Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:2:p3
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 2 (pt 3/7)
Character Range: 2919084–2922103

Toxicity surrogate approach
A number of groups of chemicals addressed in the derivation of the HILs contain a number of similar chemical constituents where there is a mix of information on individual chemicals. In cases where there is insufficient information to derive separate HILs for each individual compound, the toxicity surrogate approach has been applied to the derivation of HILs for these substances. This approach involves the generation of an HIL value for a single 'indicator' chemical and the application of this information directly to the assessment of other similar chemicals within the group.

HIL values derived using the toxicity surrogate approach include cresols (methylphenols), DDT, aldrin and dieldrin, polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs). The sum of all the individual chemical concentrations within each of these groups can be compared directly to the HIL value, based on the assumption that their effects are similar and additive.

    2.2.4         Inorganic mercury
The HIL value for inorganic mercury was derived using the physicochemical characteristics of mercuric mercury (Hg2+). This value does not include the potential for the inhalation of vapours derived from elemental mercury. A site-specific assessment should be undertaken if elemental mercury is present or suspected to be present.

    2.2.5         PCBs
The HIL value for PCBs relates to non-dioxin-like PCBs only. Where the assessment indicates the potential for a PCB source to be present on the site, the HILs may not be sufficiently protective. Hence a site-specific assessment of exposure to all PCBs, including dioxin-like PCBs should be undertaken.

    2.2.6         Interim HILs for volatile organic chlorinated compounds
Investigation levels derived for the volatile organic chlorinated hydrocarbons (VOCCs) are presented as interim HILs, as the methodology adopted in the derivation of these values is not as fully developed as that for the non-volatile HILs. The application and revision of these values will rely on improvements in the understanding of the behaviour of chlorinated solvents in transferring from soil to indoor air.

The interim HIL values derived for volatile compounds are driven by the vapour intrusion pathway (that contributes >99% of the total risk where all pathways are considered). However, it is noted that there are limitations and uncertainties associated with the assessment of volatile contaminants on the basis of soil concentrations. As these limitations are significant for volatile organic chlorinated compounds, interim HILs for soil have not been derived. Rather it is recognised that where indoor/ambient air data cannot be collected (or the data is affected by background sources), the most relevant approach to the assessment of this pathway is through the collection of soil vapour data. On this basis, interim HILs have been developed for soil vapour.

It is noted that for short-duration exposures such as during intrusive works