STATNews wrote in Correcting Robert F. Kennedy Jr.’s vaccine ‘facts’:

The human body eliminates ethylmercury from vaccines far more efficiently than it eliminates naturally occurring methylmercury.

Robert F. Kennedy Jr. writes in his book Thimerosal; Let the Science Speak:

While claims have been made that the ethylmercury in Thimerosal is safer than the much better-studied methylmercury, these claims are based on weak, questionable evidence and poorly chosen assumptions. As reviewed in Chapters 4–6 herein, available data suggests that the toxicity of these two forms of mercury is at least comparable, and that ethylmercury may leave the blood more quickly—only to persist more stubbornly in organs and tissues of the body, particularly the brain

In that chapter, he argues on page 87:

The WHO’s conclusion that ethylmercury is safer because of its “short” half-life may be based on observations that ethylmercury disappears from blood samples quicker than methylmercury. This tendency may be evidence not of ethylmercury’s comparative safety, but of its greater danger if, as science has suggested, ethylmercury is not leaving the body but simply migrating more rapidly to the organs, including the brain. Indeed, studies have shown that an ethylmercury compound’s short residence in the blood stems from its ability to more easily pass into the organs, where it can remain for long periods and possibly cause injury

Kennedy cites multiple studies in that chapter, one that he finds particularly important is described on page 92:

A particularly important study in this regard was conducted by the University of Washington’s Thomas Burbacher and was published in 2005. The researchers compared mercury levels in the blood and brains of infant macaques injected with Thimerosal-containing vaccines with monkeys who ingested equal amounts of methylmercury hydroxide via a feeding tube. The former group of primates were exposed to 20 micrograms of ethylmercury per kilogram of body weight on the day they were born and when they were seven, fourteen, and twenty-one days old, which was estimated to be within the range of doses that children at different developmental stages were receiving in the United States.


In general, the primates injected with Thimerosal in the Burbacher study retained twice the level of inorganic mercury—a breakdown product of Thimerosal that has been suggested to be responsible for the brain damage associated with methylmercury—in their brains as the methylmercury-exposed primates.

Is the body better at eliminating ethylmercury than methylmercury as the STATNews article suggests or is Kennedy's description, according to which mercury from ethylmercury accumulates more to the brain more accurate?

  • note: the claim (from the excerpts you included) does not seem to be about the elimination or retention of methy/ethyllmercury (or Thimerosal, which is broken down into ethymercury and Thiosalicate after incorporation), but rather about the retention of (unspecified) other mercury compounds that are purported to be generated from the former
    – bukwyrm
    Jun 20, 2023 at 9:59
  • @bukwyrm : You are right. I adapted the wording of the body a bit. If you have ideas about how to make the question more targeted, feel free to edit it further.
    – Christian
    Jun 20, 2023 at 10:32

1 Answer 1


Yes. Mercury from Ethylmercury (=Thimerosal) is eliminated faster.

In that 2005 paper Burbacher found three times less Hg in the Ethyl-Mercury animals than in the Methyl-Mercury animals (That lower total had a three-times higher prportion of inorganic Mercury, which is what probably got garbled to the 'higher in Ethyl-Mercury animals' claim)

The fact that it is eliminated faster, and that the way it is eliminated (and how the rest is retained) differs substantially from how it works with methylmercury indicates to Burbacher in the 2005 paper that ethyl- and methymercury are not near enough equal to make a risk assessment of one by the other:

The initial and terminal half-life of Hg in blood after thimerosal exposure was 2.1 and 8.6 days, respectively, which are significantly shorter than the elimination half-life of Hg after MeHg exposure at 21.5 days. Brain concentrations of total Hg were significantly lower by approximately 3-fold for the thimerosal-exposed monkeys when compared with the MeHg infants, whereas the average brain-to-blood concentration ratio was slightly higher for the thimerosal-exposed monkeys (3.5 ± 0.5 vs. 2.5 ± 0.3). A higher percentage of the total Hg in the brain was in the form of inorganic Hg for the thimerosal-exposed monkeys (34% vs. 7%). The results indicate that MeHg is not a suitable reference for risk assessment from exposure to thimerosal-derived Hg.

Mercury from brain of Methy-Mercury-dosed animals (note log scale!) From Burbacher 2005

Mercury from brain of Ethyl-Mercury-dosed animals (note log scale is shifted!) From Burbacher 2005

  • So basically, less total Hg in the brain but more inorganic Hg in the brain and thus it's better to see both on their own than to compare them?
    – Christian
    Jun 20, 2023 at 11:02
  • 1
    Much less total and comparable (huge variation) amounts inorganic more like. Methyl-Mercury has much more studies under its belt, so the thinking was that Ethyl-Mercury safety could be structured along those lines. That study showed otherwise. Note also that Methyl-Mercury was given orally, while the Ethyl-Mercury was injected, so the comparison is kinda weird to me (the methyl-mercury studies were mostly oral, though, and the real vaccine with ethyl-mercury is given via injection, so that was the rationalization, still weird.
    – bukwyrm
    Jun 20, 2023 at 11:28
  • They also argue against simplistic ("..just like Methyl-Mercury") ways of (damage-)assessment, i.e patients get their blood tested (because you cannot sample the brain in non-fatal cases...), and practitioners multiply the blood levels (caused here by Ethyl-Mercury) by magic-number-from-Methyl-Mercury-studies to arrive at Mercury content in brain/organs - not adivsed.
    – bukwyrm
    Jun 20, 2023 at 11:33

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