What Is Thimerosal? Why Most Vaccines Don't Contain Mercury Anymore

[LiberalArkie]

JUNE 25, 2025

This week the Centers for Disease Control and Prevention’s Advisory Committee on Immunization Practices is meeting to review and vote on several vaccine recommendations. Just in the past week, however, Secretary of Health and Human Services Robert F. Kennedy, Jr., added additional items to the agenda, including a discussion of thimerosal—a mercury-containing compound that is used in some vaccines. Thimerosal has already been removed from all childhood vaccines and detailed research has shown it does not cause neurodevelopmental disorders. The mercury in thimerosal is quickly and easily cleared by the body. Here's how we know and why we still use the compound in some adult vaccines.

WHAT IS THIMEROSAL, AND WHY HAS IT BEEN USED IN VACCINES?
Thimerosal is a preservative that was first added to the manufacturing of vaccines in the 1930s. Because it is a highly effective antiseptic, it can prevent the introduction of fungi or bacteria that could be harmful to inject. By weight, about 50 percent of thimerosal is ethylmercury, a compound that contains mercury. That sounds scary to some people because it’s well understood that mercury can be toxic to the brain. Many people are aware, for example, that eating too much tuna can be unsafe because of how much mercury the fish can contain.

“I think everyone is pretty familiar with the concept that mercury is toxic,” says Ryan Marino, a medical toxicologist at University Hospitals in Cleveland. “The thing that is not conveyed is that there are multiple different forms of mercury with very different toxicities.”

Mercury is ubiquitous in our environment, Marino says, and it arises from both natural and human sources. Volcanoes, forest fires and rock weathering all release mercury into the air, but the vast majority of the element comes from mining, the burning of coal and other fossil fuels and industrial waste.

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https://www.scientificamerican.com/article/what-is-thimerosal-why-most-vaccines-dont-contain-mercury-anymore/

[erronis]

1. Thanks for posting this - important information to counter the scare tactics of the anti-vaxx folks.

More from the article:

How does ethylmercury differ from elemental mercury and methylmercury?

Microorganisms convert inorganic mercury in the environment into the compound methylmercury, which aquatic creatures inadvertently consume. Methylmercury accumulates up the food chain, so apex predators such as sharks, tuna and swordfish have the highest concentrations. That’s why the Food and Drug Administration and the Environmental Protection Agency recommend weekly limits to the consumption of certain fish, particularly such fish consumed by children and pregnant people.

The mercury in thimerosal, however, is ethylmercury, and that one missing letter makes a big difference.

Both molecules include the element mercury, a metal that, in its elemental form, is silver-colored, liquid at room temperature and well known for its use in old thermometers. And both molecules are organic, which means they include carbon atoms. Specifically, ethylmercury’s chemical formula is C2H5Hg+, and methylmercury’s is CH3Hg+. The different numbers of carbon and hydrogen atoms in those molecules mean they have very different properties. To get a sense of the difference a single atom can make, consider that our bodies need—and are mostly made up of—water, or H2O, but if you add another oxygen atom to that molecule, you get H2O2. The latter is hydrogen peroxide, something we definitely should not drink.

Methylmercury is more easily absorbed into neurological tissues and bioaccumulates, or builds up in the body, Marino says. It can cross the blood-brain barrier, and too much of it can result in symptoms ranging from “forgetfulness, irritability and depression all the way to dementia,” he says. The half-life of methylmercury is about 50 to 80 days, so it can remain in the body for nearly four months. But ethylmercury is not absorbed as readily into tissues as methylmercury is. Ethylmercury’s half-life is just three to seven days, so the body removes it within about a week and a half.

“Ethylmercury does not behave in the same way as methylmercury,” Marino says. While too much ethylmercury can also cause poisoning, “the body can clear the amount that’s in vaccines very rapidly. You would have to get hundreds, if not thousands, of vaccines at once” to cause any problems, he says.

[IbogaProject]

2. Thank you

Last edited Fri Jun 27, 2025, 01:11 PM - Edit history (1)

Vaccines are worth the risk as they are. They can still be improved. Some are derived from cell or living animals, the purification of those may have room for improvement. Another thing is the side effects can depend in whether the shot goes into the blood too quick. U Pitt Medical Center had a COVID vaccine based on razor sharp glucose spikes w the target COVID spikes on it. It was to be delivered by patch where it would pierce the skin and get the immune response in the capillaries. This was basically suppressed as U Pitt Med partnered with Moderna on their clinical trial. This cheaper to produce, store and use technology is now sitting unused and unable to be used do to our patent and business system allowing for inventions to be suppressed as opposed to the constitution's stated reason for patents.

"To promote the progress of science and useful arts, by securing for limited times to authors and inventors the exclusive right to their respective writings and discoveries."