Researchers in the last few years have discovered that methyl mercury is a far more toxic form of mercury than the ethyl mercury found in thimerosal. This greater toxicity results from the fact that methyl mercury stays in the body almost 10 times longer than ethyl mercury, allowing its concentrations to build over time to where it reaches toxic levels. Methyl mercury is the form of mercury that most people are familiar with, being the form that accumulates in the tissues of fish such as tuna. And, methyl mercury has never been shown to be associated with autism, whether in low doses or high doses.

Low Dose Methyl Mercury

If mercury exposure caused autism, large numbers of us would have it, independent of exposure to thimerosal in vaccines. This is because thimerosal has been a relatively minor source of exposure to mercury in the big picture – in the US, except for the years 1991 to 2001, thimerosal has contributed no more than 75 or so micrograms of mercury to a human infant during their first year. And, the mercury in thimerosal is ethyl mercury, a much less potentially harmful type of mercury.

This is a relatively small amount of mercury compared to the amount that an average person is exposed to in the environment. Mercury is part of the earth’s crust, released into the environment by burning coal, rock erosion, and volcanoes. After it is released, it settles onto the surface of lakes, rivers and oceans where it is converted into methyl mercury by algae and settles in the fish we eat, the water we drink, and the breast milk we feed our babies. Because everyone drinks water, everyone has small amounts of methyl mercury in their blood, urine and hair. A typical breast fed child will ingest almost 400 micrograms of methyl mercury during the first six months of life, with some seeing much higher exposure because of normal variation in environment and diet. And, this exposure is from the easily accumulating and much more toxic methyl mercury.

If autism was caused by the harmful effects of mercury poisoning, then the thimerosal / ethyl mercury in vaccines would be a relatively minor contributor to autism. Also, autism rates should not have seen a dramatic spike as is required under the thimerosal theory of autism. Autism levels should have stayed consistently high for many generations, in response to the natural mercury in the environment and the coal that has been burned in great quantities since the industrial revolution.

High Dose Mercury

If autism is in fact a unique form of mercury poisoning, then it only stands to reason that autism frequency and severity should vary with the dose of mercury. This correspondence between exposure levels and disorder severity holds true for other heavy metals like lead. However, no such pattern of correlation has ever been established in those exposed to concentrated mercury, in either children or adults.

     Minamata Bay

The most famous case of mercury poisoning occurred in a Japanese town on a harbor that was terribly contaminated with mercury from industrial use. Mercury levels that accumulated in the sediment and transmitted to the population primarily through shellfish were thousands of times higher than recommended. Mercury levels were so high that cats in the local area, which tended to eat table scraps, developed symptoms similar to those discovered in humans and often became insane. The disease developed in humans without any prior warning, with patients complaining of a loss of sensation and numbness in their hands and feet. They became unable to grasp small objects or fasten buttons. They could not run or walk without stumbling, their voices changed in pitch and many patients complained of difficulties seeing, hearing and swallowing. In general these symptoms deteriorated and were followed by severe convulsions, coma and eventually death. However, despite the severity of the exposure, and the toxic effects the mercury had on those exposed, whether children or adults (or even cats), children from Minamata Bay who had suffered neurological damage from mercury poisoning didn’t have a greater risk of autism.

     The Seychelles / Farroe Islands

Studies in two island chains, the Seychelles and Faeroes, have shown that infants and young children who consumed large amounts of methyl mercury in fish and whales which were a primary part of their diet didn’t develop neurological problems such as autism.

     Contaminated Bread and Other Foods

Studies that followed victims of high-dose acute or chronic mercury poisoning resulting from contaminated foods in Iraq, Pakistan, Guatemala, and Ghana have not reported manifestations suggestive of autism in survivors. In contrast, many of these survivors had clinical signs such as persistent muscle coordination problems and speech control issues that are seldom seen in autism but are typical of methyl mercury poisoning.

     Infants Treated in the Early 20th Century

In the first half of the 20th century, mercury was a constituent of medications administered to treat worm infestations and teething pain. Use of these compounds was associated with illness in young children, affecting chiefly those 8 months old to 2 years old. These infants showed anorexia, skin eruption, and bright pink color of hands and feet, which peeled and were painful. This condition called pink disease was relatively common and the cause of 103 deaths in England and Wales in 1947. Survivors were not described to have behavioral disorders suggestive of autism.

     Meningitis Treatment

Just because you receive thimerosal (50% ethyl mercury) does not mean you will develop symptoms of mercury poisoning; this is likely because the ethyl mercury in thimerosal is quickly flushed from the body. For instance, shortly after it was originally introduced, in 1929, thimerosal was injected in adults as a treatment for meningitis. Adults injected with 2 million micrograms of thimerosal didn’t suffer symptoms of mercury poisoning; the amount was 10,000 times greater than the FDA later found babies had received in vaccines.