Environ. Sci. Technol. 1984, 18, 846-854
Hydrocarbon and Azaarene Markers of Coal Transport to Aquatic Sediments Robert C. Barrick,’ Edward T. Furlong, and Roy Carpenter
School of Oceanography, University of Washington, Seattle, Washington 98195 Hydrocarbon and azaarene concentrations and compositions vary systematically in 16 western Washington coal samples ranging in rank from lignite to anthracite. Subbituminous and bituminous samples within a vitrinite reflectance range of 0.4-0.8 % Ro contain hydrocarbon suites and azaarenes whose compositions correspond to those found in selected Puget Sound and Lake Washington sediments as well as coal particles sieved from a Puget Sound core. Dominant coal components include pristane, C19 and C20 tricyclic diterpanes, retene, methylated chrysenes and picenes, tetrahydrochrysenes, hydropicenes, and either 1-or 3-methylphenanthrene relative to other methylphenanthrenes. The CI9 and Cz0diterpanes are limited in their geologic occurrence and serve as distinctive fossil markers. These coals generate an overall lipid signal distinct from other fossil sources including street runoff and municipal sewage discharges. Thus, molecular markers demonstrate the transport of specific local coals to aquatic sediments in adjacent drainage basins resulting from erosion and mining activity. Introduction Coals from various parts of the world have been analyzed for hydrocarbons and related compounds &IO), yet there has been limited use of molecular markers to recognize the transport of coals in the environment. Tripp et al. (11) suggest that unburned bituminous coals are a significant source of hydrocarbons in Atlantic coastal sediments but note difficulty in distinguishing the signal of the coals examined from that of petroleum. In a more clear-cut example, Shaw and Wiggs (12)relate hydrocarbon patterns in Alaskan filter and deposit-feeding intertidal organisms to differential accumulation of petroleum vs. coal-derived material. Azaarene distributions in marine and freshwater sediments (13,14)are distinctive and have not been unambiguously related to any single potential source material such as urban air particulates, street dusts, and oils (14-17) or the few unburned coal samples studied to date (13,10). Coals are a potential major source of many sedimentary lipids also found in petroleums including hydrocarbons such as normal and isoprenoid alkanes, naphthalenes, and phenanthrenes. These compounds have received considerable attention as contaminants within modern sediments and the latter aromatic suites are of particular concern because of their potential for toxic effects in the environment. Hence, source identification is important to discriminate oil or coal sources whose substantially different physical matrices likely influence lipid transport, fate, and biological effects. We report here hydrocarbon and azaarene distributions in 16 western Washington coals ranging in rank from soft “brown” coals to anthracite. The range of coal rank and number of compound suites reported is the most extensive for coals from any one geographic region or period of formation. We demonstrate that specific geochemical marker compounds and compositional patterns charac*Address correspondence to this author at Tetra Tech, Inc., Bellevue, WA 98004. 848
Envlron. Sci. Technol., Vol. 18, No. 11, 1984
teristic of a select group of these coals give rise to an identifiable lipid signal in freshwater and marine sediments of Lake Washington and Puget Sound. Many three-, four-, and five-ring alkylated aromatic markers found in these coals have been reported in marine and lacustrine sediments, possibly resulting from rapid diagenetic formation (18-20). The present study examines compositional evidence that suggests eroded and mined coals are a major alternate source in some sediments. These and others markers provide the means to distinguish significant natural and anthropogeniccoal input from other regional fossil sources such as street runoff and fuel oils discharged in municipal wastewaters (21). Study Site
Coals in western Washington were formed during the Eocene to Oligocene epochs (22) and, thus, are similar in age to other Tertiary coals reported such as Rehnish lignites ( 4 ) and some lignites and subbituminous coals in the Midwestern US.