Environ. Sci. Technol. 2006, 40, 5636-5646
Forensic Fingerprinting of Diamondoids for Correlation and Differentiation of Spilled Oil and Petroleum Products ZHENDI WANG,* CHUN YANG, B. HOLLEBONE, AND M. FINGAS Emergencies Science and Technology Division (ESTD), Environmental Technology Centre, Environment Canada, 335 River Road, Ottawa, Ontario, Canada K1A 0H3
Diamondoids (adamantanes and diamantanes) are rigid, three-dimensionally fused cyclohexyl-ring alkane compounds that can be found in almost all crude oils and in most petroleum products. For forensic environmental investigations, the most commonly used biomarkers are high molecular weight (MW) tri- to pentacyclic terpanes and steranes. Most of these high MW biomarkers, however, are removed from the original crude oil feedstocks during the refining processes, while smaller biomarkers including diamondoids are concentrated in petroleum products. Fingerprinting diamondoids could thus provide another diagnostic means for correlation and differentiation of spilled oils and be particularly valuable for light to midrange distillates, such as jet and diesel fuels, the source of which may be difficult to identify using routine biomarker techniques. In this work, a reliable GC-MS analytical method has been developed for characterization and quantitation of diamondoids. The method detection limits for five target diamondoids were determined to be in the range of 0.060.14 µg/g oil. Distributions of diamondoids in over 100 different oils and refined products were quantitatively compared. The concentrations of four groups of target biomarkers were found, in general, to decrease in the order of sesquiterpanes > terpanes and steranes > adamantanes > diamantanes in both crude oils and refined products. A number of indices of admantanes and diamantanes have been developed and assessed as source indicators using their diagnostic powers (DP). The effects of evaporative weathering and biodegradation on alteration of diamondoid distributions have been quantitatively investigated. Finally, a spill case study by statistical evaluation of diagnostic ratios using the “two-tailed” Student’s t approach is presented to illustrate the unique utility of diamondoids for correlation and differentiation of unknown spilled diesels.
Introduction Diamondoids are rigid, three-dimensionally fused cyclohexylring alkane compounds that have a diamondlike cage structure (1-3). They consist of a pseudohomologous series with the general formula, C4n+6H4n+12, including adamantane (C10H16), dia- (C14H20), tria-, tetra-, and pentamantane (n ) * Corresponding author phone: (613)990-1597; fax: (613)991-9485; e-mail:
[email protected]. 5636 9 ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 40, NO. 18, 2006
1-5) and higher polymantanes, and their alkylated homologues. Adamantane was first discovered and isolated from a Czechoslovakian petroleum in 1933. Since then, more diamondoids and their various alkyl derivatives have been found in crude oils (3-7). Lin and Wilk (8) observed a suite of polymantanes in a gas condensate produced from a very deep petroleum reservoir located in the U.S. Gulf Coast. Dahl et al. (9) reported successful separation of higher diamondoids which contain 4-11 (undecamantane) diamond-crystal cages from petroleum. Adamantanes and diamantanes found in petroleum are thought to be formed from rearrangements of organic precursors including multiring terpenes under thermal stress with strong Lewis acids (typically clays) acting as catalysts during oil generation (1, 2). Schulz et al. (10) have successfully applied diamondoids to distinguish source rock facies. Chen et al. (1) have developed and used two diamondoid hydrocarbon ratios, methyl adamantane index (MAI) and methyl diamantane index (MDI), as novel high maturity indices (11) to evaluate the maturation and evolution of crude oils and to determine the thermal maturity of thermogenic gas and condensate in several Chinese basins, the maturity of which may be difficult to assess using routine geochemical techniques. The diamond structure endows these molecules with a high kinetic and thermodynamic stability. Laboratory thermal cracking experiments (2, 9) have shown that diamondoids have a higher thermal stability than most other hydrocarbons during thermal cracking of oil; therefore, diamondoids become increasingly enriched in the residual oil or condensate. The increase in methyldiamantane (C15) concentration is directly proportional to the extent of cracking, indicating that under the conditions of the experiments, diamondoids are neither destroyed nor created. Instead, they are conserved and concentrated and hence can be considered a naturally occurring internal standard by which the extent of oil loss can be determined. Although diamondoids have found increasing application in petroleum exploration and refining in recent years, there have been few reports of use of these compounds for forensic oil spill investigations, and there are almost no quantitative data on concentrations and distribution of diamondoids in oil and refined products. Stout and Douglas (12) recently reported an application of diamondoids in the chemical fingerprinting of natural gas condensates and gasoline. In this work, a reliable GC-MS method for identification and characterization of diamondoids is developed. Diamondoids are determined in over 100 crude oils and refined products. Distributions of diamondoids in different oils and refined products are quantitatively studied and compared. A number of diagnostic indices of diamondoids with high values of diagnostic power are developed for correlation and differentiation of oils. The effects of weathering including evaporation and biodegradation on diamondoid distributions are quantitatively investigated. Finally, a spill case on source identification of round robin oil samples by statistical evaluation of diagnostic ratios is presented to illustrate the unique utility of diamondoids for fingerprinting, correlation, and differentiation of unknown spilled diesel and suspected spill candidates. The new oil diamondoid data produced from this study will be integrated into the existing Environment Canada oil property database (13) and used to advance the oil spill fingerprinting techniques for application to environmental problems associated with oil spills.
