Tuna Consumption >> Mercury

By PSU EcoMerge Capstone - 11:13 PM

How does mercury get into the tuna we eat?
Mercury is a naturally occurring element but it is usually found in small quantities on the earth’s surface. The bulk of the world’s mercury is inside the earth and is only brought to the surface through volcanic eruption. Unfortunately with the industrial revolution and into the present we have brought mercury to the surface by way of coal. Then, when we burn coal for power it releases the mercury into the air. When it rains the mercury is brought down into the oceans and our planet’s water table.

As mercury is a metal, it is dense so it sinks to the ocean floor where it is eaten by the bottom feeders such as shrimp and small fish low on the food chain. Then a larger fish comes along and eats numerous shrimp, before it is in turn eaten by a still larger fish. Now an even bigger fish like a tuna comes by and eats the medium sized fish, but he doesn’t eat just one. Let’s say he eats thousands of medium sized fish before he is caught and served as Toro in your local sushi restaurant. With each progressive step up the food chain the mercury levels in that animal increase exponentially. By the time you get to the sushi restaurant the mercury levels are very high. Here is a link to a mercury calculator which can tell you how much mercury is in the fish you eat.
Mercury calculator: http://www.gotmercury.org/article.php?list=type&type=75

How does the mercury we get from tuna affect us?
High doses of mercury can be fatal to humans, but even small doses can have an adverse effect. Mercury acts as a neurotoxin and interferes with brain function and development. Recent studies have also shown the mercury is linked to problems of the cardiovascular, immune and reproductive systems. It is possible that it is linked to higher rates of cancer and attention deficit disorder.

“Mercury has long been recognised as a major source of toxicity in children causing reduced cognitive functioning, including reduced I.Q. However, we are now seeing that even ‘low’ exposure levels can cause damage to the developing brain of the foetus and infant. These are mercury levels that are not known to cause acute poisoning or ill health in adults. We also know that mercury is ‘stored up’ in women even before pregnancy. Therefore, preventing exposure to future children means reducing everyday exposure today.”
Gavin ten Tusscher, M.D., Ph.D., paediatrician, Department of Paediatrics and Neonatology, Westfries
Gasthuis, Hoorn, the Netherlands


How much tuna can a human eat and still be safe?

Because of the way tuna passes from mother to child, women who are pregnant or might become pregnant, or who are breastfeeding and young children should not eat more than one small portion (less than 100 g) per week of large predatory fish, such as swordfish, shark, marlin and pike. If they do eat a portion of this fish, they should not eat any other fish during the same week. Nor should they eat tuna more than twice per week.

Does one type of tuna have higher levels of mercury than another, and what kind of tuna is in canned tuna?
Here are some general guidelines I found at the National Cooperative Grocers Association website (address is below).
“Because larger tuna are more long-lived, they have higher levels of mercury. So tuna steaks are higher in mercury than smaller tuna that’s used for canning. In addition, “chunk light” tuna generally has less mercury than “white” or “albacore” tuna. There are some exceptions, however. In one study, 6 percent of the light-tuna samples contained as much or more mercury than the albacore tuna. This might be because light tuna is made from different varieties. While most is “skipjack,” a type of tuna that’s low in mercury, some is “yellow fin,” which has higher mercury content. Unfortunately, albacore is the only specific type of tuna that’s routinely labeled. In addition, imported tuna has tested twice as high in mercury than tuna canned in the U.S. You can ask your grocer about the source of your store’s canned tuna.”
References for this article:
http://www.ncga.coop/node/2251#tuna
http://www.pbs.org/now/science/mercuryinfish.html
http://www.gotmercury.org/article.php?id=1466

http://en.wikipedia.org/wiki/Tuna#Canned_tuna

http://www.fda.gov/Food/FoodSafety/Product-SpecificInformation/Seafood

Posted By Lisa Adza

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1 comments

  1. Since I looked at this article I couldnt get the picture out of my mind that shows how much mercury is in certain types of fish. I like albacore and was unaware about how much mercury they contain. I have changed my mind on the amount of mercury I will consume in the future.

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