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MARINE
ENVIRONMENTAL
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Marine Environmental Research 59 (2005) 139–163RESEARCH
Comparison of polycyclic aromatichydrocarbon distributions and
sedimentary organic matter characteristicsin contaminated, coastal sediments from
Pensacola Bay, Florida
Myrna J. Simpson a,1, Benny Chefetz b, Ashish P. Deshmukh a,Patrick G. Hatcher a,*
a Department of Chemistry, 100 W. 18th Avenue, The Ohio State University, Columbus, OH 43210, USAb Department of Soil and Water Sciences, The Hebrew University of Jerusalem, P.O. Box 12,
Rehovot 76100, Israel
Received 15 October 2002; received in revised form 10 June 2003; accepted 8 September 2003
Abstract
In this study, we examined the distribution of polycyclic aromatic hydrocarbons (PAHs) in
a contaminated coastal area and the characteristics of the natural organic matter in tandem.
We present a detailed study of PAH concentration, distribution, and organic matter charac-
teristics of three core samples from Pensacola Bay, Florida. Solid-state 13C Nuclear Magnetic
Resonance (NMR), pyrolysis gas chromatography coupled with mass spectrometry (GC-MS),
and tetramethyl ammonium hydroxide (TMAH) thermochemolysis GC-MS were applied to
obtain structural details about the sedimentary organic matter. Elemental compositions
(carbon and nitrogen) and estimates of black carbon contents are also reported. These coastal
sediments were found to contain more PAHs in the upper 15 cm layers than in the bottom 15–
25 cm samples. The samples that contained the most PAHs also contained the least amount of
aromatic carbon and contained a significant amount of paraffinic carbon. Lignin-derived
pyrolysis and TMAH thermochemolysis products were abundant and generally higher in all of
*Corresponding author. Tel.: +1-614-688-8799; fax: +1-614-688-5920.
E-mail address: hatcher.42@osu.edu (P.G. Hatcher).1 Present address: Department of Physical and Environmental Sciences, Scarborough College,
University of Toronto, 1265 Military Trail, Toronto, Ontario, Canada M1C 1A4.
0141-1136/$ - see front matter � 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.marenvres.2003.09.003
140 M.J. Simpson et al. / Marine Environmental Research 59 (2005) 139–163
the samples in comparison to those reported for modern coastal sediments, indicating a large
flux of terrestrial carbon. The black carbon contents were found to range from 4.3% to 6.8%,
which are significantly lower than other reports of black carbon in sediments, which represent
as much as 65% of the total organic carbon content. The low black carbon content suggests
that this type of refractory carbon may not be as responsible for regulating PAH distribution
as indicated by other researchers.
� 2004 Elsevier Ltd. All rights reserved.
Keywords: Sedimentary organic matter; Black carbon; Solid-state 13C NMR; Pyrolysis GC-MS; TMAH
thermochemolysis GC-MS
1. Introduction
Many contaminants accumulate in soil and coastal environments and represent
a significant risk to human and environmental health. Polycyclic aromatic hy-
drocarbons (PAHs), a group of nonionic hydrophobic organic contaminants, are
ubiquitously present in coastal areas and arise from numerous anthropogenic
activities such as: fossil fuel burning, the release of uncombusted petroleumproducts, and creosote wood treatment (Gschwend & Hites, 1981; Wakeham,
Schaffner, & Giger, 1980a; Wakeham, Schaffner, & Giger, 1980b). PAHs are es-
pecially problematic because they exhibit toxicity and mutagenicity at very low
concentrations and have a high tendency to bind to natural organic matter,
therefore impeding and often hindering remedial attempts. Typically, PAH con-
centrations in coastal waters are 10–1000 times lower than those found in sedi-
ments, with most of the PAHs residing in surface layers (Kucklick & Bidleman,
1994; Liu & Dickhut, 1997). Physical processes that result in the resuspension ofsurface sediments in the water column, such as bioturbation, may promote the
release of PAHs into coastal waters (Schaffner, Dickhut, Mitra, Lay, & Brouwer-
Riel, 1997). Consequently, it is vital to understand the nature of PAH associations
with coastal sediments such that the transport and bioavailability of the con-
taminants can be better predicted.
The equilibrium with sedimentary-bound PAHs and coastal waters has been in-
vestigated and several relationships with sediment characteristics have been devel-
oped (Grathwohl, 1990; Gustafsson, Haghseta, Chan, MacFarlane, & Gschwend,1997; Karickhoff, Brown, & Scott, 1979; Luthy et al., 1997; McGroddy, Farrington,
& Gschwend, 1996). PAH sequestration has been correlated to the amount of or-
ganic carbon in the sediment and more specifically, with aromatic organic carbon
content. Soot or black carbon, which has a high sorption capacity for PAHs (Bucheli
& Gustafsson, 2000), has also been implicated in regulating the PAH concentration
in sediments and water (Accardi-Dey & Gschwend, 2002; Gustafsson et al., 1997;
McGroddy et al., 1996). However, most reports do not include organic geochemical
investigations that yield structural information. Therefore, it is currently difficult toascertain the specific structures in sedimentary organic matter that are responsible
for regulating the distribution of PAHs in sediments.
