SUBCHRONIC RAT INHALATION STUDY WITH SKYDROL® 500B-4 FIRE RESISTANT HYDRAULIC FLUID

Skydrol® 500B-4 fire resistant hydraulic fluid, a proprietary phosphate ester mixture composed principally of dibutyl phenyl phosphate (DBPP) and tributyl phosphate (TBP) and used as a commercial airline hydraulic fluid, was evaluated in an inhalation toxicity study of Sprague-Dawley rats. Target exposure levels used in the study were 0, 5, 100, and 300 mg/m3, and exposures were maintained for 6 hr/day, 5 days/week. Mass median aerodynamic diameters determined for particles in the mid- and high-exposure inhalation chambers were 2.85 µm and 3.31 µm, with geometric standard deviations of 1.99 µm and 1.92 µm, respectively. The percentage of particles <10 µm in diameter were 96.4% in the mid-exposure chamber and 95.5% in the high-exposure chamba\ After 6 weeks of Skydrol exposure, 10 rats/sex/group were euthanized and then assessed for indications of possible chemical toxicity. Another 15 rats/sex/group were studied for a total of 13 weeks of exposure. The only clinical sign of chemical toxicity was the obser...