Environ. Sci. Techno/.1995, 29, 2684-2694
Miqwiius Tar Balls with a the Shoretines of P i k e William KEITH A. KVENVOLDEN,' F R A N C E S D . HOSTETTLER, PAUL R . CARLSON, A N D J O H N B. RAPP US. Geological Survey, 345 Middlefield Road, MS 999, Menlo Park, California 94025
CHARLES N. THRELKELD AND AUGUSTA WARDEN US.Geological Survey, Denver, Colorado 80225
Although the shorelines of Prince William Sound still bear traces of the 1989 Exxon Valdez oil spill, most of the flattened tar balls that can be found today on these shorelines are not residues of Exxon Valdez oil. Instead, the carbon-isotopic and hydrocarbonbiomarker signatures of 61 tar ball samples, collected from shorelines throughout the northern and western parts of the sound, are all remarkably similar and have characteristics consistent with those of oil products that originated from the Monterey Formation source rocks of California. The carbonisotopic compositions of the tar balls are all closely grouped ( 6 l 3 c p D B = -23.7 f0.2%0),within the range found in crude oils from those rocks, but are distinct from isotopic compositions of 28 samples of residues from the Exxon Valdezoil spill ( 6 l 3 C P D B = -29.4 fO.t%o). Likewise, values for selected biomarker ratios in the tar balls are all similar but distinct from values of residues from the 1989 oil spill. Carbon-isotopic and biomarker signatures generally relate the tar balls to oil products used in Alaska before -1970 for construction and pavements. How these tar balls with such similar geochemical characteristics became so widely dispersed throughout the northern and western parts of the sound is not known with certainty, butthe great 1964Alaska earthquake was undoubtedly an important trigger, causing spills from ruptured storage facilities of California-sourced asphalt and fuel oil into Prince William Sound.
Introduction The largest oil spill in U.S. history occurred when the tanker Exxon Vuldez grounded on Bligh Reef in Prince William Sound, AK, on March 24, 1989. The tanker spilled about * Corresponding author telephone: 415-354-3213; fax: 415-3543191; e-mail address:
[email protected].
2684 ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 29, NO. 10, 1995
41 million L [ll million (US.) gal = 258 000 bbl] ofAlaskan North Slope crude oil, some of which reached about 16% (500km) of the shorelinesof the sound; cleanup operations and natural weathering processes have now removed much of the oil from the affected shorelines (I, 2). Starting in 1990 and continuing in 1992-1994, we collected and analyzed oil-like residues from shorelines throughout the northern and western parts of the sound. In a preliminary geochemical study of eight of the first samples collected, we discovered that six samples were residuesof North Slope crude oil, presumably from the Exxon Vuldez oilspill, but two samples had molecular and carbon-isotopic characteristics suggestive of oil products that originallycame from the Monterey Formation of California (3). These two samples came from localitiesabout 100 km apart on Storey Island and Elrington Island (Figure la), leading to the conclusion that oil residues with similar geochemical characteristicsshould be commonly observed on shorelines of the sound. This conclusion has now been verified. On the basis of the carbon-isotopic and biomarker characteristics of 61 samples collected from widely dispersed localities (Figure la),we show that tar balls with a Califomiasource signature appear to be ubiquitous on the shorelines of the northern and western parts of Prince William Sound.
