Estimation of dermal absorption using the exponential saturation model

Estimates of dermal absorption are used in exposure assessment to calculate the internal dose of persons contacting pesticides and are a critical part of risk assessments. An exponential saturation model with lag time was validated against a classic dermal absorption study of 12 pesticides administered to human volunteers. The model gave dermal absorption estimates consistent with reported values in the literature. Moreover, this model gave more realistic estimates of the percentage of dermal absorption for some pesticides, which have special properties. In most submitted dermal absorption studies in animals, especially rats, "bound" skin residues (BSR) at treated skin sites were generally high when animals were sacrificed more than 24 h after the dose was administered. The direct addition of the total BSR as an absorbed dose would likely overestimate actual dermal absorption. From a well-conducted dermal absorption study, this model can be utilized to estimate maximum excretion of the administered dermal dose as a result of further absorption of bioavailable BSR. Resulting dermal absorption estimates are appropriate for regulatory purposes in the risk assessment of pesticides because they take into account the bioavailability of BSR while at the same time the estimates are not overly conservative.