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Hydrocarbon geochemistry of the Puget Sound region—III. Polycyclic aromatic hydrocarbons in sediments
Estuarine,
Coastal
and Shelf
Science
(1987) 25,175-191
Hydrocarbon Geochemistry of the Puget Sound Region-III. Polycyclic Aromatic Hydrocarbons in Sediments
Robert School U.S.A.
C. Barrick” of Oceanography,
Received
I2 August
Keywords:
and Fredrick WB-10,
1985
hydrocarbons;
University
and in revised
form
G. Prahlb of Washington, 2 September
sediment cores; distribution;
Seattle,
WA
98195
1986
Puget Sound
Polycyclic aromatic hydrocarbon (PAH) distributions and sources are characterized in 96 sediment samples from 24 ‘lOPb-dated cores collected at locations in the greater Puget Sound. The highest PAH concentrations are found within a few kilometers of several sources including industrial facilities in northern Puget Sound, urban areas in central Puget Sound, and river systems draining coalbearing strata. Regional patterns of combustion-derived PAH in surficial sediments indicate little atmospheric or waterborne exchange of PAH between different regions of the Sound. Significant subsurface maxima in combustionderived PAH concentrations ( ‘lOPb dated at the 1950s) occur only in sediment cores collected near urban centers. Perylene apparently derives from erosion of a terrestrial source with little or no evidence of in situ production at depth in sediment cores. Coal fragments are carriers of a characteristic suite of alkylated phenanthrene, chrysene, and picene derivatives concentrated near river mouths in central and southern Puget Sound. Introduction
Knowledge of the sourcesand global distribution of polycyclic aromatic hydrocarbons (PAH) in sedimentary environments is important becauseof the effects thesecompounds can have on biological systems. In addition to their potential toxicity, the chemical stability of PAH makes them useful indicators of specific anthropogenic and diagenetic contributions to sedimentary deposits. This study describes the PAH distributions in modern sediments of Puget Sound. Earlier papers have defined the non-aromatic hydrocarbon geochemistry of Puget Sound sediments (Barrick et al., 1980; Barrick & Hedges, 1981). Experimental Sample
preparation
Procedures for sediment collection (primarily by multiple corer with a hydrostatically damped rate of penetration) and extraction of hydrocarbons have been described (Barrick “Present address: Tetra Tech, Inc., 11820 Northup Way, Suite 100, Bellevue, WA 98005, U.S.A. bPresent address: College of Oceanography, Oregon State University, Corvallis, OR 97331,
U.S.A. 17.5
0272-7714/87/020175
+ 17 $03.00/O
0 1987 Academic
Press Limited
176
R. C. Barrick
&F.
G. Prahl
et al., 1980). Following a Sohxlet extraction, organic extracts were separatedinto aliphatic and aromatic hydrocarbon fractions in two chromatographic stepsusing (1) silica gel and alumina adsorbents and (2) Sephadex LH-20 (Prahl & Carpenter, 1983). Although the order of the chromatographic stepswas reversed in the earliest stagesof the study, replicate tests showed there were no statistically significant differences in the final quantitation of individual aliphatic and aromatic compounds by any of the procedures employed. Analytical precision averaged -t loo, about the mean of replicate measurements. Single-point PAH-recovery estimates were made on some sediments using 2methylanthracene as an internal recovery standard. Recoveries ranged from 60 to 85”,, (higher molecular weight PAH were generally recovered at >95O,, in spiked blanks). Corrections for differential evaporative lossesof PAH across the range of compounds analysed were not made as for aliphatic hydrocarbons (Barrick et al., 1980) becausean analogousseriesof recovery standards for PAH was not available at the time. Therefore, all concentrations reported for compounds eluting before fluoranthene, in particular, are minimum estimates. Gas chromatography
and mass spectroscopy
Each PAH fraction wasanalysed by capillary gaschromatography (GC). Data for Dabob Bay station E (Figure 1) are from an earlier study (Prahl & Carpenter, 1979) and were obtained by high pressureliquid chromatography (HPLC). The HPLC data are included for comparison purposes. Results from analyses of replicate samples by the GC and HPLC techniques differed by only +8”,, in studies reported by Prahl (1982). Thus, quantitative comparison of the earlier HPLC data with the present GC data setis justified. Gas chromatography was performed on a Hewlett-Packard 5880 instrument using either glass (W-2100) or fused silica (SE-54) capillary columns and conditions as described in Figure 4. The compositions of selected sampleswere characterized by gas chromatography/mass spectroscopy (GC/MS) using an HP5995 or a Finnigan 4000 system fitted with a fused silica (SE-54 or DB-5) capillary column operated under the same GC conditions. Bulk organic
carboll
Total organic carbon (TOC) data were obtained using either a LECO carbon analyser (Barrick et al., 1980) or a Carlo Erba elemental analyser (Barrick, 1982). Dry-weight concentrations of PAH were significantly correlated f$ < 0.01) with TOC content in Puget Sound sediments. Therefore, dry-weight PAH concentrations were normalized to TOC to dampen variations causedby patchiness or other depositional factors, and to enhance the ability to detect source-related changesin PAH input. Boehm and Farrington (1984) summarize the advantages of normalizing PAH data to TOC when evaluating environmental trends. Associations of different PAH with specific organic carbon-rich particles in sedimentsare discussedby Prahl and Carpenter (1983).
Results
and discussion
The 96 sediment samplesfrom 24 sites were analysed in detail for PAH compositions, selected aliphatic hydrocarbon concentrations and total organic carbon content. Data reported on Tables l-3 include 12 replicate analysesand eight profiles with depth in cores.
Hydrocarbon geochemistry
Distributions
of combustion-derived
177
PAH
Several pyrolysis sources produce qualitatively similar mixtures of primarily nonalkylated PAH containing typically P6 condensed rings (Lee et al., 1977). Individual combustion-derived PAH have similar spatial and temporal distributions in sediments (Table 2) and, therefore, are parameterized in the following discussion as total combustion-derived PAH (COMB) for convenience. COMB is defined asthe sum of the concentration of nine individual compounds: fluoranthene, pyrene, benzo(a)anthracene, chrysene, benzofluoroanthenes, benzo(a)pyrene, benzo(e)pyrene, indeno(c,d)pyrene, and benzo(ghi)perylene. Fuel oils in combined municipal sewageand stormwater dischargesto Puget Sound are a major source of tricyclic aromatics (e.g. phenanthrene) and lower molecular weight aromatic compounds. A comparison of source and depositional massfluxes indicated that these sewage-derived components are lost in the water column or at the sediment-water interface (Barrick, 1982). Phenanthrene and COMB concentrations correlate well, both in surface O-2 cm) sediments (r2 = 0.72, n = 28) and in the entire data set (r2 = 0.61, YZ= 83). The correlation suggests that the phenanthrene accumulating in the sediments is primarily of combustion origin. Alternative anthropogenic sourcesof nonalkylated PAH (e.g. creosote; Merrill &Wade, 1985)are of concern only in isolated areasof Puget Sound. For example, creosote contamination from a wood-treating facility in a small harbor west of Seattle apparently does not affect the main basin of Puget Sound (Tetra Tech, Inc.,, 1986). Concentrations of COMB in surface (O-2 cm) sedimentsranged from 8 to 73 pg 8-I OC (Table 1), or 16-2400 ng g- ’ dry sediment. Fluoranthene, a dominant component of the combustion series, ranged from 1 to 13 pg g- ’ OC (3-350 ng g- ’ dry sediment). Accumulation rates of COMB in surface Puget Sound sediments (Table l), calculated from “‘Pb data (Carpenter et al., 1985), are comparable to, or higher than, those measured in Washington coastal sediments (range: 7-210 ng cm-2 yr-‘; Prahl et al., 1984) and in Lake Washington sediments (220 ng cmm2yr- ‘). Comparison with data for other regions can be made only for individual PAHs. The range of accumulation rates for fluoranthrene in surface sedimentsof Puget Sound (2-220 ng cmm2y - ‘) covers the range reported for the Washington continental shelf (2-38 ng cm-’ y-‘; Prahl et al., 1984), three urban sites in New England (37-93 ng cmm2y-i) and several remote sites in the north-eastern U.S. (1-5 ng cm-’ y-l; Gschwend & Hites, 1981). Although fluoranthene accumulation rates are not reported for sediments from the Charles River and New York Bight, dry weight concentrations in these sediments are 40-times and 3-times greater, respectively, than the highest concentration measuredin Puget Sound. Total combustion PAH concentrations ( ug g - ’ OC) in midchannel surface sediments of Puget Sound range over an order of magnitude (Figure 1). This range is comparable with that observed for total aliphatic hydrocarbons in the samecores (Barrick et al., 1980). However, concentrations for these two classesof hydrocarbons display substantially different area1distributions. PAH and aliphatic hydrocarbons in Puget Sound sediments apparently derive from discrete sourcesthat are regionally differentiated. The average concentration of total aliphatic hydrocarbons, determined gravimetrically, is significantly higher (p
R. C. Barrick &F.
178
20’
G. Prahl
123”W
40’
20’
122”
49
49O
4c
40’
2c
20’
rRAl?- Of
JUAN DE FUCA
48 N
$8” N
40
-WAS
20
CONCENTRATION
‘-
47
20’
123”W
40’
20’
122”
Hydrocarbon
geochemistry
179
In contrast, urban proximity is not the only factor influencing the amount of total combustion PAH observed in sediments throughout Puget Sound. High COMB concentrations (Figure 1) are found in sedimentsfrom central Puget Sound (e.g. stations 51) and in sediments from areasfar from urban areas, e.g. southern Dabob Bay (station 89) and two northern Puget Sound locations (stations 66 and 79). Urban centers are likely the primary sources for elevated combustion PAH concentrations in central Puget Sound. However, the discharge of PAH in air particulate material and primary sewagefrom the major urban centers of central Puget Sound is insufficient to account for the amounts of total combustion PAH accumulating elsewhere (Barrick, 1982). Patterns of high COMB concentrations in distinct regions separated by low concentration at locations in between suggestthat combustion-derived PAH come from several point sourceslocated throughout Puget Sound. Simple atmospheric or estuarine dispersal from only the major urban centers of central Puget Sound cannot explain these data. The regional pattern can not be explained by differences in sediment texture. The samepattern is evident when the data are normalized to organic carbon content or expressedasabsolute accumulation rates (Table 1). Both normalizations remove the influence of sediment texture. Sediments from northern Puget Sound contain combustion-derived PAH accompanied by relatively minor amounts of other hydrocarbons (e.g. UCM from wasteoils in municipal discharges). This fact is evident from the UCMjCOMB ratio. Values of this ratio equal 35 in surface sediment samplesfrom stations 66 and 79, two locations in northern Puget Sound where the highest combustion PAH concentrations are observed (Figure 1, Table 1). These values contrast sharply with the average UCMjCOMB ratio of 160+ 34 (n = 7) measuredin central Puget Sound sediments (influenced by major municipal discharges). A small, but significant increase in COMB concentration in the surface 7 cm of sediments from station 66 in northern Puget Sound (Table 1; Figure 1) occurred in the mid1960s and corresponds, at least chronologically, to the opening of a nearby aluminium smelter at Ferndale. Although the temporal coincidence does not prove that the smelter has contributed combustion-derived PAH to sedimentsin this region, aluminium smelting plants can be important sources of combustion PAH (Palmork et al., 1973). Flare towers associated with petroleum refineries at Anacortes are potential sources of combustion-derived PAH in sediments from stations 77-79. An unconfirmed source of PAH at station 89 in southern Dabob Bay is oiled telemetry cables which are used to monitor naval torpedo experiments. Subsurface
maxima
of combustion-derived
PAH
as a time marker
Subsurface maxima in combustion-derived PAH concentrations have been noted in sediments from a variety of environments (Muller et al., 1977;Hites et al., 1977,198O; Prahl & Carpenter, 1979). Gschwend and Hites (1981) proposed that these sedimentary maxima record a decreasing rate of combustion-derived PAH emission caused by a shift in the types of fuels burned since the 1950s (Hites et al., 1977) and increased controls on industrial-waste discharge.