Experimental Section Reagents and Materials. All solvents were of the highest purity available and used without further purification. 10.1021/es060675n CCC: $33.50
Published 2006 by the Am. Chem. Soc. Published on Web 08/16/2006
FIGURE 1. GC-MS chromatograms of adamantanes (m/z 136, 135, 149, 163, and 177) and diamantanes (m/z 188, 187, 201, 215) eluting in the n-C10 and n-C13 and in the n-C15 and n-C17 range in the ESTD standard reference oil (Prudhoe Bay, 13.1% weathered). Calibration standards including d16-adamantane (internal standard) and adamantane (A); 1-methyl-admandane (1MA), 2-methyl-admandane (2-MA), 1,3-dimethyladamantane (1,3-DMA), 2-ethyl-adamantane (2-EA), and other biomarker standards (sesquiterpanes, hopanes, and steranes); n-alkane (n-C9 to n-C36) mixture (>99%); polycyclic aromatic hydrocarbon (PAH) standards (SRM 1491); and deuterated internal and surrogate PAHs were purchased from Aldrich, Chiron AS of Norway, Restek, the U.S. National Institute of Standards and Technology (NIST), and Supelco, respectively. Silica gel (100-200 mesh, 150 Å, pore 1.2 cm2/g, active surface 320
m2/g) was obtained from Fisher Scientific. The ESTD reference oil (13.1% weathered Prudhoe Bay oil), which has been well characterized in this lab (13), was used as the standard reference oil due to its significant contents of both adamantanes and diamantanes as well as all other target biomarkers and PAHs. Oil and Petroleum Product Samples. The oils and petroleum products (including gasoline, kerosene, diesel fuels, residual, bunker B, and bunker C as well as lubricating oils) were obtained from various oil companies and refineries worldwide and stored at 5 °C. The American Petroleum VOL. 40, NO. 18, 2006 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
9
5637
TABLE 1. Diamondoid Compounds Identified in Prudhoe Bay (the ESTD Reference Oil)a peak no.
compounds
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
adamantane 1-methyladamantane 1,3-dimethyladamantane 1,3,5-trimethyladamantane 1,3,5,7-tetramethyladamantane 2-methyladamantane 1,4-dimethyladamantane, cis1,4-dimethyladamantane, trans1,3,6-trimethyladamantane 1,2-dimethyladamantane 1,3,4-trimethyladamantane, cis1,3,4-trimethyladamantane, trans1,2,5,7-tetramethyladamantane 1-ethyladamantane 1-ethyl-3-methyladamantane 1-ethyl-3,5-dimethyladamantane 2-ethyladamantane
18 19 20 21 22 23 24 25 26
diamantane 4-methyldiamantane 4,9-dimethyldiamantane 1-methyldiamantane 1,4- and 2,4-dimethyldiamantane 4,8-dimethyldiamantane trimethyldiamantane 3-methyldiamantane 3,4-dimethyldiamantane
a
molecular formula
base peak
M+ (m/z)
retention index (RI)
Adamantanes A 1-MA 1,3-DMA 1,3,5-TMA 1,3,5,7-TeMA 2-MA 1,4-DMA, cis 1,4-DMA, trans 1,3,6-TMA 1,2-DMA 1,3,4-TMA,cis 1,3,4-TMA,trans 1,2,5,7-TeMA 1-EA 1-E-3-MA 1-E-3,5-DMA 2-EA
C10H16 C11H18 C12H20 C13H22 C14H24 C11H18 C12H20 C12H20 C13H22 C12H20 C13H22 C13H22 C14H24 C12H20 C13H22 C14H24 C12H20
136 135 149 163 177 135 149 149 163 149 163 163 177 135 149 163 135
136 150 164 178 192 150 164 164 178 164 178 178 192 164 178 192 164
1085 1100 1116 1128 1136 1168 1178 1183 1189 1208 1216 1221 1225 1235 1247 1252 1265
Diamantanes D 4-MD 4,9-DMD 1-MD 1,4- and 2,4-DMD 4,8-DMD TMD 3-MD 3,4-DMD
C14H20 C15H22 C16H24 C15H22 C16H24 C16H24 C17H26 C15H22 C16H24
188 187 201 187 201 201 215 187 201
188 202 216 202 216 216 230 202 216
1516 1529 1541 1570 1572 1577 1578 1594 1605
abbreviations
RIA ) 100N + 100 × [(log t′R(A) - log t′R(N))/(log t′R(N+1) - log t′R(N))].
Institute (API) gravities of these oils cover a wide range from 7° to 40°. A laboratory oil-weathering technique (14) by rotary evaporation was used to artificially weather oils with varying degrees of weight loss. This weathering technique allows for precise control of evaporative weight loss of the oil and can be directly correlated to chemical composition changes of the oil. For biodegradation study, six microbial strains (3 aliphatic and 3 aromatic degraders) comprised the standard freshwater water inoculum used in the freshwater oil biodegradation test (15). Oil was added gravimetrically (400 mg) to each flask. Noninoculated flasks served as sterile “weathering” controls (SC) to account for abiotic oil losses through volatility and dissolution during the incubation period. Flasks, which were with or without addition of a sterile standard nutrient solution containing nitrate, ammonium, and phosphate, are termed positive controls (PC) or negative controls (NC), respectively. The treatments of PC and NC were performed in duplicate or triplicate. All flasks were incubated at 10 °C in darkness with shaking at 200 rpm for 28 days. After incubation, 1.0 mL of surrogate standard solution (oterphenyl, d10-phenanthrene, and squalane) was added to monitor extraction recovery. Residual oil was exhaustively extracted with multiple aliquots of dichloromethane (DCM). The extracts were combined, dried with anhydrous sodium sulfate, concentrated, and subjected to comprehensive chemical analysis. Analytical Methods. A rapid, reliable, and effective method for fractionation and quantitation of various oilrelated samples has been developed (16). A chromatographic column (300 mm length × 10.5 mm i.d.) was dry-packed with 3 g of activated silica gel and conditioned with 20 mL of hexane. Aliquots of 200 µL of oil solutions containing ∼16 mg of oil, spiked with appropriate surrogates, were transferred into the chromatographic columns for sample cleanup and fractionation. Saturated and aromatic hydrocarbon factions (F1 and F2) were eluted in order with n-hexane (12 mL) and 5638
