Send me to a peer-reviewed medical journal that makes the connection, please. Much as I feel for those families that have been hit by PDD, that website contains no scientifically-established proof.
Toxic levels of mercury can have more than one source. There are quite a few places in the States where ground water is poisoned by mercury, and I know of at least one in Canada (the city of Sudbury, with its extensive mining operations.) If, in fact, autism is caused by mercury poisoning - and I'm not convinced of that yet, because of the lack of good medical research that I've seen on the topic - I would expect it would have a lot more to do with environmental poisoning than the tiny amounts of preservative in vaccines.
As for the rise in the number of cases - well, PDD has only really been diagnosed consistently for about twenty years. Most of what is now diagnosed as PDD/autism wasn't even recognized as a disorder when I was a child. Increased and improved diagnosis accounts for the rise in numbers, without any corresponding rise in actual cases.