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GC-MS analysis of total petroleum hydrocarbons and polycyclic aromatic hydrocarbons in seawater samples after the North Cape oil spill
Pergamon PII: S0025-326X(98)00106-4
Marine Pollution Bulletin, Vol. 38, No. 2, pp. 126-135, 1999 © 1999 Elsevier Science Ltd. All rights reserved Printed in Great Britain 0025-326X/99 $ - - see front matter
GC-MS Analysis of Total Petroleum Hydrocarbons and Polycyclic Aromatic Hydrocarbons in Seawater Samples After the North Cape Oil Spill CHRISTOPHER M. REDDY* and JAMES G. QUINN Graduate School of Oceanography, University of Rhode Island, Narragansett, RI, 02882, USA
We developed a gas chromatograph-mass spectrometer (GC-MS) method for measuring both total petroleum hydrocarbons (TPHs) and polycyclic aromatic hydrocarbons (PAHs) in seawater samples that were collected after the North Cape oil spill. After the samples are extracted with methylene chloride and hexane, the extracts are fractionated on silica-gel columns and then injected into a GC-MS operating in the selected-ion-monitoring (SIM) mode. The signal from the ion m/z 57 (C4H~), which is a major ion in aliphatic compounds, is integrated throughout the chromatogram and used to calculate the amount of TPHs. The PAHs are analyzed by using distinct quantification ions during the same run. This method is faster than conventional gas chromatography techniques that use both flame ionization detectors for aliphatics and mass spectrometers for PAHs and also gives a more positive identification due to using GC-MS. Laboratory blanks, recoveries from spiked seawater, and method detection limits for TPHs and PAHs with the simplified method are comparable to conventional methods. Over 50 seawater samples were analyzed after the North Cape oil spill, and the concentrations of TPHs and total PAHs were as high as 3940 and 115 ggl -t, respectively. © 1999 Elsevier Science Ltd. All rights reserved Keywords: oil spill; total petroleum hydrocarbons; polycyclic aromatic hydrocarbons; gas chromatography-mass spectrometry.
Most methods for measuring the semivolatile compounds of petroleum in environmental samples first extract them with an organic solvent, fractionate with chromatography, and then analyze the fractions by * C o r r e s p o n d i n g author. P r e s e n t address: Fye Laboratory, M S # 4 , W o o d s H o l e O c e a n o g r a p h i c Institution, W o o d s Hole, M A 02543, USA.
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infrared (IR) spectroscopy, ultraviolet fluorescence (UVF) spectroscopy, or gas chromatography (GC) (NRC, 1985). Each of these methods targets a particular characteristic of the extracted material and gives an operationally-defined concentration of total petroleum hydrocarbons (TPils). Although IR and UVF provide some useful information and a measure of TPHs values, they lack the specificity and sensitivity of GC methods. Most GC-based methods separate the petroleum into the aliphatic and aromatic fractions with high-performance liquid chromatography (HPLC) or conventional column-chromatography and then analyze the fractions using two different GC detectors. The aliphatic fraction is analyzed on a gas chromatograph with a flame ionization detector (GC-FID), and the TPHs are usually estimated by integrating the areas of the resolved and unresolved components (Douglas et al., 1992). The aromatic fraction, which contains the polycyclic aromatic hydrocarbons (PAHs), is analyzed with a gas chromatograph coupled to a mass spectrometer (GC-MS) (Douglas and Uhler, 1993). Unfortunately, using both detectors is expensive and time-consuming but necessary because important and different information can be derived from each analysis. The aliphatic fraction contains the majority of the compounds in petroleum (i.e., n-alkanes, branched alkanes, isoprenoids, cycloalkanes including steranes and triterpanes, as well as an unresolved complex mixture (UCM) of saturated hydrocarbons). The aromatic fraction generally contains more toxic and more persistent compounds than the aliphatic fraction and also has compounds that can help identify different types of petroleum products; for example, the ratio of phenanthrenes to dibenzothiophenes has been used to discriminate and identify different refined oils (Douglas et al., 1996). In order to combine advantages of measuring the different fractions of the petroleum, we developed a method for analyzing both TPHs and PAils in a single fraction. The extract is injected into a GC-MS
Volume 38/Number 2/February 1999 operating in the selected-ion-monitoring (SIM) mode. The signal from the ion m/z 57, which is a major ion of the aliphatics, is integrated throughout the chromatogram and used to calculate, relative to an internal standard (IS), the amount of TPHs. The PAHs are analyzed in the usual manner during the same run. This method was used to analyze seawater samples collected after the North Cape oil spill. On 19 January 1996 during a severe winter storm, the tugboat Scandia caught fire along the southern coast of Rhode Island, USA. The crew abandoned the tug and the barge it was towing, the North Cape. Both vessels ran aground near Moonstone Beach, South Kingstown, Rhode Island (41 ° 21.80' N, 71 ° 34.80' W; Fig. 1), and the barge spilled about 2700 of its 12500 metric ton cargo of two different No. 2 fuel oils; one was red-colored and the other amber-colored. (In the United States, home-heating fuel and off-road diesel fuel are dyed red for tax-exempt purposes. On-road diesel fuel stays its original color of amber/yellow). Of the 14 fuel compartments in the barge, eight breached during the grounding. Each held approximately the same volume of fuel. Four were holding the red-colored fuel, and the other four contained the amber-colored fuel.
Because of the high winds, upwards of 100 km h 1 and rough seas, 5-7 m, the oil was well-mixed and dispersed throughout the local area within 24h (NOAA, 1997). This spill closed approximately 640 km 2 of fishing and shellfishing areas for as long as 5months and killed over 10million lobsters, ~500 birds (including the federally-endangered piping plover), over 40 million surf clams, and many other benthic and pelagic fauna (NOAA, 1997), resulting in the most damaging man-made accident in the history of the state of Rhode Island.
Materials and Methods Sampling From 4 to 132 days after the spill, water samples were collected along the southern coast of Rhode Island and in Point Judith Pond (Fig. 1). The water temperature was ~2°C at the time of the spill, and the water depths ranged from -~2 to ~25 m. The samples were collected by various means including opening a bottle under water from a boat or by diver, Niskin bottle, or with a polyethylene hose connected to a peristaltic pump. None of the samples was filtered and each was preserved with methylene chloride (at least
41 ° 25'
of Refiige
41" 20'
i
km .....
0 I
-71° 40'
-71 ° 35' Fig. 1 Map of the North Cape oil spill.
-71" 30'
127
Marine Pollution Bulletin 5 ml per liter of seawater). Samples were held in either l-liter or 4-liter amber glass jugs that were Previously solvent-cleaned and had Teflon-lined caps. The methylene-chloride preserved samples were returned to the laboratory immediately after collection and more methylene chloride was added to insure adequate preservation. They were then stored at room temperature or at 25°C until extraction.
Apparatus A Hewlett-Packard 5890 Series II gas chromatograph equipped with a Hewlett-Packard 5971 Mass Selective Detector (GC-MSD) was used to analyze extracts. After splitless injection, compounds were separated with a 30-m J & W Scientific DB-XLB fusedsilica capillary column (0.25 m m i.d. and 0.25 gm film thickness). The oven was p r o g r a m m e d to start at 70°C for 1.5 min, ramped to 320°C at 10°C per minute, and then held for 10min. Data were collected with Hewlett-Packard ChemStation software. The MSD was operated in the SIM mode at a scan rate of 1.25 scans per second; however, the full-scan mode (m/z 50 to 550) was used in developing the method. Seven SIM windows were programmed, each with 20 ions
including m/z 57 and others for PAHs as well as other diagnostic ions that appear in each window (Table 1).
Extraction Samples (1 liter) were spiked with the following internal standards (ISs): 10 to 25 gg of docosane (nC22) and 2 gg each of naphthalene-d8 (nap-ds), biphenyl-dl0 (bip-dl0), acenaphthene-dl0 (acn-dl0), anthracene-d10 (ant-d10), and perylene-&2 (per-d12). The samples were shaken and extracted once with 100 ml of methylene chloride and then twice more with 100 ml of hexane. The organic extracts were combined and rotary-evaporated to --~1ml while being solvent-exchanged into hexane. The hexane extract was chromatographed, using nitrogen pressure, on a 0.5-cm (i.d.)x15-cm column containing activated silica gel (200-325 mesh size). The first fraction (F1), which contained the aliphatic and aromatic hydrocarbons, was obtained by eluting with 20 ml of a 70/30 mixture of hexane/ methylene chloride. This fraction was rotary-evaporated to a small volume ( ~ 1 0 0 gl), spiked with an external recovery standard (ES) (1.2 gg of o-terphenyl in isooctane), and then injected into the GC-MSD.