Experimental Methods Carbon-Isotopic Analyses. Oil-like residues (91 samples) from shorelines of Prince William Sound (Figure 1) and a sample of North Slope crude oil, impounded from the tanker Exxon Vuldez immediately after the 1989 oilspill, were dissolved in dichloromethane. In addition, 19 samples of oil products used in Alaska for construction and pavements were also dissolved in this solvent. The resulting solutions were filtered through glass wool and concentrated to remove the solvent;a portion (40-90 mg) of each extract was then recovered for a determination of carbon-isotopiccomposition. For this determination, at least 4 mg of each extract was placed in an evacuated quartz tube with cupric oxide and a strip of silver metal and was combusted to 840 "C. The resulting COz was purified under vacuum by differential temperature transfer and measured by isotope-ratio mass spectrometry. The results are reported in delta (6)notation in parts per thousand (%o) relative to the PeeDee belemnite (PDB) standard. Adsorption Chromatography. Remaining portions of the extracts (a total of 78 samples each weighing 20-40 mg) were redissolved in dichloromethane and filtered through a column of activated copper to remove any elemental sulfur. These resulting extract solutions were fractionated to obtain a mixture of aliphatic hydrocarbons, using adsorption chromatography. This fractionation involved exchanging the dichloromethane solvent with hexane and separating this mixture on a column that was layered from bottom to top with 2.5 g of deactivated (5% water) neutral alumina and with 2.5 g of Davison No. 62 and 5 g of Davison No. 923 activatedsilica gels. The column was eluted sequentially with 25-35 mL of each of the following solvents: hexane; 20, 40, and 60% benzene in hexane; benzene; and methanol to produce six fractions, only the first of which is considered here. The first, or hexane, fraction yielded a mixture containing n-alkanes,
This article not subject to U S . co yright Published 1995 by the American Chemical gociety:
N
I ,
,.-
-
GULF OF ALASKA 0
10 20
30 40 50
KILOMETERS
ALASKA
CANADA
PRINCE WLUAM SOUND
E R I N 0 SEA
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FIGURE 1. Prince William Sound area and southern Alaska. showing location of oil-like residue sample sites: (a) tar balls (samples 1-611 and oil products (samples 301 -309 and 3151: Ibl Exxon Valdezoil and residues lsamples 101 --1281and exceptions(samples 201. 203). dashed line indicates Exxon Valdezoil spill trajectory: (cIoil products. such as pavements lsamples 308-3191. Sample numbers are lisled in Tables 1-3
isoprenoid hydrocarbons (includingpristane and phytane), and alicyclic hiomarkers. Gas Chromatography and Mass Spectrometry. A portion of each hexane fraction was fust analyzed for the distributions of alkanes hy gas chromatographywithtlameionization detection, utilizing a 30 m x 0.3 mm DB-1 bonded-phase, fused-silica capillary column and the following instrument parameters: initial temperature, 90 "C for3 min with aramp of4 "Clmin to 310 "C and a final hold for 20 min; injector and detector temperatures, 300 "C; column-inlet pressure, 10 psi of helium; and splitless injection. After gas chromatography, a second poiion of each hexane fractionwas analyzed foralicyclic biomarken hy gas chromatographylmassspectrometry, utilizing a 30 m x 0.3 mm SE-54 bonded-phase, fused-silica capillary columnwith splitlessinjection and the followinginstrument parameters: initial temperature, 150 OC with ramps of 30 " C h i n to 200 "C and 1 " C h i n to 300 "C. Alicyclic biomarkers were analyzed by selected ion monitoring of mass-to-charge(rnfz)ratios of 177 for 25-norhopanes, 191 for terpanes (tricyclic and tetracyclic terpanes and pentacyclic triterpanes), and 217 for steranes. Identification of
25-norhopaneswas based on the work by Curiale et al. (4); compound identifications of terpanes and steranes were based in part on a previous study of North Slope crude oil (5).Selectedratiosofterpanes and steraneswere calculated from peak heights on mass chromatograms.
Results Since the 1989 E n o n Valdez oil spill, two geochemical papers (6, 3 , in addition to a preliminary report by Kvenvolden et al. (3).have considered mainly the spilled North Slope crude oil and its weathered residues. Page et al. (6)provided a comprehensive evaluation of the impact of the oil spill on the benthic (subtidall sediments. which were shown to contain a preexisting background of petroleum-seep oil, and Hostettler and Kvenvolden (7) gave a detailed description of the geochemical changes that have taken place in the spilled crude oil on the basis of shoreline residues fromnine localities. In another study, in which carhon-isotopic compositions of whole-oil residues were used as the principal method of identification and correlation, Kvenvoldenetal. (8)reportedon39samples of oil-like residues collected in an effortto understand the VOL. 29.
