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The identification of petroleum products in the marine environment by absorption spectrophotometry
Water Research Pergamon Press 1972. Vol. 6, pp. 57-69. Printed in Great Britain
THE I D E N T I F I C A T I O N OF P E T R O L E U M P R O D U C T S IN THE M A R I N E E N V I R O N M E N T BY ABSORPTION SPECTROPHOTOMETRY* E. M. LEVY Atlantic Oceanographic Laboratory, Bedford Institute, Dartmouth, Nova Scotia, Canada
(Received 25 June, 1971) Abstract--The ultra-violet absorption spectra of a variety of common petroleum products, including distillate and residual fuel oils and lubricating oils, have been examined. The absorption spectra for the fuel oils were characterized by strong absorption maxima at approximately 228 nm and comparatively less prominent peaks at 256 rim. The spectra for the lubricating oils indicated very weak absorption at 256 nm and no clearly defined peak at 228 nm. The ratio of the absorbances at 228 and 256 nm varied from 1.23 for the residual to 7.41 for the distillate fuel oils. No change in this ratio was detected for a sample of Bunker C oil that experienced almost a year's exposure to weathering processes. These results suggest a basis for an analytical procedure which may be useful for the identification of oil spills. The application of this method to the identification of the origin of oils found recently in the marine environment of Eastern Canada is discussed. INTRODUCTION As PART of a policy of controlling discharges of oil at sea it is necessary to be able to prove that a particular oil slick or deposit was caused by one of several possible tankers, cargo ships, offshore oil wells, natural seeps, or other potential sources. Recently an analytical method was required to identify the source of petroleum products found in the marine environment of Eastern Canada. Shortly after the grounding on February 4, 1970, of the oil tanker Arrow, on Cerberus Rock in Chedabucto Bay, N o v a Scotia, large quantities of a heavy residual oil drifted onto the shores o f Chedabucto Bay and, somewhat later, onto those of Sable Island (FIG. 1). There could be little doubt that the oil which fouled the shores o f Chedabucto Bay originated from the Arrow, but the source o f the oil on Sable Island, some 100 miles to the southeast, was somewhat less certain. Although the meteorological and oceanographic conditions which existed shortly after the disaster (ANON, 1970a) were such that oil from Chedabucto Bay would be transported towards Sable Island, there was a possibility that this oil might have originated from some other source. A similar situation arose in early September when the oil barge Irving Whale, which also carried a cargo of Bunker C fuel oil, sank in the G u l f of St. Lawrence (LOUCKSand LAWRENCE, 1971). Oil of unknown origin appeared shortly afterwards on the beaches of the Magdalen Islands (FIG. 1). It has been suggested that such ambiguities concerning the origin of petroleum products can only be resolved with certainty by prior addition to individual shipments of stable and readily identifiable substances that are unique to a particular cargo (HOROWITZ et al., 1969). Nevertheless, the source of an oil spill can often be established with a reasonable degree of certainty by comparing certain chemical or physical properties o f the pollutant with those possessed by the suspected source, particularly if this information can be supplemented by other evidence including records of ship traffic in adjacent areas, the amounts of oil involved, meteoro* Bedford Institute Contribution No. 265. 57
58
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Identification of Petroleum Products
59
logical and oceanographic conditions, or similar ancillary information. Gas chromatographic analyses are commonly used for this purpose and provide adequate identification of low boiling constituents but are much less effective when high boiling residual oils are involved. In this case, vanadium/nickel ratios sometimes provide a clue to the origin of the pollutant. In this paper spectrophotometric methods are described to supplement other analytical techniques for the identification of the origin of oil pollutants in the marine environment, and particularly the sources of the residual oils found on the shores of Sable Island and the beaches of the Magdalen Islands. ANALYTICAL PROCEDURES
Standards Stock solutions of several types of lubricating, distillate and residual fuel oils, including samples of Bunker C oil taken from the wreck of the Arrow and the cargo of the Whale were prepared by dissolving approximately l0 mg of each of the oils in spectroanalyzed n-hexane. Insoluble material was removed by passing these extracts through Whatman No. 42 filter papers and the filtrates were diluted to 100 ml. Although these standards contained only the n-hexane soluble fractions of the oils, they were considered to contain the equivalent of 100 mg l- 1 of the oils. Three series of standard solutions containing 20, 30, 40, 50 and 75 mg l- 1 were prepared from the Bunker C oils carried by the Arrow and Whale by appropriately diluting the stock solution. Standards containing 30 mg l - 1 of each of the other oils were used. The ultra-violet absorption spectra of these solutions were obtained relative to nhexane by scanning the region from 350 to 210 nm with a Beckman ACTA V recording spectrophotometer. In addition, the absorbances of these solutions at 256 nm and on the crest of the peak which is centered at approximately 228 nm were measured with this instrument in the double beam mode of operation.
Environmental samples Samples taken from the beaches of Sable Island and from the Magdalen Islands were mixtures of heavy black residual oils, sand and debris. Subsamples of each were treated with spectroanalyzed n-hexane and the insoluble material was removed by filtration through a Whatman No. 42 filter paper. The filtrates were diluted to 100 ml and their absorbances at 256 nm were measured. The concentrations of these extracts were then adjusted so that their absorbances were in the range of 0.4--0.8, corresponding to the absorbances of the Bunker C standards which contained 30 mg 1-1 of the oil. The absorption spectra of these solutions were then scanned over the range of 350 nm to 210 nm and their absorbances at 256 nm and at 228 nm were measured as outlined for the standards. RESULTS AND DISCUSSION
Residual fuel oils The ultraviolet absorption spectra of several residual fuel oils are shown in FIG. 2. The salient features of these spectra are the strong absorption peak at 225-228 nm
60
E . M . LEVY
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20(
I 250
r
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300
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WAVELENGTH (rim)
Fio. 2. Ultra-violet absorption spectra of some residual fuel oils. (1) Oil recovered from Sydney Harbour, N.S.; (2) Intermediate residual fuel oil; (3) Bunker C oil similar to that carded by the ferry, Patrick Morris; (4) Bunker C oil recovered from tanker, Arrow: (5) Bunker C oil recovered from barge Whale. (Spectra have been displaced vertically to avoid superimposition.) and the considerably weaker absorption peak or shoulder in the vicinity of 256 nm. Spectra I and 2, obtained from samples of oil found in Sydney Harbour, N.S., and a sample of an intermediate residual fuel oil show a more prominent absorption peak at approximately 256 nm than spectra 3, 4 and 5 which were obtained from samples of Bunker C fuel oils of the type carried by the Canadian National Railways ferry Patrick Morris, which sank off Cape Breton Island, and samples recovered from the wrecks of the Arrow in Chedabucto Bay and the Whale in the Gulf of St. Lawrence. The absorption spectrum of a residual oil reflects the composition of the original crude oil, the processes employed in relining it and fluxing processes used in preparing the residual fuel oil from the refinery residues. If the histories of various batches of residual oils differ sufficiently either in the sources of the crudes or refining and fluxing processes, it is possible to differentiate between various oils by means of their u.v. absorption spectra. For example, it is apparent that two different types of oil are indicated by the spectra in FIG. 2. Indeed, the oil found in Sydney Harbour was thought to have been derived from a Middle East crude whereas the others were of Venezuelan origin (STOART, 1971). Although minor differences exist between spectra 1 and 2 and among spectra 3, 4 and 5, the general shapes of the spectra are sufficiently similar to make it difficult to differentiate between these residual oils on this information alone. A detailed examination of these spectra reveals, however, that significant differences exist between the absorption at 228 nm relative to that at 256 nm for the different oils. As shown in TABLE 1, the values for the ratio of the absorbances at these wave-
Identification of Petroleum Products TABLE 1.
