| Comparison of Blood and Brain Mercury Levels in Infant Monkeys Exposed to Methylmercury or Vaccines Containing Thimerosal Thomas M. Burbacher,1,2,3 Danny D. Shen,4 Noelle
Liberato,1,2,3 Kimberly S. Grant,1,2,3 Elsa Cernichiari,5 and
Thomas Clarkson5 1Department of Environmental and Occupational Health Sciences, School
of Public Health and Community Medicine, 2Washington National Primate
Research Center, 3Center on Human Development and Disability, and 4Departments
of Pharmacy and Pharmaceutics, School of Pharmacy, University of Washington,
Seattle, Washington, USA; 5Department of Environmental Medicine,
University of Rochester School of Medicine, Rochester, New York, USA Abstract
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 U.S. Environmental Protection Agency guidelines for methylmercury exposure, depending on the exact vaccinations, schedule, and size of the infant. In this study we compared the systemic disposition and brain distribution of total and inorganic mercury in infant monkeys after thimerosal exposure with those exposed to MeHg. Monkeys were exposed to MeHg (via oral gavage) or vaccines containing thimerosal (via intramuscular injection) at birth and 1, 2, and 3 weeks of age. Total blood 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 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. Knowledge of the toxicokinetics and developmental toxicity of thimerosal is needed to afford a meaningful assessment of the developmental effects of thimerosal-containing vaccines. Key words: brain and blood distribution, elimination half-life, ethylmercury, infant nonhuman primates, methylmercury, thimerosal. Environ Health Perspect 113: 1015-1021 (2005) . doi:10.1289/ehp.7712 available via http://dx.doi.org/ [Online 21 April 2005]
Address correspondence to T.M. Burbacher, Department of Environmental and Occupational Health Sciences, 1705 NE Pacific St., Health Sciences Building (F555) , School of Public Health and Community Medicine, University of Washington, Seattle, WA 98195 USA. Telephone: (206) 685-1862. Fax: (206) 685-4696. E-mail: tmb@u.washington.edu We thank the staff of the Infant Primate Research Laboratory for their cooperation during this study and D. Blough for his assistance with statistical analyses. We also thank J. Treanor from the University of Rochester for supplying the vaccines used in the study. This project was supported by funds from the National Institutes of Health, grants RO1ES03745, P51HD02274, P51RR00166, P30ES07033, and NO1-A1-25460. The authors declare they have no competing financial interests. Received 2 November 2004 ; accepted 20 April 2005. The full version of this article is available for free in HTML or PDF formats. |
