Burnison, B. K. Can. J . Fish. Ag. Sci. 1980,37, 729. Hoskins, L. C.; Alexander, V. Anal. Chem. 1977,49, 695. Nichols. H. W. In "Phvcoloaical Methods," Stein, J. R. Ed.; Cambridge University Press: London, 1973; p '20. (19) Stainer, R. Y.; Junisawa, R.; Mandel, M.; Cohen-Bazire, G. Hactcriol. Reo. 1971, 35, 171. (20) Oliver, B. G. Water Chlorination: Enuiron. Impact Health E//., Proc. Con/. 3, in press. ( 2 1 ) Singer, P. C., Department of Environmental Science and En-
gineering, University of North Carolina, Chapel Hill, NC, personal communication, 1980. (22) Kerr. J. D.: Suhha Rao Monoer. Oceanoer. Methods 1966., 1., 65. (23) Aiken, G. R.; Thurman, E. M.; Malcolm, R. L.; Walton, H. F. Anal. Chem. 1979,52, 1799.
-
L
Receioed for reuiew April 8, 1980. Accepted July 24,1980.
Isolation and Identification of a Direct-Acting Mutagen in Diesel-Exhaust Particulates Stephen M. Rappaport," Yi Y. Wang, and Eddie T. Wei Department of Biomedical and Environmental Health Sciences, School of Public Health, University of California, Berkeley, California 94720
Robert Sawyer Department of Mechanical Engineering, University of California, Berkeley, California 94720
Bruce E. Watkins and Henry Rapoport Department of Chemistry, University of California, Berkeley, California 94720
Diesel-exhaust particulates contain chemicals which are directly mutagenic in the Ames test. This indicates that the mutagens are not among those classes of mutagenic compounds associated with soot, nor are they among those classes of unstable compounds which are currently known to be directly mutagenic. Reported herein are the isolation, identification, and synthesis of one direct-acting mutagen, pyrene3,4-dicarboxylic acid anhydride, from a sample of dieselexhaust particulates. Although this compound is only weakly mutagenic in the Ames test (220 net TA 98 revertantdmg), it is speculated that it is but one of a class of mutagenic dicarboxylic acid anhydrides of various polynuclear aromatic hydrocarbons in diesel exhausts. Particulate matter emitted from vehicular engines contains organic compounds, some of which are carcinogens (1-5). The classes of carcinogens identified thus far include unsubstituted polynuclear aromatic hydrocarbons (PAH), amino-substituted PAH, and nitrogen heterocyclic compounds. These carcinogens and their analogues are active in the Ames Salmonellalmicrosome mutagen bioassay (6, 7). Their activity is only observed, however, after the addition of mammalian enzymes which convert them to mutagenic forms. Recent investigations have shown that vehicular engine exhausts contain other organic compounds which are directly mutagenic in the Ames test, Le., mammalian enzymes are not required for activity to be observed (8-10) though activation by bacterial enzymes may be involved (8).These compounds, which contribute the majority of the mutagenic activity, have not been identified. I t is suspected that some are stable in the environment since direct mutagenic activity has been observed in air-pollution particulates (of vehicular origin) collected over 15 yr ago (8). We infer from these findings that the direct-acting mutagens in engine-exhaust particulates may represent a new and hitherto unrecognized class of environmental toxins. This inference is based in part upon the apparent stabilities of these mutagens after they are formed. Thus far, most compounds (9) known to be directly mutagenic are alkylating agents which are unstable in the environment since they react rapidly with commonly encountered nucleophiles such as water. This is not the case for direct-acting mutagens in engine exhausts. 0013-936X/80/0914-1505$01.00/0
A previous paper (9)suggested the futility of trying to assess the hazard that unidentified direct-acting mutagens from engine exhausts may pose to human health. Thus, it is important that the chemical identities of these mutagens be determined. This will shed light not only upon potential health hazards but also upon the environmental fates of these substances and upon their formation and control. Mutagens which have been identified can then be tested in mammalian systems to determine whether they, indeed, have deleterious effects on more complex organisms. The mutagens can also be measured in the environment and during the combustion process, so that their production can be