Appendix D Food Codes for NHANES - OEHHA

Scientific Review Panel Draft February, 2012
Comparison of data from other studies does support that in general, the
absorption in the rabbit, rat and other rodents can considerably overestimate
absorption in humans, while absorption in monkeys and miniature pigs most
closely predict human absorption (Wester and Maibach, 1975; Reifenrath et al.,
1984; Wester and Maibach, 1985; Bronaugh et al., 1990; Wester et al., 1998a).
Alternatively, Kao et al. (1985) found that in vitro permeation of testosterone and
BaP through human skin was greater than that for guinea pig, rat, or rabbit,
indicating that species-specificity differences likely depend on other factors such
as experimental conditions and tissue viability. Variability in dermal absorption
depending on the skin area exposed has been investigated (Wester and
Maibach, 1983). In humans, absorption across the skin varies by area of the
body and may be higher than the commonly used forearm (e.g. scalp, axilla,
forehead, jaw angle and scrotum).
F.2.9 Metabolism of Absorbed Chemicals in the Skin
The description of percutaneous absorption is generally based on diffusion
models that take into account the physico-chemical characteristics of chemicals
and soils. While such descriptions may help to explain the uptake of chemicals
across the stratum corneum, the role played by metabolism in the viable
epidermal and dermal layers should be included to understand the complete
permeation of chemicals through the skin (Wester and Maibach, 1983; Kao and
Carver, 1990; Bronaugh et al., 1994).
Viability of the skin refers to the status of active energy turnover, i.e. the
utilization of glucose and formation of CO2 or lactate in skin. Enzymes and
metabolic processes in skin may affect the dermal penetration of drugs and other
xenobiotics, particularly if absorbed chemicals can be metabolized in the skin.
Using production of lactose as the measure of viability, human skin placed in a
buffered solution and kept refrigerated remained viable for about 8 days following
donor death (Wester et al., 1998b). Skin frozen for storage or heat-treated to
separate the epidermis and dermis renders the skin non-viable and may change
the dermal penetration dynamics of absorbed chemicals. Some early studies
investigating the dermal penetration of chemicals used previously frozen skin
samples and may not provide a good basis for ABS determination.
Dermal metabolism of BaP was observed to be considerably reduced in several
mammalian species with use of non-viable skin, resulting in reduced penetration
of BaP through skin (Kao et al., 1985). In viable human skin, nearly half the BaP
that permeated the skin was attributed to BaP metabolites. In non-viable skin,
essentially only unchanged BaP was detected in the receptor fluid. In fact,
dermal absorption of polycyclic aromatic hydrocarbons (PAH) that include BaP
resulted in PAH-DNA adducts in human skin samples, demonstrating that skin is
a target organ due to metabolic activation of PAHs in skin (Phillips et al., 1990).
F-13