Just like the MMR controversy, the issue of mercury has been linked to autism, with its own share of proponents and nay-sayers.
It is a fact that mercury is a toxin, and there is an uncanny similarity between the traits of autism and mercury poinoning. Mercury is found in both seafood and dental metal fillings. But the main controvesy surrounds the inclusion of mercury in a preservative called "Thimerosal", which is 50% ethylmercury.
Thimerosal started to be used in vaccines in 1930. The first cases of autism were described in 1943 in children born in the early 1930's. The medical authorities in America, the CDC (Centre for Disease Control) has been challenged to address this matter in an independent manner. Many conflicting studies are raised by both sides of this debate, but again, there are legions of parents who claim that the evidence exists that thimerosal/mercury is a causal agent of autism.
To quote from Dr. Jepson's presentation
Thimerosal is nearly 50% ethyl mercury. Ethyl mercury is organic mercury, but it's different from methyl mercury. It's used as a preservative to enable the manufacturer to package their vaccines in multi-dose vials. It was known to be toxic by the manufacturer, Eli Lilly, when it was first developed. The original safety studies were very poorly done. They tested thimerosal in 1930 on 22 individuals, all of whom were sick with meningitis. They all died. Lilly concluded that it was meningitis that killed them, and that thimerosal was safe. That's the safety study. That's the "science" that grandfathered it in for use in our medical products.
The LA Times reprinted memos from the 1990s that show that Merck knew that mercury levels in the vaccine schedule had become excessive, but they chose to do nothing. Thimerosal was removed from animal vaccines in the early 1990s because the veterinarians decided it was too toxic. A bottle of thimerosal is legally required to include a skull and crossbones on the label. It seems unfathomable that anyone would take a substance required to carry this label and inject it into a baby.
Apart from the books written by biomedical practitioners such as Dr. Jepson, there is a great book Evidence of Harm, by David Kirby, which is an investigative story of how the American authorities dealt with this issue. Well worth a read ...
The issue of mercury from dental fillings has received some differing opinions, with most of the established dental associations rejecting any harm arising from them. However, the contrary view is supported by the "International Academy of Oral Medicine and Toxicology", or IAOMT.