methodologies and the reliance on establishment of a policy-driven ‘target risk’ for the evaluation of the EHRA outcomes. While there has been some movement towards accepting a threshold approach for carcinogenic responses associated with some non-genotoxic modes of action, the dominant method of dose–response assessment in Australian EHRA practice and regulatory requirements remains the non-threshold approach taken in US regulatory agencies. The detailed critique of quantitative cancer risk assessment provided in Hrudey (1998) is quite informative and still relevant. The continued use of a non-threshold approach for most carcinogenic risk assessments results in quite conservative, and potentially costly outcomes in many types of EHRA processes. 11.7 While there is strong precedent for both Australian and international regulatory systems to expect application of a non-threshold approach to risk assessment of carcinogens, in 1999 the National Health and Medical Research Council (NHMRC), acting on advice from a specialist working party, endorsed a set of guidelines for risk assessment of carcinogens on contaminated sites, which was based on a modified threshold approach, or modified benchmark dose (mBMD) methodology (NHMRC 1999a). While the NHMRC document has since been rescinded, it did outline an approach that could harmonise the HRA of cancer and non-cancer toxicological endpoints by moving away from the need to calculate or estimate a finite risk level for carcinogens alone, and the need to establish a ‘target risk’ with which this could be compared. The essential features of this alternative approach, deriving a POD for carcinogenic risk assessment were: use of a range of mathematical models to explore the data ‘fit’ to a derived dose–response relationship estimation of a BMD at the 5 per cent excess risk level (BMD05) to serve as a ‘point of departure’ (POD) for further risk assessment application of a range of modifying factors to the BMD05 dose estimate, in order to derive a ‘guideline dose’ (GD), which should be protective of human health. The NHMRC mBMD methodology has many similarities with the BMD methodology used by the US EPA to derive a POD for its carcinogen risk assessments, but there are also some important differences. The NHMRC advocates estimation of a mean BMD05 from all the curve-fitting data, after discarding those models which
methodologies and the reliance on establishment of a policy-driven ‘target risk’ for the evaluation of the EHRA outcomes. While there has been some movement towards accepting a threshold approach for carcinogenic responses associated with some non-genotoxic modes of action, the dominant method of dose–response assessment in Australian EHRA practice and regulatory requirements remains the non-threshold approach taken in US regulatory agencies. The detailed critique of quantitative cancer risk assessment provided in Hrudey (1998) is quite informative and still relevant. The continued use of a non-threshold approach for most carcinogenic risk assessments results in quite conservative, and potentially costly outcomes in many types of EHRA processes. 11.7 While there is strong precedent for both Australian and international regulatory systems to expect application of a non-threshold approach to risk assessment of carcinogens, in 1999 the National Health and Medical Research Council (NHMRC), acting on advice from a specialist working party, endorsed a set of guidelines for risk assessment of carcinogens on contaminated sites, which was based on a modified threshold approach, or modified benchmark dose (mBMD) methodology (NHMRC 1999a). While the NHMRC document has since been rescinded, it did outline an approach that could harmonise the HRA of cancer and non-cancer toxicological endpoints by moving away from the need to calculate or estimate a finite risk level for carcinogens alone, and the need to establish a ‘target risk’ with which this could be compared. The essential features of this alternative approach, deriving a POD for carcinogenic risk assessment were: use of a range of mathematical models to explore the data ‘fit’ to a derived dose–response relationship estimation of a BMD at the 5 per cent excess risk level (BMD05) to serve as a ‘point of departure’ (POD) for further risk assessment application of a range of modifying factors to the BMD05 dose estimate, in order to derive a ‘guideline dose’ (GD), which should be protective of human health. The NHMRC mBMD methodology has many similarities with the BMD methodology used by the US EPA to derive a POD for its carcinogen risk assessments, but there are also some important differences. The NHMRC advocates estimation of a mean BMD05 from all the curve-fitting data, after discarding those models which
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