related to the designs and performance of engines. We report here the characterization of one direct-acting mutagen, pyrene-3,4-dicarboxylic acid anhydride (PDAA), which was isolated from a sample of diesel-exhaust-particulate matter. Although this compound is a weak mutagen in the Ames test, we speculate that it may be but one of a class of mutagenic dicarboxylic acid anhydrides of PAH in engine exhausts. Experimental Section Generation and Collection of Diesel-Exhaust Particulates. Exhaust-particulate samples were collected from an experimental diesel engine in the Department of Mechanical Engineering, University of California, Berkeley. The engine, of a type often found in heavy-duty trucks, was mounted on an Eddy-Current dynamometer to simulate loaded operation. Pertinent specifications and operating conditions are given in Table I. Exhaust emissions were drawn through a stainless steel probe located in the center line of the exhaust pipe. Particulate matter was collected on high-efficiency glass-fiber filters a t 63-66 "C. Two types of filters were used. Forty rectangular 20.3 X 25.4 cm filters (Type A B , Gelman Instrument Co., Ann Arbor, MI) were used for -30 min each to collect a total of 20 g of particulate matter. Two pleated HEPA filters (Type 7040-L-N2N2-BBD, 47.0 X 17.5 cm, Flanders Filters Inc., Washington, NC) were used for 18 h each to collect an estimated 20 g of sample. Since the HEPA filters were contained in plywood frames, weight estimates of these samples were based upon weighings of equal areas of clean filter media and samples.
@ 1980 American Chemical Society
Volume 14, Number 12; December 1980
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paratus. Each rectangular-filter was extracted with 250 mL of CH2Cl2 for 12 h followed by extraction with CH3CN for 12 h. Pleated HEPA filters were divided into two portions which were each extracted with 1500 mL of CH2Cl2 for 24 h followed by extraction with CH&N for 24 h. Extracts of each type of filter were combined, reduced in volume by rotary evaporation a t 25-35 "C to a few milliliters and filtered through Teflon membrane filters (Type FHLP 00-25-00, 0.5-pm pore size, Millipore Corp., Bedford, MA). Aliquots of combined extracts were dried under Ne at 30-35 "C and weighed. A total of 846 mg of material was extracted from the rectangular filters (581 mg of CH2C12 265 mg of CH3CN) yielding an extraction efficiency of 4.2%. The corresponding mass of extract from the pleated HEPA filters was 987 mg (CHaC12: 489 mg; CH3CN: 498 mg) or 4.9% of the particulate. After preliminary testing showed extracts of both types of filters to have comparable mutagenic activities, extracts of each solvent were combined, yielding 1070 mg of CHpC12 extract and 763 mg of CH3CN extract. Ames Assay. Aliquots of extracts or chromatographic fractions were dried under dry N2 a t 30-35 "C, dissolved in MezSO, and applied to Salmonella typhimurium tester strain TA98. This tester strain had previously been shown to be the most sensitive indicator of mutagenicity for direct-acting mutagens in the samples. The protocol outlined by Ames et al. (11)was followed without modification. Each dose level was tested in duplicate or triplicate. Specific activities were calculated as the slopes (in linear ranges) of dose-response curves. A positive control, 2-nitrofluorene, which is a known mutagen in TA98 and a carcinogen, was run concurrently with each batch of samples. The specific activity of 2-nitrofluorene in our laboratory was 75 f 7.1 (F f s) net TA98 revertants per 1.0 pg per plate. Crude extracts of the filters were tested with and without the addition of Aroclor-induced rat-liver enzymes (S-9). Chromatographic fractions were only tested for direct-acting mutagens. Low-Resolution Liquid Chromatography. Direct-acting mutagens were concentrated from the extracts by low-resolution liquid-adsorption chromatography. Samples were injected via a 6-mL Teflon loop into a glass column (25 X 1.5 cm i.d.) containing silica gel (Bio-Si1 A, 100/200 mesh, Bio-Rad Laboratories, Inc., Richmond, CA). Glass-distilled solvents (Burdick and Jackson Laboratories, Inc., Muskegon, MI), pumped through the column a t 10 mL/min by a preparative pump (Model RP-SY-ICSC, Fluid Metering, Inc., Oyster Bay, NY), were switched in order of increasing solvent strength