Source Characterization of Polycyclic Aromatic Hydrocarbons by Using Their Molecular Indices: An Overview of Possibilities - Reviews of Environmental Contamination and Toxicology - page 49

6 Discussion and Conclusions ............................................................................................... 114

6.1 What Are the Most Important PAH Sources in the Aquatic Environment and

Which PAH Indicators Can Be Used to Unequivocally Identify Them?................... 115

6.2 What Are the Inherent Uncertainties in These Indicators and How Does the

Value of the Indicator Change After Undergoing Biogeochemical
Processes (i.e., Photochemical Oxidation, Degradation, Volatilization, etc.)
in the Aquatic Environment?...................................................................................... 117

6.3 Can the Borneff-6, 16 EPA, and 10 VROM PAHs Be Used to Calculate
the Proposed Indicator—and, if so, Which Uncertainties are
Introduced by This Approach?................................................................................... 119
7 Summary ............................................................................................................................ 120
Appendix .................................................................................................................................. 121
References ................................................................................................................................ 121

1 Introduction

The Polycyclic Aromatic Hydrocarbons (PAHs or polyaromatic hydrocarbons)
have been extensively studied to understand their distribution, fate and effects in the
environment (Haftka 2009 ; Laane et al. 1999 , 2006 , 2013 ; Okuda et al. 2002 ; Page
et al. 1999 ; Pavlova and Ivanova 2003 ; Stout et al. 2001a ; Zhang et al. 2005 ). They
are organic compounds consisting of conjoined aromatic rings without heteroatoms
(Schwarzenbach et al. 2003 ). Sander and Wise ( 1997 ) list 660 parent PAH com-
pounds (i.e., aromatic substances without alkyl groups and consisting solely of
fused rings connected to each other), ranging from the monocyclic molecule of
benzene (molecular weight = 78) up to nine-ringed structures (MW 1 up to 478).
PAHs containing one or more alkyl groups are called alkyl PAHs. Our study deals
with the parent compounds (without alkyl groups and/or heteroatoms), the alkyl
PAHs (denoted as PAH n , with n referring to the number of methyl groups; see foot-
notes in Table 1 ), and certain heterocyclic sulfur PAHs (dibenzothiophenes). The
term PAHs includes all the above, unless explicitly specified. In Table 1 , we present
the nomenclature of PAHs used in this paper.
The PAHs have high molecular weight (HMW), low volatility (Ou et al. 2004 ),
and are classified as semivolatile organic contaminants (Ollivon et al. 1999 ). They
are hydrophobic and lipophilic (Pavlova and Ivanova 2003 ). Their hydrophilicity
and mobility decrease as the number of rings increases (Iqbal et al. 2008 ). In Table 2 ,
we present the physicochemical properties of several parent PAHs. Because of their
hydrophobic characteristics, PAHs tend to rapidly adsorb to particulate organic mat-
ter in sediments or soots, rather than vaporizing or dissolving in water (Bertilsson
and Widenfalk 2002 ).
Depending on their volatility, the PAHs may be transported far from their original
source, ending up in various environmental compartments, although their main
environmental sink is the organic fraction of soils and sediments (Agarwal 2009 ;
Harris et al. 2011 ; Morillo et al. 2008a ; Stark et al. 2003 ). PAHs emitted from the
combustion of fossil fuels are transported into marine sediments by atmospheric

1 MW: molecular weight.