Wester, R. C., T. Hartway, H. Maibach, M. J Schell, D. J. Northington, B. D. Culver, and P. L. Strong. In vitro percutaneous absorption of boric acid, borax, and disodium octaborate tetrahydrate in human skin from infinite and finite dosing. The Toxicologist 42 (1-S): 389. March 1998.

boric acid - 11113-50-1; borax - 1303-96-4; disodium octaborate tetrahydrate - 12280-03-4

In vitro percutaneous absorption of boric acid, borax and disodium octaborate tetrahydrate (DOT) was done with infinite and finite doses for comparison to in vivo absorption. Inductively coupled plasma mass spectrometry made it possible to quantify in vitro percutaneous absorption of ¹⁰B present in ¹⁰B-enriched chemicals, using human cadaver skin mounted on Teflon flow-through diffusion cells over a 24 hour period. Percent boric acid absorbed was 1.2 for a 0.05% solution, 0.28 for a 0.5% solution and 0.70 for a 5.0% solution. Skin surface soap and water washes removed, respectively 72.4%, 86.0% and 81.9% of the applied doses at the end of the dosing period. Flux values were, respectively 0.25, 0.58 and 14.58 ug/cm²/hr and permeability constants (Kp) of 5.0 x 10^-4 cm/hr for the 0.05%, 0.5% and 5.0% solutions. The above in vitro doses were at "infinite", 1000 ul/cm², dosing volumes. When 5% boric acid solution was applied at a 2 ul/cm² volume (the in vivo dosing volume), flux decreased significantly to 0.07 ug/cm²/hr with a Kp of 1.4 x 10^-6 cm/hr. Borax dosed at 5.0%/1000 ul/cm² had a 0.41 percent absorbed. Flux was 8.5 ug/cm²/hr, and Kp was 1.7 x 10^-4 cm/hr. DOT dosed at 10%/1000 ul/cm² was 0.19 percent absorbed. Flux was 7.9 ug/cm²/hr and Kp was 0.8 x 10^-4 cm/hr. These in vitro results from "infinite" doses (1000 ul/cm²) were a thousand-fold higher than those obtained in the in vivo study. The results from the finite (2 ul/cm²) in vitro dose were closer to the in vivo (2 ul/cm²) results.