9
ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 40, NO. 18, 2006
followed by n-hexane:DCM (1:1, v/v, 15 mL). These two fractions were carefully concentrated under a stream of nitrogen to appropriate volumes, spiked with internal standards (IS), and then adjusted to accurate preinjection volumes of 1.0 mL for GC-MS and GC-FID analyses. F1 was spiked with the IS (d16-adamantane, C30-ββ-hopane, d18-cisdecahydronaphthalene, and 5-R-androstane) for analyses of diamondoids, terpanes and steranes, and sesquiterpanes as well as n-alkanes; and F2 was spiked with d14-terphenyl for analyses of alkylated homologous PAHs and other EPA priority PAHs. Oil samples were processed in batches (7-10 samples), and the ESTD reference oil was analyzed with each batch for quality control. Characterization of n-alkanes and the total petroleum hydrocarbons (TPH) was performed on an HP 5890 GC-FID (16, 18). Analyses of diamondoids, sesquiterpanes (17), and other biomarkers (18) were performed on the Agilent 6890 GC-5973 MSD. The GC separation was achieved using an HP-5MS capillary column (30 m × 0.25 mm i.d. × 0.25 µm film thickness) with a GC oven temperature program: 50 °C for 2 min, heated to 300 °C at 6 °C/min, and held for 15 min at 300 °C. Samples were injected in splitless mode with the injector temperature at 280 °C with helium as carrier gas. The mass spectrometer was operated in the selected ion monitoring (SIM) mode. System control and data acquisition were achieved with the Agilent Enhanced MSD ChemStation. Bicyclic sesquiterpanes, terpanes, and steranes were determined at their characteristic fragment ions at m/z 123, 191, and 217 and 218, respectively. Adamantanes eluted between n-C10 and n-C13 (boiling point range: 174-235 °C) and were analyzed at m/z 136, 135, 149, 163, and 177 for adamantane, methyl-, di-, tri-, and tetramethyladamantanes, respectively; while diamantanes eluted between n-C15 and n-C17 (boiling point range: 270-302 °C) and were analyzed at m/z 188, 187, 201, and 215 for diamantine, methyl-, di-, and trimethyldiamantanes, respectively (Figure 1). The relative response factors (RRF) were determined using
FIGURE 2. Comparison of the TIC chromatograms of adamantanes of selected crude oils (left panel) and refined products from light jet fuel to heavy fuel (right panel). authentic standard diamondoids (A, 1-MA, 2-MA, 2-EA, and 1,3-DMA) relative to the IS d16-adamantane. The RRF obtained from adamantane was used for quantitation of adamantane and diamantane (D) in oil samples. Similarly, the RRFs from 1-MA and 2-MA were used for quantitation of 1-MA, 2-MA, and methyldiamantanes; and RRF from 2-EA for quantitation of 1-EA, 1-E-3-MA, and 1-E-3,5-DMA; and RRF from 1,3-DMA for quantitation of di-, tri-, and tetramethyl-adamantanes, and other methylated diamantanes; respectively.
The method validation studies revealed the following: (1) All 5 target diamondoid standards demonstrated excellent linearity over a large concentration range from 0.005 to 10 µg/mL. (2) Mean recoveries for 5 target diamondoids ranged from 90% to 98% at the low concentration level of 0.050 µg/ mL (n ) 7) with the relative standard deviations (RSD) being in the range of 3-7%. All recoveries were close to 100% at the high concentration level of 5.00 µg/mL (n ) 3) with the RSD being target hopanes and steranes > adamantanes > diamandanes (detailed data are not shown here). On the whole, the mean content of adamantanes is roughly one-order of magnitude higher than diamantanes, which implies that adamantanes may be more discriminatory marker compounds than diamantanes for environmental VOL. 40, NO. 18, 2006 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
9
5641
TABLE 3. Quantitation Results of Diamondoid Compounds in the Biodegraded ASMB Crude Oil and Alaska Diesel under Freshwater Inoculum Conditions (28 Days at 10 °C)a ASMB Oil (ESTD, 1996) oil samples
a
(+) PC (n)3)
(-) NC (n)2)
Diesel Fuel (Alaska, 1996) SC (n)1)
(+) PC (n)2)
(-) NC (n)2)
SC (n)1)
2.54 6.09 5.88 2.18 0.45 8.34 9.36 3.29 5.93 7.34 2.32 2.80 4.37 3.92 7.81
10.5 28.1 28.0 11.6 2.48 33.5 45.9 16.8 26.4 38.8 12.2 12.1 16.7 19.7 35.4
6.57 20.3 23.1 10.2 2.34 30.1 43.7 16.1 27.4 38.7 12.6 11.8 18.5 20.7 38.0
15.9 38.1 38.3 14.7 3.21 43.4 57.2 18.3 32.6 44.4 13.6 12.9 19.6 22.3 39.1
Diamantanes (µg/g oil) 4.13 4.34 2.67 3.28 0.82 0.89 1.75 2.05 0.76 0.83 0.49 0.71 0.43 0.57 0.44 0.61 1.43 1.73 39.1 72.6 12.9 15.0 52.0 87.6
25.3 14.3 3.86 6.28 5.80 9.60 4.28 8.36 6.18 336 84.0 420
24.7 14.7 4.08 6.70 5.82 9.02 4.37 8.11 6.57 320 84.1 404
