Environ. Sci. Technol. 1990, 24. 1418-1427
Runnegar, M. T. C.; Falconer, I. R.; Jackson, A. R. B.; McInnes, A. Toxicon 1983, Suppl. 3, 377-380. Van der Westhuizen, A. J. Ph.D. Thesis, University of the Orange Free State, South Africa, 1984. Van der Westhuizen, A. J.; Eloff, J. N. 2. Pflantenphysiol.
Van Steenderen, R. A.; Lin, J. S. Anal. Chem. 1981, 53, 2157-2 158.
Standard Methods for the Examination of Water and Wastewater, 16th ed.; American Public Health Association,
Van der Westhuizen, A. J.; Eloff, J. N. Planta 1985, 163,
American Water Works Association and Water Pollution Control Federation: New York, 1985. Botes, D. P.; Kruger, H.; Viljoen, C. C. Toxicon 1982,20,
55-59.
945-954.
Van der Westhuizen, A. J.; Eloff, J. N.; Kruger, G. H. J.
Sokal, R. R.; Rohlf, F. J. Biometry, 2nd ed.; W. H. Freeman:
Arch. Hydrobiol. 1986, 108, 145-154. Watanabe, M. F.; Oishi, S. Bull. Jpn. SOC.Sci. Fish. 1983,
New York, 1981; pp 565-591. Kungsuwan,A,; Noguchi, T.; Matsunaga, S.; Watanabe, M. F.; Watabe, S.; Hashimoto, K. Toxicon 1988,26,119-125.
1983, 110, 157-163.
49, 1759.
Watanabe, M. F.; Oishi, S. Appl. Environ. Microbiol. 1985, 49, 1342-1344.
Watanabe, M. F.; Harada, K.-I.;Matsuura, K.; Watanabe, M.; Suzuki, M. J . Appl. Phycol. 1989, I , 161-165. Robarts, R. D.; Ashton, P. J.; Thornton, J. A,; Taussig, H. J.; Sephton, L. M. Hydrobiologia 1982, 97, 209-224. Ashton, P. J. J . Limnol. SOC.South. Afr. 1985, 11, 32-42. Robarts, R. D.; Zohary, T. J. Ecol. 1984, 72, 1001-1017. Zohary, T. J . Plankton Res. 1985, 7, 399-409. Ashton, P. J.; Twinch,A. J. J . Limnol. Soc. South. Afr. 1985, 11, 62-65.
Robarts, R. D.; Zohary, T. Appl. Environ. Microbiol. 1986, 51, 609-613.
Zohary, T., personal communication,CSIR,Pretoria, 1989. Zohary, T.; Robarts, R. D. J. Plankton Res. 1989,11,25-48. Scott, W. E. In Mycotoxins and Phycotoxins; Steyn, P. S., Vleggaar, R., Eds.; Elsevier Science Publishers: Amsterdam, 1986; pp 41-50.
Robarts, R. D. Hydrobiologia 1988, 162, 97-107. Received for review January 22, 1990. Revised manuscript received May 18, 1990. Accepted May 21, 1990. This work was supported by the Department of National Health and Population Development. Contribution no. 80 to the Hartbeespoort Dam Ecosystem Program.
