Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:6:p1
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 6 (pt 1/4)
Character Range: 3019207–3022283

6                   Risk characterisation  how the HILs were generated

6.1              Risk characterisation and calculation of HILs
Risk characterisation is the process through which the results of the exposure assessment and toxicity assessment processes are combined to provide numerical estimates of the potential risks to the identified receptors. The HILs have been calculated on the basis of the equations using a threshold or non-threshold approach, as appropriate. The HILs are presented in Appendix B, with the calculations presented in Appendix C. The HILs have been derived for each compound assuming intakes from all pathways of exposure are additive.

6.2              Target risk levels
The derivation of HILs, using the equations presented in Appendix B, requires the consideration of a target risk level for threshold and non-threshold calculations.

For threshold HIL calculations, a target hazard index (HI, which is the ratio of the intake of a contaminant from all sources (including the site) to the threshold TRV) over all pathways of exposure (where relevant) of 1 has been adopted. This is consistent with the discussion presented in Schedule B4.

For non-threshold HIL calculations, a tolerable (or target) incremental lifetime cancer risk associated with intakes of a contaminant (derived from a contaminated site) via all pathways of exposure of 1x10-5 has been adopted (see Schedule B4).

Tolerable incremental lifetime cancer risk values available from Australia and international agencies (refer to discussion in Schedule B4) range from 1x10-4 to 1x10-6, with the value of 1x10-5 generally adopted for the assessment of contaminated land issues in a number of individual states in Australia. The lower incremental lifetime cancer risk values (1x10-6) are commonly adopted in guidance that addresses population-wide exposures, such as those that may be derived from drinking water (and considered in the current Australian Drinking Water Guidelines (NHMRC 2011)).

6.3              Presentation of HILs
The HILs presented have been rounded to one, and no more than two, significant figures (as shown in Appendix C). The rounding reflects the level of uncertainty inherent in the range of variables used to define exposure and doseresponse. Some further discussion on uncertainty is presented below.

6.4              Uncertainty and sensitivity analysis

    6.4.1         HIL uncertainty analysis
The uncertainty analysis is a qualitative process that identifies the key assumptions and data gaps associated with a human health risk. Uncertainty can arise from missing or incomplete information, or arise from the scientific theory affecting the ability of a model to make predictions or result from uncertainty affecting a particular exposure or input parameter. Uncertainty has the potential to result in a cumulative overestimation or underestimation of potential health risks during an assessment.

The three broad types of uncertainty inherent in any risk assessment are:
    * Scenario uncertainty — uncertainty arising from missing or