61
ULTRA-VIOLET ABSORBANCE CHARACTERISTICS OF SOME RESIDUAL
FUEL O1~ Type of Oil
A ~., 22s
Sydney Harbour Intermediate residual
1.442 1.607 0.686 0.729 0.857
Patrick Morris Arrow Whale
A ,-, 2s6
(225)* (226) (228) (228) (228)
1.168 0.761 0.430 0.464 0.624
(256)* (255) (257) (256) (256)
R 1.23 2.11 1.60 1.57 1.37
* The numbers in parentheses designate the wavelengths (nm) at which the absorbances were measured.
lengths ranged from 1.23 to 2.11 for the oils investigated. There does not appear to be any difference between the oil carried by the Arrow and a sample claimed to have been taken from the same reservoir as the oil supplied to the Patrick Morris*. With this possible exception, the absorbance ratio provides a convenient and definitive criterion for distinguishing between these oils. The independence of this ratio from the concentration over the range of 10-75 mg l-1 is shown in TABLES2 and 3. The absorbance ratios for three different sets of standard solutions ranged from 1.55 to 1.59 for the oil carried by the Arrow and from 1.28 to 1.39 for that carried by the Whale. At concentrations greater than 75 mg l-1, deviations from Beer's Law at 228 nm resulted in a decrease in the absorbance ratio. As a result the absorbance ratio is a reliable criterion for identifying oils only within concentration ranges at which Beer's Law is valid at both wavelengths. Means and standard deviations calculated from these data are given in TABLE4. The null hypothesis that there is no difference between the mean absorbance ratio for the Bunker C TABLE 2.
ULTRA-VIOLET ABSORBANCE CHARACTERISTICS OF BUNKER C OIL CARRIED BY Arrow
Standard no. 1
2
3
Nominal Concentration (rag l -x)
Absorbance 228 n m
256 nm
Ratio A22s/A2s6
10 25 50 75 10 25 50 75 20 30 40 50
0.313 0.674 1.296 1.930 0.256 0.621 0.803 1.855 0.489 0.729 0.974 1.233
0.201 0.431 0.820 1.229 0.163 0.391 0.258 1.195 0.310 0.464 0.621 0.790
1.56 1.56 1.58 1.57 1.57 1.59 1.57 1.55 1.58 1.57 1.57 1.56
* The absorption spectra for the oil claimed to have been carried by the Patrick Morris and that recovered from the Arrow are exactly superina-
posable. In addition, their thin layer chromatograms are identical.
62
E.M. LEVY TABLE 3. ULTRA-VIOLET ABSORBANCE CHARACTERISTICS OF B U N K E R C OIL CARRIED BY Whale
Standard no.
Nominal Concentration (mg 1-1)
228 nm
256 nm
Ratio A22s/A256
10 25 50 75 10 25 50 75 20 30 40 50
0.287 0.750 1.487 2.139 0.267 0.649 1.310 1.922 0.455 0.857 1.131 1.389
0.219 0.564 1.119 1.672 0.205 0.500 1.006 1.502 0.328 0.624 0.826 1.020
1.31 1.33 1.33 1.28 1.30 1.30 1.30 1.28 1.39 1.37 1.37 1.36
1
2
3
Absorbance
TABLE 4. STATISTICS PERTAINING TO THE ULTRA-VIOLET ABSORBANCE DATA FOR THE BUNKER C OILS CARRIED BY THE Arrow AND THE Whale
Statistic n R o t
Arrow
Whale
12 1.57 0.0108
12 1.33 0.0377 21.2
oil carried by the Arrow a n d that carried by the Whale was f o r m u l a t e d a n d tested[by m e a n s of a t-test. The value for S t u d e n t ' s ' t ' calculated from these data show that the p r o b a b i l i t y of the null hypothesis being valid is vanishingly small a n d that the samples o f B u n k e r C oil carried b y the Arrow a n d Whale are, in fact, quite different. Similar tests, as shown in TABLE 5, prove that these oils were different from that f o u n d in Sydney H a r b o u r , the Intermediate residual fuel oil, or the fuel allegedly carried by the Patrick Morris. It is apparent, therefore, that the ratio of the a b s o r b a n c e at 228 n m to that at 256 n m provides a c o n v e n i e n t a n d definitive criterion for differentiating between various residual fuel oils. TABLE 5. U S E OF ABSORBANCE RATIOS TO DIFFERENTIATE AMONG VARIOUS RESIDUAL FUEL OILS
Oil
R
Sydney Harbour Intermediate residual Patrick Morris
1.23 2.11 1.60
Arrow Whale (R = 1.57) (R = 1.37) t t 30.25 48.04 2.67
2.54 19.88 6.88
Identification of Petroleum Products
63
Distillate fuel oils The u.v. absorption spectra of three distillate fuel oils are shown in FIG. 3. In all cases there was a prominent absorption peak at approximately 224-228 nm and a less pronounced absorption peak at 253-256 rim. Although the absorption peaks for these distillate fuel oils appeared at the same wavelengths as those of the residual fuel oils (FIG. 3), the general characteristics of the spectra for the two types are sufficiently
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250 WAVELENGTH
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FtG. 3. Ultra-violet absorption spectra of some distillate fuel oils. (1) Low ash distillate; (2) Diesel fuel; (3) Diesel fuel (slightly oxidized). different that there is no difficulty in distinguishing between them. Once again, however, it is not possible to distinguish between different oils of the same general type. Nevertheless, the absorption at 228 nm relative to that at 256 nm provides a criterion for the identification of different members within the general group and, as shown in TABLE6, the absorbance ratios for the various distillate fuel oils not only differ substantially amongst themselves, but also fall in a distinct group which is unmistakably different from that which characterizes the residual fuel oils. Although it was not known for certain, it was believed (STUART, 1971) that the two samples of diesel fuel depicted by spectra 2 and 3 (FIG. 3) were not from the same batch. Accordingly, it would appear that the differences between these spectra resulted from differences in the original compositions of the oils and are not merely reflections of changes in composition which occurred as a result of partial degradation o f the oil*. * The thin layer chromatograms of these oils indicated substantial differences in their composition.
