Envlron. Sci. Technol. 1989, 23, 170-177
Characterization of Organic Material Leached from Coal by Simulated Rainf aII Nlcholas J. Fendlnger,*stits5 Joanne C. Radway,? Jon H. Tuttle,+ and Jay C. Meanst*tpll Chesapeake Biological Laboratory, Center for Estuarine and Environmental Studies, University of Maryland, Solomons, Maryland 20688,and Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742
Laboratory leaching experiments were conducted using coals collected from the Upper, Middle, and Lower Kittaning seams in Pennsylvania and from an unspecified seam in western Maryland. Leachates were characterized by low pH (1.67-3.221, high conductivities (3300-24000 pmhos), and high concentrations of suspended material (322-3300 mg/L). Dichloromethaneextracts of the soluble and particle fractions of the leachates contained complex mixtures of aliphatic and aromatic hydrocarbons including alkyl-substituted and normal polynuclear aromatic hydrocarbons. Highest concentrations of aromatic compounds were measured in leachates from coals with the highest solvent-extractable aromatic hydrocarbon content. Comparison of results from laboratory leaching chambers with selected chemical characteristics of leachates collected at a coal storage site suggested that weathering processes occurring in environmental situations can be approximated by laboratory experiments. Introduction
The use of coal as an energy source is expected to increase dramatically in the next twenty years. This increase can be attributed to increased cost and decreased availability of other imported and domestic fossil fuels, negative public opinion toward nuclear power development, and government policy directed toward increased utilization of coal (I). Increased use of coal will result in greater outdoor storage of coal at transportation depots and various industrial and electrical generation sites. In 1978 there were 128 million metric tons of coal in outdoor storage. This figure may rise to 680 million metric tons by the year 2000 (2).Given the complex organic content of coal (3-5) and the increasing amounts of coal in outdoor storage, the potential exists for the release of large amounts of potentially toxic organic material into the environment. Very little is known about the characteristics of organic material that may be leached from coal under environmental conditions. The few studies that have been published on the environmental leaching of organic material from coal (6, 7) have neither adequately described changes that might occur in the organic content of coal leachates during weathering nor thoroughly characterized the coals being leached. In this report we describe the leaching characteristics of several widely utilized eastern coals, assess the potential environmental impact of organic material leached from coal, and relate the organic content of leachates to the chemical characteristics of the source coals. Experimental Section
Coal Collection and Characterization. The coals sampled included final-product (FP)coals and run-of-mine Chesapeake Biological Laboratory. *Department of Chemistry and Biochemistry. 8 Present address: U.S.Department of Agriculture, ARS Soil Nitrogen and Environmental Chemistry Laboratory, Beltsville, MD 20705. (1 Present address: Louisiana State University, Institute for Environmental Studies, 42 Atkinson Hall, Baton Rouge, LA 70803. 170
Environ. Sci. Technol., Vol. 23, No. 2, 1989
(ROM) coals. FP coals are blends of several ROM coals that had undergone treatment to remove inorganic sulfur and ash. ROM coals were sampled from single coal seams and were not treated. The FP coals (A-FP and H-FP) were prepared by the Power Operating Co. (Phillipsburg,PA); ROM coals were mined by the Power Operating Co. (DROM), Flango Bros. Coal Co. (Phillipsburg, PA; F-ROM), or Delta Mining Go. (Ocean, MD; E-ROM). The coals from Pennsylvania were mined from the Upper, Middle, and Lower Kittaning seams, while coal E-ROM (Redstone Rider) was mined from an unspecified rider seam in western Maryland. The Kittaning coals represent one of the most regularly