22.6 15.2 4.26 6.74 5.80 9.69 4.55 8.87 6.54 414 84.3 498
0.79 1.06 0.72 2.30 1.06 0.69 0.43 1.34 0.91 2.90 2.28 0.68 3.18 2.28 2.31 0.25 0.90 1.44
0.53 0.74 0.52 1.61 0.84 0.64 0.41 1.39 0.98 3.02 2.69 0.71 3.08 2.19 2.24 0.28 0.93 1.50
0.97 1.17 0.86 2.80 1.17 0.81 0.41 1.20 0.88 2.88 2.22 0.73 3.26 2.26 2.33 0.27 0.94 1.44
Adamantanes (µg/g oil) 0.73 2.26 2.59 0.98 0.23 4.03 5.30 1.67 3.44 4.58 1.39 1.65 2.78 2.55 4.92
A 1-MA 1,3-DMA 1,3,5-TMA 1,3,5,7-TeMA 2-MA 1,4-DMA, cis+trans 1,3,6-TMA 1,2-DMA 1,3,4-TMA, cis+trans 1,2,5,7-TeMA 1-EA 1-E-3-MA 1-E-3,5-DMA 2-EA
1.24 3.97 3.91 1.56 0.34 6.33 7.36 2.66 5.08 6.71 2.07 2.45 4.05 3.88 7.52
D 4-MD 4,9-DMD 1-MD 1,4- and 2,4-DMD 4,8-DMD TMD 3-MD 3,4-DMD sum of adamantanes sum of diamantanes total diamondoids
4.24 3.24 0.87 2.05 0.83 0.69 0.56 0.63 1.74 59.1 14.9 74.0
1-MA/2-EA 1-MA/1,2-DMA 1-MA/1,3,4-TMA 1-MA/1,2,5,7-TeMA 1,3-DMA/1,2-DMA 1,3,5-TMA/1,3,6-TMA 1,3,6-TMA/1,3,4-TMA 2-EA/1,2-DMA 2-EA/1,3,4-TMA 2-EA/1,2,5,7-TeMA 1,2-DMA/1,3,5-TMA 1,2-DMA/1,3,4-TMA 1,3,4-TMA/1,2,5,7-TeMA 4-MD/1-MD 4-MD/3,4-DMD 4,9-DMD/(1,4- and 2,4-+4,8-DMD) 4,9-DMD/TMD 3,4-DMD/TMD
Diagnostic Ratios of Target Diamondoids 0.53 0.48 0.78 0.77 0.69 1.03 0.59 0.52 0.83 1.90 1.70 2.63 0.76 0.77 0.99 0.58 0.59 0.66 0.40 0.37 0.45 1.49 1.43 1.32 1.12 1.07 1.06 3.64 3.52 3.37 3.32 3.47 2.72 0.76 0.75 0.81 3.24 3.29 3.17 1.56 1.62 1.60 1.85 1.87 1.89 0.57 0.64 0.58 1.55 1.69 1.56 3.11 3.25 3.04
PC: positive control with nutrient addition; NC: negative control without nutrient addition; SC: sterile control.
forensic investigations. (4) Light fuel oils including gasoline and kerosene contain very low quantities of adamantanes but no diamantanes, while the midrange fuels such as jet and diesel fuels have significantly higher concentrations of adamantanes and diamantanes (400-2000 and 50-600 µg/g oil, respectively). Similarly, only trace levels of adamatanes and diamantanes were detected in most lube oils. The significantly different distribution patterns of diamondoids among various refined products apparently result from the refining processes, which remove or concentrate diamondoids in the refined products from their original crude oil feedstocks. (5) Among 17 adamantanes, A, 1-MA, 2-MA, 2-EA, 1,2-DMA, 1,3-DMA, and 1,4-DMA are found to be often the most abundant; while D, 4-MD, 1-MD, and 3-MD are found to be often the dominant compounds among diamantanes. 1,3,5,7-Tetramethyladamantane was consistently found to have the lowest concentration of the adamantane series. This 5642
9
ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 40, NO. 18, 2006
is most likely due to the fact that 1,3,5,7-TeMA is less thermodynamically stable than the other adamantanes (7). The group of methyladamantanes contains only two isomers (Figure 1, peak 2: 1-MA, and peak 6: 2-MA) due to their structural symmetry. Either 1-MA (a bridgeheadsubstituted) or 2-MA is the most abundant homologue in all oils. Similarly, 4-MDA (peak 19 in Figure 1) is also a bridgehead methylated compound. The methyl substitution in adamantane or diamantane at a bridgehead position (i.e. position of a tertiary carbon in the ring structure) creates a more stable molecule than substitution at a secondary carbon atom (carbon position 2) as the later produces additional skew-butane repulsions that are not imposed by the bridgehead attachment (Wingert, 1992). Therefore, 1-MA has a higher thermal stability than 2-MA. Likewise, 4-MDA has a higher thermal stability than 1-MDA (peak 21) and 3-MDA (peak 25). Stable hydrocarbons will gradually increase in
FIGURE 4. Cross-plots of the diagnostic ratios of (1-MA/2-EA versus 1,3-DMA/1,2-DMA) and (1,3-DMA/1,2-DMA versus 1,4-DMA/1,3,5-TMA) for more than 40 oils and petroleum products. relative abundance over the less stable isomeric ones with increasing thermal stress during the oil geological formation time. The diamondoid quantitation results demonstrate this trend: the concentrations of the less thermally stable 2-MA are higher than the more thermally stable 1-MA in immature oils (such as in heavy California API 15, Platform Irene, Cold Lake Bitumen, Orinoco Bitumen, and Mars oil), while 1-MA is more abundant than 2-MA in more mature oils (such as in the lighter Alaska North Slope, Prudhoe Bay, and South Louisiana oils). Diagnostic Molecular Indices of Diamondoids. Numerous diagnostic ratios of biomarkers, many of which originated from geochemistry (19), have been developed and used in environmental forensic oil fingerprinting and spill source identification (18-30). In principle, a large number of diagnostic ratios can be produced from 26 diamondoids. Due to low abundances or poor peak separation, however, ratios of certain peaks can be heavily affected by measurement errors. Thus, proper selection of diagnostic ratios is important in order to keep the uncertainties to a minimum and yield reliable results. In this work, diagnostic power (DP) (31) is applied for selection of diagnostic ratios of admantanes. DP is defined as the relative standard deviation (RSD) of a diagnostic ratio for oils of different origins (80 samples in this work) divided by the RSDR of the same ratio calculated from six measurements of the ESTD reference oil (13.1% weathered Prudhoe Bay oil). Nine ratios of adamantanes having high DP (>10) values (1-MA/2-EA, 1-MA/1,2-DMA, 1-MA/1,3,4-TMA, 1-MA/1,2,5,7TeMA, 2-EA/1,2-DMA, 1,3-DMA/1,2-DMA, 1,4-DMA/1,3,5TMA, 1,2-DMA/1,3,5-TMA, 1,3,5-TMA/1,3,6-TMA) and 5
