Sources and Distribution of Polycyclic Aromatic ...

Soil & Sediment Contamination, 17:(6):547-563, 2008 Copyright © Taylor & Francis Group, LLC ISSN: 1532-0383 print / 1549-7887 online DOI: 10.1080/15320380802425055

Sources and Distribution of Polycyclic Aromatic Hydrocarbons in Urban Soils: Case Studies of Detroit and New Orleans GUANGDI WANG,1 QIANG ZHANG,1 PENG MA,1 JORDANIA ROWDEN,1 HOWARD W. MIELKE,2 CHRIS GONZALES,3 AND ERIC POWELL4 1

Department of Chemistry, Xavier University of Louisiana, New Orleans, LA, USA 2 Department of Chemistry, Tulane University, New Orleans, LA, USA 3 Department of Chemistry, Xavier University of Louisiana, New Orleans, LA, USA 4 Center for Bioenvironmental Research at Tulane and Xavier Universities, New Orleans, LA, USA

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous organic pollutants in urban environments. Incomplete combustion of petroleum and coal are the primary sources of elevated concentrations of urban PAHs. The purposes of the study were: 1) to determine and compare the concentration of PAHs in soils taken from two major US cities, New Orleans and Detroit; and 2) to examine the main sources of PAHs in urban soils by diagnostic PAH ratios. A total of 107 New Orleans soil samples were taken from 6 census tracts (n = 13–19 per census tract) and compared with 106 Detroit soil samples from 6 census tracts. Sampling sites included house foundations, open spaces, and soil bordering residential and busy streets. The average total PAH (sum of 17 PAH concentrations) of Detroit soils was 7,843 µg/kg, compared to 5,100 µg/kg for New Orleans soils. Several diagnostic PAH concentration ratios were calculated for source determination for Detroit and New Orleans, respectively: phenanthrene/anthracene ratios (2.97 and 5.36), benz(a)anthracene/chrysene ratios (0.99 and 0.85), benzo(b)fluoranthene/benzo(k)fluoranthene ratios (1.51 and 1.53), and benzo(a)pyrene/benzo(e)pyrene ratios (0.98 and 0.92). The ratios indicate that PAH concentrations are attributable to pyrolytic sources, mainly vehicle exhaust. Travel and gasoline consumption data in Detroit and New Orleans support these findings. Keywords sumption

PAHs, isomer ratios, GC-MS, ASE, traffic congestion, vehicle fuel con-

ABBREVIATIONS: PAHs: polycyclic aromatic hydrocarbons; ASE: accelerated solvent extraction; SPE: solid phase extraction; SIM: selected ion monitoring; CT: census tract (enumeration districts) Address correspondence to Guangdi Wang, Department of Chemistry, Xavier University of Louisiana, 1 Drexel Drive, New Orleans, LA 70125, USA. E-mail: [email protected]

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Introduction Elevated concentrations of polycyclic aromatic hydrocarbons (PAHs) and other organic pollutants have been reported in air particulates (Kavouras et al., 2001; Larsen and Baker, 2003), surface waters (Vrana et al., 2001), and sediments in urban and industrial areas (Sicre et al., 1987; Sanders et al., 2002; Wang et al., 2004). PAH contamination in urban environments has been attributed to anthropogenic sources such as vehicular emissions and factory discharges. PAHs originating from these sources are first emitted into the air as aerosols. Because of their hydrophobic nature, PAHs tend to associate with surface waters (rivers, lakes, and sea) and attach to particulate matter or enter water systems through storm runoff and deposit in sediments. Thus, sediments have been the subject of intensive studies as the sink for a variety of PAHs. A few studies have focused on urban soils as a media for deposition of PAHs (Takada et al., 1991; Mielke et al., 2001; Manta et al., 2002; Madrid et al., 2002; Krauss and Wilcke, 2003; Wang et al., 2004; Zhang et al., 2005; Iqbal et al., 2007; Wang et al., 2007). These studies show that PAHs are present at higher concentrations in urban soils than in rural soils. Source analysis in the studies of Wang et al. (2004), Zhang et al. (2005), Iqbal et al. (2007), and Wang et al. (2007) indicate that urban soil PAHs are mainly of pyrolytic origin by both mobile (e.g. motor vehicle exhausts) and stationary (e.g. power generation by coal or oil combustion and use of heating oil) emissions as the primary sources of PAHs. Further evidence has been provided by studies that report high concentrations of PAHs originating from vehicle emissions in particulate matter and road dust (Murakami et al., 2005;Pengchai et al., 2005). Monitoring PAHs quantities and their sources in urban soils is important for understanding the fate and transport of PAHs in the urban environment. Previously we found sizable PAH concentrations (up to 40,000 µg/kg) in 29 New Orleans urban soil samples (Wang et al., 2004). Source analyses of these limited soil data indicate that urban PAHs have a pyrolytic origin. The purpose of this study is expand the scope of soil sampling to include over 100 soil samples each from two major U.S. cities: New Orleans and Detroit. Six different residential community locations were chosen for soil sampling in each city. Some communities represent an urban environment with heavy traffic and other places represent a suburban environment with light traffic to distinguish the effect of traffic sources in each city. Selected diagnostic PAH ratios were calculated for source analysis of PAHs in New Orleans and Detroit soil samples.