bedded, extensively mined, and persistent coal beds found in Pennsylvania (8). Most of the coals were recently mined and were collected at the mine or preparation plant in 50-gal plastic barrels or plastic feed sacks. Coal A-FP was sampled from the Potomac Electric Power Co. (PEPCO) Chalk Point Facility (Aquasco, MD) 1 day after shipment. Coals were stored at room temperature for 3-43 days before the leaching experiments were started. The total carbon, hydrogen, and nitrogen content of the coals used in the leaching experiments were determined with a Perkin-Elmer (Norwalk, CT) Model 240B elemental analyzer. Surface areas of the coals loaded into leaching chambers (described below) were calculated from sieve analyses. Moisture, ash, sulfur, and BTU content were determined by Penniman and Brown (Baltimore, MD) using ASTM methods D-2013, D-3174-B2, D4239-C, and D-2015, respectively. Duplicate 2-g samples of each coal were extracted by sonicating in 5-10 mL of dichloromethane for 10 min (5x1, fractionated on silica gel, and characterized by GC and GC/MS as described below for the characterization of leachate suspended material. Leaching Chambers. Leaching chambers were constructed from inverted 19-L Pyrex glass carboys from which the bottoms had been removed. A silicone rubber stopper fitted with a length of Teflon tubing was placed in the neck of each carboy which contained small pieces of cut glass tubing and 15-mm glass balls to support the coal above the neck of the carboy. Coal loaded into the leaching chambers (6.8 kg) was sieved to remove particles >13.33 mm in diameter. The particles removed accounted for less than 2% (w/w) of the coal. Sieve analysis of the coals showed that over 72% of the coal particles loaded into the chambers were between 0.50 and 5.00 mm. Leaching of the coals was done at 2C-25 "C. Each leaching chamber was covered with a glass plate between leaching events. The leaching solution (1.5 L of glass-distilled, deionized water) was applied to the surface of the coal by means of a perforated bucket suspended approximately 10 cm above the coal. Leaching events occurred at 10-day (coal A-FP) or 14-day intervals (coal H-FP, D-ROM, E-ROM, and F-ROM). Drainage of the leaching chambers was complete after 1-1.5 h. Leachate Collection and Characterization. Laboratory-generated leachate samples or naturally occurring coal leachates (from PEPCO's Chalk Point Facility) were
0013-936X/89/0923-0170$01.50/0
0 1989 American Chemical Society
collected in 4-L amber glass bottles. Leachate samples from the active coal storage area at the Chalk Point facility were collected immediately following or during rainfall events. The samples were obtained in areas of standing water adjacent to the coal storage pile. Measurements for total organic carbon (TOC), pH, Eh, and conductivity were made according to standard methods (9). Leachates were filtered through precombusted glass fiber filters (Whatman GF/C). A portion of the filtrate was used for dissolved organic carbon (DOC) analysis (IO). The remaining filtrate (liquid or soluble fraction) was extracted for 24 h with dichloromethane in a continuous liquid-liquid extraction apparatus (11). Filters were air dried at room temperature to a constant weight. The suspended material collected on the filter (suspended fraction) was extracted for 24 h with pesticide-grade dichloromethane in a Soxhlet extraction apparatus (coal A-FP) or by sonication in 10-20 mL of pesticide-grade dichloromethane (5x1 for 10 min. Aliphatic and aromatic hydrocarbons associated with the liquid (soluble) and suspended fractions of the leachate were isolated by silica gel chromatography. The F-1 fraction, eluted with hexane (5 mL), contained the aliphatic isolate, and the F-2 fraction, eluted with 3:l dichloromethane/hexane (5 mL), contained the aromatic isolate. On selected leachate samples, a moderately polar fraction (F-3) was eluted from the silica with 3:l ethyl ether/hexane (5 mL). Hydrocarbon extracts were concentrated under a nitrogen gas stream at 30 "C t~ a volume of 200-500 pL. The extracts