US EPA

4978181 

Journal Article 

Blood and brain mercury levels in infant monkeys exposed to methylmercury or vaccines containing thimerosal 

Burbacher, TM; Shen, DD; Liberato, NA; Grant, KS; Cernichiari, E; Clarkson, T 

2005 

1 

Neurotoxicology and Teratology
ISSN: 0892-0362
EISSN: 1872-9738 

3 

381-382 

English 

Thimerosal is a preservative that has been used in manufacturing vaccines since the 1930s. Reports have indicated that infants can receive ethylmercury (in the form of thimerosal) at or above the EPA guidelines for methylmercury exposure, depending on the exact vaccinations, schedule, and size of the infant. This study compared the systemic disposition and brain distribution of total and inorganic mercury in infant monkeys following thimerosal exposure with infants exposed to methylmercury. Monkeys were exposed to methylmercury (via oral gavage) or vaccines containing thimerosal (via i.m. injection) at birth and 1, 2, and 3 weeks of age. Total blood mercury (Hg) levels were determined 2, 4 and 7 days after each exposure. Total and inorganic brain Hg levels were assessed 2, 4, 7 or 28 days after the last exposure. The initial and terminal half-life of Hg in blood following thimerosal exposure was 2.1 and 8.6 days, which are significantly shorter than the elimination half-life of Hg following MeHg exposure. Brain concentrations of total Hg were significantly lower by ~3-fold for the thimerosal-exposed infants, while the average brain-to-blood concentration ratio was slightly higher for the thimerosalexposed infants (3.5+/-1.0 vs. 2.5+/-0.6). A higher percentage of the total Hg in the brain was in the form of inorganic mercury for the thimerosal-exposed infants (34% vs. 7%). The current study indicates that methylmercury is not a suitable reference for risk assessment from exposure to thimerosal derived Hg. The significance of the higher inorganic Hg levels in the brain should be investigated, since this form of Hg is known to have a very long high-life, over 1 year. Knowledge of the toxicokinetics and developmental toxicity of thimerosal is needed to afford a meaningful interpretation of the developmental effects of thimerosalcontaining vaccines.