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"Mercury concentrations and metabolism in infants receiving vaccines containing thiomersal: A descriptive study"
The Lancet, Michael Pichichero, MD (November 2002)


One of the sillier studies ever performed, and the lead author is a vaccine patent-holder, no less. Absurd that this study appears on lists of studies exploring the relationship of vaccines to autism, as it doesn't even address the topic. More absurd is the author's complete misunderstanding of how mercury is excreted from the body. A laughable study written by an author as conflicted as the Marlboro Man would be studying cigarettes.

Actual Question This Study Asked & Answered:

Q: Do Thimerosal containing vaccines administered to children raise mercury blood levels above safe standards?

A: No.

Did the study look at unvaccinated children?


Conflict of Interest (from the study itself):

"The investigation was funded by the US National Institutes of Health (NIH)."

From the lead author's website:

"Dr. Pichichero was a member of the discovery team at the University of Rochester that invented, tested and licensed a Haemophilus influenzae b (Hib) conjugate vaccine (HibTITER®) now universally given to children in the U.S. [he makes vaccines, but didn't report as a conflict]"

From other studies the lead author has written:

"The author has received research grants and/or honoraria from the following pharmaceutical companies: Abbott Laboratories, Inc.; Bristol Myers Squibb Company; Eli Lilly & Company; Merck and Co.; Pasteur Merieux Connaught; Pfizer Labs; Roach Laboratories; Roussel-Uclaf; Schering Corporation; SmithKlineBeecham Pharmaceuticals; Upjohn Company; Wyeth-Lederle.

Ability to Generalize:

None. The study has nothing to do with the relationship between vaccines and autism.

Post-Publication Criticism:

Very high.

Scoring (Out of 40 possible points):

Asked the Right Question: 0

Ability to Generalize: 0

Conflict of Interest: 0

Post-Publication Criticism: 0

Total Score: 0

Choice Excerpt from the Study:

"Most of the toxic effects of organic mercury compounds take place in the central nervous system, although the kidneys and immune system can also be affected. Organic mercury readily crosses the blood-brain barrier, and fetuses are more sensitive to mercury exposure than are children or adults...No toxic effects of low-dose exposure to thiomersal in children have been reported. The effect of the small amounts of mercury contained in vaccines on concentrations of mercury in infants' blood has not been extensively assessed, and the metabolism of ethylmercury in infants is unknown."


"It's really hard to write a study that somehow implies injecting mercury in infants is safe, but I'm going to try by arguing that 'small' amounts are safe, even though I know its never been studied."

Guest Critic #1: Dr. Thomas Burbacher, Ph.D

Dr. Thomas Burbacher release a study looking at mercury levels in the brains of primates and reached a simple conclusion: ethyl-mercury leaves the blood quickly because it heads to the brain.

From WebMD:

One of the few researchers who studies the effects of ethyl mercury is Thomas Burbacher, PhD, professor of environmental and occupational health sciences and director of the infant primate research lab at the National Primate Research Center, University of Washington, Seattle. Burbacher's studies of ethyl mercury and thimerosal in primates are cited by both sides of the thimerosal debate.

Burbacher says that just because ethyl mercury is gone from an infant's blood soon after it receives a dose of thimerosal -- a half-life of just 3.7 days in the Pichichero study -- doesn't mean it's gone from the body.

"Just because it came out of the blood doesn't mean it is excreted from the body. It could have gone to the brain," Burbacher tells WebMD. "Although total mercury levels in the blood are lower following thimerosal exposure [than following methyl mercury exposure], mercury in the blood from thimerosal has an easier time getting to the brain than methyl mercury."

Summary of Burbacher's study:

Comparison of Blood and Brain Mercury Levels in Infant Monkeys Exposed to Methylmercury or Vaccines Containing Thimerosal.
Environmental Health Perspectives, Aug 2005.
Thomas Burbacher, PhD [University of Washington].

This study demonstrates clearly and unequivocally that ethyl mercury, the kind of mercury found in vaccines, not only ends up in the brain, but leaves double the amount of inorganic mercury as methyl mercury, the kind of mercury found in fish. This work is groundbreaking because little is known about ethyl mercury, and many health authorities have asserted that the mercury found in vaccines is the "safe kind." This study also delivers a strong rebuke of the Institute of Medicine's recommendation in 2004 to no longer pursue the mercury-autism connection. Excerpt:

"A recently published IOM review (IOM 2004) appears to have abandoned the earlier recommendation [of studying mercury and autism] as well as back away from the American Academy of Pediatrics goal [of removing mercury from vaccines]. This approach is difficult to understand, given our current limited knowledge of the toxicokinetics and developmental neurotoxicity of thimerosal, a compound that has been (and will continue to be) injected in millions of newborns and infants."

