Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:1:p3
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 1 (pt 3/13)
Character Range: 2372111–2374885

intakes may be nearing a significant contribution. Adoption of 1 mg/kg was considered appropriate also due to the potential for further review by S EPA where reference values for BaP may change.
Further review of BaP (and PAHs using TEFs) by Fitzgerald (1998) and Fitzgerald et al. (2004), on the basis of a derived modified benchmark dose, calculated a value of 5 mg/kg on the basis of soil ingestion only.

1.3              Significance of Exposure Pathways

    1.3.1         Oral Bioavailability
A study by Hansen et al. (2007) demonstrated bioavailability of PAHs in three different soil samples ranging from 14 40% using an in vitro bioavailability model that simulates gastric digestion. In addition, the Massachusetts DEP uses a relative absorption fraction of 28% for PAHs (MADEP 2008) in its risk assessment program. In addition it is noted that BaP (and PAHs) present in bitumen fragments are largely immobile and typically have a low bioavailability. However, as bioavailability is highly site- and source-specific, insufficient data is available to adequately define a value that differs from the default approach of 100% oral bioavailability. It is noted that a site-specific assessment of bioavailability can be undertaken where required.

    1.3.2         Dermal absorption
Review of dermal absorption of BaP has been conducted by MfE (2011). This review has identified the following, based on studies on animals and humans (rather than modelled as presented by CCME (2008)):
    * As BaP is actively metabolised in the skin, it is relevant to include both the amount that passes through the skin and that which remains bound to the skin to estimate dermal uptake.
    * US EPA (2004) recommends a dermal absorption factor of 0.13 (13%), which is based on data from Wester et al. (1990). These authors indicate that 13.2% of BaP in soil was absorbed by rhesus monkeys over a 24-hour period. However, they also indicate that a reduced amount (1.4%) was absorbed into human skin from soil over the same time period, although no partitioning into human plasma occurred, i.e. the BaP remained bound to the skin.
    * Another study on the dermal absorption of BaP from soils also showed that a minimal amount (0.1%) of BaP was absorbed through pig skin and 1.7% and 3.5% remained bound to the skin when BaP respectively in aged sandy and clay soils was applied to the skin (Abdel-Rahman et al. 2002). A higher amount (3.3% and 8.3% in clay and sandy soils, respectively) was absorbed when non-aged soil (i.e. freshly spiked) was applied to the skin.
    * A more recent study with human skin showed greater absorption through the skin, with approximately 7% of BaP passing through when applied as freshly spiked soil (Moody et al. 2007). A further 7% remained