with a six-port Teflon rotary valve. Each solvent eluted the column with three void volumes (-90 mL). The eluate was monitored by a UV (254 nm) photometer (Model 152, Altex, Inc., Berkeley, CA) equipped with a preparative flow cell of 0.5-mm path length. Serial injections of 1200 mghnjection were made until the entire sample had been used. Fractions were reduced in volume by rotary evaporation at 25-35 "C, and aliquots were removed for measurement of mass and mutagenic activity. High-Resolution Liquid Chromatography. One preparative fraction was further fractionated by high-performance LC. The high-performance LC system consisted of two Model 100 pumps, a Model 400 solvent programmer, a Model 905-42 injection valve with a 500-pL loop, and a Model 152 UV (254 nm) photometer equipped with an analytical flow cell of 10-mm path length, all obtained from Altex, Inc. (Berkeley, CA). A fully porous silica microparticle column (Partisil PXS 10/25, Whatman, Inc., Clifton, NJ) was used. Synthesis of PDAA. 1,2,3,6,7,8-Hexahydropyrene (2) (12), 4-acetyl-1,2,3,6,7,8-hexahydropyrene (3) (13),4-acetylpyrene
engine model bore X stroke piston displacement horsepower compression ratio fuel load water temp
Cummins Turbodiesel (6 cylinder) JT-6-Bl 10.5 X 12.7 cm 6570 om3 175 at 2500 rpm 15.8 to 1 diesel fuel No. 1 dynamometer, 40-45 ft Ib. at 2000 rPm 60-76 "C
+
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Environmental Science & Technology
(4) (14),and 3-oxo-3,4-dihydrocyclopenta[cd]pyrene(6) (15) were synthesized as reported in the literature with the following modifications: acylation of 2 was done in methylene chloride and aromatization of 3 was accomplished with 2,3dichloro-5,6-dicyanobenzoquinone. 4-Pyreneacetic acid ( 5 ) was prepared from 4 by the Kindler modification of the Willgerodt reaction (16) in which 0.93 g (3.8 mmol) of 4,0.20 g (6.2 mmol) of sulfur, and 10 mL of morpholine were refluxed for 40 h under a nitrogen atmosphere. The resulting thioamide was hydrolyzed to give 5 in 40% yield as in the literature ( 17). 3,4-Dioxo-3,4-dihydrocyclopenta[cd]pyrene (7) was prepared as follows. To 120 mg (0.50 mmol) of 6,dissolved in 150 mL of 70% aqueous acetic acid at 90 "C under a nitrogen atmosphere, was added to 70 mg (0.60 mmol) of SeO2, and the solution was stirred for 36 h a t 90 "C. The reaction mixture was cooled to room temperature and filtered, the filtrate was diluted with water (400 mL) and extracted with CHCl3 (2 X 100 mL), the chloroform solution was dried over sodium sulfate, and the solvent was evaporated to give a quantitative yield of crude 7: mp 260 "C (dec); IR 1730 cm-1 (C=O). High-resolution mass spectrum calcd. for ClgH802: (M+) 256.0524. Found: 256.0531. Mass spectrum, mle 228 (M+ 28), 200 (M+ - 28 - 28). A chromatographically pure sample was obtained by preparative reverse-phase high-performance LC on an Altex LiChrosorb c-18column (60% CHsCH, 40% HzO). UV A,, (CH2C12) 242 nm, 264,283,357,383; Amin 255 nm, 277,311,378. PDAA (8)was prepared as follows. To 40 mg of crude 7, suspended in 50 mL of 5% KOH, was added lo00 mol % of 30% hydrogen peroxide, and the mixture was stirred for 15 h. The reaction mixture was filtered and then acidified with concentrated HC1. The resulting precipitate was dried a t 100 "C over Pz05 in vacuo and sublimed (180 "C, 50 mmHg): yield, 50%;mp > 330 "C; mass spectrum, mle 272 (M+), 228 (M+ 44), 200 (M+ - 44 - 28); IR 1740,1765 cm-l (C=O); UVm,, (CH2C12) 285 nm (log e ) (4.22, sh), 2.95 (4.37), 313 (3.59), 329 (3.68), 278 (4.28), 387 (4.26, sh), 401 (440); Amin 273 (3.96),310 (3.58), 321 (3.50), 336 (3.60), 399 (4.12); A,, (5%aq KOH) 269 (4.22), 280 (4.40),355 (4.26),350 (4.38); Amin 256 (3.981, 273 (4.20),299 (3.60), 341 (4.21). Anal. Calcd. for Cl~H803:C, 79.4; H, 3.0. Found: C, 79.1; H, 3.0. The sample was chromatographically pure (k' = 11)on an Altex LiChrosorb Cis column (50%CH3CN, 50% H20). Analytical Procedures. Ultraviolet spectra were recorded on a Cary 219 UV-Vis spectrophotometer. Infrared spectra were recorded as KBr pellets on a Perkin-Elmer 337 infrared spectrophotometer. Mass spectra were obtained by direct insertion into the E1 sources of AEI MS-12 and CEC-21-11OB mass spectrometers. Combustion analysis was performed by the Analytical Laboratory, Department of Chemistry, University of California, Berkeley.
