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The Informed Parent

The Bottom Line on Mercury

by Louis P. Theriot, M.D., F.A.A.P.
Published on Feb. 26, 2007

I just finished Jessica's two month well-check with positive results. Then Jessica's mother reached into a folder and brought out a number of articles. "My husband and I have done some research on thimerosal. We don't want Jessica to receive her immunizations just yet," she said with some trepidation in her voice.

Billy was a robust one-year-old who came in for his well-check Before I started to do the exam his mom asked "I think Billy is supposed to get vaccinations for chicken pox and measles-mumps-rubella today. Do any of these have mercury?"

Without a doubt there is much concern and worry among parents of young children about thimerosal (mercury) as a preservative in vaccines. What role may it play in causing neurodevelopment disorders such as autism, attention deficit disorder or brain damage? I am questioned about this many times each week.

While the internet is a remarkable source of information for millions of people, one must be careful of this information they obtain. It does not have to withstand the scrutiny of peer review. Print media has also seen a plethora of articles about thimerosal and potential risks to children in the past seven or eight years. All of this information...and misinformation has frightened many parents across the country.

Let's look at mercury. It exists in three main forms. Elemental mercury is the type existing in nature in its pure form. It is one of the elements of nature. It is a metal and the only metal that is a liquid at room temperature. It is often referred to as "quicksilver". When heated it can emit mercury vapors. It has been used in thermometers and barometers for hundreds of years, and also used in batteries and electrical instruments. If one inhales a large amount of the vaporous form of elemental mercury one can sustain brain and lung damage. Elemental mercury is not used routinely anymore. The amounts that one would be exposed to in everyday life pose no real threat.

Inorganic mercury can be found in some paints, dyes and even alternative medicines. Poisoning from inorganic mercury can result in damage to the lungs as well as the brain.

There are two main forms of organic mercury: methyl and ethyl mercury. Organic mercury poisoning is mainly associated with central nervous system dysfunction. It is important to draw a distinction between methyl and ethyl mercury as they behave very differently in humans.

The main source of human exposure to methyl mercury is through the ingestion of contaminated fish such as tuna or swordfish. This form of organic mercury is highly toxic. The affects of this type of mercury poisoning are best exemplified by Minimata disease which occurred in a 1950's major outbreak in Japan. This devastating disorder was the result of the contamination of fish by waste dumped into Minimata Bay by a company that manufactured vinyl plastics. The symptoms include tremors, ataxia, malaise, blurred vision, numbness or tingling, and impaired hearing, smell and taste. This form of mercury readily crosses the placenta and can affect the developing fetus with devastation. It can cause severe neurological damage including mental retardation, spasticity with cerebral palsy, ataxia, deafness, blindness and a small head.

Exposure to excessive amounts of ethyl mercury can also be dangerous and may result in tremors, weakness, numbness and ataxia. There was, however, a case reported of a man who was exposed to a large amount of ethyl mercury and he suffered NO neurological side effects.

The mercury that is in thimerosal is ethyl mercury. It was used in miniscule amounts as a preservative in many of the childhood vaccines until 2001. During the 1990's there was considerable debate about the potential risk from this form of mercury in vaccines. Although the amount of mercury in EACH vaccine was tiny, the concern was that there could be a cumulative effect throughout the first year of life as the number of required vaccines increased.

This debate sparked much research on the subject. The main conclusion was that methyl and ethyl mercury are two very different forms as far as the human is concerned. One study exposed infant monkeys to oral methyl mercury, or intramuscular ethyl in the form of thimerosal. The findings were the ethyl mercury had cleared from the body more rapidly than the methyl. The brain concentration of ethyl was far lower than the concentration of methyl. It was removed from the brain much quicker. Most interesting was the fact that the only evidence of brain damage was in the group that received methyl mercury. One must remember that these studies involved large amounts of mercury.

Another large study concluded that ethyl mercury decomposes much faster. It is cleared much quicker from the body than methyl mercury. Ethyl has less access to the brain than does methyl mercury.

The conclusions from numerous epidemiological studies conducted in the United States, Canada and Europe proved that thimerasol in vaccines posed no risk to infants and children. However, since 2001 all of the vaccines in the United States are manufactured without thimerasol or only traces of it. This should put any fears of parents to rest. The only exception to this is the flu vaccine which is still made with small amounts of thimerasol.

Prior to 2001, the maximum cumulative amount of mercury that an infant might have received from all of the vaccines by six month of age was 187.5 micrograms. That value is now less than 3 micrograms.

It is difficult being a parent in the year 2007 with all of the information we are bombarded with each and every day. We try to stay on top of it so that we can make informed and correct decisions for our children. The issue of thimerasol, mercury and vaccines is one major dilemma that parents will not have to confront any more. Thimerasol has not been used in the manufacturing of childhood vaccines since 2001. There are only trace amounts in some vaccines in the United States.

For those children immunized before 2001, it is important to remember that ethyl mercury in thimerasol is a very different form when compared to methyl mercury. The amounts of mercury from thimerasol that an infant would have received during the first six months of life are miniscule in any event. Hopefully this will put the issue to rest, once and for all!.

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