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Applications of thermal distillation—pyrolysis to petroleum source rock studies and marine pollution
Journal of Analytical and Applied Pyrolysis, 2 (1980) 79-96 Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands
79
APPLICATIONS OF THERMAL DISTILLATION-PYROLYSIS TO PETROLEUM SOURCE ROCK STUDIES AND MARINE POLLUTION *, * *
JEAN K. WHELAN ***, JOHN M.HUNTand ALAIN Y. HUC
Chemistry Department, Woods Hole Oceanographic Institution, Woods Hole, MA 02543 (U.S.A.)
SUMMARY The technique of thermal distillation-pyrolysis involves heating a 0.5-50 mg sample of wet sediment from 100 to 800°C at 20° /min and measuring evolved hydrocarbons as a function of temperature. Unaltered absorbed hydrocarbons evolve at 100-150°C, and cracked or pyrolyzed hydrocarbons at 650-800 0 C in two well-separated peaks, PI and,P 2 • The compounds in PI and P 2 are analyzed by capillary gas chromatography (GC) and GC-mass spectrometry. An increasing ratio of P1/(P 1 + P 2 ) indicates increasing petroleum source rock maturity. Data are presented for known source rocks and a test well (COST I, Gulf of Mexico, U.S.A.). Applications of the method to examination of oil and chemical pollutants in organisms and surface sediments are given. Results to date have shown that an increasing degree of pollution causes an increasing P 1/P 2 ratio and increasing complexity of the PI peak. The hydrocarbon composition of P 2 has been used to fingerprint and trace high molecular weight organic-rich particles in the marine environment.
INTRODUCTION
We have applied the technique of thermal distillation-pyrolysis to examination of both absorbed and pyrolyzed volatile organic compounds in small (0.5-50 mg) samples of marine organisms and sediments. The frozen or wet sample is heated in a helium stream from 100 to 800° C at 20-30° Imin. A graph of temperature versus amount of organic compound evolving is recorded during the heating process as shown in Fig. 1. The organic material emerges in two well-separated peaks. Unaltered absorbed compounds appear in a low temperature peak (PI) centered at 100-150°C while cracked, or pyrolyzed, organic compounds emerge in a second peak (P 2 ) at a temperature of 650-800° C. The technique differs from conventional pyrolysis in utilizing gradual heating over a fairly long period of time. The technique has previously been applied to source rock analysis [1-3].
* Presented
at the 4th International Symposium on Analytical and Applied Pyrolysis, Budapest, June 11-15, 1979. ** Contribution No. 4377 from the Woods Hole Oceanographic Institution. *** To whom correspondence should be addressed. 0165-2370/80/0000-0000/$ 02.25 © 1980 Elsevier Scientific Publishing Company
80 HELIUM (SOml/min 1
:t
CHEMICAL DATA SYSTEM$REACTION SYSTEM 820 / HIGH TEMPERATURE PEAK (PYROLYZED HYDROCARBONS)
600
400
LOW TEMPERATURE PEAK (ABSORBED HYDROCARBONS)
200
DETECTOR SIGNAL (AMOUNT HYDROCARBON)
4- PORT
VALVE NO.3
ELECTRONIC INTEGRATOR
LOW DEAD VOLUME CONNECTIONS
1700~
FRONT lOOP OF PORASIL C COLUMN
VARIAN GAS CHROMATOGRAPH
Fig. 1. Diagram of thermal distillation-pyrolysis apparatus.
We have applied the technique in a similar manner to the analysis of source rock samples and cuttings from a test well (COST I, Gulf of Mexico, U.S.A.). We have also applied the technique in a new way - in examining small marine particles, including sediments, plants and organisms for anthropogenic pollutants such as oil. In addition, we have obtained preliminary data which show the method may be useful in following the movement of organic-rich particles in harbors and estuaries. A description of the technique and examples of our initial results are presented in this paper. EXPERIMENT AL
The wet or frozen sample is weighed into a 20 mm 'x 1 mm I.D. quartz tube and is held in place with two small plugs of quartz wool. If necessary, deionized distilled water is added to the sample from a 50-J,t! syringe to bring the total volume of water plus sample to about 1/3 to 1/2 that of the total capacity of the quartz tube. The tube is placed in the small platinum coil heater of the pyrolysis probe [Chemical Data Systems (CDS) Pyroprobe]. The probe and sample are then placed in the cooled interface of a CDS 820 Reaction System equipped as shown in Fig. 1. After the interface is flushed briefly with helium at room temperature, it is heated to 250°C and the
81
'robe coil is programmed to 800°C at 20-30° /min using the CDS Extended 'rogrammer. Volatile . organic compounds are swept out of the sample in a helium tream which is split 1 : 10 as shown in Fig. 1. The smaller stream passes hrough a thermal conductivity detector (which can be used to measure nonlydrocarbon components such as water) and then into a flame ionization letector (FID). The FID signal is plotted as a function of temperature to ~ve a pyrogram such as that shown in Fig. 1. Peak areas are measured with m electronic integrator (Columbia Scientific Industries Supergrator 3). The larger part of the helium stream is swept through the CDS Reaction ,ystem 820 (maintained at 300° C, helium flow-rate 60 ml/min) into a 4 n. X 1/8 in. O.D. stainless-steel trap packed with Tenax (80-100 mesh, Ap>lied Science Labs., State College, PA, U .8.A.). At room temperature, the renax trap absorbs C7 and higher aliphatic hydrocarbons as well as benzene, ;oluene and larger aromatic compounds while water is not retained. Two :uch traps (attached to 8-port valve No.1 in Fig. 1) are used in the system so hat peaks P 1 and P 2 may be trapped successively during the analysis. It is im)ortant that the amounts of Tenax be the same in both traps for quantitative 1V0rk since minor differences affect the back pressure and, consequently, the :plit ratio in the system. The detailed composition of P 1 or P 2 is examined by capillary gas chronatography (GC) by heating the Tenax loop to 210°C for 12 min and iweeping the compounds evolved through a heated 8-port sampling valve Carle microvolume valve No. 2014, 8-port valve No.2 in Fig. 1) into a 10 n. X 0.01 in. I.D. stainless-steel loop immersed in liquid nitrogen. The valve s then switched, the sample loop heated to 200° C for 2-3 min and the sam)le is swept into a 2 in. X 0.01 in. I.D. stainless-steel U-tube immersed in iquid nitrogen. This tube is connected to the front of the GC column via L/16 in. low dead volume fittings. Its purpose is to concentrate the sample to 1 very small volume which increases resolution in the subsequent capillary }C analysis. The liquid nitrogen bath is removed and the sample analyzed on i micro packed column (3 m, 3% OV-17, 160-180 mesh, Alltech, Arlington Heights, IL, U.S.A.) via temperature programming from 70 to 200°C at 6° / min. The chromatograph used is a Varian Aerograph 1700 equipped with iual electrometers and flame ionization detectors. Retention times and imounts of components are measured via an electronic integrator (Columbia Scientific Industries Supergrator 3). Tenax was chosen as the trapping material in this analysis because of its V'ery low bleed rate and high thermal stability compared to many other ibsorbents tested. It also does not retain water - a very useful characteristic in our analysis. We believe that water is crucial to the quantitative recovery Df the absorbed P 1 components as discussed further below. The mildness of the procedure (evolution of P 1 at about 125°C) is evidenced by our ability to quantitatively trap and desorb alkanes up to C30 (as determined by connecting the exit from the Tenax trap directly to the flame ionization detector). The GC column used is considered to be a type of capillary column - it is a small-diameter packed column utilizing typical capillary carrier gas flowrates of 1 ml/min. Capillary wall-coated open tubular (WCOT) columns have
82
