Comparison of polycyclic aromatic hydrocarbon ...departments.agri.huji.ac.il/soils/chefetz/pubfile-8.pdf · Bayou Grande is nearest to the Pensacola Naval Air Station. Bayou Chico

MARINE

ENVIRONMENTAL

www.elsevier.com/locate/marenvrev

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: [email protected] (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

mail to: [email protected]

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.


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.


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


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


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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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.


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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149

Fig. 3. Pyrolysis GC-MS chromatograms of the Bayou Grande sediment samples (top and bottom). Peak

labels are defined in Table 4.


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.


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.


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


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



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


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.


(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



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



(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

158

M.J.Sim

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al./Marin

eEnviro

nmentalResea

rch59(2005)139–163


(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.


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


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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