Environ. Sci. Technol. 1084, 18, 840-845
technique can be used for the prediction of the evaporation curve only; in general it should not be used for producing samples. It is recommended that several Arctic oils be subjected to evaporative behavior determination as described in this report. I t may also be useful to extend this work to evaporation of chemical spills.
Literature Cited National Academy of Sciences “Petroleum in the Marine Environment”;National Academy of Sciences: Washington, DC, 1975. Malins, D. C. ”Effects of Petroleum on Arctic and Subarctic Marine Environments and Organisms”, Academic Press: New York, 1977; Vol. I. Jordan, R. E.; Payne, J. R. “Fate and Weathering of Petroleum Spills in the Marine Environment”; Ann Arbor Science: Ann Arbor, MI, 1980. Yang, W. C.; Wang, H. Water Res. 1977,11,879-887. Butler, J. N. In “Transfer of Petroleum Residues from Sea to Air: Evaporative Weathering. Marine Pollutant Transfer”; Windom, H. L.; Duce, R. A., Eds.; Lexington Books: Lexington, MA, 1976; pp 201-212. Sivadier, H. 0.;Mikolaj, P. G. Symp. Prev. Control Oil Spills 1973, 475.
( 7 ) Mackay, D.; Leinonen, P. J. “Mathematical Model of the Behaviour of Oil Spills on Water with Natural and Chemical Dispersion”, prepared for Fisheries and Environmental Canada, 1977, Economic and Technical Review Report EPS-3-EC-77-19. (8) Mackay, D.; Matsugu, R. S. Can. J. Chem. Eng. 1973,51, 434-440. (9) Mackay, D.; Paterson, S.; Nadeau, S. Natl. Conf. Control Hazard. Mater. Spills 1980, 361-368. (10) Mackay, D.; Stiver, W.; Tebeau, P. A. F’roc.-Oil Spill Conf. 1983,331-337. (11) Reijnhart, R.; Rose, R. Water Res. 1982, 16, 1319-1325. (12) Payne, J. R.; Kirstein, B. E.; McNabb, G. D.; Lambach, J. L.; de Oliveira, C.; Jordan, R. E.; Ham, W. Proc.-Oil Spill Conf. 1983, 423-434. (13) Drivas, P. J. Environ. Sci. Technol. 1982, 16, 726-728. (14) Feigley, C. E. Enuiron. Sci. Technol. 1983, 17, 311-312. (15) Mackay, D.; Yuen, A. Environ. Sci. Technol. 1983, 17, 221-217. (16) Zwolinski, B. J.; Wilhoit, R. C. API Publ. 1971, No. 101 (44-TRC).
Received for review September 12,1983. Accepted May 21,1984. Financial support was provided by the Arctic Marine Oilspill Program of Environment Canada.
Aspects of the Polycyclic Aromatic Hydrocarbon Geochemistry of Recent Sediments in the Georges Bank Region Paul D. Boehm’ Batteile New England Marine Research Laboratory, Duxbury, Massachusetts 02332
John W. Farrington Coastal Research Center and Chemistry Department, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543
rn Polycyclic aromatic hydrocarbon (PAH) concentrations and compositions were determined seasonally over 1year at 22 sampling stations on and adjacent to Georges Bank, off the Northeastern U.S. coast. PAH concentrations are directly related to the total organic carbon (TOC) content of the sediments and to the slit/clay content of these sediments. Several groupings of two-ringed to five-ringed PAH compounds were quantified, and concentrations of these groups ranged from 1 to 100 ppb, dry weight. The overall compositions of the PAH compounds indicate that pyrogenic (combustion-derived) PAH dominate the assemblage at higher levels while lower levels are often associated more with a fossil fuel PAH origin. The relationship of PAH to TOC, the ratio of fossil fuel to combustion PAH, and the absolute concentrations of PAH form a useful set of monitoring parameters in these and other continental shelf regions.
Introduction The ubiquity of polycyclic aromatic hydrocarbon (PAH) residues in sediments and soils has been well established on a global basis. Previous reports of PAH distributions (1-10) have addressed aspects of the distribution of PAH in marine sediments. The distribution of PAHs, in marine sediments is governed by four transport processes: (i) aeolian transport of fossil fuel and wood combustion products followed by deposition on the sea surface and subsequent sedimentation; (ii) riverine transport of com840
Environ. Sci. Technol., Vol. 18, No. 11, 1984
bined PAH sources (e.g., stormwater runoff, municipal sewage effluents, harbor oil spillages, and industrial inputs) in estuarine systems; (iii) direct introduction of waste materials via pipeline or barge disposal; (iv) resuspension of materials reaching coastal marine sediments via (i) and (ii) and deposition in settling areas. The Georges Bank region of the continental shelf off the Northeastern United States is an area of high productivity (11, 12) and an area of dynamic sediment transport mechanisms (13,14). It is also an area of interest to the offshore petroleum industry. This study focuses on defining the levels and generic sources of PAH compounds in the sediments of Georges Bank and the areas immediately adjacent to the bank. Such information is important to the development of diagnostic parameters for use in marine monitoring programs to assess any change in the organic geochemistry of the recent sediments of the region. We also present results on relatively small scale spatial and temporal variations in PAH levels and compositions in continental shelf sediments for the first time. Aspects of the saturated hydrocarbon geochemistry of the region have been presented elsewhere (15).
Experimental Section Sampling Methods. Samples of surface sediments from the region were obtained over a period of five years (1977-1982). On several cruises, Smith-MacIntyre (0.1 m2) grab samplers were used for all collections, and a 0-3-cm
0013-936X/84/0918-0840$01.50/0
0 1984 American Chemical Society
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Figure 1. Location of sampling stations. (0)1977 sampling stations: (A)1981-1982 sampling stations.
section of sediment was obtained as a subsample from each grab. All sediment samples were stored frozen prior to laboratory processing. Sampling Locations. Sampling locations are shown in Figure 1. Samples were obtained for PAH analysis during two or more seasons from 12 stations between Feb and Nov 1977 and at eight other stations during one season of 1977. Not all stations were sampled in all seasons. Additionally, two stations (22A and 37A) were sampled in the fall of 1981 and winter of 1982. These latter two stations were located near the head of the Oceanographer Canyon and in the &mudpatch" depositional region south of Nantucket (see Figure 1). The stations sampled in this study represented the major benthic biota1 habitats and geochemical regimes (i.e., a range of coarse-grained to fine-grained sediments) in the area. Analytical Methods. Sediment samples were solvent extracted by one of a two comparable methods: (i) toluene-methanol azeotropic Soxhlet extraction of a freezedried sediment (1977-1978 samples); (ii) methylene chloride-methanol extraction by an ambient temperature shaker table, of methanol-dried sediment (1980-1981 samples) (ref 2, 15, and 16 for details). The wet sediments were spiked with an internal standard (o-terphenyl or hexaethylbenzene) prior to extraction. The solvent extracts were dried over sodium sulfate and reduced in volume by rotary evaporation to 0.5 mL. The entire solvent extract or a total of 50 mg of extractable material, whichever was less, was fractionated by alumina (5% deactivated)/silica gel (100% activated) adsorption column chromatography. The saturated (hexane eluate) and aromatic/olefinic (hexane-methylene chloride, 6040) fractions were collected. Analyses of the saturated fractions (fi) were conducted by gas chromatography with flame ionization detection (GC/FID) (15). The aromatic fraction (fi) was concentrated by rotary evaporation and gentle nitrogen blowdown to 0.5 mL. The concentrate either was analyzed directly by computer-assisted gas chromatography/mass spectrometry (GC/MS) or was further fractionated by a Sephadex LH-20 column according to the procedure of h o s and Prohaska (17). The Sephadex fraction containing PAH compounds was analyzed by GC/FID with compound identities confirmed by GC/MS. Analysis of PAH Gas Chromatography (Flame Ionization Detection). PAH compounds in the 1981-1982 samples were analyzed by GC/FID after Sephadex fractionation of the alumina/silica f i fractions. Peak areas of aromatic compounds were compared to the
internal standard amount and final compound concentrations determined after correcting for relative GC/FID response factors. PAH compounds were identified with authentic standards. Where standards were not available (e.g., for the case of alkylated homologues of PAH), compounds were identified in crude oil extracts by GC/MS, and the identified peaks on the GC/FID trace of the same oil were used as retention time standards. GC/MS Analyses of PAH. The 1977 samples were quantitatively analyzed by GC/MS for their PAH content. A subset of the 1981-1982 samples were analyzed by GC/MS to confirm the identification of components identified by GC/FID. The aromatic fractions from the silica gel/alumina column chromatography were analyzed for polynuclear aromatic hydrocarbons by GC/MS. An aliquot of the fraction was analyzed by using a Finnigan 4530 quadrupole instrument equipped with an 0.25 mm X 30 m SE 54 fused silica capillary column (J & W Scientific), which was threaded directly into the ion source. Instrumental conditions included an ionization voltage of 70 eV and scan conditions of mlz 45-450 at one scan per second. Selected ion searches were used to obtain ion chromatograms for aromatic compounds with known retention indexes that were suspected to be present in the samples. If necessary, the mass spectrum and retention time of an identified peak was retrieved and compared with an authentic standard or to a mass spectrum library to aid in its identification. Concentrations of the identified compounds were determined by measuring the peak areas of the appropriate peaks in the selected ion chromatograms and comparing them to the area of the internal standard peak (o-terphenyl). Relative response factors (relative to o-terphenyl) for each component were calculated by GC/MS analyses of quantitative analytical standards, if available, or were extrapolated when standards were not available.
Results and Discussion The concentrations of compounds within the naphthalene (two-ring) and phenanthrene/anthracene (three-ring) homologous series, including the parent (unsubstituted) and C1 (methyl) and C2 (dimethyl, ethyl) homologues, were determined, as well as the four-ringed compound groupings of fluoranthrene + pyrene and benzanthracene + chrysene + triphenylene, and five-ringed, compound groupings of benzofluoranthenes + benzopyrenes perylene. The quantitative results (Table I) indicate that there is a wide range of concentrations of these compound groupings, from less than 1 (detection limit) to 100 ppb. The grouping of station results based on seasonally averaged total (two to five rings) PAH and TOC content (Table I) indicates that three main groups can be identified. PAH levels in group 1sediments on Georges Bank proper (e.g., stations 4,9,11-13, 16, 17, 20,22A, 29, 30, and 37) are quite low with concentrations of total PAHs from 5 to 30 ppb, concentrations of phenanthrene/anthracene typically 2-5 ppb, concentrations of fluoranthene + pyrene generally 1-10 ppb, and concentrations of benzofluoranthenes + benzopyrenes + perylene typically 1%) clay content (15)and TOC values of 3-6 mg/g. These sediment stations are all located in deeper water depths along the southern edge of the bank (station 8), a t the head of Ly-
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Environ. Sci. Technol., Voi. 18, No. 11, 1984
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donia Canyon (station 23), and off the northern edge of the bank (stations 36 and 40). Station 36 on the northern slope and station 23 a t the head of the Lydonia Canyon contain similar PAH levels: phenanthrene/anthracene at 5-10 ppb; fluoranthene/pyrene at 10-40 ppb, and the benzofluoroanthenes/benzopyrenes/peryleneat 1G50 ppb. The results of station 1 and 33 are anomalous in that elevated PAH levels are apparently not accompanied by elevated TOC levels. Note that the PAH composition of station 33 is also somewhat anomalous in that most of its PAH content appears to be petroleum derived, with the naphthalene and phenanthrene homologues dominant. The highest total PAH concentrations, 100-400 ppb, are found a t group 1stations 6, 7, 37A, and 42, all with clay content >lo% and TOC content greater than 6.0 mg/g. Station 42 is found within the Gulf of Maine depositional area known as Murray Basin while stations 6 and 37A are located in the “mud patch” region west of Georges Bank. Station 42 values are quite similar to those determined by Windsor and Hites (7) at a station just to the north. The relationships of PAH levels to silt/clay content and hence to TOC (Table 1; Figure 2) suggest that sedimentological trends, which result in deposition in certain areas, largely determine the PAH levels in a given region. The relationship of phenanthrene/anthracene to TOC levels (Figure 2) and that of the four- and five-ringed compounds to TOC (not shown) suggest a strong positive correlation ( r = 0.93) between the concentrations of the larger PAH molecules and TOC levels. Therefore, there is also a direct relationship between the depositional environment and the PAH content. The area known as the “mud patch” (stations 37A, 6, and 7) is an active depositional area (15,19) and hence is characterized by high PAH levels. Intermediate PAH concentrations are found at stations receiving some fine-grained material, which contains greater amounts of PAHs. Such PAH-laden silt/clay is eroded from the shallower Georges Bank area or transported to these relatively quiescent regions by bottom currents in the deeper regions. The Lydonia Canyon head, station 23, is quite interesting in that studies (20)have shown this area to be a depositional area due to the presence of a hydrographically quiescent zone and/or due to possible up-canyon transport of fine-grained materials with associated PAH loads (15). Temporal changes in PAH levels at certain stations were investigated through the seasonal sampling in 1977. Data 842
Environ. Sci. Technol., Vol. 18, No. 11, 1984
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are plotted for five of th_e stations in Figure 3. The coefficient of variation ( S / X )for the seasonable data range from 0.17 to 0.81 for phenanthrene and 0.26 to 1.1 for fluoranthene pyrene. Greatest variability occurred at station 8. Variability due to sampling &e., the variability in PAH contents between six samples taken at the same station during one sampling time, Aug 1977) has been previously examined for saturated hydrocarbon components of the same sediments examined in this study (21). The mean coefficient of variation due to sampling (Le., six replicate grab samples) for 22 stations examined for individual alkane (nonacosane) and pristane levels was 0.53 and 0.59, respectively. Combining all the data in Figure 3 yields a mean coefficient of variation of 0.54 for these PAH data. Thus,small-scalespatial variability rather than any temporal trends explains all of the variability observed in Figure 3. A strong relationship exists between absolute levels of certain PAH compounds (e.g., phenanthrene, fluoranthene + pyrene) and several other geochemical parameters in the sediments. Figures 2 and 4 illustrate the strong covariance of phenanthrene levels with both TOC and levels of nonacosane (n-C,). Nonacosane is derived from terrigenous plant material (22)and is present in crude oil. However, where the carbon preference (i.e., ratio of odd carbon-chain n-alkanes to even carbon-chain n-alkanes) is high, a ter-
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Table I. Summary of PAH Data in Surface Sediments (ng/g = ppb)”
station 1
4
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C1-G phenanthrene/ Cl-Cp fluoroanthene naphthnaphthanthracene phenanthrenes pyrene alenes sea- alene sonc (128)b (156 + 170) (178) (192 + 206) (202) 8.7 28 2.5 9.4 4.2 1 5.8 15 5.0
