Dermal absorption of benzene in occupational settings: Estimating flux and applications for risk assessment

Abstract

There is growing emphasis in the United States and Europe regarding the quantification of dermal exposures to chemical mixtures and other substances. In this paper, we determine the dermal flux of benzene in neat form, in organic solvents, and in aqueous solutions based on a critical review and analysis of the published literature, and discuss appropriate applications for using benzene dermal absorption data in occupational risk assessment. As part of this effort, we synthesize and analyze data for 77 experimental results taken from 16 studies of benzene skin absorption. We also assess the chemical activity of benzene in simple hydrocarbon solvent mixtures using a thermodynamic modeling software tool. Based on the collective human in vivo, human in vitro, and animal in vitro data sets, we find that the steady-state dermal flux for neat benzene (and benzene-saturated aqueous solutions) ranges from 0.2 to 0.4 mg/(cm²•h). Observed outlier values for some of the animal in vivo data sets are possibly due to the use of test species that have more permeable skin than humans or study conditions that resulted in damage to the skin barrier. Because relatively few dermal absorption studies have been conducted on benzene-containing organic solvents, and available test results may be influenced by study design or vehicle effects, it is not possible to use these data to quantify the dermal flux of benzene for other types of solvent mixtures. However, depending on the application, we describe several potential approaches that can be used to derive a rough approximation of the steady-state benzene dermal flux for these mixtures. Important limitations with respect to quantifying and evaluating the significance of dermal exposures to benzene in occupational settings include a lack of data on (1) factors that affect the dermal uptake of benzene, (2) the dermal flux of benzene for different organic solvent mixtures, (3) meaningful metrics for evaluating the dermal uptake of benzene, (4) steady-state versus non-steady-state dermal flux values for benzene, (5) the effect of skin damage on the dermal flux of benzene, (6) standardized test methods for estimating the dermal flux of benzene, and (7) robust estimates of the evaporation rate of benzene from different liquid vehicles.

Keywords::

• Benzene
• dermal absorption
• dermal flux
• OSHA PEL
• risk assessment

Acknowledgments

We thank John Persichetti in the Chemical Engineering Department at the Colorado School of Mines for his assistance identifying useful activity coefficient methods to use in our analysis of the chemical activity of benzene.

Declaration of interest

The authors’ affiliation is as shown on the cover page. Three of the authors (Dr. Williams, Ms. Sahmel, and Mr. Spencer) currently work for scientific consulting firms that specialize in environmental science, industrial hygiene, exposure assessment, risk assessment, and related disciplines and which provide environmental, health, and safety services to private and public-sector clients. Dr. Knutsen is a Chemical Engineer at the Colorado School of Mines who is currently investigating the mass and momentum transport within various suspensions and fluids. Dr. Bunge, Professor Emeritus in the Chemical Engineering Department at the Colorado School of Mines, is an expert in the mass transfer of chemicals into human skin from a variety of media including water, non-aqueous solutions, and soils. No outside financial assistance was received by any of the authors for their work on this manuscript, and the authors had sole responsibility for the writing and content of the paper. Three of the authors (Dr. Williams, Ms. Sahmel, and Mr. Spencer) currently serve as expert witnesses in litigation related to occupational benzene exposures.