Identification of two forms of fluorine in tissues of rats inhaling hydrogen fluoride

Nonionizable fluorine has been detected in the plasma of several species including the human, however, the exact nature and source of this fluorocompound(s) remain unknown. In the current investigation, the fluoride ion sensitive electrode was employed to determine the fluoride content of ashed (total F) and unashed (ionic F-) tissues of rats exposed to hydrogen fluoride (HF). Total fluorine concentration consistently exceeded ionic fluoride concentration in tissues of HF-exposed rats, suggesting the presence of fluorine in unashed tissue which did not respond to the F- ion sensitive electrode. The concentration of this nonresponding fluorine fraction, termed the delta F fraction, was estimated by subtracting the ionic F- from the total F concentration of each sample. Pulmonary and plasma delta F concentrations increased with time following whole body inhalation exposure to HF. It was possible to separate delta F from ionic F- by calcium phosphate adsorption, indicating that the delta F fraction consists of nonionizable fluorine. Upon Sephadex G-25 gel chromatography, plasma delta F migrated near the bed volume, providing evidence that it is of low molecular weight. Finally, a strong correlation (r = 0.99, p less than 0.01) between plasma delta F concentration and airborne HF concentration was observed, indicating that inorganic fluoride (as HF) is the ultimate source of the low-molecular-weight, nonionizable fluorine species present in tissues of HF-exposed rats.