Polycyclic Aromatic Hydrocarbon Emissions from the Combustion of Crude Oil on Water Bruce A. Benner, Jr.," Nelson P. Bryner, Stephen A. Wise, and George W. Mulholland National Institute of Standards and Technology, Gaithersburg, Maryland 20899
Robert C. Lao and Mervin F. Fingas Environment Canada, Ottawa, Canada K 1A OH3
This work involved an investigation of some of the factors necessary to assess the environmental impact of an in situ burn: the fraction of an oil layer that can be burned, the quantity of smoke, and the concentrations of 18 polycyclic aromatic hydrocarbons (PAHs) in the smoke, crude oil, and burn residue. Alberta Sweet crude in 2-, 3-, 5-, lo-, and 30-mm layers on water was burned and smoke samples were collected at elevated and ambient temperatures and analyzed by two independent laboratories. While burning the crude oil produced less total PAHs than were in the original crude oil, the concentrations of PAHs with five or more rings were 10-20 times greater in the smoke than in the oil. The organic carbon fraction of the smoke was in the range of 14-21 5%. As the fuel layer thickness was increased from 2 to 10 mm, the smoke yield increased from 0.035 to 0.080 g of smoke/g of fuel, and the percentage of oil residue decreased from 46 to 17%. By consuming much of the oil spill and reducing the amount of PAHs in the water, and by dispersing the combustion products over a larger area, in situ burning can mitigate the local environmental impact of an oil spill. There appears to be a range of conditions, such as in Arctic ice fields, where in situ burning might be the most viable cleanup method. Introduction Since 1970 over 4000 off-shore oil wells ( I , 2 )have been drilled, and off-shore drilling continues to venture into more remote locations, such as the Arctic Ocean. Oil drilling in remote areas and large tankers transporting the crude oil from these wells have increased the possibility of a major oil spill occurring in a remote location. Con1418
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ventional oil spill countermeasures can be effective when the cleanup equipment and ships quickly reach the oil spill, but remote off-shore drilling locations, such as the Canadian Arctic, would be difficult to reach quickly and the hostile weather could seriously impede cleanup operations. The Exxon Valdez oil spill off the Alaskan coast demonstrated some of the difficulties of quickly transporting conventional cleanup equipment to an oil spill. To overcome implementation difficulties with conventional cleanup techniques, in situ burning, igniting the oil and allowing it to burn off, has been suggested. Many aspects of an in situ burn, including oil slick ignition techniques (3),burning rates (4-7),weathering (8, 9), effects of ice (IO, I I ) , and the dispersion of the smoke plume (12),have received attention. Thompson et al. (3) have extensivelydefined the conditions under which in situ burning might be used. However, the environmental implications of such a burn have not been quantified. The present study is directed at clarifying some aspects of the environmental impact of in situ burning, including the fraction of an oil layer that can be burned, the composition of unburned residue, and the quantity and composition of smoke generated. Examining the levels of polycyclic aromatic hydrocarbons (PAHs) in the crude, residue, and smoke is critical for assessing the environmental impact, since some PAH species are believed to be carcinogenic (13-16). It is known that there are some PAHs in the crude oil itself and also that PAHs are produced by the burning of hydrocarbon fuels, but there are no quantitative data on the relative amount of PAHs in the crude oil versus the amount emitted from burning the oil. In this study involving the
0013-936X/90/0924-1418$02.50/0
@ 1990 American Chemical Society
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burning of Alberta Sweet crude oil in 2-, 3-, 5-, lo-, and 30-mm layers on water, 18 individual PAH components in the crude oil, in the burn residue, and in the smoke were identified and quantified. Two laboratories analyzed the particulate- and vapor-phase emissions as well as crude oil and burn residue for the PAH species. From the results of the fraction of oil burned, the amount of smoke generated per mass of fuel burned and the PAH content of the smoke, crude, and residue, an estimate of total PAHs released was obtained.
Experimental Section Particulate- and vapor-phase samples were collected during burns of Alberta Sweet crude oil (boiling point range during distillation from 37 "Cto over 350 "C,density at 20 "C, 840 kg/m3, flash point, 7 "C). The crude oil was burned in a 0.6-m-diameter pan positioned under a 2.4 m X 2.4 m collection hood (Figure 1). A propane torch was used to ignite the oil, which was floating on water that was approximately 4 cm deep. A water-cooled load cell, located under the pan, continuously monitored the mass loss rate
