In vivo percutaneous absorption of boron as boric acid, borax, and disodium octaborate tetrahydrate in humans
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Literature from the first half of this century reports concern for toxicity from topical use of boric acid, but assessment of percutaneous absorption has been impaired by lack of analytical sensitivity. Analytical methods in this study included inductively coupled plasma-mass spectrometry, which now allows quantitation of percutaneous absorption of10B in10B-enriched boric acid, borax, and disodium octaborate tetrahydrate (DOT) in biological matrices. This made it possible, in the presence of comparatively large natural dietary boron intakes for the in vivo segment of this study, to quantify the boron passing through skin. Human volunteers were dosed with10B-enriched boric acid, 5.0%, borax, 5.0%, or disodium octaborate tetrahydrate, 10% in aqueous solutions. Urinalysis, for boron and changes in boron isotope ratios, was used to measure absorption.
Boric acid in vivo percutaneous absorption was 0.226 (SD = 0.125) mean percent dose, with flux and permeability constant (K p ) calculated at 0.009 μg/cm2/h and 1.9 x 10-7 cm/h, respectively. Borax absorption was 0.210 (SD = 0.194) mean percent dose, with flux andK p calculated at 0.009 μg/cm2/h and 1.8 x 10-7 cm/h, respectively. DOT absorption was 0.122 (SD = 0.108) mean percent, with flux andK p calculated at 0.01 μg/cm2/h and 1.0 x 10-7 cm/h, respectively. Pretreatment with the potential skin irritant 2% sodium lauryl sulfate had no effect on boron skin absorption.
These in vivo results show that percutaneous absorption of boron, as boric acid, borax, and disodium octaborate tetrahydrate, through intact human skin is low and is significantly less than the average daily dietary intake. This very low boron skin absorption makes it apparent that, for the borates tested, the use of gloves to prevent systemic uptake is unnecessary. These findings do not apply to abraded or otherwise damaged skin.
Index EntriesBoron analysis isotope ratio excretion dietary boron
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- 2.R. C. Wester, X. Hui, T. Hartway, H. I. Maibach, K. Bell, M. J. Schell, et al., In vivo percutaneous absorption of boric acid, borax and disodium octaborate tetrahydrate in humans compared to in vitro absorption in human skin from infinite and finite doses,Toxicol. Sci. 45, 42–51, (1998).PubMedGoogle Scholar