NO. 10.1995 I ENVIRONMENTAL SCIENCE &TECHNOLOGY m 2685
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ENVIRONMENTAL SCIENCE &TECHNOLOGY / VOL. 29, NO. 10,1995
source and fate of oil spilled in Prince William Sound. The present study expands our preliminary work to include the carbon-isotopic compositions of 111 samples (1 oil and 110oil-like residues) and the molecular compositionsof 78 of these same samples. The results are summarized in Tables 1-3. The gas chromatographic distributions of alkanes in representative shoreline residues are shown in Figure 2. Figure 2a compares the distributions in sample 1 (asphalt mat at an old asphalt-storage plant) with sample 25 (tar ball on Storey Island), typical of the distribution of alkanes in all of the other tar ball residues listed in Table 1 (see Figure l a for locations). In general, n-alkanes are absent or present in low amounts, as are the isoprenoid hydrocarbons (pristane and phytane). An unresolved complex mixture (UCM) of alkanes is typical of these residues as well as of other weathered crude oils (9). Figure 2b comparesthe distributions of alkanes in sample 101 (Exxon Vuldez oil) with those in sample 115 (oil residue on Knight Island), which is typical of all the other residues listed in Table 2 (see Figure l b for locations). The n-alkanes and isoprenoid hydrocarbons are present in the Exxon Vuldez oil but are generally absent or present in very low amounts in the weathered residues of this oil, and a UCM is present in all the residues. Figures 3 and 4 compare mass chromatograms of the terpanes (mlz 191) and steranes (mlz 2171, respectively, in the same samples shown in Figure 2. A good correlation exists between the two tar samples (Figures3a and 4a) and between the Exxon Vuldez oil and residue samples (Figures 3b and 4b); however, the mass chromatograms of the tar samples and the other samples listed in Table 1 and the ExxonValdez-related samples (Table 2) are distinctly different. The distributions of terpanes and steranes can be described in part by various biomarker ratios. For the purposes of this paper, we selected the following parameters, the values of which are listed in Tables 1-3: (a) Tm/Ts, 17a-22,29,30-trisnorhopane/l8a-22,29,30trisnomeohopane. This ratio was proposed as both asource and a maturity parameter by Seifert and Moldowan (10). (b) Triplet, [Czs-tricyclic terpane (S?) C26-tricyclic terpane (R?)]/Ca4-tetracyclicterpane. This source parameter was first noticed in a study of North Slope crude oil (5) in which the ratio is -2. Exxon Vuldez oil (an Alaskan North Slope crude oil) and its residues have triplet ratios of -2; in contrast, tar balls of the sound have triplet ratios of -5 (Tables 1 and 2). (e) C30/C29,17a,21fl(H)-hopanel17a,21fl(H)-30-norhopane. This ratio was used by Palacas et al. (11) as a sourcerock parameter. (4 CJ1 S/(S+R), 17a,21fi(H)-homohopane(22S)/17a, 21/?(H)-homohopane(22s) (22R). This epimer ratio is a typical terpane-maturity parameter used extensively in petroleum geochemistry (12, 13). (e)BTO, 17a,18a,21fl(H)-28,30-bisnorhopane, 17a,18a, 21,!?(H) -25,28,30-trisnorhopane (the dominant 25-norhopane), and oleanane. These compounds are absent in the Alaskan North Slope crude oil, spilled from the &on Vuldez tanker, but are present in tar balls of the sound and in oil products that originally came from crude oils produced in California and likely sourcedfrom the Monterey Formation
+
+
(3). (fl CZ9S/ (S+R),24-ethyl-5a,14a,17a(H)-cholestane (2OS)/ 24-ethyl-5a,14a,17a(H)-cholestane (20s) (20R). This
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VOL. 29, NO. 10, 1995 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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I-
---
rrl
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FIGURE 2. Gas chromatograms of alkanes in oil-like residues on shorelines of Prince William Sound (see Figure 1 for locations): (a) comparison of distributions of alkanes in sample 1 (asphalt mat at site of old asphalt-storage plant) and sample 25 (tar ball from Storey Island); (b) comparison of distribution of alkanes in sample 101 (Exxon Yaldezoil) and sample 115 (oil residua on Knight Island). Pr, pristane; Ph, phytane; UCM, unresolved complex mixture; nC17 and RCB, nalkanes in an homologous series.
sterane-epimer ratio is commonly used in petroleum geochemistry as a maturity parameter (14). (g)C28/C29, 24-methyl-5a,14a,l7a(H)-cholestane(20R)/ 24-ethyl-5a,14a,17a(H)-cholestane (20R). This source parameter has been modified from discussions of Grantham and Wakefield (15) and Waples and Machihara (16). All of these ratios have been adapted from petroleumgeochemical applications and applied by us for correlation and differentiation among the sample sets.
