Sherry Barbadillo

Percutaneous absorption of arsenic from environmental media

Current knowledge of percutaneous absorption of arsenic is based on studies of rhesus monkeys using soluble arsenic in aqueous solution, and soluble arsenic mixed with soil (Wester et al., 1993). These studies produced mean dermal absorption rates in the range of 2.0-6.4% of the applied dose. Subsequently, questions arose as to whether these results represent arsenic absorption from environmental media. Factors such as chemical interactions, the presence of other metals, and the effects of weathering on environmental media all can affect the nature of arsenic and its potential for percutaneous absorption. Therefore, research specific to more relevant matrices is important. The focus of this effort is to outline study design considerations, including particle size, application rates, means of ensuring skin contact and appropriate statistical evaluation of the data. Appropriate reference groups are also important. The potential for background exposure to arsenic in the diet possibly obscuring a signal from a dermally applied dose of arsenic will also be addressed. We conclude that there are likely to be many site-or sample-specific factors that will control the absorption of arsenic, and matrix-specific analyses may be required to understand the degree of percutaneous absorption.

In vitro human nail penetration and kinetics of panthenol

The in vitro absorption of panthenol into and through the human nail was examined in this study. Panthenol, the alcohol form of pantothenic acid (vitamin B5), is believed to act as a humectant and improve the flexibility and strength of nails. A liquid nail treatment formulated with panthenol (2%) was compared to a solution of panthenol (2%) in water. Fingernail specimens were dosed daily for 7 days with either the nail treatment (non‐lacquer film forming) formulation or aqueous solution with sampling performed every 24 h. Panthenol concentrations were determined in the dorsal surface, interior (by drilling and removal) and in the supporting bed under the human nail. Panthenol levels in the dorsal nail (R2 = 0.87; P < 0.001), nail interior (R2 = 0.94; P < 0.001) and nail supporting bed (R2 = 0.79; P < 0.003) showed a significant linear increase with each day of dosing. Significantly more panthenol was delivered into the interior nail and supporting bed by a nail treatment formulation than from an aqueous solution. The film acts not only as a reservoir of panthenol, but also acts to increase the hydration of the nail and the thermodynamic activity of panthenol as well, thereby enhancing diffusion.

In vitro percutaneous absorption of benzene in human skin

The in vitro percutaneous absorption of carbon-14-labeled benzene ([14C]benzene) in dermatomed human skin was determined using 2 cleaning products containing benzene. This study utilized cleaning solutions commonly used in the workplace. As Environmental Protection Agency (EPA) guidelines cover dose occlusion for volatile chemicals, the treatments were both nonoccluded and occluded, with low (10 μL/cm2), high (30 μL/cm2), and multiple (10 μL/cm2 × 3 at 0, 30, and 60 min) doses. In an open-to-air test, the benzene quickly evaporated, and only 0.5%–1.4% of the original dose remained after 30 minutes. In the diffusion studies, human skin absorption of benzene peaked in the first few hours without occlusion, but was sustained for 24 hours with occlusion. The absorption of a high single dose was 1.2 ± 0.16 times (mean ± standard deviation) greater than that of a multiple dose, whereas theory would predict 1.0. The low-dose to high- or multiple-dose ratio was 3.6 ± 2.2, so there was a clear dose response. The effect of occlusion was significant. In this study occlusion increased absorption by 40.1 ± 24.6 times. These data place into partial perspective the role of occlusion in benzene flux, but should not be generalized until other volatile substances are studied in the experimental system and further validated with in vivo systems.