Appendix D Food Codes for NHANES - OEHHA

Scientific Review Panel Draft February, 2012
60 times the weight fraction of organic carbon. The models were then used to
estimate the relative effect of changing exposure conditions (e.g., changes in soil
loading, contamination levels, chemical, etc.) compared to published
experimental studies. Although the models were generally consistent with the
experimental results for some chemicals, such as benzo(a)pyrene (BaP), they
were considerably divergent from the experimental results for other chemicals,
such as lindane (gamma-hexachlorocyclohexane).
The authors suggested that the fast soil release kinetics on which the models are
based may not fit with what was observed experimentally for some chemicals
(Bunge and Parks, 1997). Fast soil release kinetics assumes the primary
resistance that controls transfer of the chemical from soil to skin resides in the
dermal barrier, and that the kinetics of soil desorption are relatively insignificant.
Lindane may exhibit slow soil release characteristics in various soils (i.e., soil
desorption of the chemical is the controlling influence for dermal absorption),
which limits the amount of dermal absorption predicted by the models.
Alternatively, Shatkin et al. (2002) developed a two-stage fugacity-based model
specifically for BaP that incorporated both a fast soil desorption phase and a slow
desorption phase of BaP from soil. Based on the several parameters
investigated that would affect dermal bioavailability, the authors predicted that
the fast desorption kinetics of a soil had a greater impact on predicted dermal
uptake than any other parameter, including organic carbon content of a soil.
These examples show that the effect of soil on the dermal uptake of organic
compounds can be difficult to predict without experimental data. However,
dermal absorption by metal salts can be expected to be a more complex process
than dermal absorption of organic compounds. Factors affecting absorption of
soil-bound metals include pH, metal oxidation state, counter ion, size and
solubility (Hostynek, 2003). For example, lead becomes more soluble and
available for uptake in soil at low pH. However, a low soil pH tends to convert
chromium (VI) to the larger less permeable chromium (III) ion. This reduction in
chromium valence can also occur in transit through the skin and considerably
slow the absorption of chromium through skin.
F.2.4 Effect of Soil Organic Content on Dermal Absorption
For the soil pollutants discussed in this section, one of the most common soil
variables explored for effect on dermal absorption of a chemical is the organic
carbon or organic matter content. The chemical adsorbed to the organic carbon
phase will generally be less available for transfer to skin than neat chemical
present in a separate liquid phase in the soil, largely due to strong adsorption of
the chemical to the organic carbon fraction (Bunge and Parks, 1996). Dermal
bioavailability of a chemical in soil also tends to decrease with increasing organic
carbon content of the soil (Sheppard and Evenden, 1994; Bunge and Parks,
1997). Consequently, a number of studies compared the effect of varying the
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