Discussion Carbon-isotopic compositions and biomarker ratios clearly differentiate two populations of oil-like residues on the shorelines of northern and western Prince William Sound One is composed of flattened tar balls and a few tar mats (collectively referred to here as tar balls), and the other is made up of weathered residues from the Exxon Vuldez oil spill. Typically, the tar balls occur as small splotches on the rocks, generally near the high-tide line. Commonly, the tar balls are hard and break with a shiny, conchoidal fracture. Some of the tar balls were sticky, especially those 2690 B ENVIRONMENTAL SCIENCE &TECHNOLOGY / VOL. 29, NO. 10.1995
exposed to the sun on a warm day. The tar balls were observed on shorelines from the site of the old town of Valdez at the east end of Port Valdez in the north end of the sound to the southwest end of the sound at Elrington Island (Figure la). Residues from the Exxon Vuldez oil spill vary in appearance, depending on the degree ofweathering,and range in consistency from light-brown oil, through sticky black oil and tar, to a powder-like solid. With increasing weathering,residuesfrom the Exxon Vuldezoil spill become increasinglydifficult to distinguishfrom non-Exxon Vuldez tar balls by appearance only; that is, some of the Exxon Vuldezresidues have acquired a tar ball look. Exxon Vuldez residues, with one exception, were found on shorelines in the western part of the sound from south of Bligh Reef to Elrington Island (Figure lb). Sample 128 (UnakwikInlet), which was from a locality north of the oil-spill trajectory, likely floated north from the area of the oil spill and stranded in Mueller Cove on the west shore of the inlet. The nonExxon Vuldez tar balls are dispersed over a larger area than are the Exxon Vuldez residues. Carbon Isotopes. The carbon-isotopic compositions (6%, abbreviated 6 in the following text) of the 61 tar ball samples from shorelines throughout northern and western Prince William Sound average -23.7 f 0.2%0 (Table 1). These 6 values are all remarkably similar and distinct from those of Exxon Vuldez oil and the 27 residue samples, which have 8 values averaging -29.4 f 0.1%0 (Table 2). The carbon-isotopic compositions of the tar balls are similar to those of old oil products (-23.7 f 0.7%0)used in Alaska for constructionand pavements before -1970 (Table 31. These products include caulking materials, fluids used in mining, stored oil, street pavements from the town ofwhittier, and pavements at old airport runways in southern Alaska extending from Gustavus in the east to Attu in the west (Figure IC). These oil products were shipped to Alaska by barge from California (17). Whittier, on the west edge of the sound, and Valdez, at the north end, served for more than 50 years as ports for storage of fuel oil and asphalt from California. The newer pavements at five airport runways (Table 3) have 6 values significantly lighter (-28.2 f l.1%0)than the old runways, suggesting sources of oil products other than from California. Table 4 summarizes the average values of carbon-isotopic compositions of the tar balls, oil, oil residues, and oil products listed in Tables 1-3.