Figure 1. Study area. Stations are indicated by numbers. The radius of the circle about each station is proportional to the total concentration (pg g- ’ OC) of nine combustionderived PAH (see COMB, Table 1).
o-2 2628
O-2 2&28 G2 13-15
60
61
62
O-2 4345
B’ B B
*2 15-17 l&12 15-17 40-43
59
57
P P P r P
&2 4244 46-49 95-98 138-141 184-187 230-233
56
G2 5-7 lo-12 15-17 2&22 25-27 30-32 35-37 39-41
1970 1892 1968 1888
1969 < 1825
n.d. n.d.
1975 1963 1959 1949 1919
1975 1951 < 1825 <1825 <1825 <1825 <1825
1971 1869
1976 1965 1955 1944 1933 1921 1909 1897 1886
(Y)
(cm)
c&2 15-17
tr
Age”
data
1.09 1.01 1.17 0.715
0.244 0.236
0.508 1.19
2.42 3.22 3.15 3.16 3.3
2.62 3.01 0.856 0.814 0.879 0.824 0.986
1.69 1.16
2.10 2.18 2.09 2.14 2.10 2.03 1.88 1.76 1.80
“” OC
1. Summary
Sample interval
52
51
Station No.
TABLE
240 270 120 260
230 260
170 150
310 460 n.d. n.d. n.d.
200 260 260 240 200 360 240
220 230
300 270 280 250 290 220 250 170 160
n-ALK*
for Puget
hydrocarbon
2400 160
6300 5200 n.d. n.d. n.d.
3800 5200 260 220 330 410
6600 3300
9500 8100 7600 5700 7000 3200 2300 290 110
UCM
Sound
28 56 13 27
27 15
14 1.7
44 40 41 95 17
30 52 2.4 5.1 3.7 4.8 4.6
33 24
6Ok5 120 145 83 39 53 38 7.7 4.4
COMBd
Organic
2.5 7.5 0.94 0.60
0.66 0.30
0.94 0.24
4.2 7.1 7.1 11 6.4
2.0 3.3 2.3 3.6 2.5 2.1 2.4
1.6 0.33
7.2 4.8 6.5 4.0 n.d. 3.3 1.5 0.86
6.4+
1.1
(pg g- ‘)
Phenanthrene
carbon
cores
4.3 5.3 1.8 2.3
2.7 5.0
1.4 5.6
4.2 2.7 3.3 4.3 1.4
1.9 5.2 8.4 6.0 1.7 8.0 6.4
2.0 1.8
4.9kO.3 5.8 5.3 5.2 2.1 5.3 6.2 6.6 5.7
Perylene
2.4 4.2 1.2 11
6.5 17
4.2 1.1
21 36 61 50 97
7.9 8.6 n.d. n.d. n.d. 4.3 n.d.
4.4 5.0
4.1 kO.4 6.5 n.d. 13.0 11.0 n.d. 13.0 4.8 2.2
Retene
27
100
14
n.d.
300
600
62
290
COMB flux’
1.23 1.02 1.33 1.13
0.88 0.76
1.03 1.54
0.71 0.70 0.58 0.62 0.50
0.87 1.02 1.27 1.55 1.38 1.18 1.38
1.14 0.99
1.28+0.3 1.28 n.d. 0.95 1.00 1.01 0.88 1.09 1.13
MPR’
1.9 1.1 2.2 6.8
3.3 8.1
2.0 3.2
3.5 2.8 3.3 1.9 3.3
2.1 2.1 1.1 1.2 1.3 2.8 2.0
1.6 7.2
1.0+0.3 1.1 n.d 1.7 2.0 1.6 2.4 2.7 3.8
MPh/Phs
2.1 2.6 2.0 1.9
1.9 2.3
2.2 1.1
2.6 1.9 3.3 3.1 4.4
1.5 1.8 > 100 74 75 > 100 70
1.5 1.5
2.OkO.3 1.7 1.3 1.5 2.7 1.7 1.7 2.0 6.5
FL/IN”
1970 < 1825
1973 1957 1940 1906 1872 1856 1838 1825 1973 1903
1972 1883
1961 < 1825
1972 < 1825
1974 1953
O-2 3&32
o-2 5-7 lo-12 20-22 30-32 35-37 40-42 43-45 O-2 21-23
2-4 34-36
o-2 32-34
c-2 34-36
O-2 m-22
68
70 du
73
77
78
79
72
1974 1929
O-2 26-28
67
1973 1965 1955 1937 1919 1911
o-2 5-7 lo-12 20-22 30-32 35-37
66 du
1964 1948 1921 1872 < 1825 < 1825 < 1825
o-2 2-4 5-7 lo-12 15-17 19-21 21-23
65
1.18 1.16
2.36 2.15
0.723 0.966
4.05 3.34
0.827 0.688 0.712 0.858 1.12 1.13 0,908 0.820 0,958 1.20
0.536 1.52
0.512 0.579
0.802 0.682 0.808 0,732 0.911 0.915
1.10 1.61 0.964 0.248 0,349 0.300 0.300
170 320
220 100
380 100
170 250
380 470 370 420 270 16 320 280 390 550
260 150
130 160
350 360 270 340 240 240
200 250 170 620 330 360 n.d.
2200 2900
1400 760
3500 160
2100 790
2200 3700 2400 100 210 130 570 610 3100 2500
1900 230
900 200
2500 2900 1900 100 780 480
1700 1400 1400 1300 400 590 n.d.
62 22
19 11
35 8.6
20 2.3
21+6 36 39 27 7.0 5.2 6.2 9.0 37 26
16 26
21 8.2
72k8 52 41 49 8.5 22
14 11 24 23 11 10 11
8.1 1.8
1.7 5.2
3.6 2.4
1.7 n.d.
4.2 5.1 6.9 0.20 0.13 0.08 2,2 3.3 4.3 3.1
1.7 3.3
4.5 2.7
3.2 1.5
5.8 16.0
1.8 3.6
4.1kO.5 3.5 4.7 5.6 5.1 5.7 5.7 6.7 4.2 2.3
3.5 3.3
4.4 4.3
5,0* 1.9 4.1 4.8 5.1 4.2 5.8
7.6k7.1 7.8 6.3 7.0 3.0 2.3 1.1 0.03
2.4 1.7 3.1 8.7 10.0 10.0 10.0
0.91 0.87 2.5 2.1 2.4 2.5 2.2
7.1 1.5
2.8 1.7
2.6 3.4
1.3 0.86
3.7 4.4 4.4 4.2 2.9 0.36 3.4 4.3 2.8 3.2
n.d. n.d.
3.2 0.24
4.3kO.l 4.7 5.1 5.2 4.7 2.8
24 1.1 2.3 2.6 5.2 6.9 6.3
660
120
12
98
110
34
18
44
200
11
1.16 1.00
1.06 1.10
l-10 1.14
1.54 ad.
1.04 1.09 1.03 0.96 0.96 n.d. 1.18 1.26 1.86 1.43
1.14 l-13
1.10 ad.
1.33kO.2 1.15 1.16 1.18 1.14 1.33
0.95 0.95 1.0 0.85 0.72 0.84 0.84
1.1 3.1
1.4 0.7
1.6 2.9
2.1 n.d.
2.2 2.3 1.8 15.0 15.0 10.5 3.5 3.0 2.18 2.7
2.6 1.5
3.9 13.0
1.7rf: 1.3 1.7 1.8 1.7 3.2 3.6
2.6 2.2 1.8 2.8 2.5 2.5 2.5
3.9 2.0
4.7 7.0
2.9 10.0
2.2 1100
4.0 3.7 3.6 2.2 3.0 0.45 8.7 5.7 3.1 2.1
3.7 8.3
2.4 n.d.
3.9* 1.0 5.2 3.8 3.2 5.9 3.0
2.7 2.2 2.1 1.4 1.5 2.8 3.5
o-2 35-37
o-2 35-37
o-2 24-26
92
95
98 du
(&3
O-2 2628
89
WASH
o-2 46 lo-12 20-22 3G32
82 B B B qu B B
LK 11
Sample interval (cm)
Station
4.2
2.84 2.38
0.350 0,640
0,868 1.05
3.23 3.53
0,772 0,544 0.610 0.606 0,644
OC
n.d.
190 270
350 310
210 200
260 170
190 225 230 240 190
n-ALK’
n.d.
2800 4000
650 790
1600 300
2100 1100
n.d. n.d. n.d. n.d. n.d.
UCM’
81
26_+3 40
8.0 7.9
28 4.7
73 5.6
22 36 20 32k3 21
COMBd
Organic
(pg g - ’ )
6-5
2.OkO.3 3-l
0.20 0.33
2.4 1.4
3.4 0.18
3.0 3.8 2-6 3.52 2.6
I’henanthrene
carbon
8.2
6.5k3.8 6.3
3.6 6-3
4.4 4.6
10.0 4.0
2.9 4.9 2.5 4.oio.2 3.1
Perylene
10
2.7 + 0.2 4.6
2.9 1.3
3.1 2.4
6.2 0.41
16 25 22 30*3 21
Retene
220
270
n.d.
66
400
62
flUX’
COMB
1.32
1.07+0.08 1.19
1.20 1.11
1.12 1.10
1.08 1.44
0.60 0.60 0.59 0.59f0.05 0.66
MPRJ
“Ages computed using “%‘b data of Carpenter e’t al. (1985). ‘Sum of the normal alkanes C,,-C,,. “Total unresolved complex mixture (UCM) as defined by Barrick et ~11. (1980). “Sum of fluoranthene, pyrene, benz(a)anthracene, chrysene, total benzofluoranthrenes, benzo(e)pyrenc, benzo(a)pyrene, benzo(g,h,i)perylene as determined by GC/FID. ‘Surface accumulation rate (ng cm ’ y ’ ) of the combustion-derived PAH series defined in footnote d. lMethyl phenanthrene ratio =2-methylphenanthrene/l-methylphenanthrene iRadke t’i ul., 1982). dTotal mono-methylphenanthrenes to phenanthrene ratio. hFluoranthene to indeno(c,d)pyrene ratio. ‘Piston core. Sample intervals correspond io depth in core; 0.5 m or more ufburfacr material was lost in coring. All other cores unless specified. ‘Box core. du, Duplicate analysis; tr, triplicate analysis; qu, quadruplicate analysis; n.d., not determined.
