Appendix D Food Codes for NHANES - OEHHA

Scientific Review Panel Draft February, 2012
soil organic content on the dermal absorption of a chemical. The health
protective approach for estimating an ABS would be to base the value on the
higher dermal absorption from these studies, often from the soil with lower
organic carbon content.
The length of time required for a chemical to partition to the soil organic material
may be quite short (a few days) or longer (more than a month), depending on the
nature of the deposited chemical, the soil and the weather (Bunge and Parks,
1996). However, early dermal absorption studies of chemicals in soil were
usually conducted with freshly spiked soil just prior to exposure. Regardless of
the partitioning time to the soil organic carbon, addition of a chemical to soil can
often result in a reduction of dermal bioavailability relative to the pure chemical.
For a group of selected organic compounds (e.g., DDT, BaP, PCBs, etc.) and
arsenic, addition to soil just before loading onto skin reduced the overall dermal
uptake by an average of about 60% compared to dermal uptake of the pure
chemical (Wester and Maibach, 1999). However, a reduction in absorption from
soil relative to a neat solution cannot be predicted for all chemicals. Dermal
absorption for some chemicals such as arsenic in soil was found to be essentially
unchanged compared to absorption from the neat solution.
F.2.5 Soil Aging Effects
The ABS point estimates presented here are primarily based on soils that were
freshly spiked with contaminants and placed on skin for roughly 24 hrs. As such,
the ABS point estimates largely represent the initial fast phase of decreased
bioavailability when a chemical is freshly added to soil prior to skin exposure
(Alexander, 1995; Bunge and Parks, 1997). This phase is generally a reversible
process, such that a chemical sorbed to soil may become desorbed and be
available for uptake during the skin exposure.
However, over time many chemicals added to soil undergo a slower second
phase of decreased bioavailability. The soil-deposited chemicals tend to move
from the external surface of soil particles to internal and more remote sites within
the soil matrix so that chemicals become increasingly more desorption-resistant,
a process known as aging (Alexander, 1995). A number of recent dermal
absorption studies discussed below have observed reductions in dermal
absorption occurring for up to 3-6 months following addition of the chemical to
soil. Reductions of about 50% have been observed for dermal absorption of BaP
aged in soil compared to soils freshly spiked prior to skin application (Roy and
Singh, 2001). Abdel-Rahman et al. (1999) observed up to a 7.5-fold reduction in
dermal absorption for arsenic aged in soil.
The continuous input of chemicals deposited on soils in the vicinity of “Hot Spots”
stationary sources will likely result in the less recently deposited chemicals
undergoing soil aging. For toxic inorganic metals in soil, the dermal dose
equation (Eq. 6.1) does not account for decreased bioaccessibility over time due
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