I
I
I
I
I200 -CH2Cl2
Extract
I
/
-I
CHJCN E x t r o c l
Figure 1.
Dose response curves of extracts of diesel-exhaustpartic-
ulates.
Results and Discussion The results shown in Figure 1 indicate that virtually all of the mutagenic activity of extracts of diesel-exhaust particulates was direct acting. Addition of S-9 to the extracts diminished their activities, a result previously observed for both air-pollution particulates (8) and gasoline-engine particulates (8, IO). Figure 1also suggests that these direct-acting mutagens were efficiently extracted from the particulates by CH2Clz since the specific activity of the CH2C12 extract was 3.5 times that of the CH3CN extract (5.5 vs. 1.7 net TA98 revertantslpg). A series of low-resolution chromatographic separations concentrated the direct-acting mutagens in fractions of intermediate polarity (Table 11). This was accomplished by sequentially eluting first the extracts (separation L-1) and then fractions thereof (separations L-2 and L-3) from the
silica-gel column with mobile phases of increasing solvent strength. In each case, the fraction with the highest specific activity was used as the sample in the next separation. Table I1 leads one to conclude that the direct-acting mutagens cannot be isolated in a single fraction on the basis of polarity. Although specific activities of various fractions increased, the percentage of total activity represented by each fraction continuously decreased. For instance, fraction 11 with a specific activity of 25.2 net TA98 revertants/pg accounted for less than 10% of the activity of the crude extracts. This suggests that the direct-acting mutagenicity of diesel particulates is based upon the collective action of several mutagens and probably of several distinct chemical classes of mutagens. Fraction 11 was subfractionated by high-performance LC on a microparticle silica column. First, it was divided into three fractions by sequential elution with CH2C12, CHSCN, and CH30H (separation H-1). As shown in Table 11, all three fractions were mutagenic with the highest specific activity in the CH30H eluate (fraction 16). Fraction 16 was reinjected into the column and eluted with a CH3CNICH30H gradient (separation H-2). As shown in Figure 2 , the 5.3 mg of fraction 16 was separated into 16 subfractions, each containing less than 1 mg. After the Ames test was performed, fraction 18 contained -90 pg, with a specific activity of 50 net TA98 revertantslpg. Approximately l/4 of this fraction was used to obtain mass spectra. Because the fraction obviously contained more than one component, the source temperature of the mass spectrometer was slowly increased from 50 to 250 "C to allow successive sublimation of the various compounds. Two distinct pulses of total ion current were observed. Mass spectra of the first (and larger) pulse were characterized by a mixture of oxygenated aliphatic and aromatic compounds of indeter minate structures. The second pulse, however, yielded spectra which were dominated by three intense ions at mle 272,228, and 200. This was highly suggestive of a dicarboxylic acid anhydride (molecular weight 272) of a PAH, which specifically eliminates CO2 and C203. The presence of dicarboxylic acid anhydrides of PAH in engine-exhaust particulates has apparently never been reported. A possible source of these compounds would be the oxidation of certain PAH at elevated combustion temperatures, particularly those PAH containing five-membered unsaturated rings, e.g., cyclopenta[cd]pyrene, cyclopenta[cd]benzo[ghi]perylene, and cyclopenta[jk]naphtho-
Table II. Mutagenic Activities of Fractions of Diesel-Particulate Extracts Prepared by Liquid Chromatography separatlon no.