( 2 , 3 ) . Washington bituminous and anthracitic coals, however, are 50-250 million years younger than coals of similar rank that form the bulk of lipid analyses reported in recent literature ( 1 , 5 , 7-11). Volcanic ash is present in most Washington coal beds, and the small area containing authentic anthracite has been subjected to intense deformation (22). Glaciation and river channeling has exposed many coal seams, but extensive folding and faulting in the Puget Sound area make mining and complete characterization of the beds difficult. Commerical coal production began in 1854, peaked by 1918, and has since steadily declined (22). Only one western Washington mining company operated in 1982, although expansion plans are again under consideration. Experimental Section Sample Collection and Workup. Coal samples were collected from 16 sites in western Washington, selected with the aid of state geologists and geological reports. An additional sample of coal particles was seived from a box core collected near the Puyallup River delta in Puget Sound (Figure 1). Samples were crushed in a solventrinsed ball mill and passed through a 43-mesh seive and then subsampled for elemental, vitrinite reflectance and organic analyses. Extraction of hydrocarbons and azaarenes from coals was nearly identical with that already reported for sediments in earlier papers (13, 23, 24) and similar to that standardly used for bitumen (e.g., see ref 4). Powdered samples ranging from 20 to 35 g of coal were Soxhlet extracted (45 h; 1:l benzene-methanol). Following pentane fractionation, extracts were split, with l/lo used for hydrocarbons and the remainder for azaarenes. After removal of elemental sulfur, aliphatic hydrocarbons were isolated by using silica gel chromatography. Polycyclic aromatic hydrocarbons (PAH) were further purified by using Sephadex LH-20 as were azaarenes following acidbase partitioning. Gas Chromatography and Mass Spectroscopy. Hydrocarbon extracts were redissolved in isooctane containing an internal injection standard and then analyzed
0013-936X/84/0918-0846$01.50/0
0 1984 American Chemical Society
made to those of authentic standards. Bulk Parameters. A Carlo-Erba elemental analyzer was used to determine weight percentages of organic carbon, hydrogen, and nitrogen in duplicate untreated coal samples. Average percent difference about the mean of the duplicates was 1.8%, 1.8%, and 2.9% for carbon, hydrogen, and nitrogen, respectively. Vitrinite reflectance (Ro),typically measured as the mean reflectivity of 50 observations, was determined on vitrinite components by using polished mounts of disaggregated coal fragments. Oil immersion microscopy was performed a t a wavelength of 546 nm with a Zeiss photometer. A comparison of hand-crushed and ball-millcrushed coal samples showed no statistical difference in Ro. Vitrinite reflectance is one of a number of ranking parameters, and although we report Ro values for all coals studied, it typically has been used for ranking bituminous coals. Our emphasis is not on precisely ranking these coals but to provide an independent and generally accepted indicator of coalification (26).
Results
45'
5c
1
123.
45'
30'
1220w
45'
30'
Flgure 1. Location of coal sampling skes and aquatlc sediment coring sites. Circled numbers on the land mass Mentlfy coals listed in Table I. Closed circles Mentlfy coring stations 57 and 82 in Puget Sound and station 11 in Lake Washington.
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on a Hewlett-Packard (HP) 5880 gas chromatograph (GC) fitted with 30 m length X 0.25 mm i.d. glass SP-2100 or fused silica SE-54 capillary columns (J&W Scientific). GC conditions were as follows: splitless injection at 75 "C then ramped at 15 "C/min to 130 "C followed by temperature programming a t 4 "C/min to 275 "C and held; hydrogen carrier gas at 12 psi to the flame ionization detector (FID). Azaarenes were analyzed by using an HP-5730A GC equipped with a 30 m X 0.25 mm i.d. Carbowax 20M fused silica capillary (J&W) and a N-selective FID coupled to a Columbia Scientific Supergrator I11 integrator. GC conditions were as follows: splitless injection (chloroform) at 20 "C and then ramped at 32 "C/min to 150 "C followed by programming at 4 "C/min to 250 "C and held; helium carrier gas at 29 psi. Peak areas quantitated relative to hexamethylbenzene (hydrocarbons) or n-octadecane nitrile (azaarenes) internal injection standards and a daily series of calibration standards over each analytical range were subsequently checked for validity. Corrections for evaporative losses of low molecular weight components as reported previously for trace alkanes in sediment samples (23)were not necessary because of the high organic loadings in coal samples. Procedural blanks contained negligible amounts of organics in comparison to coal extracts. Precision of our analytical scheme meets or exceeds that of *10-20% for most compounds previously reported (13, 21,23, 25). Peak identities in selected coal samples were confirmed by GC-mass spectroscopy by using an H P 5993 GC/MS system equipped with a DB-5 or Carbowax 20M fused silica capillary (J&W), When possible, comparisons of compound retention times and mass spectra were also