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during each burn. In the first phase of this study (phase I), the smoke produced by burning a 30-mm crude oil layer was collected at high temperature (100 "C) and at ambient temperatures (25 "C). In the second phase (phase 111, crude oil layers of 2-, 3-, 5-, and 10-mm thicknesses were burned while particulate- and vapor-phase samples were simultaneously collected at ambient temperatures. Two different filter systems located above the collection hood were used to collect the samples. The filter collection system used in phase I (Figure 2) allowed for collection of up to three particulate-phase samples during each burn. The sample flow rate (10 L/min) and nozzle inlet diameter (0.44cm) were selected for isokinetic sampling at an inlet velocity of approximately 11m/s. For high-temperature collection, the transfer line, manifold, and filter holders were all heated to match the stack temperatures in order to minimize evaporation/condensation effects and losses to the walls of the collection system. For the low-temperature collection, a dilution section was inserted just downstream of the sampling tip and the heaters were switched off. Smoke was drawn through the isokinetic Environ. Sci. Technol., Voi. 24, No. 9, 1990
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sampling probe into the dilution section where it was diluted 2:l (mass basis) with 0 "C air, which cooled the smoke to within 2 "C of ambient. At both temperatures, a pair of Teflon filter samples were collected sequentially during the steady phase of the burn. After collection, each Teflon filter sample was weighed, sealed in Petri dishes, and stored under dry ice until transferred to a freezer (-20 "C). While higher collection temperatures were utilized to minimize the losses in the phase I experiments, lower collection temperatures were used in phase I1 to simulate the cooling that smoke experiences upon dilution in the atmosphere. The collection system used in phase I1 (Figure 3) allowed collection of both vapor- and particu1420
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late-phase samples. With the same isokinetic sampling tip and dilution system from the earlier burns, the diluted smoke was collected in parallel by two sampling sets each consisting of a 64 mm diameter Teflon filter followed by two polyurethane foam (PUF) plugs in a glass tube, 37-mm diameter and 150-mm length. The PUF plugs were positioned downstream of the Teflon filters and collected both vapor-phase PAHs as well as those PAHs desorbed from the filter during the sampling process. In contrast to the phase I crude oil burns, during which samples were collected for short periods during the steady-state burning, in the phase I1 burns parallel sets of particulate- and vapor-phase samples were collected continuously from ignition until burning ceased. In order to collect sufficient
mass for analysis, multiple burns were necessary for the 2-, 3-, and 5-mm oil layer thicknesses. Upon completion of a burn or series of burns, the Teflon filters were weighed and sealed in Petri dishes, while the PUF tubes were stored in aluminum foil. Both Teflon filters and PUF filters were stored under dry ice until transferred to a freezer. In addition to the Teflon and PUF filters, five samples of the crude oil before the burn and seven residue samples after the burn were also collected for chemical analysis. To determine the mass of oil remaining after the pool fire stopped burning, oleophilic batting was weighed and then used to soak up the unburned oil. Since the oleophilic batting preferentially adsorbed oil, only minute quantities of water were collected and subsequently the oil-soaked batting could be weighed to determine the mass of unburned oil. Soot samples were collected on quartz fiber filters for thermal-optical analysis of elemental versus organic carbon content. Standard precautions were taken to avoid sample contamination before sample collection by heating the filter for several hours at 700 "C and also heating the aluminum foil used to line the sample containers to 500 "C for several hours. The second collection system was used for the quartz filters, but the PUF samples were not collected. Because the thermal-optical technique requires much less soot per filter, smoke sampling flow rates averaged 2 L/min.
PAH and Carbon Quantification The PAH analyses of 23 Teflon filters and 12 PUF samples were performed by the Environment Canada (EC) at Ottawa and the Center for Analytical Chemistry at the National Institute of Standards and Technology (NIST). The analyses at NIST involved gas chromatography (GC) with flame-ionization detection, while EC used GC with mass spectrometric detection (GC-MS) for quantifying the individual PAHs. In addition, PAH analyses were performed on five crude oil samples and seven burn residue samples. The Teflon filters and PUF samples analyzed at NIST were spiked with appropriate amounts of an internal standard containing phenanthrene-& and l-n-butylpyrene and then Soxhlet extracted with dichloromethane (DCM) for 13-18 h. A response/recovery solution containing known amounts of 17 PAHs was spiked and processed in the same manner as the samples. The extracts were concentrated by rotary evaporation to approximately 5 mL and further concentrated under nitrogen to 1 mL. Half of each extract was transferred to a silica solid-phase extraction cartridge, which was then eluted with 15 mL of 10% DCM in pentane. The remaining halves of the extracts were stored in a refrigerator at 4 "C. The eluates were concentrated to near dryness under N2 and solvent exchanged to a 5% solution of DCM in pentane. The samples were injected onto a 9 mm X 25 cm aminosilane liquid chromatographic column and eluted with a 5% DCM in pentane mobile phase at 5 mL/min, collecting a PAH fraction beginning with phenanthrene and ending with coronene. The PAH fractions were concentrated by rotary evaporation to