been used successfully in this analysis. However, the micro packed column was chosen in spite of its lesser resolution because it is much less sensitive to overloading and other abuses commonly occurring during this analysis. The use of capillary columns in this analysis is made 'possible by the use of the 8-port sampling valve (No.2 in Fig. 1) in front of the gas chromatograph. This valve allows compounds eluting from the Tenax traps to be swept out of the Reaction System 820 at the high flow-rate required (60 ml/min) for trapping and desorption and to then be injected into the gas chromatograph at the low flow-rate (1 ml/min) required by the capillary column. Use of the 8-port valve allows the switching to be accomplished without disturbing the flow-rate of either stream. We are currently able to analyze hydrocarbons up to CIS from the PI peak via capillary GC as determined by recovery of standards injected into wet sediment samples. Thus, we cannot presently analyze by capillary GC all of the components evolved and swept into the Tenax traps during initial sample heating. The higher molecular weight components do not elute from the GC column we are using. The temperature at which PI evolves from these samples is 100-150°C as measured by the resistance of the platinum coil heater around the sample tube. At this temperature, water plus absorbed organic compounds volatilize out of the sample in a process similar to steam distillation. The resulting PI peak is fairly sharp and is well separated from the pyrolysis peak (P 2 ). The volatilization process is very mild as shown by our ability to quantitatively recover hydrocarbon standards as discussed previously. In addition, GCmass spectral (MS) analysis (see discussion of the method below) has shown the presence of some fairly labile compounds such as aldehydes, alkenes, and alkyl chlorides (Fig. 15). We believe that water may be crucial to the mildness of the P I desorption from the results of the following experiments. Both wet and dry sediment samples were subjected to the analysis. Two different drying procedures were used on a muddy sediment ooze. In one, the material was dried for a few hours at 110°C. In another, the wet sediment was allowed to stand on a watch glass at ambient temperature overnight. The wet sediment showed a significant PI peak which had disappeared completely in the dried sediment. Similar experiments with deeper more lithified sediments showed a significant PI peak even with dry samples. However, these samples gave higher and more reproducible P I yields after water was added. Considering the high boiling points of the alkanes making up PI (98°C for n-heptane and progressively higher temperatures for higher homologues) and the increase in PI yield when water is added to dry samples, steam distillation is the most reasonable explanation for the low temperature of PI evolution. A qualitative analysis of Cc~s hydrocarbons in either PI or P 2 can be carried out on a Porasil C column as shown in Fig. 1. The compounds are swept into the column (through 8-port valve No.1 and through the Tenax traps kept at room temperature) by switching 4-port valve No.3 and immersing a 4-in. loop in the front of the column in liquid nitrogen. Gas chromatographic analysis is then carried out by removing the nitrogen bath and heating the column (6 ft. X 1/8 in. O.D. X 0.085 in I.D. stainless steel packed with noctane/Porasil C, 100-120 mesh, Alltech) to 50°C. We can currently detect
83
the relative amounts of light hydrocarbons by this procedure. However, total amounts recovered show considerable variability caused by flow-rate changes whicp occur when the packed column is switched into the system. We are currently working on instrument modifications which will allow quantitative C1-C S determinations in the future. Samples are trapped for GC-MS analysis in 3 in. X 1/8 in. O.D. stainlesssteel tubes packed with Tenax. The traps (which fit snugly into the injection port of the Varian 1400 gas chromatograph which is part of our MS system) are heated for 5 h or more at 350°C in a helium stream and stored in a vacuum desiccator until used. These tube traps are connected to the trap vent, which comes from the Tenax traps of the Reaction System 820, via a small piece of silicone rubber tubing. The compounds are desorbed into the tube traps (kept at room temperature) from the Reaction System 820 traps which are heated to 210°C for 12 min. The tube traps are then sealed in glass ampoules under nitrogen in the freezer until MS analysis. For injection into the GC-MS system, the tubes are sealed at 25° C in the injection port of the gas chromatograph and are then heated to 210° C in a helium stream for 10-15 min. The compounds evolved are trapped in a 2 in. X 0.01 in. LD. stainless-steel U-tube immersed in liquid nitrogen and attached to the Micropak column in the GC oven of the GC-MS system. The GC analysis is then carried out as described previously using a Finnigan Quadrupole GC-MS-computer system. The entire capillary GC eluant enters the mass spectrometer without splitting. Compounds were identified by comparison of mass spectra to standards run under identical conditions in the case of hydrocarbons and by comparison to standard reference spectra [7] in the cases of other compounds.
RESULTS AND DISCUSSION
Source rock analysis Representative pyrograms for petroleum source rock cuttings from a test well (COST I, Gulf of Mexico, U.S.A.) are shown in Fig. 2. Two clearly separated peaks are apparent in each analysis. The first, PI, released by heating the sample from 100 to 250°C, is related to the free and absorbed hydrocarbons which are steam distilled out of the rock. They are considered to be hydrocarbons previously produced in the subsurface under natural conditions. The second peak (P 2 ) occurs at higher temperatures by further heating of the sample to 800°C. The release of hydrocarbons at such temperatures is the result of a thermal breakdown (or pyrolysis) of the complex high molecular weight organic material called kerogen. Thus, the area of P2 might be considered as the potential of the rock to generate petroleum if the natural evolution continues. . Fig. 2 illustrates the way the shape.of the pyrograms changes as the depth of burial increases. The main feature is the increasing size of the low temper-
84 SOUTH PADRE ISL.
13,230 ft
15,570 ft
11,700 It
Fig. 2. Pyrograms of test well of COST I (South Padre Island, Gulf of Mexico, U.S.A.).
ature peak PI relative to the high temperature peak as depth increases. This trend is a reflection of the increasing generation of hydrocarbons as depth of burial (and temperature) increase. The low temperature peak (Pd is small in the shallower recent sediments where the hydrocarbons consist primarily of lipids of biological precursors. The P 2 peak is large because the kerogen has not lost hydrocarbons via natural thermally induced breakdown. In contrast, in deeper samples where petroleum generation is more advanced, P I becomes much larger. The change can be expressed quantitatively as a generation or production index (P.L) as proposed by Barker [1] and Espitalie et al. [3]: PI P.L=p-p 1 + 2 where PI and P 2 are the areas of the low temperature and the high temperature peaks, respectively. A plot of this parameter P.L versus depth is shown for the COST I well in Fig. 3. The graph shows that the ratio stays fairly constant down to 10,000 feet below which a great increase occurs as the depth of intense hydrocarbon generation is reached. Examples of pyrograms for well-studied mature oil shales are shown in Figs. 4 and 5 for the La Luna and Posidonien shales, respectively. The La Luna shale is a Cretaceous calcareous shale from Columbia and Venezuela. It is known to be the source rock for the Cretaceous oils in the area. The Posidonien shale is Jurassic black shale which covers a wide area in western Europe including France, Luxembourg and Germany. Capillary GC analyses of the P I peaks from Figs. 4 and 5 are shown in Figs. 6 and 7, respectively. The n-alkanes are clearly visible as well-resolved peaks above to unresolved complex hump typical of petroleum. Information related to nature, level of maturation, and the migration of organic matter
85 PRODUCTION INDEX = AREA PEAK 1/AREA PEAK(I t2 J 01
2000
4000
i:::'
03
0.4
0.5
SOUTH PADRE ISLAND U.S. GULF COAST COST# 1
6000
t:J
-.,
~
j!::
••
02
8000
~
~
10000
12000
14000
16000
.•_.e_e_ : - ...::::--.-
Fig. 3. Production Index versus depth of test well of COST I (South Padre Island, Gulf of Mexico, U.S.A.).
can be obtained by observing how patterns of this kind change with depth. For example, it is normal for lighter hydrocarbons to predominate at greater depths in more mature source rocks in the absence of migration [4]. It is also well known that a biodegraded oil will retain the unresolved petroleum hump (representing cydoalkanes and aromatic compounds) while showing the disappearance of the sharp n·alkane peaks. Examples of capillary GC analyses for the La Luna and Posidonien P 2 peaks are shown in Figs. 8 and 9, respectively. The chromatographic analyses of these pyrolyzed products must be interpreted more carefully. The thermal breakdown of the organic matter brings complex changes in characteristics of the released molecules such as aromatization, un saturation and condensa-
LA LUNA SHALE
so. AMERICA
Fig. 4. Pyrogram of La Luna shale (South America).
