MOUNTING EVIDENCE LINKS MERCURY, NEUROLOGICAL IMPAIRMENT

Many children have elevated mercury levels because they live near mercury- emitting industrial plants, eat diets high in mercury-containing fish, or have been exposed to medications and vaccines containing mercury. Mounting evidence indicates that these children are at increased risk of brain impairment and associated learning and behavior problems.

At a 2005 Congressional policy meeting, Susan West Marmagas of Physicians for Social Responsibility summarized research findings about methylmercury (the form of mercury that contaminates fish), saying that "exposure to methylmercury in the womb can cause adverse developmental and cognitive effects in children, even at low doses that do not result in effects in the mother.... Recent epidemiologic studies have [also] found that children exposed to even low levels of mercury before birth experience subtle symptoms of neurologic damage. Specific effects include poor performance on neuro- behavioral tests, particularly on tests of attention, fine motor function, language, visual-spatial abilities (e.g. drawing) and memory."

In research published last year, Philippe Grandjean et al. followed up on children involved in a long-term study in the Faroe Islands. Many children in these islands, off the coast of Denmark, are exposed to high levels of methylmercury because their diet is high in meat from pilot whales. An earlier study of the children when they were 7 years old, reported in 1998, found that "increased prenatal mercury exposure was associated with deficits in several brain functions including attention, language, verbal memory, spatial function and motor speed."

In their 2004 follow-up, Grandjean and colleagues evaluated the same children at age 14. The researchers' evaluation included brainstem auditory evoked potential (BAEP) testing, which measures the brain's electrical response to a stimulus—in this case, a signal transmitted from the acoustic nerve through several "relays" to the brainstem. In children exposed to higher levels of prenatal mercury, the researchers found, this response lagged significantly compared to the response of children with lower mercury exposure. "This was true at both 7 and at 14 years," Grandjean says, "suggesting that this effect of mercury on the developing brain is irreversible." Delays in a different component of signal transmission also were detected and appear to be due to postnatal mercury exposure.

Grandjean commented, "It is noteworthy that these children at age 14 had an average exposure that was similar to the exposure limit used by the U.S. Environmental Protection Agency, and that 95 percent of them had exposures below the level which has previously been considered safe by the Food and Drug Administration. Yet, at these exposure levels, we saw a steady slope of increasing delays of the electrical signals, the higher the mercury exposure."

Grandjean concluded, "The importance of brain functions means even a small deficit, whether measured as a decrease in IQ points or otherwise, is likely to impact on an individual's quality of life, academic success and economic prospects in life. Even though the children we examined were all basically normal, we have documented detectable deficits that appear to be permanent."

The effects of prenatal methylmercury exposure are still a subject of controversy, because another large-scale study—this one of children in the Seychelles, where fish is a staple of the diet—showed no adverse effects related to elevated prenatal methylmercury levels. A third large-scale study, this one in New Zealand in 1998, was consistent with the Faroe study, finding subtle psychological and academic decrements in children exposed to elevated levels of mercury in utero. The differences between the findings of the Seychelles study and those of the Faroe and New Zealand studies may be due to different measurement techniques, psychological testing methods, or population groups, or to other factors.

Grandjean notes that his own work has been replicated in other areas, saying, "We have also seen adverse effects in studies of mercury-exposed children from Brazil and Madeira, where developmental exposure levels were determined from current hair-mercury concentrations." He also notes that a second group of Faroese children, recruited in 1994, exhibited "mercury- associated decreases in the neonatal Neurological Optimality Score and in postnatal growth." The findings of Grandjean and the New Zealand researchers are of particular importance in light of an analysis suggesting that as many as one in every six pregnant women may have elevated mercury levels (see related article, Crime Times, 2004, Vol. 10, No. 2, Page 7).