sample
CH&
extract
L- 1
eluant
hexane CH2Cl2 CH30H
CH&N extract
fractions 2
fraction 8 fraction 11
+5
L- 1
L-2
L-3
H- 1
hexane CH2C12 CH30H 17 % CHpC12/hexane 2 % IPA/CH&12 IPA CH30H 0.5% IPA/CH&12 2 % IPA/CH2C12 CH30H CH2C12
CH3CN CH3OH
fraction no.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
mass of fractlon, mg
708 158 150 27 100 755 149 67 47 23 19 31 10 5.1 7.1 5.3
specific actlvlty, net TAB8 revlpg
1.6 16.0 2.9 4.4 11.0 1.1 6.2 11.2 1.2 3.7 25.2
7.0 6.0 36.2 17.0 70.2
total actlvlty, net TAB8 rev x 105
11.3 25.3 4.4 1.2 11.0 8.3 9.2 7.5 0.6 0.8 4.8 2.2 0.6 1.8 1.2 3.7
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-
I _
1 4
3%
CH30H/CH3CN
Increase CH30H ot 3 2%/rnin
-
CH30H
Mobile Phase
1-pyreneacetic acid (10) (Scheme 11).All attempts to cyclize 10 to 11 in polyphosphoric acid or phosphorous pentoxide in methanesulfonic acid gave only polymeric material. The acid R
Scheme II
23 24
9 Froctlon No
Time (mtn)
Figure 2. High-performance LC chromatogram or traction 16. Column: Partisil PXS 10125. Flow rate: 1 .O mL/min.
[l,O,’l-efg]pyrene, all of which have been identified in engine exhausts (4).It is also possible that these compounds could be formed, at least partially, during air sampling by oxidation of PAH on the filter surface. The presence in carbon black adsorbates of both cyclopenta[cd]pyrene and a dicarboxylic acid anhydride of molecular weight 272 has been reported (18).Possibly, cyclopenta[cd]pyrene, which is a potent indirect-acting mutagen (19),could be oxidized to produce a dicarboxylic acid anhydride (PDAA) of molecular weight 272. The synthesis of PDAA was accomplished according to the route shown in Scheme I. Pyrene (1) was reduced to 1,2,3,5,7,8-hexahydropyrene (2) by sodium metal in amyl alcohol after which 2 was acetylated and then dehydrogenated to give 4-acetylpyrene (4)in 19%yield from 1. The conversion of 4 to 4-pyreneacetic acid ( 5 ) has been reported by use of the classical Willgerodt reaction. This reaction involves using a
sealed tube at high temperature and thus is limited to a small scale. T o avoid this problem we applied the Kindler modification to the Willgerodt reaction (16). Initially, 5 was obtained in only 10%yield; however, the yield was increased to 40% by extending the reaction time to 40 h. Cyclization of acetic acid 5 to ketone 6 in liquid HF proceeded as reported (15)and was oxidized by selenium dioxide in aqueous acetic acid to the a-diketone 7. Crude 7 was oxidized in alkaline hydrogen peroxide to pyrene-3,4-dicarboxylic acid which formed PDAA (8) upon acidification. We initially tried to prepare 8 by way of the easily accessible 1508
Environmental Science & Technology
10
11
chloride of 10 was made, and cyclization was attempted with aluminum chloride in methylene chloride. This also gave polymeric material, in agreement with the literature (15, 20-22). Synthesis of PDAA confirmed that this anhydride was present in fraction 18. The mass spectrum showed the same fragmentation pattern, and high-performance LC retention times were the same in both normal- and reverse-phase systems. When tested in the Ames test, PDAA was directly mutagenic with a relatively low specific activity of 220 net TA98 revertantdmg. The fact that engine-exhaust particulates contain the dicarboxylic acid anhydride of one PAH and probably others is intriguing. These compounds theoretically possess all of the attributes needed to be among the direct-acting mutagens sought; i.e., (1)they