Mercury in Fish- What's the Deal?

Mercury in Fish- What's the Deal?

There is a growing concern about consuming fish and the mercury level, and I am often asked if it is safe to consume fish.  The short answer is yes, however it is important to get informed and understand what the concern is all about.  Not all fish are the same and it is good to know which fish are great to eat regularly and which are best to consumed less frequently.  Here we will try to clear up some of the fear, and misinformation about eating fish and what it is that we should actually be looking for.

What is Mercury?

Methylmercury is the dominant form of the element mercury found in aquatic animals, including fish.  At elevated levels, it can be harmful to the developing nervous systems of babies, in utero and young children, affecting cognitive, motor, and sensory functions.

The more methylmerucry that accumulates in a person's bloodstream, the longer the exposure time, and the younger in age of the person, the more severe the affects can be.

For pregnant women, nursing moms, or children, the FDA and EPA advise against eating fish that might contain high levels of mercury.  Since effects from too much mercury can also incur in all adults, the consumption of fish that may contain high levels of mercury should be limited.

Don't be afraid, it isn't all bad news.

How Does Mercury Accumulate in Fish?

Although mercury occurs naturally in the environment, the primary source of mercury in the oceans is from the burning of coal, in addition to some industrial mining activities.

Through rain, snow and runoff, mercury can enter streams, oceans, rivers and lakes where, through the influence of certain bacteria, it undergoes a chemical transformation to methylmercury, which can be toxic.  Methylmercury (which we will simply call mercury for this article) is greatly concentrated by planktonic microorganisms from seawater and then is absorbed into the animals that eat these microorganisms.  Fish absorb mercury from their food as they feed on aquatic organisms, but almost none of the mercury that they consume leaves their bodies through the digestive process.  Thus, as larger, longer living species feed on prey lower on the food chain, they continue to accumulate mercury over time.  And, we humans are the top of the food chain- we are for all intents and  purposes what we eat, eats...  Cooking, heat or freezing do not reduce mercury levels.

So, this is a conundrum.  The National Academy of Sciences stated in 2000, in attempt to ease concern:

"Because of the beneficial effects of fish consumption, the long term goal needs
to be a reduction in the concentrations of mercury in the fish rather than the
replacement of fish in the diet by other foods.  In the interim, the best method of
maintaining fish consumption and minimizing mercury exposure is the consumption
of fish known to have lower methymerucry concentrations."

Which Fish Might Contain the Highest Levels of Mercury?

The following chart, produced by the FDA helps clarify which fish are the safest to consume, and which to avoid.  Note that a serving is approximately 4 ounces.

What About Tuna- We Can't Live Without It?

Tuna has become the most popularly consumed fish globally and is extremely important commercially, particularly in the US and in Japan.  A tuna is a saltwater fish and is broken down into 2 families:  yellowfin and bluefin.  Both of these, when caught fresh have elevated levels of mercury.  Since canned "light" tuna is processed from smaller species of tuna, it typically has lower concentrations of mercury than either canned albacore ("white") tuna or tuna steaks.  Accordingly, the FDA and EPA advise limiting intake of both albacore tuna and tuna steaks to up to 6 ounces per week.

But there is more to the tuna story...

Since tuna has become so popular globally, it has become fraught with other issues including overfishing.  This overfishing has resulted in the status of some of the most sought after tuna to become a major issue.  According to the International Union for Conservation of Nature (IUCN), albacore and yellowfin tuna supplies are now near threatened, the pacific bluefin vulnerable and the atlantic bluefin endangered.

This has caused stricter global restrictions, increased prices and unfortunately a black market for tuna.  Tokyo's famous Tsukiji fish market has seen record-setting prices for bluefin tuna during opening day auctions, reflecting market demand.  A Japanese sushi chain boss has the current record-  $1.76 million) for a 487 lb bluefin; that's $3,603/lb!!!

As a result of the vulnerability of the fish, as well as the price and demand for tuna, sustainable/responsible farming and ranching have become more prevalent.  When done well (make sure that it is 3rd party verified to be responsibly farmed such as seafood sold at Whole Foods) you can ensure that the seafood isn't genetically modified or cloned, no antibiotics, growth hormones or synthetic parasiticides are used and that no poultry or mammalian by-products were allowed in the feed.  And, most importantly, the that there is farm-to-fishmonger traceability.  If these standards are in place, the fish is cleaner, safer, and lower in mercury level.  Also, we can reduce the environmental impact of eating fish.  

Eat Your Fish; Within Reason

Don't be afraid of eating fish, it is great for you and the best source of Omega-3 essential fatty acids.  Just make sure you know what you are buying and try to limit the amount of mercury that you consume.  Responsibly-farmed fish is a excellent option, especially great choice if you love tuna and sushi!

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