Fluoride Action Network

EPA seeking more information on fluorosilicates

Source: International Fluoride Information Network | May 24th, 2002

Dear All,

For many, the following exerpts from an US EPA Request for Assistance is going to read like a lot of gobbledy-gook and thus I will take some time to put it into historical and scientific perspective.

In 1999, Roger Masters and Myron Coplan published a paper in the International Journal of Environmental Studies, in which they showed a statistical correlation between the use of silicofluorides (but not sodium fluoride) to fluoridate water supplies and the blood lead level of children living in Massachusetts.

The CDC responded in the way they usually respond when any research threatens their “precious” fluoridation program, they proceeded to attack the methodology – behind the scenes. They did this also with Phyllis Mullenix’s paper on rat behavior. This is a political approach to science. A scientific approach is to critique the paper openly in the scientific literature.

Then two US EPA scientists Edward T. Urbansky and Michael R. Schock published a paper in the same journal as Masters and Coplan, critiquing their findings on theoretical grounds. In this article they argued that there was no difference between the use of silicofluorides and sodium fluoride to fluoridate drinking water, because according to their computations and observations, “we can dispense with the issue of incomplete hydrolysis entirely. There is essentially no hexafluorsilicate remaining in drinking water at equilibrium”. The implication being that all the hexafluorosilicate would be converted to free fluoride ion on dilution at the public water works.

This was an important argument because Masters and Coplan had to find an explanation as to why the fluorosilicates would increase the uptake of lead into children’s blood but not sodium fluoride. They postulated some interaction between lead and a fluorosilicate species.

On the basis of the Urbansky and Schock paper officials behind the scenes continued to denigrate Masters and Coplan’s work.

Masters and Coplan responded to the Urbansky and Schock critique by producing a Ph.D thesis published in Germany in 1975 by Johannes Westendorf. The thesis which they had translated and made available on their web site (http://www.dartmouth.edu/~rmasters/ahabs.htm), showed that under physiological conditions the hexafluorosilcate ion was not completely converted in water (hydrolysed) to free fluoride ion but instead two fluoride ions remained attached to the silicon. Moreover, Westendorf also showed that the toxicological properties of this species differed from free fluoride ion in its inhibition of the enzyme acetylcholinesterase.

Meanwhile, of course the US EPA has had to admit to Congress that they have no toxicological data on the hexafluorosilicates even though these are used in over 90% of the fluoridation programs in the US.

Now, we are ready for the EPA’s Request For Assistance, titled: MEASUREMENT OF FLUOROSILICATES IN DRINKING WATER (Announcement date:April 25,2002).

The following exerpt from the RFA provides the background and research objective as follows:



Hexafluorosilicic acid (H2SiF6) and sodium hexafluorosilicate (Na2SiF6)are the most commonly used fluoridating agents by potable water systems in the U.S.These species dissociate and hydrolyze to produce fluoride anion (F -).The release of fluoride proceeds through a complex,multi-step equilibrium process that is not well-understood. A variety of models have been proposed,and the speciation remains a matter of debate as does the existence of some fluorosilicates. A review of the relevant chemical literature detailing the complexities,disagreement,and scientific facts has been prepared by the EPA.This review is available to prospective applicants, and they are encouraged to request a copy prior to preparing a proposal.

In addition to the silicon(IV)present from the fluoridating agent,many natural water supplies contain soluble oxo-and hydroxosilicates,which further complicates the speciation.The EPA seeks information on the utility of techniques and methods for monitoring the species formed during the dissociation and hydrolysis of hexafluorosilicate as well as those species present once equilibrium is achieved.These data are expected to aid in the development of pharmacokinetic and toxicokinetic
studies and to further the understanding of the fate of fluoride,including its interactions with other species in drinking water.As such,the results of this study will be of use to state agencies,water utilities,and other governmental or scientific bodies who seek to ensure the quality of the nation ‘s drinking water supplies.


The primary objective of this RFA is to investigate the reactions that take place when fluorosilicates are added to drinking water supplies and what concentrations of which fluorosilicate species may monitored in finished drinking water supplies and what techniques may be used for such monitoring.”

Now this statement contains within it an uncertainty which is far removed from the earlier statement of Urbansky and Schock quoted above, where they said “we can dispense with the issue of incomplete hydrolysis entirely. There is essentially no hexafluorosilicate remaining in drinking water at equilibrium”. Clearly, there is a lot the EPA does not know about the species formed in water when hexafluorosilicate is added to it. Clearly, the statement that there is no difference between the use of sodium fluoride (on which all the toxicological testing has been done) and hexafluorosilcic acid or its sodium salt, is erroneous. Only now, some 40 years or more since using these fluorosilicates is the EPA trying to find out what that difference is! Meanwhile, Masters and Coplan have published a second paper in which they found the same association between hexafluorosilicate use (this time in New York State) and greater uptake of lead into children’s blood.

Of particular interest, is that the RFA was issued under the name of Edward T. Urbansky.

Edward T. Urbansky,
U.S.Environmental Protection Agency
National Risk Management Research Laboratory
Water Supply and Water Resources Division
26 West Martin Luther King Drive,MS 681

That looks like a scientific apology to Masters and Coplan to me.

Paul Connett.

The full RFA can be accessed at http://www.epa.gov/ORD/NRMRL/wswrd/rfa-fluoride.pdf

All the references cited above can be obtained on Masters’ web site: http://www.dartmouth.edu/~rmasters/ahabs.htm