are acylating agents and, therefore, likely to interact with biochemical nucleophiles; ( 2 ) their planar structures may facilitate access to DNA; (3) their production during or following combustion is the plausible result of oxidation of known components of engine exhausts; and (4)they are stable in the presence of weak environmental nucleophiles such as water. (PDAA is quite resistant to hydrolysis in the absence of alkali; it can be hydrolyzed to the dianion by heating with 5% KOH.) We speculate that, although PDAA is the only anhydride identified in diesel-exhaust particulate thus far, it is likely that several other anhydrides are also present. Whether one or more of these compounds are potent direct-acting mutagens remains to be determined. It is apparent from the foregoing discussion that diesel particulates contain an extraordinary assortment of organic adsorbates among which are many direct-acting mutagens of as yet undetermined structures. Among these mutagens, PDAA is indicative of anhydrides and other oxygenated PAH whose identities, toxicological properties, and environmental fates remain unknown. Additional research should be directed toward identifying the direct-acting mutagens so that their significance to human health may be determined. Given the complexity of the analytical matrix, it is essential that large quantities of diesel-exhaust particulates be available for study. Our efforts with 40 g of particulates have been only partially successful since pure compounds have only been resolved in quantities of 10-50 pg. Such small samples are difficult to manipulate by conventional methods and seldom allow rigorous characterization of chemical structure. We estimate that at least 1 kg of particulates is required to provide sufficient quantities of pure compounds for identification. Such large samples are difficult to acquire since few facilities are available for generating and collecting them. L i t e r a t u r e Cited (1) Kotin, P.; Falk, H. L., Thomas, M. AMA Arch. Ind. Hyg. Occup. Med. 1954,9, 164.
(2) Kotin, P.; Falk, H. L.; Thomas, M. AMA Arch. Ind. Hyg. Occup. Med. 1955,11, 113. (3) Hoffmann, D.; Theisz, E.; Wynder, E. L. J. Air Pollut. Control Assoc 1965,15, 162. (4) Grimmer, G. “Analysis of Automobile Exhaust Condensates” In “Air Pollution and Cancer in Man”; Mohr, U., Schmahl, D., Tomatis, L., Eds; IARC Publication No. 16, Lyon, France, 1977. (5) Shalbad, L. M. “The Carcinogenicity of Automobile Exhausts, from Data Obtained in the USSR”In “Air Pollution and Cancer
R.; Tejada, S.; Bumgarner, J.; Duffield, F.; Waters, M.; Simmon, V. F.; Hare, C.; Rodriguez, C.; Snow, L. Washington, D.C., Sept
(14) Gerasimenko, Y. E.; Schevchuk,I. N. Zh. Org. Khim. 1968,4, 2198. (15) Konieczny, M.; Harvey, R. G. J . Org. Chem. 1979,44, 2158. (16) Cormack, M.; Spielman, M. A. Org. React. (N.Y.)1946,3, 83. (17) Newman, M. S. J. Org. Chem. 1944,9, 518. (18) Gold, A. Anal. Chem. 1975,47, 1469. (19) Eisenstadt,E.;Gold,A.Proc. Natl. Acad. Sci. U.S.A. 1978,75, 1667. (20) Gold, A.; Schultz, J.; Eisenstadt, E. Tetrahedron Lett. 1978, 4491. (21) Ittah, Y.; Jerima, D. M. Tetrahedron Lett. 1978,4495. (22) Ruehle, P. H.; Fischer, D. L.; Wiley, J. C., Jr. J . Chem. Soc., Chem. Commun. 1979,302.
1978, EPA-60019-28-027. (11) Ames, B. N.; McCann, J.; Yamasaki, E. Mutat. Res. 1975,31, 347. (12) Cook, J. W.; Hewett, C. L. J . Chem. SOC. 1933,401. (13) Vollmann, H.; Becker, H.; Corell, M.; Streeck, H. Liebigs Ann. Chem. 1937,531, 1.