64
E. M. LEVY TABLE 6. ULTRA-VIOLET ABSORBANCE CHARACTERISTICS OF SOME DISTILLATE FUEL OILS
Type of oil
A ~ 22s
Low ash distillate Diesel Diesel (partially oxidized) BI diesel
A ,,~ 256
2.86 (228)* 1.822 (226) 0.971 (224) 0.749 (220)
0.632 0.264 0.131 0.111
(252)* (254) (253) (256)
R 4.52 6.90 7.41 6.75
* The numbers in parentheses designate the wavelengths (nm) at which the absorbances were measured.
Lubricating oils The u.v. absorption spectra of several types of lubricating oils are shown in FIG. 4. In contrast with those of both the residual and distillate types of fuel oils, these spectra indicated only very weak and in some cases virtually no absorption of ultraviolet light at wavelengths greater than 250 nm and no clearly defined absorption peak in the neighbourhood of 228 nm. These features by themselves are sufficient to distinguish lubricating oils from the residual and distillate fuel oils. However, with the exception of the spectrum for the stern tube lubricating oil, a type which is continuously lost through the stern tubes of many ships and is, therefore, a common pollutant in marine environments, these spectra for the various lubricating oils do not differ sufficiently in appearance to provide a means of distinguishing between them. The slight differences in spectra 3, 4 and 5 result from changes in composition that have resulted from using the oil. Because of the absence of a clearly defined absorption peak in the neighbourhood of 228 nm, however, the absorbance ratio is a much less useful criterion for distinguishing between the various types of lubricating oils than it was
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2
200
250 WAVELENGTH
300
350
(nm)
FIG. 4. Ultra-violet absorption spectra of some lubricating oils. (1) Stern tube; (2) Diesel; (3) Turbine; (4) Turbine (used); (5) Diesel (used). (These spectra have been displaced vertically
to avoid superimposition.)
65
Identification of Petroleum Products TABLE 7. ULTRA-VIOLET ABSORBANCECHARACTERISTICS OF SOME LUBRICATING OILS Type of oil
A ~ 22s
Stern-tube Diesel Turbine Turbine (used) Diesel (used) BI-lubricating
0.683 0.195 0.096 0.198 0.272 0.154
A~
(226)* (228) (228) (228) (228) (220)
0.267 0.042 0.018 0.048 0.088 0.041
R
256
(260)* (255) (255) (256) (256) (256)
2.56 4.64 5.33 4.13 3.09 3.76
* The numbers in parentheses designate the wavelengths (nm) at which the absorbances were measured.
for the fuel oils. As shown in TABLE7, the absorbance ratios for lubricating oils form a distinct group which, for the most part, is unmistakably different from those obtained for either the residual or the distillate types of fuel oils.
Environmental samples The u.v. absorption spectra of samples of oils collected at Babin's Cove, Chedabucto Bay, N.S., in January 1971 (spectra 1 and 2) and from Sable Island (spectra 3) shortly after the grounding of the Arrow are shown in FXG.5. From the general features of these spectra alone it could be concluded that the two samples from Babin's Cove were identical and that the sample from Sable Island probably came from the same source. This supposition is substantiated by comparing these spectra with those obtained for various concentrations of Bunker C oil recovered from the wreck of the Arrow (FIG. 6). The spectra of FIG. 5 and 6 are strikingly similar. Closer examination reveals that spectra 1 and 2, for the oil collected at Babin's Cove, are exactly congruent with the spectra obtained from the Arrow Bunker C oil at concentrations of 50 and
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200
250 WAVELENGTH
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300
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FIG. 5. Ultra-violet absorption spectra of samples of oils collected at Babin's Cove (1 and 2) (Chedabucto Bay), and Sable Island (3). w ^ ~ R 6/I--E
66
E.M. LEVY
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0.5
200
250
550
300
WAVELENGTH (nm)
FIG. 6. Ultra-violet absorption of Bunker C oil recovered from the Arrow. (1) 50 mg l - ' ; (2) 40 mg 1-1 ; (3) 30 mg 1- ~; (4) 20 mg 1-1. 40 m g 1- ~ respectively, a n d similarly that the s p e c t r u m for the oil f o u n d on Sable I s l a n d is identical in all respects with t h a t o b t a i n e d from a solution c o n t a i n i n g 20 m g 1-1 o f the Arrow oil. There seems little d o u b t , therefore, that the oils on the beaches o f B a b i n ' s Cove a n d on Sable I s l a n d o r i g i n a t e d f r o m a c o m m o n source a n d furtherm o r e t h a t this source was the cargo o f the Arrow. This conclusion is s u b s t a n t i a t e d by c o m p a r i n g the a b s o r b a n c e r a t i o s for the samples f r o m B a b i n ' s Cove a n d t h a t f r o m Sable Island, as given in TABLE 8, with those in TABLE 2 for the oil carried b y the Arrow. O f c o n s i d e r a b l e significance also is the fact t h a t the samples f r o m B a b i n ' s Cove were collected in J a n u a r y 1971, a l m o s t a y e a r after the g r o u n d i n g o f the Arrow. This inTABLE 8. ULTRA-VIOLET ABSORBANCE CHARACTERISTICS OF RESIDUAL OILS FOUND AT BABrN'S COVE, N.S., SABLE ISLAND AND THE MAGDALEN ISLANDS, P.Q.
