Dangers of Fish Toxins

woman holding fish
August 14, 2015 (Updated: August 16, 2018)
Lily Moran

What was once among our finest food sources is now on the no-fry (or poach or bake) list.

Billions of fish—from sources all over the world—contain very dangerous toxins.

So we must now approach these beautiful providers of top-quality protein, omega-3 fatty acids and so many other healthful nutrients with caution.

It’s a tragic reminder of how poorly we’ve treated our planet and how our mistakes inevitably come back to haunt us.

Top toxins #1: Mercury

Mercury is spewed into the air by power plants, chemical manufacturers, and other industries. It’s used to produce hundreds of everyday products, from auto brakes to hats to cosmetics to cement.

When mercury meets the ocean or other waterway, natural bacteria absorb it and turn it into methyl mercury. That’s when the trouble starts.

Methyl mercury doesn’t dissolve, break down, or otherwise become harmless. It remains mercury. So as small fish eat bacteria-laden algae…and then big fish eat contaminated smaller fish, this potent toxin makes its way up the food chain.

The bigger fish—shark, swordfish, mackerel, tuna, to name a few—can have mercury concentrations in their bodies that are 10,000 times higher than those of the water they live in. It is virtually undetectable. It is extremely dangerous. And we humans absorb it easily.

Once it’s in our bodies, it acts as a neurotoxic poison, threatening and interfering with the brain and nervous system.

In adults, mercury poisoning has been linked to fertility and blood pressure problems, memory loss, tremors, vision loss and numbness of the fingers and toes. There’s also increasing evidence of a link to heart disease.

Children, from the womb to early adulthood, are especially vulnerable, as their brains develop over time and their bodies have no defensive detection mechanism for mercury. Even slight exposure can lead to development problems—delayed walking and talking, shortened attention span, autism, and learning disabilities. Prenatal and infant exposure can cause mental retardation, cerebral palsy, deafness and blindness.

Top toxins # 2: PCBs

PCBs (polychlorinated biphenyls) are synthetic chemicals that were once widely used in many heavy manufacturing processes. Though banned in the U.S. since 1979, their legacy is worldwide environmental contamination, especially in fish.

The “upward toxicity” food chain model is the same as with mercury: big fish eat contaminated little fish, and PCB consumption accumulates. One bottle-nosed dolphin had PCB levels of 2,000 parts per million—40 times the amount considered hazardous waste. Some Inuit in the U.S. Northwest have such high PCB levels that their breast milk and body tissues could be classified as hazardous waste.

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Evidence linking PCBs to increased cancer risk, decreased mental functioning, and damage to sexual health is as abundant as healthy fish once were.

Farm-Raised Fish: Pros and Cons

As overfishing to meet growing demand depletes the wild stock of many fine fish, fish farms have become increasingly popular.

Take our beautiful wild salmon. They’re now so rare that 80 percent of the salmon consumed in the U.S. comes from fish farms. It’s a great example of meeting a major nutrition challenge. And if the farms are properly managed, the fish are fine to eat.

But there are too many examples of mismanagement. What are some farmed fish fed? Wild fish that consumers won’t touch—many are unregulated and heavily toxic.

And just as in some cattle, pork and poultry farms, there is overcrowding and heavy use of antibiotics, disinfectants, and pesticides. These breed all sorts of dangerous outcomes: antibiotics leaching into city drinking water, antibiotic-resistant “superbugs,” and increased risk of cancer, heart disease, nerve damage, and more.

To make matters worse, farmed salmon, naturally gray in color, are dyed pink to look like wild salmon. These dyes can cause retinal damage.

The Environmental Working Group estimates that 800,000 people in the U.S. have an increased lifetime cancer risk from eating farmed salmon alone.

And that’s just salmon. There are plenty of fish in the sea—and they’re all now dangerous to some degree.

How to protect yourself

As always, your best protection is to buy only local, fresh, organic fish—and buy with informed caution. Ask even your most trusted local vendor where the fish come from, if they’re wild or farmed. Eat only fish you are assured is from a healthy environment.

Opinions and healthy eating options are endless. Some recommend limiting consumption of certain fish to once per week, some to once per month, some to never, depending on amount. Distinctions are made between canned and fresh fish, light vs dark tuna, tuna in oil vs water, etc. You should do some homework.

One thing all agree on is that pregnant or nursing mothers should pretty much forget about fish other than truly wild salmon. Even slight amounts of contaminant can badly damage the fetal brain and contaminate breast milk.

I recommend buying none of these, the most likely to contain the highest levels of toxins:

  • Eel of all types
  • Imported farmed shrimp, orange roughy, tilapia, Chilean sea bass and imported catfish (also known as basa, swai, tra or pangasius)
  • Swordfish, shark, king mackerel, and tilefish

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