A new method for estimating dermal absorption from chemical exposure: 2. Effect of molecular weight and octanol-water partitioning.

A new method for estimating dermal absorption including the effects of exposure time and chemistry is described generally in Part 1 of this series. This method accounts for the larger absorption rates during the initial exposure period as well as the hydrophilic barrier which the viable epidermis presents to lipophilic chemicals. A key parameter in this procedure, the ratio of the stratum corneum and epidermis permeabilities (B) depends on molecular weight and octanol-water partitioning. Several approaches for approximating B and its affect on the dermal absorption prediction are discussed here. Generally, the parameter B is only important for highly lipophilic chemicals which also have relatively small molecular weights. When B is important, the recommended prediction for B is based on the Potts and Guy correlation for human stratum corneum permeability.