Experimental Sample Collection Figures 1 and 2 illustrate the 6 census tract locations (i.e. enumeration districts) of New Orleans and Detroit, respectively. The 6 census tracts of New Orleans are 58, 78, 92, 17.24, 271, and 306.03 where up to 19 soil samples per census tract were collected. The samples from New Orleans were collected between 1998 and 2000 (Mielke et al., 2002, 2005). In Detroit, soil samples were also collected from 6 census tracts, 1417, 1420, 5004, 5064, 5103, and 5264. Soil samples were collected in Detroit during July-October 2002 according to the same methods developed by Mielke et al. (2002, 2005) for New Orleans. In all, 107 soil samples were collected from New Orleans and 106 soil samples from Detroit. For each census tract in both cities four types of soil samples were obtained: 1) samples from the soil bordering residential streets (light to moderate traffic); 2) soils bordering busy streets (with heavier traffic); 3) soils from within 1 m of house foundations (drip lines); and 4) soils from open space away from streets or buildings.

Sources and Distribution of PAHs in Detroit and New Orleans Soils

Figure 1. Soil sampling map of New Orleans stratified by census tracts.

Figure 2. Soil sample map of Detroit stratified by census tracts.

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All samples were collected within the top 2.5 cm of the surface, air-dried, and ground with a porcelain mortar and pestle. The mortar and pestle were cleaned with deionized water and acetone between samples. The soil samples were then sieved through a 2 mm stainless steel sieve (Fisher Scientific, Fair Lawn, NJ) and stored at room temperature before extraction.

Sample Preparation For PAH recovery studies in soil, 1.0 g aliquots of clean rural soil (i.e. soil samples known to have PAH concentrations below detection limits) were prepared and fortified with 20 µL standard PAH solution to give soil concentrations of 2.0 µg/g of dried soil for each PAH. The fortified sample aliquots (n=3) were then mixed with 1.0 g anhydrous Na2 SO4 before R cells. For analysis of they were transferred into the Accelerated Solvent Extraction (ASE) all soil samples, three 5.0 g aliquots of each sample were mixed with 5 g anhydrous Na2 SO4 and extracted with methylene chloride by ASE. To evaluate the effect of drying methods on possible loss of PAHs, two aliquots of soil samples were subjected to freeze-drying and air-drying before solvent extraction. Results from the two different drying methods were compared and it was concluded that there were no differences between individual PAH concentrations. Both show relatively low concentrations of volatile PAHs (e.g., naphthalene, acenaphthene).

Materials and Regents Standard PAH mixtures, 2-fluorodiphenyl, 4,4-difluorobiphenyl, and p-terphenyl-d14 were obtained from Ultra Scientific (North Kingstown, RI). The standard mixture contains 16 PAHs listed as EPA priority pollutants each at 100 µg/ml in methanol. The calibration standard solutions were prepared by diluting the mixture to concentrations ranging from 0.1 µg/mL to 5.0 µg/mL with methylene chloride. 4,4-difluorobiphenyl and p-terphenyl-d14 and were used as internal standards, and they were added to the final extracts prior to GC-MS analysis. Florisil (100-200 mesh size), solid phase extraction cartridges, GC grade solvents (hexane, methylene chloride, acetone, and acetonitrile), and Ottawa Sand Standard were all purchased from Aldrich Chemicals (St. Louis, MO).

