Absorption adjustment factor (AAF) distributions for polycyclic aromatic hydrocarbons (PAHS)

Abstract In human health risk assessment, a correction factor is needed to account 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 used to adjust the human exposure (potential) dose to account for differences in bioavailability between laboratory vehicles and environmental matrices. AAFs are defined for oral and dermal risk assessment of polycyclic aromatic hydrocarbons (PAHs) in soils. AAF distributions and point estimates are defined. Because there are very few studies that measure oral and dermal absorption of PAHs from soils in any species under any conditions, all available data from the principal studies were given equal weight in AAF derivation. The oral‐soil AAF distribution for all PAHs is a Beta4 distribution with the following characteristics: Beta4 (a=l, 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 following characteristics: Beta4 (a=l, b=5, c=0.146908, d=0) over the range 0 to 0.12. The denominator is a Beta4 distribution with the following characteristics: Beta4 (a=4, b=l, 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 factor distribution is applied to the dermal‐soil AAF for potentially carcinogenic PAH. The uncertainty factor is defined as a uniform distribution from 1 to 10. Defining the point estimate of the uncertainty factor as 5, the point estimate for the dermal‐soil AAF for noncarcinogenic PAHs is 0.10. Key words: bioavailabilityabsorptionsoilPAHs Notes 239 Littleton Road, Suite 7C, Westford, MA 01886; Tel: (508) 692–9090; Fax: (508) 692–6633 P.O. Box 382669, Harvard Square Station, Cambridge, MA 02238; Tel: (617) 864–4300; Fax: (617) 864–9954