Polyaromatic Hydrocarbons (PAHs) are a group of organic compounds which have two or more benzene rings in their structure. Most PAHs in the environment are from incomplete combustion of carbon containing materials such as oil, coal, gas etc. They are often absorbed onto particles of soot emitted from combustion sources. Some PAHs may cause cancer and genetic damage.
PAHs are analysed by extracting the environmental sample with solvent and then analysis by Gas Chromatography Mass Spectrometry (GCMS).
Identifying the Source of PAHs
Identification of the source of Polycyclic Aromatic Hydrocarbons (PAHs) can be important to ascertain if contamination has originated from site, or from external/historical sources. The composition of the PAHs depends on its source and how it has been treated.
SOCOTEC has a long history in the forensic analysis of sites, identifying PAH sources and comparing contamination by the use of double ratio plots and alkylated PAH distribution patterns.
The three main sources of PAHs are:
- Petrogenic – formed through slow, long term moderate temperatures (for example, fossil fuels, petroleum products)
- Pyrogenic – formed through rapid, high temperature combustion (e.g. coal tars, combustion products)
- Phytogenic – derived from plant sources
By plotting the PAH ratios, such as Fluoranthene:Pyrene to Benzo(a)anthracene:Chrysene, the double ratio plot pattern of where these ratios cluster will help in identifying the source. These double ratio plots are also useful in comparing samples to ascertain if the sources are related.
Understanding Polyaromatic Hydrocarbons
There are thousands of PAH compounds but the groups that are generally required in environmental testing are US EPA 16 Priority PAHs:
Coronene is an additional PAH which is required when testing PAHs for Waste Acceptance Criteria (WAC) testing.
The "Oil 8" PAHs are required by the EA Guidance document "Interpretation of the classification of hazardous waste". These are: benz(a)anthracene, chrysene, benzo(b) benzo(k) & benzo(j)fluoranthene, benzo(a)pyrene, dibenzo(a,h) anthracene and indeno (1,2,3-c,d) pyrene.
Matrix PAHs Method MDL soil 16 or 17 PAHs with quantification of "Oil 8" if required Solvent extraction / GCMS 0.08 mg/kg waters 16 or 17 PAHs Solvent extraction / GCMS 10 ppt.