IFIN BULLETIN #577: EPA seeking more information on fluorosilicates.
May 24, 2002.
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
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
Now, we are ready for the EPA's Request For Assistance, titled:
MEASUREMENT OF FLUOROSILICATES IN DRINKING WATER (Announcement
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
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.
The full RFA can be accessed at www.epa.gov/ORD/NRMRL/wswrd/rfa-fluoride.pdf
All the references cited above can be obtained on Masters' web site: