Source Characterization of Polycyclic Aromatic Hydrocarbons by Using Their Molecular Indices: An Overview of Possibilities - Reviews of Environmental Contamination and Toxicology - page 56

(Page et al. 1996 ; Wang and Fingas 2003 ; Wang et al. 1999a , 2001 ). For example,
many of the monomethyl PAH derivatives are preserved in petroleum because of
their low formation temperatures (<150 °C) (Mitra et al. 1999 ). The proportion of
thermally stable phenanthrene isomers increases as the crude matures (Stout
et al. 2002 ). Furthermore, the dibenzothiophene abundance in source rock, i.e.,
the rock in which the oil matured, is a function of anoxia (leading to reduced
sulfur), and therefore reflects the type of source rock facies (Peters et al. 2005 ;
Stout et al. 2002 ).
The main PAH components of a petroleum source include the EPA 16 parent
PAHs and the petroleum-specific alkylated (PAH1-PAH4) homologues of selected
PAHs: viz., alkylated naphthalene, phenanthrene, dibenzothiophene, fluorene, and
chrysene series, which are also called “the alkylated five” or “ “five target ” (Bertilsson
and Widenfalk 2002 ; Wang et al. 1999a ; Zeng and Vista 1997 ). These PAHs are
source-specific (concentrations vary among different oils) and their abundance in
sediment is taken to indicate petrogenic sources (Boll et al. 2008 ; De Luca et al.
2004 ; Stout and Wang 2007 ; Wang et al. 2001 ). For example, dibenzothiophenes,
together with phenanthrenes, are widely used for PAH source apportionment
because of their numerous isomers and their mild and similar degradabilities (abso-
lute concentrations of the methyldibenzothiophenes increase during weathering)
(Page et al. 1996 ; Stout and Wang 2007 ; Wang and Fingas 1995 , 2003 ; Wang et al.
1999a , 2001 ).
Figure 1a-d show that petroleum products contain mainly two- to three-ringed
PAHs and only the heavier ones (Fig. 1c, d ) contain significant amounts of four-
ringed PAHs. In all instances (except Fig. 1e ), five- and six-ringed PAHs, and occa-
sionally compounds such as acenaphthylene (AY), anthracene (A0) and fluoranthene
(FL0) (e.g., Fig. 2 ; Fig. S3, Supporting Material), are undetectable in crude oil and
its refined products (Stout et al. 2002 ). For instance, benz[ a ]anthracene (BaA),
benzo[ a ]pyrene (BaP), benzo[ b ]luoranthene (BbF), benzo[ k ]luoranthene (BkF)
and chrysene (C0) are minor constituents of petroleum products, if present at all
(e.g., Irwin et al. 1997 ; Jiang et al. 2009 ; Shreadah et al. 2011 ; Wang et al. 2001 ).
Figure 1e , given for comparison, shows a mixture of pyrogenic and petrogenic prod-
ucts, as is common in used lubricants.
In crude oil, the content of LMW PAHs (containing two or three fused aromatic
rings), and especially their alkylated homologues far exceed the unsubstituted par-
ent PAHs. The petroleum PAHs exhibit a characteristic bell-shaped pattern within
their homologue series (Fig. 1a-d ; Figs. S2-S5, Supporting Material): PAH3 or
PAH2 alkylated PAHs predominate and amounts of PAH0-PAH2 and PAH4 homo-
logues decrease (Douglas et al. 2007a ; Stout 2007 ). Thus, much more information
is contained in the alkylated homologue series of crude oil than in the parent
PAHs, i.e., the abundance of alkylated PAHs, bell-shaped patterns and depletion of
HMW PAHs (compare Figs. S1 vs. S2; Figs. S5 and S6 vs S9, Supporting Material).
This information allows us to differentiate between petrogenic products and to
distinguish them from pyrogenic forms, regardless of the oil formation environ-