Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:3:p1
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 3 (pt 1/9)
Character Range: 2876931–2879824

3                   Attachment B

3.1         Worked Example: Calculation of HIL A for benzo(a)pyrene

This attachment provides further detail on the calculation of the low-density residential (HIL A) calculation for benzo(a)pyrene (BaP) based on the equations presented in this appendix, exposure assumptions presented in Table 5 of the main schedule and the information presented in Appendix A for BaP. The calculations presented are also summarised in Appendix C.
Based on the information presented in Appendix A, BaP has been considered to be a genotoxic carcinogen where the HIL has been calculated on the basis of a non-threshold approach, considering exposures over a lifetime (i.e. as a child and adult). The assessment of BaP is complex (as outlined in Appendix A), where the following have been considered in the derivation of the HIL:

As discussed in Appendix A, when determining the HIL A value, calculations have been undertaken for BaP where the TRVo from MfE (2011) and WHO (2011) have been considered, where early lifetime exposures have been considered and where the dermal-specific toxicity reference value has also been considered. For the purpose of this worked example, calculations have been presented that support the HIL A value adopted, which is based on the TRVo available from WHO (2011), consideration of early lifetime exposures and no additional consideration of the dermal-specific toxicity reference value.

Calculation for Ingestion of Soil/dust

Based on Equations 3 and 4, as well as the age-adjustment factors outlined by US EPA (2005), the HILingestion is calculated for BaP as follows:

            Equation 4

          Equation 5

where:

         TRVo  = toxicity reference value relevant for the quantification of oral intakes, (as (mg/kg/day)-1 for non-threshold contaminants) = 0.5 (mg/kg/day)-1
         TR = target risk for non-threshold contaminants (unitless) = 1x10-5
         ∑ = signifies the sum over all receptor groups x considered (in the HILs derived, these groups include a child (C) and adult (A))
         IRsX  = ingestion rate of soil/dust by each receptor group x (mg/day) = 50 mg/day for adults and 100 mg/day for young children
    BAo = oral bioavailability (unitless) = 100% or 1 for BaP
    CF = conversion factor of 1x10-6 to convert mg to kg
         EFx = exposure frequency relevant to exposures by each receptor group x (days/year) = 365 days/year for both adults and children
         EDx = exposure duration relevant to exposures by each receptor group x (years) = 6 years for young children and 29 years for adults
    BWx = body weight relevant to each receptor group x (kg) = 15kg for young children and 70 kg for adults
    ATNT = averaging time for non-threshold contaminants (days, = 70 years x 365 days) = 25 550 days

The calculated intake factor has taken into account age-adjustment factors that relate