86 t
CIO
CII
Cg
~
POSIOONIEN SHALE
LA LUNA SHALE PI
Cs
EUROPE
©l ~
©r
P2 C7
Fig. 5. Pyrogram of Posidonien shale (Europe). Fig. 6. Capillary gas chromatogram of the Pi peak (absorbed hydrocarbons) of La Luna shale (South America).
tion. For example, the well-resolved double peaks in Figs. 8 and 9 represent alkane plus alkene of the same carbon number which are generated from the organic or kerogen matrix by the thermal cracking process. However, preliminary results show that the GC pattern of pyrolytic products produced is very reproducible and characteristic and might be useful in fingerprinting the source materials for petroleum, the parent kerogens. Currently, there are very few other methods available for examining these extremely complex substances. Cs
LA LUNA SHALE P2
Cs
POSIDONIEN SHALE PI
Fig. 7. Capillary gas chromatogram of the Pi peak (absorbed hydrocarbons) of Posidonien shale (Europe). Fig. 8. Capillary gas chromatogram of the P 2 peak (pyrolyzed hydrocarbons) of La Luna shale (South America).
87
POSIDONIEN SHALE
C8
P2 C9
'@
CIO
~
ig.9. Capillary gas chromatogram of the P 2 peak (pyrolyzed hydrocarbons) of Posimien shale (Europe).
nalysis of recent marine sediments, particles, and organisms The thermal distillation-pyrolysis method has also been applied to examling organic pollutants in marine sediments, plants, and animals. Fig. lOA lOWS the pyrogram of an organic rich (11% organic carbon) diatom ooze )ntaining only biogenic absorbed hydrocarbons (PI small, P2large) and Fig. OB shows an organic lean sediment which has been spiked with fuel oil (100 fuel oil per g dry weight of sediment) (P I large, P2 small). In this case as 'ell as in surface sediments, a high PdP 2 ratio generally indicates the presnee of petroleum or other anthropogenic organic compounds while a very )W PdP 2 ratio shows little or no pollution. Some examples of applications f the method to analysis of surface sediments are shown in Fig. 11. The lree pyrograms represent two sediments collected from around Cape Cod, lA, U.S.A. (Monomescoit and Wild Harbor) and a third obtained from nder a bridge in a metropolitan area in Seattle, WA, U.S.A. Monomescoit is n island and has been found to be virtually unaffected by activities of man 8]. The sediment from Wild Harbor is contaminated with fuel oil which ame from a massive oil spill which occurred in September, 1969. It can be een that the PI peak is very small in the unpolluted Monomescoit sample nd large in the petroleum contaminated Wild Harbor sample. In the Seattle ample, the PI peak is small, but relatively large in comparison to P 2 showing hat absorbed organic compounds may be contributing significantly as xpected in such an urban area. The area of PI can be integrated to give a total absorbed hydrocarbon 'ield that compares well with values obtained by more conventional extracion methods as shown in Table 1. Extraction data for Wild Harbor and for learby Sippewissett Marsh, which was unaffected by the spill, were collected .y Burns and Teal [5] and by Blumer et al. [6] for several years following he spill. Data of Burns and Teal show considerable local variation in Wild
**
*
Extraction
Extraction
Wild Harbor (surface) Wild Harbor (surface) Wild Harbor (surface) Wild Harbor (surface) Wild Harbor (surface, sandy, high marsh) Wild Harbor (biogenic) *** Wild Harbor (biogenic) *** Wild Harbor (surface) Wild Harbor (surface) Sippewissett Marsh (surface) Sippewissett Marsh (surface) Sippewissett Marsh (surface)
'78 '71 '71 '78 '78
Jan. '71 May'72 July'73 Nov. '73 Mar. '73 Jan. '71 May'72 Dec. '69 May'70 Jan. '71 Nov. '71 Mar. '73
Oct. Sep. Sep. Oct. Oct.
Date collected
3080 989 234-2661 675 134 21 9 400-900 250-400 5.2 17.6 46
144 312 203 1-9 11-22
Hydrocarbon yield
Teal [5]. Sediment was saponified. The non-saponifiable lipids extracted with pentane and chromatographed on alumina. Yields are based on total hydrocarbons eluted with pentane. ** Blumer et al. [6]. Method similar to that of Burns and Teal. *** Sediment from a core; sub-bottom depth was 70-85 cm. Burns and Teal [5] determined the hydrocarbons in this sediment to be biogenic only.
* Burns and
*
Wild Harbor (surface, sandy) Wild Harbor (surface) Wild Harbor (surface) Si ppewissett Marsh (surface) Sippewissett Marsh (surface)
Thermal distillation-pyrolysis
Extraction
Sample (depth)
Method
Hydrocarbon yields in micrograms of hydrocarbon per gram wet weight of sediment.
Comparison of petroleum hydrocarbon levels in surface sediments determined by thermal distillation-pyrolysis and by solvent extraction
TABLE 1
(Xl (Xl
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oil:
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~ B
600
I 500
400
300
200
100
Temperature of sample (OC)
Fig. 10. Pyrograms of (A) organic-rich diatomaceous surface ooze (11% organic carbon) containing only biogenic absorbed hydrocarbons; (B) organic lean sediment spiked with fuel oil (100 g hydrocarbon per gram dry weight of sediment).
MONOMESCOIT 25.7mg WET SEDIMENT
WILD HARBOR, MASS. 33.3 mg WET SURFACE SEDIMENT
I
1eO°C
>-X8
SEATTLE,WASHINGTON 39 mg WET SEDI MENT
~
-+-X8 Xi6
f--
X32
680·C 135 "'c
I 690°C
0---
X16
Fig. 11. Pyrograms of surface sediments of Monomescoit (unpolluted area), Wild Harbor (subjected to an oil spill) and Seattle, WA (sample from urban area).
90
Harbor fuel oil levels, but that values of about 100-3000 Ilg hydrocarbon per g of wet sediment persisted for a period of at least three years after the spill. Data of Blumer et al. show levels of 250-900 Ilg hydrocarbon per g of wet sediment. For samples collected in the uncontaminated Sippewissett Marsh, or from deeper (uncontaminated) Wild Harbor sediments, hydrocarbon levels were in the range of 5-46 Ilg/g. In this work, thermal distillationpyrolysis measurements of absorbed hydrocarbons (P I) for a Wild Harbor surface sediment showed a hydrocarbon level of 312 Ilg/g as compared to Sippewissett Marsh values of 1-22 Ilg/g. The Wild Harbor sample, provided by Teal, was collected about one year after the oil spill and was kept frozen until the time of this analysis. We also analyzed a second Wild Harbor sample collected within the last six months by Stegeman. The fine particles isolated from a predominantly sandy sediment showed a PI peak area corresponding to 144 Ilg hydrocarbon per g wet sediment. This value corresponds well to that of Burns and Teal of a sandy sediment taken from the high marsh area of Wild Harbor in spring of 1973, viz. 134 Ilg hydrocarbon per g wet sediment. Thus, calculation of the total amount of absorbed hydrocarbon represented by the area of PI agrees well with extraction data, both for petroleum contaminated and uncontaminated areas. Capillary GC analysis of PI gives additional information about the presence of anthropogenic hydrocarbon as shown in Fig. 12. Monomescoit, the unpolluted sediment, shows a very simple distribution of compounds, while both Wild Harbor and Seattle give a much more complex pattern including a substantial unresolved complex mixture under the hump, as is typical for a surface sediment containing an anthropogenic hydrocarbon input. Thus, the complexity of the capillary gas chromatogram of peak P I rapidly gives a qualitative estimation that an area is receiving a petroleum hydrocarbon or other anthropogenic organic input. Two other examples in Fig. 13 show capillary GC analyses for PI from Fig. 10. The simple absorbed hydrocarbon pattern shows the absence of pollution in the organic-rich sediment (Fig. 13A), while the complexity of the fuel oil spike is clearly evident in Fig. 13B. The thermal distillation-pyrolysis method has also been applied to materials with a high lipid content of their own as shown in Fig. 14. The samples consist of some tail meat from small (2 cm long) shrimp, one taken from petroleum contamined Wild Harbor and the other from uncontaminated Sippewissett Marsh. The capillary GC analyses of the absorbed hydrocarbons representing the PI peak clearly show the complex unresolved fuel oil signal for the Wild Harbor shrimp. Since the method requires only small samples, preliminary results suggest that the method may be valuable in determining where pollutants, such as oil, concentrate in the animal. More complete identification of components in Pi can be carried out by GC-MS analysis. For example, some of the compounds identified in the sandy sediment sample collected in the last 6 months from Wild Harbor are shown in Table 2 (not the same sample as shown in Fig. 15). The oxygenated compounds, such as aldehydes, ketones, phenol, cresol, benzofuran and benzaldehyde may be related to microbiological breakdown of the petroleum which, as mentioned earlier, was spilled at this site in 1969. The table
91
MONOMESCOIT . (Unpolluted)
PI
X8
WILD HARBOR 33.3mg WET SURFACE SEDIMENT PI
X8
SEATTLE PI 39mg WET SEDIMENT
Fig. 12. Capillary GC analyses of PI peak (absorbed hydrocarbons); same samples as Fig. 11.
