Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:1850:p112
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 1850 (pt 112/117)
Character Range: 684761–687717

part of dioxin and dioxin-like compounds. PCBs are a class of organic compounds with 1 to 10 chlorine atoms attached to the biphenyl molecule. There are 209 possible PCB congeners although only 130 were found in commercial PCB mixtures.

The World Health Organization (Van den Berg et al. 2006) identified 29 dioxins and dioxin-like compounds of environmental concern based on similar toxicological profiles. These include 7 PCDD, 10 PCDF and 12 co-planar 'dioxin-like' PCBs. While these substances have similar toxicological profiles, they have differing toxicological potencies. Thus, their concentrations in environmental and biological media are reported using toxicity equivalence (TEQ) relative to a reference compound, which in this case is 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD). The relative toxicity of each compound is expressed as a toxicity equivalency factor (TEF) and the product of the concentration and the TEF for each substance in the mixture results in a TEQ concentration relative to 2,3,7,8-TCDD. The sum of the resultant TEQ for each substance yields a single concentration for the TEQ of the mixture.

The history of TEQ systems is as follows:
    * the international TEQ (I-TEQ) was developed largely by the United States Environmental Protection Agency (US EPA) in 1990
    * the WHO modified the I-TEQ in 1998 by incorporating 'dioxin-like' PCBs; this was known as the WHO98 TEQ
    * in 2005 the WHO98 TEQ system was updated to WHO05 TEQ (Van den Berg et al. 2006).
The WHO 2005 TEQ values are recommended for use in site assessment work involving dioxins and dioxin-like compounds. Further information on the TEF approach and the necessary adjustments required to normalise historical data to WHO 2005 TEQ can be found in enHealth (2012).

21.2          Occurrence of dioxins and dioxin-like compounds
The major causes of soil contamination by dioxin and dioxin-like compounds are from accidental or incidental spillages in the manufacture, transport, storage and use of various chlorinated compounds and past disposal of these compounds. Land uses associated with waste disposal, pulp and paper mills and chemical manufacturing may have resulted in soil contamination by these compounds.

Other industrial sources of dioxin and dioxin-like compounds such as thermal or combustion sources and reservoir sources such as sludges may be less significant as contaminant sources for soil.

Dioxins and dioxin-like compounds also occur naturally and are released into the atmosphere from creation or entrainment during bush fires and from volcanic activity.

21.3          Results from the National Dioxins Program (May 2004)
As part of the National Dioxins Program (NDP), soils from around Australia were collected and analysed for dioxins. Dioxin-like chemicals were found in all but one of the 114 Australian soils sampled, with concentrations ranging from the limit of detection (0.05 pg TEQ g-1 dwt) to 43 pg TEQ g-1