Appendix D Food Codes for NHANES - OEHHA

Scientific Review Panel Draft February, 2012
conditions. For example, the ABS will decrease as an organic chemical is
increasingly loaded onto skin. In other words, absorption of an organic chemical
through skin is flux-limited, and loading more chemical onto skin in a defined
area will not increase flux, but will decrease the ABS value.
To aid interpretation of dermal absorption-related phenomena, Kissel (2011)
proposed a dimensionless variate representing the ratio of mass delivery to
plausible absorptive flux under experimental or environmental conditions. High
values of this dimensionless dermal variate connote surplus supply (ie., fluxlimited)
conditions. This situation is similar to loading skin with chemical-bound
soil above monolayer levels. The potential mismeasure of dermal absorption
with chemicals applied neat to skin is addressed below for every chemical in
which an ABS is derived in this way.
F.2.7 In Vivo Vs. In Vitro Experiments
It is generally recognized that the most reliable method for assessing skin
absorption of a chemical is to measure penetration in vivo using the appropriate
animal model or human volunteers (Kao, 1990). Thus, in vivo data are preferred
over in vitro data for determination of a chemical ABS in this exposure
assessment. In vivo data may be lacking for some chemicals of interest in this
document due to economical considerations for conducting tests in humans and
other mammalian species, or due to ethical concerns for testing in humans.
In vitro studies have the benefit of measuring dermal absorption under more
easily controlled environments. Human skin can be tested without the inherent
risks of a clinical study, and absorption through skin and retention in skin can be
directly measured. Consequently, in vitro dermal absorption studies are
frequently performed and provide the basis for an ABS for some chemicals
presented in this section, following careful consideration for relevance to in vivo
human exposure.
Although good agreement has been found when comparing in vivo and in vitro
absorption results for some chemicals, trends towards lower absorption with in
vitro exposure have been observed. For example, lipophilic compounds
frequently have limited solubility in the buffered aqueous receptor fluids often
used for in vitro cell systems, impeding the flow into the receptor fluid and
resulting in an underestimation of skin penetration (Wester and Maibach, 1999).
In vivo, lipophilic compounds penetrate the stratum corneum and diffuse through
skin and, because of the solubilizing and emulsifying abilities of biological fluid,
may readily be taken away by the blood in the dermal vasculature.
A reduction in skin viability of excised skin samples may occur due to storage
conditions prior to use and may affect dermal absorption measurements. For
example, the metabolic properties of human skin are reduced if the skin samples
were previously frozen. Some polycyclic aromatic compounds (PAHs) undergo
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