Sample Babin's Cove 1 2 Sable Island Magdalen Islands ! 2 3 4 5
A228
,42s6
R
1.089 (228) 1.322 (229) 0.616 (230) 0.456 (228)
0.696 0.847 0.402 0.291
(255) (257) (254) (256)
1.56 1.56 1.53 1.57
0.562 0.920 0.674 0.730 0.522 0.315 0.801 0.655 0.726 0.779
0.438 0.685 0.522 0.560 0.376 0.235 0.599 0.491 0.557 0.572
(255) (256) (255) (256) (256) (256) (255) (256) (256) (256)
1.28 1.34 1.29 1.30 1.39 1.34 1.34 1.34 1.30 1.36
(228) (224) (228) (224) (228) (224) (228) (228) (228) (228)
Identification of Petroleum Products
67
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O u} ca
I
200
I
250
J
300
WAVELENGTH
350
(nm)
FIG. 7. Ultra-violet absorption spectra o f samples o f oil collectedlon the Magdalen Islands.
dicates that weathering of these samples had not significantly altered the relative concentrations of the compounds responsible for the u.v. absorption characteristics. Changes in composition due to weathering severely limit gas chromatographic and trace metal analyses in the identification of the sources o f petroleum products in the marine environment. The use of the ultra-violet absorption approach is illustrated further by the spectra in FIG. 7, obtained from five samples of residual oils collected at various sites on the west side of the Magdalen Islands. It is apparent from the spectra that the samples were probably derived from a common substance, the spectral differences being solely those which result from slight concentration differences. These spectra are superimposable onto those (FIG. 8) solutions containing 20-30 mg 1-t of Bunker C oil carried by the Whale, thereby providing convincing evidence that the oil which con-
I.Z0.9 0"60'3'
200
I
250 300 WAVELENGTH (nm)
,
350
FIG. 8. Ultra-violet absorption spectra of Bunker C oil recovered from the Whale. (1) 50 mg 1-1; (2) 40 mg 1- 1; (3) 30 mg 1- 1; (4) 20 mg 1-1.
68
E.M. LEVY
taminated the beaches of the Magdalen Islands originated from the sinking of this barge. This conclusion is confirmed by comparing the absorbance ratios for these samples (TABLE 8) with those obtained for the Bunker C oil carried by the Whale (TABLE 3). Again, this degree of agreement would be extremely unlikely unless the compositions of the samples were identical. There can be little doubt, therefore, that the oil which polluted the beaches of the Magdalen Islands resulted from the Whale incident.
Comparison of analytical methods to identify the sources of oil pollution The most commonly used methods for the identification of the source of oil pollution are gas chromatographic and trace metal analyses (ANON, 1970b ; HOROWITZet al., 1969). Some of the lower boiling constituents may be identified by gas chromatographic analyses and this information may, in some cases, be used to isolate the source of oil pollution. This method is particularly suited to the identification of the source o f crude oils, distillate fuel oils and other petroleum fractions which contain significant concentrations of low boiling constituents. However, it is subject to serious ambiguities which may arise when the volatile compounds evaporate or other constituents dissolve or become altered by chemical weathering or microbial action. It is much less suitable for the identification of residual oils because of the refractory nature of the compounds, which remain in these materials after the volatile fluxes have escaped. The identification of oil pollutants by means of their trace metal contents is similarly suitable for dealing with certain restricted situations. Few metals are present in petroleum products in sufficiently high concentrations for this purpose, and nickel and vanadium are most commonly used. Since some fractions of the oil might have disappeared, concentrating the involatiles, the absolute concentrations of these metals does not provide reliable information. Accordingly, the ratio of the vanadium and nickel contents is taken as the criterion for identification purposes. However, these metals are commonly present in petroleum in forms that may be volatile or water soluble or may become water soluble on exposure to sea water and thereby escape from the oil as it weathers. The ultra-violet absorbance method used in this investigation does not appear to be subject to most of these uncertainties. In contrast with gas chromatographic techniques, no attempt is made in this method to identify all or even a few of the compounds present in the oil--an extremely difficult task in view of the variety and complexity of the structures that may be present in many petroleum products, particularly in heavy and residual oils or in tarry substances. Instead, the contributions from all the compounds capable of absorbing light in the appropriate region of the spectrum are considered as a group. The approach described in this paper does not provide any information concerning saturated hydrocarbons or other compounds that do not absorb light and is, therefore, only applicable to oils that contain suitable concentrations of absorbing species. There is, however, an abundance of such structures in the heavier oils and particularly in the residual oils. Furthermore, because of the chemical nature of these compounds there is little danger of them escaping from the oil soon after the spill or of them undergoing rapid changes because of weathering processes. Indeed, it has been shown that Bunker C oil from the Arrow had not changed ostensibly, as far as this method of identification is concerned, after almost a year's exposure to weathering processes.
Identification of Petroleum Products
69
A further advantage o f the ultra-violet absorption technique is that it requires a very small amount, approximately 0.06 m g o f the oil. Consequently, it m a y be used for the identification o f the source o f oil dispersed t h r o u g h o u t the water column, where only a small a m o u n t o f the oil might be available, as well as that floating on the surface o f the water or lying on the beaches. SUMMARY Ultra-violet absorption spectra provide a convenient m e t h o d for the identification o f the source o f petroleum products present in the marine environment. The absorbance at 228 n m relative to that at 256 n m has been shown to be a sensitive and reliable criterion for distinguishing between different members o f similar types o f oils and is not subject to m a n y o f the uncertainties o f other methods o f identification. This m e t h o d was successfully applied to the identification o f the sources o f residual oils f o u n d on the shores o f C h e d a b u c t o Bay, Sable Island and the Magdalen Islands. Acknowledgements--The competent technical assistance of Mrs. SHARON H.~TLING and Mrs.
COLLEENMcCORMACKis gratefully acknowledged. The author is particularly indebted to Mr. R. A. SrU,~T, Defence Research Establishment Atlantic, who provided most of the samples of oils used as standards for this investigation, and to Dr. A. WALTONand Mr. A. R. COOTEwho reviewed the manuscript. REFERENCES ANON(1970a) "The ARRO W lncident". Report of the Scientific Coordination Team to the Head of the Task Force Operation Oil. Prepublication edition, pp. 6-15. Compiled at Atlantic Oceanographic Laboratory, Bedford Institute, Dartmouth, Nova Scotia. ANON(1970b) Analytical methods for the identification of the source of pollution by oil of the seas, rivers and beaches. J. Inst. Petroleum 56, 107-117. HOROWITZJ., GOMTZ G. D., NEMCrm~ R. G. and MELOYT. P. (1969) Identification of oil spills: Comparison of several methods. Proceedings--Joint Conference on Prevention and Control of Oil Spills sponsored by American Petroleum Institute and Federal Water Pollution Control Administration, December 15-17, pp. 283-296. LoucKs R. H. and LAWRENC~D. J. (1971) Reconnaissance of an oil spill. Marine Pollut. Bull. 2, 92-94. STUARTR. A. (1971) Private communication.
