Thomas Burbacher

Thomas Burbacher, PhD, is an associate professor of environmental and occupational health sciences and the director of the Infant Primate Research Laboratory at the University of Washington in Seattle. Burbacher is best known for his research into alterations in primate brain development and function triggered by prenatal exposure to neuroactive substances. His research garnered significant media attention in 2005, when he reported that the neurotoxic effects of ethylmercury, used as a preservative in thimerosal containing vaccines (TCVs), potentially could cause more serious damage to the developing nervous system of children than previously believed.

Education
Burbacher earned his bachelor's degree in psychology from the University of Cincinnati in 1973, and his doctorate from the University of Washington in 1983, also in psychology.

Research
Burbachers research interests include behavioral toxicology and the neurodevelopmental effects of pre- and postnatal exposure to environmental contaminants, including pesticides and heavy metals. His studies using primate models have revealed significant long-term effects of prenatal exposure to methylmercury, a common neurotoxin, and to methanol, a potential motor fuel alternative. In-utero exposure to methylmercury has been linked to mental retardation, sensory disturbances such as blindness and deafness, and significant delays in motor development.

Infant Primate Research Laboratory
Over one hundred monkeys reside at the University of Washington's Infant Primate Research Laboratory (IPRL), where Burbacher and other researchers conduct some of the world's most expensive and exclusive medical research. "It's one of the only facilities in the country where we can observe animals as they mature from infancy," said Thomas Burbacher

Burbacher studied a group of macaque monkeys, from birth to sixteen years of age, to evaluate near- and long-term effects of in-utero methylmercury exposure on physical development, cognition, and sensory function. The similarity of macaque monkey DNA to that of humans, 92% identical, makes them useful as models of the human body and brain. Burbacher's research on macaques has been used in the development of safety policies aimed at setting maximum human exposure levels for environmental contaminants associated with adverse health effects and developmental disabilities.

Differing effects of ethylmercury in thimerosal containing vaccines
In 2005, a study Burbacher conducted confirmed that thimerosal is distributed to the brain much more readily than methylmercury, and he is now working on a follow-up project will examine the effects of the vaccine preservative on primate development. Burbacher's primate studies, funded by the National Institute of Health (NIH), have included comparisons of the effects of injected ethylmercury, the primary active ingredient in thimerosal, to those of orally administered methylmercury on macaques. His research sought to determine whether federal safety limits for methylmercury exposure are a suitable reference for assessing the effects of ethylmercury found in thimerosal containing vaccines (TCVs). His research revealed significant differences between methyl- and ethylmercury metabolism., ,

Burbacher determined that injected ethylmercury cleared from the bloodstream much more rapidly than ingested methylmercury. However, his study also found that a larger fraction of the ethylmercury remained in the brains of the macaques, where it was converted to potentially more harmful inorganic compounds. Burbacher did not draw conclusions regarding the relative toxicity of ethylmercury versus methylmercury, but did warn that methylmercury is unlikely to be a suitable reference for evaluating ethylmercury toxicity. The problem, according to Burbacher, is that regulators trying to assess the potential harm of TCVs used methylmercury, a widely studied compound, as a benchmark for mercury exposure, rather than the little-known compound called ethylmercury used in TCVs.

Burbacher has said "The bottom line is that trying to assess the effects of a compound with very little or no data is not a good thing to do. ... Unfortunately, we started doing studies on this compound way too late. Basic information like this should've been available decades ago."

Publications

 * Thomas M. Burbacher, Danny D. Shen, Noelle Liberato, Kimberly S. Grant, Elsa Cernichiari, and Thomas Clarkson, "Comparison of Blood and Brain Mercury Levels in Infant Monkeys Exposed to Methylmercury or Vaccines Containing Thimerosal", Environmental Health Perspectives, vol 113, no 8, August, 2005