Accelerated Solvent Extraction R was used for all sample extractions. Extraction A Dionex (Sunnyvale, CA) ASE200 parameters have been previously described (Wang et al., 1999; Richter et al., 1996). Briefly, a cellulose paper was placed at the bottom of each 11-mL Dionex extraction cell before samples were loaded. The extra space in the cell was filled up with Ottawa Sand Standard before closing and sealing cell. ASE operation parameters included a 5-min. heating-up time, two sequential 5-min. static extraction periods followed by a 1.5-min. purge time. The extraction pressure was held at 1500 psi within the cell and the temperature was kept at 100◦ C in the oven. The total extraction volume was 20 mL of methylene chloride. The ASE extracts were collected in 40-mL glass vials with Teflon septum caps.


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Post-Extraction Clean-Up Procedures The extracts were first evaporated to approximately 2 mL under a nitrogen stream. The concentrated extracts were then loaded onto the top of the solid phase extraction cartridges containing 2 g Florisil. The cartridge was allowed to dry for 5 minutes. PAHs were eluted from the column with 10 mL methylene chloride using a Visiprep SPE Vacuum Manifold (Supelco, Bellefonte, PA). The collected eluent was evaporated down to 1 mL followed by the addition of internal standards prior to GC-MS analysis. All evaporation and clean-up procedures were carried out in a fume hood to minimize PAH and organic solvent vapor contamination of the laboratory. Quantitative Analysis of PAHs An Agilent 6890N gas chromatograph (GC) equipped with a 5973N mass selective detector (Agilent Technologies, Palo Alto, CA) was used for the quantitative determination of PAHs. The GC column used was an HP-5MS, crosslinked 5% phenyl methyl siloxane capillary column, 30 m × 0.25 mm id, with film thickness of 0.25 µm. The GC-MS was operated under the following conditions. The temperature of the injection port and the detector was held at 290◦ C. The oven temperature was set at 40◦ C initially (1 min. hold), increased to 250◦ C at 12◦ C/min., and to 310◦ C at a rate of 5◦ C/min. (3 min. hold). The temperatures of the ion source and the quadrupole mass analyzer were kept at 250 and 100◦ C, respectively. Helium gas was used as the carrier gas at a constant flow rate of 0.8 mL/min. An automatic sample injector (HP 6890) was used to introduce 1.0 µL of each sample extract in an intermittent standard injection sequence. The retention time of each PAH component was determined by injecting individual PAH solutions under constant GC-MS instrumental conditions. The SIM mode (selected ion monitoring) was then used for quantification in which three ions were selected for calculating the chromatographic peak area of each PAH (Wang et al., 1999). The response factors of PAHs relative to the two internal standard compounds were determined at five PAH concentrations (from 0.10 to 5.0 µg/mL) to obtain standard calibration curves. For PAH quantifications in all soil samples, internal standards were added to the final extracts before GC-MS analysis. A standard reference material from National Institute of Standards and Technology (NIST) SRM1941b was analyzed for verification of the quantification method. The recoveries of the NIST reference materials ranged from 80% to 125%. Detection Limits of PAHs Table 1 lists the detection limits for the individual PAHs. The detection limits were determined as the lowest PAH concentrations that yielded chromatographic peaks with a signal to noise ratio (S/N) equal to or greater than 3. The detection limit ranged from 1.12 ppm for naphthalene to 4.84 ppm for dibenz(a,h)anthracene.

Results and Discussion The PAHs measured in this study include the 16 originally listed by the United States Environmental Protection Agency (U.S. EPA, 1993) as priority pollutants, naphthalene, acenaphthylene, acenaphthene, fluorene, phenanthrene, anthracene, fluoranthene, pyrene, benz(a)anthracene, chrysene, benzo[b]fluoranthene, benzo[k]fluoranthene, benzo(a)pyrene, indeno[1,2,3-cd]pyrene, dibenz[a,h]anthracene, benzo[g,h,i]perylene plus

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G. Wang et al. Table 1 Detection Limits for PAHs PAHs Naphthalene Acenaphthylene Acenaphthene Fluorene Phenanthrene Anthracene Fluoranthene Pyrene Benz(a)anthracene Chrysene Benzo(b)fluoranthene Benzo(k)fluoranthene Benzo(e)Pyrene Benzo(a)pyrene Indeno(1,2,3-cd)pyrene Dibenz(a,h)anthracene Benzo(g,h,i)perylene

Detection Limit (µg/kg soil) 1.12 1.15 1.21 1.28 1.29 1.31 2.52 1.46 2.61 1.33 3.14 2.23 1.35 2.95 4.32 4.84 3.38

benzo(e)pyrene. Benzo(e)pyrene is included for the purpose of PAH source analysis using characteristic PAH ratios. The dataset of over 200 samples each yielding 17 PAH results is summarized by the median and average results for each PAH and total PAHs.