also shows that the method can be applied to pollutants other than petroleum. For example, the presence of chlorobenzene was detected by mass scan of m/z 112 and 114. Capillary GC analyses of the cracked P2 components from the Monomescoit, Wild Harbor and Seattle surface sediments are shown in Fig. 15. As expected for sediments collected from different areas, the patterns are different for the three samples. As mentioned earlier, we have found this pattern to give a highly reproducible fingerprint for a particular type of particle. For example, three surface sediment samples and four sediment trap samples collected from Boston Harbor gave almost identical P2 capillary GC patterns as shown in Fig. 16 for two of the samples. Minor changes in intensity and composition of early eluting peaks are ignored since losses of more volatile components are caused by minor changes in analytical conditions. The analyses show that the high molecular weight organic material is very similar in both suspended matter and sediments throughout the harbor.
92
A ~
'"
n
-<
6 z
1
C7
Cs
-;~
s:-<
Orn
8
Co
z-< -<0
n::O 0", S:rn
~ '" n
"(I) -< 0"'0 6 CO z
3~ t
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INCREASING RETENTION TIME
Fig. 13. Capillary GC analyses of PI peak (absorbed hydrocarbons); same samples as Fig. 10. (A) Biogenic hydrocarbons; (B) fuel oil spiked sample.
SIPPEWISSETT MARSH SHRIMP PI l.4mg TAIL
WILD HARBOR SHRIMP PI O.97mg TAIL
'"c '"
x8
XI6 1
Fig. 14. Capillary GC analyses of PI peak of shrimp tail meat of Wild Harbor, MA (oil contaminated area) and nearby Sippewissett Marsh (relatively contamination free).
93 TABLE 2 Absorbed organic compounds identified from PI of Wild Harbor sample by gas chromatography-mass spectrometry n-Heptane C 7 H l4 alkene 3-Hexanone Cyclohexene C s aldehyde or ketone Phenol C s alkane (3 isomers) CSHl6 alkene Xylene (3 isomers) Styrene Chlorobenzene 3-Heptanal Alkylbenzene (4 compounds)
MONOMESCOIT (Unpolluted)
n-Propylbenzene Dialkylbenzene (2 compounds) Trialkylbenzene (3 compounds) Benzaldehyde Benzofuran Cresol C 6 aldehyde Naphthalene Methylnaphthalene (2 isomers) Alkyl chloride Alkylthiophene C I6 H 32 alkene C ls H 3S alkane
P2
m
u
Q)JQ)~
~ ~ ~f ,E
WILD HARBOR P2 33.3 mg WET SURFACE SEDI ME NT
SEATTLE P2 39 mg WET SEDIMENT
_ _X_'6_
Fig. 15. Capillary GC analyses of P 2 peaks (pyrolyzed or cracked organic compounds) from recent surface sediments. Same samples as in Figs. 11 and 12.
94
P2 BOSTON HARBOR SEDIMENT TRAP OT
\
\ \ \ \
\ \ \ \ P2 BOSTON HARBOR GRAB 27
\ \
Fig. 16. Capillary GC analyses of P2 peaks (pyrolyzed organic compounds) from Boston Harbor particles. OT is midwater sediment trap sample; GRAB 27 is a surface sediment sample.
In contrast, the capillary GC patterns for the PI peaks from the same samples show distinct differences in absorbed organic material as shown in Fig. 17. The PI peaks for the two bottom sediment trap samples (IB and OB) are similar in showing a "hump" and in being very different from those of a bottom sediment sample (Grab 27) and a mid-water sediment trap sample (OT). The capillary GC PI patterns also indicate the similarity of absorbed organic material on the sediment sample (Grab 27) and the mid-water sediment trap sample, ~T. The detailed interpretation of these results must await further work. However, these data indicate the usefulness of the method in tracing the movement of organic matter in a marine estuary. The differences observed in absorbed organic matter on the particles is probably strongly influenced by the presence of a sewage outfall near the location where these samples were collected and by the presence of strong lateral tidal currents into and out of the harbor. The results presented here illustrate the value of the thermal distillationpyrolysis method for examining organic matter on several types of samples where large sample requirements have previously prevented such analyses, including marine particles and parts of small marine animals. In addition, the speed and ease of the method make it valuable as a screen for determining which samples should be examined more extensively using other more specialized and time-consuming methods. Initial results show that the method gives amounts of absorbed hydrocarbons in both petroleum contaminated and uncontaminated sediments which compare well with values measured by solvent extraction techniques. In addition, capillary GC patterns of the P2 pyrolysis peak may be useful in fingerprinting high molecular weight organic material on sediment particles, fecal pellets, and other small marine particles,
95 PI BOSTON HARBOR GRAB 27
: PI BOSTON HARBOR I SEDIMENT TRAP OT
PI BOSTON HARBOR SEDI MENT TRAP I B
Fig. 17. Capillary GC analyses of PI peaks (absorbed organic compounds) from Boston Harbor particles. IB and OB are inner and outer harbor bottom sediment trap samples, respectively. Other designations same as in Fig. 16.
a process that is currently very difficult or impossible by any other technique. ACKNOWLEDGEMENTS
We wish to thank Nelson Frew for gas chromatographic-mass spectral analysis. We are grateful to John Teal, John Stegeman, Mike Fitzgerald and John Milliman for providing samples. The construction of the pyrolysis unit and the petroleum source rock studies were supported by Department of Energy Contract No. EG-77-S-02-4392. The marine pollution studies were supported by Sea Grant Contract No. 04-8-MOl-149. REFERENCES 1 C. Barker, Amer. Ass. Petrol. Geol. Bull., 58 (1974) 2349. 2 G.E. Claypool and P.R. Reed, Amer. Ass. Petrol. Geol. Bull., 60 (1976) 608. 3 J. Espitalie, J.L. Laporte, M. Madec, F. Marquis, P. Leplat, J. Paulet and A. Boutejeu, Rev. Inst. Fr. Petrole Ann. Combust. Liquides, 32 (1977) 23. 4 B.P. Tissot and D.H. Welte, Petroleum Formation and Occurrence, Springer-Verlag, New York, 1978, pp. 185 and 414.
96 5 K. Burns and J. Teal, Estuarine and Coastal Marine Science, 8 (1979) 349. 6 M. Blumer, J. Sass, G. Souza, H. Sanders, F. Grassle and G. Hampson, The West Falmouth Oil Spill, Woods Hole Oceanographic Institution Technical Report, Reference No. 70-44, Woods Hole, MA, 1970, p. 29. 7 A. Cornu and R. Massot, Compilation of Mass Spectral Data, 2nd ed., Heyden and Son, London, 1975. 8 J. Stegeman, private communication.
79
APPLICATIONS OF THERMAL DISTILLATION-PYROLYSIS TO PETROLEUM SOURCE ROCK STUDIES AND MARINE POLLUTION *, * *
JEAN K. WHELAN ***, JOHN M.HUNTand ALAIN Y. HUC
Chemistry Department, Woods Hole Oceanographic Institution, Woods Hole, MA 02543 (U.S.A.)
