Comparison of Blood and Brain Mercury Levels in Infant Monkeys Exposed to Methylmercury or Vaccines Containing Thimerosal

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http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1280342

Recent

publications have proposed a direct link between the use of

thimerosal-containing vaccines and the significant rise in the number of

children being diagnosed with autism, a serious and prevalent developmental

disorder (for review, see IOM

2001). Results from an initial IOM review of the safety of vaccines found

that there was not sufficient evidence to render an opinion on the relationship

between ethylmercury exposure and developmental disorders in children (IOM

2001). The IOM review did, however, note the possibility of such a

relationship and recommended further studies be conducted. A recently published

second review (IOM

2004) appears to have abandoned the earlier recommendation as well as

backed away from the American

Academy of Pediatrics

goal. 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.

The key

findings of the present study are the differences in the disposition kinetics

and demethylation rates of thimerosal and MeHg. Consequently, MeHg is not a

suitable reference for risk assessment from exposure to thimerosal-derived Hg.

Knowledge of the biotransformation of thimerosal, the chemical identity of the

Hg-containing species in the blood and brain, and the neurotoxic potential of

intact thimerosal and its various biotransformation products, including

ethylmercury, is urgently needed to afford a meaningful interpretation of the

potential developmental effects of immunization with thimerosal-containing

vaccines in newborns and infants. This information is critical if we are to respond

to public concerns regarding the safety of childhood immunizations.