The 16 coal samples reported range in total carbon from 9% to 75% C and cover a vitrinite reflectance range of 0.34-3.5% Ro (Table I). A wide variation in hydrocarbon and azaarene distributions also is observed as can be seen in a summary of coal parameters in Table I. Compositional variability is an intrinsic property in coals of varying rank, and specific trends within each compound class are given below. These results allow us under Discussion to not only identify coal transport to aquatic sediments but also narrow possible source materials to coals of a relatively specific rank within each drainage basin. Overall, with increasing rank there is a general trend of an increased proportion of low molecular weight n-alkanes relative to other aliphatic assemblages, increased unsubstituted PAH relative to alkylated homologues, and increased three-ring relative to two-ring azaarenes. Of the three compound classes, the most continuous change in composition as a function of vitrinite reflectance is found in the azaarenes (see Figure 2). Selected compound identifications are reported in Table 11. n -Alkanes. A shift from high molecular weight, predominantly odd-numbered n-alkanes in lignitic low rank coals to low molecular weight n-alkanes with little oddeven predominance (or low carbon preference index, CPI) in high rank coals has been noted previously ( 1 , 5 , 6 , 2 6 ) . A similar general trend is apparent in Table I which gives the CPI over two different alkane ranges and the ratio of low molecular weight (C14-Cm)to higher molecular weight n-alkanes (C21-C35). Normal alkanes in coals of less than about 0.4% Ro show a strong plant wax signature from n-C%to n-C31 while n-alkanes in coals of greater than about 0.8% Ro are dominated by a low CPI suite from n-Clo at or higher the bottom of the analytical range through 71-c~~ (Table I). Coals from 0.4% to 0.8% Ro are transitional between these two end members; however, the progression with increasing rank is by no means continuous (Table I). The discontinuity is marked by Fulton and McKay bituminous coals from the Green River district which contain strong plant wax alkane signatures (high CP12+34).Even when all Green River district coals are ordered according to stratigraphic sequence, the discontinuity persists. The McKay and Fulton beds are overlain by Kummer coals classified as subbituminous on the basis of their mineral-matter-free BTU values (22), including the Todnem Mine Kummber sample (Table I) which has a low CPI and Envlron. Scl. Technol., Vol. 18, No. 11, 1984
847
1.3% R,) where the CI6 or C18isoprenoid alkanes can dominate. Highest concentrations (>50 pg/g of carbon) of pristane (and other isoprenoids) occur in subbituminous and bituminous coals between 0.4% and 0.8% Ro (Figure 3A). Cyclic "Aliphatic"Hydrocarbons. A suite of C19and Czotricyclic diterpenoid hydrocarbons is a distinguishing feature of most Washington coal extracts studied. Components of this assemblage have identical retention times and mass spectra with those previously characterized in sediments of Puget Sound (25, 27) and also have been 848
Environ. Sci. Technoi., Vol. 18, No. 11, 1984
Cl&z
1 bI'
Ro MAXIMUM OITERPANES, RETENE
/0.51%
Table 11. Selected Compounds Tentatively Identified in Western Washington Coals and Aquatic Sediments Influenced by Coal Transport
400[
Normal Alkanes" (numbers denote carbon numbers; see Figure 4)
0.66% Ro MAXIMUM PRISTANE
A
Isoprenoid Alkanes 1 2,6,lO-trimethylundecane 4 2,6,10-trimethylpentadecane
2 2,6,10-trimethyldodecane 5 pristane" 3 2,6,1&trimethyltridecane 6 phytane" Unidentified Sesquiterpenes 7 series of C16bicyclic terpenoid hydrocarbons (M,206 and 208) Tricyclic Diterpanes (See ref 27 and 29 for Additional Discussion) primarane- and abietane-skeletal types C19H34norditerpanes (fichtelite not detected) 8-10 CzoHs4diterpenes and CzoHs diterpanes 11-14 Triterpenoid Hydrocarbons 15 17aH,2l@H-nornopane 17 (R,S)-17aH,2lpH-homohopane 18 unidentified triterpenes 16 17aH,2l@H-hopane Aromatic and Polynuclear Aromatic Hydrocarbons 31 octahydrochrysenes (M, 20 naphthalene 292) 32 3,4,7-trimethyl-1,2,3,421 methylnaphthalenes tetrahydrochrysene (M,274) 33 3,3,7-trimethyl-1,2,3,422 Cz naphthalenes tetrahydrochrysene (M,274) 34 dimethylchrysene (M, 23 C3 naphthalenes 256) 35 perylene" 24 C4 naphthalenes 36 unidentified PAH 25 dibenzothiophene" 37 1,2-dimethyl-1,2,3,426 phenanthrene" tetrahydropicene (M, 310) 27 methylphananthrenes (3-MPH, 38 methylpicene (M,292) 2-MPH, 9-MPH, 1-MPH) 39 2,2,9-trimethyl-1,2,3,428 Cz phenanthrenes tetrahydropicene (M, 324) 29 C3 phenanthrene (M, 220) 40 2,9-dimethylpicene (M, 306) 30 retene" 41 42 43 44 45
Azaarenes 2,6-dimethylquinoline" 46 3,4-dimethylquinoline" 47 2,3-dimethylquinolinea 48 7,8-benzoquinolinea 49 acridine"
5,6-benzoquinolinea 3,4-benzoquinolinea 2-azafluoranthene' 7-azafluoranthene"
" Indicates compounds for which confirmations have been made by comparison of GC retention data and GC/MS analysis of samples and authentic standards.
