Acute Dermal Toxicity of Dilute Hydrofluoric Acid

While it is well known that concentrated solutions of hydrofluoric acid (HF) are highly corrosive to the skin, very little information is available on exposures to dilute solutions. Dilute aqueous solutions of HF (w/w) were evaluated for dermal toxicity in male albino rabbits using an occlusive patch procedure. A 2% solution of HF was corrosive to rabbit skin when applied topically for durations of 1 and 4 hr. Total serum fluoride levels were markedly elevated at 1 hr following cessation of exposure. The weight of the testes was significantly lower in those rabbits exposed to 2% HF for 4 hr. Dilute solutions of HF (0.01-2%) proved corrosive following exposure durations as short as 5 min. Two percent HF was noncorrosive with 1 min exposure (lesser concentrations were not tested at this time period). The incidence of lesions resulting from exposure to HF solutions of 0.5% or less at exposure durations ranging from 5 min to 60 min was variable and no correlation could be drawn between the severity of the lesions and the exposure duration and HF concentration. The results suggest that marked dermal injury and systemic fluoride poisoning could result to humans following dermal contact with HF solutions at concentrations as low as 2% for durations as short as 1 hr. Solutions of HF at concentrations as low as 0.01% could possibly cause injury to the more sensitive areas of human skin following exposures as short as 5 min.