TABLE 1 List of PAHs, internal standards, quantification ions, and quality control parameters". Compound
Symbol
Internal standard (IS)
Quantification ion (m/z)
Methoddetection limit (MDL) b (ng 1-i)
Naphthalene* 2-Methylnaphthalene 1-Methyinaphthalene C1-Napthalenes* C2-Napthalenes* C3-Napthalenes* C4-Napthalenes* 1,1'.Biphenyl* 2,6.Dimethylnaphthalene Acenaphthene* Dibenzofnran* 1,6,7-Trimethylnaphthalene Fiuorene* C1-Fluorenes* C2-Fluorenes* C3-Fluorenes* Dihenzothiophene* C1-Dibenzothiophene* C2-Dibenzothiophene* C3-Dibenzothiophene* Phenanthrene* Anthracene* 1-Methylphenanthrene C1-Phenanthrenes/Anthracenes* C2-Phenanthrenes/Anthracenes* C3-Phenanthrenes/Anthracenes* C4-Phenanthrenes/Anthracenes* Fluoranthene* Pyrene* C1-Fluoranthenes/Pyrenes* C2-Fluoranthenes/Pyrenes* Total PAHsc
No 2MN 1MN N1 N2 N3 N4 BIP DMN ACN DBF TMN Fo F1 F2 F3 Do D1 D2 D3 Po ANT 1MP P1 P2 P3 P4 FLT PYR F/P1 F/P2
Nap-d8 Nap-d8 Nap-d8 Nap-d8 Bip-dl0 Acn-dl0 Acn-dl0 Bip-dl0 Bip-dl0 Acn-dl0 Acn-dl0 Acn-dl0 Acn-dl0 Acn-dl0 Acn-dl0 Acn-dl0 Acn-dl0 Acn-dl0 Acn-dl0 Acn-dl0 Ant-dl0 Ant-d10 Ant-dl0 Ant-dl0 Ant-dl0 Ant-dl0 Ant-dl0 Ant-d10 Ant-dl0 Ant-dl0 Ant-dl0
128 142 142 142 156 170 184 154 156 154 168 170 166 180 194 208 184 198 212 226 178 178 192 192 206 220 234 202 202 216 230
4.5 7.2 6.6 15 15 15 15 4.8 2.3 7.9 5.6 2.4 5.3 15 15 15 8.4 15 15 15 5.7 5.1 6.3 15 15 15 15 6.7 6.9 15 15
~Laboratoryblanks for individual PAHs are usually below 3 ng 1- i. Recoveries of internal standards range from 40 to 120%. Recoveries of PAHs when oil or standards are spiked into seawater or distilled water range from 70 to 110%. bFor the bold PAHs, MDLs were determined using (Glaser et al., 1981). MDLs for the other PAHs were estimated. CTotal PAHs is the sum of the PAHs marked with an '*'
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Volume 38/Number2/February1999
Cafibration We obtained a neat sample of the red-colored North Cape oil (NCO) a few days after the spill; it was collected by the United States Coast Guard from the No. 3 starboard compartment. A stock standard of 32mgm1-1 of red-colored NCO in hexane was prepared and used to make a four-level calibration. Approximately 2, 6.5, 13 and 20 mg of NCO were added to 70 lag of nC22 and 90 tag of each perdeuterated PAHs ISs (all in hexane), mixed, and chromatographed on silica-gel columns (same as above). The F1 fraction was rotary-evaporated to ~-.1 mL, transferred to a 2-ml volumetric flask, and made to volume with hexane. One microliter of each calibration standard was injected into the GC-MSD; this provided a fourlevel calibration curve of 1.0 to 10 ~tg of NCO. The response factor of TPHs was determined by integrating the extracted-ion-current profile (EICP) of m/z 57 from 6 to 27 rain. Because NCO contained a very small amount of nC22, we had to subtract its area from the total area of the nC22 peak. To do this, we estimated the area of m/z 57 produced from the nC22 in the oil by interpolating the areas of n-cosane (nC20), n-eicosane (nC21), and n-tricosane (nC23). For NCO, the area of nC22 was about half of the area of nC20; this was corrected in all samples. (We have since changed the internal standard from nC22 to perdeuterated nC24, which eliminates this problem). A response factor relative to the corrected nC22 was calculated for each level, and the average was calculated. To calculate the concentration of n-alkanes in samples, response factors using m/z 57 were generated with a standard mixture, NIST SRM 1494. The response of m/z 57 relative to the internal standard for the red-colored NCO was tested against three other No. 2 fuel oils. The amber-colored NCO, the other oil in the barge, was collected by the National Oceanic Atmospheric Administration (NOAA) from the No. 1 port compartment of the barge. We received a sample about 1 year after spill. The other two oils were the American Petroleum Institute (API) reference No. 2 oil (Anderson et al., 1974) and the Marine Ecosystem Research Laboratory (MERL) No. 2 oil (Gearing et al., 1979). Table 1 shows the PAHs measured and also their respective quantification ions and method detection limits (MDLs). Response factors for the bold-faced PAHs were generated with calibration standards prepared with NIST SRM 2260. Response factors for the other PAHs, which are groups o f several alkylated PAHs treated as one analyte, were estimated by two approaches. The first approach was to use the response of one isomer for a whole group. For example, we used the response of 1,6,7-trimethylnaphthalene for the C3-naphthalenes. This was done if there was an appropriate standard available. Otherwise, the response factor of the parent compound was used (Sauer and Boehm, 1991).
Method validation Clean seawater was analyzed in the same manner as the samples to measure the procedural blank. The accuracy of the method was tested by spiking ~50 to 1000 ~tg of the red-colored NCO into 900 ml of clean seawater. Precision was estimated from multiple analyses of spiked samples. The MDL was determined by analyzing seven replicates of seawater spiked with a concentration of 50 lag of oil 1-1 and calculated according to procedures outlined by the USEPA as described by Glaser et al. (1981). To compare the simplified method against other methods, nine samples of clean seawater were each spiked with 867 btg of the red-colored NCO: three samples were analyzed with the proposed method, three by GC-FID, and three by IR. The GC-FID and IR analyses were performed by commercial laboratories. The GC-FID analysis followed a modified Massachusetts (USA) Department of Environmental Protection 'Extractable Petroleum Hydrocarbons' method (MDEP, 1995). The water samples were extracted with methylene chloride, and the solvent extracts were analyzed for resolved and unresolved compounds. Resolved compounds (n-alkanes, pristane, and phytane) were calculated with response factors generated from pure standards. The unresolved compounds were determined by integrating the 'hump' or UCM and subtracting the areas of the resolved compounds and standards; the concentration of the unresolved compounds was calculated with the response factor of hexadecane. For this method, the sum of the resolved and unresolved hydrocarbons is the TPHs. The IR method was USEPA method 418.1 'Total Recoverable Petroleum Hydrocarbons by Infrared Spectroscopy' (USEPA, 1983), in which-the oil was extracted with a total of 100 ml of 1,1,2-trichloro-l,2,2-trifluoroethane. After 3 g of silica gel is added to the extract, the IR absorbance is measured at 2930 cm -1. To increase the sensitivity of this method, the extract was concentrated ten-fold before IR analysis.
Results and Discussion Method development The full-scan total ion chromatogram (TIC) of the red-colored NCO is shown in Fig. 2(a). It shows a distribution of n-alkanes (resolved) from undecane (nCll~ to pentacosane (nC25) as well as an UCM. This is a characteristic chromatogram of No. 2 fuel oil. Also shown in Fig. 2(b) is the EICP of m/z 57 (C4H~), which clearly mirrors the full-scan chromatogram, but has a weaker signal for the unresolved compounds. We chose to use the m/z 57 to quantify the TPHs because it was the major ion in the average mass spectrum of the red-colored NCO (Fig. 3(a)); the average mass spectrum is an average of all of the mass spectra for the peaks that elute within the boiling range of the oil. (The other three oils investigated in this study had very 129
Marine Pollution Bulletin The calibration curve is shown in Fig. 4. The response of the red-colored NCO was linear from 1.0 to 10lag, with an average response factor of 0.259 +0.006. The relative percentage deviation (RPD) of the responses of the amber-colored NCO, API No. 2 fuel oil, and the M E R L No. 2 fuel oil to the standard curve were 15, 1, and 25%, respectively. Considering that these four oils have significantly different amounts of PAHs and hence an overall different composition, the similarity of the responses is good. (The red-colored NCO, amber-colored NCO, API No. 2, and the M E R L No. 2 have 7.3, 4.6, 13 and 8.3% PAHs, respectively; Reddy, 1997). Based on these results, if a source oil after a particular spill of No. 2 oil was not
similar mass spectra). Because the mass spectra of PAHs contain little or no m/z 57, the value of TPHs is relatively independent of the PAHs concentration. When compared to the mass spectrum of n-pentadecane (nC~s), one of the most abundant n-alkanes in the red-colored NCO (Fig. 3(b)), the average mass spectrum of NCO is similar, with a base peak of m/z 57. However, the NCO spectrum has many additional ions from the unresolved compounds, the PAHs, and other hydrocarbon s . Other ions or combination of ions (e.g., m/z 55, m/z 71, and m/z 85) could also be used to quantify for TPHs and may be more useful in other situations, but we chose m/z 57 because it was the most abundant ion in all of the No. 2 fuels that were studied.
