Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:4:p1
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 4 (pt 1/5)
Character Range: 2956074–2959107

4                   Toxicity assessment
The toxicity assessment component of the derivation of the HILs involved the review of the published toxicity reference values that have been developed by various published peer-reviewed government authorities and other agencies, and selection of the appropriate reference value for each of the soil contaminants.

For all contaminants considered in the derivation of HILs, toxicity reference values (TRVs) have been identified following review of relevant information from published peer reviewed sources. The term TRV has been adopted as a general term that is used to define the health-based toxicity value used to derive an HIL. TRVs include both threshold and non-threshold toxicity values.

For threshold chemicals, TRVs reflect a measure of tolerable daily exposure and include values that are presented by different agencies using a range of different terms. Most commonly these include an ADI (acceptable daily intake), TDI (tolerable daily intake), TC (tolerable concentration in air), RfD (reference dose), RfC (reference concentration), MRL (minimal risk level), and REL (reference exposure level).

For non-threshold chemicals, TRVs reflect a cancer risk value commonly referred to as a cancer slope factor (CSF) or unit risk (UR).

TRVs used in the derivation of HILs are presented in Appendix A. The approach that applies to the identification of all the TRVs used in the derivation of HILs is described herein. Where both threshold and non-threshold TRVs have been considered, both approaches have been considered; however, the HIL presented is the lowest value derived based on the more sensitive effect.

4.1              Sources of toxicity data
The TRVs used in the derivation of the HILs have been sourced from peer reviewed references using the data sources presented in Schedule B4.

4.2              Approach for carcinogenic contaminants
For the purpose of deriving the HILs, chemicals that are classified by the International Agency on Research on Cancer (IARC) as Category 1, 2A or 2B carcinogens have been considered to be carcinogenic and those classified Category 3 and 4 have been considered non-carcinogenic. There are limitations with this assumption; however, Category 3 and 4 chemicals rarely have adequate data for assessment as carcinogens. There are a number of Category 2 chemicals that also lack adequate carcinogenic dose response data and have, therefore, been assessed using non-cancer toxicity criteria; this is highlighted in the toxicity summary where relevant.

Consistent with the approach outlined in Schedule B4, the approach adopted for the assessment of carcinogens has been determined based on the mode of action. For genotoxic carcinogens, a non-threshold approach has been adopted (where data is available); however, for carcinogens that are non-genotoxic, a threshold approach has been adopted.

4.3              Toxicity approach for dermal exposure
Where specific dermal TRVs are available, these were used for the assessment of dermal