M.J. Simpson et al. / Marine Environmental Research 59 (2005) 139–163 141
In this study, we applied several geochemical methods to investigate the structural
characteristics of contaminated, coastal sediments from Pensacola Bay, Florida, in
cooperation with conventional PAH analysis. Pensacola Bay sediments have been
examined for PAHs and heavy metals (Lewis et al., 2001) but the organic matter
characteristics have not yet been examined in detail. Solid-state 13C Nuclear Mag-
netic Resonance (NMR) spectroscopy can be used to obtain a semi-quantitativedistribution of the total organic carbon in whole, untreated samples and provides
information regarding the relative abundance of different carbon types in the sample
(Hatcher, Breger, Dennis, & Maciel, 1983; Malcolm, 1989). Pyrolysis gas chroma-
tography-mass spectrometry (GC-MS) and tetramethyl ammonium hydroxide
(TMAH) thermochemolysis GC-MS are also employed to identify the organic
matter source biomarkers. Pyrolysis GC-MS is a thermally degradative technique
that results in bond cleavage and release of volatile products such that qualitative
identification of polysaccharides, proteins, lipids, lignin and other biomarkers can bemade (Almendros, Dorado, Gonzalez-Vila, & Martin, 1997; Fabbri et al., 1998;
Hatcher, Dria, Kim, & Frazier, 2001; Kogel-Knabner, 2000; Pouwels, Eijkel, &
Boon, 1989; Ralph & Hatfield, 1991). Alternatively, TMAH thermochemolysis is a
chemolytic procedure that hydrolyzes and methylates ester and ether linkages, as-
sisting polymer fragmentation and methylation of lignin (Clifford, Carson,
McKinney, Bortiatynski, & Hatcher, 1995; Filley, Minard, & Hatcher, 1999;
Hatcher et al., 2001) and has been employed to characterize organic matter in whole
soil (Chefetz, Chen, Clapp, & Hatcher, 2000a) and sediment samples (Deshmukh,Chefetz, & Hatcher, 2001). By combining 13C NMR, pyrolysis and TMAH ther-
mochemolysis GC-MS, one is able to obtain a detailed compositional picture of
organic matter. We present this information, in cooperation with PAH and black
carbon measurements, to examine the correlation between sedimentary organic
matter characteristics and PAH distributions in coastal sediments.
2. Materials and methods
2.1. Sample collection and site description
Samples were collected from two tidal bayous located near the northwest corner
of Pensacola Bay, Escambia County, Florida (Fig. 1). One sample was obtained
from Bayou Grande and two were collected from within Bayou Chico (Brown’s
Marina and Mahogany Landing). All of these bayous have freshwater inputs,
however, are subject to several sources of contamination from anthropogenic ac-tivity (Lewis et al., 2001). Several areas within Escambia county are Superfund sites
and are on the National Priorities List of the Environmental Protection Agency.
Bayou Grande is nearest to the Pensacola Naval Air Station. Bayou Chico has
anthropogenic inputs from several industrial sources including those associated with
agrochemicals, creosote treatment of wood, and waste oil recovery.
At each site, a 25 cm sediment core was collected using a cylindrical plastic coring
device with a diameter of 7 cm, fitted with a long handle. The lower end of the core
Fig. 1. Map displaying the sample site and sample areas within Pensacola Bay.
142 M.J. Simpson et al. / Marine Environmental Research 59 (2005) 139–163
was closed using a rubber stopper, and sealed with electric tape. The upper end wasclosed with a plastic cap, and sealed with electric tape. The sealed cores were stored
vertically until they were extruded later on the shore. Top (0–15 cm) and bottom (15–
25 cm) samples were transferred into 1 L glass jars, capped with seawater, then
purged with nitrogen and sealed. Samples were shipped on ice to the laboratory, and
stored at 4 �C until analyzed.
2.2. Sample preparation, carbon, nitrogen and PAH analysis
Immediately upon reaching the laboratory, sub-samples were freeze-dried, ground
to pass a 1 mm sieve and stored at room temperature. Total carbon and nitrogen
compositions were measured with a Carlo-Erba NA 1500 Series 2 Elemental Ana-
lyzer (CE Elantech, Inc., Lakewood, NJ). Ash contents were determined from mass
lost after heating at 550 �C, until a constant mass was obtained. Total carbon, ni-
trogen and ash contents are listed in Table 1.
To remove excess salts, approximately 25 g of freeze-dried sediment was placed in
250 mL centrifuge bottles, and mixed with 150 mL of deionized water at 200 rpm atroom temperature for 2 h. The bottles were then centrifuged (3200g for 15 min) and
the supernatant was discarded. To isolate the PAHs, the sediment samples were then
extracted with 150 mL of 2:1 (v/v) mixture of dichloromethane and methanol. The
sediment–solvent mixtures were then sonicated (pulse mode, 45 s; Branson sonifier
250), and shaken at 200 rpm for 24 h. After this time, the bottles were centrifuged
(3200g for 30 min) and the organic solvent removed. The remaining sediment was
treated with 5% HF and 5% HCl solution to remove minerals and concentrate the
organic matter. The sediment was mixed with the HF/HCl mixture for a week, afterwhich the supernatant was decanted and replaced with a freshly prepared acid
Table 1
Basic sediment characteristics
Sample Carbon (%) Nitrogen (%) Ash content (%) Black carbon
(% of TOC)a
Bayou Grande Top 11.26 0.66 73.1 4.3
Bayou Grande Bottom 11.62 0.58 74.6 nd
Brown’s Marina Top 2.83 0.09 92.9 6.8
Brown’s Marina Bottom 2.26 0.06 95.7 nd
Mahogany Landing Top 7.45 0.38 79.9 6.4
Mahogany Landing Bottom 14.31 0.55 64.9 nd
nd, Not determined; black carbon measurements were performed on the top sediment layers only.a Expressed as the percentage of total organic carbon that is in the form of black carbon.
M.J. Simpson et al. / Marine Environmental Research 59 (2005) 139–163 143
solution. This procedure was repeated three times such that the ash content was
reduced to an acceptable level for the proposed analytical methods. After the de-ashing procedure, the residue was repeatedly rinsed with deionized water (acidified to
pH 2 with dilute HCl), freeze-dried and stored for further analysis.
An aliquot of the organic solvent extract was sampled and concentrated under a
stream of nitrogen for the determination of PAHs. The dry extract was mixed with
100 mg of silica gel (Aldrich, Milwaukee WI) and hexane and then transferred onto a
silica gel column saturated with hexane (Deshmukh et al., 2001). Separation of
components was performed by elution of hexane followed by benzene (5 mL, each).
The column effluents (i.e. hexane and benzene fractions) were concentrated andanalyzed by high performance liquid chromatography (HPLC). PAH concentrations
were measured with a Waters 2690 High Performance Liquid Chromatograph
(HPLC) fitted with a Waters 996 photodiode array detector, and Supelcosil LC-PAH
reverse-phase column (25 cm� 2.1 mm� 5 lm; Supelco, Bellefonte, PA). Instrument
parameters were as follows: an absorbance wavelength of 254 nm, injection volume
of 10 lL, a flow rate of 0.25 mL/min, and a gradient program starting with 50%
methanol and 50% water reaching a solvent composition of 100% methanol by 30
min, holding this composition for 10 more minutes, and then returning to a com-position of 50% methanol and 50% water by 45 min. An external standard con-
taining 16 PAHs (EPA 610 polynuclear aromatic hydrocarbons mix, Supelco) was
used for quantification of peak areas.