Guest Critic #2: Mark Blaxill and Boyd Haley, Ph.D., letter to the editor of Lancet

Infant stool eliminates vaccinal mercury slowly suggesting high retention in tissue

To the editor,

In a study in The Lancet, Pichichero et al 1 argued that ethylmercury administered to infants through vaccines is eliminated rapidly from the blood and effectively excreted in stool. Our analysis of this data, combined with a more recent analysis2 of mercury excretion in baby hair suggests a more worrisome interpretation, one that offers support for the hypothesis3 linking early mercury exposures with autism.

Our calculations suggest that Pichichero et al. overstated the significance of their excretion findings. Although their data support a rapid rate of ethylmercury elimination from blood, instead of similarly rapid stool elimination, their findings demonstrate slow stool excretion in many infants, suggesting that significant amounts of ethylmercury from vaccines may be retained in infant tissue.

Most methyl mercury is eliminated from the body through stool and ethyl mercury from vaccines most likely follows the same path. Both mercury species must pass out of the blood to allow excretion in feces or (in lesser amounts) hair. 4 Nevertheless elimination from blood also allows for mercury transport into tissue, without prompt excretion. Our analysis of mercury excretion in autistic and control baby hair demonstrated that, although mercury was excreted at high rates in hair of normal infants, hair of autistic infants contained very little mercury, only 0.47 mcg/g versus 3.63 mcg/g in controls. This finding raises the possibility of increased mercury retention in the tissue of autistic infants, who also had higher rates of prenatal mercury exposure.

Pichichero et al provide data specific to infant mercury excretion through feces. They measured mercury concentrations in stool of 22 normal infants exposed to thimerosal in vaccines, ages two and six months, and found a range of 23-141 nanograms of mercury per gram of stool (dry weight). The authors interpreted these levels, mere parts per billion, as positive evidence of mercury elimination.

But these mercury concentrations are extremely low, not nearly enough to allow rapid excretion. Infant dry weight stool volumes have been measured at between 1-3 grams per kilogram (kg) per day.5 Based on the 50th percentile weight progression from 3.5-8 kg in the zero-six month period, infant stool volumes may be expected to range from 6-18 grams (dry weight) per day. Taking the stool concentration range for mercury from Pichichero et al, we calculated the time required for an infant to excrete the ethylmercury (187.5 mcg) that U.S. infants received by six months of age during the 1990s.

Stool Hg concentration Daily Hg excretion Days to excrete 187.5 mcg

(ng/g) (mcg/day) (days)

Minimum: 23 0.14-0.41 457-1,339
Maximum: 140 0.84-2.52 74-223

In the case of maximum excretion, early vaccine exposures are eliminated within the time period of exposure, but for those children with stool concentrations at the low end of the range, the infant elimination rate rises to nearly four years. For autistic infants, with evidence of reduced excretion in hair and additional fetal exposures2 (from maternal amalgam filling, fish consumption and Rho D immunoglobulin injections) these excretion times were likely far longer.

Our analysis contradicts the optimism expressed by Pichichero et al and suggests that low mercury excretion rates in some infants may underlie the link between mercury exposures and autism.

Mark F. Blaxill
Director, Safe Minds

Boyd E. Haley, PhD
Professor of Chemistry and Department Chairman
University of Kentucky


1. Pichichero ME, Cernichiari E, Lopreiato J, Treanor J. Mercury concentrations and metabolism in infants receiving vaccines containing thiomersal: a descriptive study. Lancet. 2002;360(9347):1737-1741

2. Holmes AS, Blaxill MF, Haley BE. Reduced levels of mercury in first baby haircuts of autistic children. Int J Toxic. 2003;111(4):277-285

3. Bernard S, Enayati A, Redwood L, Roger H, Binstock T. Autism: a novel form of mercury poisoning. Med Hypotheses. 2001;56:462-471

4. Clarkson TW. The three modern faces of mercury. Environ Health Perspect. 2002;110 Suppl 1:11-23

5. Chou C, Studies on the use of soybean food in infant feeding in China and the development of formula 5410. Food Nutr Bull. 1983;5(1) :10-11 - Contents

Guest Critic #3: SafeMinds Press Release

Safe Minds and Mercury Policy Project Statement on "Mercury concentrations and metabolism in infants receiving vaccines containing mercury: a descriptive study"

Washington, DC, Nov. 29 -/E-Wire/-- According to Safe Minds and Mercury Policy Project, few, if any, definitive conclusions can be drawn from this latest thimerosal study.

