Envlron. Sci. Technol. 1984, 18, 687-693
Polycyclic Aromatic Hydrocarbons in Washington Coastal Sediments: An Evaluation of Atmospheric and Riverine Routes of Introduction Fredrlck 0. Prahl," Eric Creceilus,+ and Roy Carpenter School of Oceanography, WB-I 0, University of Washington, Seattle, Washington 98 195
rn Polycyclic aromatic hydrocarbon (PAH) compositions were characterized monthly over a 1-year period in atmospheric particulate material (APM) collected from three locations in western Washington state and riverine suspended particulate material (SPM) collected near the mouth of the Columbia River. PAH mixtures of APM are dominated by compounds of combustion origin, with minor levels of the resin acid-derived PAH retene often present. SPM contained comparable levels of individual combustion PAH, retene, and perylene. Atmospheric and riverine contributions of individual combustion PAH to the Washington coastal environment were estimated from these data and other available information. Comparison of estimates with respective PAH accumulation rates measured in lead-210 dated coastal sediments shows that >30% of all combustion PAH, retene, and perylene in these sediments is supplied by SPM discharge from the Columbia River and direct atmospheric input accounts for at most 10% of the combustion PAH. Atmospherically transportable PAH are removed from the air over land to soils and freshwaters within the river drainage basin, eroded on particles, and discharged into the Washington coastal environment along with other nonatmospherically transportable PAH such as perylene as intrinsic constituents of the Columbia River's suspended sediment load. ~~
Introduction Polycyclic atomatic hydrocarbons (PAH) of natural and anthropogenic origin are widely distributed in soils and sediments throughout the world. PAH as a class of compounds are environmentally significant because particular compounds are recognized as potent carcinogens. A clear knowledge of the various sources, phase associations, and modes of dispersal of individual PAH is necessary to adequately assess what effect the presence of these compounds has on the health of the environment. Eolian transport of PAH-enriched soot generated during high-temperature burning of fuel materials explains the appearance of specific PAH in soils and sediments remote from combustion source regions (1, 2). The role of the atmosphere in the dispersal of PAH from sources other than combustion is recognized (3); however, it is less well-defined. Gschwend and Hites (4) estimated present day delivery rates of individual combustion PAH to remote sediment locations to be 1ng/(cm2.year), based on sediment core data. Higher PAH delivery rates measured in sediments closer to urban centers are ascribed to greater atmospheric fallout of PAH-enriched particles near the combustion source, augmented by inputs from erosion, transport, and redeposition of sediments containing combustion PAH. Although atmospheric and erosional processes are often used to explain PAH distributions in Sediments ( 2 , 5 ) ,these processes have primarily been inferred rather than actually evaluated. *To whom correspondence should be addressed at the School of Oceanography, Oregon State University, Corvallis, OR 97331. Present address: Sequim Marine Laboratory, Battelle Northwest, Sequim, WA 98382. 0013-936X/84/0918-0687$01.50/0
In this paper, complete PAH compositions of airborne and riverborne particulate material are qualitatively and quantitatively characterized. These data combined with other atmospheric and sedimentological information are used to evaluate the relative roles of the atmosphere and the Columbia River as input routes for all PAH to the Washington coastal environment. Experimental Section Sample Collection. Atmospheric particulate material (APM) was collected monthly for 1 year, beginning Jan 1979, at three sites in western Washington: Quillayute, Sequim, and Seattle (Figure 1). APM was filtered from ambient air onto precombusted (400 OC, 8 h) and preweighed Gelman spectrograde glass-fiber filters (20 cm X 25 cm) by using a flow controlled high volume air sampler (Sierra Instruments, Inc.). The sampler was operated at a constant flow (1.2 m3/min) for 4-5 days for each sample. All samples were stored at 4 "C after collection until hydrocarbon analysis. Riverborne suspended particulate material (SPM) was collected monthly for 1 year, beginning Jan 1980, from a midchannel sampling location in the Columbia River near Tongue Point (Figure l),a freshwater regime at the river mouth. Water from 1- to 2-m depth was pumped into clean glass carboys. Immediately upon collection, 26 L of water was transferred into a large PVC cylinder and filtered through a precleaned Gelman type A/E glass-fiber filter (0.5-pm pore size; 142-mm diameter) by using an overpressure (2.5 kg/cm2) of prepurified nitrogen. Particulate material retained by the