Source Characterization of Polycyclic Aromatic Hydrocarbons by Using Their Molecular Indices: An Overview of Possibilities - Reviews of Environmental Contamination and Toxicology - page 119

7 Summary

In recent decades, an exponential increase in the concentration of anthropogenic
Polycyclic Aromatic Hydrocarbons (PAHs; see Table 1 for a list of PAH abbrevia-
tions) has been observed worldwide. Regulators need to know the sources if con-
centrations are to be reduced and appropriate remediation measures taken. “Source
characterization of PAHs” involves linking these contaminants to their sources.
Scientists place PAH sources into three classes: pyrogenic, petrogenic, and natural.
In this review, we investigate the possibility of using PAH molecular ratios indi-
vidually or in combination for the purpose of deducing the petrogenic or pyrogenic
origin of the contamination in sediments. We do this by reviewing the characteristic
PAH patterns of the sources and by taking into account the fate of PAHs in the
aquatic environment. Many PAH indicators have been developed for the purpose of
discriminating different PAH sources. In Table 4 we summarize the applicability of
different PAH ratios and threshold values.
The analysis of two- to four-ringed alkylated PAHs offers the possibility to dis-
tinguish two or more single sources or categories of pollution in greater detail. For
example, the FL0/PY0, the PPI, and P0/A0 ratios can be used to discriminate
between pyrogenic and petrogenic sources of contamination. When petrogenic con-
tamination is suspected, chrysenes, PAHs lighter than C0, and in particular, alkyl-
ated PAHs can usually be of use. For unburned coal PAHs, the methylphenanthrenic
ratios (MPIs), the 1-D1/4-D1, and BbF/BkF are promising, since they are some-
times correlated with vitrinite reflectance (coal ranks). Alkylphenanthrenes can be
used to detect biomass combustion. Higher molecular weight parent and alkylated
PAHs are appropriate for pyrogenic discriminations. When PAH indices are coupled
with discriminant analysis techniques such as PMF (positive matrix factorization),
the origin of multiple sources in even the most complex environments can be traced
and measured.
Even so, the most stable isomer pairs degrade differentially, depending on their
thermodynamic stability, the environmental conditions, and the type of degradation.
If PAH ratios are to be used, it is usually necessary to have prior knowledge of the
degradation state of the matrices examined (air, sediment, etc.) and of how the PAH
ratio behaves under such conditions. PAH indices (e.g., N0/C0 or LPAH/HPAH) can
be applied for distinguishing differential degradation gradients (photodegradation,
biodegradation, etc.). Degradation does not significantly affect the ratio of parent to
alkylated PAHs and the PI. The degradation arrow in Table 4 and Figs. 9 , 10 , 11 , 12 ,
13 , 14 , 15 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , and 24 shows how the ratio usually changes
with degradation.
Merely detecting the six PAHs of Borneff-6 is not enough to establish petrogenic
contamination, because Borneff6 includes mainly HMW PAHs. The ʣPAH16
appears to be the most suitable for identifying pyrogenic and petrogenic sources.
For more specific information on sources and their discrimination it is recom-
mended to further take into account important parent PAHs such as N0, BeP, PER,
D0, and-most importantly-alkylated PAHs.