Of the 91 samples of shoreline residues, only three have anomalous carbon-isotopic compositions (Table 2). Samples 202 (6 = -26.6%0) and 203 (6 = -27.8%0) from Green and Culross Islands, respectively,have 6 values that fall between the two principal populations of 6 values of the oil-like residues that we found in the sound (Figure 5a). These two samples likely come from sources unrelated to either the Monterey-sourcedtar balls or to the Emon Vuldez oil residues. Sample 201 is analytically suspect (81 and is omitted from Figure 5a. Biomarkers. Biomarkers are geochemical organic compounds that have carbon skeletons which can be related to their biologic precursors. In our study, we focused on terpanes and steranes because these biomarkers are common in crude oils and are more resistant to degradation and weathering than n-alkanes and isoprenoid hydrocarbons (18).Average values of biomarker ratios (Table 41, as defined previously, support our contention that two principal populations of oil-like residues are present on
a
b
Exxon Vddez Oil 101
t
.E:s,a
A
a"
t
J
B 6 ::
Knight Island
a"
Time
-
Time
-
FIGURE 3. Mass chromatograms of terpanes (dz191) in oil-like residues on shorelines of Prince William Sound (see Figure 1 for locations): (a) comparison of distributions of terpanes in sample 1 (asphalt mat at site of old asphelt storage plant) and sample 25 (tar ball from Storey Island); (b) comparison of distribution of terpanes in sample 101 (Exxon Yelder oil) and sample 115 (oil residue on Knight Island). Triplet, [Cdetracyclic terpane, &tricyclic terpane (R?), &tricyclic terpane (S?)l;Ts. 18a-22,29,30-trisnomeohopane; Tm, 17a-22,29,3O-trisnorhopane; 6, bisnorhopane [17a,18a2lB(H)-28,3O-bisnorhopanel; 0, oleanane; I& 17a2l/?(H)-30-norhopane; Ca, 17a,21/3(H)-hopane; Csl (R and S), 17a,21/3(H)-homohopane (22R and 22s).
the shorelines of northern and western Prince William Sound. All biomarker ratios of shoreline residues show two populations: one composed of Exxon Valdez oil and its residues, and the other composed of the tar balls (Figure 5). These two populations are clearly differentiated by the triplet ratios (Figure 5c) and the epimer ratios of C B ~ homohopane and CZ9sterane (Figure 5e and 0. The C Z ~ sterane-epimer ratios of Exxon Valdez residues vary widely (0.44-0.73, Table 4);the four values exceeding 0.53 [the approximate equilibrium value of this ratio (1911are likely the result of biodegradation, involving preferential loss of the 20R epimer (20, 21). Another characteristic of the two residue populations is that the tar balls all contain the biomarkers 28,30-bisnorhopane, 25,28,30-trisnorhopane,and oleanane,whereas these compounds are absent in the Exxon Valdez oil and its weathered residues (Tables 1, 2, and 4). Furthermore, the values of biomarker ratios of the tar ball samples are similar to those of the old oil products used in Alaska (compare Tables 1,3, and 41, although the values for the old oil products vary more widely than do those of the shoreline tar balls. Also present in the old oil products are 28,30-bisnorhopane,25,28,30-trisnorhopane,and oleanane (Table 3). California Source. Not only does a geochemical correlation exist between the shoreline tar balls and the old oil products, but these substances also have geochemical characteristicsthat demonstrate a common origin: that is, they appear to have originated from crude oils produced