1976
1974 1943
n.d. n.d.
1973 1867
1975 1927
1973 1960 1940 1907 1870
Age” (Y)
TABLE 1. Comi,zued
samples
are from
indenojc,d)pyrene
0.39
1.2+0.2 1.2
3.7 3.4
2.1 3.5
2.3 3.3
2.1 2.4 2.6 2.6 2.4
MPh/Ph#
and
multiple
I.0
2.2kO.4 2.2
2.1 1.8
3.1 > 100
1.2 1.4
2.8 2.1 3.6 2,0*0.2 I.9
FL/INh
Hydrocarbon
geochemistry
TABLE 2. Coefficients differing ring size
of determination
Surface (O-2 cm) S. of Admiralty Inlet (n = 9)”
4-ringh 5-ring’
5-ring
6-ringd
0.87
0.85 0.87 “Total averaged b4-ring ‘5-ring d6-ring
185;
(r*)
for non-alkylated
combustion
Surface (G2 cm) All stations (n=28)
4-ring 5-ring
sample size before the combustion combustion combustion
5-ring
6-ring
0.79
0.44 0.75
PAH
of
Total data set (n = 84)” 5-ring 4-ring 5-ring
6-ring
0.66
0 18 0 32
(n) is the number of sites (i.e. any replicate analyses at a site were correlation analysis was conducted). PAH: fluoranthene, pyrene, benzo(a)anthracene, chrysene. PAH: total benzofluoranthenes, benzo(e)pyrene, benzo(a)pyrene. PAH: indeno(c,d)pyrene, benzo(g,h,i)perylene.
TABLE 3. Concentrations of alkylated phenanthrenes, chrysene and picene and diterpanes in Puget Sound sediments (pg g- ’ organic carbon) Sta. 82 (n = 5) Total monomethylphenanthrenes I-Methylphenanthrene Total dimethylphenanthrenes MW =220 (C-3 phenanthrene)” Retene (C-4 phenanthrene) Tetramethyl-1,2,3,4,4a,l1,12,12aoctahydrochrysene (MW = 292) MW = 290” 3,3,7-Trimethyl-1,2,3,4tetrahydrochrysene (MW =274) Dimethylchrysene (MW = 256)” 2,2,9-Trimethyl-1,2,3,4tetrahydropicene (MW = 324) 2,9-Dimethylpicene (MW = 306) Total diterpane@
7.7kl.5 2.6 kO.57 15.0+3-3 6,5+ l-5 23.Ok5.1 2,8& 2.4+
1,3 1.4
1.3iO.46 3.0* 1.9 7.0 * 5.5 7.8 k 3.2 23,0+6-2
Sta. 57 (n=5) 20,0+3.2 7.6& 1.4 25.0* 9.0 19.025.7 53.0129.0
derivatives,
Remainder in=691 5.3*3
4-8 + 2.4 1,4* 1.1 4,7+4 1
2.5k2.05 2.1 k2.2
0.72 *0,66 0.48kO.42
1.6+ 5.1+
1.0*0,62 0.7010-44
1.1 1.2
8.3k3.6 9.6k6.1 80.0+20.0
3
2.32 1-9 1.4io.9 12.0* 14.0
“Major mass spectral ions (intensity) include: MW =220--nzjz 220 (loo”,), 205 (78”,,), 189 (32”,,); MW=29(tmiz 290 (45”,,), 275 (loo”,,), 247 (lo”,); MW=256--m,‘z 256 (1000,), 239 (28”,,), 226 (S”,). “Total diterpanes are the sum of C 19 and C,, diterpanes (see Barrick & Hedges, 1981) from the same cores analysed for PAH.
The range of maxima measured in profiles of fluoranthene concentration with depth for eight sediment cores collected throughout Puget Sound is shown in Figure 2. Because complete data for the nine combustion PAH were not obtained for the Dabob Bay station E core (Prahl & Carpenter, 1979), fluoranthene concentrations are plotted rather than COMB depth profiles in cores (where complete data are available). Fluoranthene and COMB concentrations (Table 1) exhibit similar depth profiles in cores. Thus, fluoranthene profiles represent a valid proxy of total combustion-derived PAH. Significant
R. C. Barrick & F. G. Prahl
184
FLUORANTHENE
CONCENTRATION
(ng,g OC)
Figure 2. Age profiles of fluoranthene concentrations (pg g-’ OC) in eight sediment cores from Puget Sound. Additional data points are shown for the top and bottom 2-cm intervals of cores from the remaining 16 stations, and station 11 in Lake Washington (LW). Average dates of sediment deposition are 210Pb-derived and are not corrected for mixing [see Carpenter et al. (1985) for details on procedures and precision].
subsurfaceconcentration maxima are observed only at stations 51 and 57, located directly adjacent
to Seattle
and
Tacoma.
The
occurrence
of these
two
subsurface
maxima
bears
no relationship to the relative amount of combustion-derived PAH observed in surface sediments. Instead, the presenceof this feature depends on urban proximity and is not a ubiquitous time marker in greater Puget Sound region. PAH data from a core collected near station 5 1 (Bates et al., 1984) generally corroborate the subsurface feature at station 51, but suggestthat PAH input hasheld relatively constant sincethe late 1960s. Background
levels of combustion-derived
PAH
COMB concentrations at most Puget Sound stations have fluctuated between 10 and 50 ug g- ’ OC since about 1870. The median surface concentration measuredin this study is about 30 ug g- ’ OC, nearly five-times lessthan maximum concentrations at station 5 1
Hydrocarbon
geochemistry
185
.
cL-=-- ---‘----A - -.-.--‘- - -,-+ v-
Figure 3. Age profile of perylene normalized to Puget Sound. Additional cores from the remaining
3
(a) perylene normalized to dry weight (ng g-’ DW) and (b) organic carbon (ng g- ’ OC) in eight cores from throughout data points are shown for the top and bottom 2-cm intervals of 16 stations. See caption to Figure 2 for dating information.
in the mid 1950s.The average COMB concentration in sediment pre-dating 1825, including a Pleistocene grey clay at station 65, is 9 + 6 ug g- ’ (n= 12), or a factor of three less than the median surface concentration. The pre-1825 sedimentswere deposited at least 50 years before major urban development began in the region and reflect the natural background of combustion-derived PAH from natural burning processes,such asforest fires. Compositional
variation
in the combusion-derived
PAHpattern
The dominant sourcesof combustion PAH in central and southern Puget Sound and areas south of Admiralty Inlet (Figure 1) are the adjacent urban centers. Not surprisingly, the group of nine combustion-derived PAH exhibit strong, and nearly equivalent, correlations between the total four-ring, five-ring and six-ring components (Table 2), indicating a fairly constant composition for combustion-derived PAH mixtures throughout this region.
R. C. Barrick & F. G. Prahl
186
MW 220 ALKYL
NAPHTHALENES
REl
STATION 57 COAL FRAGMENTS PAH
22c DMPH v
,LKYL 1
STATION 57 BULK SEDIMENT PAH
NAPHTHALENES I
MW 306
Cl
PR
DITERPANES I
I
STATION 57 COAL FRAGMENTS ALIPHATIC HYDROCARBONS
il
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c25
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C27
STATION 57 BULK SEDIMENT ALIPHATICS
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___
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Hydrocarbon
geochemistry
187
Specific compositional indicators were used to test for variability in the composition of the combustion-derived PAH mixtures recorded in Puget Sound sediments. Ratios, such as phenanthrene/anthracene and total mono-methylphenenthrene/phenanthrene, have been used to discriminate different PAH sources sedimentary mixtures (Lake et al., 1979; Prahl & Carpenter, 1984). Although fossil PAH mixtures are easily distinguished from those of combustion origin by such ratios, different sourcesof combustion PAH are very difficult to distinguish becausethey all produce strikingly similar mixtures (Youngblood & Blumer, 1975; Lee et al., 1977). Of the ratios tested, only values offluoranthene to indeno(c,d)pyrene (FL/IN) showed a consistent geographic pattern in Puget Sound sediments(Table 1). Average FL/IN values in surface sediments within central and southern Puget Sound (1.9 k 0.5, n = 13) are significantly lower at the > 99”,, confidence level than average values computed for sur,face sediments from the northern region (3.3f0.8, n= 11; Table 1). The temporal patterns for values of FL/IN with depth in sediment cores do not show a clear trend. The FL/IN data suggestthat combustion-derived PAH mixtures in sedimentsnear municipal sources may be compositionally distinguished from those in sediments near specific industrial discharges. The sensitivity of this parameter to distinguish further between modern industrial sources of combustion-derived PAH and the natural background of combustion-derived PAH remains uncertain. Perylene diagenesis Detailed plots of perylene concentrations and sediment age for the eight cores examined are displayed in Figure 3. Orr and Grady (1967) and Aizenshtat (1973) proposed that rapid sedimentation enhances preservation of perylene precursors and, under anoxic conditions, subsequent conversion of these precursors to perylene. Oxic conditions in near-surface sediments of Puget Sound are most likely not conducive to preservation or, more importantly, diagenetic transformation of such precursors. The data for the core collected at station 57, and possibly station 70, provide the only evidence of ingrowth of perylene, and only when the data are normalized to dry sediment weight [Figure 3(a)]. In situ production rates for perylene have been calculated (Wakeham, 1977and references therein) from data for sediment cores from Santa Barbara Basin (0.1 ltg-’ per 1000y), Saanich Inlet (0.2-0.8 ug g-i per IOOOy) and Lake Washington (4 ug g- i per 1000y). If the trends in perylene concentration ( ug g- ’ DW) recorded in sediments from stations 57 and 70 reflect in situ production with depth, rates of 2 and 0.3 ug g-’ per 1000y are calculated, respectively. These calculations would be in order with previous estimates of perylene production rates for other sedimentary environments.
Figure 4. Gas chromatograms of (a) PAH and (c) aliphatic hydrocarbons in coal fragments sieved from sediments (approximately 20-50 cm) collected at station 57; (b) PAH and (d) aliphatic hydrocarbons in sediment (40-43 cm) from a different core collected at the same station. Codes for chromatographic peaks include: PH, phenanthrene; MI%, methylphenanthrenes;DMPh,dimethylphenanthrenes;RET,retene;CHRY,chrysene; BFL, benzofluoranthenes; PERY, perylene; n-alkanes are identified by carbon number; DIPL, diploptene. See Table 3 for identification of peaks indicated by GC conditions: splitless injection in isooctane at 75 “C; initial temperature program 75-130 ‘C at 15 “C and 13&275 “Cat 5 “C min-‘, using prepurified hydrogen carrier gas. min-’
188
R. C. Barrick & F. G. Prahl
However, average perylene concentrations ( ug g- r OC) generally are constant or increaseby at most a factor of 15 between present day sedimentsand those deposited over 150 years ago [Figure 3(b)]. Regardless of how the data are normalized, there is little evidence to support the occurrence of significant in situ production of perylene within recent sediments from Puget Sound as a whole. Rather, the present data substantiate earlier conclusions in Dabob Bay and off the Washington and Alaskan coasts that perylene is introduced to the region primarily as a preformed, detrital hydrocarbon through erosionalprocesses(Prahl & Carpenter, 1979,1984; Venkatesan & Kaplan, 1982).