THE I D E N T I F I C A T I O N OF P E T R O L E U M P R O D U C T S IN THE M A R I N E E N V I R O N M E N T BY ABSORPTION SPECTROPHOTOMETRY* E. M. LEVY Atlantic Oceanographic Laboratory, Bedford Institute, Dartmouth, Nova Scotia, Canada
(Received 25 June, 1971) Abstract--The ultra-violet absorption spectra of a variety of common petroleum products, including distillate and residual fuel oils and lubricating oils, have been examined. The absorption spectra for the fuel oils were characterized by strong absorption maxima at approximately 228 nm and comparatively less prominent peaks at 256 rim. The spectra for the lubricating oils indicated very weak absorption at 256 nm and no clearly defined peak at 228 nm. The ratio of the absorbances at 228 and 256 nm varied from 1.23 for the residual to 7.41 for the distillate fuel oils. No change in this ratio was detected for a sample of Bunker C oil that experienced almost a year's exposure to weathering processes. These results suggest a basis for an analytical procedure which may be useful for the identification of oil spills. The application of this method to the identification of the origin of oils found recently in the marine environment of Eastern Canada is discussed. INTRODUCTION As PART of a policy of controlling discharges of oil at sea it is necessary to be able to prove that a particular oil slick or deposit was caused by one of several possible tankers, cargo ships, offshore oil wells, natural seeps, or other potential sources. Recently an analytical method was required to identify the source of petroleum products found in the marine environment of Eastern Canada. Shortly after the grounding on February 4, 1970, of the oil tanker Arrow, on Cerberus Rock in Chedabucto Bay, N o v a Scotia, large quantities of a heavy residual oil drifted onto the shores o f Chedabucto Bay and, somewhat later, onto those of Sable Island (FIG. 1). There could be little doubt that the oil which fouled the shores o f Chedabucto Bay originated from the Arrow, but the source o f the oil on Sable Island, some 100 miles to the southeast, was somewhat less certain. Although the meteorological and oceanographic conditions which existed shortly after the disaster (ANON, 1970a) were such that oil from Chedabucto Bay would be transported towards Sable Island, there was a possibility that this oil might have originated from some other source. A similar situation arose in early September when the oil barge Irving Whale, which also carried a cargo of Bunker C fuel oil, sank in the G u l f of St. Lawrence (LOUCKSand LAWRENCE, 1971). Oil of unknown origin appeared shortly afterwards on the beaches of the Magdalen Islands (FIG. 1). It has been suggested that such ambiguities concerning the origin of petroleum products can only be resolved with certainty by prior addition to individual shipments of stable and readily identifiable substances that are unique to a particular cargo (HOROWITZ et al., 1969). Nevertheless, the source of an oil spill can often be established with a reasonable degree of certainty by comparing certain chemical or physical properties o f the pollutant with those possessed by the suspected source, particularly if this information can be supplemented by other evidence including records of ship traffic in adjacent areas, the amounts of oil involved, meteoro* Bedford Institute Contribution No. 265. 57
58
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E . M . LEVY
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Identification of Petroleum Products
59
logical and oceanographic conditions, or similar ancillary information. Gas chromatographic analyses are commonly used for this purpose and provide adequate identification of low boiling constituents but are much less effective when high boiling residual oils are involved. In this case, vanadium/nickel ratios sometimes provide a clue to the origin of the pollutant. In this paper spectrophotometric methods are described to supplement other analytical techniques for the identification of the origin of oil pollutants in the marine environment, and particularly the sources of the residual oils found on the shores of Sable Island and the beaches of the Magdalen Islands. ANALYTICAL PROCEDURES
Standards Stock solutions of several types of lubricating, distillate and residual fuel oils, including samples of Bunker C oil taken from the wreck of the Arrow and the cargo of the Whale were prepared by dissolving approximately l0 mg of each of the oils in spectroanalyzed n-hexane. Insoluble material was removed by passing these extracts through Whatman No. 42 filter papers and the filtrates were diluted to 100 ml. Although these standards contained only the n-hexane soluble fractions of the oils, they were considered to contain the equivalent of 100 mg l- 1 of the oils. Three series of standard solutions containing 20, 30, 40, 50 and 75 mg l- 1 were prepared from the Bunker C oils carried by the Arrow and Whale by appropriately diluting the stock solution. Standards containing 30 mg l - 1 of each of the other oils were used. The ultra-violet absorption spectra of these solutions were obtained relative to nhexane by scanning the region from 350 to 210 nm with a Beckman ACTA V recording spectrophotometer. In addition, the absorbances of these solutions at 256 nm and on the crest of the peak which is centered at approximately 228 nm were measured with this instrument in the double beam mode of operation.
Environmental samples Samples taken from the beaches of Sable Island and from the Magdalen Islands were mixtures of heavy black residual oils, sand and debris. Subsamples of each were treated with spectroanalyzed n-hexane and the insoluble material was removed by filtration through a Whatman No. 42 filter paper. The filtrates were diluted to 100 ml and their absorbances at 256 nm were measured. The concentrations of these extracts were then adjusted so that their absorbances were in the range of 0.4--0.8, corresponding to the absorbances of the Bunker C standards which contained 30 mg 1-1 of the oil. The absorption spectra of these solutions were then scanned over the range of 350 nm to 210 nm and their absorbances at 256 nm and at 228 nm were measured as outlined for the standards. RESULTS AND DISCUSSION
Residual fuel oils The ultraviolet absorption spectra of several residual fuel oils are shown in FIG. 2. The salient features of these spectra are the strong absorption peak at 225-228 nm
60
E . M . LEVY
? bJ 0 Z <~ {I: 0 O3 nn
20(
I 250
r
I
300
:350
WAVELENGTH (rim)
Fio. 2. Ultra-violet absorption spectra of some residual fuel oils. (1) Oil recovered from Sydney Harbour, N.S.; (2) Intermediate residual fuel oil; (3) Bunker C oil similar to that carded by the ferry, Patrick Morris; (4) Bunker C oil recovered from tanker, Arrow: (5) Bunker C oil recovered from barge Whale. (Spectra have been displaced vertically to avoid superimposition.) and the considerably weaker absorption peak or shoulder in the vicinity of 256 nm. Spectra I and 2, obtained from samples of oil found in Sydney Harbour, N.S., and a sample of an intermediate residual fuel oil show a more prominent absorption peak at approximately 256 nm than spectra 3, 4 and 5 which were obtained from samples of Bunker C fuel oils of the type carried by the Canadian National Railways ferry Patrick Morris, which sank off Cape Breton Island, and samples recovered from the wrecks of the Arrow in Chedabucto Bay and the Whale in the Gulf of St. Lawrence. The absorption spectrum of a residual oil reflects the composition of the original crude oil, the processes employed in relining it and fluxing processes used in preparing the residual fuel oil from the refinery residues. If the histories of various batches of residual oils differ sufficiently either in the sources of the crudes or refining and fluxing processes, it is possible to differentiate between various oils by means of their u.v. absorption spectra. For example, it is apparent that two different types of oil are indicated by the spectra in FIG. 2. Indeed, the oil found in Sydney Harbour was thought to have been derived from a Middle East crude whereas the others were of Venezuelan origin (STOART, 1971). Although minor differences exist between spectra 1 and 2 and among spectra 3, 4 and 5, the general shapes of the spectra are sufficiently similar to make it difficult to differentiate between these residual oils on this information alone. A detailed examination of these spectra reveals, however, that significant differences exist between the absorption at 228 nm relative to that at 256 nm for the different oils. As shown in TABLE 1, the values for the ratio of the absorbances at these wave-
Identification of Petroleum Products TABLE 1.
