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Appendix D Food Codes for NHANES - OEHHA

Appendix D Food Codes for NHANES - OEHHA

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Scientific Review Panel Draft February, 2012<br />

human skin, respectively. When the skin was occluded, the absorption at 72 hrs<br />

was significantly enhanced, reaching 13.3 and 32.9% <strong>for</strong> rat and human skin,<br />

respectively. MDA that remained in human skin at 72 hrs was 23.8 and 37.4% of<br />

the applied dose <strong>for</strong> unoccluded and occluded skin, respectively. For the rat,<br />

MDA content of the skin at 72 hrs was 57.6 and 53.1% of the applied dose <strong>for</strong><br />

unoccluded and occluded skin, respectively. Although the data were only<br />

graphically presented, absorption through human skin into the receptor fluid at 24<br />

hrs can be estimated at 8% of the applied dose <strong>for</strong> unoccluded skin and 20% of<br />

the applied dose <strong>for</strong> occluded skin.<br />

The permeability of rat and human skin in vitro to MDA was assessed by Kenyon<br />

et al. (2004) over a large dose range, and the potential <strong>for</strong> skin to act as a<br />

reservoir <strong>for</strong> MDA was investigated. Dose levels of 0.01, 0.1 and 1 mg per 0.32<br />

cm 2 skin were applied in ethanol:water (50:50) onto occluded skin <strong>for</strong> 24 hrs. No<br />

statistical difference in skin permeability was observed between rat and human<br />

skin. After 24 hrs, 27 to 52% of applied MDA had penetrated human skin to the<br />

receptor fluid. The percentage of applied MDA retained in human skin was 20%.<br />

In another in vitro experiment, Kenyon et al. (2004) applied 0.1 mg MDA to<br />

human skin <strong>for</strong> 4 hrs, then removed excess MDA on the skin surface and the<br />

experiment continued <strong>for</strong> another 4 hrs. The cumulative absorption rate of MDA<br />

into the receptor fluid remained the same <strong>for</strong> the last 4 hrs, with only a slight<br />

decrease noted between 7 and 8 hrs. Of the total 11% of the MDA found in the<br />

skin, 5% was removed by tape stripping the stratum corneum. The remaining<br />

6% of MDA was found in the digested skin, suggesting this amount would have<br />

been absorbed had the experiment continued longer. Considering that the lag<br />

time <strong>for</strong> appearance of MDA in receptor fluid was about 4 hrs, the authors<br />

presumed that the MDA remaining in the stratum corneum at 8 hrs would not be<br />

absorbed systemically.<br />

No literature could be located regarding dermal absorption of MDA from soil.<br />

However, the fate of MDA added to soil has been investigated. MDA rapidly and<br />

strongly absorbs to loam soil which contained a total organic content of 1.3%<br />

(Cowen et al., 1998). However, MDA does not appear to <strong>for</strong>m complexes with<br />

humic materials or <strong>for</strong>m other irreversible soil binding processes. In one year,<br />

the aerobic biodegradation of MDA in silt loam soil was 40%.<br />

F.4.7.2 Discussion and Recommendation <strong>for</strong> a 4,4’ –Methylenedianiline ABS<br />

Dermal absorption of MDA in workers is considered a more significant route of<br />

exposure than inhalation (Brouwer et al., 1998). The in vivo worker data support<br />

the in vitro human data in that dermal absorption is considerable. However, the<br />

exposure/application of MDA involved other organic solvents. The effect of<br />

solvent vehicle on absorption was not investigated.<br />

F-67

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