Environmental Engineering Reference
In-Depth Information
When the PAH ratios for sources are known, the ratios can be classified according
to their diagnostic power (DP), so that the most suitable ones are selected for the
study area (Christensen and Tomasi
2007
; Christensen et al.
2004
). Christensen and
Tomasi (
2007
) evaluated the diagnostic power of 25 PAH ratios of oil spill samples.
They reported high diagnostic power for ratios such as alkylated phenanthrenes to
alkylated dibenzothiophenes, fluoranthene to pyrene, methylphenanthrenes to phen-
anthrenes and other less common ratios.
A standardized and simple means of comparing chemical fingerprints (Fig.
6
—
tier III) of different oil spills is the Nordtest (Douglas et al.
2007b
; Stout et al.
2005
).
It entails plotting several diagnostic ratios (generally accepted, or calculated for the
occasion) for the source and the sample, together with the 98% and 95% confidence
intervals (Fig.
7
) (Stout et al.
2005
).
Douglas et al. (
2007b
) described the Nordtest method (limited to spilled oils and
refined oil products in water) in more detail and showed how to establish new can-
didate ratios for discriminating between two known sources. They also recom-
mended a list of 10 diagnostic ratios for identifying oil spills. Phenanthrenes and
dibenzothiophenes are included on this list because they are common in all oils. The
concentrations of methylfluoranthenes, methylpyrenes and benzofluorenes also
vary among different oils and are included on the list (Douglas et al.
2007b
).
Principal component analysis (PCA) (Davis
2002
; Luo et al.
2008
) is one of the
most suitable tools for identifying potential sources of PAHs. PCA allows for greater
resolution among different sources and for reduced variance than does the Nordtest
Fig. 7
The Nordtest method. All ratios match the possible source (i.e., the ratios in the sample and
source are within a 95% confidence interval). Adapted from Stout et al. (
2005
), with permission,
© Taylor & Francis Inc
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