Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:6:p2
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 6 (pt 2/12)
Character Range: 1054497–1057559

appreciation that it is part of a larger assessment that also encompasses ecological risk assessment.
    * To protect public health and the environment, an appropriate degree of conservatism should be adopted to account for uncertainties.
    * Actions should always adequately protect public health and the environment, putting these responsibilities before all other considerations.

6.3              Risk estimation
Risk estimation combines the estimated intakes calculated in the exposure assessment with the TRVs (threshold and non-threshold where relevant) from the toxicity assessment to produce numerical indices of likely health effect. The risk estimation methodology differs for threshold and non-threshold compounds due to the different modes of chemical effect.

    6.3.1          Threshold risk estimation
For threshold compounds, the intake for each exposure pathway is divided by the appropriate threshold TRV (allowing for intakes from other sources where relevant) to produce a simple ratio, termed a hazard quotient (HQ) or risk quotient (RQ). The HQs for all exposure pathways for each contaminant can be summed to produce a total hazard index (HI) or risk index (RI).

Hazard Quotient (HQ)  =  Intake (mg/kg-day)
                         Threshold TRV (mg/kg-day)
Hazard Index (HI)     =  Σ Hazard Quotients

The HQs for all exposure pathways for all contaminants should be summed to produce a total HI, unless evidence is available to show that this is not appropriate. When summing these HQs, the following should be taken into consideration:
    * HIs should be calculated for each age group (category) separately.
    * HIs should be calculated separately for chronic, sub-chronic and shorter-duration exposures.
    * Ideally, HIs should be categorised into groups of chemicals that induce the same type of effects or that act by the same mechanism of action. However, this process is not simple and requires a good understanding of the toxicology of the chemicals concerned and should only be undertaken by an appropriately qualified toxicologist. If this segregation is not performed carefully, an underestimate of the true hazard could result. When toxicological information is lacking or unclear, it should be assumed that the chemicals act by the same mechanism of action and hence summation of the HQs is appropriate.
    * HIs should represent the exposure pathways that have the potential to expose the same individual or subpopulation, making sure to consider areas of highest exposure for each pathway for both current and future land uses. All exposure pathways should be summed unless information is available that indicates the same individual or subpopulation cannot be exposed by a particular pathway(s).

    6.3.2          Non-threshold risk estimation
Where non-threshold TRVs are adopted (that is, assuming a linear low-dose relationship), risks are estimated as the incremental probability of an individual developing cancer over a lifetime as a result of exposure to the carcinogen. The estimated intake for each