Dartmouth University wrote in 2001:
In a recent article in the journal NeuroToxicology, a research team led by Roger D. Masters, Dartmouth College Research Professor and Nelson A. Rockefeller Professor of Government Emeritus, reports evidence that public drinking water treated with sodium silicofluoride or fluosilicic acid, known as silicofluorides (SiFs), is linked to higher uptake of lead in children.
Sodium fluoride, first added to public drinking water in 1945, is now used in less than 10% of fluoridation systems nationwide, according to the Center for Disease Control's (CDC) 1992 Fluoridation Census. Instead, SiF's are now used to treat drinking water delivered to 140 million people. While sodium fluoride was tested on animals and approved for human consumption, the same cannot be said for SiFs.
Also requiring further examination is German research that shows SiFs inhibit cholinesterase, an enzyme that plays an important role in regulating neurotransmitters. "If SiFs are cholinesterase inhibitors, this means that SiFs have effects like the chemical agents linked to Gulf War Syndrome, chronic fatigue syndrome and other puzzling conditions that plague millions of Americans," said Masters. "We need a better understanding of how SiFs behave chemically and physiologically."The USGS also noted in a 2000 report:
Fluorosilicic acid is a byproduct of the phosphate fertilizer industry and is not manufactured for itself alone ...In other words, even though neither the EPA or any other government agency has studied the effects of long-term ingestion of fluorosilicic acid, it is being used instead of sodium fluoride because it is cheaper.