SUMMARY The technique of thermal distillation-pyrolysis involves heating a 0.5-50 mg sample of wet sediment from 100 to 800°C at 20° /min and measuring evolved hydrocarbons as a function of temperature. Unaltered absorbed hydrocarbons evolve at 100-150°C, and cracked or pyrolyzed hydrocarbons at 650-800 0 C in two well-separated peaks, PI and,P 2 • The compounds in PI and P 2 are analyzed by capillary gas chromatography (GC) and GC-mass spectrometry. An increasing ratio of P1/(P 1 + P 2 ) indicates increasing petroleum source rock maturity. Data are presented for known source rocks and a test well (COST I, Gulf of Mexico, U.S.A.). Applications of the method to examination of oil and chemical pollutants in organisms and surface sediments are given. Results to date have shown that an increasing degree of pollution causes an increasing P 1/P 2 ratio and increasing complexity of the PI peak. The hydrocarbon composition of P 2 has been used to fingerprint and trace high molecular weight organic-rich particles in the marine environment.
INTRODUCTION
We have applied the technique of thermal distillation-pyrolysis to examination of both absorbed and pyrolyzed volatile organic compounds in small (0.5-50 mg) samples of marine organisms and sediments. The frozen or wet sample is heated in a helium stream from 100 to 800° C at 20-30° Imin. A graph of temperature versus amount of organic compound evolving is recorded during the heating process as shown in Fig. 1. The organic material emerges in two well-separated peaks. Unaltered absorbed compounds appear in a low temperature peak (PI) centered at 100-150°C while cracked, or pyrolyzed, organic compounds emerge in a second peak (P 2 ) at a temperature of 650-800° C. The technique differs from conventional pyrolysis in utilizing gradual heating over a fairly long period of time. The technique has previously been applied to source rock analysis [1-3].
* Presented
at the 4th International Symposium on Analytical and Applied Pyrolysis, Budapest, June 11-15, 1979. ** Contribution No. 4377 from the Woods Hole Oceanographic Institution. *** To whom correspondence should be addressed. 0165-2370/80/0000-0000/$ 02.25 © 1980 Elsevier Scientific Publishing Company
80 HELIUM (SOml/min 1
:t
CHEMICAL DATA SYSTEM$REACTION SYSTEM 820 / HIGH TEMPERATURE PEAK (PYROLYZED HYDROCARBONS)
600
400
LOW TEMPERATURE PEAK (ABSORBED HYDROCARBONS)
200
DETECTOR SIGNAL (AMOUNT HYDROCARBON)
4- PORT
VALVE NO.3
ELECTRONIC INTEGRATOR
LOW DEAD VOLUME CONNECTIONS
1700~
FRONT lOOP OF PORASIL C COLUMN
VARIAN GAS CHROMATOGRAPH
Fig. 1. Diagram of thermal distillation-pyrolysis apparatus.
We have applied the technique in a similar manner to the analysis of source rock samples and cuttings from a test well (COST I, Gulf of Mexico, U.S.A.). We have also applied the technique in a new way - in examining small marine particles, including sediments, plants and organisms for anthropogenic pollutants such as oil. In addition, we have obtained preliminary data which show the method may be useful in following the movement of organic-rich particles in harbors and estuaries. A description of the technique and examples of our initial results are presented in this paper. EXPERIMENT AL
The wet or frozen sample is weighed into a 20 mm 'x 1 mm I.D. quartz tube and is held in place with two small plugs of quartz wool. If necessary, deionized distilled water is added to the sample from a 50-J,t! syringe to bring the total volume of water plus sample to about 1/3 to 1/2 that of the total capacity of the quartz tube. The tube is placed in the small platinum coil heater of the pyrolysis probe [Chemical Data Systems (CDS) Pyroprobe]. The probe and sample are then placed in the cooled interface of a CDS 820 Reaction System equipped as shown in Fig. 1. After the interface is flushed briefly with helium at room temperature, it is heated to 250°C and the
81
'robe coil is programmed to 800°C at 20-30° /min using the CDS Extended 'rogrammer. Volatile . organic compounds are swept out of the sample in a helium tream which is split 1 : 10 as shown in Fig. 1. The smaller stream passes hrough a thermal conductivity detector (which can be used to measure nonlydrocarbon components such as water) and then into a flame ionization letector (FID). The FID signal is plotted as a function of temperature to ~ve a pyrogram such as that shown in Fig. 1. Peak areas are measured with m electronic integrator (Columbia Scientific Industries Supergrator 3). The larger part of the helium stream is swept through the CDS Reaction ,ystem 820 (maintained at 300° C, helium flow-rate 60 ml/min) into a 4 n. X 1/8 in. O.D. stainless-steel trap packed with Tenax (80-100 mesh, Ap>lied Science Labs., State College, PA, U .8.A.). At room temperature, the renax trap absorbs C7 and higher aliphatic hydrocarbons as well as benzene, ;oluene and larger aromatic compounds while water is not retained. Two :uch traps (attached to 8-port valve No.1 in Fig. 1) are used in the system so hat peaks P 1 and P 2 may be trapped successively during the analysis. It is im)ortant that the amounts of Tenax be the same in both traps for quantitative 1V0rk since minor differences affect the back pressure and, consequently, the :plit ratio in the system. The detailed composition of P 1 or P 2 is examined by capillary gas chronatography (GC) by heating the Tenax loop to 210°C for 12 min and iweeping the compounds evolved through a heated 8-port sampling valve Carle microvolume valve No. 2014, 8-port valve No.2 in Fig. 1) into a 10 n. X 0.01 in. I.D. stainless-steel loop immersed in liquid nitrogen. The valve s then switched, the sample loop heated to 200° C for 2-3 min and the sam)le is swept into a 2 in. X 0.01 in. I.D. stainless-steel U-tube immersed in iquid nitrogen. This tube is connected to the front of the GC column via L/16 in. low dead volume fittings. Its purpose is to concentrate the sample to 1 very small volume which increases resolution in the subsequent capillary }C analysis. The liquid nitrogen bath is removed and the sample analyzed on i micro packed column (3 m, 3% OV-17, 160-180 mesh, Alltech, Arlington Heights, IL, U.S.A.) via temperature programming from 70 to 200°C at 6° / min. The chromatograph used is a Varian Aerograph 1700 equipped with iual electrometers and flame ionization detectors. Retention times and imounts of components are measured via an electronic integrator (Columbia Scientific Industries Supergrator 3). Tenax was chosen as the trapping material in this analysis because of its V'ery low bleed rate and high thermal stability compared to many other ibsorbents tested. It also does not retain water - a very useful characteristic in our analysis. We believe that water is crucial to the quantitative recovery Df the absorbed P 1 components as discussed further below. The mildness of the procedure (evolution of P 1 at about 125°C) is evidenced by our ability to quantitatively trap and desorb alkanes up to C30 (as determined by connecting the exit from the Tenax trap directly to the flame ionization detector). The GC column used is considered to be a type of capillary column - it is a small-diameter packed column utilizing typical capillary carrier gas flowrates of 1 ml/min. Capillary wall-coated open tubular (WCOT) columns have
82
been used successfully in this analysis. However, the micro packed column was chosen in spite of its lesser resolution because it is much less sensitive to overloading and other abuses commonly occurring during this analysis. The use of capillary columns in this analysis is made 'possible by the use of the 8-port sampling valve (No.2 in Fig. 1) in front of the gas chromatograph. This valve allows compounds eluting from the Tenax traps to be swept out of the Reaction System 820 at the high flow-rate required (60 ml/min) for trapping and desorption and to then be injected into the gas chromatograph at the low flow-rate (1 ml/min) required by the capillary column. Use of the 8-port valve allows the switching to be accomplished without disturbing the flow-rate of either stream. We are currently able to analyze hydrocarbons up to CIS from the PI peak via capillary GC as determined by recovery of standards injected into wet sediment samples. Thus, we cannot presently analyze by capillary GC all of the components evolved and swept into the Tenax traps during initial sample heating. The higher molecular weight components do not elute from the GC column we are using. The temperature at which PI evolves from these samples is 100-150°C as measured by the resistance of the platinum coil heater around the sample tube. At this temperature, water plus absorbed organic compounds volatilize out of the sample in a process similar to steam distillation. The resulting PI peak is fairly sharp and is well separated from the pyrolysis peak (P 2 ). The volatilization process is very