ratios of more degradation resistant diamantanes within the same isomeric groups and between isomeric groups with different alkylation levels (Tables 2 and 3) are selected from more than 60 possible diagnostic ratios as more sensitive and reliable parameters for correlation and differentiation of oils and petroleum products. As an example, Figure 4 depicts the cross plots of (1-MA/2-EA versus 1,3-DMA/1,2DMA) and (1,3-DMA/1,2-DMA versus 1,4-DMA/1,3,5-TMA) for more than 40 oils and petroleum products. There is a large scatter in the cross-plot data: 1-MA/2-EA, 1,3-DMA/ 1,2-DMA, and 1,4-DMA/1,3,5-TMA fall in the ranges of 0.54.0, 0.5-4.5, and 1.0-7.0, respectively. The ratios with low DP values, particularly those developed from low abundant diamondoids, should be applied very cautiously. Otherwise, high analytical uncertainties related to these indices may lead to an erroneous conclusion when applied for spill source identification. Effects of Evaporative Weathering and Biodegradation on Diamondoid Distribution. When oil is released into the environmentswater or land, it undergoes a series of changes in chemical compositions and physical properties that in combination are termed “weathering”. Weathering can strongly influence how oils move and behave in the environment (32-34). Each of the weathering processes affects a hydrocarbon family differently. In the short term after an oil spill, evaporation is usually the dominant weathering process (35), particularly for the light petroleum products. The effects of evaporative weathering on diamondoid distributions in a number of oils (including light to medium oils Prudhoe Bay, Maya, Troll, and Arabian Heavy) and petroleum products (including midrange jet and diesel fuels) VOL. 40, NO. 18, 2006 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
9
5643
TABLE 4. Statistical Evaluation of Diagnostic Ratios of Diamondoids in Three Round Robin Oil Samplesa oil samples A 1-MA 1,3-DMA 1,3,5-TMA 1,3,5,7-TeMA 2-MA 1,4-DMA, cis 1,4-DMA, trans 1,3,6-TMA 1,2-DMA 1,3,4-TMA,cis 1,3,4-TMA, trans 1,2,5,7-TeMA 1-EA 1-E-3-MA 1-E-3,5-DMA 2-EA D 4-MD 4,9-DMD 1-MD 1,4- and 2,4-DMD 4,8-DMD TMD 3-MD 3,4-DMD sum of adamantanes sum of diamantanes total diamondoids
oil sample 1
oil sample 2
Adamantanes (µg/g oil) 21.0 (1.5) 36.2 (2.6) 25.9 (1.1) 9.21 (2.0) 1.66 (6.3) 37.4 (4.2) 20.2 (5.4) 19.4 (1.5) 13.3 (2.1) 21.6 (4.2) 12.9 (1.7) 15.0 (2.8) 9.5 (1.0) 12.2 (5.9) 21.6 (0.9) 19.3 (7.2) 35.5 (2.4)
oil sample 3
21.5 (3.0) 40.8 (5.1) 29.0 (2.8) 10.6 (2.4) 2.03 (0.4) 46.8 (3.8 23.1 (2.6) 22.1 (4.1) 15.2 (2.0) 23.6 (2.9) 14.3 (2.2) 16.2 (0.9) 10.6 (2.3) 12.7 (3.9) 22.2 (1.9) 19.6 (7.5) 39.2 (1.7)
16.4 (4.6) 31.2 (0.9) 23.5 (0.1) 8.34 (2.2) 1.37 (3.6) 36.2 (3.0) 19.4 (7.5) 19.3 (5.6) 13.7 (0.3) 22.1 (4.0) 13.3 (5.6) 16.3 (4.2) 10.5 (3.3) 16.8 (1.8) 26.7 (1.5) 16.3 (3.4) 34.6 (1.4)
Diamantanes (µg/g oil) 16.3 (3.1) 15.1 (0.5) 9.88 (5.4) 9.22 (6.2) 2.51 (3.1) 2.48 (2.9) 7.40 (3.5) 6.56 (5.6) 3.45 (4.5) 3.21 (3.7) 4.20 (6.2) 3.95 (4.1) 2.64 (5.0) 2.88 (3.7) 5.26 (4.1) 5.16 (1.5) 4.33 (3.0) 4.34 (4.8) 332 (1.5) 370 (2.2) 55.9 (0.7) 53.1 (1.9) 388 (1.4) 423 (1.9)
16.2 (4.0) 10.1 (3.4) 2.96 (2.4) 7.42 (2.7) 3.38 (3.5) 4.15 (4.4) 2.98 (4.1) 5.20 (5.4) 5.30 (1.2) 326 (2.2) 58.0 (2.4) 384 (1.5)
diagnostic ratios
samples 2 and 1
samples 2 and 3
t2,3
match
5.37 5.85 10.7 8.41 7.01 11.4 2.05 3.07 8.89 1.88 2.96 2.92 3.99 4.16
no no no no no no yes no no yes no no no no
diagnostic ratios of target diamondoids
sample 1
sample 2
sample 3
t2,1
1-MA/2-EA 1,3-DMA/1,2-DMA 1,3,5-TMA/1,3,6-TMA 1-MA/1,2-DMA 1-MA/1,3,4-TMA 1-MA/1,2,5,7-TeMA 2-EA/1,2-DMA 1,4-DMA/1,3,5-TMA 1,2-DMA/1,3,5-TMA 4-MD/1-MD 4-MD/3,4-DMD 4,9-DMD/(1,4- and 2,4- + 4,8-DMD) 4,9-DMD/TMD 3,4-DMD/TMD
1.02 (4.9) 1.20 (3.1) 0.69 (1.6) 1.67 (2.5) 1.30 (0.7) 3.81 (1.7) 1.64 (6.0) 4.30 (2.3) 2.35 (2.5) 1.34 (8.0) 2.28 (7.6) 0.33 (4.0) 0.95 (5.5) 1.65 (8.0)
1.04 (4.2) 1.23 (1.6) 0.70 (0.5) 1.73 (2.2) 1.33 (4.3) 3.85 (2.8) 1.66 (2.5) 4.25 (0.2) 2.22 (1.1) 1.43 (1.7) 2.17 (7.3) 0.35 (5.6) 0.86 (3.5) 1.51 (6.7)
0.90 (0.8) 1.07 (4.0) 0.61 (2.4) 1.42 (3.6) 1.05 (3.7) 2.98 (2.7) 1.57 (4.3) 4.64 (4.7) 2.65 (3.0) 1.38 (2.8) 1.89 (2.3) 0.39 (5.1) 0.99 (4.9) 1.78 (2.9)
0.55 1.16 1.38 1.65 1.13 0.67 0.27 0.77 3.52 1.47 0.85 1.38 2.62 1.48
match yes yes yes yes yes yes yes yes no yes yes yes yes yes
a The concentrations and diagnostic ratios were determined from three measurements. The values in parentheses are %RSD of 3 measurements. The critical value of t(R)0.05,4) is 2.78 for this case study. If ti,j exceeds 2.78, two samples do not match; reversely, if ti,j is less than 2.78, two samples match each other.