2.3. Cross polarization magic angle spinning (CPMAS) 13C NMR
Solid-state 13C NMR was performed on the HF/HCl treated sediments to gain
information about the carbon distribution in the sediments. NMR analysis wasperformed on the HF/HCl treated sediments rather than the bulk sediment samples
because the removal of minerals concentrates the organic matter and results in en-
hancements of the signal-to-noise ratio and reduction of interferences from para-
magnetic minerals (Schmidt, Knicker, Hatcher, & Kogel-Knabner, 1997). The
CPMAS 13C NMR spectra were acquired on a Bruker Avance 300 MHz NMR
144 M.J. Simpson et al. / Marine Environmental Research 59 (2005) 139–163
spectrometer, equipped with a 4 mm H-X MAS probe, and using the standard ramp-
CP pulse program (Dria, Sachleben, & Hatcher, 2002; Cook, Langford, Yamdagni,
& Preston, 1996). Approximately 100 mg of sample was packed into a 4 mm zir-
conium rotor with a Kel-F cap. The acquisition parameters were as follows: spectral
frequency of 75 MHz for 13C and 300 MHz for 1H, spinning rate of 13 kHz, ramp-
CP contact time of 2 ms, 1 s recycle delay, 25,000 scans per sample and linebroadening of 100 Hz. The spectra were integrated into the following chemical shift
regions: aliphatic carbon (0–50 ppm); methoxyl carbon (50–60 ppm); o-alkyl carbon
(60–110 ppm); aromatic carbon and phenolic carbon (110–160 ppm); carboxyl and
amide carbon (160–190) and carbonyl carbon (190–215 ppm) (Hatcher, Bortiatynski,
Minard, Dec, & Bollag, 1993; Malcolm, 1989).
2.4. Pyrolysis GC-MS
Pyrolysis-GC-MS was performed using a Carlo Erba Mega 500 series gas chro-
matograph (Carlo Erba, Milan, Italy) operating in split mode (20:1), equipped with a
CDS Analytical pyroprobe-2000 controller, a CDS AS-2500 pyrolysis autosampler
and a 30 m fused silica capillary column coated with chemically bound DB-5
(0.25 mm i.d., film thickness 0.25 lm; Restek Corp., Bellefonte, PA). The interface
temperature was held at 273 �C. Helium was used as a carrier gas with flow rates of
2 mLmin�1 through the column and 20 mLmin�1 through the split at a head-
pressure of 65 kPa. The following oven temperature program was used: initialtemperature 40 �C (held for 2 min); heating rate 8 �Cmin�1; final temperature 300 �C(held for 10 min). The gas chromatograph was connected to a Kratos MS-25 RFA
mass spectrometer operating at an electron impact potential of 50 eV with a mass
range of 40–510 m/z and a cycle time of 0.7 s (electron beam current 120 lA, source
temperature 250 �C).HF/HCl treated sediment samples (�0.5 mg) were weighed and transferred onto a
minimal amount of silica wool on top of a solid fused silica spacer inside a quartz
tube. The tube was dropped by the pyrolysis autosampler into the pyrolysis chamber,which was flushed with the gas prior to pyrolysis, at 70 mLmin�1 for a period of 6 s.
The pyrolysis chamber was subsequently heated to 615 �C at a rate of 5 �C/ms and
was held at this temperature for 15 s. After pyrolysis, the chamber was flushed with
the carrier gas flow for 21 s. Data acquisition and analysis were performed using a
Dart/Kratos Mach 3 data system. Pyrolysis products were identified based on their
mass spectra and GC retention times (Pouwels et al., 1989; Van der Kaaden et al.,
1984). The total ion current (TIC) chromatograms of the pyrolysis GC-MS runs
were integrated allowing semi-quantitation of the pyrolysis products.
2.5. TMAH thermochemolysis GC-MS
Freeze-dried samples (2–5 mg) were weighed and placed in glass tubes with
200 lL of TMAH (25% by weight in methanol; Aldrich). The methanol was
evaporated under a stream of nitrogen. The tubes were sealed under vacuum, and
subsequently placed in an oven at 250 �C for 30 min. After cooling, the tubes were
M.J. Simpson et al. / Marine Environmental Research 59 (2005) 139–163 145
cracked open, internal standard (1.95 lg of n-eicosane) was added and the inside
surfaces of the tubes were extracted (3 times) using ethyl acetate. The combined
extracts were reduced to approximately 50 lL under a stream of N2. Gas chro-
matographic analyses were performed using a Hewlett-Packard 6890 gas chro-
matograph (Hewlett Packard, Palo Alto, CA), equipped with a 15 m fused silica
capillary column coated with chemically bound DB-5 (0.25 mm i.d., film thickness0.1 mm; Supelco, Bellefonte, PA). Samples (1 lL) were injected using an autoin-
jector (Hewlett-Packard 7683 series), with a split ratio of 5 and an inlet temper-
ature of 310 �C. Helium was used as carrier gas with a flow rate of 1 mL/min;
electronic flow control was set for constant flow. The gas chromatographic oven
temperature was programmed from 40 to 300 �C at the rate of 8 �Cmin�1. The GC
was directly coupled to a Pegasus II (Leco� Corporation, St. Joseph, MI) time-of-
flight mass spectrometer by a deactivated fused silica transfer-line heated to
300 �C. Mass spectra from 33 to 700 m=z were accumulated at 9 scans/s. Mostpeaks were assigned by comparison with the National Institute of Standards and
Technology library (NIST, version 1.6).
2.6. Black carbon analysis
The sorption/desorption, sequestration, and distribution of PAHs in sedimentary
organic matter has been attributed to the presence of soot or charcoal, often referred
to as black carbon (Gustafsson et al., 1997; McGroddy et al., 1996). A chemicaloxidation procedure (hypochlorite oxidation) described by Hatcher, Spiker, and
Orem (1986) was employed to determine if black carbon is present in the Pensacola
Bay sediments. Oxidation with sodium hypochlorite cleaves the uncondensed aro-
matic rings that would otherwise overlap with the NMR signal of black carbon.
