Dermal uptake directly from air under transient conditions: advances in modeling and comparisons with experimental results for human subjects

Abstract

To better understand the dermal exposure pathway, we enhance an existing mechanistic model of transdermal uptake by including skin surface lipids (SSL) and consider the impact of clothing. Addition of SSL increases the overall resistance to uptake of SVOCs from air but also allows for rapid transfer of SVOCs to sinks like clothing or clean air. We test the model by simulating di-ethyl phthalate (DEP) and di-n-butyl phthalate (DnBP) exposures of six bare-skinned (Weschler et al. 2015, Environ. Health Perspect., 123, 928) and one clothed participant (Morrison et al. 2016, J. Expo. Sci. Environ. Epidemiol., 26, 113). The model predicts total uptake values that are consistent with the measured values. For bare-skinned participants, the model predicts a normalized mass uptake of DEP of 3.1 (μg/m )/(μg/m ), whereas the experimental results range from 1.0 to 4.3 (μg/m )/(μg/m ); uptake of DnBP is somewhat overpredicted: 4.6 (μg/m )/(μg/m ) vs. the experimental range of 0.5-3.2 (μg/m )/(μg/m ). For the clothed participant, the model predicts higher than observed uptake for both species. Uncertainty in model inputs, including convective mass transfer coefficients, partition coefficients, and diffusion coefficients, could account for overpredictions. Simulations that include transfer of skin oil to clothing improve model predictions. A dynamic model that includes SSL is more sensitive to changes that impact external mass transfer such as putting on and removing clothes and bathing.

Dermal uptake of phthalates from clothing: Comparison of model to human participant results

“…Wearing freshly laundered clothing resulted in much lower uptake from phthalate enriched chamber air. A recently developed model of transdermal uptake produces estimates that reasonably match measurements for bare‐skinned subjects. However, compared to measurements, the model substantially overpredicts DnBP uptake from clothing.…”

“…The model described in Morrison et al . is updated with the addition of a more realistic clothing layer.…”

“…Transport from clothing to skin lipids is assumed to take place through a thin quiescent layer of air between the clothing and the surface of the lipids by gas‐phase diffusion. From skin lipids to blood, dermal uptake is modeled as in Morrison et al . Advective transport through clothing is assumed to be negligible .…”

How to prevent skin damage from air pollution. Part 1: Exposure assessment

“…Exposure assessment methods were developed primarily for the assessment of occupational exposure to chemicals, and only a few studies are available for selected hazardous air pollutants (Gong et al, 2014;Krais et al, 2018;Morrison et al, 2016;Weschler et al, 2015).…”

“…Sensitivity analysis shows that the absorption flux into blood tends to be more sensitive to the SC thickness and effective diffusion coefficient in SC than the other parameters Morrison, Weschler, and Bekö (2016). This model considers convective mass-transfer resistance through the boundary layer of air adjacent to the skin surface, as well as through the SC and viable epidermis.…”