were transferred to storage vials and the final volumes adjusted to 300 or 500 pL with hexane. With the exception of leachate extracts from coal A-FP and F-1 isolates, an internal standard of hexamethylbenzene (5 pg) was added to each extract following the concentration step. The hydrocarbon extracts were analyzed with a Hewlett-Packard (HP, Palo Alto, CA) Model 5840 gas chromatograph, equipped with a flame-ionization detector (FID) or a nitrogen/phosphorus-specific detector (NPD). Chromatographic separation of components in the isolates was accomplished by using a 30 m X 0.25 mm fused silica SPB-5 capillary column. The chromatographic conditions were as follows: injection, splitless; injector temperature, 250 "C; initial column temperature, 50 "C for 4 min; initial ramp, 10 "C/min to 100 "C; secondary ramp, 5 "C/min to 270 "C; linear velocity, 43 cm/s, He; detector temperature, 270 "C. Confirmation of peak identities and analyses of alkyl-substituted naphthalenes and three- and four-ringed polycyclics were performed on selected samples with a HP Model 5985 GC/MS system operated in the selective ion monitoring mode (SIM) with chromatographic conditions similar to those listed above. Quantitation of specific PAHs was accomplished by comparison with external standards (coal A-FP leachate extracts) or by detector response relative to hexamethylbenzene. External calibration curves were determined daily when that calibration method was used. Total aromatic and aliphatic concentrations of the leachates were determined by summing the areas of the resolvable peaks from the chromatogram of each fraction. The total areas for the aliphatic and aromatic fractions were compared to the detector response of hexadecane and anthracene, respectively. Procedural blanks accounted for less than 10% of the total peak areas observed in both the aromatic and aliphatic fractions. Recoveries of 12 known PAHs from distilled water ranged from 74 to 106%. To compare Soxhlet and ultrasonication extraction techniques, tripli-
Table I. Results of the Chemical Characterizations of the Coals Used in the Leaching Experiments parameter or substance"
A-FP
SA C H N S ash BTU/lb T. aliphatic T. aromatic CPIb naphthalene acenaphthene fluorene phenanthrene pyrene chrysene
2.3 69.0 4.8 1.2 3.4 14.8 12833 29.85 62.40 0.99 0.57 0.59 0.20 0.46 0.35 1.17
coal D-ROM E-ROM F-ROM
H-FP
4.5 47.2 4.3 0.9 3.7 18.2 11976 6.22 17.61 1.00 0.39 0.38 0.13 0.30 0.10 0.46
5.2 71.4 4.2 1.0 2.0 13.8 13085 5.59 27.94 1.00 0.65 0.62 0.36 0.44 0.24 0.72
6.1 83.1 4.9 1.3 2.5 9.8 13908 13.45 32.27 1.03 0.34 0.34 0.12 0.10 0.41 0.55
5.0 75.8 4.6 1.4 5.2 18.5 12422 3.40 17.72 1.01 0.38 0.34 0.09 0.08 0.04 0.25
"Listed: surface area (SA, m2/kg); percent C, H, N, S, and ash; gross BTU content; and total aliphatic, aromatic, and PAH concentrations (expressed in wg/g). * CPI, carbon preference index (12).
cate coal samples were amended with deuterium-labeled naphthalene (-d8),anthracene (-&), and chrysene (-&) and extracted by both techniques. The ultrasonication technique gave lower extraction efficiencies for deuterium-labeled naphthalene and anthracene (44-51 % ) compared to Soxhlet extraction (60-67 %). The extraction efficiency for deuterium-labeled chrysene was higher with ultrasonication (91%) than with Soxhlet extraction (83%). Because of the range of extraction efficiencies for different PAHs, correction factors were not applied to PAH or total aromatic hydrocarbon concentrations reported for the suspended material. Therefore, concentrations of PAH reported for suspended material and unweathered coal samples should be considered minimum value estimates of the actual concentrations present. Ratios of parent to alkyl-substituted PAH were determined from areas under selected ion plots of the respective molecular ions. Although this measurement does not enable direct quantitation or isomer-specific identification of alkyl-substituted PAH compounds, it does provide an estimate of the relative concentrations of the alkyl-substituted compounds compared to the unsubstituted parent molecules.