Evidence of fossil PAH
contributions
Average concentrations (ug g- r OC) or major C,-, C,-, C,- and C,-phenanthrenes in sedimentsfrom station 57 near the mouth of the Puyallup River at Tacoma, from station 82 near the mouth of the Nisqually River (Figure I), and from all remaining stations are given in Table 3. Methylphenanthrene (MP) concentrations (ug g- ’ OC) show considerable spatial and temporal variability in Puget Sound sediments. More constant and substantially elevated levels of Ml’ occur throughout the core collected at station 57 and, to a lesserdegree, at station 82. I-Methylphenanthrene is the dominant isomer in sediments from these two stations. Other alkylated derivatives of phenanthrene, including several dimethylphenanthrenes (especially 1,7-dimethylphenanthrene: pimanthrene), a C,-phenanthrene (MW =220) and retene, a C,-phenanthrene (Figure 4, Table 3), are also present at elevated concentrations at stations 57 and 82. Previous studies (LaFlamme & Hites, 1978; Wakeham et al., 1980; Barnes & Barnes, 1983) linked the presenceof retene and other alkylated phenanthrenes in certain soilsand sedimentsto a rapid, in situ diagenesisof higher plant resins (e.g. abietic acid in conifers; Stonecipher & Turner, 1970). The following evidence suggeststhat retene and several other alkylated phenanthrenes have a major fossil source in Puget Sound sediments that far outweighs any in situ diagenetic production from somenatural precursor. Furlong and Carpenter (1982) first noted coal fragments in a core from station 57. Large quantities of coal fragments from a subsequentcore at station 57 were analysed for hydrocarbons (Barrick et al., 1984). As shown in Figure 4, the coal fragments account for many of the aliphatic and aromatic compounds found in bulk sedimentsfrom stations 57 and 82. Major exceptions include the group of combustion-derived PAH, perylene and the UCM, all of which are absent in the coal fragments. Stations 57 and 82 lie off the mouths of rivers whose drainage basinscontain coal exposed by erosion or mining (Beikman et al., 1961). Furthermore, sedimentsfrom station 57 off Tacoma, a major coal trans-shipment center until the 192Os,contained the highest concentration of alkylated phenanthrenes (Table 2). A dimethylchrysenes (MW = 256) and a suite of picene derivatives (MW = 306, MW = 310, MW = 324) display high concentrations at stations 57 and 82, and are enriched in coal fragments from station 57 (Figure 4). The average sediment concentrations of MW = 256 and the two major picene derivatives (MW = 306, MW = 324) are given in Table 3. The picene composition of the coal fragments doesnot exactly match that of the bulk sediment. This discrepancy may reflect sampling variability since the core, sieved for coal fragments, was collected at a different time than that analysed for bulk hydrocarbon composition. Radke et al. (1982) proposed that values of the ratio of 2-methylphenanthrene to lmethylphenanthrene (MPR) provide an index of coal maturity: i.e. MPR increaseswith
Hydrocarbon
geochemistry
18’9
increasing coal rank in bituminous coals. Despite the complexity of sedimentary matrices, this ratio also shows a clear trend in Puget Sound (Table 1). The combined samples from stations 57 and 82 display a significantly lower value of MPR (0.61+ 0.11, n = 10) than do the remaining samples (1.13 f 0.20, YI= 65). This difference reflects an abundance of coal particles concentrated in sediments at these two stations. Additional sources could contribute picene derivatives to the sediments. LaFlamme and Hites (1979), Wakeham et al. (1980) and Tan and Heit (1981) reported the same suite of pentacyclic aromatic hydrocarbons in other sediments and assigned their origin to the early diagenesis of some triterpenoid natural product. The present evidence cannot discount early diagenesis as a possible minor source of the compounds; however, it implies a major contribution from a natural fossil source at least for sediments from stations 57 and 82. A series of C,, and C,, diterpanes are thought to mark the presence of coal fragments uniquely (Barrick et al., 1984). These diterpanes are found in high concentrations at stations 57 and 82, and in small but measurable concentrations elsewhere (Table 3). Hence, coal fragments may contribute picene derivatives to sediments in areas of Puget Sound distant from major river sources. A tetrahydrochrysene (MW =274) is present in bulk sediments and coal fragments (Figure 4). Unlike the PAH clearly associated with coal fragments, MW = 274 is measured in only slightly higher concentrations at stations 57 and 82 than at other stations (Table 3). A series of octahydrochrysenes (MW =292) and a related compound (MW =290) are conspicuously absent in coal fragments and in western Washington coals (Barrick er ul’. , 1984), but occur in sediments from stations 57 and 82 at three- to five-times the average concentration of the remaining sediments (Figure 4, Table 3). The distribution and chemical structure of these compounds suggest a biological contribution. Conclusions
Runoff or well-mixed particulate material in atmospheric fallout are major routes of introduction for combustion-derived PAH to Lake Washington and Puget Sound. However, well-defined gradients of PAH concentrations in surface sedimentsare seenin three separateareasof Puget Sound, including areaswhere aliphatic hydrocarbons show little variation. This pattern of comparable maxima for combustion-derived PAH concentrations in surface sediments from isolated regions of the sound, separatedby minima in concentration for regions lying in between, arguesagainst simple dispersalof thesechemicals from only the major municipal areasof central Puget Sound. The pattern suggests, rather, that there are other regional sourcesof combustion-derived PAH besidesthe major municipalities of central Puget Sound. PAH in the greater Puget Sound region are apparently not widely dispersedby air or water transport, but are rapidly removed to sediments within a few kilometers of each source. Combustion-derived PAH concentrations in sediment cores directly adjacent to urban centers in central Puget Sound maximized during the mid-1950s and have gradually decreasedin more recent deposits. This subsurface feature is not a general trend throughout Puget Sound and cannot always be used asa marker for this time period: cores from most stations distant from urban centres display highest combustion-derived PAH concentrations at the surface and a gradual decreasewith time in the past. Surface concentrations are on the average 2.5-times higher than concentrations in sediments deposited before major anthropogenic influence.
190
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&F.
G. Prahl
Perylene is ubiquitous in Puget Sound sediments. This PAH derives erosionally from some natural terrestrial source. Evidence of in situ diagenetic production from some natural precursor is, in general, not observed. Natural erosion of coal seams by rivers and historical transshipment of mined coal in Puget Sound, peaking in the early 19OOs, have contributed various PAH to the sediments, including a characteristic suite of alkylated phenanthrene, chrysene and picene derivatives. Acknowledgements Review of this manuscript and research support by Dr Roy Carpenter was appreciated. The authors thank T. S. Bates for use of GCjMS facilities at the Pacific Marine Environmental Laboratories (NOAA) in Seattle. This research was supported by U.S. Environmental Protection Agency/Department of Energy Contract DE-AT06-76-EV70040 and U.S. Environmental Protection Agency Contract R-811249-01-0. Although research described in this article has been funded in part by the EPA through Interagency Agreement EPA-79-D-X0533 to the University of Washington, it has not been subjected to EPA review and therefore does not necessarily reflect the views of EPA, and no official endorsement should be inferred. Contribution No. 1703, School of Oceanography, University of Washington, WB-10, Seattle, WA 98195.
References Aizenshtat, 2.1973 Perylene and its geochemical significance. Geochimica et Cosmochimica Acta 37,559-567. Barnes, M. A. & Barnes, W. C. 1983 Oxic and anoxic diagenesis of diterpenes in lacustrine sediments. In: Advances in Organic Geochemistry 1981 (Bjoroy, ed.). Wiley, New York, pp. 287-298 Barrick, R. C. 1982 Flux of aliphatic and polycyclic aromatic hydrocarbons to central Puget Sound from Seattle (Westpoint) primary sewage effluent. Environmental Science and Technology l&682-692. Barrick, R. C. &Hedges, J. I. 1981 Hydrocarbon geochemistry of the Puget Sound Region-II. Sedimentary diterpenoid, steroid and triterpenoid hydrocarbons. Geochimica et Cosmochimica Acta 45,381-392. Barrick, R. C., Hedges, J. I. &Peterson, M. L. 1980 Hydrocarbon geochemistry of the Puget Sound RegionI. Sedimentary acyclic hydrocarbons. Geochimica et Cosmochimica Acta 44, 1349-1362. Barrick, R. C., Furlong, E. T. & Carpenter, R. 1984 Hydrocarbon and azaarene markers of coal transport to aquatic sediments. Environmental Science and Technology 18,846-854. Bates, T. S., Hamilton, S. E. & Cline, J. 1984 Vertical transport of hydrocarbons in central Puget Sound. Environmental Science and Technology l&299-305. Beikman, H. M., Gower, H. D. & Dana, T. A. M. 1961 Coal Reserves of Washingron State. Bulletin no. 47, Division of Mines and Geology, Washington Dept. of Conservation, Olympia, WA. Boehm, I’. D. & Farrington, J. W. 1984 Aspects of the polycyclic aromatic hydrocarbon geochemistry of recent sediments in the Georges Bank Region. Environmental Science and Technology 18,840-845. Carpenter, R., Peterson, M. L. &Bennett, J. T. 1985 Z’“l?b-derived sediment accumulation and mixing rates for the greater Puget Sound region. Marine Geology 64,291-312. Furlong, E. T. & Carpenter, R. 1982 Azaarenes in Puget Sound sediments. Geochimica et Cosmochimica Acta 46,1385-1396. Gschwend, I’. M. & Hites, R. A. 1981 Fluxes of polycyclic aromatic hydrocarbons to marine and lacustrine sediments in the north-eastern United States. Geochimica et Cosmochimica Acta 45,2359-2367. Hites, R. A., LaFlamme, R. E. & Farrington, J. W. 1977 Polycyclic aromatic hydrocarbons in recent sediments: the historical record. Science 198,829-831. Hites, R. A., LaFlamme, R. E., Windsor Jr, J. G., Farrington, J. W. & Deuser, W. G. 1980 Polycyclic aromatic hydrocarbons in an anoxic sediment core from the Pettaquamscutt River (Rhode Island, U.S.A.). Geochimica et Cosmochimica Acta 44,873-878. LaFlamme, R. E. & Hites, R. A. 1978 The global distribution of polycyclic aromatic hydrocarbons in recent sediments. Geochimica et Cosmochimica Acta 42,289-303. LaFlamme, R. E. & Hites, R. A. 1979 Tetra- and pentacyclic, naturally occurring aromatic hydrocarbons in recent sediments. Geochimica et Cosmochimica Acra 43,1687-1691. Lake, J. L., Norwood, C., Dimock, C. & Bowen, R. 1979 Origins of polycyclic aromatic hydrocarbons in esruarine sediments. Geochimica et Cosmochimica Acta 43, 1847-1854.
