Risk assessment implications of site-specific oral relative bioavailability factors and dermal absorption fractions for polycyclic aromatic hydrocarbons in surface soils impacted by clay skeet target fragments.

Risk assessment conclusions for a site may differ when using site-specific versus default values for the relative bioavailability factor (RBAF) and dermal absorption fraction (ABS.d), because these inputs affect both surface soil screening levels and risk/hazard estimates. Indeed, our case study demonstrates that different conclusions may be reached as to regulatory need for remedial action to protect human health when evaluating soil sampling data for seven carcinogenic polycyclic aromatic hydrocarbons (PAHs) using site-specific versus default TCEQ and USEPA residential soil screening levels. Use of site-specific RBAF and ABS.d values increased carcinogenicity-based TCEQ and USEPA surface soil screening levels for PAHs by 4.4- and 6-fold on average, respectively. Soil screening levels for PAHs were more sensitive to changes in ingestion exposure route parameters than to changes in dermal exposure route parameters. Accordingly, site-specific RBAF and ABS.d information has important implications for screening chemicals at PAH-impacted sites, and in addition provides more realistic estimates of risks/hazards posed by PAHs in soil with reduced uncertainty compared to estimates based on default RBAF and ABS.d values. Although default values are generally deemed acceptable by regulatory agencies, use of risk/hazard estimates based on these default values may compel insufficiently justified remedial action in some instances.