15
Abundance
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8.00 l o . o o laioo f4'.oo 16100 f8200 20'.00 22.00 Time (minutes) Fig. 2 (a) Total ion chromatogram (TIC) of North Cape oil (red-colored), acquired in full-scan mode on a DB-XLB column. The n-alkanes with 11 to 25 carbons are labelled (pristane and phytane co-elute with nC17 and nC~8, respectively, on the DB-XLB column). (b) The extracted ion chromatogram (EICP) of m/z 57 of the sample in (a).
130
.
Volume 38/Number 2/February 1999 5-10~tg1-1 of TPHs. The relative recoveries of red-colored NCO spiked into seawater were very good and ranged from 90 to 110% (Table 3). The M D L of the TPHs was calculated with the following equation (Glaser et al., 1981):
available, it appears that any of several different No. 2 oils could be used to calibrate and would b e accurate enough for preliminary damage assessment and fate studies. When calculating the concentrations of TPHs after the NCO spill, the mean response factor for the two different oils, the red and amber, was used.
MDL
where t is the student's t distribution for 6 degrees of freedom at the 99% confidence level (3.143) and S is the standard deviation of the seven replicate analyses. The standard deviation was ~ 5 ~tg 1-~, which yielded a M D L of 16 tag 1-~. The precision for multiple analyses,
Method performance The results of blanks, relative recoveries, MDL study, and the precision of this method are summarized in Table 2. Seawater blanks contained less than
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The average mass spectrum of N o r t h Cape oil (red-colored). (b) The mass spectrum of pentadecane (nC15). 131
Marine Pollution Bulletin
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Fig. 4 Calibration of North Cape oil (red-colored), which represents 1 to 10 lag of oil injected on-column to the GC-MSD (average response factor = 0.259 ± 0.006). Also shown are the responses of the North Cape oil (amber-colored), API No. 2 oil, M E R L No. 2 oil.
for the IR method was very large (370 ~tg) compared to the mean value (560pg). For the GC-FID and GC-MSD methods, the laboratory blanks were very small, the precision good (RSDs<3%), and the RPD between the two methods was 29%. The most probable reason for differences in the GC-FID and GC-MSD is that the GC-FID was not standardized for the specific oil analyzed, while the GC-MSD was calibrated by mass with the same oil that was spiked into the seawater. For each n-alkane, both GC methods were similar with the exception of the low-boiling nCl2 and nC13 for which the GC-FID method gave lower recoveries, which is most likely due to sample preparation.
as expressed by the relative standard deviation, was less than 10% and in most cases, less than 4%. The absolute recoveries of the nC22 IS in the blanks, matrix spikes, and MDL study ranged from 50 to 80% relative to the ES.
Comparison to other methods The TPHs results from the intercomparison are shown in Table 4. The IR method gave a smaller recovery than the other two techniques, with a considerably larger RSD (25%). Also, the laboratory blank
TABLE
2
Field samples From 4 to 132 days after the North Cape oil spill, we analyzed 54 water samples that were collected within ~12 km of the barge. The total-ion chromatogram, acquired in SIM mode, and the EICP of m/z 57 of a sample collected the seventh day after the spill are shown in Fig. 5. Overall, the concentrations of TPHs
Quality control parameters of GC-MS method for TPHs. Parameter Blanks Relative recoveries MDL Precision
Value 5-10 lag 1-1 90-110% for ~50-1000 lag of TPHs spiked 1-1 16 lag 1-1 < 10% RSD
TABLE
3
Recoveries of red-colored North Cape Oil spiked into 900 ml of seawater. Mass spiked (lag) 48.8 122 488 867 976
Conc. (lag 1-1)
No. of replicates
54.2 136 542 963 1080
7 2 2 3 2
abased on internal standard.
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Mass recovered ± SD a (lag) 45.5 ±4.6 134±0 482±18 865 ± 17 1060±42
Relative standard deviation (RSD)
Recovery (%)
10% 0% 3.7% 2.0% 4.0%
93 110 99 100 109
Volume 38/Number 2/February 1999 TABLE 4
Results of intercomparison of the three techniques for seawater that was spiked with 867 gg of North Cape oil. Mass recovered, gg (RSD~,%) Hydrocarbon
GC-FID (N = 3)
GC-MS (N = 3)
IR (N = 3)
n-Dodecane (nCl2) n-Tridecane (nC13) n-Tetradecane (nCl4) n-Pentadecane (nC15) n-Hexadecane (nC16) n-Heptadecane (ne17)+pristanec n-Octadecane (nC18)+phytane c n-Nonadecane (nCw) n-Eicosane (nC2o) n-Heneicosane (nC21)
5.08 (5.5) 6.01 (5.5) 9.38 (5.9) 9.37 (5.2) 9.44 (2.4) 14.5 (3.0) 11.3 (2.1) 5.26 (1.8) 4.54 (3.0) 2.63 (1.8)
7.15 (6.9) 8.66 (3.0) 9.91 (3.9) 9.32 (2.9) 10.1 (5.8) 14.3 (3.1) 9.68 (2.9) 5.56 (3.4) 4.43 (1.3) 3.21 (6.1)
NAb NA NA NA NA NA NA NA NA NA
Total petroleum hydrocarbons (TPHs) Blank values of TPHs
64l (0.81) < 20
863 (2.9) < 20
560 (25) 370
aRelative standard deviation (RSD) for triplicate analyses. bNot analyzed. CFor GC-FID, this is the sum of the two individual compounds. For the GC-MS, these compounds were not separated on the DB-XLB column and are treated as one analyte. a n d P A H s w e r e as high as 3940 a n d l l 5 g g 1 - 1 ( T a b l e 5), respectively, a n d a r e s o m e of the highest values ever r e p o r t e d for a m a r i n e oil spill; see N e f f a n d Stubblefield (1995) for a r e c e n t review. T h e R P D s for d u p l i c a t e s a m p l e s w e r e < 7 % for T P H s a n d < 3 % for Abundance
total P A H s . Also, 7 days after the spill, b o t h the USEPA and our laboratory collected and analyzed s a m p l e s f r o m a p p r o x i m a t e l y the s a m e area. T h e i r s a m p l e s w e r e only analyzed for T P H s with a G C - F I D , b u t they gave similar results to o u r s a m p l e s f r o m that
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Time (minutes) Fig. 5 (a) Total ion chromatogram and (b) EICP of m/z 57 of one of the field samples collected on day 7 after the North Cape oil spill. These chromatograms were acquired in the SIM mode. 133
Marine Pollution Bulletin TABLE 5
Summary of results for all water samples collected after the North Cape oil spill. Compound
Symbol
No. of times detected above the MDL out of 54 samples
Mean (gg 1-l)
Std. dev. (gg 1-1)
Max. (gg 1-1)
Naphthalene* 2-Methylnaphthalene 1-Methylnaphthalene C1-Naphthalenes* C2-Naphthalenes* C3-Naphthalenes* C4-Naphthalenes* 1,1'-Biphenyl* 2,6-Dimethylnaphthalene Acenaphthene* Dibenzofuran* 1,6,7-Trimethylnaphthalene Fluorene* C1-Fluorenes* C2-Fluorenes* C3-Fluorenes* Dibenzothiophene* C1-Dibenzothiophene* C2-Dibenzothiophene* C3-Dibenzothiophene* Phenanthrene* Anthracene* 1-Methylphenanthrene C1-Phenanthrenes/Anthracenes* C2-Phenanthrenes/Anthracenes* C3-Phenanthrenes/Anthracenes* C4-Phenanthrenes/Anthracenes* Fluoranthene* Pyrene* C1-Fluor anthenes/Pyrenes* C2-Fluoranthenes/Pyrenes * ZPAHs a
No 2MN 1MN N1 N2 N3 N4 BIP DMN ACN DBF TMN Fo F1 F2 F3 Do D1 D2 D3 Po ANT IMP PI P2 P3 P4 FLT PYR F/P1 F/P2 -
50 50 49 50 53 53 45 40 48 36 32 40 39 41 43 39 31 35 39 39 47 33 41 49 49 45 36 30 40 32 32 53
0.498 1.55 1.04 2.57 3.71 4.06 2.95 0.292 1.01 0.0948 0.0986 0.367 0.291 0.702 1.12 1.18 0.0834 0.346 0.550 0.475 0.448 0.0704 0.233 1.44 1.64 1.01 0.536 0.0352 0.115 0.180 0.125 21.9
0.668 1.93 1.20 3.13 4.18 4.38 3.30 0.283 1.08 0.0651 0.0631 0.297 0.222 0.601 1.17 1.32 0.0535 0.294 0.606 0,560 0.429 0.0587 0.206 1.57 2.07 1.31 0.596 0.0278 0.107 0.179 0.135 24.2
3.06 6.83 4.16 11.0 13.8 20.5 18.5 0.938 3.58 0.222 0.213 1.34 0.759 2.54 6.28 7.26 0.194 1.54 3.36 3.15 1.56 0.305 1.11 8.30 12.1 7.68 3.34 0.138 0.578 0.994 0.750 115
-
46
TPHs
483
648
3940
a52PAHs is the sum of the PAHs marked with an '*'.
area; their TPHs values ranged from 150 to 820 lag 1-1, while ours ranged from 160 to 580 lag 1-1 .
