The theory with mercury amalgam is that the mothers of children with autism might have exposed the fetus to mercury, or that a child exhibited symptoms after getting fillings. As with mercury-based inoculation preservatives, filling mercury exposes a person to very small levels of mercury.
Other sources of mercury contamination with much higher levels, both historically and currently were/are:
Thermometers - Some thermometers contain(d) mercury, and if the glass is broken, mercury is released.
Felt-making - You've heard the term "Mad as a Hatter?" That was mercury poisoning from the felt-making process. Hats were made out of felt.
Gold extraction - Mercury is still used in the process of panning for gold in some countries. Mercury combines with small particles of gold, and when the mercury is vaporized, the gold remains.
Coal mining - Mercury, a natural element, is present in coal. When coal is mined, miners are exposed to mercury through skin contact as well as breathing coal dust.
Burning coal for electricity - Power plants that burn coal, if they do not capture the particles in the smoke, can spew mercury and other metals into the atmosphere.
Eating predatory fish - As rain falls and flows to the seas, metals naturally present in the soil, or sent into the atmosphere by coal burning and certain manufacturing processes are carried along and concentrate in large bodies of water. Larger fish that eat other fish can have elevated levels of mercury in their systems.
Mercury is a VERY POISONOUS METAL, and it can damage the central nervous system, the brain, and DNA/chromosomes. Research is still being done to determine if there is a link to autism, and what level of mercury might cause damage.
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