The findings suggest that the high levels of mercury that have been found in tuna and other ocean fish may not be coming from pollution, but from natural sources. The report will appear in the Dec. Nearly all fish contain trace amounts of mercury, but longer-lived predators — like tuna, swordfish and sharks — generally have higher levels.
The U. Food and Drug Administration warns pregnant women against eating large amounts of fish to avoid harming an unborn child's developing nervous system. Mercury enters the environment naturally and through industrial pollution, mostly from coal-fired power plants. Scientists have estimated that the amount of mercury in the atmosphere today is about two to three times what it was years ago.
But maybe mercury that occurs in fish is a natural thing, and it may have been there all along. The first step in exploring this assumption is to clarify the chemical nature of mercury in the environment.
Mercury concentrations in the air are of little concern, but when mercury enters water, microorganisms transform it to a highly toxic form — methylmercury — that builds up in fish. Unfortunately, scientists are not yet able to measure methylmercury in ocean surface waters, so Morel and his coworkers approached the problem from a different angle. They measured methylmercury levels in yellowfin tuna caught off the coast of Hawaii in and compared the numbers to a similar study from the same area in The food chain takes it from there, with methylmercury getting absorbed by phytoplankton microscopic marine algae , which are gobbled up by zooplankton tiny marine animals , which are then feasted upon by small fish.
These small fish and organisms are eaten by bigger fish who are then eaten by even bigger fish, and on and on. The methylmercury is absorbed by the bigger animal, and — since the bigger the fish, the longer it lives and the more it eats — larger fish species accumulate a lot more methylmercury in their body.
The largest predatory fish in the sea, like sharks, swordfish and tuna, can have methylmercury concentrations in their muscles — the meat of the fish — that are 10 million times higher than those of their surrounding habitat. Which is why parents are advised against giving their kids too much canned tuna fish.
Of course, who is higher than the largest fish on the food chain? Accordingly, seafood is the source of nearly all the methylmercury that we acquire in our bodies.
But there is little debate that methylmercury presents the greatest risk to fetuses, infants and children, whose growing brains and nervous systems can be adversely affected.
So how do we reduce our exposure to mercury? First, since all fish contain at least traces of methylmercury, what fish can we eat and how much? In infants and fetuses, high doses can lead to cognitive difficulties, cerebral palsy , deafness , and blindness. In adults, mercury poisoning can affect fertility and blood pressure regulation.
Chunk light is made mostly from skipjack tuna, a smaller species of tuna. Albacore tuna is a larger species and contains higher levels of mercury. Canned white albacore tuna typically contains about 0.
Canned light tuna contains about 0. The following table contains the recommended amount of canned tuna that an individual should eat according to their body weight:.
The figures in the table above are taken from U. The FDA recommends avoiding fresh albacore tuna and tuna steak during pregnancy. It is only safe to eat up to one serving of less than g per week. Canned tuna, however, is safe to eat during pregnancy. If you are still looking for the boost in protein and omega-3 fatty acids that fish can provide, try replacing albacore tuna and any large, predatory fish in the diet with salmon, herring, sardine, or anchovy.
These contain less mercury, as they are lower down the food chain. In humans, if mercury levels in the blood are found to be high, they can take up to 6 months or longer to reduce to a safe level. Children should be consuming considerably less canned tuna, otherwise their risk of serious mercury poisoning could become a public health issue in….
If you're wondering what foods you should be including in your diet, look no further.
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