Contrary to widely-promoted assertions, the Hertz-Picciotto et al 2010 study does not in the slightest constitute evidence that mercury has not been involved in causation of autism.
They found no association of mercury blood levels with autism. Which is not surprising as the autism would be caused not by mercury in blood but by mercury in brain cells. It's been known for decades that blood levels of mercury are near-useless as an indicator of body burden of mercury and chronic mercury poisoning.
“The distribution of mercury into the body tissues is highly variable and there appears to be little correlation between levels in urine, blood or hair and toxic effects.” —NIDH/ADA Workshop on Biocompatibility of Metals, Journal of the American Dental Association 109 (September 1984).
Further references for the uselessness of blood mercury levels can be found in the critique by Joachim Mutter of the fraudulent SCENIHR report, and in Mutter, Naumann, Guethlin. Comments on the Article "The toxicology of mercury and its chemical compounds". Crit Rev Toxicol 2007 37:537-549.
Even my mere common-or-garden general practitioner ("family doctor") was able to tell me years ago that a blood test of mercury would be worthless for diagnosing chronic mercury poisoning.
A great way to get the wrong answers is to ask the wrong questions. A far more right question to have asked would have been whether there is an association between number of mothers' amalgams (i.e. a cause) and autistic behaviors (i.e. the key effect of interest). Some such studies have already been done and found significantly positive results. They are far easier to carry out than this one requiring going round sucking blood from children rather than just counting their mothers' fillings.
Another right question would be the association of lack of outdoor air with autism, and again significantly positive results have been found by Waldman & Adilov.