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Abstract— To evaluate systemic chemical exposure, the permeability coefficient can be used to estimate absorption. This parameter characterizes the transfer rate of a substance in a vehicle across a membrane. The biological membrane thickness is a factor of resistance to permeability. Thus, it seems interesting to take this parameter into consideration in the calculation of the absorption.
In this study, a calculation model of systemic exposure through the skin and the nail has been developed for finite dose conditions. It represents a new approach to systemic exposure assessment and is based on the following assumption: systemic exposure to a molecule is achieved when this substance has completely crossed the biological membranes. We used skin and nail thickness to integrate the permeability coefficient in the formula. The permeability coefficient, the membrane thicknesses and the contact time represent what is called the systemic absorption factor which can be incorporated in external exposure formulas. Presented in an exponential form, it can be used to determine the amount absorbed versus time and to assess the systemic exposure to an applied amount which is finite.