Applications The proposed method is an alternative way to measure TPHs while also measuring PAHs in seawater samples recently impacted by an oil spill. This. is not the first attempt to use GC-MS to study aliphatic hydrocarbons in the environments; others have, such as Roques et al. (1994) and Kaplan et al. (1997). However, this is the first method that quantitatively measures TPHs with a GC-MS. Because this method essentially measures the n-alkane component of oil, it is most useful for analyzing TPHs in areas recently impacted by fuel oil because n-alkanes are the first compounds to be microbially dggraded (Singer and Finnerty, 1984). Hence, the relative signal for m/z 57 will decrease and estimates of TPHs in severely degraded oil will be underestimated using the GC-MS method. This is the distinct quantitative disadvantage between integrating the whole chromatogram obtained with a GC-FID versus an EICP of m/z 57 from a GC-MS. The signal
134
from the FID is based on the mass of carbon combusted, which should be relatively insensitive to the chemical nature of the compounds. Conversely with a GC-MS, the signal from m/z 57 depends more on the molecular structure of the compounds and not the total amount of carbon. Alternative methods could use m/z 55 (C4H~), which are the major ions produced by cycloalkanes (McLafferty and Yurecek, 1993), because these compounds do not degrade as quickly as the n-alkanes (Singer and Finnerty, 1984). Preliminary results from measuring TPHs in marine sediments with m/z 55 and GC-FID are very similar; in this case, both the GC-FID and GC-MS are calibrated with used crankcase oil (Lamontagne et al., unpublished data). Alternatively, samples could also be analyzed in the full-scan mode by integrating the total ion signal, but with lower sensitivity.
Conclusion A simple and rapid method was developed for measuring TPHs and PAHs in seawater and possibly other environmental samples. The blanks, accuracy, precision, and MDLs are comparable to GC-FID
Volume 38/Number 2/February 1999 m e t h o d s ( D o u g l a s et al., 1992; D o u g l a s a n d U h l e r , 1993). T h i s m e t h o d is p a r t i c u l a r l y u s e f u l for a n a l y z i n g s a m p l e s t h a t have b e e n r e c e n t l y i m p a c t e d by a r e f i n e d p e t r o l e u m p r o d u c t . F o r e x a m p l e , t h e m e t h o d was successfully u s e d to d e t e r m i n e the T P H s a n d P A H s in field s a m p l e s after t h e North Cape oil spill. We would like to thank: Mr D. Cobb, Dr J. Latimer, Mr R. McKinney, Dr R. Pruell, and Mr B. Taplin of the Atlantic Ecology Division of the United States Environmental Protection Agency (Narragansett, RI); Dr R. Cairns, Mr W. DeLeo, Mr M. DiMatteo, Dr C. Kincaid, Lt Cmdr. J. Sifting (USCG), Mr S. Sylva, and Ms J. White of the Graduate School of Oceanography (GSO), University of Rhode Island; Mr G. Mauseth of Beak Consultants (Kirkland, WA); and the crew of the R/V Cap'n Bert (University of Rhode Island). This work was supported in part by a grant from Eklof Marine. CMR was also supported by a Narragansett Electric Coastal Fellowship and a GSO alumni award. The GC-MSD was donated to our laboratory through the Hewlett-Packard University Grants Program. Anderson, J. W., Neff, J. M., Cox, B. A., Tatem, H. E. and Hightower, G. M. (1974) Characteristics of dispersions and watersoluble extracts of crude and refined oils and their toxicity to estuarine crustaceans and fish. Marine Biology 27, 75-89. Douglas, G. S., Bence, A. E., Prince, R. C., McMillen, S. J. and Butler, E. L. (1996) Environmental stability of selected petroleum source and weathering ratios. Environmental Science and Technology 30, 2332-2339. Douglas, G. S., McCarthy, K. J., Dahlen, D. T., Seavey, J. A., Steinhauer, W. G., Prince, R. C. and Elmendorf, D. L. (1992) The use of hydrocarbon analyses for environmental assessment and remediation. Journal of Soil Contamination 1, 197-216. Douglas, G. S. and Uhler, A. D. (1993) Optimizing EPA methods for petroleum-contaminated site assessments. Environmental Testing and Analysis May/June, 1-6. Gearing, J. N., Gearing, P. J., Wade, T. L., Quinn, J. G., McCarty, H. B., Farrington, J. and Lee, R. F. (1979) The rates of transport and fates of petroleum hydrocarbons in a controlled marine ecosystem, and a note on analytical variability. In Proceedings of the 1979 Oil Spill Conference. Prevention, Behavior, Control, Cleanup, pp. 555-564. American Petroleum Institute, United States Environ-
mental Protection Agency, United States Coast Guard, Los Angeles. Glaser, J. A., Foerst, D. L., Quave, S. A. and Budde, W. L. (1981) Trace analyses for wastewaters. Environmental Science and Technology 15, 1426-1435. Kaplan, I. R., Galperin, Y., Shan-Tan, L. and Ru-Po, L. (1997) Forensic environmental geochemistry: Differentiation of fueltypes, their sources and release time. Organic Geochemistry 27, 289-317. MDEP (1995) Method for the Determination of Extractable Petroleum Hydrocarbons (EPH). Massachusetts Department of Environmental Protection, Boston, MA. McLafferty, F. W. and Turecek, F. (1993) Interpretation of Mass Spectra. University Science Books, Mill Valley, CA. NOAA (1997) Restoration Plan and Environmental Assessment for the January, 19, 1996 North Cape Oil Spill, DRAFT, dated 16 May 1997. National Oceanic and Atmospheric Administration, Rhode Island Department of Environmental Management, and United States of the Interior. Neff, J. M. and Stubblefield, W. A. (1995) Chemical and toxicological evaluation of water quality following the Exxon Valdez oil spill. In Exxon Valdez Oil Spill." Fate and Effects in Alaskan Waters, eds P. G. Wells, J. N. Butler and J. S. Hughes, pp. 141-177. ASTM Special Technical Publication 1219, American Society for Testing and Materials, Philadelphia. NRC (1985) Oil in the Sea: Inputs, Fates, and Effects. National Research Council, National Academy Press, Washington, DC. Reddy, C. M. (1997) Studies of the fates of organic contaminants in aquatic environments. Ph.D. dissertation, University of Rhode Island, Kingston, RI. Roques, D. E., Overton, E. B. and Henry, C. B. (1994) Using gas chromatography/mass spectrometry fingerprint analyses to document process and progress of oil degradation. Journal of Environmental Quality 23, 851-855. Sauer, T. and Boehm, P. D. (1991) The use of defensible analytical chemical measurements for oil spill natural resource damage assessment. In Proceedings of the 1991 Oil Spill Conference. Prevention, Behavior, Control, Cleanup, pp. 363-369. American Petroleum Institute, Washington DC. Singer, M. E. and Finnerty, W. R. (1984) Microbial metabolism of straight-chain and branched alkanes. In Petroleum Microbiology, ed. R. Atlas, pp. 1-60. McMillan Publishing Co, New York. USEPA (1983) Methods for the Analysis of Water and Wastes. United States Environmental Protection Agency, Washington, DC.
