ABSORPTION ADJUSTMENT FACTOR (AAF) DISTRIBUTIONS FOR POLYCYCLIC AROMATIC-HYDROCARBONS (PAHS)

In human health risk assessment, a correction factor is needed to acco unt for differences between absorption in the dose-response study and absorption likely to occur upon human exposure. This correction factor is defined as the absorption adjustment factor, or AAF. The AAF is us ed to adjust the human exposure (potential) dose to account for differ ences in bioavailability between laboratory vehicles and environmental matrices. AAFs are defined for oral. and dermal risk assessment of po lycyclic aromatic hydrocarbons (PAHs) in soils. AAF distributions and point estimates are defined. Because there are very few studies that m easure oral and dermal absorption of PAHs fi om soils in any species u nder any conditions, all available data from the principal studies wer e given equal weight in AAF derivation. The oral-soil AAF distribution for all PAHs is a Beta4 distribution with the following characteristi cs: Beta4 (a=1, b=3, c=0.944964, d=0.0699) over the range of 0.07 to 1 .00. The point estimate for the oral-soil AAF is 0.29. The dermal-soil AAF distribution for potentially carcinogenic PAHs is defined as two distributions. The numerator is a Beta4 distribution with the followin g characteristics: Beta4 (a=1, b=5, c=0.146908, d=0) over the range 0 to 0.12. The denominator is a Beta4 distribution with the following ch aracteristics: Beta4 (a=4, b=1, c=0.397, d=0.602697) over the range 0. 63 to 1.00. The point estimate for the dermal-soil AAF for potentially carcinogenic PAH is 0.02. For noncarcinogenic PAHs, an uncertainty fa ctor distribution is applied to the dermal-soil AAF for potentially ca rcinogenic PAH. The uncertainty factor is defined as a uniform distrib ution from 1 to 10. Defining the point estimate of the uncertainty fac tor as 5, the point estimate for the dermal-soil AAF for noncarcinogen ic PAHs is 0.10.