have been quantitatively studied. As an example, Table 2 presents quantitation results of evaporative weathering on diamondoids in the Prudhoe Bay oil and Ottawa diesel (2002). As Table 2 illustrates, the losses of diamondoids by evaporative weathering are largely determined by their boiling points (that is, the chromatographic elution sequence) and by the type and nature of the oil but not by their molecular sizes: (1) The loss of the first eluted adamantane increases as the weathering percentage increases. (2) The diesel shows different depletion patterns of adamantanes from crude oils by evaporative weathering. The concentrations of adamantanes slightly increase with an increase of weathering percentages (at 6.3 and 13.1%) of the Prudhoe Bay oil. However, increase in weathering up to 19.7% leads to significant reduction in abundances of all adamantanes. In contrast, weathering had less effect on the relative abundances of adamantanes in the diesel. Concentrations of the 5644
9
ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 40, NO. 18, 2006
late eluted adamantanes (starting from 1,4-DMA) increased with increased weathering up to the highest weathered percentage of 22%. This is mainly because diesel has a narrow composition range of less volatile components in comparison with crude oils (36). (3) The late eluted diamantanes are almost not affected by evaporative weathering: concentrations of all diamantanes increase nearly in proportion with an increase of the weathering percentages for both Prudhoe Bay oil and the diesel. (4) More importantly, diagnostic ratios of the late eluted adamantanes and, particularly, ratios of diamantanes are essentially unaltered for the weathered series of the diesel. Biodegradation of hydrocarbons by natural populations of microorganisms is generally a long-term weathering process and represents the primary mechanisms by which petroleum and other hydrocarbon pollutants are eliminated from the environment (37, 38). The quantitative and qualita-
tive aspects of biodegradation depend on the composition of the microbial community; the type, nature, and amount of oil; and the ambient and seasonal environmental conditions. It has been well established that tricyclic to pentacyclic terpanes and steranes are highly resistant to biodegradation (19, 24, 30). As for bicyclic sesquiterpanes, it has been also reported that their distribution patterns were nearly unaltered in biodegraded oil, even after the n-alkanes and isoprenoids had been completely depleted (17, 39, 40). The biodegradation studies conducted in this lab indicate that different from other cyclic biomarkers adamantanes are quite biodegradable, but diamantanes are found much less affected by biodegradation (Table 3). Compared with the sterile controls, concentrations of admandanes in both the inoculated PC and NC of the Alberta Sweet Mixed Blend (ASMB, 1996) oil and diesel no. 2 (Alaska, 1996) are significantly reduced. The sums of adamantanes are determined to be 336, 320, and 414 µg/g oil for PC, NC, and SC of the diesel no. 2 and 59, 39, and 73 µg/g oil for PC, NC, and SC of the ASMB oil; respectively. These imply that approximately 19-23% and 20-47% of adamantanes in the diesel no. 2 and ASMB were degraded after 28 days of freshwater incubation at 10 °C (with or without nutrient addition), respectively. Many diagnostic ratios of adamantanes are also found to be significantly altered in the PC and NC in comparison with the SC (Table 3). In contrast, diamantanes are relatively stable. The sums of diamantanes are determined to be nearly the same (84, 84, and 84 µg/g oil) for PC, NC, and SC of the diesel no. 2 and 15, 13, and 15 µg/g oil for PC, NC, and SC of the ASMB oil; respectively. Diagnostic ratios of target diamantanes are almost unchanged. Obviously, these findings can be applied for correlation and differentiation of spilled diesels at their lightly to moderately weathered stages. Source Identification of Round Robin Oil Samples and Statistical Evaluation of Diagnostic Ratios of Diamondoids. Three oil samples were collected from a harbor spill in The Netherlands in 2004. A thick layer of oil (sample 2) was found between a bunker boat and the quay next to the bunker center. Fuel oils from the bunker boat (sample 1) and the bunker center 2 (sample 3) were collected as suspected sources. To defensively correlate the spill oil to suspected source candidates, triplicate analyses of three samples were performed. Diamondoid characterization results reveal that (1) adamantanes were quite abundant, but diamantanes were less abundant (Table 4); (2) the distribution patterns of adamantanes of samples 2 and 1 were more similar to each other than to samples 2 and 3; (3) more importantly, target diagnostic ratios of adamantanes (with high DP values) and diamantanes (Table 4) matched very well for samples 2 and 1 but were quite different for samples 2 and 3; and (4) spill sample 2 was slightly weathered. The “two-tailed” Student’s t approach (31, 41) was used to statistically evaluate the differences between the target diagnostic ratios of the spill oil and the suspected source samples. This statistical evaluation approach is based on the overall null hypothesis (H0) that the difference between the mean ratio values of triplicate analyses for two oil samples is not significant (µ1 ) µ2), in other words, the spilled oil and the tested source oil are identical (positive match). In this two-tailed t-test, we set an error level of R ) 0.05 (or 95% confidence limit), the critical value of t(R)0.05,df) is 2.78 for 4 degrees of freedom (df ) ni + nj - 2). If ti,j exceeds t(R)0.05,4), the null hypothesis will be rejected, saying that the suspected source oil does not match the spill oil and is unlikely the source of the spill. Conversely, if ti,j is less than t(R)0.05,4), the null hypothesis will be retained, and it can be concluded that the suspected oil is not significantly different from the source oil (with 95% confidence). As seen from Table 4, 8 of 9 selected diagnostic ratios of adamantanes with high DP
values and 4 of 5 diagnostic ratios of more degradationresistant diamantanes support the null hypothesis that suspected source sample 1 matches the spill sample 2; while for samples 3 and 2, 8 of 9 diagnostic ratios of admantanes and 4 of 5 ratios of diamantanes do not support the null hypothesis, leading to a “nonmatch” conclusion for oil samples 3 and 2. This conclusion is consistent with the conclusion obtained from the characterization results of bicyclic sesquiterpanes and alkylated PAHs (17). This case study implies that the diamondoid group could provide another useful diagnostic means for spill source identification, particularly for forensic correlation and differentiation of spilled light to midrange distillates in which high-molecular weight tri- to pentacyclic terpanes and steranes are present if at all in only trace amounts.
Literature Cited (1) Chen, J.; Fu, J.; Sheng, G.; Liu, D.; Zhang, J. Diamondoid hydrocarbon ratios: novel maturity indices for highly mature crude oils. Org. Geochem. 1996, 25, 179-190. (2) Dahl, J.; Moldowan, M.; Peters, K.; Claypool, G.; Rooney, M.; Michael, G.; Mellos, M.; Kohnen, M. Diamondoid hydrocarbons as indicators of natural cracking. Nature 1999, 399, 54-56. (3) Grice, K.; Alexander, R.; Kagi, R. Diamondoid hydrocarbons as indicators of biodegradation in Australian crude oils. Org. Geochem. 2000, 31, 67-73. (4) Bender, A. O.; Said, E. Z.; Abdulsada, A. K. Gas chromatographic identification of adamantanes in some Iraqi crude oils. Analyst 1986, 111, 575-576. (5) Petrov, A. A. Petroleum Hydrocarbons; Springer-Verlag: Berlin, Germany, 1987. (6) Williams, J. A.; Bjoroy, M.; Dolcater, D. L.; Winters, J. C. Biodegradation in South Texas Eocene oils-effects on aromatics and biomarkers. Org. Geochem. 1986, 10, 451-461. (7) Wingert, W. S. GC-MS analysis of diamondoid hydrocarbons in Smackover petroleums. Fuel 1992, 71, 37-43. (8) Lin, R.; Wilk, Z. A. Natural occurrence of tetramantane (C22H28), pentamantane (C26H32) and hexamantane (C30H36) in a deep petroleum reservoir. Fuel 1995, 74, 1512-1521. (9) Dahl, J. E.; Liu, S. G.; Carlson, R. M. K. Isolation and structure of higher diamondoids, nanometer-sized diamond molecules. Science 2003, 299, 96-99. (10) Schulz, L. K.; Wilhelms, A.; Rein, E.; Steen, A. S. Application of diamondoids to distinguish source rock facies. Org. Geochem. 2001, 32, 365-375. (11) Li, J. G.; Philip, P.; Cui, M. Z. Methyl diamantane index (MDI) as a maturity parameter for Lower Palaeozoic Carbonate rocks at high maturity and overmaturity. Org. Geochem. 2000, 31, 267-272. (12) Stout, S. A.; Douglas, G. S. Diamondoid hydrocarbons-application in the chemical fingerprinting of natural gas condensate and gasoline. Environ. Forensics 2004, 5, 225-235. (13) ETC, Environmental Technology Center Database, www.etcentre.org/database/spills_e.html, 2005. (14) Wang, Z. D.; Hollebone, B. P.; Fingas, M.; Fieldhouse, B.; Sigouin, L.; Landriault, M.; Smith, P.; Noonan, J.; Thouin, G. Characteristics of Spilled Oils, Fuels, and Petroleum Products: 1. Composition and Properties of Selected Oils; EPA/600/R-03/072; U.S. EPA: Washington, DC, 2003. Also available from http:// www.epa.gov/athens/publications. (15) Wang, Z. D.; Fingas, M.; Blenkinsopp, S.; Sergy, G.; Landriault, M.; Sigouin, L.; Foght, J.; Semple, K.; Westlake, D. W. S. Oil composition changes due to biodegradation and differentiation between these changes to those due to weathering. J. Chromatogr., A 1998, 809, 89-107. (16) Wang, Z. D.; Fingas, M.; Li, K. Fractionation of ASMB Oil, identification and quantitation of aliphatic, aromatic and biomarker compounds by GC/FID and GC/MSD. J. Chromatogr. Sci. 1994, 32, 361-366 (Part I) and 367-382 (Part II). (17) Wang Z. D.; Yang, C.; Fingas, M.; Hollebone, B.; Peng, X. Z.; Hansen A. B.; Christensen J. H. Characterization, Characterization, weathering, and application of sesquiterpanes to source identification of spilled oils. Environ. Sci. Technol. 2005, 39, 8700-8707. (18) Wang, Z. D.; Fingas, M.; Sergy, G. Study of 22-year-old Arrow oil samples using biomarker compounds by GC/MS. Environ. Sci. Technol. 1994, 28, 1733-1746. VOL. 40, NO. 18, 2006 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