61
ULTRA-VIOLET ABSORBANCE CHARACTERISTICS OF SOME RESIDUAL
FUEL O1~ Type of Oil
A ~., 22s
Sydney Harbour Intermediate residual
1.442 1.607 0.686 0.729 0.857
Patrick Morris Arrow Whale
A ,-, 2s6
(225)* (226) (228) (228) (228)
1.168 0.761 0.430 0.464 0.624
(256)* (255) (257) (256) (256)
R 1.23 2.11 1.60 1.57 1.37
* The numbers in parentheses designate the wavelengths (nm) at which the absorbances were measured.
lengths ranged from 1.23 to 2.11 for the oils investigated. There does not appear to be any difference between the oil carried by the Arrow and a sample claimed to have been taken from the same reservoir as the oil supplied to the Patrick Morris*. With this possible exception, the absorbance ratio provides a convenient and definitive criterion for distinguishing between these oils. The independence of this ratio from the concentration over the range of 10-75 mg l-1 is shown in TABLES2 and 3. The absorbance ratios for three different sets of standard solutions ranged from 1.55 to 1.59 for the oil carried by the Arrow and from 1.28 to 1.39 for that carried by the Whale. At concentrations greater than 75 mg l-1, deviations from Beer's Law at 228 nm resulted in a decrease in the absorbance ratio. As a result the absorbance ratio is a reliable criterion for identifying oils only within concentration ranges at which Beer's Law is valid at both wavelengths. Means and standard deviations calculated from these data are given in TABLE4. The null hypothesis that there is no difference between the mean absorbance ratio for the Bunker C TABLE 2.
ULTRA-VIOLET ABSORBANCE CHARACTERISTICS OF BUNKER C OIL CARRIED BY Arrow
Standard no. 1
2
3
Nominal Concentration (rag l -x)
Absorbance 228 n m
256 nm
Ratio A22s/A2s6
10 25 50 75 10 25 50 75 20 30 40 50
0.313 0.674 1.296 1.930 0.256 0.621 0.803 1.855 0.489 0.729 0.974 1.233
0.201 0.431 0.820 1.229 0.163 0.391 0.258 1.195 0.310 0.464 0.621 0.790
1.56 1.56 1.58 1.57 1.57 1.59 1.57 1.55 1.58 1.57 1.57 1.56
* The absorption spectra for the oil claimed to have been carried by the Patrick Morris and that recovered from the Arrow are exactly superina-
posable. In addition, their thin layer chromatograms are identical.
62
E.M. LEVY TABLE 3. ULTRA-VIOLET ABSORBANCE CHARACTERISTICS OF B U N K E R C OIL CARRIED BY Whale
Standard no.
Nominal Concentration (mg 1-1)
228 nm
256 nm
Ratio A22s/A256
10 25 50 75 10 25 50 75 20 30 40 50
0.287 0.750 1.487 2.139 0.267 0.649 1.310 1.922 0.455 0.857 1.131 1.389
0.219 0.564 1.119 1.672 0.205 0.500 1.006 1.502 0.328 0.624 0.826 1.020
1.31 1.33 1.33 1.28 1.30 1.30 1.30 1.28 1.39 1.37 1.37 1.36
1
2
3
Absorbance
TABLE 4. STATISTICS PERTAINING TO THE ULTRA-VIOLET ABSORBANCE DATA FOR THE BUNKER C OILS CARRIED BY THE Arrow AND THE Whale
Statistic n R o t
Arrow
Whale
12 1.57 0.0108
12 1.33 0.0377 21.2
oil carried by the Arrow a n d that carried by the Whale was f o r m u l a t e d a n d tested[by m e a n s of a t-test. The value for S t u d e n t ' s ' t ' calculated from these data show that the p r o b a b i l i t y of the null hypothesis being valid is vanishingly small a n d that the samples o f B u n k e r C oil carried b y the Arrow a n d Whale are, in fact, quite different. Similar tests, as shown in TABLE 5, prove that these oils were different from that f o u n d in Sydney H a r b o u r , the Intermediate residual fuel oil, or the fuel allegedly carried by the Patrick Morris. It is apparent, therefore, that the ratio of the a b s o r b a n c e at 228 n m to that at 256 n m provides a c o n v e n i e n t a n d definitive criterion for differentiating between various residual fuel oils. TABLE 5. U S E OF ABSORBANCE RATIOS TO DIFFERENTIATE AMONG VARIOUS RESIDUAL FUEL OILS
Oil
R
Sydney Harbour Intermediate residual Patrick Morris
1.23 2.11 1.60
Arrow Whale (R = 1.57) (R = 1.37) t t 30.25 48.04 2.67
2.54 19.88 6.88
Identification of Petroleum Products
63
Distillate fuel oils The u.v. absorption spectra of three distillate fuel oils are shown in FIG. 3. In all cases there was a prominent absorption peak at approximately 224-228 nm and a less pronounced absorption peak at 253-256 rim. Although the absorption peaks for these distillate fuel oils appeared at the same wavelengths as those of the residual fuel oils (FIG. 3), the general characteristics of the spectra for the two types are sufficiently
b.I ¢J Z
0 03
200
250 WAVELENGTH
300 (rim)
350
FtG. 3. Ultra-violet absorption spectra of some distillate fuel oils. (1) Low ash distillate; (2) Diesel fuel; (3) Diesel fuel (slightly oxidized). different that there is no difficulty in distinguishing between them. Once again, however, it is not possible to distinguish between different oils of the same general type. Nevertheless, the absorption at 228 nm relative to that at 256 nm provides a criterion for the identification of different members within the general group and, as shown in TABLE6, the absorbance ratios for the various distillate fuel oils not only differ substantially amongst themselves, but also fall in a distinct group which is unmistakably different from that which characterizes the residual fuel oils. Although it was not known for certain, it was believed (STUART, 1971) that the two samples of diesel fuel depicted by spectra 2 and 3 (FIG. 3) were not from the same batch. Accordingly, it would appear that the differences between these spectra resulted from differences in the original compositions of the oils and are not merely reflections of changes in composition which occurred as a result of partial degradation o f the oil*. * The thin layer chromatograms of these oils indicated substantial differences in their composition.
