Mercury in tuna.

July 8, 2017 Facebook Twitter LinkedIn Google+ Tuna information

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Mercury levels in tuna seem to be increasing. In the early 90’s there was a comparison done of tuna levels over the years. The study took fish that had been preserved at the Smithsonian Museum and compared them to fish caught in the early 90’s. The levels of mercury were fairly stable at that time. But that fact is rapidly changing.

Mercury levels in tuna have been increasing steadily since that test, Mercury levels have been rising at the rate of 3.8% per year. There is both mercury from the ocean floor and the atmosphere. The mercury from the ocean floor can be differentiated from atmospheric mercury. The increased mercury concentration is coming from atmospheric mercury.

Mercury in the atmosphere comes from 2 main sources: burning coal and artisanal gold mining. Artisanal gold mining is used in underdeveloped countries , mostly in Africa. Mercury is mixed with a gold containing compound to draw out the gold. It is burned sending the mercury into the air. It poisons the miners and the air.

When mercury enters the ocean, bacterial action converts it to methylmercury which is extremely toxic. Plankton eat the bacteria, small fish eat the plankton, large fish eat the small fish…and the mercury accumulates in higher concentrations as it travels up the food chain. Eventually, it winds up in tuna, swordfish, and other of our seafood favorites.

Tests have been done on confined tuna to determine the effects of mercury. The tests show that as mercury levels increase, reproduction decreases. Males produce less sperm and seem to lose interest. Females produce fewer eggs. This could lead to a disaster for wild tuna which are already threatened.

How much tuna can you eat

f you weigh 130 pounds, you should eat no more than 4 ounces of fish typically medium high in mercury (tuna, halibut, grouper, northern pike, bass) a week. If you weigh 170 pounds, then you can eat as much as 5.3 ounce a week.  These figures assume that you eat no other seafood that week.

Canned tuna can also be a problem. The white albacore tuna in cans is higher in mercury than the light canned tuna. The light canned tuna is mostly skipjack which are  lower in mercury .






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