Appendix D Food Codes for NHANES - OEHHA

Scientific Review Panel Draft February, 2012
Age may be a factor in the absorption of TCDD-like compounds. Anderson et al.
(1993) applied radiolabeled TCDD in acetone (111 pmol/cm 2 applied over 1.8
cm 2 ) to the interscapular region of 3-, 5-, 8-, 10-, and 36-week-old rats and
measured dermal absorption 72 hrs later. Dermal absorption was greatest in 3week-old
rats at 64%, decreasing to about 40% in 5-, 8-, and 10-week-old rats,
and to about 22% in 36-week-old rats. Although the reason for the age-related
changes in dermal absorption was not explored, the authors suggested
increased lipids in skin of the young may be a factor.
F. 4.2.2 Discussion and Recommendation for a Polychlorinated Dibenzo-pdioxin
and Dibenzofuran ABS
Human skin has the capacity to store TCDD in vitro (Weber et al., 1991; Roy et
al., 2008). Once absorbed in skin, lipophilic compounds such as TCDD are
anticipated to be eventually absorbed into the systemic circulation. Data for
another lipophilic pollutant, lindane, indicates that the chemical retained in skin
will be eventually systemically absorbed (Dick et al., 1997a).
Several methods for assessing the dermal exposure data by US EPA (1992) and
Roy et al. (2008) were employed above to obtain a total fractional absorption
(i.e., amount that reached the bloodstream + amount retained in skin) for TCDD
ABS. Since the fractional dermal absorption values presented in this document
are based on 24-hr exposure, the most relevant means for estimating an ABS is
to rely only on the 24-hr absorption results. The resulting human 24-hr fractional
TCDD absorption rate by this method is 1.4%. Roy et al. (2008) employ a
monolayer adjustment factor in their assessment, noting that the human in vitro
skin test used a soil load of 6 mg/cm 2 , which was greater than monolayer load by
a factor of 2. Multiplying by this factor, the 24-hr TCDD fractional absorption for
human skin is estimated at 2.8% for LOS, which is then rounded up to 3%.
Although both Shu et al. (1988) and Poiger and Schlatter (1980) estimated
dermal absorption fractions in rats near 2%, neither study specified the organic
carbon content of the TCDD-contaminated soil. The organic carbon content of
soil is a major determinant for TCDD dermal absorption. At 96 hrs, USEPA
(1992) noted that the ratio of TCDD absorption from low organic carbon soil
(0.45% organic carbon) in rat skin measured in vitro to absorption from high
organic carbon soil (11.2% organic carbon) in the same system was 7.5. Without
the organic carbon content of the soil, it is difficult to compare the findings of Shu
et al. (1988) and Poiger and Schlatter (1980) with that of the USEPA study.
TCDD aged in soil prior to dermal application had little effect on absorption,
which is supported by the long half-life of TCDD in soil. Shu et al. (1988)
observed similar dermal absorption estimates when TCDD was freshly added to
soil in the lab and soil that had been environmentally contaminated with TCDD
and presumably aged in the soil. In addition, soil aging of polychlorinated
biphenyls (PCBs), a group of soil contaminants with some structural similarities
F-53