Seattle, Everett, and most US cities that fluoridate, do so with silicofluoride (SiF); around 8% use sodium fluoride (NaF).
SiF and NaF are much more toxic than naturally occurring calcium fluoride (CaF). CaF can be fairly pure if it is naturally occurring. CaF can be produced from fluorosilicic acid, in which case it can be as contaminated as fluorosilicic acid.
SiF AND NAF are carcinogens, mutagens, poisons. As little as seven grams of SiF or NaF, the weight of seven paper clips, can kill an adult. It would take a half pound of naturally occurring CaF to do the same. The one milligram of SiF per liter which our cities add to water is of course not immediately fatal, however, a healthy adult is only able to excrete half of all fluoride consumed, while the body retains the other half. Fluoride seeks out calcium and is retained in calcium rich areas of the body. Once in our bones, fluoride has a long half life and can be excreted only slowly – or if we continue to consume fluoride, not at all.
NaF is industrial grade but relatively pure; SiF is industrial grade toxic waste, highly contaminated with heavy metals. SiF contains and breaks down into hydrogen fluoride, one of the most poisonous and penetrating of all substances.
The relative harmfulness of fluoride depends on the ratio of fluoride to calcium and magnesium and other minerals.
When fewer minerals are present in water, water is said to be soft more acidic, and fluoride is much more harmful when it is found in such soft water, such as Everett water.