Feb 04 2008

Mercury Excretion in Infants

Blogging on Peer-Reviewed ResearchA new toxicological study adds to the growing evidence that the mercury-based vaccine preservative, thimerosal, is safe for use in children. I have blogged frequently about the myth that vaccines in general or thimerosal in vaccines is linked to autism. Last week I discussed that new evidence is allowing for the diagnosis of autism at a younger and younger age – potentially all the way back to birth – thereby falsifying the contention that vaccines are a cause of autism. I have also recently discussed that the removal of thimerosal from childhood vaccines in the United States did not result in a decrease in new autism diagnoses, as would be predicted if thimerosal caused or even contributed to autism rates. Meanwhile research is teaching us more and more about autism as a genetic disorder. Therefore epidemiological, historical, clinical, and genetic evidence is all pointing to the firm conclusion that thimerosal and vaccines generally are not a cause of autism or other neurological disorders.

While at present there is no significant scientific debate on this conclusion, there is an ongoing public debate driven mostly by ideological groups who have an anti-vaccine agenda. These groups rely upon increasingly implausible and desperate rationalizations, conspiracy mongering, and simply bad logic. But they have also based many of their arguments on a separate line of scientific evidence, that of toxicology – studying the effects of mercury and thimerosal on cells and in the body. In fact it is increasingly looking as if toxicological evidence will be the last stand for the “mercury militia” on this issue.

The reason for this is simple – mercury is a neurotoxin. No one denies that. Proponents of the thimerosal-autism hypothesis essentially argue that we can know that thimerosal causes autism because it is toxic to the brain, or at least we should assume that unless and until we prove beyond doubt that it is not toxic. This of course is an impossible standard and also we know the result of this question, mercury is a toxin.

But this arguments misses two key points. The first is that toxicological evidence can never answer the question of whether or not a substance actually did cause harm. In this respect epidemiological evidence trumps toxicological evidence – and all the epidemiological evidence says that thimerosal is not linked to any harm.

The second point is that toxicity is all about dose – any substance is safe in a small enough dose and anything is toxic (even oxygen, even water) in a high enough dose. What the anti-vaccine mercury militia has not demonstrated is that the mercury found in thimerosal is toxic at the doses given in vaccines. Related to the question of dose is that of access – is the toxin in question getting exposed to brain cells in a sufficient dose to cause neurotoxicity? Sure, mercury damages brain cells when you pour it on top of neurons in a petri dish, but this does not necessarily mean that thimerosal in vaccines causes a sufficient exposure of mercury to brain cells in people to cause toxicity. Because the epidemiological evidence shows no connection to autism, the assumption has been that the dose of mercury in vaccines is too small and it is cleared too quickly from the body for it to cause any measurable toxicity.

This brings us to the current study, which looked at blood, stool, and urine levels of mercury in children following their newborn, 2 month old, and 6 month old vaccinations. The study was performed in Argentina because, as I have said, thimerosal has been removed from all routine childhood vaccines in the US. The study, conducted by lead author Michael Pichichero from the University of Rochester, is titled: Mercury Levels in Newborns and Infants After Receipt of Thimerosal-Containing Vaccines and is published in this month’s issue of Pediatrics. They calculated the half-life of mercury in the blood of 72 healthy children in each age group and found that the mean half-life (the time it takes for half of remaining mercury to be cleared from the blood) is 3.7 days, without a significant difference between the age groups. Levels of mercury in the blood returned to pre-vaccination levels in about 30 days. These results are significant for various reasons.

First we need to know that there are various types of organic mercury, the two most important being methyl mercury (the type found in certain fish) and ethyl mercury (the type found in thimerosal). Methyl mercury is more toxic than ethyl mercury and is cleared more slowly, but data on the exact clearance rate for ethyl mercury was lacking. For this reason when calculating safety limits for human exposure the higher toxicity and slower clearance rates for methyl mercury were assumed. The half life of methyl mercury is about 30 days. This means that ethyl mercury (at least in young children, it is probably slower for adults) is cleared about 10 times more quickly than was previously assumed.

This is critical because the argument made for the potential toxicity of thimerosal was based upon the cumulative dose of ethyl mercury of all childhood vaccines. The argument was that ethyl mercury was building up from vaccine to vaccine, and that even if the dose from a single vaccine were safe the cumulative dose is what was toxic. This new study shows fairly conclusively that all the ethyl mercury given in one vaccine will be cleared by the time the next vaccine is due to be given – so their is no build-up, no cumulative dose. This effectively shoots down the last remaining scientific argument of the mercury militia.

The authors also noted that the levels of mercury they measured in the blood were generally low, writing:

We also observed that the highest levels in samples that were taken from children shortly after vaccination were <=8 ng/mL. The importance of blood levels of ethyl mercury for assessing toxicity is unknown, but blood levels have been shown to be a predictor of toxicity for methyl mercury exposure. The low levels of mercury detected in this study suggests relatively low risk for toxicity from this exposure.

