Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:1:p8
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 1 (pt 8/13)
Character Range: 2385340–2388126

studies associated with exposure to coke oven emissions or coal tar pitch aerosols. BaP is not volatile and hence the relevance of these studies to the assessment of dust issues derived from contaminated sites is not clear. It is therefore recommended that the WHO oral reference value be considered for the assessment of all pathways of exposure.

1.4.2.1         Note on Dermal Exposures
BaP is suggested to act largely as a point-of-contact carcinogen (Knafla et al. 2006), as opposed to systemically, hence it is more appropriate to derive soil guideline values for the dermal route of exposure using a route-specific slope factor, as opposed to consideration on the basis of systemic absorption and use of the oral slope factor.

For most compounds such data is not available but for BaP, Knafla et al. (2011) have derived a dermal slope factor, normalised to a per unit skin surface area basis, that is relevant to the assessment of BaP in soil in skin. The dermal slope factor of 3.5 (µg/cm2/day)-1 was derived by Knafla et al. (2011) and appropriate methods and parameters have been suggested for the use of this factor in the assessment of soil exposures. The dermal slope factor is an extension of previous work published by Knafla et al. (2006), where a dermal slope factor was derived on the basis of skin carcinogenicity from skin painting studies with mice. The revised dermal slope factor (Knafla et al. 2011) considered various factors for interspecies extrapolation, particularly in relation to sensitivity (to tumour development) and differences in epidermal (target tissue) thickness. This dermal slope factor has not yet been adopted for use by other international agencies, however CCME (2008) indicate that Health Canada may consider the revised dermal slope factor once published (as occurred in 2011).

The dermal slope factor as proposed by Knafla et al. (2011) has been considered in the derivation of the HIL for BaP, in addition to the use of the oral TRV. The calculations have been conducted for garden soil using default values presented by Knafla et al. (2011) for loading rates and epidermal thickness.

    1.4.3         Recommendation
On the basis of the discussion above, the following toxicity reference values (TRVs) have been adopted for BaP in the derivation of HILs:

1.5              Calculated HILs for BaP and Carcinogenic PAHs (as BaP TEF)
It is noted that the discussion above has identified that further consideration of early lifetime exposures to BaP may need to be considered in the quantification of exposure (calculated as per US EPA 2006). Other uncertainties have also been noted in the above discussion, particularly in relation to the selection of the oral TRV (where the value from MfE (2011) may also be considered, although it