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Lee, M. L., Prado, G. I’., Howard, J. B. & Hites, R. A. 1977 Source identification of urban airborne polycyclic aromatic hydrocarbons by GC/MS and HRMAS. Biomedical Mass Spectroscopy 4, 182-186. Merrill, E. G. & Wade, T. L. 1985 Carbonized coal products as a source of aromatic hydrocarbons to sediments from a highly industrialized estuary. Environmental Science and Technology 19,597-603. Muller, G., Grimmer, G. & Boehnke, H. 1977 Sedimentary record of heavy metals and polycyclic aromatic hydrocarbons in Lake Constance. Naturwissenshaften 64,427-431. Orr, W. L. & Grady, J. R. 1967 Perylene in basin sediments off southern California. Geochimica et Cosmochimica Acta 31,1201-1209. Palmork, K. H., Wilhelmson, S. & Neppelberg, T. 1973 The contribution from various industries of polynuclear aromatic hydrocarbons to the marine environment. International Council for Exploration of the Sea, Fisheries Improvement Committee Report No. 1973/E33,20 pp. Prahl, F. G. 1982 The geochemistry of polycyclic aromatic hydrocarbons in Columbia River and Washington coastal sediments. Ph.D. thesis, School of Oceanography, University of Washington, 209 pp. Prahl, F. G. & Carpenter, R. 1979 The role of zooplankton fecal pellets in the sedimentation of polycyclic aromatic hydrocarbons in Dabob Bay, Washington. Geochimica et Cosmochimica Acta 43,1959-1972. Prahl, F. G. & Carpenter, R. 1983 Polycyclic aromatic hydrocarbon @‘AH)-phase associations in Washington coastal sediment. Geochimica et Cosmochimica Acta 41,1013-1023. Prahl, F. G. & Carpenter, R. 1984 Hydrocarbons in Washington coastal sediments. Journal of Estuarine and Coastal Marine Science 18,703-720. Prahl, F. G., Crecelius, E. A. & Carpenter, R. 1984 Polycyclic aromatic hydrocarbons in Washington coastal sediments: an evaluation of atmospheric and riverine routes of introduction. Environmental Science and Technology 18,687-693. Radke, M., Willsch, H. Leythaeuser, 13. & Teichmuller, M. 1982 Aromatic components of coal: relation of distribution pattern to rank. Geochimica et Cosmochimica Acra 46, 1831-1848. Stonecipher, W. D. & Turner, R. W. 1970 Rosin and rosin derivatives. Encyclopedia of Polymer Science and Technology 12, 139161. Tan, Y. L. & Heit, M. 1981 Biogenic and abiogenic polynuclear aromatic hydrocarbons in sediments from two remote Adirondack lakes. Geochimica et Cosmochimica Acta 45,2267-2279. Tetra Tech, Inc. 1986 Eagle Harbor preliminary investigation. Draft report prepared for the hazardous waste cleanup program of the Washington Department of Ecology. Tetra Tech, Inc, Bellevue, WA. Venkatesan, M. I. & Kaplan, I. R. 1982 Distribution and transport of hydrocarbons in surface sediments of the Alaskan Outer Continental Shelf. Geochimica et Cosmochimica Acta 46,2135-2149. Wakeham, S. G. 1977 Synchronous fluorescence spectroscopy and its application to indigenous and petroleum derived hydrocarbons in lacustrine sediments. Environmenral Science and Technology 11, 272-276. Wakeham, S. G., Schaffner, C. & Giger, W. 1980 Polycyclic aromatic hydrocarbons in Recent lake sediments-II. Compounds derived from biogenic precursors during early diagenesis. Geochimica et Cosmochimica Acta 44,415-429. Youngblood, W. W. & Blumer, M. 1975 Polycyclic aromatic hydrocarbons in the environment: homologous series in soils and recent marine sediments. Geochimica et Cosmochimica Acta 39,1303-1314.
Coastal
and Shelf
Science
(1987) 25,175-191
Hydrocarbon Geochemistry of the Puget Sound Region-III. Polycyclic Aromatic Hydrocarbons in Sediments
Robert School U.S.A.
C. Barrick” of Oceanography,
Received
I2 August
Keywords:
and Fredrick WB-10,
1985
hydrocarbons;
University
and in revised
form
G. Prahlb of Washington, 2 September
sediment cores; distribution;
Seattle,
WA
98195
1986
Puget Sound
Polycyclic aromatic hydrocarbon (PAH) distributions and sources are characterized in 96 sediment samples from 24 ‘lOPb-dated cores collected at locations in the greater Puget Sound. The highest PAH concentrations are found within a few kilometers of several sources including industrial facilities in northern Puget Sound, urban areas in central Puget Sound, and river systems draining coalbearing strata. Regional patterns of combustion-derived PAH in surficial sediments indicate little atmospheric or waterborne exchange of PAH between different regions of the Sound. Significant subsurface maxima in combustionderived PAH concentrations ( ‘lOPb dated at the 1950s) occur only in sediment cores collected near urban centers. Perylene apparently derives from erosion of a terrestrial source with little or no evidence of in situ production at depth in sediment cores. Coal fragments are carriers of a characteristic suite of alkylated phenanthrene, chrysene, and picene derivatives concentrated near river mouths in central and southern Puget Sound. Introduction
Knowledge of the sourcesand global distribution of polycyclic aromatic hydrocarbons (PAH) in sedimentary environments is important becauseof the effects thesecompounds can have on biological systems. In addition to their potential toxicity, the chemical stability of PAH makes them useful indicators of specific anthropogenic and diagenetic contributions to sedimentary deposits. This study describes the PAH distributions in modern sediments of Puget Sound. Earlier papers have defined the non-aromatic hydrocarbon geochemistry of Puget Sound sediments (Barrick et al., 1980; Barrick & Hedges, 1981). Experimental Sample
preparation
Procedures for sediment collection (primarily by multiple corer with a hydrostatically damped rate of penetration) and extraction of hydrocarbons have been described (Barrick “Present address: Tetra Tech, Inc., 11820 Northup Way, Suite 100, Bellevue, WA 98005, U.S.A. bPresent address: College of Oceanography, Oregon State University, Corvallis, OR 97331,
U.S.A. 17.5
0272-7714/87/020175
+ 17 $03.00/O
0 1987 Academic
Press Limited
176
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&F.
G. Prahl
et al., 1980). Following a Sohxlet extraction, organic extracts were separatedinto aliphatic and aromatic hydrocarbon fractions in two chromatographic stepsusing (1) silica gel and alumina adsorbents and (2) Sephadex LH-20 (Prahl & Carpenter, 1983). Although the order of the chromatographic stepswas reversed in the earliest stagesof the study, replicate tests showed there were no statistically significant differences in the final quantitation of individual aliphatic and aromatic compounds by any of the procedures employed. Analytical precision averaged -t loo, about the mean of replicate measurements. Single-point PAH-recovery estimates were made on some sediments using 2methylanthracene as an internal recovery standard. Recoveries ranged from 60 to 85”,, (higher molecular weight PAH were generally recovered at >95O,, in spiked blanks). Corrections for differential evaporative lossesof PAH across the range of compounds analysed were not made as for aliphatic hydrocarbons (Barrick et al., 1980) becausean analogousseriesof recovery standards for PAH was not available at the time. Therefore, all concentrations reported for compounds eluting before fluoranthene, in particular, are minimum estimates. Gas chromatography
and mass spectroscopy
Each PAH fraction wasanalysed by capillary gaschromatography (GC). Data for Dabob Bay station E (Figure 1) are from an earlier study (Prahl & Carpenter, 1979) and were obtained by high pressureliquid chromatography (HPLC). The HPLC data are included for comparison purposes. Results from analyses of replicate samples by the GC and HPLC techniques differed by only +8”,, in studies reported by Prahl (1982). Thus, quantitative comparison of the earlier HPLC data with the present GC data setis justified. Gas chromatography was performed on a Hewlett-Packard 5880 instrument using either glass (W-2100) or fused silica (SE-54) capillary columns and conditions as described in Figure 4. The compositions of selected sampleswere characterized by gas chromatography/mass spectroscopy (GC/MS) using an HP5995 or a Finnigan 4000 system fitted with a fused silica (SE-54 or DB-5) capillary column operated under the same GC conditions. Bulk organic
carboll
Total organic carbon (TOC) data were obtained using either a LECO carbon analyser (Barrick et al., 1980) or a Carlo Erba elemental analyser (Barrick, 1982). Dry-weight concentrations of PAH were significantly correlated f$ < 0.01) with TOC content in Puget Sound sediments. Therefore, dry-weight PAH concentrations were normalized to TOC to dampen variations causedby patchiness or other depositional factors, and to enhance the ability to detect source-related changesin PAH input. Boehm and Farrington (1984) summarize the advantages of normalizing PAH data to TOC when evaluating environmental trends. Associations of different PAH with specific organic carbon-rich particles in sedimentsare discussedby Prahl and Carpenter (1983).
Results
and discussion
The 96 sediment samplesfrom 24 sites were analysed in detail for PAH compositions, selected aliphatic hydrocarbon concentrations and total organic carbon content. Data reported on Tables l-3 include 12 replicate analysesand eight profiles with depth in cores.
Hydrocarbon geochemistry
Distributions
of combustion-derived
177
PAH
Several pyrolysis sources produce qualitatively similar mixtures of primarily nonalkylated PAH containing typically P6 condensed rings (Lee et al., 1977). Individual combustion-derived PAH have similar spatial and temporal distributions in sediments (Table 2) and, therefore, are parameterized in the following discussion as total combustion-derived PAH (COMB) for convenience. COMB is defined asthe sum of the concentration of nine individual compounds: fluoranthene, pyrene, benzo(a)anthracene, chrysene, benzofluoroanthenes, benzo(a)pyrene, benzo(e)pyrene, indeno(c,d)pyrene, and benzo(ghi)perylene. Fuel oils in combined municipal sewageand stormwater dischargesto Puget Sound are a major source of tricyclic aromatics (e.g. phenanthrene) and lower molecular weight aromatic compounds. A comparison of source and depositional massfluxes indicated that these sewage-derived components are lost in the water column or at the sediment-water interface (Barrick, 1982). Phenanthrene and COMB concentrations correlate well, both in surface O-2 cm) sediments (r2 = 0.72, n = 28) and in the entire data set (r2 = 0.61, YZ= 83). The correlation suggests that the phenanthrene accumulating in the sediments is primarily of combustion origin. Alternative anthropogenic sourcesof nonalkylated PAH (e.g. creosote; Merrill &Wade, 1985)are of concern only in isolated areasof Puget Sound. For example, creosote contamination from a wood-treating facility in a small harbor west of Seattle apparently does not affect the main basin of Puget Sound (Tetra Tech, Inc.,, 1986). Concentrations of COMB in surface (O-2 cm) sedimentsranged from 8 to 73 pg 8-I OC (Table 1), or 16-2400 ng g- ’ dry sediment. Fluoranthene, a dominant component of the combustion series, ranged from 1 to 13 pg g- ’ OC (3-350 ng g- ’ dry sediment). Accumulation rates of COMB in surface Puget Sound sediments (Table l), calculated from “‘Pb data (Carpenter et al., 1985), are comparable to, or higher than, those measured in Washington coastal sediments (range: 7-210 ng cm-2 yr-‘; Prahl et al., 1984) and in Lake Washington sediments (220 ng cmm2yr- ‘). Comparison with data for other regions can be made only for individual PAHs. The range of accumulation rates for fluoranthrene in surface sedimentsof Puget Sound (2-220 ng cmm2y - ‘) covers the range reported for the Washington continental shelf (2-38 ng cm-’ y-‘; Prahl et al., 1984), three urban sites in New England (37-93 ng cmm2y-i) and several remote sites in the north-eastern U.S. (1-5 ng cm-’ y-l; Gschwend & Hites, 1981). Although fluoranthene accumulation rates are not reported for sediments from the Charles River and New York Bight, dry weight concentrations in these sediments are 40-times and 3-times greater, respectively, than the highest concentration measuredin Puget Sound. Total combustion PAH concentrations ( ug g - ’ OC) in midchannel surface sediments of Puget Sound range over an order of magnitude (Figure 1). This range is comparable with that observed for total aliphatic hydrocarbons in the samecores (Barrick et al., 1980). However, concentrations for these two classesof hydrocarbons display substantially different area1distributions. PAH and aliphatic hydrocarbons in Puget Sound sediments apparently derive from discrete sourcesthat are regionally differentiated. The average concentration of total aliphatic hydrocarbons, determined gravimetrically, is significantly higher (p