"An initial analysis of the Pichichero et al. study of blood mercury concentrations in infants after vaccination with thimerosal-containing vaccines clearly demonstrates that this is a poorly designed study", said Sallie Bernard, president of Safe Minds.

Nevertheless, in the article and accompanying commentary, the authors make the following sweeping statements:

  1. "Overall, the results of this study show that amounts of mercury in the blood of infants receiving vaccines formulated with thiomersal are well below concentrations potentially associated with toxic effects."
  2. "Administration of vaccines containing thimerosal does not seem to raise blood concentrations of mercury above safe values in infants."

"This study gives comforting reassurance about the safety of ethyl mercury as a preservative in childhood vaccines."

"This report looks very much like agenda research and not an unbiased study," said Michael Bender of the Mercury Policy Project.

According to the groups, these statements cannot be supported by the study design and results, for the following reasons.

  1. The blood mercury concentrations found in the study are not necessarily below the established safety limits: the authors cite a 1994 study by Grandjean to provide a safety level for methylmercury of 29 ppb (parts per billion) and state that this level is ten times lower than the mercury level needed to see a decrease in cognitive performance in children. However, this comparison does not utilize the latest safety data research. In 1998, Grandjean published an article (Grandjean et al., "Cognitive performance of children prenatally exposed to "safe" levels of methylmercury", Environmental Research, 1998) in which he rejected the conclusions of his earlier research and found performance declines when the average cord blood mercury concentration was 59 ppb. His later study was validated as the "gold standard" by the National Academy of Science in their 2000 report "Toxicological Effects of Methylmercury" in which they found that the lowest dose for which adverse neurological effects are found is when cord blood is 58 ppb. In the Pichichero study, there was one infant out of 33 (3%) in which blood mercury was measured who has a mercury concentration of 20.55 ppb. This infant was exposed to 37.5 micrograms of mercury, and the blood draw was taken on day 5. The authors state that the half life of ethylmercury is probably about 6-7 days. Thus, this infant's peak mercury concentration would be much higher than 20.55 ppb. Many infants in the 1990s were exposed to 62.5 micrograms of mercury at age 2 months, or nearly double what the study infant recieved. Therefore, it is probable that the blood levels of some infants given the full regimen of thimerosal vaccines in the 1990s would exceed the 58 ppb threshhold for adverse effects. THerefore, the results from the Pichichero study can hardly be seen as "reassuring" to any parent.
  2. Samples of blood were taken at various time points after exposure, but each study subject only had one apparent blood draw. Standard study design for a parmacokinetic study, even a simple one, is to obtain multiple draws from each subject. Otherwise, it is not possible to make definitive statements about distribution, elimination, and half life, which this study seems to do.
  3. The reference point that they use to establish safety levels for thimerosal is methylmercury, a different compound than the ethylmerucry in thimerosal. Simply because a compound is similar does not mean it is as safe. A good example is thalidomide, a sedative drug that was prescribed to pregnant women from 1957 into the early 60's. It was present in at least 46 countries under different brand names. When taken during the first trimester of pregnancy, Thalidomide prevented the proper growth of the foetus, resulting in horrific birth defects in thousands of children around the world. The reason is the Thalidomide molecule is chiral, with left and right-handed versions. The drug that was marketed was a 50/50 mixture. One of the molecules was a sedative, whereas the other was found later to cause foetal abnormalities. The tragedy could have been avoided had the physiological properties of the individual thalidomide [molecules] been tested prior to commercialization. Molecules that look almost exactly alike can behave very differently. The FDA is very rigid about testing the precise molecule being approved.
  4. The conclusions are based on blood draws from 33 exposed children, which is a small sample upon which to draw far reaching conclusions. It is also a convenience sample without random assignment of subjects and not even an attempt to make sure that comparison groups were age-sex matched.
  5. There was variability in the thimerosal doses given, and little attempt to incorporate dose differences in the half life model or safety assessment.
  6. With a claimed half life of 6-7 days, it is remiss that there is no collection within 3 days of exposure, when peak mercury levels would be obtained. It would be impossible to make any conclusions about safety without these measures.

For these reasons alone, Safe Minds and the Mercury Policy Project believe that the conclusions of this study should not be used in deliberations of thimerosal safety. Rather, more and better research is needed.

SOURCE: Mercury Policy Project
CONTACT: contact Sallie Bernard, Safe Minds