Source Characterization of Polycyclic Aromatic Hydrocarbons by Using Their Molecular Indices: An Overview of Possibilities - Reviews of Environmental Contamination and Toxicology - page 111

Since LMW PAHs are more susceptible to degradation (microbial, volatilization,
and dissolution), sediments exhibit lower LMW/HMW ratios than the contamina-
tion source (Zakaria et al. 2002 ). As a workaround, De Luca et al. ( 2005 ) suggested
using P0 as a possible marker of LPAH pollution in Olbia harbor (Italy). Furthermore,
some combustion sources may produce LMW PAHs (Guo et al. 2007 ). Hence,
source apportionment assignments using two- to three-ringed parent PAHs may
become compromised after moderate weathering (Yan et al. 2006 ), rendering the
LMW/HMW ratios (i.e., L/H, LPAH/HPAH) inadequate for discriminating crude
oil from other major sources of sedimentary PAHs.
For the above reasons, the LPAH/HPAH ratio was used as a proxy of PAH weath-
ering by Stout et al. ( 2003 ), who noted that if the LPAH/HPAH ratio becomes low
(≈0.2), then the ratios of BaA/C0, BbF/BkF, BeP/BaP decrease sharply and may fail
to indicate the contaminant sources (Fig. 19 ). However, Costa and Sauer ( 2005 ) did
not observe such trends for these ratios, and used the LPAH/HPAH ratio as a weath-
ering index. Consequently, the L/H ratio is consistent with degradation and as such it
was used to interpret the degradation in oil tarballs in Malaysia (Zakaria and Takada
2007 ). Summarizing, if LPAH/HPAH >2.3, then recent input of petrogenic products
is implied. Degradation or pyrogenic sources are likely when 0.2 < LPAH/HPAH
<0.4, whereas at values of LPAH/HPAH <0.2, degradation is likely to have occurred.

5.8.3 Ratios of Alkyl to Parent PAHs

The sum of the parent PAHs with masses 128, 178, 202, and 228, divided by the
total PAH1-PAH4 homologues of these PAHs (N0, P0, A0, FL0, PY0, BaA, C0) is
called the parent to alkyl (Par/Alkyl) ratio:

NNNNPA PA 1 234 1 +++++++++

+++

2 312 PA FP FP BC 1

The Par/Alkyl ratio was used by Yan et al. ( 2005 , 2006 , 2007 ) to distinguish
petrogenic (>2.3-4) and pyrogenic (<1) sources (e.g., in oil spills even after
extensive weathering in sediments). Apportionment values for petroleum combus-
tion (1.1) and coal combustion (0.35) have also been reported (Yan et al. 2007 ). The
correlation of Par/Alkyl with ʴ 13 C Py , FL0/PY0 and Ring456/TPAH (discussed
below), implies that Par/Alkyl is a reliable PAH source indicator over large geo-
graphic areas or even long timespans (Yan et al. 2005 , 2006 ).
Yunker et al. 2002 used an alkyl/ʣPAH ratio to infer pyrogenic or petrogenic
sources in sediments. In this case, ʣPAH is the ʣ(178-278) parent PAHs:
NNNNDDPA PA

NPA P C 0 0 0 0

++++++ ++
+++++++kF ghi

1 23412 1 2 PA 3

++++

PA 0 FP 0 BC 0 BePBaP BbFBjF B IP DA DcA

and when alkyl/ʣPAH ≤ 0.35, coal is ruled out, since natural background sources
(e.g., shales, coal, and bitumen) have a ratio of 2.3-3.2 (Yunker et al. 2002 ).