But there are still unanswered questions, some legitimate and some desperate. The authors of the current study acknowledge the limitations of their evidence. They measured mercury levels in the blood, but did not separate methyl mercury from ethyl mercury. However, if anything this would tend to overestimate the amount of ethyl mercury remaining in the blood. They also measured mercury in the stool and urine. After vaccination mercury levels in the stool also rose and then slowly cleared, suggesting that the ethyl mercury from vaccines is primarily cleared by the liver and deposited into the feces. Levels did not significantly rise in the urine, which suggests that the kidneys are not a significant mode of clearance of ethyl mercury.

However, another possible interpretation of this evidence is that mercury was cleared from the blood but was not all directly cleared by the liver. Instead it rapidly spread to another compartment in the body (such as fatty tissue), and then was cleared from this second compartment by the liver. This is less likely given the rapidity with which mercury appeared in the stool, but it is not ruled out by this current study. A follow up study is required, one that will not only measure spot levels in the urine and stool but will examine 24 hour samples so that the actual amount of ethyl mercury that is being removed from the body can be estimated. This will better track where all the mercury is going and will help rule out the possibility that it is hiding for a time in another compartment of the body (and therefore not measured in the blood).

This is unlikely to change the ultimate conclusions of this study, but science works by considering all possibilities and then conducting experiments to eliminate all alternatives until the one true answer is all that remains.

The response from the mercury militia is predictable. They will claim, as they have in the past, that the average clearance of ethyl mercury in children may be rapid, but that certain individual children genetically have impaired mercury clearance. For these individuals the ethyl mercury from thimerosal will build up in the body from vaccine to vaccine, causing toxicity. At present there is no compelling evidence for this. I will also note that in the present study there were no individual children who had significantly different clearance than the average – no outliers with impaired mercury clearance – but the numbers of children in the study were too small to rule this out as an uncommon occurrence.

In conclusion, the toxicological evidence is moving in line with the epidemiological and other independent lines of evidence toward the conclusion that thimerosal given in childhood vaccines is not a contributor or cause of autism or other neurological disorder. There are more studies to be done, but there always are – science is a messy and complex business. But it is reassuring to know that children clear ethyl mercury 10 times more quickly than was previously assumed, and that levels do not build up from vaccine to vaccine. At least it is reassuring to those of us who look at all the evidence to formulate our opinions.

14 responses so far

14 thoughts on “Mercury Excretion in Infants”

  1. ellazimm says:

    Clear, concise, informative and therapeutic (for you) after the Super Bowl?

    Anyway, thanks again for keeping us informed. The Wakefield ripples still occur in England and I like to be able to bring some data to dinner table conversations. In a couple of years it might be worth having someone publish a handbook or pamphlet with all the pertinent research for distribution by GPs.

  2. mattdick says:

    It’s amazing the amount of effort that is being required for the mercury militia folks to get the message. You can’t argue that they are insincere in their dedication to finding the cause for Autism. So why can’t they see that their energies can be so much better spent elsewhere?

    Imagine if they turned their energies toward gene therapy, or earlier diagnosis? What a great militia they would then become!

  3. ellazimm says:

    mattdick: I was going to say it’s too bad we can’t figure out a way to make money out of cognitive dissonance but I think it’s already been done: alcohol.

  4. jeanruss says:

    A good review of this topic and the junk science of this study can be found at jonbarron.com. As more parents learn, as I did, how damaging vaccines can be, they will be increasingly reluctant to donate their children’s health to science.

  5. Jon Barron is hardly a reliable source – he is just trying to sell his own quack detox programs. So he directly profits from the bad science he is selling.

    He wrote:
    “Just because blood levels of mercury drop doesn’t necessarily mean that the mercury has been excreted from the body — only that it has left the bloodstream.

    * Shame on the doctors for using such faulty logic to reach their conclusions.
    * Shame on the vaunted peer review process for allowing such blatantly faulty logic to go unnoticed
    * Shame on Forbes, Associated Press, Science Daily, and the more than 200 other news outlets that have already published the results of the study without challenging the absurdity of its logic. Hey, no medical knowledge is required to figure this out — just simple logical. You’re supposed to be reporters — not shills.”

    Apparently Jon Barron – who wants to chelate the mercury out of you – either did not actually read the study or just doesn’t care about the facts as long as he can sell his products. Urine mercury was measured, although levels did not rise significantly. But he does not mention that stool mercury was measured and the level of mercury rose and fell in the stool just as it did in the blood. This strongly suggests that at least some of the mercury is being excreted in the stool.

    Also – the study authors honestly discussed the limitations of their study, that only spot levels were done and not 24 hour levels, and a future study looking at 24 hour stool mercury excretion would account in more detail for how much of the mercury is being excreted. They also specifically discussed the 2-compartment hypothesis – that the mercury leaving the blood does not necessarily mean it’s leaving the body. That means that Jon Barron is a dishonest crank. He criticizes reporters for shilling for Big Pharma meanwhile he is shilling for his own quack nostrums.

  6. Scotty B says:

    “This will better track where all the mercury is going and will help rule out the possibility that it is hiding for a time in another compartment of the body (and therefore not measured in the blood).”

    Would it be possible to put a radioactive “tag” on the Thimerosal molecule to track where it goes in other apes?