Partially de-mineralized samples were mixed with 10 g of sodium chlorite, 10 mL of
acetic acid and 100 mL of deionized water per gram of sediment. The mixture was
stirred overnight until the reaction ceased and then repeated two more times. The
mixture was centrifuged (3200g for 25 min) and the residue was repeatedly rinsedwith deionized water until excess salts were removed. The residue was then freeze-
dried, re-analyzed for total carbon content and examined by solid-state 13C NMR.
The amount of black carbon was calculated from the mass balance of total carbon
and the integration of the aromatic region of the CPMAS 13C NMR spectrum before
and after chemical oxidation. Black carbon values for the surface layer of the three
sediment cores are listed in Table 1.
3. Results
3.1. PAH analysis
The measured PAHs and their respective concentration in each sample are listed
in Table 2. The Bayou Grande and Mahogany Landing sediment samples contained
the highest and lowest concentration of total PAHs (P
PAHs), respectively. These
Table 2
Average PAH concentration in bulk sediment extracts from Pensacola Bay sediments expressed in lg/kg of dry sediment
Concentration (lg/kg) Molecular
formula
Molecular
weight
(g/mol)
logKowa Bayou
Grande
Top
Bayou
Grande
Bottom
Brown’s
Marina
Top
Brown’s
Marina
Bottom
Mahogany
Landing
Top
Mahogany
Landing
Bottom
Naphthalene C10H8 128.2 3.37 bdl bdl bdl bdl bdl bdl
Acenaphthylene C12H8 152.2 4.00 bdl bdl bdl Bdl bdl bdl
Acenaphthene C12H10 154.2 3.92 bdl bdl bdl bdl bdl bdl
Fluorene C13H10 166.2 4.18 bdl bdl bdl bdl bdl bdl
Phenanthrene C14H10 178.2 4.57 302.2� 3.9 bdl 135.6� 28.2 69.9� 12.3 40.2� 9.7 39.9� 9.6
Anthracene C14H10 178.2 4.54 74.5� 3.6 bdl 30.9� 9.5 bdl bdl 43.3� 5.2
Fluoranthene C16H10 202.3 5.22 576.5� 66.5 bdl 343.3� 16.5 203.7� 49.8 200.8� 16.4 436.6� 116.7
Pyrene C16H10 202.3 5.18 144.3� 13.2 200.9� 14.4 368.4� 419.9 452.5� 113.9 382.1� 25.7 36.1� 3.4
Benzo(a)anthracene C18H12 228.3 5.91 163.9� 15.9 47.6� 2.6 78.2� 1.4 45.6� 3.0 17.8� 4.1 32.3� 20.6
Chrysene C18H12 228.3 5.86 290.3� 45.3 106.0� 18.5 bdl bdl bdl bdl
Benzo(b)fluoranthene C20H12 252.3 5.80 189.0� 30.6 145.1� 22.4 bdl bdl 20.5� 0.3 bdl
Benzo(k)fluoranthene C20H12 252.3 6.00 333.8� 47.6 328.6� 26.9 bdl bdl bdl bdl
Benzo(a)pyrene C20H12 252.3 6.04 290.3� 26.3 209.7� 10.2 154.1� 4.1 bdl 48.5� 2.1 bdl
Dibenz(a,h)anthracene C20H12 278.4 6.75 bdl bdl 118.8� 10.8 bdl bdl bdl
Benzo(g,h,i)perylene C22H12 276.3 6.5 10.0� 0.9 17.0� 13.3 455.0� 23.4 685.9� 59.4 197.3� 31.5 bdl
Indeno(1,2,3-cd)pyrene C22H12 276.3 7.66 193.9� 30.9 141.4� 32.2 80.4� 4.9 133.7� 0.5 63.4� 5.1 bdl
PPAHs 2568.6 1196.4 1764.6 1164.2 970.5 588.3
Kow is the octanol–water partition coefficient.
bdl, below detection limits of 0.01 mg/L.a From MacKay, Shui, and Ma (1992).
146
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M.J. Simpson et al. / Marine Environmental Research 59 (2005) 139–163 147
observations are consistent with the qualitative signs of contamination made during
sampling and reports of PAHs detected by other researchers (Elder & Dresler, 1988).
All three sites contained more total PAHs in the top than in the bottom sample. The
PAH distribution between the top and bottom samples differs at each of the three
sites. In general, higher molecular weight PAHs were detected in the top layer more
so than in the bottom layer. Phenanthrene, anthracene and fluoranthene were notdetected in the bottom Bayou Grande sediment layer but are present in the top layer.
Similarly, the Brown’s Marina bottom layer did not contain any anthracene and less
phenanthrene and fluoranthene than in the top layer. In contrast, the bottom sample
of the Mahogany Landing site contained more fluoranthene and anthracene in the
bottom layer and comparable amounts of phenanthrene in both the top and bottom
samples. The PAH distribution from all three sites was dominated by the higher
molecular weight compounds, such as pyrene, benzo(a)anthracene and higher, and is
indicative of their resistance to degradation, high sorptive capacity and overall en-vironmental persistence.
Fig. 2. Cross polarization magic angle spinning 13C NMR spectra of HF/HCl treated sediments.
148 M.J. Simpson et al. / Marine Environmental Research 59 (2005) 139–163
3.2. NMR analysis
The CPMAS 13C NMR spectra of the PAH extracted and HF/HCl treated
samples are displayed in Fig. 2. The integration results and relative carbon group
distribution are listed in Table 3. The spectra only reveal subtle differences between
the top and bottom samples at each site, however, exhibit marked differences be-tween the different sites. The carbon character of the Brown’s Marina samples is
unlike the samples from the other two sites. The Brown’s Marina samples are more
aromatic and are more typical of organic matter found in terrestrial samples
(Hatcher, Rowan, & Mattingly, 1980; Hedges & Oades, 1997). In addition, the
Brown’s Marina samples contain more methoxyl carbon (56 ppm) in conjunction
with aromatic/phenolic carbon (110–160 ppm). This NMR signature is consistent
with lignin from terrestrial organic matter additions to the sedimentary environment.
The spectra for the other two sites also suggest the presence of lignin biopolymerswith peaks at 56 ppm for methoxyl carbons and at 150 ppm for aryl-o carbons.
