Print PageThe more terrestrial the life history cycle of a tetrapod is, the more likely it is to use the skin to regulate its water content in order to maintain hydration. As a result, selection-related differences within the tetrapod classes causes significant variability in skin permeability. These differences can have significant impacts on the chemical exposure rates from dermal uptake. For pesticides, hydrophilic and lipophilic molecules have distinct pathways for dermal exposure, with neutral, lipophilic molecules traditionally getting the most attention in humans and other mammals. However, preferential water uptake by the seat patch in amphibians increases the effective surface area for osmosis and may enhance the potential for low Kow dermal contaminant exposures; while adaptations such as fur, feathers, and keratinized skin in mammals, birds, and reptiles can limit dermal exposure to a degree. Therefore, although amphibian epidermis has some capability to limit exposures to contaminants, positive linear relationships between Kow and contaminant flux across amphibian skin are significantly higher in amphibians versus mammals. In addition, sustained direct contact with soil from life history traits, daily movement patterns, overnight burrowing, and aestivation/hibernation periods further complicates chronic exposure estimation in all classes.
Results/Conclusions
We construct class-specific parameters and methods to estimate the relative contribution of dermal exposure (dermal dose versus total dose from all pathways) for chemicals with low, medium, and high Kow values with exposure models for each of the four classes of tetrapods (amphibians, reptiles, birds, and mammals). For all classes, doses were higher for chemicals with higher Kow values. The relative contribution of dermal exposure is significantly greater for amphibians than for other classes. For reptiles, the relative contribution is strongly dependant on the Kow, being high for high-Kow chemicals but not significant for low Kow pesticides. The relative contribution of dermal exposure is relatively small for birds and mammals. These results have implications for terrestrial ecological risk assessment estimation for low Kow contaminants, especially considering the common practice of selecting sets of representative species that do not contain all four classes of terrestrial vertebrates.