Results Coal Characterization. Results of the chemical characterization of the coals used in the leaching experiments are listed in Table I. Total carbon, nitrogen, hydrogen, sulfur, ash, and BTU analyses of the coals showed no consistent differences between ROM and FP coals. Solvent extracts of the coals contained complex mixtures of aliphatic and aromatic hydrocarbons (Figure 1). According to the carbon preference index (CPI) defined by Maxwell et al. (12), neither odd- nor even-numbered normal aliphatic hydrocarbons dominated the F-1 isolates. GC/FID chromatograms of F-2 isolates from FP and ROM coals were similar. Chromatograms of F-2 isolates were dominated by compounds eluting within the same retention region as phenanthrene. The concentrations of individual PAHs were generally greater in FP coals than in ROM coals. Chemical Characteristics of Laboratory-Generated Leachates. Leachates from FP and ROM coals had low pH values (1.67-3.22), high conductivities (3300-24 000 Environ. Scl. Technol., Vol. 23, No. 2, 1989
171
Table 11. Average Concentrations of DOC (mg/L), Total Aliphatic (pg/L), Total Aromatic (pg/L), and PAH (pg/L) Measured in the Soluble Fraction of Leachates from FP and ROM Coalsa leaching event no. coal
A-FP
compound or substance DOC T. aliphatic
T. aromatic
D-ROM
naphthalene acenaphthene fluorene phenanthrene pyrene DOC T. aliphatic
T. aromatic E-ROM
DOC T. aliphatic
T. aromatic F-ROM
DOC T. aliphatic
T. aromatic H-FP
DOC
1
2
3
0.99 4.63 (1.26) 2.69 (1.15) 0.42 0.13 0.15
2.83 2.31 (0.50) 0.92 (0.56) 0.36 0.47 22.05 3.08 (1.02) 0.61 (0.12) 23.49 1.88 (0.03) 0.64 (0.07) 9.40 1.75
4.46 4.82 (0.57) 15.46 (7.89) 0.37 0.47 0.19 0.19
-
0.05 20.70 2.25 (-) 0.21 (-) 25.91 0.96 (-) 0.31 (0.07) 27.70 1.99 (0.26) 2.38 (0.30) 22.50
(-1
2.48 (1.59) 12.75
-
19.63 2.64 (0.87) 0.85 (0.52) 21.48 1.94 (0.04) 0.20 (0.01) 9.50 1.73 (0.18) 1.90
6) 16.45
5
6
7
8
4.13 4.81 (1.21) 9.48 (2.58) 0.34
2.40 1.90 (0.00) 2.6 (--)
2.07 4.49 (1.12) 16.69 (0.08) 0.97 0.06 0.06 0.01
NDc
4 A
3.91 (1.51) 6.30 (1.33) 0.37 0.19 0.19 14.07
ND 0.61 (-) 16.42 2.03
(4
0.40 (0.03) 7.45 2.01 (0.33) 3.01 (0.71) 17.78
-
0.29
-
0.33 16.40 1.80 (0.08) 0.49
(-1
21.26 1.89 (-)
0.33 (-) 6.02 1.63 (0.33) 1.88 (0.50) 17.36
ND -
-
1.19 (0.21) 2.28 (1.35) 0.04 -
-
10.87 1.94 (0.01) 0.16 (0.02) 18.80 0.96 (0.48) 0.17 (0.01)
1
Values shown in parentheses are one-half the range for leachates collected from two (coals D-ROM, E-ROM, and F-ROM) or three (coal A-FP) replicate chambers. *- indicates concentration C0.02 pg/L. ND indicates no data.
