Appendix D Food Codes for NHANES - OEHHA

Scientific Review Panel Draft February, 2012
underestimate dermal absorption obtained by in vivo methods (USEPA, 1992;
Wester et al., 1993b). A reason for this underestimation may be the limited
lipophilicity of the receptor fluid used with the in vitro systems.
F. 4.2 Polychlorinated Dibenzo-p-dioxins and Dibenzofurans
"Dioxin" emissions are reported as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)
equivalents. Therefore, for purposes of the Hot Spots program, all
polychlorinated dibenzo-p-dioxins and dibenzofurans are considered to have the
same dermal absorption characteristics as TCDD.
Recommended point estimate for dermal uptake from soil: 3%
F. 4.2.1 Studies Considered
A. Key Studies
The dermal absorption of TCDD from high organic (HOS) and low organic (LOS)
soils in rats in vitro, and in human skin in vitro and rats in vivo from LOS only,
was investigated during exposure intervals up to 96 hours (U.S. EPA, 1992; Roy
et al., 2008). The LOS was comprised mostly of silt with an organic carbon
content of 0.45% and a particle size range within 0.05-2 mm. For the in vitro
studies, the TCDD concentration in the LOS was 1 ppm with soil loading of 10
mg/cm 2 on the rat skin and 6 mg/cm 2 on the human skin. After 24 hrs, 0.28%
and 1.17% of the applied dose had penetrated human and rat skin, respectively,
to the receptor fluid (Table F-3). Although the dose of TCDD remaining in skin
was not determined at 24 hrs, the 96 hr exposure estimate in human and rat skin
following skin surface wiping was 0.17 and 1.41%, respectively. The percent of
applied dose reaching the receptor fluid at 96 hrs was 2.25% in human skin and
6.32% in rat skin.
The percent of dose absorbed from LOS by rats in vivo was 7.9% at 24 hrs and
16.3% at 96 hrs (Table F-3). TCDD absorbed was estimated indirectly by
dividing the percent of applied dose found in the excreta by the fraction of applied
dose in the excreta at the same time after i.v. administration. However, TCDD
systemically absorbed at 96 hrs was also quantified in all urine, feces and
tissues, resulting in 16.3% of dose absorbed. To derive an ABS for human in
vivo uptake of TCDD from LOS (0.45% organic carbon content) and HOS (11.2%
organic carbon content), USEPA (1992) applied corrections by direct ratios to
account for rat in vivo, rat in vitro, and human in vitro data. For human TCDD
absorption from LOS, the in vivo absorption in rat at 24 hrs was multiplied by the
ratio of human to rat total absorption in vitro measured at 96 hrs. The 96 hrs
data were used because this was the only measurement in which TCDD in skin
was quantified. The final ABS was 2.5% (8.0% x 2.42% / 7.74%).
F-50