mild as shown by our ability to quantitatively recover hydrocarbon standards as discussed previously. In addition, GCmass spectral (MS) analysis (see discussion of the method below) has shown the presence of some fairly labile compounds such as aldehydes, alkenes, and alkyl chlorides (Fig. 15). We believe that water may be crucial to the mildness of the P I desorption from the results of the following experiments. Both wet and dry sediment samples were subjected to the analysis. Two different drying procedures were used on a muddy sediment ooze. In one, the material was dried for a few hours at 110°C. In another, the wet sediment was allowed to stand on a watch glass at ambient temperature overnight. The wet sediment showed a significant PI peak which had disappeared completely in the dried sediment. Similar experiments with deeper more lithified sediments showed a significant PI peak even with dry samples. However, these samples gave higher and more reproducible P I yields after water was added. Considering the high boiling points of the alkanes making up PI (98°C for n-heptane and progressively higher temperatures for higher homologues) and the increase in PI yield when water is added to dry samples, steam distillation is the most reasonable explanation for the low temperature of PI evolution. A qualitative analysis of Cc~s hydrocarbons in either PI or P 2 can be carried out on a Porasil C column as shown in Fig. 1. The compounds are swept into the column (through 8-port valve No.1 and through the Tenax traps kept at room temperature) by switching 4-port valve No.3 and immersing a 4-in. loop in the front of the column in liquid nitrogen. Gas chromatographic analysis is then carried out by removing the nitrogen bath and heating the column (6 ft. X 1/8 in. O.D. X 0.085 in I.D. stainless steel packed with noctane/Porasil C, 100-120 mesh, Alltech) to 50°C. We can currently detect
83
the relative amounts of light hydrocarbons by this procedure. However, total amounts recovered show considerable variability caused by flow-rate changes whicp occur when the packed column is switched into the system. We are currently working on instrument modifications which will allow quantitative C1-C S determinations in the future. Samples are trapped for GC-MS analysis in 3 in. X 1/8 in. O.D. stainlesssteel tubes packed with Tenax. The traps (which fit snugly into the injection port of the Varian 1400 gas chromatograph which is part of our MS system) are heated for 5 h or more at 350°C in a helium stream and stored in a vacuum desiccator until used. These tube traps are connected to the trap vent, which comes from the Tenax traps of the Reaction System 820, via a small piece of silicone rubber tubing. The compounds are desorbed into the tube traps (kept at room temperature) from the Reaction System 820 traps which are heated to 210°C for 12 min. The tube traps are then sealed in glass ampoules under nitrogen in the freezer until MS analysis. For injection into the GC-MS system, the tubes are sealed at 25° C in the injection port of the gas chromatograph and are then heated to 210° C in a helium stream for 10-15 min. The compounds evolved are trapped in a 2 in. X 0.01 in. LD. stainless-steel U-tube immersed in liquid nitrogen and attached to the Micropak column in the GC oven of the GC-MS system. The GC analysis is then carried out as described previously using a Finnigan Quadrupole GC-MS-computer system. The entire capillary GC eluant enters the mass spectrometer without splitting. Compounds were identified by comparison of mass spectra to standards run under identical conditions in the case of hydrocarbons and by comparison to standard reference spectra [7] in the cases of other compounds.
RESULTS AND DISCUSSION
Source rock analysis Representative pyrograms for petroleum source rock cuttings from a test well (COST I, Gulf of Mexico, U.S.A.) are shown in Fig. 2. Two clearly separated peaks are apparent in each analysis. The first, PI, released by heating the sample from 100 to 250°C, is related to the free and absorbed hydrocarbons which are steam distilled out of the rock. They are considered to be hydrocarbons previously produced in the subsurface under natural conditions. The second peak (P 2 ) occurs at higher temperatures by further heating of the sample to 800°C. The release of hydrocarbons at such temperatures is the result of a thermal breakdown (or pyrolysis) of the complex high molecular weight organic material called kerogen. Thus, the area of P2 might be considered as the potential of the rock to generate petroleum if the natural evolution continues. . Fig. 2 illustrates the way the shape.of the pyrograms changes as the depth of burial increases. The main feature is the increasing size of the low temper-
84 SOUTH PADRE ISL.
13,230 ft
15,570 ft
11,700 It
Fig. 2. Pyrograms of test well of COST I (South Padre Island, Gulf of Mexico, U.S.A.).
ature peak PI relative to the high temperature peak as depth increases. This trend is a reflection of the increasing generation of hydrocarbons as depth of burial (and temperature) increase. The low temperature peak (Pd is small in the shallower recent sediments where the hydrocarbons consist primarily of lipids of biological precursors. The P 2 peak is large because the kerogen has not lost hydrocarbons via natural thermally induced breakdown. In contrast, in deeper samples where petroleum generation is more advanced, P I becomes much larger. The change can be expressed quantitatively as a generation or production index (P.L) as proposed by Barker [1] and Espitalie et al. [3]: PI P.L=p-p 1 + 2 where PI and P 2 are the areas of the low temperature and the high temperature peaks, respectively. A plot of this parameter P.L versus depth is shown for the COST I well in Fig. 3. The graph shows that the ratio stays fairly constant down to 10,000 feet below which a great increase occurs as the depth of intense hydrocarbon generation is reached. Examples of pyrograms for well-studied mature oil shales are shown in Figs. 4 and 5 for the La Luna and Posidonien shales, respectively. The La Luna shale is a Cretaceous calcareous shale from Columbia and Venezuela. It is known to be the source rock for the Cretaceous oils in the area. The Posidonien shale is Jurassic black shale which covers a wide area in western Europe including France, Luxembourg and Germany. Capillary GC analyses of the P I peaks from Figs. 4 and 5 are shown in Figs. 6 and 7, respectively. The n-alkanes are clearly visible as well-resolved peaks above to unresolved complex hump typical of petroleum. Information related to nature, level of maturation, and the migration of organic matter
85 PRODUCTION INDEX = AREA PEAK 1/AREA PEAK(I t2 J 01
2000
4000
i:::'
03
0.4
0.5
SOUTH PADRE ISLAND U.S. GULF COAST COST# 1
6000
t:J
-.,
~
j!::
••
02
8000
~
~
10000
12000
14000
16000
.•_.e_e_ : - ...::::--.-
Fig. 3. Production Index versus depth of test well of COST I (South Padre Island, Gulf of Mexico, U.S.A.).
can be obtained by observing how patterns of this kind change with depth. For example, it is normal for lighter hydrocarbons to predominate at greater depths in more mature source rocks in the absence of migration [4]. It is also well known that a biodegraded oil will retain the unresolved petroleum hump (representing cydoalkanes and aromatic compounds) while showing the disappearance of the sharp n·alkane peaks. Examples of capillary GC analyses for the La Luna and Posidonien P 2 peaks are shown in Figs. 8 and 9, respectively. The chromatographic analyses of these pyrolyzed products must be interpreted more carefully. The thermal breakdown of the organic matter brings complex changes in characteristics of the released molecules such as aromatization, un saturation and condensa-
LA LUNA SHALE
so. AMERICA
Fig. 4. Pyrogram of La Luna shale (South America).
86 t
CIO
CII
Cg
~
POSIOONIEN SHALE
LA LUNA SHALE PI
Cs
EUROPE
©l ~
©r
P2 C7
Fig. 5. Pyrogram of Posidonien shale (Europe). Fig. 6. Capillary gas chromatogram of the Pi peak (absorbed hydrocarbons) of La Luna shale (South America).
tion. For example, the well-resolved double peaks in Figs. 8 and 9 represent alkane plus alkene of the same carbon number which are generated from the organic or kerogen matrix by the thermal cracking process. However, preliminary results show that the GC pattern of pyrolytic products produced is very reproducible and characteristic and might be useful in fingerprinting the source materials for petroleum, the parent kerogens. Currently, there are very few other methods available for examining these extremely complex substances. Cs
LA LUNA SHALE P2
Cs
POSIDONIEN SHALE PI
Fig. 7. Capillary gas chromatogram of the Pi peak (absorbed hydrocarbons) of Posidonien shale (Europe). Fig. 8. Capillary gas chromatogram of the P 2 peak (pyrolyzed hydrocarbons) of La Luna shale (South America).
