Appendix D Food Codes for NHANES - OEHHA

Scientific Review Panel Draft February, 2012
residue of 16%. The fraction of applied dermal dose reaching the systemic
circulation was estimated at 22%, with 0.85% of the applied dose in stratum
corneum following tape stripping of the TCB-exposed skin.
Because of the higher tissue residue levels following dermal absorption of TCB,
the researchers noted that dermal absorption of chemicals similar to TCB may be
underestimated without a full mass balance analysis (Qiao and Riviere, 2001). In
other words, estimating dermal absorption by comparing urinary excretion or
blood AUC data with data obtained by the iv route (which represents 100%
absorption) would underestimate actual TCB dermal absorption. Use of these
indirect methods of absorption would provide a calculated dermal absorption of
6.3-10%.
In addition to their in vivo monkey study described above, Wester et al. (1993b)
also estimated in vitro dermal absorption of PCBs through human skin from soil.
The percent dose penetrating to the receptor fluid after 24 hr exposure was
0.04% for both Aroclor 1242 and Aroclor 1254. The percent dose absorbed in
skin was 2.6% for Aroclor 1242 and 1.6% for Aroclor 1254. The low in vitro
dermal absorption compared to their in vivo monkey study results was thought to
result from tissue viability issues or solubility limits with receptor fluid. However,
in vitro dermal absorption and penetration using water as the vehicle resulted in a
fractional absorption of 44-46% for both PCB formulations.
The dermal absorption of purified TCB from soil was studied in rat and human
skin in vitro (USEPA, 1992). The soil was comprised mostly of silt with an
organic carbon content of 0.45% and a particle size range within 0.05-2 mm.
The TCB concentration in the soil was 1000 ppm and soil loading was 10 mg/cm 2
for the rat skin and 6 mg/cm 2 for the human skin. After 96 hours, 7.10% of the
applied dose had penetrated the human skin into the perfusate, with another
0.26% remaining in skin after washing. In comparison, total dermal absorption in
rat skin was over 4-fold higher. A similar experiment was conducted with rat skin
in vitro using a soil with a high organic carbon content of 11.2%. Total dermal
absorption of TCB was reduced over 3-fold compared to total absorption from the
low organic carbon soil.
Dermal absorption of PCBs was estimated by the disappearance method in a
single volunteer exposed to a mixture of 13 C-labeled tetra-, penta-, hexa-, and
heptachlorobiphenyls (Schmid et al., 1992). Five mg of the PCB mixture were
applied to a 4 cm 2 cotton cloth in methylene chloride vehicle and dried. The
cotton cloth was then applied to the tip of the forefinger or inner side of the
forearm without occlusion for 8 hrs. After recovery of PCBs from the carrier and
skin surface, disappearance of the remaining label suggested dermal absorption
was 7 and 47% of total dose applied to finger and forearm, respectively.
However, plasma concentrations of 13 C-label were at or below the limit of
detection (10-20 pg/ml) and were not considered reliable. Application of PCBs to
aluminum foil, then rubbed into the skin of the forearm for 10 min, resulted in a
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