R. C. Barrick &F.
178
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Hydrocarbon
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In contrast, urban proximity is not the only factor influencing the amount of total combustion PAH observed in sediments throughout Puget Sound. High COMB concentrations (Figure 1) are found in sedimentsfrom central Puget Sound (e.g. stations 51) and in sediments from areasfar from urban areas, e.g. southern Dabob Bay (station 89) and two northern Puget Sound locations (stations 66 and 79). Urban centers are likely the primary sources for elevated combustion PAH concentrations in central Puget Sound. However, the discharge of PAH in air particulate material and primary sewagefrom the major urban centers of central Puget Sound is insufficient to account for the amounts of total combustion PAH accumulating elsewhere (Barrick, 1982). Patterns of high COMB concentrations in distinct regions separated by low concentration at locations in between suggestthat combustion-derived PAH come from several point sourceslocated throughout Puget Sound. Simple atmospheric or estuarine dispersal from only the major urban centers of central Puget Sound cannot explain these data. The regional pattern can not be explained by differences in sediment texture. The samepattern is evident when the data are normalized to organic carbon content or expressedasabsolute accumulation rates (Table 1). Both normalizations remove the influence of sediment texture. Sediments from northern Puget Sound contain combustion-derived PAH accompanied by relatively minor amounts of other hydrocarbons (e.g. UCM from wasteoils in municipal discharges). This fact is evident from the UCMjCOMB ratio. Values of this ratio equal 35 in surface sediment samplesfrom stations 66 and 79, two locations in northern Puget Sound where the highest combustion PAH concentrations are observed (Figure 1, Table 1). These values contrast sharply with the average UCMjCOMB ratio of 160+ 34 (n = 7) measuredin central Puget Sound sediments (influenced by major municipal discharges). A small, but significant increase in COMB concentration in the surface 7 cm of sediments from station 66 in northern Puget Sound (Table 1; Figure 1) occurred in the mid1960s and corresponds, at least chronologically, to the opening of a nearby aluminium smelter at Ferndale. Although the temporal coincidence does not prove that the smelter has contributed combustion-derived PAH to sedimentsin this region, aluminium smelting plants can be important sources of combustion PAH (Palmork et al., 1973). Flare towers associated with petroleum refineries at Anacortes are potential sources of combustion-derived PAH in sediments from stations 77-79. An unconfirmed source of PAH at station 89 in southern Dabob Bay is oiled telemetry cables which are used to monitor naval torpedo experiments. Subsurface
maxima
of combustion-derived
PAH
as a time marker
Subsurface maxima in combustion-derived PAH concentrations have been noted in sediments from a variety of environments (Muller et al., 1977;Hites et al., 1977,198O; Prahl & Carpenter, 1979). Gschwend and Hites (1981) proposed that these sedimentary maxima record a decreasing rate of combustion-derived PAH emission caused by a shift in the types of fuels burned since the 1950s (Hites et al., 1977) and increased controls on industrial-waste discharge.
Figure 1. Study area. Stations are indicated by numbers. The radius of the circle about each station is proportional to the total concentration (pg g- ’ OC) of nine combustionderived PAH (see COMB, Table 1).
o-2 2628
O-2 2&28 G2 13-15
60
61
62
O-2 4345
B’ B B
*2 15-17 l&12 15-17 40-43
59
57
P P P r P
&2 4244 46-49 95-98 138-141 184-187 230-233
56
G2 5-7 lo-12 15-17 2&22 25-27 30-32 35-37 39-41
1970 1892 1968 1888
1969 < 1825
n.d. n.d.
1975 1963 1959 1949 1919
1975 1951 < 1825 <1825 <1825 <1825 <1825
1971 1869
1976 1965 1955 1944 1933 1921 1909 1897 1886
(Y)
(cm)
c&2 15-17
tr
Age”
data
1.09 1.01 1.17 0.715
0.244 0.236
0.508 1.19
2.42 3.22 3.15 3.16 3.3
2.62 3.01 0.856 0.814 0.879 0.824 0.986
1.69 1.16
2.10 2.18 2.09 2.14 2.10 2.03 1.88 1.76 1.80
“” OC
1. Summary
Sample interval
52
51
Station No.
TABLE
240 270 120 260
230 260
170 150
310 460 n.d. n.d. n.d.
200 260 260 240 200 360 240
220 230
300 270 280 250 290 220 250 170 160
n-ALK*
for Puget
hydrocarbon
2400 160
6300 5200 n.d. n.d. n.d.
3800 5200 260 220 330 410
6600 3300
9500 8100 7600 5700 7000 3200 2300 290 110
UCM
Sound
28 56 13 27
27 15
14 1.7
44 40 41 95 17
30 52 2.4 5.1 3.7 4.8 4.6
33 24
6Ok5 120 145 83 39 53 38 7.7 4.4
COMBd
Organic
2.5 7.5 0.94 0.60
0.66 0.30
0.94 0.24
4.2 7.1 7.1 11 6.4
2.0 3.3 2.3 3.6 2.5 2.1 2.4
1.6 0.33
7.2 4.8 6.5 4.0 n.d. 3.3 1.5 0.86
6.4+
1.1
(pg g- ‘)
Phenanthrene
carbon
cores
4.3 5.3 1.8 2.3
2.7 5.0
1.4 5.6
4.2 2.7 3.3 4.3 1.4
1.9 5.2 8.4 6.0 1.7 8.0 6.4
2.0 1.8
4.9kO.3 5.8 5.3 5.2 2.1 5.3 6.2 6.6 5.7
Perylene
2.4 4.2 1.2 11
6.5 17
4.2 1.1
21 36 61 50 97
7.9 8.6 n.d. n.d. n.d. 4.3 n.d.
4.4 5.0
4.1 kO.4 6.5 n.d. 13.0 11.0 n.d. 13.0 4.8 2.2
Retene
27
100
14
n.d.
300
600
62
290
COMB flux’
1.23 1.02 1.33 1.13
0.88 0.76
1.03 1.54
0.71 0.70 0.58 0.62 0.50
0.87 1.02 1.27 1.55 1.38 1.18 1.38
1.14 0.99
1.28+0.3 1.28 n.d. 0.95 1.00 1.01 0.88 1.09 1.13
MPR’
1.9 1.1 2.2 6.8
3.3 8.1
2.0 3.2
3.5 2.8 3.3 1.9 3.3
2.1 2.1 1.1 1.2 1.3 2.8 2.0
1.6 7.2
1.0+0.3 1.1 n.d 1.7 2.0 1.6 2.4 2.7 3.8
MPh/Phs
2.1 2.6 2.0 1.9
1.9 2.3
2.2 1.1
2.6 1.9 3.3 3.1 4.4
1.5 1.8 > 100 74 75 > 100 70
1.5 1.5
2.OkO.3 1.7 1.3 1.5 2.7 1.7 1.7 2.0 6.5
FL/IN”
1970 < 1825
1973 1957 1940 1906 1872 1856 1838 1825 1973 1903
1972 1883
1961 < 1825
1972 < 1825
1974 1953
O-2 3&32
o-2 5-7 lo-12 20-22 30-32 35-37 40-42 43-45 O-2 21-23
2-4 34-36
o-2 32-34
c-2 34-36
O-2 m-22
68
70 du
73
77
78
79
72
1974 1929
O-2 26-28
67
1973 1965 1955 1937 1919 1911
o-2 5-7 lo-12 20-22 30-32 35-37
66 du
1964 1948 1921 1872 < 1825 < 1825 < 1825
o-2 2-4 5-7 lo-12 15-17 19-21 21-23
65
1.18 1.16
2.36 2.15
0.723 0.966
4.05 3.34
0.827 0.688 0.712 0.858 1.12 1.13 0,908 0.820 0,958 1.20
0.536 1.52
0.512 0.579
0.802 0.682 0.808 0,732 0.911 0.915
1.10 1.61 0.964 0.248 0,349 0.300 0.300
170 320
220 100
380 100
170 250
380 470 370 420 270 16 320 280 390 550
260 150
130 160
350 360 270 340 240 240
200 250 170 620 330 360 n.d.
2200 2900
1400 760
3500 160
2100 790
2200 3700 2400 100 210 130 570 610 3100 2500
1900 230
900 200
2500 2900 1900 100 780 480
1700 1400 1400 1300 400 590 n.d.
62 22
19 11
35 8.6
20 2.3
21+6 36 39 27 7.0 5.2 6.2 9.0 37 26
16 26
21 8.2
72k8 52 41 49 8.5 22
14 11 24 23 11 10 11
8.1 1.8
1.7 5.2
3.6 2.4
1.7 n.d.
4.2 5.1 6.9 0.20 0.13 0.08 2,2 3.3 4.3 3.1
1.7 3.3
4.5 2.7
3.2 1.5
5.8 16.0
1.8 3.6
4.1kO.5 3.5 4.7 5.6 5.1 5.7 5.7 6.7 4.2 2.3
3.5 3.3
4.4 4.3
5,0* 1.9 4.1 4.8 5.1 4.2 5.8
7.6k7.1 7.8 6.3 7.0 3.0 2.3 1.1 0.03
2.4 1.7 3.1 8.7 10.0 10.0 10.0
0.91 0.87 2.5 2.1 2.4 2.5 2.2
7.1 1.5
2.8 1.7
2.6 3.4
1.3 0.86
3.7 4.4 4.4 4.2 2.9 0.36 3.4 4.3 2.8 3.2
n.d. n.d.
