Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:3:p7
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 3 (pt 7/9)
Character Range: 936890–939867

to derive HIL-equivalent screening criteria. Sources of toxicity reference values should be considered in the same way as has been done for those chemicals with HILs (same hierarchy and other considerations). Exposure scenarios should be used as laid out in Schedule B7. This should only be undertaken by suitably qualified professionals. The resulting values may be used in the same way as HILs. All assumptions and calculations should be transparent, clearly referenced and justified.

Tier 1 values may be adopted from external peer reviewed sources only if the assumptions used to generate the values are equivalent or more conservative than those used to develop the HILs and are suitable for use. In these cases, the relevance of the values and assumptions included in the development of the proposed Tier 1 values should be clearly justified and referenced.

Exceedences of the HILs should be identified and considered. HIL exceedences do not imply that a risk is necessarily present but that further assessment may be justified. HILs are not intended to indicate a clear demarcation between acceptable and unacceptable. Marginal exceedences may not require quantitative Tier 2 risk assessment to conclude that further assessment is not necessary. The magnitude of the exceedence should be considered in the context of the CSM (that is, whether the exposure pathways are plausible and whether exposure will result in harm).

Background concentrations may also be an important consideration at the Tier 1 screening stage. If it can be clearly demonstrated that site concentrations are consistent with natural regional background levels (natural or anthropogenic), this can provide evidence that site contamination has not significantly increased the background level and further assessment is not justified. However, it is important to note that background concentrations in some cases may present a risk: for example emissions from motor vehicles can result in higher exposure to residents in a transport corridor. Residences adjacent to refuelling stations may be exposed to high hydrocarbon background. Naturally elevated background can result from highly mineralised geologic environments, resulting in enrichments of potentially toxic trace metals or from anthropogenic inputs such as atmospheric deposition in highly industrialised areas that are often found in major Australian cities. In such cases, consultation with local environment regulators and health protection agencies would be appropriate.

Tier 1 screening criteria (including HILs and HSLs) should only be used where there has been adequate characterisation of a site (that is, appropriate representative sampling has been carried out). At the very least, the maximum and the 95% UCL should be compared to relevant Tier 1 screening criteria. Where sufficient data is available it may be appropriate for the arithmetic mean (AM) to be compared to the relevant Tier 1 criteria. However, the implications