Received for review April 25,1980. Accepted July 21,1980. This work was supported in part by a Biomedical Research Support Grant, National Institutes of Health, in part by a Faculty Research Grant, University of California, Berkeley, and by the Northern California Occupational Health Center.
in Man"; Mohr, U., Schmahl, D., Tomalis, L., Eds.; IARC Publication No. 16, Lyon, France, 1977. (6) McCann, J.; Ames, B. N. Proc. Natl. Acad. Sci. U.S.A. 1976,73, 950. (7) McMahon, R. E.; Cline, J. C.; Thompson, C. Z. Cancer Res. 1979, 39, 682. (8) Wang, Y. Y.; Rappaport,S. M.; Sawyer, R. F.; Talcott, R. E.; Wei, E. T. Cancer Lett. (Shannon, Irel.) 1978,5, 39. (9) Wei, E. T.; Wang, Y. Y.; Rappaport, S. M. J . Air Pollut. Control Assoc. 1980,30, 267. (10) Huisingh, J.; Bradow, R.; Jungers, R.; Claxton, L.; Zweidinger,
Dispersion and Weathering of Chemically Treated Crude Oils on the Ocean Clayton D. McAuliffe" Chevron Oil Field Research Company, La Habra, California 90631
Jaret
C. Johnson and Stephen H. Greene
JBF Scientific Corporation, Wilmington, Massachusetts 01887
Gerard P. Canevari Exxon Research and Engineering Company, Florham Park, New Jersey 09732
Thomas D. Sear1 Exxon Research and Engineering Company, Linden, New Jersey 07036
Four research oil spills of Murban and La Rose crude oils were made off New Jersey. Two slicks were immediately sprayed with a dispersant; two, after 2 h. Average oil contents by IR analysis of a CC14 extract of water samples collected 30-90 min under immediately treated slicks a t 1, 3,6, and 9 m were 0.7,0.7,0.3, and 0.2 mg/L for La Rosa and 3.1,2.4,0.5, and 0.4 for Murban. The highest concentrations were 3 mg/L for La Rose and 18 mg/L for Murban. Oil concentrations for dispersion delayed 2 h were 11.1mg/L, slightly higher than found under untreated oil sampled immediately after discharge. The dispersed oil weathered very rapidly with evaporation of C1-Clo hydrocarbons greatly exceeding solution. Dissolved hydrocarbons were not found a t the method detection limit of 0.01 pg/L. The measured C1-Clo hydrocarbons were residual in dispersed oil droplets, and their sum did not exceed 50 M/L. Introduction
Four research crude oil spills discharged on the open ocean were chemically treated with a dispersant. The underlying water was then analyzed to determine (a) the dispersion of oil into the water column and (b) the rate of loss (weathering)of low-molecular-weight hydrocarbons from the dispersed oil. These tests were conducted in a manner similar to those for untreated spills conducted in 1975 (1,2). The 1975 untreated oil studies showed relatively low initial concentrations of nonvolatile hydrocarbons in the water column under the slicks (generally less than 1 mg/L) that decreased to background values in 1-2 h. Those samples containing naturally dispersed oil showed very rapid weathering. The Cl-Clo hydrocarbons detected were residual in the oil droplets, and truly dissolved
hydrocarbons were apparently not present at detection limits of a few ng/L (1,2).Samples of oil collected over time from the surface slicks showed slower weathering. Chemical dispersion is thought to accelerate the natural weathering processes. This would result in higher concentrations of oil penetrating to greater depths, and accelerated escape of volatile hydrocarbons to the atmosphere. The mechanism for this behavior was expected to be the mixing of dispersed droplets having high specific surface areas in near-surface water, causing rapid loss of volatile hydrocarbons. An untreated slick, although constantly exposed to the atmosphere, may be less susceptible to evaporation than dispersed oil because its lower surface-to-volume ratio tends to retard transport (by diffusion) of volatile hydrocarbons. Oil emulsified in water is removed from most of the wind's influence, so that it does not travel as far as a surface slick. This minimizes the possibility of oil stranding or entering biologically sensitive areas. Review and discussion of the alteration of oil on a water surface provide greater details of the processes (3). Experimental Methods
General Operations. In November 1978, four spills were conducted -40 km off New Jersey and 95 km south of Long Island, New York. Each spill was 1.67 m3 of one of two crude oils (Murban from Abu Dhabi and La Rosa from Venezuela). Each spill was discharged from a 1.9-m3 tank mounted on the research vessel through two 7.6-cm hoses. The ends of the hoses were on plywood floats, causing the oil to discharge horizontally on the water surface. This minimized both evaporation losses due to discharge above the water, and
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14, Number 12, December 1980
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