Michael Morrissey at the OSU Seafood Lab wrote an informative advisory that notes the tremendous variation in mercury content among the various tuna species. This makes it confusing when a general level is published in FDA tables and applied to all tunas. This information then gets picked up in the media as has happened most recently in Newsweek.
Newsweek showed fresh/frozen tuna as having 0.32 ppm of mercury with no distinction among the different species. According to Morrissey, the mercury data for tunas range from 1.30 to 0.05 ppm but it is not possible to differentiate between the species the way the data are reported. Therefore, for example, coastal albacore caught on the West Coast is unfairly associated with other tuna species, which might have higher levels of mercury.
Morrissey notes that all fish have trace amounts of methyl mercury. The levels vary widely and most fish have less than 0.1 ppm.
Canada and the U.S. have established guidelines for allowable levels of mercury content in fish and seafood products. The U.S. limit is 1.0 ppm while Canada Health guidelines are 0.5 ppm.
Studies have shown that the highest levels of mercury are found in sharks, swordfish, tilefish, king mackerel and large tuna.
According to Morrissey, the good news is that several species in the Pacific Northwest have been shown to have low mercury levels. Preliminary work with troll-caught coastal albacore showed levels below FDA and Canadian guidelines, which makes sense since coastal troll-caught albacore is small (12-17 lbs.).
Salmon also is very low in mercury as well as sardines, flounders, sablefish, halibut, cod, pollock shrimp, oysters and other species. There has not been sufficient research to make strong scientific statements about many of the species off the Pacific Northwest and differences that may occur in size and locations. He says more research is needed in this area.
Morrissey concludes, “So, what do you tell your customers? Buying and selling local caught salmon, albacore, oysters and other species is an easy choice and there is no mercury concern. There is also good evidence that eating these species is very beneficial from a health standpoint. They are high in omega-3 fatty acids and a steady diet of fish high in omega-3s has been shown to reduce the incidence of heart attacks, improve mental health and as well as other health benefits. So eat and enjoy, cut down some on the blue fin tuna sushi and remember that fish is a nutritious food that confers numerous health benefits as well as tasting great.â€
Source: Seafood.com