pmhos), and high concentrations of suspended material (322-3300 mg/L). The high Ehvalues (+548 to +865 mV) of leachates indicate that oxidizing conditions existed in the leaching chambers. Indeed, the experimental coalleaching chambers contained large nos. of iron-oxidizing bacteria (13). Mean conductivities of leachates from coals D-ROM (10612 pmhos), E-ROM (13408 pmhos), and F-ROM (17 910 pmhos) were greater than in leachates from FP coals A-FP (9966 pmhos) and H-FP (9940 pmhos). The average concentrations of total soluble aliphatics and total soluble aromatics and PAHs in leachates from coal A-FP, H-FP, D-ROM, E-ROM, and F-ROM are listed in Table 11. Soluble aliphatic hydrocarbon concentrations of leachates from both FP and ROM coals remained nearly constant of failed to exhibit coherent patterns of increase or decrease between leaching events. Highest concentrations of total soluble aliphatics were found in leachates from coal A-FP (mean = 3.51 pg/L, eight leaching events). Lower concentrations were measured in leachates from coals D-ROM (mean = 2.34 mg/L, six leaching events), and F-ROM (mean = 1.82 mgg/L, five leaching events). These data were not collected for coal H-FP. Concentrations of total soluble aromatics in leachates from each of the coals (averaged over all leaching events) were as follows: 7.05 pg/L, coal A-FP; 0.49 pg/L, coal E-ROM; 2.37 pg/L, coal F-ROM. These data were not collected for coal H-FP. The total soluble aromatic hydrocarbon content of the leachates from coals D-ROM, E-ROM, and F-ROM remained relatively constant during the 10-12-week leaching experiments but was highly variable in leachates from coal A-FP (Table 111). The total soluble aromatic hydrocarbon content was greater than the total soluble aliphatic hydrocarbon content of most leachates from coals A-FP and F-ROM, but lower than the total aliphatic hydrocarbon content of leachates from coals D-ROM and E-ROM. PAHs were not detected in the soluble fraction of the leachates from coals D-ROM, EROM, and F-ROM. However, the soluble fraction of 172 Environ. Scl. Technol., Vol. 23, No. 2, 1989
leachates from coal A-FP contained PAHs that were dominated by naphthalene or acenaphthene at most leaching events (Table 11). Concentration of total aliphatics, total aromatics, and PAHs associated with the leachate suspended material are summaried in Table 111. Average concentrations (calculated over complete leaching experiments)of total aliphatic hydrocarbons associated with the particle fraction of leachates were as follows: 30.77 pg/g, coal A-FP; 27.89 pg/g, coal D-ROM; 7.40 pg/g, coal E-ROM; 25.01 pg/g, coal H-FP; 25.41 pg/g, coal F-ROM The aliphatic content of leachate suspended material averaged over entire leaching experimentsapproximated that of the source coals for coals A-FP and E-ROM but was enriched for coals D-ROM, F-ROM, and H-FP. Concentrations of particleassociated total aliphatic hydrocarbons increased rapidly between the first and the second leaching event in leachates from coals H-FP, D-ROM, and F-ROM and then decreased or were variable thereafter. Particle-associated total aliphatics showed no apparent pattern in leachates from coal A-FP. Concentration trends for particle-associated total aromatics were identical with those observed for aliphatics