Interesting site, ((( Smiles )))

Good question...

It is of public interest to ask, why thimerosal and
dental amalgam, which both consists of about 50% of
the most toxic nonradioactive element [16] and, in the
case of amalgam, additionally of other heavy metals
(eg. tin, copper, silver, zinc), have been used since 70
and 170 years, respectively, and, have been allowed to
bypass governmental toxicological testing.

http://www.crossroadsinstitute.org/newsletter/nlarticles/apr06/mercuryautism.pdf