in California; the source rock for these crude oils is the Monterey Formation. Carbon-isotopic compositions (6 values) and biomarker ratios support this assertion. First, the 6 values of the tar balls and old oil products, ranging from -22.7 to -24.8%0, are heavier than those of most known crude oils, except those from California that were produced from the Monterey Formation. The 6 values of these Californiacrude oils fall in the unusual range of about -25 to -21% (4, 22, 23). Thus, the carbon-isotopic compositionsof the tar balls and old oil products fall within the range of values characteristic of Monterey-sourced California crude oils. Second, two of the biomarker ratios in the tar ball samples are characteristic of the Monterey-sourced California crude oils studied by Curiale et al. ( 4 ) . For example, the hopane- and sterane-epimer ratios of the tar balls [C31 S/(S+R) = 0.54 f 0.01 and C29 S/(S+R) = 0.34 & 0.02, respectively (Table 411 and of the old oil products [CN S/(S+R) = 0.53 f 0.02 and C2g S/(S+R) = 0.35 f 0.04, respectively (Table 4)) are unusually low and fall within the low ranges found in the California crude oil, in which hopane-epimer ratios range from 0.51to 0.61 and steraneepimer ratios from 0.22 to 0.52. Perhaps most important in assigning a possible source, the tar balls and old oil products contain 17a,18a,21B(H)-28,30-bisnorhopane, 17a,18a,21j3(HJ-25,28,30-trisnorhopane, and oleanane,biomarkers that are characteristic of many Monterey-sourced Californiacrude oils ( 4 ) . These same biomarkers,however, are absent in the Alaskan North Slope crude oil spilled by VOL. 29, NO. 10, 1995 I ENVIRONMENTALSCIENCE &TECHNOLOGY
2691
a
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Knight Island 115
Time Time
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FIGURE 4. Mass chromatogramsof steranes (ntlt217) in oil-like residues on shorelines of Prince William Sound (see Figure 1 for locations): (a) comparison of distributions of steranes in sample 1 (asphalt mat at site of old asphalt storage plant) and sample 25 (tar ball from Storey Island); (b) comparison of distribution of steranes in sample 101 (hen Yaldez oil) and sample 115 (oil residua on Knight Island). Ca (R), 24-methyl-5a.l4a,l7a(H)-cholestane (MR);Ca (SI,2eethyl-5cL14a,17a(H)-cholestane(20s); CZS (R), 24-ethyl-5a.l4a,17a( H)-cholestane (20R). TABLE 4
Mean, Staudd Deviation, and Range of Carbon-lse~cCompositions and Biomarker Ratios in Oil-like Residues and Products Related in Prince William Sound, AKB mlz 191 S'3C
(")
Tm/Ts
tar balls (Table 1)
-23.7f0.2 1.6f0.1 -22.8 to -24.6 1.3 to 1.9 (61) (39) Exxon Valdez oil and residues -29.4 f 0.1 1.3 f 0.2 (Table2) -29.1 t o -29.6 0.82 t o 1.6 (28) (25) products and pavements before -23.7 f 0.7 2.1 f 0.6 -22.7 to -24.8 1.8 to 2.7 -1970 (Table3) (14) (8) pavements after -1970 (Table3) -28.2 f 1.1 1.4 i 0.2 -27.1to-29.6 1.2t01.5 (5) (3)
nl/z 217
triplet
Cd&
5.1f0.5 3.8 t o 5.9 (39) 2.0 f 0.1 1.6 to 2.2 (25) 4.7 f 1.6 2.5 to 7.5
1.8f0.1 1.6 to 2.1 (39) 1.5 f 0.1 1.3 to 1.7 (25) 1.6 f 0.2 1.4 t o 2.1
0.54f0.01 0.34f0.12 0.51 to 0.57 0.30 to 0.43 (39) (39) (39) 0.59 f 0.02 - 0.51 f 0.07 0.57 t o 0.62 0.44 t o 0.73 (25) (25) (25) 0.53 f 0.02 0.35 f 0.04 0.50 t o 0.56 0.28 to 0.41
(81
(8)
(8)
Cn S/(S+R)
ET0
CB S/(S+R)
+
+
1.8 f 0.3 1.7 f 0.2 0.57 f 0.01 1.6to2.1 1.5to1.9 0.56to0.58 (3) (3) (3)
(8) (8)
-
CdC, l.lfO.l 0.96 t o 1.2 (39) 0.57 f 0.09 0.40 to 0.73 (25) 1.2 f 0.1 1.1 t o 1.4
(8)
0.43 f 0.04 0.66 f 0.07 0.39 to 0.46 0.62 to 0.74 (3) (3) (3)
"Abbreviations are as defined in Table 1. The number of samples is given in parentheses.
