Appendix D Food Codes for NHANES - OEHHA

Scientific Review Panel Draft February, 2012
Table F.3. Percent Dermal Absorption of TCDD over Time from Low
Organic Soil a
Time (hr) Rat – in vivo Rat – in vitro Human in vitro
24 7.9 1.17 0.28
96 16.3 6.32 2.25
96 (Dose in skin
sample after
wiping)
NA b 1.4 0.2
96 (Total) 16.3 7.7 2.4
a
Data from US EPA (1992) and Roy et al., 2008
b
Not applicable
Roy et al. (2008) note that steady state conditions for the TCDD concentration in
skin from LOS are reached by 24 hours for the in vitro experiments. Thus it
should be reasonable to assume that the amount in the skin after 96 hours is
about the same as after 24 hours. The researchers also observed that the rat in
vivo percent absorbed results were about twice as high as the rat in vitro results
after 96 hours. Assuming the human in vitro results would operate in a similar
fashion Roy et al. obtained a human 24-hr fractional TCDD absorption rate of
0.96% (0.48% x 16.3% / 7.7%). Additionally, a fractional absorption value of
0.1% was derived for TCDD absorbed from HOS (soil with an organic content
>10%).
Alternately, it may be more relevant to multiply the rat in vivo percent absorbed at
24 hours (7.9%) by the estimated in vitro rat-to-human ratio for total percent
TCDD absorbed at 24 hours (0.48% / 2.75%), rather than rely on any of the
results from 96 hr exposure. The resulting human 24-hr fractional TCDD
absorption rate by this method is 1.4%.
B. Supporting Studies
Shu et al. (1988) applied soil-bound TCDD to the backs of rats, clipped of hair.
Laboratory contaminated TCDD soil was prepared from soil obtained from Times
Beach MO and determined not to contain TCDD before the experimental addition
of the chemical. Environmentally contaminated soil was also obtained from
Times Beach, MO and determined to contain 123 ppb TCDD after sieving
through a 40-mesh screen. The organic carbon content of the soils was not
specified. Soil loading was 20.8 mg soil/cm 2 skin on a total skin area of 12 cm 2 .
The TCDD content of the laboratory prepared soil was 10 or 100 pg/mg soil.
Occlusion of the skin was minimized by the use of a perforated aluminum eye
patch to cover the exposed area. Dermal exposure duration to the TCDD-laden
soil was 24 hours and recovery was measured 48 hours following initiation of
exposure. In some experiments, 0.5 or 2.0 percent (w/w) used crankcase oil was
added to the soil before the addition of TCDD.
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