However, these peaks are present to a lesser extent than in the Brown’s Marina
sample. The CPMAS 13C NMR spectra of the Bayou Grande and Mahogany
Landing samples are more characteristic of organic matter found in typical estuarine
sedimentary environment (Hatcher et al., 1980; Hedges & Oades, 1997).
The sediment samples display a varying level of carbohydrate content with no-
table signals at 72 (ring C atoms of polysaccharides) and 105 ppm (anomeric carbon
of polysaccharides). The Brown’s Marina sample has the highest carbohydratecontent (28% of the total signal) followed by the Bayou Grande and Mahogany
Landing samples (25% and 22%, respectively). There is a decline in the relative
amount of carbohydrates with depth in the Bayou Grande and Mahogany Landing
samples, and this decline is most prominent in the Bayou Grande sample where the
carbohydrate signal decreases from 24% to 17%. With depth, the enrichment of
paraffinic carbon is observed in the Bayou Grande and Mahogany Landing samples.
Particularly, the signals at 30–32 ppm, which are known to arise from long methy-
lenic chains (Hu, Mao, Xing, & Schmidt-Rohr, 2000), are prominent in the BayouGrande and Mahogany Landing samples.
3.3. Pyrolysis GC-MS
Total ion current (TIC) chromatograms of the Py-GC-MS analysis of the Bayou
Grande, Brown’s Marina and Mahogany Landing samples are presented in Figs. 3–
5, respectively. The main groups of compounds identified are: alkanes and alkenes
(AL), fatty acids (FA), lignin-derived compounds (LG), polysaccharide-derivedcompounds (PS), protein-derived compounds (PR), and resin-derived structures
(Table 4). Compounds that could not be assigned to a single structural source (such
as methyl benzene and methyl phenols) were classified as unassigned (US).
The major peaks in the Py-GC-MS chromatograms of the Bayou Grande top and
bottom samples (Fig. 3) are: lignin-derived compounds such as phenol (LG1), 2-
methoxyphenol (LG2), 4-ethyl-2-methoxyphenol (LG5) and 4-vinylphenol (LG6);
unassigned compounds such as methylbenzene (US1) and methylphenol (US2); and
Table 3
Cross polarization magic angle spinning 13C NMR integration results
Relative carbon distribution
Alkyl
(0–50 ppm)
Methoxyl
(50–60 ppm)
o-Alkyl
(60–110 ppm)
Aromatic
(110–160 ppm)
Carboxyl/amide
(160–190 ppm)
Carbonyl
(190–220 ppm)
Bayou Grande Top 33 7 24 26 8 2
Bayou Grande Bottom 44 7 17 23 8 1
Brown’s Marina Top 24 8 28 36 4 1
Brown’s Marina Bottom 25 8 28 35 3 1
Mahogany Landing Top 34 7 22 29 7 1
Mahogany Landing Bottom 38 6 18 30 6 2
After chemical oxidation
Bayou Grande Top 54 5 21 15 5 0
Brown’s Marina Top 33 6 38 20 3 0
Mahogany Landing Top 56 6 19 15 4 0
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Fig. 3. Pyrolysis GC-MS chromatograms of the Bayou Grande sediment samples (top and bottom). Peak
labels are defined in Table 4.
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a series of alkanes and alkenes (C7–C41). Similar markers were found in both the top
and bottom sample with the exception of the resin-derived compounds (RS3), which
are only detected in the top layer. The Py-GC-MS chromatograms recorded for theBrown’s Marina samples (Fig. 4) are dominated by lignin-derived biomarkers, and
this is consistent with the CPMAS 13C NMR observations. The major biomarkers
detected include: 2-methoxyphenol (LG2), 2-methoxy-4-methylphenol (LG3), 2-
methoxy-4-vinyl phenol (LG7), and 2-methoxy-4-allyl phenol (LG12). In addition,
methyl benzene (US1), methyl phenol (US2) and catechol are also identified. Unlike
the Bayou Grande samples, only trace amounts of alkanes and alkenes are observed
and the major components are predominantly those arising from lignin biomarkers.
There are only minor differences between the top and bottom Brown’s Marinachromatogram as most compounds are observed in both layers with similar TIC
intensities. The Py-GC-MS chromatograms of the Mahogany Landing samples
(Fig. 5) contain both lignin-derived compounds along with a series of alkane and
alkene pairs (C7–C27). The major difference between the top and bottom sediment
samples is the relatively lower intensity of the LG3 and LG12 peaks in the bottom
Fig. 4. Pyrolysis GC-MS chromatograms of the Brown’s Marina sediment samples (top and bottom).
Peak labels are defined in Table 4.
M.J. Simpson et al. / Marine Environmental Research 59 (2005) 139–163 151
sample. Resin-derived compounds (RS2, RS3, RS4) are also detected but are less
abundant in the bottom layer compared to the top layer.
The major differences between the sediment samples from the different sample
locations are the following: (i) the Py-GC-MS chromatograms of the Brown’s Ma-
rina samples are dominated by lignin-derived biomarkers, (ii) the phenol signature
(LG1), which can also be protein-derived, was more prominent in the Bayou Grandeand Mahogany Landing samples, (iii) the alkane and alkene peaks are more pro-
nounced in the Bayou Grande and Mahogany Landing samples than in Brown’s
Marina samples, and (iv) only slight, minor differences are detected between the top
and bottom sediment layers for all three sites.
3.4. TMAH-GC-MS
The fragments that result from the TMAH process can be linked to specificsources. For instance, fatty acid methyl esters (FAMEs) and dicarboxylic acid me-
thyl esters (DAMEs) originate from: triglycerides and other lipids, plant cuticles,
suberin residues, and algal residues. Heterocyclic nitrogen compounds arise from
peptides or intact proteins. Specific lignin monomers, which arise from different
Fig. 5. Pyrolysis GC-MS chromatograms of the Mahogany Landing sediment samples (top and bottom).
Peak labels are defined in Table 4.
152 M.J. Simpson et al. / Marine Environmental Research 59 (2005) 139–163
types of terrestrial plants, guaiacyl (G compounds), p-hydroxyphenol (P com-pounds), and syringyl (S compounds), are easily recognized by the TMAH method
(Filley et al., 1999). Consequently, terrestrial inputs, sources and degree of humifi-
cation can be distinguished with ease.
