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A Comparison of the Toxicity of Fluorine in the Form of Cryolite Administered in Water and in Food^1,2,

Division of Animal Nutrition, and Department of Horticulture, University of Illinois, Urbana

Experiments are reported on twelve pairs of rats designed to measure the relative toxicity of fluorine (as cryolite) when consumed in equal amounts either in food or in water. The feeding experiments were carried out according to the paired-feeding technic, and were supplemented with sixteen fluorine balance trails of 14 days each and analyses of the bones, teeth and soft tissues of all rats at the termination of the feeding period. The fluorine was fed in amounts equivalent to 10 p.p.m. of solid food; 9% of the fluorine intake was contained in the basal diet in unknown forms.

The results of the experiment seem to justify the following conclusions, under the experimental conditions above specified:

1. The method of administration of fluorine at low levels of intake whether in water or in food has no apparent effect on the rate of growth of animals. Administered in the water, however, fluorine definitely depresses the appetite of rats and induces a transient hematuria.

2. No considerable difference in the time of appearance of striations in the lower incisor teeth of rats result from the administration of fluorine in food or in water in low concentration.

3. Doses of fluorine in the food are retained to a less extent in bones, teeth and soft tissues than equal doses of fluorine in the drinking water. Considering the total retention of fluorine in the carcass, this impairement in assimilability amounts to 20%. It seems to be the result entirely of an impairment in absorption from the alimentary tract.

4. Continued ingestion of low concentrations of fluorine in food or in water by growing animals results in a smaller percentage retention in the body.

5. Considering both the difference in the usual consumption of food and of water in practical human nutrition, and the difference in potential toxicity of fluorine in water and in food, a concentration of 1 p.p.m. of fluorine in the drinking water defining the upper limit of safety, is the hygienic equivalent of from 2.4 to 4.8 p.p.m. of fluorine in the total food, depending upon the proportion of the water intake that contains fluorine in the critical concentration.

² This investigation was conducted under the supervision of a Committee on the Physiological Effects of Spray Chemicals, appointed by the director of the Agricultural Experiment Station and consisting of the following members: H. H. Mitchell, W. A. Ruth, W. P. Flint and Julia P. Outhouse.

Manuscript received 29 March 1939.

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