Chemical exposure in most environmental and occupational settings involves complicated chemical mixtures, not individual chemicals. However, current health risk assessment of dermal absorption is based on permeation data for individual chemicals due to lack of available quantitative methods or experimental data from chemical mixtures. In the system coefficient approach, a set of solute descriptors, represents the molecular interaction strengths of a chemical of interest, while a set of system coefficients, [r, s, a, b, v], represents those of the skin/medium system. The permeation coefficient or partition coefficient (logK) is correlated with the system coefficients and the solute descriptors via Abraham's linear free energy relationship. The major components of the mixture determine the system coefficients. When the major components change in composition or proportion, the system coefficients will be changed. When 25% of ethanol was added to the water solution of the 32 calibration compounds, the system coefficient changes of the polyacrylate/water system were [-0.12, 0.17, 0.23, 0.33, -0.42], respectively. When 1% of sodium lauryl sulfate was added to the water solution, the system coefficient changes were [-0.41, 0.34, 0.23, 0.74, -1.53], respectively. In practical risk assessments, the changes in system coefficients can be treated as sufficiently similar mixtures. If the system coefficients of the mixture of concern and the system coefficients of the sufficiently similar mixtures are determined, the permeability or partition coefficient of any chemical can be obtained by using the system coefficient approach.
The Toxicologist. Society of Toxicology 44th Annual Meeting and ToxExpo, March 6-10, 2005, New Orleans, Louisiana