64
E. M. LEVY TABLE 6. ULTRA-VIOLET ABSORBANCE CHARACTERISTICS OF SOME DISTILLATE FUEL OILS
Type of oil
A ~ 22s
Low ash distillate Diesel Diesel (partially oxidized) BI diesel
A ,,~ 256
2.86 (228)* 1.822 (226) 0.971 (224) 0.749 (220)
0.632 0.264 0.131 0.111
(252)* (254) (253) (256)
R 4.52 6.90 7.41 6.75
* The numbers in parentheses designate the wavelengths (nm) at which the absorbances were measured.
Lubricating oils The u.v. absorption spectra of several types of lubricating oils are shown in FIG. 4. In contrast with those of both the residual and distillate types of fuel oils, these spectra indicated only very weak and in some cases virtually no absorption of ultraviolet light at wavelengths greater than 250 nm and no clearly defined absorption peak in the neighbourhood of 228 nm. These features by themselves are sufficient to distinguish lubricating oils from the residual and distillate fuel oils. However, with the exception of the spectrum for the stern tube lubricating oil, a type which is continuously lost through the stern tubes of many ships and is, therefore, a common pollutant in marine environments, these spectra for the various lubricating oils do not differ sufficiently in appearance to provide a means of distinguishing between them. The slight differences in spectra 3, 4 and 5 result from changes in composition that have resulted from using the oil. Because of the absence of a clearly defined absorption peak in the neighbourhood of 228 nm, however, the absorbance ratio is a much less useful criterion for distinguishing between the various types of lubricating oils than it was
hJ t.) Z flD tv"
0 CO m
2
200
250 WAVELENGTH
300
350
(nm)
FIG. 4. Ultra-violet absorption spectra of some lubricating oils. (1) Stern tube; (2) Diesel; (3) Turbine; (4) Turbine (used); (5) Diesel (used). (These spectra have been displaced vertically
to avoid superimposition.)
65
Identification of Petroleum Products TABLE 7. ULTRA-VIOLET ABSORBANCECHARACTERISTICS OF SOME LUBRICATING OILS Type of oil
A ~ 22s
Stern-tube Diesel Turbine Turbine (used) Diesel (used) BI-lubricating
0.683 0.195 0.096 0.198 0.272 0.154
A~
(226)* (228) (228) (228) (228) (220)
0.267 0.042 0.018 0.048 0.088 0.041
R
256
(260)* (255) (255) (256) (256) (256)
2.56 4.64 5.33 4.13 3.09 3.76
* The numbers in parentheses designate the wavelengths (nm) at which the absorbances were measured.
for the fuel oils. As shown in TABLE7, the absorbance ratios for lubricating oils form a distinct group which, for the most part, is unmistakably different from those obtained for either the residual or the distillate types of fuel oils.
Environmental samples The u.v. absorption spectra of samples of oils collected at Babin's Cove, Chedabucto Bay, N.S., in January 1971 (spectra 1 and 2) and from Sable Island (spectra 3) shortly after the grounding of the Arrow are shown in FXG.5. From the general features of these spectra alone it could be concluded that the two samples from Babin's Cove were identical and that the sample from Sable Island probably came from the same source. This supposition is substantiated by comparing these spectra with those obtained for various concentrations of Bunker C oil recovered from the wreck of the Arrow (FIG. 6). The spectra of FIG. 5 and 6 are strikingly similar. Closer examination reveals that spectra 1 and 2, for the oil collected at Babin's Cove, are exactly congruent with the spectra obtained from the Arrow Bunker C oil at concentrations of 50 and
kl.I Z < if] IY. 0 #tl <
I
200
250 WAVELENGTH
I
300
I
3,50
(nm)
FIG. 5. Ultra-violet absorption spectra of samples of oils collected at Babin's Cove (1 and 2) (Chedabucto Bay), and Sable Island (3). w ^ ~ R 6/I--E
66
E.M. LEVY
iii
0.9
z
I
re
2
O
o9 m
0.5
200
250
550
300
WAVELENGTH (nm)
FIG. 6. Ultra-violet absorption of Bunker C oil recovered from the Arrow. (1) 50 mg l - ' ; (2) 40 mg 1-1 ; (3) 30 mg 1- ~; (4) 20 mg 1-1. 40 m g 1- ~ respectively, a n d similarly that the s p e c t r u m for the oil f o u n d on Sable I s l a n d is identical in all respects with t h a t o b t a i n e d from a solution c o n t a i n i n g 20 m g 1-1 o f the Arrow oil. There seems little d o u b t , therefore, that the oils on the beaches o f B a b i n ' s Cove a n d on Sable I s l a n d o r i g i n a t e d f r o m a c o m m o n source a n d furtherm o r e t h a t this source was the cargo o f the Arrow. This conclusion is s u b s t a n t i a t e d by c o m p a r i n g the a b s o r b a n c e r a t i o s for the samples f r o m B a b i n ' s Cove a n d t h a t f r o m Sable Island, as given in TABLE 8, with those in TABLE 2 for the oil carried b y the Arrow. O f c o n s i d e r a b l e significance also is the fact t h a t the samples f r o m B a b i n ' s Cove were collected in J a n u a r y 1971, a l m o s t a y e a r after the g r o u n d i n g o f the Arrow. This inTABLE 8. ULTRA-VIOLET ABSORBANCE CHARACTERISTICS OF RESIDUAL OILS FOUND AT BABrN'S COVE, N.S., SABLE ISLAND AND THE MAGDALEN ISLANDS, P.Q.
