This letter discusses the meeting of Manhattan Project scientists in 1943, where they agreed upon the need for a secret wartime conference to discuss the “toxicity of fluorine compounds…with the view to orienting those concerned with the specific problems which may arise.”


29 September 1943

SUBJECT: Report on Meeting of 31 August 1943 for discussion of Toxicology Program.

On 31 August a meeting was held to discuss the allocation of a portion of the experimental program involving the study of the toxicologic effect of various special materials. Present at the meeting were: Dr. Col. Ruhoff, Major Hadlock, Lt. Sturgie (Special Materials), Dr. Wensel, Dr. Stone, Dr. Tannenbaum (Chicago Project), Dr. Hodge (Rochester Project), Dr. Warren, Major Friedell, Capt. (Medical Section).

It was decided that a conference on the toxicity of fluorine compounds should be held with the view to orienting those concerned with the specific problems which may arise. It was recommended that a program be arranged by the Public Health Service since some of their members have more exhaustive studies into the biological effects of fluorine and its compounds. The tentative arrangements met with approval of Lt. Col. Ruhoff, and it was contemplated that those companies actively engaged in the production of F, F2, and fluorides be invited. The meeting was also to be attended by representatives of the Manhattan District but their association with the District would be concealed by appropriate measures.

Dr. Tannenbaum and Dr. Hodge reviewed the data which they have accumulated on experimental feeding and ingestion of the various T (Uranium) compounds in rats and mice and in general the following results were obtained: It was reported by Dr. Hodge that T nitrate fed by mouth in large enough quantities can cause the death of rats weighing approximately 100 grams. TO2 in similar quantities produced no demonstrable effect on ingestion, and TF4 in large quantities produced some interference with growth but no deaths were encountered. Specifically, the infromation was presented in the following manner:

TNO3 .5% of diet (50 millig./day) to rats — same growth as controls.

1% of diet (100 millig./day) to rats — gave slightly depressed growth rates as compared to normal.


cc: Lt. Col. Ruhoff
Dr. R.S. Stone

Note from FAN: This is the list of attendees to the Manhattan Project’s fluoride conference. As noted in the document above, many of the attendees were representatives of “companies actively engaged in the production of F, F2, and fluorides” (e.g. DuPont, Kellex, ALCOA, Harshaw, and Mallinckrodt). Along with industry representatives, the conference was attended by scientists from the Manhattan Project, scientists from industry-friendly laboratories (e.g. Kettering Institute), and, conspicuously, three of the lead dental researchers of the day – David Ast, B.S. Bibby, and S.B. Finn. It was just over one year later when the first US fluoridation experiments began, and David Ast was to lead one of them (Newburgh/Kingston, New York). According to the minutes of the conference, “tests are being planned in which fluorine is to be introduced in municipal water supplies. The evidence seemed to indicate that teeth are definitely improved when some fluorine is present.”

The Manhattan Project’s interest in fluoridation was not known at the time of the experiments, indeed it wasn’t known until some 50 years later. In the late 1990s, David Ast was questioned about his participation in the conference. Ast claimed to have no knowledge of it, and denied the fact that he was in attendance as the document below clearly shows. (Griffiths & Bryson, 1997).


15 january 1944

Subject: Conference on Fluoride Metabolism 6 January 1944

MEMORANDUM to Major H.L. Friedell, U.S. Engineer Office, Knoxville, Tennessee

1. The following persons attended the above mentioned conference. The organization to which they are attached is indicated:

Harry C. Anderson John Hopkins University
Capt. John A. Anthes U.S. Engineer, Madison Square Area
Dr. W.D. Armstrong University of Minnesota
Dr. David B. Ast Dental Hygiene, State of New York
Dr. A.N. Benning Du Pont de Nemours Co.
Lt. O.P. Bergelin Wilmington Area
Dr. B.S. Bibby Tufts Dental School
Capt. E.B. Brown U.S. Engineer, Madison Square Area
Fred A. Bryan University of Rochester
Herbert O. Calvery Food and Drug Administration
Graham Cook Columbia Area
James E. Curran Kellex Corporation
W.E. Crutchfield, Jr. Merck & Company
Dr. A.G. Cranch Union Carbide and Carbon Company
Dr. Peter P. Dale University of Rochester
Dr. H. Dean National Institute of Health
J.M.A. duBruyne Bell Telephone Company
Dr. L.T. Fairhall National Institute of Health
Joseph T. Faust District Safety Section
Dr. Chas. M. Fehr Pennsylvannia Salt Company
Capt. J.L. Ferry U.S. Engineer, Manhattan District
S.B. Finn New York State Dept. of Health
Robert D. Fowler Columbia Area
Dr. Francis C. Frary Aluminum Company of America
Frank J. Giaccio Kellex Corporation
Elroy M. Gladrow Iowa State College
L.L. Hedgepeth Pennsylvania Salt Company
Dr. Francis F. Heyroth Kettering Laboratory
Dr. Harold C. Hodge Rochester University
Dr. Edward J. Largent Kettering Laboratory
H.B. McCauley U.S. Engineer, Rochester Area
T.J. McKinzie Kellex Corporation
Dr. Paul A. Neal National Institute of Health
Dr. J.J. Nickson University of Chicago
John J. Prendergast Chrysler Corporation
Dr. R. Rosen Kellex Corporation
Dr. H.H. Schrenk Bureau of Mines
S.C. Schuman Kellex Corporation
Dr. J.H. Sterner Tennessee Eastman
S. Warren Stetler District Safety Section
Dr. H.E. Stokinger University of Rochester
George M. Suter University of Rochester
Dr. C.F. Swinehart Harshaw Chemical Company
Ann T. Tarbell University of Rochester
Harold E. Thayer Mallinckrodt Electrochemical Co.
John Turkevice Princeton University
Robert A.N. Turner, Jr. Du Pont de Nemours Co.
Les Van Orden Kellex Corporation
Dr. Carl Vogtlin University of Rochester
Col. S.L. Warren U.S. Engineers, Manhattan District
Carrol S. Weil University of Rochester
Richard S. Weiss Mallinckrodt Electrochemical Co.