Silicofluorides added to drinking water contains a host of additional elements and compounds – including: lead, arsenic, and mercury.
When fluoridation began in the 1940s only sodium fluoride was used. All early fluoridation tests on humans and animals were done and have almost always been done using pharmaceutical grade sodium fluoride.
Although neither type of fluoridation material is safe for internal consumption, there are clear indications that silicofluorides are worse than sodium fluoride.
Currently no federal or state agency tests or approves the silicofluoride which is currently used by Seattle and by 92% of the water districts in the country which practice water fluoridation.