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Get Angry About Mercury in Fish, Not in Vaccines.

Last month, the measles outbreak in Washington State prompted its governor to declare a state of emergency. Some parents have wised up and finally vaccinated their kids. But others have dug in, even gathering to protest universal vaccine policies.

As a researcher who knows how thoroughly the autism-vaccine hypothesis has been debunked*, it’s hard to watch videos of parents protesting vaccines—arguably the greatest health advance in the last hundred years—without wondering: What could we do with that all that energy, if better directed?

*(The original paper, promoting this hypothesis, published in The Lancet in 1998, was later withdrawn; the medical license of its lead author, Andrew Wakefield, revoked for failure to disclose industry ties and falsifying data. Thimerosal, the mercury-based preservative, was removed from all routine childhood vaccinations in 2001.)

What if we channeled all that passion towards a real public health issue? We could even choose one that involves mercury. Like, say, the mercury pollution contaminating our air and water, that makes its way into our fish and seafood. 

Methylmercury versus Ethylmercury

How can mercury in the air be dangerous but mercury in vaccines be fine? The difference lies in the type of mercury.

Ethylmercury,  The Type Once Found in Vaccines

Before its removal in 2001, nearly all vaccines contained a preservative known as thimerosal. Thimerosal, breaks down into ethylmercury in our bodies. It was added in trace amounts to vaccines to prevent bacterial and fungal contamination. And it continues to be used in wide variety of antibiotics, eye ointment, and other medical supplies.

Here’s why exposure to ethylmercury is nothing to fear:

  1. Since 2001, routine vaccines for children under six no longer contain thimerosal. Teens and adults can also request thimerosal-free vaccines. (The incidence of autism has continued to rise since thimerosal’s removal. This provides strong evidence that thimerosal was not behind the rise in autism.)
  2. The amount of mercury in a thimerosal-containing vaccine is tiny. According to the FDA, “a vaccine containing 0.01% thimerosal as a preservative contains… roughly the same amount of elemental mercury contained in a 3 ounce can of tuna fish.”
  3. Ethylmercury is water soluble, so your body excretes it. Put bluntly, you pee it out. This prevents ethylmercury from building up to harmful levels in your body.

Methylmercury, THe Type in OUr Fish

In contrast to ethylmercury, methylmercury, a bi-product of mercury pollution, is highly toxic.  

Methylmercury  is not water soluble. Your body cannot easily excrete it. Instead it accumulates in our organs. Thus, nearly all of us have some level of methylmercury in our bodies, mainly from eating contaminated fish.

Methylmercury, pregnancy, and the developing brain

Methylmercury is not good for anyone, but it is especially dangerous during pregnancy. The developing brain is especially vulnerable to its toxic effects

Extreme cases of exposure to mercury in utero have led to devastating birth defects. Its toxic effects were first documented among Japanese children living in Minamata City during the 1950s and 1960s, who were exposed to mercury contaminated fish. Iraqi children exposed to a mercury-based fungicide in the early 1970s suffered similar extreme effects, including numbness and vision loss.

Methylmercury is especially toxic to the developing brain. 

Lower levels of mercury have been linked with shortened attention spans, increased hyperactivity, and a below normal IQ. As with lead, there is no known safe level of mercury exposure. The lower, the better.

mercury in fish

What could we do about contaminated fish?

Mercury is a naturally occurring element. But the methylmercury in the fish we eat is not natural. It comes from industrial pollution. In the U.S., power plants are the main source.

It doesn’t have to be this way. Since the 1990s, several industries have cut mercury pollution by over 95%. It’s the stragglers that continue to harm us.

“In 1990, three industry sectors made up approximately two-thirds of total U.S. mercury emissions: medical waste incinerators, municipal waste combustors, and power plants. The first two… have reduced their mercury emissions by more than 95 percent,” according to the EPA.

The methylmercury in the fish we eat does not come from nature. It comes from industrial pollution, mainly power plants that lack modern pollution controls.

Unfortunately, the third sector, power plants, continues to fight tooth and nail against cutting their emissions. They have refused to install modern pollution controls on their older plants, claiming they are too costly.

And they are winning. This year, the Trump administration’s EPA effectively sided with the power plants. The EPA now claims new pollution controls would be overly burdensome, despite the fact that they would generate an estimated $7-9 billion a year in health benefits.

mercury in fish

The irony is painful. A mercury-based preservative once found in traces amounts in vaccines, which was never harmful, caused widespread panic. But mercury pollution contaminating our food supply, which is absolutely harmful, gets a pass.

It makes me want to shout, Hey protesters, look over here!

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About Amy

Amy Kiefer is a researcher by training, and earned her Ph.D. from the University of Michigan. She currently lives in the Bay Area with her husband and three children where she writes about fertility, pregnancy, and breastfeeding. Check out her blog,, for more great evidence-based pregnancy and parenting info.


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