The TMAH-GC-MS chromatograms of the sediment samples are displayed in
Figs. 6–8 and peak identifications are listed in Table 5. The most notable peaks in the
TMAH-GC-MS chromatograms are: fatty acid methyl esters (FAMEs), methylated
lignin-derived compounds, dicarboxylic acid methyl esters (DAMEs), non-lignin
aromatic structures, heterocyclic nitrogen compounds and methylated resin-derivedcompounds. The main peaks in the Bayou Grande top and bottom chromatograms
(Fig. 6) are: C4, C5, C6, and C9 DAMEs; p-hydroxyphenyl compounds (P3, P4, P5,
P6, and P18), guaiacyl structures (G5 and G6), syringyl structures (S1, S2, S5, and
S6) and C14–C30 FAMEs. Aromatic, non-lignin derived structures such as benzal-
dehyde and methoxymethyl benzene and N-containing compounds such as 1-methyl-
2,5-pyrrolidinedione and 2-methyl-1H-isoindole-1,3-dione (peak number 7 and 13,
respectively) are also detected. The TMAH-GC-MS chromatograms of the Brown’s
Marina samples contain: benzaldehyde, methoxymethyl benzene, benzoic acid
Table 4
Peak identification of pyrolysis gas chromatography-mass spectrometry products
Alkanes and alkenes
1-Heptene AL2
1-Octene AL4
Nonane AL5
1-Nonene AL6
Decane AL7
1-Decene AL8
Undecane AL9
1-Undecene AL10
Dodecane AL11
1-Dodecene AL12
Tridecane AL13
1-Tridecene AL14
Tetradecane AL15
Tetradecene AL16
Pentadecane AL17
1-Pentadecene AL18
Hexadecane AL19
1-Hexadecene AL20
Heptadecane AL21
1-Heptadecene AL22
Octadecane AL23
1-Octadecene AL24
Nonadecane AL25
1-Nonadecene AL26
Eicosane AL27
1-Eicosene AL28
Heneicosane AL29
1-Heneicosene AL30
Docosane AL31
1-Docosene AL32
Tricosane AL33
1-Tricosene AL34
Tetracosane AL35
1-Tetracosene AL36
Pentacosane AL37
1-Pentacosene AL38
Hexacosane AL39
1-Hexacosene AL40
Heptacosane AL41
1-Heptacosene AL42
Branched C19 alkene AL43
Fatty acids
Hexadecanoic acid FA1
Octadecanoic acid FA2
Lignin-derived structures
Phenol LG1
2-Methoxyphenol LG2
2-Methoxy-4-methyl phenol LG3
Ethylphenol LG4
M.J. Simpson et al. / Marine Environmental Research 59 (2005) 139–163 153
Table 4 (continued)
4-Ethyl-2-methoxyphenol LG5
4-Vinylphenol LG6
2-Methoxy-4-vinyl phenol LG7
2-Methoxy-4-(2-propyl)-phenol LG8
2-Methoxy-4-propyl phenol LG9
2-Methoxy-4-ethyl phenol LG10
4-Allyl phenol LG11
2-Methoxy-4-allyl phenol LG12
2,6-Dimethoxy-4-methylphenol LG13
1-(4-Hydroxy-3-methoxyphenyl)-ethanone LG14
2,6-Dimethoxy-4-vinylphenol LG15
1-(3,5-Dimethoxy-4-hyroxyphenyl)-ethanol LG16
(1-Hydroxy-2-methoxy phenyl)-propanone LG17
2,6-Dimethoxy-4-propenyl phenol LG18
4-Hydroxy-3-methoxy-benzeneacetic acid LG19
Protein-derived structures
Pyridine PR1
Styrene PR2
2,5-Pyrolidinedione PR3
Indole PR4
Polysaccharide-derived structures
2-Furancarboxaldehyde PS1
2-Furancarboxaldehyde, 5-methyl- PS2
b-DD-Glucofuranose, 1,5:3,6-dianhydro- PS3
b-DD-Glucopyranose, 1,6-anhydro- PS4
Resin-derived structures
Dimethyl phenanthrene RS1
Trimethyl phenanthrene RS2
1-Methyl-7-(1-methylethyl)-phenanthrene RS3
Unassigned structures
Methyl benzene US1
Ethyl benzene US2
m-, p-, or o-Xylene US3
m-, p-, or o-Xylene US4
m-, p-, or o-Xylene US5
Camphene US6
Trimethyl benzene US7
C3 Benzene US8
Indene US9
C4 Benzene US10
1-Methyl indene US11
Methyl phenol US13
Endo borneol US14
Methyl phenol US15
154 M.J. Simpson et al. / Marine Environmental Research 59 (2005) 139–163
methyl ester (peaks 1, 2 and 6, respectively) and lignin biomarkers that are primarily
guaiacyl-derived (G1, G2, G3, G4, G5, G6, G22). In addition to these peaks, both
surface and subsurface chromatograms exhibit prominent resin-derived peaks
Fig. 6. TMAH thermochemolysis GC-MS chromatograms of the Bayou Grande sediment samples (top
and bottom). Fatty acid methyl esters (FAMEs) and dicarboxylic methyl esters (DAMEs) are labeled
based on the number of carbons in the chain. All other peaks are defined in Table 5.
M.J. Simpson et al. / Marine Environmental Research 59 (2005) 139–163 155
(17–23) (Clifford, Hatcher, Botto, Muntean, & Anderson, 1999). The Mahogany
Landing samples also contain syringyl-, guaiacyl- and p-hydroxyphenyl-derived
compounds, C14–C30 FAMEs, C3, C5, and C9 DAMEs, N-containing compounds
(8), and resin-derived compounds (17–23).In general, only small differences exist between the top and bottom sediment
layers at each site for TMAH thermochemolysis products. For instance, compounds
detected in the top sample may not have been observed or are present in lesser
quantities in the bottom layer. Several distinctions in organic matter geochemistry
for each sample are revealed by the TMAH-GC-MS chromatograms. The Bayou
Grande sample contains more FAMEs and DAMEs, and less lignin-derived bio-
markers than the Bayou Chico samples. The Bayou Grande samples are also devoid
of resin-derived compounds. Mainly guaiacyl-derived and resin-derived compoundsdominate the TMAH GC-MS chromatograms of the Brown’s Marina samples, in-
dicating that the sedimentary organic components are primarily from terrestrial and
anthropogenic inputs being altered from the more aliphatic components normally
expected for these sediments. Lignin-derived biomarkers and resin-derived structures
are also present in the Mahogany Landing sample, but these are matched by the
presence of FAMEs and DAMEs, suggesting that inputs to this sample’s
Fig. 7. TMAH thermochemolysis GC-MS chromatograms of the Brown’s Marina sediment samples (top
and bottom). Fatty acid methyl esters (FAMEs) and dicarboxylic methyl esters (DAMEs) are labeled
based on the number of carbons in the chain. All other peaks are defined in Table 5.