the Exxon Vuldez tanker and in the weathered residues from that spill. ubiquitous Tar Balls. Still in doubt, however, is an explanation for the widespread dispersal of Californiaderived tar balls with such similar carbon-isotopic and biomarker characteristics throughout the northern and western parts of Prince William Sound. Kvenvolden et al. (8)suggested that oil products were spilledduringthe great 1964Alaska earthquake from asphalt- and fuel oil-storage facilitiesat the old Valdez townsite in the Port Valdez fjord (Figure la) and then transported southward through the sound. New support for this suggestion comes from the observation that 61 of the flattened tar balls that we examined are geochemically nearly identical in carbonisotopic and biomarker compositions to the asphalt mat 2692
ENVIRONMENTAL SCIENCE &TECHNOLOGY / VOL. 29, NO. 10, 1995
found at the site of the asphalt-storage plant and tank farm at the old Valdez townsite. Only one of these tar balls [sample 13, from north of Elf Point (Table 111 has a 6 value (-22.8%) significantlyheavier than the average for all 61 tar ball samples (6 = -23.7 & 0.2%0),suggesting a different origin; however, the biomarker ratios in this sample are similar to those in the other tar balls (Table 1). According to Wilson and T0rum (24),-30% of the areal extent of the fjord of Port Valdez was contaminated with asphalt from the damaged tank farm after the earthquake. We could find no record of any asphalt cleanup, and it is possible that the asphalt moved from the east end of Port Valdez into the main body of Prince William Sound. The transport process, in very cold water, by which asphalt managed to leave essentially a point source in Port Valdez and end up
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FIGURE 5. Histograms showing distributions of the following parameters in tar balls lblack barsl and EXXOII Yaldez oil and residues (gray bank (a1 8°C: Ibl Tmlls: IC1 triplet: Id1 CdCn: lel 41S/IS-Rl: Ill Ca S/IS-R): and Is) Ca(Rl/CnlR). Parameters are defined in the ten and in Table 1.
on various shorelines as far south as Elringron Island is uncertain (Figure la). Alternatively. the tar balls on the shorelines of northern and western Prince William Sound might be from multiple
small spills of oil products that have occurred over time from other storage facilities such as at Whinier and from canneries. fisheries, docks, and residences, an idea that might hener explain the widespread distributionoftarballs. VOL. 29. NO. 10.1995 I ENVIRONMENTAL SCIENCE &TECHNOLOGY. 2693
Our study of old oil products used in Alaska (Table 31, however, shows that their range of carbon-isotopic and biomarker compositionsare generally wider than those of the ubiquitous tar balls on the shorelines (Table 4). If the tar balls resulted from multiple small spills of different oil products, we would expect a wider variation in carbonisotopic and biomarker compositions than we observed. Thus, the most reasonable explanationthus far is that the ubiquitous tar balls came mainly from one spill, triggered by the 1964 Alaska earthquake. If more than one spill was involved, then the various spilled oil products must have been nearly identical in their geochemical characteristics.
Summary Non-Exxon Vuldeztar balls are widely dispersed throughout the northern and western parts of Prince William Sound, over an area larger than that in which Exxon VuZdezresidues can still be found. These non-Exxon Vuldez tar balls are residues of oil products that were originally shipped from California, and they were likely spilled into the sound as a result of the great 1964 Alaska earthquake. These tar balls can be found on many protected shorelines, generally near the high-tide line. On any given shoreline, the occurrence of tar balls has never been observed to be extensive. Carbon-isotopicand biomarker compositions of these tar balls were used to characterize and distinguish the oil-like residues found throughout the northern and western parts of the sound. Of the 90 samples of shoreline residues that we examined, only two came from unidentified sources. The other residues came either from a spill or spills of California-sourced oil product (61 samples) or from the Exxon Vuldez oilspill (27 samples). This report demonstrates the utility of carbon-isotopic and biomarker compositions in tracking environmental contamination of petroleum-related residues in estuarine systems.
Acknowledgments This research was supported by the U.S. GeologicalSurvey and the Minerals Management Service of the Department of the Interior. We are grateful to the officers, crew, and scientific parties aboard the U.S. National Oceanic and Atmospheric Administration ships McArthur and Rainier, especially W. Grondlund of the U.S. National Marine Fisheries Service, for their interest and assistance on the sampling cruises. We thankP. Barnes of the U S . Geological Survey for serving as captain of the research vessel Kurluk N. and J. Lethcoe of Alaskan Wilderness Sailing Safaris for providing logistical support and vital information on sampling locations; L. Evanoff of Chenega Bay for guidance to sampling locations on Evans Island; and the Alaska Department of Environmental Conservation for discussion of oil-spill trajectory and sample locations.
Literature Cited
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Received for review April 5, 1995. Revised manuscript received June 15, 1995. Accepted June 15, 1995.@
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2694 1 ENVIRONMENTAL SCIENCE &TECHNOLOGY / VOL. 29, NO. 10,1995
‘Abstract published in Advance ACS Abstracts, August 1, 1995.