9
5645
(19) Peters K. E.; Moldowan J. M. The Biomarker Guide: Interpreting Molecular Fossils in Petroleum and Ancient Sediments; Prentice Hall: Englewood Cliffs, NJ, 1993. (20) Page, D. S.; Boehm, P. D.; Douglas, G. S.; Bence, A. E. Identification of Hydrocarbon Sources in the Benthic Sediments of Prince William Sound and the Gulf of Alaska Following the Exxon Valdez Spill. In Exxon Valdez Oil Spill: Fate and Effects in Alaska Waters; Wells, P. G., Butler, J. N., Hughes, J. S., Eds.; ASTM: Philadelphia, PA, 1995. (21) Daling, P. S.; Faksness, L. G.; Hansen, A. B.; Stout, S. A. Improved and standardized methodology for oil spill fingerprinting. Environ. Forensics 2002, 3, 263-278. (22) Short, J. W.; Kvenvolden, K. A.; Carlson, P. R.; Hostettler, F. D.; Rosenbauer, R. J.; Wright, B. A. Natural hydrocarbon background in benthic sediments of Prince William Sound, Alaska: oil vs coal. Environ. Sci. Technol. 1999, 33, 34-42. (23) Kaplan, I. R.; Galperin, Y.; Lu, S.; Lee, R. P. Forensic environmental geochemistry differentiation of fuel-types, their sources, and release time. Org. Geochem. 1997, 27, 289-317. (24) Stout, S. A.; Uhler, A. D.; McCarthy, K. J.; Emsbo-Mattingly, S. Chapter 6: Chemical Fingerprinting of Hydrocarbons. In Introduction to Environmental Forensics; Murphy, B. L., Morrison, R. D., Eds.; Academic Press: London, 2002; pp 139-260. (25) Kvenvolden, K. A.; Hostettler, F. D.; Carleson, P. R.; Rapp, J. B.; Threlkeld, C. N.; Warden, A. Ubiquitous tar balls with a California-source signature on the shorelines of Prince William Sound, Alaska. Environ. Sci. Technol. 1995, 29, 2684-2694. (26) Boehm, P. D.; Douglas, G. S.; Burns, W. A.; Mankiewicz, P. J.; Page, D. S.; Bence, A. E. Application of petroleum hydrocarbon chemical fingerprinting and allocation techniques after the Exxon Valdez oil spill. Mar. Pollut. Bull. 1997, 34, 599-613. (27) Bence, A. E.; Kvenvolden, K. A.; Kennicutt, M. C., II Organic geochemistry applied to environmental assessments of Prince William Sound, Alaska, after the Exxon Valdez oil spill - a review. Org. Geochem. 1996, 24, 7-42. (28) Volkman, J. K.; Revil, A. T.; Murray, A. P. Application of biomarkers for identifying sources of natural and pollutant hydrocarbons in aquatic environments. In Molecular Markers in Environmental Geochemistry; Eganhouse, R. P., Ed.; American Chemical Society: Washington, DC, 1997; pp 83-99. (29) Zakaria, M. P.; Horinouchi, A.; Tsutsumi, S.; Takada, H.; Tanabe, S.; Ismail, A. Oil pollution in the Straits of Malacca, Malaysia:
5646
9
ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 40, NO. 18, 2006
(30) (31)
(32)
(33)
(34)
(35)
(36)
(37) (38) (39)
(40)
(41)
Application of molecular markers for source identification. Environ. Sci. Technol. 2000, 34, 1189-1196. Wang, Z. D.; Fingas, M.; Page, D. S. Oil spill identification. J. Chromatogr., A 1999, 843, 369-411. Christensen, J. H.; Hansen, A. B.; Tomasi, G.; Mortensen, J.; Andersen O. Integrated methodology for forensic oil spill identification. Environ. Sci. Technol. 2004, 38, 2912-2918. Jordan, R. E.; Payne, J. R. Fate and weathering of petroleum spills in the marine environment: a literature review and synopsis; Ann Arbor Science Publishers: Ann Arbor, MI, 1980. Wang, Z. D.; Fingas, M. Study of the effects of weathering on the chemical composition of a light crude oil using GC/MS and GC/FID. J. Microcolumn Sep. 1995, 7, 617-639. NRC (National Research Council). Oil in the Sea III: Inputs, Fates, and Effects; The National Academies Press: Washington, DC, 2002. Fingas, M. A literature review of the physics and predictive modelling of oil spill evaporation. J. Hazard. Mater. 1995, 42, 157-175. Fingas, M. Studies on evaporation of crude oils and petroleum products: boundary layer regulation. J. Hazard. Mater. 1998, 57, 41-58. Prince, R. C. Petroleum spill bioremediation in marine environment. Crit. Rev. Microbiol. 1993, 36, 724-728. Leahy, J. G.; Colwell, R. R. Microbial degradation of hydrocarbons in the environment. Microbiol Rev. 1990, 54, 305-315. Noble, R. A. A Geochemical Study of Bicyclic Alkanes and Diterpenoid Hydrocarbons in Crude Oils, Sediments, and Coals, Ph.D. Thesis, Department of Organic Chemistry, University of Western Australia, 1986; 365 pp. Stout, S. A.; Allen, D. U.; Kevin, J. M. Middle distillate fuel fingerprinting using drimane-based bicyclic sesquiterpanes. Environ. Forensics 2005, 6, 241-252. Trochim, W. The Research Methods Knowledge Base, 2nd ed.; Atomic Dog Publishing: Cincinnati, OH, 2000.
Received for review March 21, 2006. Revised manuscript received June 16, 2006. Accepted June 30, 2006. ES060675N
