Mercury sources and toxicity
Mercury is a highly toxic metal associated with damage to the kidneys and central nervous system. Mercury vapour is emitted from volcanoes, coal-burning power stations, and municipal incinerators and returns to the earth through rain contaminated with metallic mercury. Metallic mercury is methylated to methyl mercury in oceans and lakes and enters the food chain via fish and other seafood. Long-lived predator fish such as shark, swordfish, tilefish, king mackerel, and pike and bass in fresh water are the main sources of methyl mercury. Dental amalgams are an important source of mercury vapour and the vaccine preservative thimerosal is a significant source of ethyl mercury.
- Mercury vapour, methyl mercury and ethyl mercury all target the central nervous system and mercury vapour and ethyl mercury also target the kidneys. Inorganic (metallic) mercury primarily targets the kidneys and stomach.
- Chelators such as DMSA are effective in removing all forms of mercury from the body, but cannot reverse central nervous system damage.
- The allowable or safe intake of mercury has recently been reduced to 0.1 microgram/day per kilogram of body weight.
- The concentration of mercury in the brain, blood and urine correlates with the number of amalgam fillings in one's mouth. The concentration increases markedly with increased chewing. Long-term use of nicotine gum by people with amalgam (silver) fillings may increase levels by a factor of 10, thus approaching occupational safety limits.
- There is concern, but no clear evidence, that mercury emitted from amalgam fillings may cause or worsen degenerative diseases such as ALS, Alzheimer's disease, multiple sclerosis, and Parkinson's disease.
- Ethyl mercury (thimerosal) is used as a preservative in vaccines. Recent concerns about its toxicity have caused US authorities to take steps to remove it by switching from multi-dose vials to single-dose vials that do not require a preservative.
- A recent move by power companies to replace mercury containing pressure-control devices for domestic gas supplies has led to numerous spills of mercury in homes. Some 200,000 homes were affected in one recent incident. The liquid mercury is difficult to remove and gives off highly toxic vapours, which are particularly harmful to infants and children.
- Several studies have found an association between mercury exposure and cardiovascular disease, but other studies have failed to confirm the connection.
ADA fighting the mercury battle
The Australian Dental Association (ADA) has launched a campaign to discourage patients from having their amalgam (silver) fillings removed. Many patients and sometimes even their physicians believe that mercury, the main component of amalgams, plays a role in promoting such varied diseases as Alzheimer's, multiple sclerosis, and autism. The ADA says the evidence is not there and their Code of Ethics forbids dentists from advising their patients that there could be a link. Scientists at the University of Milan disagree with the ADA and point out that several studies have confirmed that mercury from amalgam dental fillings does enter tissues and that the mercury content of brain, thyroid, kidney, and pituitary gland tissue is proportional to the number of amalgam fillings. They conclude that the health effects of amalgam fillings are not at all clear and need further investigation. German researchers point out that some of the composite materials used in the replacement of amalgam fillings may in themselves be toxic.
Mercury and removed amalgam fillings are classified as hazardous materials and require extreme caution in disposal. Why they would be hazardous outside the mouth, but not inside defies comprehension. It is also a scientifically proven fact that the blood level of mercury is twice as high in dentists as in non-dentists. This fact and the fact that savvy patients don't want mercury in their mouths is no doubt what is leading many dentists to put a, albeit discrete, sign in their waiting rooms "Mercury-free practice"!