PAH analysis

Poly Aromatic Hydrocarbons

The sum of the target 16 EPA listed PAHs is a commonly needed parameter used to classify the soil contamination status. A special set of filters, exclusive to QROS, can be supplied for the UVF-3100 that allows the user to determine this value. This set of filters, used in conjunction with the standard filter set can also identify the ratio of lighter PAHs to the mid weight PAHs and the ratio of heavy PAHs to the mid weight PAHs. This is useful for establishing a treatability index for hydrocarbon polluted sites. Samples that show a high percentage of heavy end PAH content are more difficult to bioremediate or soil wash than those with a high light end content.

The total fluorescence value obtained when calibrated to the PAH calibrator set can also be correlated to the TPH value of a sample from MGP sites. The TPH value includes the PAHs found in coal tars and for coal tars, the PAHs form the majority of the hydrocarbons present. For risk assessment purposes, it is the PAHs in the TPH fraction that pose the health risks. The aliphatic hydrocarbons present, when the PAHs are removed can be found in moisturising creams for the face and hands as well as in candle wax.

The benefits of ratio analysis using on site analysis

Naphthalenes, as well as flourene, acenaphthene and acenaphthylene are relatively volatile compounds. Naphthalene is unusual in that it sublimes (goes from a solid to a gas without passing through a liquid phase) at room temperature. These compounds can easily be lost during the sampling, transportation and subsequent analysis in a laboratory resulting in an erroneous interpretation put on the site. The UVF 3100 analyser will give a better indication of the actual concentration of these compounds on the site so that appropriate precautions can be made if they are present, to collect, preserve and analyse validation samples in the laboratory.

The ratio analysis is a very good indicator for these light PAHs. The higher the light to mid % above 100%, the more light end aromatics are present. Fresh diesel will give a typical value of >200%. Samples with % light to mid below 70% contain no or very low light end aromatics and also have low concentrations of the mid weight compounds such as phenanthrene and acenaphthene.

The heavy to mid ratio is also a good predictor of the presence of benzo (a) pyrene. This toxic compound is one of the few PAHs to be reviewed by the EA and is often selected as a target compound that dictates clean up criteria. The UVF 3100 can detect as little as 0.1 mg/kg of BaP in soil and protocols are available to detect even lower concentrations if required.