156 M.J. Simpson et al. / Marine Environmental Research 59 (2005) 139–163
geochemistry have been influenced by a variety of other sources than those observed
in the Brown’s Marina area.
3.5. Black carbon analysis
The removal of uncondensed aromatic structures in sedimentary organic matter
by chemical oxidation facilitates the identification of non-oxidizable aromaticstructures such as soot or black carbon by solid-state 13C NMR. After oxidation,
there is a decline in the aromatic carbon content of the samples (Table 3). For in-
stance, the Bayou Grande sample aromaticity declined from 26% to 15%, the
Brown’s Marina sample aromaticity declined from 36% to 20% and the Mahogany
Landing sample declined from 29% to 15%. The black carbon values for these
sediments range from 4.3% to 6.8% of the total organic carbon (Table 1). These
values are lower than other reports that suggest that black carbon may constitute as
much as 65% of sedimentary organic matter (Middelburg, Nieuwenhuize, & vanBreugel, 1999; Schmidt & Noack, 2000). The reported values were obtained using a
thermal oxidative method, which is prone to producing artifacts because during the
heating process, non-pyrogenic carbon may be transformed into black carbon
Fig. 8. TMAH thermochemolysis GC-MS chromatograms of the Mahogany Landing sediment samples
(top and bottom). Fatty acid methyl esters (FAMEs) and dicarboxylic methyl esters (DAMEs) are labeled
based on the number of carbons in the chain. All other peaks are defined in Table 5.
M.J. Simpson et al. / Marine Environmental Research 59 (2005) 139–163 157
(Derenne & Largeau, 2001). The chemical oxidation method does not react nor does
it transform charred material but it simply removes non-pyrogenic carbon such thatpyrogenic carbon can be measured by solid-state 13C NMR spectroscopy. Conse-
quently, the values reported in this study are likely more representative because the
method is not prone to artifacts from the transformation of non-pyrogenic carbon
into pyrogenic carbon as with thermal oxidative methods.
4. Discussion
The total amount of PAHs was found to be greater in the top than in the bottom
sediment layer in all samples studied. This trend is consistent with the hydrophobic
nature and high affinity of PAHs for sedimentary organic matter (Liu & Dickhut,
1997). Interestingly, the lower molecular weight PAHs, namely naphthalene,
acenaphthylene, acenaphthene and fluorene, are not detected at any of the three
sites. These compounds also have the lowest octanol–water partition coefficient
Table 5
Peak identification of TMAH thermochemolysis products
Lignin-derived biomarkers Other compounds
p-Hydroxyphenyl-derived structures Benzaldehyde 1
(4-Methoxyphenyl)-ethene P3 Methoxymethyl benzene 2
Benzaldehyde, 4-methoxy P4 1,3-Dimethoxy-3,4-dimethyl, 2-pentanone 3
4-Methoxyacetophenone P5 Propanoic acid, 2-(methylthio) methyl ester 4
4-Methoxybenzoic acid methyl ester P6 Butanedioic acid, methyl-, dimethyl ester 5
3-(4-Methoxyphenyl)-2-propenoic acid methyl ester P18 Benzoic acid, methyl ester 6
Guaiacyl-derived structures 2,5-Pyrrolidinedione, 1-methyl- 7
1,2-Dimethoxybenzene G1 Unknown N-containing compound 8
3,4-Dimethoxytoluene G2 1,4-Dimethoxy benzene 9
Benzene, 4-ethyl-1,2-dimethoxy G3 Benzenepropanoic acid, methyl ester 10
3,4-Dimethoxy benzaldehyde G4 2-Propenoic acid, 3-phenyl-, methyl ester 11
3,4-Dimethoxyacetophenone G5 1,3,5-Trimethoxy benzene 12
3,4-Dimethoxybenzoic acid methyl ester G6 2-Methyl-1H-Isoindole-1,3(2H)-dione 13
3-(3,4-Dimethoxyphenyl)propanoic acid, methyl ester G12 3,4-Dimethoxyphenylacetone 14
trans-4-(3,4-Dimethoxyphenyl) acrylic acid, methyl ester G18 3(Methylthio)propanoic acid methylester 15
1-(3,4-Dimethoxyphenyl)-2-propanone G22 1,4-Dimethoxy 2,3,5,6 tetramethyl benzene 16
2-Methoxy-1-(3,4-dimethoxyphenyl)propane G23 Isopimarate 17
Syringyl-derived structures dihydro isopimarate, methyl ester 18
1,2,3-Trimethoxybenzene S1 Methyl pimarate 19
2,3,4-Trimethoxytoluene S2 Dehydro methylabietate, methyl ester 20
3,4,5-Trimethoxyacetophenone S5 Methyl cis-communate 21
3,4,5-Trimethoxybenzoic acid methyl ester S6 Methyl trans-communate 22
Methyl abietate 23
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M.J. Simpson et al. / Marine Environmental Research 59 (2005) 139–163 159
(Kow) values, are more water soluble, volatile, and biodegradable than the higher
molecular weight PAHs. Consequently, these PAHs may have been degraded,
transformed, volatilized and/or transported such that they were no longer detected in
the sediment samples.
The characterization of the organic matter in these coastal sediments indicates
that the sediment geochemistry has been influenced both through anthropogenicand terrestrial organic matter additions. Furthermore, the anthropogenic activity
has resulted in the contamination of these sediments with a range of PAHs (this
study) and heavy metals (Lewis et al., 2001). Sedimentary organic matter is
characteristically rich in paraffinic carbon because the main input is typically from
non-terrestrial plant and animal material, such as algae and contains only small
amounts of aromatic carbon and methoxyl carbon. The lignin content of modern
coastal sediments is reported to be approximately 3–5% (Hedges & Oades, 1997).