87
POSIDONIEN SHALE
C8
P2 C9
'@
CIO
~
ig.9. Capillary gas chromatogram of the P 2 peak (pyrolyzed hydrocarbons) of Posimien shale (Europe).
nalysis of recent marine sediments, particles, and organisms The thermal distillation-pyrolysis method has also been applied to examling organic pollutants in marine sediments, plants, and animals. Fig. lOA lOWS the pyrogram of an organic rich (11% organic carbon) diatom ooze )ntaining only biogenic absorbed hydrocarbons (PI small, P2large) and Fig. OB shows an organic lean sediment which has been spiked with fuel oil (100 fuel oil per g dry weight of sediment) (P I large, P2 small). In this case as 'ell as in surface sediments, a high PdP 2 ratio generally indicates the presnee of petroleum or other anthropogenic organic compounds while a very )W PdP 2 ratio shows little or no pollution. Some examples of applications f the method to analysis of surface sediments are shown in Fig. 11. The lree pyrograms represent two sediments collected from around Cape Cod, lA, U.S.A. (Monomescoit and Wild Harbor) and a third obtained from nder a bridge in a metropolitan area in Seattle, WA, U.S.A. Monomescoit is n island and has been found to be virtually unaffected by activities of man 8]. The sediment from Wild Harbor is contaminated with fuel oil which ame from a massive oil spill which occurred in September, 1969. It can be een that the PI peak is very small in the unpolluted Monomescoit sample nd large in the petroleum contaminated Wild Harbor sample. In the Seattle ample, the PI peak is small, but relatively large in comparison to P 2 showing hat absorbed organic compounds may be contributing significantly as xpected in such an urban area. The area of PI can be integrated to give a total absorbed hydrocarbon 'ield that compares well with values obtained by more conventional extracion methods as shown in Table 1. Extraction data for Wild Harbor and for learby Sippewissett Marsh, which was unaffected by the spill, were collected .y Burns and Teal [5] and by Blumer et al. [6] for several years following he spill. Data of Burns and Teal show considerable local variation in Wild
**
*
Extraction
Extraction
Wild Harbor (surface) Wild Harbor (surface) Wild Harbor (surface) Wild Harbor (surface) Wild Harbor (surface, sandy, high marsh) Wild Harbor (biogenic) *** Wild Harbor (biogenic) *** Wild Harbor (surface) Wild Harbor (surface) Sippewissett Marsh (surface) Sippewissett Marsh (surface) Sippewissett Marsh (surface)
'78 '71 '71 '78 '78
Jan. '71 May'72 July'73 Nov. '73 Mar. '73 Jan. '71 May'72 Dec. '69 May'70 Jan. '71 Nov. '71 Mar. '73
Oct. Sep. Sep. Oct. Oct.
Date collected
3080 989 234-2661 675 134 21 9 400-900 250-400 5.2 17.6 46
144 312 203 1-9 11-22
Hydrocarbon yield
Teal [5]. Sediment was saponified. The non-saponifiable lipids extracted with pentane and chromatographed on alumina. Yields are based on total hydrocarbons eluted with pentane. ** Blumer et al. [6]. Method similar to that of Burns and Teal. *** Sediment from a core; sub-bottom depth was 70-85 cm. Burns and Teal [5] determined the hydrocarbons in this sediment to be biogenic only.
* Burns and
*
Wild Harbor (surface, sandy) Wild Harbor (surface) Wild Harbor (surface) Si ppewissett Marsh (surface) Sippewissett Marsh (surface)
Thermal distillation-pyrolysis
Extraction
Sample (depth)
Method
Hydrocarbon yields in micrograms of hydrocarbon per gram wet weight of sediment.
Comparison of petroleum hydrocarbon levels in surface sediments determined by thermal distillation-pyrolysis and by solvent extraction
TABLE 1
(Xl (Xl
89
,""
(/)
\
I
,,
,
\
\
......,
I
,, I
,
I
I
A
'"
, '"
, ,,
,,
I I
~
1
\
(/)
W
Z 0 (D Q: «
-,
,
~"'U
(/)-
Zz 00 a.(D (/)Q: W« Il: U Q:O
oil:
1-0 U>wI l-
3:~
...,
1-«0 «WIl: Il:a. 0 W >a.(/) I ::!:-O W(/)W t-~~
W
"'Z «0 WID a.1l: « wU Q:O :::>Il: 1-0 «>Q:I Wo a.W ::!:(D WQ: 1-0
\
\
g~ -'" , , ,, ,
u.~
I,
, \
,
,----- --------
IO~ ~g:1l:
UIWz 0:::> 0 0 ..... ::!:
-,
I
~--
Ia.~
~ B
600
I 500
400
300
200
100
Temperature of sample (OC)
Fig. 10. Pyrograms of (A) organic-rich diatomaceous surface ooze (11% organic carbon) containing only biogenic absorbed hydrocarbons; (B) organic lean sediment spiked with fuel oil (100 g hydrocarbon per gram dry weight of sediment).
MONOMESCOIT 25.7mg WET SEDIMENT
WILD HARBOR, MASS. 33.3 mg WET SURFACE SEDIMENT
I
1eO°C
>-X8
SEATTLE,WASHINGTON 39 mg WET SEDI MENT
~
-+-X8 Xi6
f--
X32
680·C 135 "'c
I 690°C
0---
X16
Fig. 11. Pyrograms of surface sediments of Monomescoit (unpolluted area), Wild Harbor (subjected to an oil spill) and Seattle, WA (sample from urban area).
90
Harbor fuel oil levels, but that values of about 100-3000 Ilg hydrocarbon per g of wet sediment persisted for a period of at least three years after the spill. Data of Blumer et al. show levels of 250-900 Ilg hydrocarbon per g of wet sediment. For samples collected in the uncontaminated Sippewissett Marsh, or from deeper (uncontaminated) Wild Harbor sediments, hydrocarbon levels were in the range of 5-46 Ilg/g. In this work, thermal distillationpyrolysis measurements of absorbed hydrocarbons (P I) for a Wild Harbor surface sediment showed a hydrocarbon level of 312 Ilg/g as compared to Sippewissett Marsh values of 1-22 Ilg/g. The Wild Harbor sample, provided by Teal, was collected about one year after the oil spill and was kept frozen until the time of this analysis. We also analyzed a second Wild Harbor sample collected within the last six months by Stegeman. The fine particles isolated from a predominantly sandy sediment showed a PI peak area corresponding to 144 Ilg hydrocarbon per g wet sediment. This value corresponds well to that of Burns and Teal of a sandy sediment taken from the high marsh area of Wild Harbor in spring of 1973, viz. 134 Ilg hydrocarbon per g wet sediment. Thus, calculation of the total amount of absorbed hydrocarbon represented by the area of PI agrees well with extraction data, both for petroleum contaminated and uncontaminated areas. Capillary GC analysis of PI gives additional information about the presence of anthropogenic hydrocarbon as shown in Fig. 12. Monomescoit, the unpolluted sediment, shows a very simple distribution of compounds, while both Wild Harbor and Seattle give a much more complex pattern including a substantial unresolved complex mixture under the hump, as is typical for a surface sediment containing an anthropogenic hydrocarbon input. Thus, the complexity of the capillary gas chromatogram of peak P I rapidly gives a qualitative estimation that an area is receiving a petroleum hydrocarbon or other anthropogenic organic input. Two other examples in Fig. 13 show capillary GC analyses for PI from Fig. 10. The simple absorbed hydrocarbon pattern shows the absence of pollution in the organic-rich sediment (Fig. 13A), while the complexity of the fuel oil spike is clearly evident in Fig. 13B. The thermal distillation-pyrolysis method has also been applied to materials with a high lipid content of their own as shown in Fig. 14. The samples consist of some tail meat from small (2 cm long) shrimp, one taken from petroleum contamined Wild Harbor and the other from uncontaminated Sippewissett Marsh. The capillary GC analyses of the absorbed hydrocarbons representing the PI peak clearly show the complex unresolved fuel oil signal for the Wild Harbor shrimp. Since the method requires only small samples, preliminary results suggest that the method may be valuable in determining where pollutants, such as oil, concentrate in the animal. More complete identification of components in Pi can be carried out by GC-MS analysis. For example, some of the compounds identified in the sandy sediment sample collected in the last 6 months from Wild Harbor are shown in Table 2 (not the same sample as shown in Fig. 15). The oxygenated compounds, such as aldehydes, ketones, phenol, cresol, benzofuran and benzaldehyde may be related to microbiological breakdown of the petroleum which, as mentioned earlier, was spilled at this site in 1969. The table
91
MONOMESCOIT . (Unpolluted)
PI
X8
WILD HARBOR 33.3mg WET SURFACE SEDIMENT PI
X8
SEATTLE PI 39mg WET SEDIMENT
Fig. 12. Capillary GC analyses of PI peak (absorbed hydrocarbons); same samples as Fig. 11.