  7. Steve Page says:

    Great article Dr S, but unfortunately, the vaccine-as-cause-of-autism group (I tried to think of an acronym that spent MENTAL but I’ve had too much Famous Grouse) will ignore it and continue unabated. The poster above yours, jeanruss, is a typical example; ignore the study, ignore the evidence, find someone to blame for your misfortune.

    I don’t mean to sound hard; my brother has Asperger’s Syndrome, so I have spent a great deal of time examining autistic spectrum disorders (ASD) and the conclusion that I’ve reached is that ASDs are nothing to do with vaccines. I’m not looking for anyone to blame though, so my conclusion will undoubtedly be different from those who are.

  8. _Arthur says:

    Apropos of Jon Barron speculation, if the hidden mercury is not in the blood, how is chelation supposed to remove it ?

    Can the chelating agent reach into, say, fatty deposits ?
    As far I can figure it out chelation would mostly remove mercury from the blood, if any.

  9. healthman says:

    Numerous studies have shown that not all mercury leaves in the urine and feces. Sizeable amounts stay behind in body tissue–particularly brain tissue–and it’s cumulative. As a neurologist, Dr. Novella, you would know this. It’s very confusing that you “seem” to be implying that all of the mercury your body takes in is quickly eliminated in the urine and feces.


    Are you saying that these studies, and all of the others that come to similar conclusions, are wrong?

    And chelation (this is the term the medical community uses) is not quackery. It is the standard medical treatment for mercury toxicity, with charcoal (one of the “nostrums” you refer to) recommended as one of the treatments for removing mercury from GI tissue.


  10. healthman – Your links do not support your position. The first two links deal with methyl or inorganic mercury, not ethylmercury (the kind found in thimerosal and the subject of this study). The third study shows that methylmercury is not a good model for ethylmercury, and further only looked at tissue levels out to 7 days. Also, the amount of mercury that found it’s way into the brain was 0.22% – hardly a “sizeable amount.”

    This current study looks at the half-life of ethylmercury from vaccine injections in actual human infants. That half-life suggests that the total amount of mercury returns to pre-vaccine levels at 30 days.

    I am not saying the studies you reference are wrong. I am saying you are cherry picking and misinterpreting those studies. Here is a 2014 study calculating half-life of mercury from thimerosal in mice: (http://www.ncbi.nlm.nih.gov/pubmed/?term=ethylemercury%2C+half-life%2C+brain+tissue)

    “Estimated half-lives (in days) were 8.8 for blood, 10.7 for brain, 7.8 for heart, 7.7 for liver and 45.2 for kidney. Taken together, our findings demonstrated that TM (etHg) kinetics more closely approximates Hg(2+) than methylmercury (meHg) while the kidney must be considered a potential target for etHg toxicity.”

    10.7 day half-life for brain tissue. So yes – when you look at all the available evidence it suggests that any mercury from one set of vaccines should be entirely cleared before the next scheduled vaccines – if, that is, vaccines still contained mercury, which they don’t.

    I also never said that chelation therapy was not legitimate. I have written elsewhere that it is a perfectly legitimate treatment for actual heavy metal poisoning. It is quackery when used to treat conditions that are not heavy metal poisoning.

  11. healthman says:

    Dr. Novella:

    You accuse me of cherry picking studies, but, in fact, there have been a number of studies over the years, including several recent studies, that conclude that ethylmercury does not clear the brain as completely or as quickly as you imply—and they are very specific in their conclusions. For example, the 2013 meta-review in Current Medicinal Chemistry states, “Mercury load in fetuses, neonates, and infants resulting from Thimerosal-containing vaccines remains in blood of neonates and infants at sufficient concentration and for enough time to penetrate the brain and to exert a neurologic impact and a probable influence on neurodevelopment of susceptible infants.” Such study conclusions really don’t require much “interpretation.” They are quite explicit.

    N Am J Med Sci. 2014 Oct;6(10):519-31 http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4215490/

    Curr Med Chem. 2013;20(32):4060-9. http://www.ncbi.nlm.nih.gov/pubmed/23992327

    Also, your statement that vaccines no longer contain mercury is only half true. Yes, it is true that vaccines specifically targeted for children no longer contain mercury, but it appears that you are unaware that several versions of the flu vaccine, which is strongly recommended for children, do indeed still contain Thimerosal. http://www.cdc.gov/flu/protect/vaccine/thimerosal.htm.

    The bottom line is that given the facts that (a) mercury is a known neurotoxin, (b) children are more susceptible to its effects than adults, (c) there is at least some evidence that ethylmercury does indeed have an affinity for brain tissue, how can you justify using it in any vaccine that would be administered to children? Perhaps in your desire to counter the people who conflated Thimerosal and autism you ended up overstating your. Let’s dismiss the Thimerosal/Autism theory. I agree that there is little to no evidence to support it. But that doesn’t mean that Thimerosal isn’t harmful in other ways long term when administered repeatedly to children. And considering that there are preservatives that don’t use mercury, defending its use in any vaccine that might be given to children seems to be a case of defending the undefendable.

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