Sample Babin's Cove 1 2 Sable Island Magdalen Islands ! 2 3 4 5
A228
,42s6
R
1.089 (228) 1.322 (229) 0.616 (230) 0.456 (228)
0.696 0.847 0.402 0.291
(255) (257) (254) (256)
1.56 1.56 1.53 1.57
0.562 0.920 0.674 0.730 0.522 0.315 0.801 0.655 0.726 0.779
0.438 0.685 0.522 0.560 0.376 0.235 0.599 0.491 0.557 0.572
(255) (256) (255) (256) (256) (256) (255) (256) (256) (256)
1.28 1.34 1.29 1.30 1.39 1.34 1.34 1.34 1.30 1.36
(228) (224) (228) (224) (228) (224) (228) (228) (228) (228)
Identification of Petroleum Products
67
I.M
(J =,, ,< m re
O u} ca
I
200
I
250
J
300
WAVELENGTH
350
(nm)
FIG. 7. Ultra-violet absorption spectra o f samples o f oil collectedlon the Magdalen Islands.
dicates that weathering of these samples had not significantly altered the relative concentrations of the compounds responsible for the u.v. absorption characteristics. Changes in composition due to weathering severely limit gas chromatographic and trace metal analyses in the identification of the sources o f petroleum products in the marine environment. The use of the ultra-violet absorption approach is illustrated further by the spectra in FIG. 7, obtained from five samples of residual oils collected at various sites on the west side of the Magdalen Islands. It is apparent from the spectra that the samples were probably derived from a common substance, the spectral differences being solely those which result from slight concentration differences. These spectra are superimposable onto those (FIG. 8) solutions containing 20-30 mg 1-t of Bunker C oil carried by the Whale, thereby providing convincing evidence that the oil which con-
I.Z0.9 0"60'3'
200
I
250 300 WAVELENGTH (nm)
,
350
FIG. 8. Ultra-violet absorption spectra of Bunker C oil recovered from the Whale. (1) 50 mg 1-1; (2) 40 mg 1- 1; (3) 30 mg 1- 1; (4) 20 mg 1-1.
68
E.M. LEVY
taminated the beaches of the Magdalen Islands originated from the sinking of this barge. This conclusion is confirmed by comparing the absorbance ratios for these samples (TABLE 8) with those obtained for the Bunker C oil carried by the Whale (TABLE 3). Again, this degree of agreement would be extremely unlikely unless the compositions of the samples were identical. There can be little doubt, therefore, that the oil which polluted the beaches of the Magdalen Islands resulted from the Whale incident.
Comparison of analytical methods to identify the sources of oil pollution The most commonly used methods for the identification of the source of oil pollution are gas chromatographic and trace metal analyses (ANON, 1970b ; HOROWITZet al., 1969). Some of the lower boiling constituents may be identified by gas chromatographic analyses and this information may, in some cases, be used to isolate the source of oil pollution. This method is particularly suited to the identification of the source o f crude oils, distillate fuel oils and other petroleum fractions which contain significant concentrations of low boiling constituents. However, it is subject to serious ambiguities which may arise when the volatile compounds evaporate or other constituents dissolve or become altered by chemical weathering or microbial action. It is much less suitable for the identification of residual oils because of the refractory nature of the compounds, which remain in these materials after the volatile fluxes have escaped. The identification of oil pollutants by means of their trace metal contents is similarly suitable for dealing with certain restricted situations. Few metals are present in petroleum products in sufficiently high concentrations for this purpose, and nickel and vanadium are most commonly used. Since some fractions of the oil might have disappeared, concentrating the involatiles, the absolute concentrations of these metals does not provide reliable information. Accordingly, the ratio of the vanadium and nickel contents is taken as the criterion for identification purposes. However, these metals are commonly present in petroleum in forms that may be volatile or water soluble or may become water soluble on exposure to sea water and thereby escape from the oil as it weathers. The ultra-violet absorbance method used in this investigation does not appear to be subject to most of these uncertainties. In contrast with gas chromatographic techniques, no attempt is made in this method to identify all or even a few of the compounds present in the oil--an extremely difficult task in view of the variety and complexity of the structures that may be present in many petroleum products, particularly in heavy and residual oils or in tarry substances. Instead, the contributions from all the compounds capable of absorbing light in the appropriate region of the spectrum are considered as a group. The approach described in this paper does not provide any information concerning saturated hydrocarbons or other compounds that do not absorb light and is, therefore, only applicable to oils that contain suitable concentrations of absorbing species. There is, however, an abundance of such structures in the heavier oils and particularly in the residual oils. Furthermore, because of the chemical nature of these compounds there is little danger of them escaping from the oil soon after the spill or of them undergoing rapid changes because of weathering processes. Indeed, it has been shown that Bunker C oil from the Arrow had not changed ostensibly, as far as this method of identification is concerned, after almost a year's exposure to weathering processes.
Identification of Petroleum Products
69
A further advantage o f the ultra-violet absorption technique is that it requires a very small amount, approximately 0.06 m g o f the oil. Consequently, it m a y be used for the identification o f the source o f oil dispersed t h r o u g h o u t the water column, where only a small a m o u n t o f the oil might be available, as well as that floating on the surface o f the water or lying on the beaches. SUMMARY Ultra-violet absorption spectra provide a convenient m e t h o d for the identification o f the source o f petroleum products present in the marine environment. The absorbance at 228 n m relative to that at 256 n m has been shown to be a sensitive and reliable criterion for distinguishing between different members o f similar types o f oils and is not subject to m a n y o f the uncertainties o f other methods o f identification. This m e t h o d was successfully applied to the identification o f the sources o f residual oils f o u n d on the shores o f C h e d a b u c t o Bay, Sable Island and the Magdalen Islands. Acknowledgements--The competent technical assistance of Mrs. SHARON H.~TLING and Mrs.
COLLEENMcCORMACKis gratefully acknowledged. The author is particularly indebted to Mr. R. A. SrU,~T, Defence Research Establishment Atlantic, who provided most of the samples of oils used as standards for this investigation, and to Dr. A. WALTONand Mr. A. R. COOTEwho reviewed the manuscript. REFERENCES ANON(1970a) "The ARRO W lncident". Report of the Scientific Coordination Team to the Head of the Task Force Operation Oil. Prepublication edition, pp. 6-15. Compiled at Atlantic Oceanographic Laboratory, Bedford Institute, Dartmouth, Nova Scotia. ANON(1970b) Analytical methods for the identification of the source of pollution by oil of the seas, rivers and beaches. J. Inst. Petroleum 56, 107-117. HOROWITZJ., GOMTZ G. D., NEMCrm~ R. G. and MELOYT. P. (1969) Identification of oil spills: Comparison of several methods. Proceedings--Joint Conference on Prevention and Control of Oil Spills sponsored by American Petroleum Institute and Federal Water Pollution Control Administration, December 15-17, pp. 283-296. LoucKs R. H. and LAWRENC~D. J. (1971) Reconnaissance of an oil spill. Marine Pollut. Bull. 2, 92-94. STUARTR. A. (1971) Private communication.