MERCURY EXPOSURE
Toxic mercury exposure can occur from industrial effluents, environmental contamination, occupational exposure, volcanic gasses, and from emissions by coal fired power plants. Metallic mercury is relatively non toxic and is not significantly absorbed, even when swallowed by mouth. Metallic mercury does evaporate, however, and prolonged breathing of the fumes in a closed space can lead to toxicity. Lead exposure has greatly diminished in recent years, since the switch to unleaded gasoline, and lead based paints have been taken off the market. Potentially toxic metals have always existed in the earth's crust and also in every human body at safely tolerated levels. We have good scientific data on which to base the upper safe limits before metal toxicity occurs.
A recent study by the University of Rochester shows that eating ocean fish an average of 12 meals per week did not cause toxicity from mercury, even in pregnant women and small children. Myers GJ, Davidson PW, Cox C, Shamlaye CF, Palumbo D, Cernichiari E, Sloane-Reves J, Wilding GE, Kost J, Huang LS, Clarkson TW. Prenatal methylmercury exposure from ocean fish consumption in the Seychelles child development study. Lancet. 2003 May 17;361(9370):1686-92.
By carefully studying large populations of people known to have been poisoned in epidemics mercury exposure, it has been possible to determine the blood, urine and hair levels that resulted in toxic symptoms. This was done at Minamata Bay in Kyushu, Japan. Mercury was there was disposed of into the the bay by a chemical manufacturing company, Chisso, that used mercury as a catalyst in the production of acetylaldehyde. Victims were poisoned by contaminated fish and shellfish from the bay. Another mercury epidemic occured in Iraq, caused by bread made with wheat that had been treated with a methyl mercury fungicide.
A study was done in the Faro Islands on a population of people who accumulated mercury by eating large amounts of whale meat. Whale meat contains a a significant concentration of PCBs, that confused the picture, and whale eating was in binges when whales were caught. A more recent study in the Seychelles Islands involved mercury accumulation from ocean fish that were not contaminated with PCBs and were consumed on a regular basis 12 or more times every week. Data from these studies indicates that the danger is less than previously feared.
HOW MUCH MERCURY IS TOO MUCH? QUESTIONS AND ANSWERS FROM THE UNIVERSITY OF ROCHESTER
How is mercury exposure measured? Scientists can determine a person's exposure to mercury (especially methyl mercury, the most toxic form) by measuring mercury content in hair. By comparing these levels to the results of very sophisticated batteries of tests, scientists try to determine the lowest level that might be harmful.
At what level does mercury become harmful? Based on scientific results from exhaustive studies of known episodes of poisoning, the World Health Organization has placed the level at which risk begins at 50 ppm of mercury in hair for most people. The WHO then applied a safety factor of 10, estimating that a level of 5 or less is safe for even the most vulnerable populations. More recently the University of Rochester conducted an extensive study in the Seychelles Islands of the most sensitive population (pregnant women and their young children from birth onward) where the average hair mercury level is about 7 ppm, about 10 times the level of the U.S. population. These people ate ocean fish 12 or times or more often every week. Scientists found no harm from mercury at levels up to 15 ppm, nearly twice the average Seychelles level and about 20 times higher than the average U.S. level. Despite those reports, hair analysis laboratories in the U.S. continue to report of toxicity at only 1 ppm.
As you can see immediately above, it is customary for the EPA and for clinical laboratories to apply a safety factor of 10 on report forms. If the lowest known level associated with toxicity is 50 ppm, the WHO sets the recommended range for the general public below 5 ppm. Thus, is it highly unlikely that toxicity is responsible for symptoms unless the measured level is at least 10 time the upper limit on a laboratory report form. For industrial workers who are regularly exposed to mercury on the job, OSHA sets the allowable limits much higher, closer to a proven toxic level, before removing a worker from further exposure.
CLINICAL INTERVENTIONS
1) Minimize exposure! Prevention is always better than treatment. Be aware of your environment, what you eat and drink, what you apply to your skin and chemicals used in the home or at work. If a mercury thermometer or mercury switch breaks, carefully clean up the metallic mercury residue. Waste disposal facilities usually have a safe way to dispose of toxic substances. Avoid exposure and the body eliminates mercury rapidly without treatment.
2) With special laboratory tests, experienced health care professionals can evaluate the mercury load within the body. This can be done by measuring whole blood levels. Urine can also be used if not provoked with a chelator. This should be performed by a reputable laboratory, and can now be done confidentially without the order of a licensed health care professional. When urine is measured, no chelator should be given that could increase provoked excretion and cause false positives.
3) EDTA has little or no effect on mercury in the body, probably because mercury binds more tightly to other molecules and is present as organic methyl mercury.
4)DMPS is potentially too toxic to use and no longer has no place in the practice of medicine.
RELATED RESEARCH/ARTICLES:
Mercury Fillings: Are they Really Safe?
Clinical Toxicology of Mercury
Testing for Toxic Elements.
How to Interpret Toxic Metal Blood and Urine Tests.
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