Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:1:p1
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 1 (pt 1/13)
Character Range: 2366361–2369294

1                   Benzo(a)pyrene

1.1              General
Several comprehensive reviews of polycyclic aromatic hydrocarbons (PAHs) and benzo(a)pyrene (BaP) in the environment and their toxicity to humans are available and should be consulted for more detailed information not presented in this summary (ATSDR 1995; WHO 1998; CCME 2008). The following provides a summary of the key aspects of these compounds that are relevant to the derivation of a soil HIL.

PAHs are a large group of organic compounds with two or more fused aromatic rings made up of carbon and hydrogen atoms. PAHs are formed from incomplete combustion of organic materials such as the processing of coal, crude oil, combustion of natural gas, refuse, vehicle emissions, heating, cooking and tobacco smoking, as well as natural processes including carbonisation. The natural background level is due to PAH production in plant species. Because of such widespread sources, PAHs are present almost everywhere. Food is considered to be the major source of human exposure to PAH, due to the formation of PAH during cooking or from atmospheric deposition of PAHs on grains, fruits and vegetables (WHO 1998).

There are several hundred PAHs, including derivatives of PAHs. The best known (and studied) is BaP. While there are hundreds of PAHs, typically only 16 individual PAHs are analysed in site contamination investigations. These individual PAHs address a broad range of the equivalent carbon spectrum and are therefore more commonly reported and assessed (where there is more data available on these PAHs).

The major sources of PAHs to soils at any given location invariably contribute a mixture of PAHs, not just single compounds. Various PAH source types can be distinguished based on the characteristic compositions of PAH mixtures and information on the site history, but the contaminated soil matrix is nonetheless challenging from an environmental risk assessment perspective, since in a PAH-contaminated soil there is likely to be a diverse compositional range of non-carcinogenic and carcinogenic PAHs of varying potency.

The major approach advocated by regulatory agencies such as the NEPC (NEPC 1999; Fitzgerald 1991; Fitzgerald 1998), California EPA (OEHHA), Netherlands (RIVM 2001), England and Wales (DEFRA & EA 2002), Canada (CCME 2008) and US EPA (2010 draft) for assessing the human health risks of PAH-containing mixtures involves the use of toxicity equivalence factors (TEFs). This approach relates the toxicity of other (potentially carcinogenic) individual PAHs relative to that of BaP, the most widely studied PAH.

There are more than a dozen sets of equivalency numbers that have been proposed over the last two decades. The most recent (published final) review of TEF and their basis, presented by CCME (2008), suggests the use of TEF recommended by the World Health Organization (WHO 1998), with minor modifications. This is a scheme