While these studies focused on methylmercury, other research is investigating the effects of ethylmercury. Once considered to be safer than methylmercury, and widely used in vaccines and other medicinal products until recent years, ethylmercury is now being investigated as a possible factor in rising rates of autism and learning disabilities (see book review, Crime Times, 2005, Vol. 11, No. 4, Page 5). While epidemiological studies have reached conflicting results, clinical studies are causing increasing concern. Among the findings:

• In a 2005 study, Thomas Burbacher and colleagues gave injected ethylmercury and oral methylmercury to newborn monkeys, and found that thimerosal was cleared from the monkeys' systems faster than methylmercury and that brain concentration of total mercury was three times lower in the monkeys exposed to ethylmercury. However, Burbacher et al. found that ethylmercury rapidly crossed the blood-brain barrier, where it was converted to inorganic mercury incapable of leaving the brain. The result: compared to methylmercury, ethylmercury exposure may result in twice as much mercury being trapped in the brain.
• Mady Hornig and colleagues report that low-level exposure to ethylmercury can cause behavioral changes resembling autism in mice vulnerable to autoimmune disorders. Hornig et al. exposed both normal mice and autoimmune disease-susceptible mice to thimerosal (a vaccine preservative that is 50 percent mercury) in doses calibrated to be comparable to those received by children in vaccines, and found that the susceptible mice showed increased brain size and abnormalities in brain structure, particularly in areas involved in emotion and cognition. They also exhibited abnormal responses to new surroundings, a limited behavioral repertoire, and reductions in exploratory behavior.
• Richard Deth and colleagues found that thimerosal inhibits biochemical pathways involved in methylation, a process crucial to "turning off" or "turning on" genes at the proper times. Deth et al. found that thimerosal disrupted methylation at doses 100 times lower than children receive in a single dose of a thimerosal-containing vaccine. (Children received multiple vaccines containing thimerosal through the late 1990s until the FDA recommended its discontinuation, and stockpiles of thimerosal-containing vaccines are still being used.)

Testimony of Susan West Marmagas, Director, Environment and Health Program, Physicians for Social Responsibility, April 19, 2005, at a Senate Democratic Policy Committee Hearing.

"Delayed brainstem auditory evoked potential latencies in 14-year-old children exposed to methylmercury," K. Murata, P. Weihe, E. Budtz-Jorgensen, P. J. Jorgensen, and P. Grandjean, Journal of Pediatrics, Vol. 144, No. 2, 2004, 177-83. Address: Philippe Grandjean, Dept. of Environmental Health, Harvard School of Public Health, Landmark Center, 3-110, 401 Park Drive, Boston, MA 02215, pgrand@hsph.harvard.edu.

Philippe Grandjean, testimony at the Mercury MACT Rule Hearing, Maine State House, Augusta, Maine, March 1, 2004.

"Comparison of blood and brain mercury levels in infant monkeys exposed to methylmercury or vaccines containing thimerosal," Thomas Burbacher, Danny Shen, Noelle Liberato, Kimberly Grant, Elsa Cernichiari, and Thomas Clarkson, Environmental Health Perspectives, April 21, 2005 (epub). Address: Thomas Burbacher, Department of Environmental and Occupational Health Sciences, Box 357234, University of Washington, Seattle, WA 98195.

"Neurotoxic effects of postnatal thimerosal are mouse strain dependent," M. Hornig, D. Chian, and W. I. Lipkin, Molecular Psychiatry, June 8, 2004 (epub). Address: Mady Hornig, Jerome L. and Dawn Greene Infectious Disease Laboratory, Department of Epidemiology, Mailman School of Public Health, Columbia University, 722 W. 168th St., New York, NY 10032.

"Thimerosal, found in childhood vaccines, can increase the risk of autism- like damage in mice," news release, Molecular Psychiatry, June 8, 2004.

"Activation of methionine synthase by insulin-like growth factor-1 and dopamine: a target for neurodevelopmental toxins and thimerosal," M. Waly, H. Olteanu, R. Banerjee, S. W. Choi, J. B. Mason, B. S. Parker, S. Sukumar, S. Shim, A. Sharma, J. M. Benzecry, V. A. Power-Charnitsky, and R. C. Deth, Molecular Psychiatry, January 27, 2004 (epub). Address: Richard C. Deth, Department of Pharmaceutical Sciences, Northeastern University, Boston, MA 02115.

"Study suggests vaccine, autism link," Salynn Boyles, WebMD, February 5, 2004.

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