Time constant for the dermal absorption of semivolatile organic compounds from the gas phase of indoor air

A Laplace transform-based technique was applied to solve a mechanistic model and simulate scenarios often encountered in the percutaneous absorption studies of semivolatile organic compounds (SVOCs) from indoor air. The system included the stratum corneum layer, a skin surface lipid region and the viable epidermis. The new framework made it possible to provide analytical expressions for the effective time constant (t_eff). This dynamic key performance indicator helped estimate the time required to reach either a steady-state absorption rate or the total amount of SVOC absorbed into the bloodstream. In the case of a constant concentration C_g of the chemical, the flux reached 98.1% of its steady-state value at 4t_eff. When participants were exposed to 29.4 µg/cm³ of m-xylene vapors during an 8-hour period and zero concentration thereafter, the mass of m-xylene entering the bloodstream and the time constant were 4.40 mg and 1.02 h, respectively. The mass transfer coefficient between the air and the surface of the lipid layer (h_m) remained unchanged. The methodology calculated t_eff in cases of varying h_m and temporary C_g when an SVOC was absorbed into the capillaries after a relatively short exposure time.