filter was stored frozen for subsequent hydrocarbon analysis. River water SPM concentrations (mg/L) were determined by vacuum filtering 1.0 L of water through preweighed Nucleopore filters (0.5-pm pore size; 47-mm diameter). From these concentrations, the weight of SPM collected for hydrocarbon analysis was determined. SPM from Nov 1980 was also isolated from river water by continuous flow centrifugation (15 000 rpm, 100 cm3/min). This isolate was examined for hydrocarbon content and intercompared with results from samples isolated by filtration. Analytical Methods. The procedure used for extraction and isolation of aliphatic hydrocarbon and PAH mixtures from these particulate samples is described by Prahl and Carpenter (6). PAH mixtures from APM and all aliphatic hydrocarbon mixtures were analyzed by using capillary gas chromatography (GC) and standard flame ionization detection (FID). Specific chromatographic details are given in the legends of Figure 2 and 3. Individual PAH and alkanes were quantified by using corresponding external standards and hexamethylbenzene as an internal injection standard. The overall variability for individual PAH and n-alkanes (CZ2through CS3),including infield sampling, chemical workup, and GC variability, was generally 5 *lo% about the mean of two measurements (7). PAH mixtures from riverborne SPM samples were analyzed by reverse-phase high-performance liquid chroma-
0 1984 American Chemical Society
Environ. Sci. Technoi., Vol. 18, No. 9, 1984 687
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BRITISH
COLUMBIA
A S H INGTON
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SAMPLING LOCATIONS DAMS I
Flgure 1. Map of the study area. The three atmospherlc (Quiilayute, Sequlm, and Seattle)and one riverine (Tongue Polnt) sampling locations are indlcated. The section of the Washington continental shelf and slope discussed in the text Is enclosed by dotted lines.
Table I. Comparison of GC and HPLC Methods for PAH Analysis
compd fluoranthene (FLUO) pyrene (PYR) benzo[ b]fluoranthene (BbF) benzo[k]fluoranthene (BkF) benzo[a]pyrene (BaP) perylene (PERY) benzo[ghi]perylene (BPERY)
concn, ng/g of dry sediment GC" HPLCb 33 30 35
25 31 32
26c
12
21
21
68 23
60
-
12
" Suspended particulate material isolated by centrifugation. Suspended particulate material isolated by filtration. Combined concentration of p] and [k] isomers. tography (HPLC) using a 4.7 mm i.d. X 25 cm Zorbax ODS column in a Micromeritics Model 7000 HPLC equipped with a Dupont Model 836 UV fluorescence detector. A detailed description of this procedure is given by Prahl and Carpenter (8). The ability to introduce the complete PAH isolate from a given sample onto the HPLC column afforded adequate detector response for reliable quantitative measurement of individual PAH in these size-limited samples. The small injection volumes and hence low FID response prevented routine usage of capillary GC for these analyses. Seven individual PAH (fluoranthene, pyrene, benzo[b]fluoranthene, benzo [k]fluoranthene, benzo [a]pyrene, perylene, and benzo[ghi]perylene) were quantified by using external standards. Individual PAH concentrations in SPM collected simultaneously but isolated by filtration and centrifugation were analyzed by HPLC and GC, respectively. The results are compared in Table I and generally show that the two different chromatographic techniques yield internally consistent values for quantitation of individual PAH within a sample. Results of the two techniques agree within i 1 5 % of the mean for each compound except benzo[k]fluoranthene and benzo[ghi]perylene. This variation includes both sampling and chemical workup variability. The poorly resolved doublet peak in the GC traces (Figure 2) corresponding to benzofluoranthenes represents a mixture of three structural isomers: [ b ] ,PI, and [k]. These isomers are completely 688
Envlron. Sci. Technol., Vol. 18, No. 9, 1984
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Flgure 2. GC chromatograms of PAH mixture In (A) Washlngton coastal sediments, (S) atmospheric particulate materlai from Seattle, and (C) rlverborne suspended particulate material from the Columbia River. Peaks are labeled P for phenanthrene, MP for methylphenanthrenes, asterisk for 4,5-methylenephenanthrene, C for combustion PAH (from left to right: fluoranthene, pyrene, benzo[a 1anthracene, chrysene, benzofiuoranthenes, benzo [e] pyrene, benzo[alpyrene, lndeno[c,d] pyrene, benzo[ghl] perylene), R for retene, and PERY for perylene. HMS (hexamethylbenzene) and I (Bmethylanthracene) were added as an internal GC injection standard and recovery standard, respectively. Chromatographic conditions were the following 30 m X 0.25 mm 1.d. SE-54 fused slllca capillary column (J & W Scientific); splltiess injection using temperature programming from 75 to 130 OC at 15 OC/min and from 130 to 270 OC at 5 'C/mln and hydrogen as a carrier gas.
