Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:1:p4
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 1 (pt 4/13)
Character Range: 2374651–2377456

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 bound to the skin.
    * As ageing soils decrease the bioavailability of BaP, the dermal absorption data from freshly spiked soils can provide a worst-case estimate of dermal absorption. The geometric mean of dermal absorption using freshly spiked soils from the above studies (including in vivo studies) is 6%, while using data for aged soils yields a geometric mean of 2.6% (Abdel-Rahman et al. 2002).
Review by MfE (2011) resulted in the adoption of a dermal absorption factor of 2.6%, the arithmetic mean of data from aged soil (Abdel-Rahman et al. 2002). In the derivation of soil HILs in this review, the higher arithmetic mean value of 6% (based on data from freshly spiked soil and noted by MfE (2011) as a worst-case value that is supported by studies from Wester et al. (1990), Abdel-Rahman et al. (2002) and Moody et al. (2007)) has been adopted and is considered relevant for all source types.

    1.3.3         Inhalation of Dust
BaP (and other carcinogenic PAHS) are not considered sufficiently volatile to be of significance and inhalation exposures associated with particulates outdoors and indoors are expected to be of less significance than ingestion of soil. Exposure via inhalation of dust is estimated to be less than 1% of the total exposure.

    1.3.4         Plant Uptake
CCME (2008) notes that concentrations of PAHs in uncooked produce depend principally on its source. Plants grown on PAH-contaminated soils, however, have only a limited ability to take in through the roots and translocate anthropogenic PAHs to the aboveground plant biomass—especially for higher molecular weight PAHs. One mode of plant contamination is via the deposition of PAH-containing fine particulates onto plant surfaces.

PAHs may be bound within soils (via lignification), mineralised (ultimately to CO2 and water) or metabolised outside or within the plant (CCME 2008). Higher molecular weight PAHs such as BaP (and other carcinogenic PAHs) are considered persistent and are strongly absorbed to the soil. Lipophilic organic compounds such as PAHs (and BaP), with a low solubility in water, high Henry's law constant and high Kow(>104), are bound strongly to the root surface and/or soils and are not readily translocated within plants (Schnoor 1997). These generally tend to partition into the epidermis or outer layers of the root tissue (or peel) and remain there bound to lipids in cell walls; transfer into the inner root or xylem is very slow or non-existent. CCME (2008) notes that the general consensus in the literature is that the root uptake pathway