurant sushi tuna has on average 50% more mercury than sushi tuna sold in supermarkets, and is much less likely to have more than twice the EPA action level of mercury. Of fresh tuna species, on average, bluefin tune has the most mercury, then bigeye tuna, and then yellow fin tuna.
Canned tuna has less mercury but is still a serious concern, because it accounts "for at least one-quarter of domestic seafood consumption" but the risk in this case also varies by type. White tuna is mostly albacore, which poses a greater mercury risk and poses a risk similar to store bought sushi tuna, while light tuna is mostly shipjack tuna which poses a lower mercury risk. The average level of mercury in solid and chunk white tuna is right at the EPA action level and more than four percent of it exceeds twice the EPA action level. Light tuna averages a mercury contamination level of a little more than half the EPA action level.
A 55 pound child can safely eat one serving of canned white tuna every two weeks, without facing too much mercury contamination, and can safetly eat one serving of canned light tuna less than once a week.