135
Marine Pollution Bulletin, Vol. 38, No. 2, pp. 126-135, 1999 © 1999 Elsevier Science Ltd. All rights reserved Printed in Great Britain 0025-326X/99 $ - - see front matter
GC-MS Analysis of Total Petroleum Hydrocarbons and Polycyclic Aromatic Hydrocarbons in Seawater Samples After the North Cape Oil Spill CHRISTOPHER M. REDDY* and JAMES G. QUINN Graduate School of Oceanography, University of Rhode Island, Narragansett, RI, 02882, USA
We developed a gas chromatograph-mass spectrometer (GC-MS) method for measuring both total petroleum hydrocarbons (TPHs) and polycyclic aromatic hydrocarbons (PAHs) in seawater samples that were collected after the North Cape oil spill. After the samples are extracted with methylene chloride and hexane, the extracts are fractionated on silica-gel columns and then injected into a GC-MS operating in the selected-ion-monitoring (SIM) mode. The signal from the ion m/z 57 (C4H~), which is a major ion in aliphatic compounds, is integrated throughout the chromatogram and used to calculate the amount of TPHs. The PAHs are analyzed by using distinct quantification ions during the same run. This method is faster than conventional gas chromatography techniques that use both flame ionization detectors for aliphatics and mass spectrometers for PAHs and also gives a more positive identification due to using GC-MS. Laboratory blanks, recoveries from spiked seawater, and method detection limits for TPHs and PAHs with the simplified method are comparable to conventional methods. Over 50 seawater samples were analyzed after the North Cape oil spill, and the concentrations of TPHs and total PAHs were as high as 3940 and 115 ggl -t, respectively. © 1999 Elsevier Science Ltd. All rights reserved Keywords: oil spill; total petroleum hydrocarbons; polycyclic aromatic hydrocarbons; gas chromatography-mass spectrometry.
Most methods for measuring the semivolatile compounds of petroleum in environmental samples first extract them with an organic solvent, fractionate with chromatography, and then analyze the fractions by * C o r r e s p o n d i n g author. P r e s e n t address: Fye Laboratory, M S # 4 , W o o d s H o l e O c e a n o g r a p h i c Institution, W o o d s Hole, M A 02543, USA.
126
infrared (IR) spectroscopy, ultraviolet fluorescence (UVF) spectroscopy, or gas chromatography (GC) (NRC, 1985). Each of these methods targets a particular characteristic of the extracted material and gives an operationally-defined concentration of total petroleum hydrocarbons (TPils). Although IR and UVF provide some useful information and a measure of TPHs values, they lack the specificity and sensitivity of GC methods. Most GC-based methods separate the petroleum into the aliphatic and aromatic fractions with high-performance liquid chromatography (HPLC) or conventional column-chromatography and then analyze the fractions using two different GC detectors. The aliphatic fraction is analyzed on a gas chromatograph with a flame ionization detector (GC-FID), and the TPHs are usually estimated by integrating the areas of the resolved and unresolved components (Douglas et al., 1992). The aromatic fraction, which contains the polycyclic aromatic hydrocarbons (PAHs), is analyzed with a gas chromatograph coupled to a mass spectrometer (GC-MS) (Douglas and Uhler, 1993). Unfortunately, using both detectors is expensive and time-consuming but necessary because important and different information can be derived from each analysis. The aliphatic fraction contains the majority of the compounds in petroleum (i.e., n-alkanes, branched alkanes, isoprenoids, cycloalkanes including steranes and triterpanes, as well as an unresolved complex mixture (UCM) of saturated hydrocarbons). The aromatic fraction generally contains more toxic and more persistent compounds than the aliphatic fraction and also has compounds that can help identify different types of petroleum products; for example, the ratio of phenanthrenes to dibenzothiophenes has been used to discriminate and identify different refined oils (Douglas et al., 1996). In order to combine advantages of measuring the different fractions of the petroleum, we developed a method for analyzing both TPHs and PAils in a single fraction. The extract is injected into a GC-MS
Volume 38/Number 2/February 1999 operating in the selected-ion-monitoring (SIM) mode. The signal from the ion m/z 57, which is a major ion of the aliphatics, is integrated throughout the chromatogram and used to calculate, relative to an internal standard (IS), the amount of TPHs. The PAHs are analyzed in the usual manner during the same run. This method was used to analyze seawater samples collected after the North Cape oil spill. On 19 January 1996 during a severe winter storm, the tugboat Scandia caught fire along the southern coast of Rhode Island, USA. The crew abandoned the tug and the barge it was towing, the North Cape. Both vessels ran aground near Moonstone Beach, South Kingstown, Rhode Island (41 ° 21.80' N, 71 ° 34.80' W; Fig. 1), and the barge spilled about 2700 of its 12500 metric ton cargo of two different No. 2 fuel oils; one was red-colored and the other amber-colored. (In the United States, home-heating fuel and off-road diesel fuel are dyed red for tax-exempt purposes. On-road diesel fuel stays its original color of amber/yellow). Of the 14 fuel compartments in the barge, eight breached during the grounding. Each held approximately the same volume of fuel. Four were holding the red-colored fuel, and the other four contained the amber-colored fuel.
Because of the high winds, upwards of 100 km h 1 and rough seas, 5-7 m, the oil was well-mixed and dispersed throughout the local area within 24h (NOAA, 1997). This spill closed approximately 640 km 2 of fishing and shellfishing areas for as long as 5months and killed over 10million lobsters, ~500 birds (including the federally-endangered piping plover), over 40 million surf clams, and many other benthic and pelagic fauna (NOAA, 1997), resulting in the most damaging man-made accident in the history of the state of Rhode Island.
Materials and Methods Sampling From 4 to 132 days after the spill, water samples were collected along the southern coast of Rhode Island and in Point Judith Pond (Fig. 1). The water temperature was ~2°C at the time of the spill, and the water depths ranged from -~2 to ~25 m. The samples were collected by various means including opening a bottle under water from a boat or by diver, Niskin bottle, or with a polyethylene hose connected to a peristaltic pump. None of the samples was filtered and each was preserved with methylene chloride (at least
41 ° 25'
of Refiige
41" 20'
i
km .....
0 I
-71° 40'
-71 ° 35' Fig. 1 Map of the North Cape oil spill.
-71" 30'
127
Marine Pollution Bulletin 5 ml per liter of seawater). Samples were held in either l-liter or 4-liter amber glass jugs that were Previously solvent-cleaned and had Teflon-lined caps. The methylene-chloride preserved samples were returned to the laboratory immediately after collection and more methylene chloride was added to insure adequate preservation. They were then stored at room temperature or at 25°C until extraction.
Apparatus A Hewlett-Packard 5890 Series II gas chromatograph equipped with a Hewlett-Packard 5971 Mass Selective Detector (GC-MSD) was used to analyze extracts. After splitless injection, compounds were separated with a 30-m J & W Scientific DB-XLB fusedsilica capillary column (0.25 m m i.d. and 0.25 gm film thickness). The oven was p r o g r a m m e d to start at 70°C for 1.5 min, ramped to 320°C at 10°C per minute, and then held for 10min. Data were collected with Hewlett-Packard ChemStation software. The MSD was operated in the SIM mode at a scan rate of 1.25 scans per second; however, the full-scan mode (m/z 50 to 550) was used in developing the method. Seven SIM windows were programmed, each with 20 ions
including m/z 57 and others for PAHs as well as other diagnostic ions that appear in each window (Table 1).
Extraction Samples (1 liter) were spiked with the following internal standards (ISs): 10 to 25 gg of docosane (nC22) and 2 gg each of naphthalene-d8 (nap-ds), biphenyl-dl0 (bip-dl0), acenaphthene-dl0 (acn-dl0), anthracene-d10 (ant-d10), and perylene-&2 (per-d12). The samples were shaken and extracted once with 100 ml of methylene chloride and then twice more with 100 ml of hexane. The organic extracts were combined and rotary-evaporated to --~1ml while being solvent-exchanged into hexane. The hexane extract was chromatographed, using nitrogen pressure, on a 0.5-cm (i.d.)x15-cm column containing activated silica gel (200-325 mesh size). The first fraction (F1), which contained the aliphatic and aromatic hydrocarbons, was obtained by eluting with 20 ml of a 70/30 mixture of hexane/ methylene chloride. This fraction was rotary-evaporated to a small volume ( ~ 1 0 0 gl), spiked with an external recovery standard (ES) (1.2 gg of o-terphenyl in isooctane), and then injected into the GC-MSD.