reported in Gulf of Alaska sediments and particulate material in the Green-Duwamish River in Washington (28, 29). The major Clg diterpanes identified in Figure 4 are related structurally (27) to pimaric acid (methyl, ethyl branched; e.g., peak 8) and abietic acid (methyl, propyl branched; e.g., peak 9). In general, pimarane-type C19 diterpane concentrations in these coals exceed those of abietane-type C19 diterpanes. The major C20diterpane (peak 12, Figure 4) is also of the pimarane skeletal type and dominates in lower ranked coals. Reported sources of these diterpanes to date have been limited to fossil matrices such as coal (4,26,30),nonmarine carboniferous Australian crude oils (30),and resins in Canadian Mackenzie basin drill cuttings (31). Highest concentrations (>lo0 pg/g of carbon) of total diterpanes (the s u m of all C19and Cz0diterpanes detected) occur in coals ranging from 0.45% to 0.66% R,,. These
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0.45% Ro HYDROPICENE MAXIMUM
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TOTAL HYDROPICENES, ,ug/g C TOTAL METHYLATED PICENES TETRAHYOROCHRYSENE
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VlTRlNlTE REFLECTION (70 R o l
Flguro 3. Concentrations of coal hydrocarbon sultes including (A) pristane, dlterpanes, and retene and (6)various picenes and hydropicenes, all normalized to total carbon In each coal sample and graphed as a function of vkrlnlte reflectance (Ro). All samples listed In Table I are plotted In order of increasing Ro with the exception of the Falrfax coal sample whose reflectance value was not determined.
include the Newcastle, River Gorge, Todnem Mine, and Spiketon samples (Figure 3A). The Icy Creek and Flaming Geyser coals have intermediate levels (between 50 and 100 p g / g of carbon) while the remainder have lower or zero levels (Figure 3A). All four coals with the highest diterpane concentrations lie in a narrow (uncorrected) BTU range of about 1000011000 (21),and all coals with higher (uncorrected) BTU values fall in the final group of low or zero diterpane levels, suggesting that their presence as significant components may be predicted by the raw calorific value of coals. For unknown reasons, this BTU-diterpane correlation is no longer apparent when mineral-matter-free BTU values are used (corrections for ash and sulfur content) for the bituminous coals. Triterpenes are present in only a few of the lower rank coals such as Icy Creek and Newcastle. A series of 17a(H), 21p(H) C29-C30hopanes, characteristic of mature petroleums (32)and coals having an elevated thermal history (21, is present in haIf the samples and at maximum concentrations in coals with about 0.65% Ro (Spiketon and Todnem Mine samples). Most notable is the absence from all coal samples of an unresolved complex mixture (UCM) Envlron. Scl. Technol., Vol. 18, No. 11, 1984 849
D,+erpanes
SPIKETON COAL ALIPHATICS
Naphthalenes
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phenanthrenes I
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SPIKETON COAL
PAH
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STA. 51 COAL FRAGMENTS ALIPHATICS
DlterPanes
NEWCASTLE COAL ALIPHATICS
’ 18
-Naphthalenes
23 24 n n
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Sesquiterpenes 7
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1~17
Phenanthrenes
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NEWCASTLE COAL
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39b I
LAKE WASHINGTON SEDIMENT PAH ca.1915 33 35
LAKE WASHINGTON SEDIMENT 172 ALIPHATICS ca. 1915
, 30 FF I -
1
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Figure 4. Comparisons of source coals and sedimentary material for (a) aliphatic and corresponding PAH extracts of Newcastle coal and Lake Washington sedlment and (b) aliphatlc and corresponding PAH extracts of Spiketon coal and sedimentary coal fragments isolated from a Puget Sound core. The aliphatlc Lake washington extract contains a significant biogenic signal above n-C,, includlng a homologous suite of monoalkenes preceding the normal alkanes. GC conditions are described in text; peak Identitles are given in Table 11. DIPL = diploptene; C = in Lake Washington sediment PAH chromatogram denotes component of a “combustionderlved”PAH suite (23). A portion of phenanthrene in the lake sediment PAH chromatogram also likely derives from combustion processes.
