Reasons for Renewed Interest
Periodically the EPA reexamines its information on regulated drinking water contaminants to determine if further study is required. Fluoride is one such contaminant undergoing review. The chemical literature indicates that some deficiencies exist in our understanding of the speciation of fluoride derived from fluorosilicate additives used to treat drinking water; hexafluorosilicic acid is the most commonly used additive. In addition, legislation governing the use of fluoridating agents has been proposed recently at the state level. One such bill under consideration includes language that specifically addresses issues such as partial dissociation products, products formed by reactions with other dissolved matter, and total release of F-, and it imposes requirements that any such species be measurable at concentrations as low as 1 ng mL-1 in potable water. Consequently, there is renewed interest in the chemistry of fluoridation processes and additives. The principal objectives of this review are as follows: (1) to enumerate unresolved chemical issues germane to understanding fluoridation and ascertaining the fate of fluoride and fluorospecies, (2) to critically review what is known or reported, and (3) to assemble a knowledge base to provide a starting point for future study.
A number of misconceptions and oversimplifications frequently appear in the literature, and the discussion below is intended to address them. Some of the issues are the result of recent studies, laws, or regulations, but some basic issues resurface from time to time. In 1957, a paper called “The state of fluoride in drinking water” was published, addressing many of these cyclical issues. Since that time, more experimental work has been done and the knowledge base is larger, but the message is apparently being lost as many of the key outcomes have not changed. Key points may be grouped into the following categories: drinking water regulation, standards for drinking water additives, fluoridation advocacy/requirement, available fluoridation additives, testing, and the definition of complete and fast reaction. An overview of these issues is helpful for any researcher undertaking study of fluorosilicates as there is a wealth of misinformation available.