3.2 0.24
4.3kO.l 4.7 5.1 5.2 4.7 2.8
24 1.1 2.3 2.6 5.2 6.9 6.3
660
120
12
98
110
34
18
44
200
11
1.16 1.00
1.06 1.10
l-10 1.14
1.54 ad.
1.04 1.09 1.03 0.96 0.96 n.d. 1.18 1.26 1.86 1.43
1.14 l-13
1.10 ad.
1.33kO.2 1.15 1.16 1.18 1.14 1.33
0.95 0.95 1.0 0.85 0.72 0.84 0.84
1.1 3.1
1.4 0.7
1.6 2.9
2.1 n.d.
2.2 2.3 1.8 15.0 15.0 10.5 3.5 3.0 2.18 2.7
2.6 1.5
3.9 13.0
1.7rf: 1.3 1.7 1.8 1.7 3.2 3.6
2.6 2.2 1.8 2.8 2.5 2.5 2.5
3.9 2.0
4.7 7.0
2.9 10.0
2.2 1100
4.0 3.7 3.6 2.2 3.0 0.45 8.7 5.7 3.1 2.1
3.7 8.3
2.4 n.d.
3.9* 1.0 5.2 3.8 3.2 5.9 3.0
2.7 2.2 2.1 1.4 1.5 2.8 3.5
o-2 35-37
o-2 35-37
o-2 24-26
92
95
98 du
(&3
O-2 2628
89
WASH
o-2 46 lo-12 20-22 3G32
82 B B B qu B B
LK 11
Sample interval (cm)
Station
4.2
2.84 2.38
0.350 0,640
0,868 1.05
3.23 3.53
0,772 0,544 0.610 0.606 0,644
OC
n.d.
190 270
350 310
210 200
260 170
190 225 230 240 190
n-ALK’
n.d.
2800 4000
650 790
1600 300
2100 1100
n.d. n.d. n.d. n.d. n.d.
UCM’
81
26_+3 40
8.0 7.9
28 4.7
73 5.6
22 36 20 32k3 21
COMBd
Organic
(pg g - ’ )
6-5
2.OkO.3 3-l
0.20 0.33
2.4 1.4
3.4 0.18
3.0 3.8 2-6 3.52 2.6
I’henanthrene
carbon
8.2
6.5k3.8 6.3
3.6 6-3
4.4 4.6
10.0 4.0
2.9 4.9 2.5 4.oio.2 3.1
Perylene
10
2.7 + 0.2 4.6
2.9 1.3
3.1 2.4
6.2 0.41
16 25 22 30*3 21
Retene
220
270
n.d.
66
400
62
flUX’
COMB
1.32
1.07+0.08 1.19
1.20 1.11
1.12 1.10
1.08 1.44
0.60 0.60 0.59 0.59f0.05 0.66
MPRJ
“Ages computed using “%‘b data of Carpenter e’t al. (1985). ‘Sum of the normal alkanes C,,-C,,. “Total unresolved complex mixture (UCM) as defined by Barrick et ~11. (1980). “Sum of fluoranthene, pyrene, benz(a)anthracene, chrysene, total benzofluoranthrenes, benzo(e)pyrenc, benzo(a)pyrene, benzo(g,h,i)perylene as determined by GC/FID. ‘Surface accumulation rate (ng cm ’ y ’ ) of the combustion-derived PAH series defined in footnote d. lMethyl phenanthrene ratio =2-methylphenanthrene/l-methylphenanthrene iRadke t’i ul., 1982). dTotal mono-methylphenanthrenes to phenanthrene ratio. hFluoranthene to indeno(c,d)pyrene ratio. ‘Piston core. Sample intervals correspond io depth in core; 0.5 m or more ufburfacr material was lost in coring. All other cores unless specified. ‘Box core. du, Duplicate analysis; tr, triplicate analysis; qu, quadruplicate analysis; n.d., not determined.
1976
1974 1943
n.d. n.d.
1973 1867
1975 1927
1973 1960 1940 1907 1870
Age” (Y)
TABLE 1. Comi,zued
samples
are from
indenojc,d)pyrene
0.39
1.2+0.2 1.2
3.7 3.4
2.1 3.5
2.3 3.3
2.1 2.4 2.6 2.6 2.4
MPh/Ph#
and
multiple
I.0
2.2kO.4 2.2
2.1 1.8
3.1 > 100
1.2 1.4
2.8 2.1 3.6 2,0*0.2 I.9
FL/INh
Hydrocarbon
geochemistry
TABLE 2. Coefficients differing ring size
of determination
Surface (O-2 cm) S. of Admiralty Inlet (n = 9)”
4-ringh 5-ring’
5-ring
6-ringd
0.87
0.85 0.87 “Total averaged b4-ring ‘5-ring d6-ring
185;
(r*)
for non-alkylated
combustion
Surface (G2 cm) All stations (n=28)
4-ring 5-ring
sample size before the combustion combustion combustion
5-ring
6-ring
0.79
0.44 0.75
PAH
of
Total data set (n = 84)” 5-ring 4-ring 5-ring
6-ring
0.66
0 18 0 32
(n) is the number of sites (i.e. any replicate analyses at a site were correlation analysis was conducted). PAH: fluoranthene, pyrene, benzo(a)anthracene, chrysene. PAH: total benzofluoranthenes, benzo(e)pyrene, benzo(a)pyrene. PAH: indeno(c,d)pyrene, benzo(g,h,i)perylene.
TABLE 3. Concentrations of alkylated phenanthrenes, chrysene and picene and diterpanes in Puget Sound sediments (pg g- ’ organic carbon) Sta. 82 (n = 5) Total monomethylphenanthrenes I-Methylphenanthrene Total dimethylphenanthrenes MW =220 (C-3 phenanthrene)” Retene (C-4 phenanthrene) Tetramethyl-1,2,3,4,4a,l1,12,12aoctahydrochrysene (MW = 292) MW = 290” 3,3,7-Trimethyl-1,2,3,4tetrahydrochrysene (MW =274) Dimethylchrysene (MW = 256)” 2,2,9-Trimethyl-1,2,3,4tetrahydropicene (MW = 324) 2,9-Dimethylpicene (MW = 306) Total diterpane@
7.7kl.5 2.6 kO.57 15.0+3-3 6,5+ l-5 23.Ok5.1 2,8& 2.4+
1,3 1.4
1.3iO.46 3.0* 1.9 7.0 * 5.5 7.8 k 3.2 23,0+6-2
Sta. 57 (n=5) 20,0+3.2 7.6& 1.4 25.0* 9.0 19.025.7 53.0129.0
derivatives,
Remainder in=691 5.3*3
4-8 + 2.4 1,4* 1.1 4,7+4 1
2.5k2.05 2.1 k2.2
0.72 *0,66 0.48kO.42
1.6+ 5.1+
1.0*0,62 0.7010-44
1.1 1.2
8.3k3.6 9.6k6.1 80.0+20.0
3
2.32 1-9 1.4io.9 12.0* 14.0
“Major mass spectral ions (intensity) include: MW =220--nzjz 220 (loo”,), 205 (78”,,), 189 (32”,,); MW=29(tmiz 290 (45”,,), 275 (loo”,,), 247 (lo”,); MW=256--m,‘z 256 (1000,), 239 (28”,,), 226 (S”,). “Total diterpanes are the sum of C 19 and C,, diterpanes (see Barrick & Hedges, 1981) from the same cores analysed for PAH.
The range of maxima measured in profiles of fluoranthene concentration with depth for eight sediment cores collected throughout Puget Sound is shown in Figure 2. Because complete data for the nine combustion PAH were not obtained for the Dabob Bay station E core (Prahl & Carpenter, 1979), fluoranthene concentrations are plotted rather than COMB depth profiles in cores (where complete data are available). Fluoranthene and COMB concentrations (Table 1) exhibit similar depth profiles in cores. Thus, fluoranthene profiles represent a valid proxy of total combustion-derived PAH. Significant
R. C. Barrick & F. G. Prahl
184
FLUORANTHENE
CONCENTRATION
(ng,g OC)
Figure 2. Age profiles of fluoranthene concentrations (pg g-’ OC) in eight sediment cores from Puget Sound. Additional data points are shown for the top and bottom 2-cm intervals of cores from the remaining 16 stations, and station 11 in Lake Washington (LW). Average dates of sediment deposition are 210Pb-derived and are not corrected for mixing [see Carpenter et al. (1985) for details on procedures and precision].
subsurfaceconcentration maxima are observed only at stations 51 and 57, located directly adjacent
to Seattle
and
Tacoma.
The
occurrence
of these
two
subsurface
maxima
bears
no relationship to the relative amount of combustion-derived PAH observed in surface sediments. Instead, the presenceof this feature depends on urban proximity and is not a ubiquitous time marker in greater Puget Sound region. PAH data from a core collected near station 5 1 (Bates et al., 1984) generally corroborate the subsurface feature at station 51, but suggestthat PAH input hasheld relatively constant sincethe late 1960s. Background
levels of combustion-derived
PAH
COMB concentrations at most Puget Sound stations have fluctuated between 10 and 50 ug g- ’ OC since about 1870. The median surface concentration measuredin this study is about 30 ug g- ’ OC, nearly five-times lessthan maximum concentrations at station 5 1
Hydrocarbon
geochemistry
185
.
cL-=-- ---‘----A - -.-.--‘- - -,-+ v-
Figure 3. Age profile of perylene normalized to Puget Sound. Additional cores from the remaining
3
(a) perylene normalized to dry weight (ng g-’ DW) and (b) organic carbon (ng g- ’ OC) in eight cores from throughout data points are shown for the top and bottom 2-cm intervals of 16 stations. See caption to Figure 2 for dating information.
in the mid 1950s.The average COMB concentration in sediment pre-dating 1825, including a Pleistocene grey clay at station 65, is 9 + 6 ug g- ’ (n= 12), or a factor of three less than the median surface concentration. The pre-1825 sedimentswere deposited at least 50 years before major urban development began in the region and reflect the natural background of combustion-derived PAH from natural burning processes,such asforest fires. Compositional
variation
in the combusion-derived
PAHpattern
The dominant sourcesof combustion PAH in central and southern Puget Sound and areas south of Admiralty Inlet (Figure 1) are the adjacent urban centers. Not surprisingly, the group of nine combustion-derived PAH exhibit strong, and nearly equivalent, correlations between the total four-ring, five-ring and six-ring components (Table 2), indicating a fairly constant composition for combustion-derived PAH mixtures throughout this region.
R. C. Barrick & F. G. Prahl
186
MW 220 ALKYL
NAPHTHALENES
REl
STATION 57 COAL FRAGMENTS PAH
22c DMPH v
,LKYL 1
STATION 57 BULK SEDIMENT PAH
NAPHTHALENES I
MW 306
Cl
PR
DITERPANES I
I
STATION 57 COAL FRAGMENTS ALIPHATIC HYDROCARBONS
il
I!
c25
C23 I
C27
STATION 57 BULK SEDIMENT ALIPHATICS
I
___
_---
_ ------
---
---
__----
“:’
17cqHJ.