TABLE 1 List of PAHs, internal standards, quantification ions, and quality control parameters". Compound
Symbol
Internal standard (IS)
Quantification ion (m/z)
Methoddetection limit (MDL) b (ng 1-i)
Naphthalene* 2-Methylnaphthalene 1-Methyinaphthalene C1-Napthalenes* C2-Napthalenes* C3-Napthalenes* C4-Napthalenes* 1,1'.Biphenyl* 2,6.Dimethylnaphthalene Acenaphthene* Dibenzofnran* 1,6,7-Trimethylnaphthalene Fiuorene* C1-Fluorenes* C2-Fluorenes* C3-Fluorenes* Dihenzothiophene* C1-Dibenzothiophene* C2-Dibenzothiophene* C3-Dibenzothiophene* Phenanthrene* Anthracene* 1-Methylphenanthrene C1-Phenanthrenes/Anthracenes* C2-Phenanthrenes/Anthracenes* C3-Phenanthrenes/Anthracenes* C4-Phenanthrenes/Anthracenes* Fluoranthene* Pyrene* C1-Fluoranthenes/Pyrenes* C2-Fluoranthenes/Pyrenes* Total PAHsc
No 2MN 1MN N1 N2 N3 N4 BIP DMN ACN DBF TMN Fo F1 F2 F3 Do D1 D2 D3 Po ANT 1MP P1 P2 P3 P4 FLT PYR F/P1 F/P2
Nap-d8 Nap-d8 Nap-d8 Nap-d8 Bip-dl0 Acn-dl0 Acn-dl0 Bip-dl0 Bip-dl0 Acn-dl0 Acn-dl0 Acn-dl0 Acn-dl0 Acn-dl0 Acn-dl0 Acn-dl0 Acn-dl0 Acn-dl0 Acn-dl0 Acn-dl0 Ant-dl0 Ant-d10 Ant-dl0 Ant-dl0 Ant-dl0 Ant-dl0 Ant-dl0 Ant-d10 Ant-dl0 Ant-dl0 Ant-dl0
128 142 142 142 156 170 184 154 156 154 168 170 166 180 194 208 184 198 212 226 178 178 192 192 206 220 234 202 202 216 230
4.5 7.2 6.6 15 15 15 15 4.8 2.3 7.9 5.6 2.4 5.3 15 15 15 8.4 15 15 15 5.7 5.1 6.3 15 15 15 15 6.7 6.9 15 15
~Laboratoryblanks for individual PAHs are usually below 3 ng 1- i. Recoveries of internal standards range from 40 to 120%. Recoveries of PAHs when oil or standards are spiked into seawater or distilled water range from 70 to 110%. bFor the bold PAHs, MDLs were determined using (Glaser et al., 1981). MDLs for the other PAHs were estimated. CTotal PAHs is the sum of the PAHs marked with an '*'
128
Volume 38/Number2/February1999
Cafibration We obtained a neat sample of the red-colored North Cape oil (NCO) a few days after the spill; it was collected by the United States Coast Guard from the No. 3 starboard compartment. A stock standard of 32mgm1-1 of red-colored NCO in hexane was prepared and used to make a four-level calibration. Approximately 2, 6.5, 13 and 20 mg of NCO were added to 70 lag of nC22 and 90 tag of each perdeuterated PAHs ISs (all in hexane), mixed, and chromatographed on silica-gel columns (same as above). The F1 fraction was rotary-evaporated to ~-.1 mL, transferred to a 2-ml volumetric flask, and made to volume with hexane. One microliter of each calibration standard was injected into the GC-MSD; this provided a fourlevel calibration curve of 1.0 to 10 ~tg of NCO. The response factor of TPHs was determined by integrating the extracted-ion-current profile (EICP) of m/z 57 from 6 to 27 rain. Because NCO contained a very small amount of nC22, we had to subtract its area from the total area of the nC22 peak. To do this, we estimated the area of m/z 57 produced from the nC22 in the oil by interpolating the areas of n-cosane (nC20), n-eicosane (nC21), and n-tricosane (nC23). For NCO, the area of nC22 was about half of the area of nC20; this was corrected in all samples. (We have since changed the internal standard from nC22 to perdeuterated nC24, which eliminates this problem). A response factor relative to the corrected nC22 was calculated for each level, and the average was calculated. To calculate the concentration of n-alkanes in samples, response factors using m/z 57 were generated with a standard mixture, NIST SRM 1494. The response of m/z 57 relative to the internal standard for the red-colored NCO was tested against three other No. 2 fuel oils. The amber-colored NCO, the other oil in the barge, was collected by the National Oceanic Atmospheric Administration (NOAA) from the No. 1 port compartment of the barge. We received a sample about 1 year after spill. The other two oils were the American Petroleum Institute (API) reference No. 2 oil (Anderson et al., 1974) and the Marine Ecosystem Research Laboratory (MERL) No. 2 oil (Gearing et al., 1979). Table 1 shows the PAHs measured and also their respective quantification ions and method detection limits (MDLs). Response factors for the bold-faced PAHs were generated with calibration standards prepared with NIST SRM 2260. Response factors for the other PAHs, which are groups o f several alkylated PAHs treated as one analyte, were estimated by two approaches. The first approach was to use the response of one isomer for a whole group. For example, we used the response of 1,6,7-trimethylnaphthalene for the C3-naphthalenes. This was done if there was an appropriate standard available. Otherwise, the response factor of the parent compound was used (Sauer and Boehm, 1991).
Method validation Clean seawater was analyzed in the same manner as the samples to measure the procedural blank. The accuracy of the method was tested by spiking ~50 to 1000 ~tg of the red-colored NCO into 900 ml of clean seawater. Precision was estimated from multiple analyses of spiked samples. The MDL was determined by analyzing seven replicates of seawater spiked with a concentration of 50 lag of oil 1-1 and calculated according to procedures outlined by the USEPA as described by Glaser et al. (1981). To compare the simplified method against other methods, nine samples of clean seawater were each spiked with 867 btg of the red-colored NCO: three samples were analyzed with the proposed method, three by GC-FID, and three by IR. The GC-FID and IR analyses were performed by commercial laboratories. The GC-FID analysis followed a modified Massachusetts (USA) Department of Environmental Protection 'Extractable Petroleum Hydrocarbons' method (MDEP, 1995). The water samples were extracted with methylene chloride, and the solvent extracts were analyzed for resolved and unresolved compounds. Resolved compounds (n-alkanes, pristane, and phytane) were calculated with response factors generated from pure standards. The unresolved compounds were determined by integrating the 'hump' or UCM and subtracting the areas of the resolved compounds and standards; the concentration of the unresolved compounds was calculated with the response factor of hexadecane. For this method, the sum of the resolved and unresolved hydrocarbons is the TPHs. The IR method was USEPA method 418.1 'Total Recoverable Petroleum Hydrocarbons by Infrared Spectroscopy' (USEPA, 1983), in which-the oil was extracted with a total of 100 ml of 1,1,2-trichloro-l,2,2-trifluoroethane. After 3 g of silica gel is added to the extract, the IR absorbance is measured at 2930 cm -1. To increase the sensitivity of this method, the extract was concentrated ten-fold before IR analysis.
Results and Discussion Method development The full-scan total ion chromatogram (TIC) of the red-colored NCO is shown in Fig. 2(a). It shows a distribution of n-alkanes (resolved) from undecane (nCll~ to pentacosane (nC25) as well as an UCM. This is a characteristic chromatogram of No. 2 fuel oil. Also shown in Fig. 2(b) is the EICP of m/z 57 (C4H~), which clearly mirrors the full-scan chromatogram, but has a weaker signal for the unresolved compounds. We chose to use the m/z 57 to quantify the TPHs because it was the major ion in the average mass spectrum of the red-colored NCO (Fig. 3(a)); the average mass spectrum is an average of all of the mass spectra for the peaks that elute within the boiling range of the oil. (The other three oils investigated in this study had very 129
Marine Pollution Bulletin The calibration curve is shown in Fig. 4. The response of the red-colored NCO was linear from 1.0 to 10lag, with an average response factor of 0.259 +0.006. The relative percentage deviation (RPD) of the responses of the amber-colored NCO, API No. 2 fuel oil, and the M E R L No. 2 fuel oil to the standard curve were 15, 1, and 25%, respectively. Considering that these four oils have significantly different amounts of PAHs and hence an overall different composition, the similarity of the responses is good. (The red-colored NCO, amber-colored NCO, API No. 2, and the M E R L No. 2 have 7.3, 4.6, 13 and 8.3% PAHs, respectively; Reddy, 1997). Based on these results, if a source oil after a particular spill of No. 2 oil was not
similar mass spectra). Because the mass spectra of PAHs contain little or no m/z 57, the value of TPHs is relatively independent of the PAHs concentration. When compared to the mass spectrum of n-pentadecane (nC~s), one of the most abundant n-alkanes in the red-colored NCO (Fig. 3(b)), the average mass spectrum of NCO is similar, with a base peak of m/z 57. However, the NCO spectrum has many additional ions from the unresolved compounds, the PAHs, and other hydrocarbon s . Other ions or combination of ions (e.g., m/z 55, m/z 71, and m/z 85) could also be used to quantify for TPHs and may be more useful in other situations, but we chose m/z 57 because it was the most abundant ion in all of the No. 2 fuels that were studied.
