Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:4:p23
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 4 (pt 23/24)
Character Range: 1004029–1007009

their own chemical signatures and the composition of the same product can vary depending on where it was distilled and the source of its crude oil. This makes environmental assessment of these products difficult and an approach has been developed that can assess the broad and varying range of compounds in a uniform manner.

Internationally recognised publications on the composition and assessment of petroleum hydrocarbons are available from the TPH Criteria Working Group (TPHCWG 1997a, 1997b, 1998). These documents present criteria for breaking total petroleum hydrocarbons (TPH) down into aromatic and aliphatic fractions with associated data available on the physical chemistry and toxicity of each fraction. It is based on choosing a relevant substance in each fraction and assuming that all the chemicals that are included in that fraction have the same toxicity as the surrogate chemical.

The TPHCWG approach was developed to provide a consistent and transparent method for dealing with petroleum hydrocarbons in risk assessment. Application of the TPHCWG approach requires the assessment of carcinogenic indicator compounds (such as benzene and benzo(a)pyrene) in addition to the TPH fractions. The alternative to adopting the TPHCWG approach is either to assume that the risks from petroleum mixtures can be adequately assessed using indicator substances such as benzene and hexane, or to attempt to analyse for individual substances and assess each one separately.

The former approach is practical; however, it creates problems in determining transparent clean-up criteria for the bulk of the TPH, since absence of benzene and benzo(a)pyrene does not obviously ensure absence of risk. The latter approach would be rigorous, but given that there are thousands of compounds in TPH mixtures, it would not be practical. The TPHCWG method is therefore the recommended approach.

Analytical data for soil, groundwater and phase-separated hydrocarbons can be obtained on the aromatic-aliphatic composition of TPH compounds in terms of carbon numbers, and can be grouped into their corresponding TPHCWG fractions.

TPHCWG does not provide inhalation reference values for carbon numbers greater than C16 as these fractions are not considered to be volatile (refer to definition in Section 4.4.1). With respect to the inhalation pathway for TPH C16-C36 (aliphatic and aromatic fraction), TPHCWG (1998) states that:

'there are no appropriate data available for the development of RfCs [inhalation reference concentrations] in this carbon range. Also, the development of an inhalation RfC from this fraction was determined to be inappropriate because the compounds in this carbon range are not volatile and inhalation will not be a relevant exposure pathway'.

Where the inhalation of dust is of importance in a risk assessment, it may be appropriate to use route extrapolation of oral TRVs for the assessment of TPH C16-C36 (aliphatic and aromatic fraction).

HSLs have been