Technical Report No. 2
Dr Henry N. Berko - Department of Environmental Protection, Western Australia
Environment Australia, October 1999
ISBN 0 6425 4780 7
About this report
'Polycyclic aromatic hydrocarbons' (PAHs) are a complex class of organic compounds containing two or more fused aromatic rings, and containing only carbon and hydrogen atoms. The physical and chemical properties of PAHs are determined by their conjugated p-electron systems, which are dependent on the number of aromatic rings and the molecular mass (see Appendix B for the ring structure of some PAHs).
The smallest member of the PAH family is naphthalene, a two-ring compound, which is found in the vapour phase in the atmosphere. Three to five ring-PAHs can be found in both the vapour and particulate phases in air. PAHs consisting of five or more rings tend to be solids adsorbed onto other particulate matter in the atmosphere. The term 'polycyclic aromatic compounds' or 'polycyclic organic matter' is used to include similar compounds with nitrogen, oxygen or sulfur substituents such as nitro-PAHs, hydroxy-PAHs and heterocyclic compounds.
This report will concentrate only on compounds that fall in the category of polycyclic aromatic hydrocarbons. Sometimes the term 'polynuclear' is used in the literature instead of 'polycyclic' to describe these compounds.
PAHs are released into the atmosphere as a complex mixture of compounds during incomplete combustion of organic matter. They can be emitted from wood burning heaters, agricultural waste burning, motor vehicle exhaust, cigarette smoke, asphalt road and roofing operations. PAHs are widespread contaminants of the environment and a number of them are either known or suspected carcinogens. Benzo(a)pyrene, a widely reported five-ring PAH, is known for its carcinogenic potency. Although hundreds of PAHs have been identified in atmospheric particles (Lao et al., 1973; Lee et al., 1976), toxicological endpoint and/or exposure data are available for only 33 PAHs.
During the past ten years, a number of studies on polycyclic aromatic hydrocarbons in various Australian cities have been conducted. These studies identified and quantified several PAH compounds in samples collected from the air environment.
At present, there is no Australian standard method to be used for PAH monitoring. Further, since different suites of PAH compounds have been monitored in the various studies, it is very difficult to compare PAH levels in different Australian cities. Hence, there is currently no straightforward way of determining the comparability of data between jurisdictions. For example, the traditional method for PAH sample collection involves the use of a filter only. Although non-volatile PAHs would remain on the filters, semi-volatile PAHs would be lost as a result of post-collection volatilisation. Using solid absorbents to collect the vapour, in conjunction with filters, can reduce this loss.
Given the carcinogenicity of these PAHs and their presence in ambient air from a range of sources, a collation of available international and national information is required to enable the appropriate development of strategies to investigate the potential health impact of PAHs in air in Australia. A comparison of sampling and analytical methods is also required to provide information on the comparability of results from different jurisdictions.
This report covers the studies done in Australia, between 1990 and 1999, and utilises information gathered and reviewed for ANZECC (Victorian EPA, 1998; Denison, L.S., 1998).