Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:3:p2
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 3 (pt 2/9)
Character Range: 923179–926241

can be fully defined by reference to individual specific substances (for which toxicity data is available), it is preferable to assess these specific substances.

Chemical analyses providing detailed breakdowns for groups of organic compounds into individual substances (e.g. PAH), or a limited range of individual indicator compounds plus fractions containing groups of compounds with similar physicochemical properties (e.g. petroleum hydrocarbon fractions) are commercially available. It is commonly necessary to undertake such analyses of mixtures in order to understand the mixture sufficiently to assess risk, because individual compounds within these groups have very different physicochemical and toxicological properties.

    3.2.2          Metals speciation
The toxicity of metals and metalloids can be highly dependent on the form in which they occur in the environment. A common example is chromium (Cr), where the environmentally stable Cr (III) oxidation state is relatively harmless to humans, but the more oxidised Cr (VI) state is more hazardous to humans. For most metals and metalloids, the HIL assumes that the most toxic form is 100% of the contaminant present in soil. This is very unlikely to be true in most cases, and knowledge of the actual or probable form can be very useful at Tier 2.

Routine metal speciation analysis is commercially available in Australia for species and compounds of arsenic (As), selenium (Se), mercury (Hg), tin (Sn) and lead (Pb), while metal speciation of some other elements is routinely conducted internationally. At sites where potentially toxic metals are present, consideration should be given to whether speciated metal analysis would be relevant to the assessment. Speciated metals data can be useful in refining the risk assessment process. Further discussion on the toxicity of metal species is provided in this Schedule in Section 5.4.3.

    3.2.3          Background concentrations
It is helpful to understand the prevailing background concentrations of chemical substances, since in some circumstances background concentrations may already exceed screening criteria.

For metal contaminants, if reliable ambient background concentrations cannot be measured, then either the estimation method of Hamon et al. (2004) or collations of ambient background data such as Olszowy et al. (1995) for four Australian cities could be used. To use the Hamon et al. method, it is necessary to establish whether the iron and manganese concentrations of the soil at the site in question are elevated by co-contamination, as the Hamon et al. relationships are based on soils from sites with no known history of contamination other than farming. Further information on these two methods can be found in Section 2.4.9 of Schedule B5b.

Most organic contaminants of interest at contaminated sites have no natural background concentration, though there are notable exceptions, including polycyclic aromatic hydrocarbons. Therefore, ambient background concentrations should either be measured at a suitable reference