21/i(H)
“:
_----
--_
-
Hydrocarbon
geochemistry
187
Specific compositional indicators were used to test for variability in the composition of the combustion-derived PAH mixtures recorded in Puget Sound sediments. Ratios, such as phenanthrene/anthracene and total mono-methylphenenthrene/phenanthrene, have been used to discriminate different PAH sources sedimentary mixtures (Lake et al., 1979; Prahl & Carpenter, 1984). Although fossil PAH mixtures are easily distinguished from those of combustion origin by such ratios, different sourcesof combustion PAH are very difficult to distinguish becausethey all produce strikingly similar mixtures (Youngblood & Blumer, 1975; Lee et al., 1977). Of the ratios tested, only values offluoranthene to indeno(c,d)pyrene (FL/IN) showed a consistent geographic pattern in Puget Sound sediments(Table 1). Average FL/IN values in surface sediments within central and southern Puget Sound (1.9 k 0.5, n = 13) are significantly lower at the > 99”,, confidence level than average values computed for sur,face sediments from the northern region (3.3f0.8, n= 11; Table 1). The temporal patterns for values of FL/IN with depth in sediment cores do not show a clear trend. The FL/IN data suggestthat combustion-derived PAH mixtures in sedimentsnear municipal sources may be compositionally distinguished from those in sediments near specific industrial discharges. The sensitivity of this parameter to distinguish further between modern industrial sources of combustion-derived PAH and the natural background of combustion-derived PAH remains uncertain. Perylene diagenesis Detailed plots of perylene concentrations and sediment age for the eight cores examined are displayed in Figure 3. Orr and Grady (1967) and Aizenshtat (1973) proposed that rapid sedimentation enhances preservation of perylene precursors and, under anoxic conditions, subsequent conversion of these precursors to perylene. Oxic conditions in near-surface sediments of Puget Sound are most likely not conducive to preservation or, more importantly, diagenetic transformation of such precursors. The data for the core collected at station 57, and possibly station 70, provide the only evidence of ingrowth of perylene, and only when the data are normalized to dry sediment weight [Figure 3(a)]. In situ production rates for perylene have been calculated (Wakeham, 1977and references therein) from data for sediment cores from Santa Barbara Basin (0.1 ltg-’ per 1000y), Saanich Inlet (0.2-0.8 ug g-i per IOOOy) and Lake Washington (4 ug g- i per 1000y). If the trends in perylene concentration ( ug g- ’ DW) recorded in sediments from stations 57 and 70 reflect in situ production with depth, rates of 2 and 0.3 ug g-’ per 1000y are calculated, respectively. These calculations would be in order with previous estimates of perylene production rates for other sedimentary environments.
Figure 4. Gas chromatograms of (a) PAH and (c) aliphatic hydrocarbons in coal fragments sieved from sediments (approximately 20-50 cm) collected at station 57; (b) PAH and (d) aliphatic hydrocarbons in sediment (40-43 cm) from a different core collected at the same station. Codes for chromatographic peaks include: PH, phenanthrene; MI%, methylphenanthrenes;DMPh,dimethylphenanthrenes;RET,retene;CHRY,chrysene; BFL, benzofluoranthenes; PERY, perylene; n-alkanes are identified by carbon number; DIPL, diploptene. See Table 3 for identification of peaks indicated by GC conditions: splitless injection in isooctane at 75 “C; initial temperature program 75-130 ‘C at 15 “C and 13&275 “Cat 5 “C min-‘, using prepurified hydrogen carrier gas. min-’
188
R. C. Barrick & F. G. Prahl
However, average perylene concentrations ( ug g- r OC) generally are constant or increaseby at most a factor of 15 between present day sedimentsand those deposited over 150 years ago [Figure 3(b)]. Regardless of how the data are normalized, there is little evidence to support the occurrence of significant in situ production of perylene within recent sediments from Puget Sound as a whole. Rather, the present data substantiate earlier conclusions in Dabob Bay and off the Washington and Alaskan coasts that perylene is introduced to the region primarily as a preformed, detrital hydrocarbon through erosionalprocesses(Prahl & Carpenter, 1979,1984; Venkatesan & Kaplan, 1982).
Evidence of fossil PAH
contributions
Average concentrations (ug g- r OC) or major C,-, C,-, C,- and C,-phenanthrenes in sedimentsfrom station 57 near the mouth of the Puyallup River at Tacoma, from station 82 near the mouth of the Nisqually River (Figure I), and from all remaining stations are given in Table 3. Methylphenanthrene (MP) concentrations (ug g- ’ OC) show considerable spatial and temporal variability in Puget Sound sediments. More constant and substantially elevated levels of Ml’ occur throughout the core collected at station 57 and, to a lesserdegree, at station 82. I-Methylphenanthrene is the dominant isomer in sediments from these two stations. Other alkylated derivatives of phenanthrene, including several dimethylphenanthrenes (especially 1,7-dimethylphenanthrene: pimanthrene), a C,-phenanthrene (MW =220) and retene, a C,-phenanthrene (Figure 4, Table 3), are also present at elevated concentrations at stations 57 and 82. Previous studies (LaFlamme & Hites, 1978; Wakeham et al., 1980; Barnes & Barnes, 1983) linked the presenceof retene and other alkylated phenanthrenes in certain soilsand sedimentsto a rapid, in situ diagenesisof higher plant resins (e.g. abietic acid in conifers; Stonecipher & Turner, 1970). The following evidence suggeststhat retene and several other alkylated phenanthrenes have a major fossil source in Puget Sound sediments that far outweighs any in situ diagenetic production from somenatural precursor. Furlong and Carpenter (1982) first noted coal fragments in a core from station 57. Large quantities of coal fragments from a subsequentcore at station 57 were analysed for hydrocarbons (Barrick et al., 1984). As shown in Figure 4, the coal fragments account for many of the aliphatic and aromatic compounds found in bulk sedimentsfrom stations 57 and 82. Major exceptions include the group of combustion-derived PAH, perylene and the UCM, all of which are absent in the coal fragments. Stations 57 and 82 lie off the mouths of rivers whose drainage basinscontain coal exposed by erosion or mining (Beikman et al., 1961). Furthermore, sedimentsfrom station 57 off Tacoma, a major coal trans-shipment center until the 192Os,contained the highest concentration of alkylated phenanthrenes (Table 2). A dimethylchrysenes (MW = 256) and a suite of picene derivatives (MW = 306, MW = 310, MW = 324) display high concentrations at stations 57 and 82, and are enriched in coal fragments from station 57 (Figure 4). The average sediment concentrations of MW = 256 and the two major picene derivatives (MW = 306, MW = 324) are given in Table 3. The picene composition of the coal fragments doesnot exactly match that of the bulk sediment. This discrepancy may reflect sampling variability since the core, sieved for coal fragments, was collected at a different time than that analysed for bulk hydrocarbon composition. Radke et al. (1982) proposed that values of the ratio of 2-methylphenanthrene to lmethylphenanthrene (MPR) provide an index of coal maturity: i.e. MPR increaseswith
Hydrocarbon
geochemistry
18’9
increasing coal rank in bituminous coals. Despite the complexity of sedimentary matrices, this ratio also shows a clear trend in Puget Sound (Table 1). The combined samples from stations 57 and 82 display a significantly lower value of MPR (0.61+ 0.11, n = 10) than do the remaining samples (1.13 f 0.20, YI= 65). This difference reflects an abundance of coal particles concentrated in sediments at these two stations. Additional sources could contribute picene derivatives to the sediments. LaFlamme and Hites (1979), Wakeham et al. (1980) and Tan and Heit (1981) reported the same suite of pentacyclic aromatic hydrocarbons in other sediments and assigned their origin to the early diagenesis of some triterpenoid natural product. The present evidence cannot discount early diagenesis as a possible minor source of the compounds; however, it implies a major contribution from a natural fossil source at least for sediments from stations 57 and 82. A series of C,, and C,, diterpanes are thought to mark the presence of coal fragments uniquely (Barrick et al., 1984). These diterpanes are found in high concentrations at stations 57 and 82, and in small but measurable concentrations elsewhere (Table 3). Hence, coal fragments may contribute picene derivatives to sediments in areas of Puget Sound distant from major river sources. A tetrahydrochrysene (MW =274) is present in bulk sediments and coal fragments (Figure 4). Unlike the PAH clearly associated with coal fragments, MW = 274 is measured in only slightly higher concentrations at stations 57 and 82 than at other stations (Table 3). A series of octahydrochrysenes (MW =292) and a related compound (MW =290) are conspicuously absent in coal fragments and in western Washington coals (Barrick er ul’. , 1984), but occur in sediments from stations 57 and 82 at three- to five-times the average concentration of the remaining sediments (Figure 4, Table 3). The distribution and chemical structure of these compounds suggest a biological contribution. Conclusions
Runoff or well-mixed particulate material in atmospheric fallout are major routes of introduction for combustion-derived PAH to Lake Washington and Puget Sound. However, well-defined gradients of PAH concentrations in surface sedimentsare seenin three separateareasof Puget Sound, including areaswhere aliphatic hydrocarbons show little variation. This pattern of comparable maxima for combustion-derived PAH concentrations in surface sediments from isolated regions of the sound, separatedby minima in concentration for regions lying in between, arguesagainst simple dispersalof thesechemicals from only the major municipal areasof central Puget Sound. The pattern suggests, rather, that there are other regional sourcesof combustion-derived PAH besidesthe major municipalities of central Puget Sound. PAH in the greater Puget Sound region are apparently not widely dispersedby air or water transport, but are rapidly removed to sediments within a few kilometers of each source. Combustion-derived PAH concentrations in sediment cores directly adjacent to urban centers in central Puget Sound maximized during the mid-1950s and have gradually decreasedin more recent deposits. This subsurface feature is not a general trend throughout Puget Sound and cannot always be used asa marker for this time period: cores from most stations distant from urban centres display highest combustion-derived PAH concentrations at the surface and a gradual decreasewith time in the past. Surface concentrations are on the average 2.5-times higher than concentrations in sediments deposited before major anthropogenic influence.
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Perylene is ubiquitous in Puget Sound sediments. This PAH derives erosionally from some natural terrestrial source. Evidence of in situ diagenetic production from some natural precursor is, in general, not observed. Natural erosion of coal seams by rivers and historical transshipment of mined coal in Puget Sound, peaking in the early 19OOs, have contributed various PAH to the sediments, including a characteristic suite of alkylated phenanthrene, chrysene and picene derivatives. Acknowledgements Review of this manuscript and research support by Dr Roy Carpenter was appreciated. The authors thank T. S. Bates for use of GCjMS facilities at the Pacific Marine Environmental Laboratories (NOAA) in Seattle. This research was supported by U.S. Environmental Protection Agency/Department of Energy Contract DE-AT06-76-EV70040 and U.S. Environmental Protection Agency Contract R-811249-01-0. Although research described in this article has been funded in part by the EPA through Interagency Agreement EPA-79-D-X0533 to the University of Washington, it has not been subjected to EPA review and therefore does not necessarily reflect the views of EPA, and no official endorsement should be inferred. Contribution No. 1703, School of Oceanography, University of Washington, WB-10, Seattle, WA 98195.
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