Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:5:p12
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 5 (pt 12/18)
Character Range: 3002974–3005769

A number of limitations were identified including the limited range of compounds tested (namely PAHs, PCBs and dioxins) and problems with study data (in reporting dry or fresh weight and whether data was from roots, shoots, fruits or tubers), highlighting the level of caution that should be considered in applying these models. Overall, the EA (2006) review concluded that the model performance was highly variable and all but one model over-predicted root uptake by at least an order of magnitude.

On this basis, MfE recommended to simply use CFs based on available data, and only resort to models (for organic compounds only) when measured values are not available. This approach has been adopted in the derivation of HIL A.

For metal contaminants and other inorganics (except cyanide), default values of CFx for As, Cd Ni, Hg and Se have been derived from detailed reviews provided by the EA (EA 2009a, 2009b, 2009c, 2009d). The potential significance of plant uptake and the approach adopted for other metals has been addressed on a compound-specific basis in Appendix A.

For organic contaminants (where relevant), soil-to-plant concentration factors (CFy) have been calculated according to the algorithms described by EA (2009e) and summarised in Appendix B. With the exception of the assumption regarding the fraction of soil organic carbon, assumptions about soil properties are generally the same as those used in the vapour pathway, and are described elsewhere in this Schedule. The contaminant-specific physical and chemical properties are given in the relevant toxicity profile in Appendix A.

An assumption of 0.3% organic carbon has been applied to the vapour intrusion exposure pathway for the interim HILs for VOCCs, as this value is consistent with the characteristics of an average sandy soil, as defined by US EPA (2004a). An assumption of 2% organic carbon has been applied only to the calculation of CFy values, due to likely increases in soil organic carbon levels following the long-term cultivation of home-grown produce.

5.4              Blood lead modelling
Blood lead levels are considered to be the best index of lead exposure and risk in humans. For this reason, the HILs for lead are calculated using a different approach from that for all other HILs. For the purpose of deriving the HILs, lead has been assumed to act as a threshold contaminant and a blood lead concentration of 10 µg/dL has been applied, as all Australians should have a blood lead level below this level (NHMRC 2009). It should be noted that it is generally recognised that there may be no threshold for the neurotoxic action of lead (DEFRA 2002).

    5.4.1         Modelling adult exposures to lead
Adult exposures to lead have been estimated based upon the methodology developed by US EPA