or detectable amounts of steranes present in many petroleums and contaminated sediments. Phenanthrenes and Naphthalenes. Phenanthrene, a series of methyl- and dimethylphenanthrenes, and a single major C3-phenanthrene and retene (7-isopropyl-lmethylphenanthrene) comprise a variable suite of threering coal PAH. Lower rank coal samples typically are dominated by retene and contain only trace quantities of phenanthrene, while the opposite is true in high ranked coals (Table I). An exception is the CCA “brown” coal sample (0.34% R,) which contains both retene and phenanthrene in similar concentrations. Peak retene concentrations occur in samples at 0.45451% Ro (Figure 3A). The major methylphenanthrene (MPH) isomer in the two lowest rank coals (0.34% R,) is identified tentatively as 9-MPH, although coelution of related isomers is possible. In the six high ranked coals (>0.80% R,), the intrinsically more stable 2-MPH dominates (Table I) as has been observed elsewhere (8). The four major methylphenanthrene isomers are identified with reference to the literature (8,19) on the basis of GC/MS and their relative retention times compared with a 2-methylphenanthrene standard. All six coals in the intermediate 0.4-0.08% Ro range in the Green River and Lake Washington districts contain elevated levels of 3-MPH. In contrast, methylphenwthrenes in the single coal of similar rank from the 850
Environ. Sci. Technol., Vol. 18, No. 11, 1984
Puyallup River basin to the south (Spiketon, 0.65% R,; Table I) are dominated by 1-MPH. Changes in distributions between naphthalene and its alkylated homoloues mirror those in the phenanthrenes. Methylated Chrysenes and Picenes. Methylchrysenes and a major dimethylchrysene are present in several of the coals, in addition to methyl-, dimethyl- and C3-picenes (e.g., Figure 4). Mass spectra of the dimethylchrysene (MI256) and methylated picenes (MI292, 306, and 320) are similar in that all show major M+ - 17 and M+ - 30 ions, verified in high-resolution GC/MS by their precise masses as losses equivalent in m/z to CH6+ and C2H6+,respectively (25).Therefore, possible identification as oxygenated PAH, as suggested for compounds in emissions from brown coal-fired stoves having strikingly similar mass spectra and retention times (33),was definitively ruled out. Dimethylchrysene generally is present in coals ranging from 0.5% to 1.2% Ro and absent in higher ranked coals. Alkylated picene concentrations are highest in the 0.448% Ro range and are present at variable levels in all but the highest ranked coals (>2.0R0;Figure 3B). Picene itself (MI278) was not detected in lower ranked coals but is identified tentatively by GC/MS in some of the higher ranked bituminous coals (for example, Gale Creek at 1.32% R,).
Hydrochrysenes a n d Hydropicenes. 3,3,7-Trimethyl-1,2,3,4-tetrahydrochrysene(M,274)) tentatively identified by comparison of its mass spectra with that published by Wakeham et al. (19), is the major hydrochrysene in coal samples less than 0.8% Ro (e.g., Figure 4). Its concentration in coals as a function of vitrinite reflectance is shown in Figure 3B. In general, Washington coals at greater than 0.8% Ro only occasionally contain partially aromatized hydrocarbons (Figure 3B). Quantifiable amounts of the 3,4,7-trimethyl isomer of this compound are present only in the Icy Creek, Newcastle, and Flaming Geyser coals (0.34-0.57 % Ro). Octahydrochrysenes are below detection limits of 2-10 ppb dry weight (DW) (depending on injection dilution) in all samples studied. A variable suite of hydropicenes with molecular weights 310, 324, and occasionally 338 has been detected and identified by GC/MS by comparison with published mass spectra (19), (Figure 4). The major M,310 and 324 hydropicenes in most samples tentatively are identified as containing a gen-dimethyl group as does the major tetrahydrochrysene compound. Hydropicenes are below detection limits (