However, the CPMAS 13C NMR spectra (Fig. 2) illustrate that large amounts oflignin and other aromatic carbon is present in these sediments. The CPMAS 13C
NMR spectra of the Bayou Grande and Mahogany Landing sediments are more
typical of modern coastal sediments in that they contain a lesser contribution from
lignin, evident from a smaller methoxyl carbon (56 ppm) and aromatic carbon
signal (110–160 ppm), than the Brown’s Marina sample. The removal of the lignin
fraction with chemical oxidation facilitates an estimate of the relative lignin aro-
maticity from the NMR spectrum before and after oxidation. For instance, the
top layer of the Bayou Grande sediment contains 26% aromatic carbon but afteroxidation, this value is reduced to 15% of the total carbon signal (Table 3).
Consequently, the aromatic contribution from lignin can be estimated to be 11%
of the total organic carbon. Similarly, the aromatic lignin content for the Brown’s
Marina and Mahogany Landing samples is determined to be 16% and 14%,
respectively.
The presence and in some samples, prominence of lignin biomarkers is confirmed
by both the pyrolysis GC-MS and TMAH thermochemolysis GC-MS data. The
notable amount of lignin in these coastal sediments is likely the result of terrestrialplant inputs in combination with contamination from anthropogenic practices and
urbanization. For instance, the Brown’s Marina site, which is closest in proximity to
a former creosote plant, contains remnants of that activity. The pyrolysis GC-MS
chromatogram (Fig. 4) and TMAH thermochemolysis GC-MS chromatogram (Fig.
7) of the Brown’s Marina sample displays mostly lignin biomarkers and several
compounds associated with resins (Anderson, Winans, & Botto, 1992; Clifford et al.,
1999). The contribution of DAMEs, FAMEs, and biomarkers from peptides and
polysaccharides to the organic matter, relative to the other two samples, is negligible.The TMAH thermochemolysis GC-MS of the Brown’s Marina samples contains
mostly guaiacyl (noted as ‘‘G’’ compounds on the chromatograms) monomers and
are biomarkers of gymnosperm woods, such as pine (del Rio et al., 1998). It is likely
that woods, such as pine, were treated at the creosote plant near where the Brown’s
Marina sample was obtained. The presence of resinous compounds (labeled as
17–23) in both the top and bottom sediment layer is also consistent with the prox-
imity to a wood treatment facility.
160 M.J. Simpson et al. / Marine Environmental Research 59 (2005) 139–163
Interestingly, the same lignin biomarkers and resinous compounds were detected
in the other Bayou Chico sample (Mahogany Landing), but to a lesser extent. Other
lignin monomers (P and S compounds) were also found indicating that this coastal
area is less influenced by inputs from the wood treatment facility as the Brown’s
Marina site, but also subject to organic matter inputs from other terrestrial sources,
such as grasses and angiosperm woods. The PAH data also indicate that despite theproximity of the Bayou Chico samples to each other (samples were obtained within a
mile of each other), the Mahogany Landing area is less effected than the Brown’s
Marina site. For instance, the total PAHs in the Mahogany Landing samples are
approximately half the concentration of those found in the Brown’s Marina samples.
Furthermore, the higher molecular weight PAHs are not detected in the bottom
Mahogany Landing layer. Therefore, an anthropogenic activity, such as a creosote
treatment plant, does not only dictate the level and distribution of PAHs, but also
alters its sedimentary organic matter characteristics and perhaps the diageneticpathways in organic matter formation.
The aromatic portion of organic matter is believed to be the main component that
sequesters PAHs in soils and sediments (Luthy et al., 1997). Other reports suggest
that the presence of soot or black carbon may regulate the distribution of PAHs in
sedimentary environments (Accardi-Dey & Gschwend, 2002). However, these sedi-
ments are not found to contain as much black carbon as others have reported for
marine sediments (Masiello & Druffel, 1998; Middelburg et al., 1999). For instance,
Masiello and Druffel (1998) reported that black carbon represented 15–21% of thetotal sedimentary organic carbon. Middelburg et al. (1999) extended the range of
black carbon contents from 15% to 30%. The lower quantities of black carbon in
these sediments suggests that the role of black carbon in governing PAH distribution
in these sediments may be limited. Recently, it has been demonstrated that paraffinic
domains of organic matter, namely those arising from algal or cuticular residues, can
uptake more PAH than highly aromatic organic matter (Chefetz, Deshmukh,
Guthrie, & Hatcher, 2000b; Mao, Hundal, Thompson, & Schmidt-Rohr, 2002;
Salloum, Chefetz, & Hatcher, 2002) and may explain why PAHs have been retainedthe top layer of these sediments.
In this study, both paraffinic domains and black carbon were identified and
measured, as well as a host of other components found in sedimentary organic
matter. However, it is evident from this case study that PAH concentration and
distribution may not be regulated by a single organic matter component such as
black or paraffinic carbon. For instance, the Bayou Grande samples have the highest
total PAHs, but the sample is low in total aromatic carbon and black carbon. Both
the pyrolysis and TMAH thermochemolysis GC-MS analyses reveal that the bio-markers are predominantly in the form of alkanes, alkenes, FAMEs, and DAMEs
and the abundance/presence of paraffinic carbon is confirmed by solid-state 13C
NMR. The most ‘‘aromatic’’ sample did not correspond to the most PAH con-
taminated sample, indicating that lignin nor black carbon can not be used to explain
PAH distribution in contaminated sediments. More studies that examine contami-
nation from industrial practices and urbanization need to consider the changes to
sedimentary organic matter characteristics because contaminants may or may not be
M.J. Simpson et al. / Marine Environmental Research 59 (2005) 139–163 161
intimately tied to specific organic matter structures, but to a combination of struc-
tures that govern the distribution and transport of contaminants in coastal envi-
ronments.
Acknowledgements
The Natural Science and Engineering Research Council (NSERC) of Canada is
gratefully acknowledged for granting a postdoctoral fellowship to M.J.S. The Na-
tional Science Foundation – Environmental Molecular Science Institute (CHE-
0089147) and the Office of Naval Research (ONR-Grant no. N00014-99-1-0073) –
provided financial support for this research. We also thank Dr. Elizabeth Guthrie-Nichols for assistance during sample collection.
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