15
Abundance
(a)
16
17+pristane
I
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18+phytane
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8.00 l o . o o laioo f4'.oo 16100 f8200 20'.00 22.00 Time (minutes) Fig. 2 (a) Total ion chromatogram (TIC) of North Cape oil (red-colored), acquired in full-scan mode on a DB-XLB column. The n-alkanes with 11 to 25 carbons are labelled (pristane and phytane co-elute with nC17 and nC~8, respectively, on the DB-XLB column). (b) The extracted ion chromatogram (EICP) of m/z 57 of the sample in (a).
130
.
Volume 38/Number 2/February 1999 5-10~tg1-1 of TPHs. The relative recoveries of red-colored NCO spiked into seawater were very good and ranged from 90 to 110% (Table 3). The M D L of the TPHs was calculated with the following equation (Glaser et al., 1981):
available, it appears that any of several different No. 2 oils could be used to calibrate and would b e accurate enough for preliminary damage assessment and fate studies. When calculating the concentrations of TPHs after the NCO spill, the mean response factor for the two different oils, the red and amber, was used.
MDL
where t is the student's t distribution for 6 degrees of freedom at the 99% confidence level (3.143) and S is the standard deviation of the seven replicate analyses. The standard deviation was ~ 5 ~tg 1-~, which yielded a M D L of 16 tag 1-~. The precision for multiple analyses,
Method performance The results of blanks, relative recoveries, MDL study, and the precision of this method are summarized in Table 2. Seawater blanks contained less than
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The average mass spectrum of N o r t h Cape oil (red-colored). (b) The mass spectrum of pentadecane (nC15). 131
Marine Pollution Bulletin
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100
150
I
'
200
'
'
Mass ratio (oil/nCz 2)
'
I
'
'
i
i
t00
250
Fig. 4 Calibration of North Cape oil (red-colored), which represents 1 to 10 lag of oil injected on-column to the GC-MSD (average response factor = 0.259 ± 0.006). Also shown are the responses of the North Cape oil (amber-colored), API No. 2 oil, M E R L No. 2 oil.
for the IR method was very large (370 ~tg) compared to the mean value (560pg). For the GC-FID and GC-MSD methods, the laboratory blanks were very small, the precision good (RSDs<3%), and the RPD between the two methods was 29%. The most probable reason for differences in the GC-FID and GC-MSD is that the GC-FID was not standardized for the specific oil analyzed, while the GC-MSD was calibrated by mass with the same oil that was spiked into the seawater. For each n-alkane, both GC methods were similar with the exception of the low-boiling nCl2 and nC13 for which the GC-FID method gave lower recoveries, which is most likely due to sample preparation.
as expressed by the relative standard deviation, was less than 10% and in most cases, less than 4%. The absolute recoveries of the nC22 IS in the blanks, matrix spikes, and MDL study ranged from 50 to 80% relative to the ES.
Comparison to other methods The TPHs results from the intercomparison are shown in Table 4. The IR method gave a smaller recovery than the other two techniques, with a considerably larger RSD (25%). Also, the laboratory blank
TABLE
2
Field samples From 4 to 132 days after the North Cape oil spill, we analyzed 54 water samples that were collected within ~12 km of the barge. The total-ion chromatogram, acquired in SIM mode, and the EICP of m/z 57 of a sample collected the seventh day after the spill are shown in Fig. 5. Overall, the concentrations of TPHs
Quality control parameters of GC-MS method for TPHs. Parameter Blanks Relative recoveries MDL Precision
Value 5-10 lag 1-1 90-110% for ~50-1000 lag of TPHs spiked 1-1 16 lag 1-1 < 10% RSD
TABLE
3
Recoveries of red-colored North Cape Oil spiked into 900 ml of seawater. Mass spiked (lag) 48.8 122 488 867 976
Conc. (lag 1-1)
No. of replicates
54.2 136 542 963 1080
7 2 2 3 2
abased on internal standard.
132
Mass recovered ± SD a (lag) 45.5 ±4.6 134±0 482±18 865 ± 17 1060±42
Relative standard deviation (RSD)
Recovery (%)
10% 0% 3.7% 2.0% 4.0%
93 110 99 100 109
Volume 38/Number 2/February 1999 TABLE 4
Results of intercomparison of the three techniques for seawater that was spiked with 867 gg of North Cape oil. Mass recovered, gg (RSD~,%) Hydrocarbon
GC-FID (N = 3)
GC-MS (N = 3)
IR (N = 3)
n-Dodecane (nCl2) n-Tridecane (nC13) n-Tetradecane (nCl4) n-Pentadecane (nC15) n-Hexadecane (nC16) n-Heptadecane (ne17)+pristanec n-Octadecane (nC18)+phytane c n-Nonadecane (nCw) n-Eicosane (nC2o) n-Heneicosane (nC21)
5.08 (5.5) 6.01 (5.5) 9.38 (5.9) 9.37 (5.2) 9.44 (2.4) 14.5 (3.0) 11.3 (2.1) 5.26 (1.8) 4.54 (3.0) 2.63 (1.8)
7.15 (6.9) 8.66 (3.0) 9.91 (3.9) 9.32 (2.9) 10.1 (5.8) 14.3 (3.1) 9.68 (2.9) 5.56 (3.4) 4.43 (1.3) 3.21 (6.1)
NAb NA NA NA NA NA NA NA NA NA
Total petroleum hydrocarbons (TPHs) Blank values of TPHs
64l (0.81) < 20
863 (2.9) < 20
560 (25) 370
aRelative standard deviation (RSD) for triplicate analyses. bNot analyzed. CFor GC-FID, this is the sum of the two individual compounds. For the GC-MS, these compounds were not separated on the DB-XLB column and are treated as one analyte. a n d P A H s w e r e as high as 3940 a n d l l 5 g g 1 - 1 ( T a b l e 5), respectively, a n d a r e s o m e of the highest values ever r e p o r t e d for a m a r i n e oil spill; see N e f f a n d Stubblefield (1995) for a r e c e n t review. T h e R P D s for d u p l i c a t e s a m p l e s w e r e < 7 % for T P H s a n d < 3 % for Abundance
total P A H s . Also, 7 days after the spill, b o t h the USEPA and our laboratory collected and analyzed s a m p l e s f r o m a p p r o x i m a t e l y the s a m e area. T h e i r s a m p l e s w e r e only analyzed for T P H s with a G C - F I D , b u t they gave similar results to o u r s a m p l e s f r o m that
(a) nC22 (IS)
TIC (SlM)
.
6.00
.
.
.
.
.
.
i
. . . .
i
i
•
8.00 i0.00 12.00 14.00 16.00 18.00 20.00 22.00
Time (minutes) Abundance
(b)
!nC22 (IS)
E I C P m/z 57 I
•
6.00
y .~
i
.~:
i
;.
.
.
.
. . i
.
.
.
. . i
.
.
.
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.
.
.
i
i
. - ; l !,I ~,:,:-
8.00 10.00 12.00 14.00 16.00 18.00 20.00 22.00
Time (minutes) Fig. 5 (a) Total ion chromatogram and (b) EICP of m/z 57 of one of the field samples collected on day 7 after the North Cape oil spill. These chromatograms were acquired in the SIM mode. 133
Marine Pollution Bulletin TABLE 5
Summary of results for all water samples collected after the North Cape oil spill. Compound
Symbol
No. of times detected above the MDL out of 54 samples
Mean (gg 1-l)
Std. dev. (gg 1-1)
Max. (gg 1-1)
Naphthalene* 2-Methylnaphthalene 1-Methylnaphthalene C1-Naphthalenes* C2-Naphthalenes* C3-Naphthalenes* C4-Naphthalenes* 1,1'-Biphenyl* 2,6-Dimethylnaphthalene Acenaphthene* Dibenzofuran* 1,6,7-Trimethylnaphthalene Fluorene* C1-Fluorenes* C2-Fluorenes* C3-Fluorenes* Dibenzothiophene* C1-Dibenzothiophene* C2-Dibenzothiophene* C3-Dibenzothiophene* Phenanthrene* Anthracene* 1-Methylphenanthrene C1-Phenanthrenes/Anthracenes* C2-Phenanthrenes/Anthracenes* C3-Phenanthrenes/Anthracenes* C4-Phenanthrenes/Anthracenes* Fluoranthene* Pyrene* C1-Fluor anthenes/Pyrenes* C2-Fluoranthenes/Pyrenes * ZPAHs a
No 2MN 1MN N1 N2 N3 N4 BIP DMN ACN DBF TMN Fo F1 F2 F3 Do D1 D2 D3 Po ANT IMP PI P2 P3 P4 FLT PYR F/P1 F/P2 -
50 50 49 50 53 53 45 40 48 36 32 40 39 41 43 39 31 35 39 39 47 33 41 49 49 45 36 30 40 32 32 53
0.498 1.55 1.04 2.57 3.71 4.06 2.95 0.292 1.01 0.0948 0.0986 0.367 0.291 0.702 1.12 1.18 0.0834 0.346 0.550 0.475 0.448 0.0704 0.233 1.44 1.64 1.01 0.536 0.0352 0.115 0.180 0.125 21.9
0.668 1.93 1.20 3.13 4.18 4.38 3.30 0.283 1.08 0.0651 0.0631 0.297 0.222 0.601 1.17 1.32 0.0535 0.294 0.606 0,560 0.429 0.0587 0.206 1.57 2.07 1.31 0.596 0.0278 0.107 0.179 0.135 24.2
3.06 6.83 4.16 11.0 13.8 20.5 18.5 0.938 3.58 0.222 0.213 1.34 0.759 2.54 6.28 7.26 0.194 1.54 3.36 3.15 1.56 0.305 1.11 8.30 12.1 7.68 3.34 0.138 0.578 0.994 0.750 115
-
46
TPHs
483
648
3940
a52PAHs is the sum of the PAHs marked with an '*'.
