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revealed no signs of fluorosis, and their urinary fluoride concentrations were normal. Animal experiments with extracts of stack effluents revealed no adverse effects at the concentrations used. The authors concluded that there was no evidence of an association of fluorine or fluorides with the observed skin conditions (Cavagna et al., 1969).

Lyon (1962) reported that 61 workers exposed to fluorine who excreted fluoride at an average of 1.1 mg/L for 7 yr (2,535 determinations) had better health records than the 2,000 employees used as controls and had fewer respiratory complaints. The average F2 exposure was not known, but the author speculated that it was “greatly in excess of 0.1 ppm.” The same author observed that intermittent industrial exposures to F2 at up to 30 ppm for 5–30 min had no ill effects. No other reports of uncontrolled F2 exposures, accidental or occupational, are known to the Committee.

Controlled Exposure

Outdoor “spill” tests conducted by the U.S. Air Force revealed that single “short-term” F2 exposures at 25 ppm (duration not reported) were “intolerably irritating,” and exposure at 50 ppm made breathing impossible (Rickey, 1959). The number of subjects involved in this study was not reported.

Belles (1965) observed nine male volunteers exposed to F2 under controlled conditions. Most of the subjects found that 15–25 ppm caused some nasal and eye irritation after two or three breaths. All subjects tolerated repeated short-term (duration unspecified) exposures at up to 10 ppm without discomfort. Additional details of this study were not available to the Committee.

Keplinger and Suissa (1968) exposed 5 volunteers (aged 19–50) to F2 under a variety of conditions that permitted accurate measurement of F2 concentrations. Exposure took place under a mask that covered the eyes and nose, but not the mouth. Thus, the effects of F2 on respiration were not routinely measured (some subjects did inhale and some data on respiratory effects were obtained). The results of this study are summarized in Table 19. The authors also noted that, when exposure was repeated weekly, the subjects did not perceive as much irritation as they had on first exposure. The apparent development of tolerance is consistent with that seen in experimental animals. Finally, the authors studied the effects of exposure at 10 ppm for 3–5 min every 15 min for 2 or 3 h. All subjects tolerated such repeated exposures with only slight irritation of the eyes and skin.

EFFECTS ON ANIMALS

Acute exposure

Almost all animal studies of F2 toxicity known to the Committee were acute (single exposures). The most comprehensive of such studies, and the only ones involving actual measurement of the concentrations of F2 at which the animals were exposed, were reported by Keplinger and Suissa (1968). The only known earlier studies were conducted during World War II; they involved only lethal concentrations (the



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