287
17.2 Markers of Preservation
17.2.1 Hydrocarbons
Organic molecules formed by carbon and hydrogen (hydrocarbons) are found
widely in nature (e.g., plants, animal tissues, oil). In environmental geochemistry,
and specifically in chemical fingerprinting of spilled oils, studies have often focused
on the quantification of saturates (straight- and branched-chain molecules, cycloalkanes, terpanes, steranes), aromatics (e.g., 2–6-ring polycyclic aromatic hydrocarbons (PAHs) and their homologues) and, more recently, oxidation products of
weathered oil (Ruddy et al. 2014). Sediment samples and spilled oils are dominated
by saturates such as n-alkanes (carbon range C8–C41) and isoprenoids (pristine and
phytane). The ratio of these saturates in sediments are frequently used to distinguish
between natural and oil sources and the degree of degradation of the organic matter
(Wang et al. 2006, 2016). Other saturates such as terpanes and steranes are used as
source-specific markers for oil identification due to its stability during weathering
in the environment (e.g., hopanes C27–C32; Aeppli et al. 2014; Romero et al. 2015;
Wang et al. 2016). Some exceptions have been found, where specific biomarkers
(e.g., hopanes C33–C35) have shown to change due to particular weathering processes (Aeppli et al. 2014). In this case, using compounds that are more recalcitrant
(e.g., compared to n-alkanes) enables quantifying not only the degradation levels
but also the active processes at advanced stages of weathering (Aeppli et al. 2014).
Aromatic compounds, such as PAHs, are used to identify natural (e.g., terrestrial
plants, degradation products), pyrogenic (e.g., incomplete combustion of coal, oil,
and wood), and petrogenic (crude and weathered oil, seeps) sources in environmental samples (Wang et al. 2006, 2016). Moreover, some PAHs present toxic, mutagenic, and/or carcinogenic properties (Louvado et al. 2015), critical for understanding
the ecotoxicological nature and health of natural systems. Due to the complex mixture of hydrocarbons in crude oil and residues, it is critical to include in geochemical studies, a wide range of chemical compounds to better understand the ecosystem
health and weathering of organics in the environment after an oil spill. Due to the
advances in gas chromatography, now coupled with tandem mass spectrometry and
operated in multiple reaction monitoring mode (GC/MS/MS-MRM), it is possible
to identify multiple target compounds (e.g., n-alkanes, terpanes, steranes, PAHs)
from complex matrices in one analytical run, thereby enabling the identification and
quantification of compounds at very low concentrations with no interferences. The
application of these techniques over time and space allows characterization of preservation and weathering processes that affect hydrocarbons deposited in the marine
and coastal environments.
In coastal environments, oil slicks were transported and deposited during the
DWH oil spill in 2010. Several studies indicated a severe decrease (up to ~80%) in
the abundance of low-molecular-weight (LMW) compounds after 19–24 months of
the spill in areas like beaches and wetlands (Aeppli et al. 2014; Gros et al. 2014;
Turner et al. 2014). Different weathering processes have been identified like
17 Long-Term Preservation of Oil Spill Events in Sediments: The Case…
17.2 Markers of Preservation
17.2.1 Hydrocarbons
Organic molecules formed by carbon and hydrogen (hydrocarbons) are found
widely in nature (e.g., plants, animal tissues, oil). In environmental geochemistry,
and specifically in chemical fingerprinting of spilled oils, studies have often focused
on the quantification of saturates (straight- and branched-chain molecules, cycloalkanes, terpanes, steranes), aromatics (e.g., 2–6-ring polycyclic aromatic hydrocarbons (PAHs) and their homologues) and, more recently, oxidation products of
weathered oil (Ruddy et al. 2014). Sediment samples and spilled oils are dominated
by saturates such as n-alkanes (carbon range C8–C41) and isoprenoids (pristine and
phytane). The ratio of these saturates in sediments are frequently used to distinguish
between natural and oil sources and the degree of degradation of the organic matter
(Wang et al. 2006, 2016). Other saturates such as terpanes and steranes are used as
source-specific markers for oil identification due to its stability during weathering
in the environment (e.g., hopanes C27–C32; Aeppli et al. 2014; Romero et al. 2015;
Wang et al. 2016). Some exceptions have been found, where specific biomarkers
(e.g., hopanes C33–C35) have shown to change due to particular weathering processes (Aeppli et al. 2014). In this case, using compounds that are more recalcitrant
(e.g., compared to n-alkanes) enables quantifying not only the degradation levels
but also the active processes at advanced stages of weathering (Aeppli et al. 2014).
Aromatic compounds, such as PAHs, are used to identify natural (e.g., terrestrial
plants, degradation products), pyrogenic (e.g., incomplete combustion of coal, oil,
and wood), and petrogenic (crude and weathered oil, seeps) sources in environmental samples (Wang et al. 2006, 2016). Moreover, some PAHs present toxic, mutagenic, and/or carcinogenic properties (Louvado et al. 2015), critical for understanding
the ecotoxicological nature and health of natural systems. Due to the complex mixture of hydrocarbons in crude oil and residues, it is critical to include in geochemical studies, a wide range of chemical compounds to better understand the ecosystem
health and weathering of organics in the environment after an oil spill. Due to the
advances in gas chromatography, now coupled with tandem mass spectrometry and
operated in multiple reaction monitoring mode (GC/MS/MS-MRM), it is possible
to identify multiple target compounds (e.g., n-alkanes, terpanes, steranes, PAHs)
from complex matrices in one analytical run, thereby enabling the identification and
quantification of compounds at very low concentrations with no interferences. The
application of these techniques over time and space allows characterization of preservation and weathering processes that affect hydrocarbons deposited in the marine
and coastal environments.
In coastal environments, oil slicks were transported and deposited during the
DWH oil spill in 2010. Several studies indicated a severe decrease (up to ~80%) in
the abundance of low-molecular-weight (LMW) compounds after 19–24 months of
the spill in areas like beaches and wetlands (Aeppli et al. 2014; Gros et al. 2014;
Turner et al. 2014). Different weathering processes have been identified like
17 Long-Term Preservation of Oil Spill Events in Sediments: The Case…