also shows that the method can be applied to pollutants other than petroleum. For example, the presence of chlorobenzene was detected by mass scan of m/z 112 and 114. Capillary GC analyses of the cracked P2 components from the Monomescoit, Wild Harbor and Seattle surface sediments are shown in Fig. 15. As expected for sediments collected from different areas, the patterns are different for the three samples. As mentioned earlier, we have found this pattern to give a highly reproducible fingerprint for a particular type of particle. For example, three surface sediment samples and four sediment trap samples collected from Boston Harbor gave almost identical P2 capillary GC patterns as shown in Fig. 16 for two of the samples. Minor changes in intensity and composition of early eluting peaks are ignored since losses of more volatile components are caused by minor changes in analytical conditions. The analyses show that the high molecular weight organic material is very similar in both suspended matter and sediments throughout the harbor.
92
A ~
'"
n
-<
6 z
1
C7
Cs
-;~
s:-<
Orn
8
Co
z-< -<0
n::O 0", S:rn
~ '" n
"(I) -< 0"'0 6 CO z
3~ t
1___._
INCREASING RETENTION TIME
Fig. 13. Capillary GC analyses of PI peak (absorbed hydrocarbons); same samples as Fig. 10. (A) Biogenic hydrocarbons; (B) fuel oil spiked sample.
SIPPEWISSETT MARSH SHRIMP PI l.4mg TAIL
WILD HARBOR SHRIMP PI O.97mg TAIL
'"c '"
x8
XI6 1
Fig. 14. Capillary GC analyses of PI peak of shrimp tail meat of Wild Harbor, MA (oil contaminated area) and nearby Sippewissett Marsh (relatively contamination free).
93 TABLE 2 Absorbed organic compounds identified from PI of Wild Harbor sample by gas chromatography-mass spectrometry n-Heptane C 7 H l4 alkene 3-Hexanone Cyclohexene C s aldehyde or ketone Phenol C s alkane (3 isomers) CSHl6 alkene Xylene (3 isomers) Styrene Chlorobenzene 3-Heptanal Alkylbenzene (4 compounds)
MONOMESCOIT (Unpolluted)
n-Propylbenzene Dialkylbenzene (2 compounds) Trialkylbenzene (3 compounds) Benzaldehyde Benzofuran Cresol C 6 aldehyde Naphthalene Methylnaphthalene (2 isomers) Alkyl chloride Alkylthiophene C I6 H 32 alkene C ls H 3S alkane
P2
m
u
Q)JQ)~
~ ~ ~f ,E
WILD HARBOR P2 33.3 mg WET SURFACE SEDI ME NT
SEATTLE P2 39 mg WET SEDIMENT
_ _X_'6_
Fig. 15. Capillary GC analyses of P 2 peaks (pyrolyzed or cracked organic compounds) from recent surface sediments. Same samples as in Figs. 11 and 12.
94
P2 BOSTON HARBOR SEDIMENT TRAP OT
\
\ \ \ \
\ \ \ \ P2 BOSTON HARBOR GRAB 27
\ \
Fig. 16. Capillary GC analyses of P2 peaks (pyrolyzed organic compounds) from Boston Harbor particles. OT is midwater sediment trap sample; GRAB 27 is a surface sediment sample.
In contrast, the capillary GC patterns for the PI peaks from the same samples show distinct differences in absorbed organic material as shown in Fig. 17. The PI peaks for the two bottom sediment trap samples (IB and OB) are similar in showing a "hump" and in being very different from those of a bottom sediment sample (Grab 27) and a mid-water sediment trap sample (OT). The capillary GC PI patterns also indicate the similarity of absorbed organic material on the sediment sample (Grab 27) and the mid-water sediment trap sample, ~T. The detailed interpretation of these results must await further work. However, these data indicate the usefulness of the method in tracing the movement of organic matter in a marine estuary. The differences observed in absorbed organic matter on the particles is probably strongly influenced by the presence of a sewage outfall near the location where these samples were collected and by the presence of strong lateral tidal currents into and out of the harbor. The results presented here illustrate the value of the thermal distillationpyrolysis method for examining organic matter on several types of samples where large sample requirements have previously prevented such analyses, including marine particles and parts of small marine animals. In addition, the speed and ease of the method make it valuable as a screen for determining which samples should be examined more extensively using other more specialized and time-consuming methods. Initial results show that the method gives amounts of absorbed hydrocarbons in both petroleum contaminated and uncontaminated sediments which compare well with values measured by solvent extraction techniques. In addition, capillary GC patterns of the P2 pyrolysis peak may be useful in fingerprinting high molecular weight organic material on sediment particles, fecal pellets, and other small marine particles,
95 PI BOSTON HARBOR GRAB 27
: PI BOSTON HARBOR I SEDIMENT TRAP OT
PI BOSTON HARBOR SEDI MENT TRAP I B
Fig. 17. Capillary GC analyses of PI peaks (absorbed organic compounds) from Boston Harbor particles. IB and OB are inner and outer harbor bottom sediment trap samples, respectively. Other designations same as in Fig. 16.
a process that is currently very difficult or impossible by any other technique. ACKNOWLEDGEMENTS
We wish to thank Nelson Frew for gas chromatographic-mass spectral analysis. We are grateful to John Teal, John Stegeman, Mike Fitzgerald and John Milliman for providing samples. The construction of the pyrolysis unit and the petroleum source rock studies were supported by Department of Energy Contract No. EG-77-S-02-4392. The marine pollution studies were supported by Sea Grant Contract No. 04-8-MOl-149. REFERENCES 1 C. Barker, Amer. Ass. Petrol. Geol. Bull., 58 (1974) 2349. 2 G.E. Claypool and P.R. Reed, Amer. Ass. Petrol. Geol. Bull., 60 (1976) 608. 3 J. Espitalie, J.L. Laporte, M. Madec, F. Marquis, P. Leplat, J. Paulet and A. Boutejeu, Rev. Inst. Fr. Petrole Ann. Combust. Liquides, 32 (1977) 23. 4 B.P. Tissot and D.H. Welte, Petroleum Formation and Occurrence, Springer-Verlag, New York, 1978, pp. 185 and 414.
96 5 K. Burns and J. Teal, Estuarine and Coastal Marine Science, 8 (1979) 349. 6 M. Blumer, J. Sass, G. Souza, H. Sanders, F. Grassle and G. Hampson, The West Falmouth Oil Spill, Woods Hole Oceanographic Institution Technical Report, Reference No. 70-44, Woods Hole, MA, 1970, p. 29. 7 A. Cornu and R. Massot, Compilation of Mass Spectral Data, 2nd ed., Heyden and Son, London, 1975. 8 J. Stegeman, private communication.