area; their TPHs values ranged from 150 to 820 lag 1-1, while ours ranged from 160 to 580 lag 1-1 .
Applications The proposed method is an alternative way to measure TPHs while also measuring PAHs in seawater samples recently impacted by an oil spill. This. is not the first attempt to use GC-MS to study aliphatic hydrocarbons in the environments; others have, such as Roques et al. (1994) and Kaplan et al. (1997). However, this is the first method that quantitatively measures TPHs with a GC-MS. Because this method essentially measures the n-alkane component of oil, it is most useful for analyzing TPHs in areas recently impacted by fuel oil because n-alkanes are the first compounds to be microbially dggraded (Singer and Finnerty, 1984). Hence, the relative signal for m/z 57 will decrease and estimates of TPHs in severely degraded oil will be underestimated using the GC-MS method. This is the distinct quantitative disadvantage between integrating the whole chromatogram obtained with a GC-FID versus an EICP of m/z 57 from a GC-MS. The signal
134
from the FID is based on the mass of carbon combusted, which should be relatively insensitive to the chemical nature of the compounds. Conversely with a GC-MS, the signal from m/z 57 depends more on the molecular structure of the compounds and not the total amount of carbon. Alternative methods could use m/z 55 (C4H~), which are the major ions produced by cycloalkanes (McLafferty and Yurecek, 1993), because these compounds do not degrade as quickly as the n-alkanes (Singer and Finnerty, 1984). Preliminary results from measuring TPHs in marine sediments with m/z 55 and GC-FID are very similar; in this case, both the GC-FID and GC-MS are calibrated with used crankcase oil (Lamontagne et al., unpublished data). Alternatively, samples could also be analyzed in the full-scan mode by integrating the total ion signal, but with lower sensitivity.
Conclusion A simple and rapid method was developed for measuring TPHs and PAHs in seawater and possibly other environmental samples. The blanks, accuracy, precision, and MDLs are comparable to GC-FID
Volume 38/Number 2/February 1999 m e t h o d s ( D o u g l a s et al., 1992; D o u g l a s a n d U h l e r , 1993). T h i s m e t h o d is p a r t i c u l a r l y u s e f u l for a n a l y z i n g s a m p l e s t h a t have b e e n r e c e n t l y i m p a c t e d by a r e f i n e d p e t r o l e u m p r o d u c t . F o r e x a m p l e , t h e m e t h o d was successfully u s e d to d e t e r m i n e the T P H s a n d P A H s in field s a m p l e s after t h e North Cape oil spill. We would like to thank: Mr D. Cobb, Dr J. Latimer, Mr R. McKinney, Dr R. Pruell, and Mr B. Taplin of the Atlantic Ecology Division of the United States Environmental Protection Agency (Narragansett, RI); Dr R. Cairns, Mr W. DeLeo, Mr M. DiMatteo, Dr C. Kincaid, Lt Cmdr. J. Sifting (USCG), Mr S. Sylva, and Ms J. White of the Graduate School of Oceanography (GSO), University of Rhode Island; Mr G. Mauseth of Beak Consultants (Kirkland, WA); and the crew of the R/V Cap'n Bert (University of Rhode Island). This work was supported in part by a grant from Eklof Marine. CMR was also supported by a Narragansett Electric Coastal Fellowship and a GSO alumni award. The GC-MSD was donated to our laboratory through the Hewlett-Packard University Grants Program. Anderson, J. W., Neff, J. M., Cox, B. A., Tatem, H. E. and Hightower, G. M. (1974) Characteristics of dispersions and watersoluble extracts of crude and refined oils and their toxicity to estuarine crustaceans and fish. Marine Biology 27, 75-89. Douglas, G. S., Bence, A. E., Prince, R. C., McMillen, S. J. and Butler, E. L. (1996) Environmental stability of selected petroleum source and weathering ratios. Environmental Science and Technology 30, 2332-2339. Douglas, G. S., McCarthy, K. J., Dahlen, D. T., Seavey, J. A., Steinhauer, W. G., Prince, R. C. and Elmendorf, D. L. (1992) The use of hydrocarbon analyses for environmental assessment and remediation. Journal of Soil Contamination 1, 197-216. Douglas, G. S. and Uhler, A. D. (1993) Optimizing EPA methods for petroleum-contaminated site assessments. Environmental Testing and Analysis May/June, 1-6. Gearing, J. N., Gearing, P. J., Wade, T. L., Quinn, J. G., McCarty, H. B., Farrington, J. and Lee, R. F. (1979) The rates of transport and fates of petroleum hydrocarbons in a controlled marine ecosystem, and a note on analytical variability. In Proceedings of the 1979 Oil Spill Conference. Prevention, Behavior, Control, Cleanup, pp. 555-564. American Petroleum Institute, United States Environ-
mental Protection Agency, United States Coast Guard, Los Angeles. Glaser, J. A., Foerst, D. L., Quave, S. A. and Budde, W. L. (1981) Trace analyses for wastewaters. Environmental Science and Technology 15, 1426-1435. Kaplan, I. R., Galperin, Y., Shan-Tan, L. and Ru-Po, L. (1997) Forensic environmental geochemistry: Differentiation of fueltypes, their sources and release time. Organic Geochemistry 27, 289-317. MDEP (1995) Method for the Determination of Extractable Petroleum Hydrocarbons (EPH). Massachusetts Department of Environmental Protection, Boston, MA. McLafferty, F. W. and Turecek, F. (1993) Interpretation of Mass Spectra. University Science Books, Mill Valley, CA. NOAA (1997) Restoration Plan and Environmental Assessment for the January, 19, 1996 North Cape Oil Spill, DRAFT, dated 16 May 1997. National Oceanic and Atmospheric Administration, Rhode Island Department of Environmental Management, and United States of the Interior. Neff, J. M. and Stubblefield, W. A. (1995) Chemical and toxicological evaluation of water quality following the Exxon Valdez oil spill. In Exxon Valdez Oil Spill." Fate and Effects in Alaskan Waters, eds P. G. Wells, J. N. Butler and J. S. Hughes, pp. 141-177. ASTM Special Technical Publication 1219, American Society for Testing and Materials, Philadelphia. NRC (1985) Oil in the Sea: Inputs, Fates, and Effects. National Research Council, National Academy Press, Washington, DC. Reddy, C. M. (1997) Studies of the fates of organic contaminants in aquatic environments. Ph.D. dissertation, University of Rhode Island, Kingston, RI. Roques, D. E., Overton, E. B. and Henry, C. B. (1994) Using gas chromatography/mass spectrometry fingerprint analyses to document process and progress of oil degradation. Journal of Environmental Quality 23, 851-855. Sauer, T. and Boehm, P. D. (1991) The use of defensible analytical chemical measurements for oil spill natural resource damage assessment. In Proceedings of the 1991 Oil Spill Conference. Prevention, Behavior, Control, Cleanup, pp. 363-369. American Petroleum Institute, Washington DC. Singer, M. E. and Finnerty, W. R. (1984) Microbial metabolism of straight-chain and branched alkanes. In Petroleum Microbiology, ed. R. Atlas, pp. 1-60. McMillan Publishing Co, New York. USEPA (1983) Methods for the Analysis of Water and Wastes. United States Environmental Protection Agency, Washington, DC.
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