resolvable by reverse-phase HPLC. The coelution of P] and [k] isomers by capillary GC accounts for the higher reported value of benzo[k]fluoranthene by this method (Table I). A similar coelution problem may explain the discrepancy between GC and HPLC measurements of benzo[ghi]perylene (7), although this still remains to be shown. Results and Discussion Polycyclic aromatic hydrocarbons attributed to three dominant sources are recognized in Washington coastal sediments (9). Representative compounds from these sources are indicated in Figure 2A as (1) C for combustion-derived PAH, (2) R for retene, a resin-derived compound, and (3) PERY for perylene, a natural PAH of otherwise undefined origin. The components labeled P for phenanthrene and MP for methylphenanthrene are of a dual combustion and fossil origin (6). (A) Atmospheric Transport. (1) PAH Compositions in Atmospheric Particulate Material. PAH were analyzed in samples collected from three locations in western Washington state (Quillayute,Sequim, and Seattle; Figure 1) in order to determine which of the three major PAH types identified in coastal sediment can be dispersed atmospherically and whether these compounds are introduced anthropogenically into the atmosphere. The three sampling locations, respectively, were chosen to represent
areas increasingly influenced by human activities. Figure 2B shows the typical qualitative composition of the PAH mixture contained in all APM samples examined regardless of collection site. PAH from combustion of fuel materials were the dominant components observed in all cases. The combustion PAH mixtures in APM qualitatively resemble those found in coastal sediments (Figure 2A). However, relative abundances of specific components within mixtures display notable differences. For example, fluoranthene and pyrene are generally the most abundant individual combustion PAH observed in sediments from the Washington coastal region (9) and throughout the world (10, 11). Higher molecular weight compounds such as chrysene and benzofluoranthenes were the most abundant individual PAH measured in the average APM from all three locations. Giger and Schaffner (12)and Cautreels and Van Cauwenberghe (13) noted a similar difference between atmospheric and sedimentary combustion PAH mixtures and attributed it to a sampling artifact. It was suggested that higher vapor pressure, lower molecular weight PAH are selectively evaporated from APM during the high volume air filtering collection procedure. Van Vaeck et al. (14) have shown through laboratory experiments that such selective volatilization can alter n-alkane distributions in APM. However, any such alteration of hydrocarbon distributions must occur quite reproducibly from sample to sample as analyses of aliphatic hydrocarbons and PAH in two APM samples simultaneously collected at the same location produced very similar results in this study (7). 4,5-Methylenephenanthreneof combustion origin (15) was observed in several APM samples in high abundance relative to methylphenanthrenes (Figure 2B). This compound is also measurable in PAH mixtures from coastal sediments, but it is present a t only a minor level relative to the combustion-derived methylphenanthrenes. A lower intrinsic chemical stability may explain this observation. PAH mixtures from both combustion and unburned, fossil sources contain phenanthrene and a series of methylated homologues. Despite this qualitative compositional similarity, phenanthrene suites from these two independent sources are distinguishable through examination of the relative abundance of total methylphenanthrenes to phenanthrene (MP/P). Values of MP/P measured in combustion mixtures are generally
