Oral and Dermal Bioavailability Studies of Polycyclic Aromatic Hydrocarbons from Soils Containing Weathered Fragments of Clay Shooting Targets

The relative oral bioavailability and dermal absorption of chemical substances from environmental media are key factors that are needed to accurately estimate site-specific risks and manage human exposures. This study evaluated the in vivo relative oral bioavailability and in vitro dermal absorption of several polycyclic aromatic hydrocarbons (PAHs) found in soils collected from two formerly used Department of Defense sites impacted by weathered fragments of clay shooting targets. Concentrations of individual carcinogenic PAHs in the <= 250 mu m fraction of soil ranged from approximately 0.1 to 100 mg/kg. A novel sample preparation method was developed to produce accurate and precise test diets for oral studies. The resulting test diets showed consistent concentrations of PAHs in soil- and soil-extract-amended diets and a consistent PAH concentration profile. Mean oral relative bioavailability factors (RBAFs) and dermal absorption fractions (ABS(d)) for benzo(a)pyrene ranged from 8 to 14% and 0.58 to 1.3%, respectively. Using the RBAF and ABS(d) values, measured here, for benzo(a)pyrene in USEPA's regional screening level equations yields concentrations for residential soils that are approximately eight times higher than those when default values are used (e.g., 9.6 vs 1.2 mg/kg at a target excess risk of 1 x 10(-5)).