in leachates from coals H-FP, D-ROM, E-ROM, and FROM (Table 111). Interpretable patterns in particle-associated aromatics were not evident in leachates from coals A-FP, either as a function of leaching event or relative to variations in particle-associated aliphatics. Average concentrations for particle-associated aromatics were as follows: 144.28 pg/g, coal A-FP; 66.79 pg/g, coal D-ROM; 23.37 pg/g, coal E-ROM 38.17 pg/g, coal H-FP; 26.75 M/g, coal F-ROM. The aromatic content of the suspended material averaged over entire leaching experiments was enriched compared to the source coals for all leachates examined. Possible reasons for the observed concentration differences between leachate suspended material and unweathered coals are discussed later. Leachates from coals F-ROM and H-FP contained fewer PAHs after successive
Table 111. Average Concentrations ( p g l g ) of Total Aliphatic, Total Aromatic, and PAH Measured in the Suspended Fraction of Leachates from FP and ROM Coalsa leaching event no. coal A-FP
1
2
3
4
5
6
7
8
151.83
6.29 (4.28) 309.00 (110.00) 3.68 2.26 2.78 2.28 2.33 11.20 33.51 (7.32) 115.19 (38.73) 0.10 0.47 0.16 0.38 0.57 1.66 4.87 (9.46) 19.87 (9.46) 0.07 0.08 0.22 0.10
26.00 (19.54) 28.45 (16.15) 0.38 0.32 0.34 0.53 1.59 -
76.08 (24.89) 322.85 (86.35) 4.12 2.21 2.60 3.58 2.11 3.10 5.76 20.12 (4.55) 65.06 (6.81) 0.47 0.42 0.20 0.26 0.26 1.31 4.60
7.97 (2.37) 90.20 (67.50) 5.22 1.06 1.80 6.12 5.15 -
8.00 (3.54) 36.75 (2.85)
66.96 (41.54) 234.32 (134.30) 1.55
24.06 (1.69) 27.64 (1.81) 0.58 0.47 0.64 -
compound or substance
T. aliphatic
NDb
T. aromatic
D-ROM
naphthalene acenaphthene fluorene phenanthrene pyrene chrysene fluoranthene T. aliphatic
T. aromatic
E-ROM
naphthalene acenaphthene fluorene phenanthrene pyrene chrysene fluoranthene T. aliphatic
T. aromatic
F-ROM
naphthalene acenaphthene fluorene phenanthrene pyrene chrysene fluoranthene T. aliphatic
T. arormatic
105.00 (8.00) 0.81 1.31 1.37 2.51 1.92 10.43
-
23.04 (4.71) 59.07 (-) 0.36
-
0.13 0.20 0.28 1.26 -
ND ND -
-
25.72 (11.94) 12.15
0.15 0.10 0.23
54.59 (-) 53.21 (3.22) 0.23 0.31 0.20 0.50 0.43 0.90
6.80 (-) 49.91 (37.07) 0.89 0.68 0.31 1.46 0.59 0.81 -
66.22 (32.32) 65.09 (2.71) 1.64 1.59 0.47 1.90 0.57 1.23 -
(-)
H-FP
naphthalene acenaphthene fluorene phenanthrene pyrene chrysene fluoranthene T. aliphatic
T. aromatic naphthalene acenaphthene fluorene phenanthrene pyrene chrysene fluoranthene
ND ND ND
-
0.10 Dd
-
-
-
19.56 (7.34) 28.49 (28.49) 0.18 0.14 0.10 0.05 0.10 0.36
-
21.11 (62.82) 77.51 (62.82) 0.59 0.81 0.31
-
1.08 28.91 (11.10) 39.27 (11.30) 1.15 0.43 0.13 1.22 0.34 0.63
-
43.96 (17.51) 44.74 (13.88) -
-
2.19 0.56 1.23 0.50
-C
-
-
46.06
3.78 3.89 3.79 25.03
ND
ND
80.95 (8.78) 0.45 0.44 0.23 0.33 0.66 1.63 2.15
52.01 (18.43) 0.27 0.30 0.10 0.22 0.17 1.02 4.27
ND
ND
ND
7.51
0.40
11.58
ND
-
ND
-
ND -
0.65 0.23 0.15 13.95 (0.69) 19.59 (5.30) 0.14 0.59 0.14 0.12
-
0.38 0.16
3.89 (1.29) 9.55 (6.82) -
-
-
4.91 (1.71) 12.14 (6.80)
-
0.12 0.12
D -
-
-
-
0.72 0.94 -
-
-
-
-
0.13
-
3.20
-
18.95
-
0.25 0.25 D
-
Values shown in parentheses are one-half the range for leachate samples collected from two (coals D-ROM, E-ROM, F-ROM, and H-FP) or three (coal A-FP) replicate chambers. Data for source coals are found in Table I. *ND indicates no data. indicates concentration
