As summarized in Ross et al. (2000), skin is the primary route of exposure to pesticides accounting for as much as 30% of the potential indoor toddler exposure (Ross et al., 1992) and 90% of agricultural worker exposure (Wolfe, 1976), especially when the pesticide has low vapor pressure. Yet dermal absorption and dermal acquisition are more protracted when compared to the oral route, inhalation, or injection. Therefore, in the calculation of exposure to pesticides, dermal absorption becomes an important variable for which the value to be used should not be arbitrarily assumed if at all possible.

As humans are largely unsuitable test subjects due to ethical issues, the rat is the most commonly used model to estimate dermal absorption. To ensure that the animal results are credible and easily interpretable, U.S. EPA (1998a) has published guidelines for the proper conduct of dermal penetration studies in rats. The European scientific community (EVCAM, 1996) likewise has drafted guidance for this movement.

Some substances with low water solubility are poorly absorbed into the body. Portal blood from the gastrointestinal tract passes through the liver before reaching the general systemic circulation. Foreign compounds that are absorbed orally can thus be excreted directly into bile and eliminated with feces. Due to the volatility of the chemical, in some cases inhalation uptake (that brought to the lungs) and inhalation intake (that brought into the circulation) could each be < 50%. In short, attention should be given to these absorption factors when estimating the intake portions of the applied doses.