Comparison of PAHs for Different Types of Soil Samples Table 2 summarizes the New Orleans results of PAH concentrations for 4 different types of soil samples. The average concentrations of most PAHs increase in order from open space, foundation, residential street, and busy street soil samples. For example, the mean concentration of benzo(a)pyrene range from a low of 132 µg/kg for open space soils to 410 µg/kg for busy street soil samples. The mean concentration range of dibenz[a, h]anthracene is found from 44 to 93 µg/kg, again with soil samples from open space exhibiting the lowest amount, and those from busy street having the highest content of dibenz[a, h]anthracene. The same trend is observed with total PAHs for the four types of soil samples with an increase in the order from open space (2,404 µg/kg), foundation (2,712 µg/kg), residential street (5,237 µg/kg), and busy street (7,189 µg/kg). Typically, open space and foundation sampling sites are 5 to 10 meters or farther from streets and buildings, whereas street side and busy street soils were taken within 1 meter of the road pavement. With the exception of 2 foundation soil samples that contained unusually high PAH concentrations, possibly due to incidental local contamination (e.g., bits of roofing asphalt), PAHs are generally found at significantly higher concentrations in soils bordering roads with moderate to heavy traffic. The PAH concentrations of Detroit soil samples, summarized in Table 3, follow the same trend observed in New Orleans soils. The average benzo(a)pyrene concentration is 188 µg/kg for open space soils, 217 µg/kg for foundation soils, 367

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Sources and Distribution of PAHs in Detroit and New Orleans Soils Table 2 Results Summary for PAH Concentrations (µg/kg) in New Orleans Soil Samples Open Space n = 18) Sample Type PAHs

Foundation (n = 18)

Street Side (n = 47)

Busy Street (n = 24)

Median Average Median Average Median Average Median Average

Naphthalene 19.7 34.7 15.9 47.5 19.3 36.7 27.5 Acenaphthylene 1.2 7.7 1.2 11.2 1.2 18.0 2.4 Acenaphthene 5.1 11.5 2.5 23.6 1.2 26.5 2.9 Fluorene 3.8 13.7 1.3 27.9 1.3 20.6 1.3 Phenanthrene 129 250 142 507 128 501 274 Anthracene 7.7 36.5 8.4 76.5 4.5 63.1 38.3 Fluoranthene 204 365 179 949 197 936 330 Pyrene 154 378 133 751 150 793 424 Benz(a)anthracene 101 221 93.3 335 83.5 318 243 Chrysene 97.9 193 84.4 403 125 388 271 Benzo(b)fluoranthene 106 182 106 405 104 505 319 Benzo(k)fluoranthene 64.8 138 63.4 253 45.5 225 176 Benzo(e)pyrene 67.4 136 156 363 70.4 343 336 Benzo(a)pyrene 28.8 132 122 287 62.3 305 272 Indeno (1,2,3-cd)pyrene 4.3 153 23.6 349 16.2 448 310 Dibenz(a,h)anthracene 4.8 43.5 4.8 64.5 4.8 80.7 4.8 Benzo(g,h,i)perylene 27.6 101 72.9 198 39.1 227 236 Tot PAHs 1241 2404 1337 2712 1056 5237 3408

68.1 27.3 25.1 23.2 543 97.1 1241 1149 549 583 648 4116 424 410 550 92.5 339 7189

µg/kg for residential street soils, and 1,040 µg/kg for busy street soils. Similarly, dibenz[a, h]anthracene concentrations are found at 63, 73, 131, and 255 µg/kg, respectively, for the same order of sample types listed above. The average total PAH concentrations range from 2,299 µg/kg for open space soils to 20,900 µg/kg for soils along busy streets. While the PAH data follows comparable trends for the soil types between New Orleans and Detroit, Detroit samples are found to contain higher levels of PAHs than New Orleans samples. The median PAH results (the 50th percentile) indicate that Detroit soils have consistently higher concentrations of PAHs. For example, the median concentrations of benzo(a)pyrene in Detroit soils are approximately 2–6 times higher than the New Orleans counterparts; the median total PAH concentrations in Detroit soils are found between 1.3 and 1.8 times higher than those in New Orleans soils. Furthermore, when all sample types are combined, the average total PAH concentration of Detroit soils is calculated at 7,843 µg/kg, compared to 5,100 µg/kg for New Orleans soils, a ratio between the two cities of 1.5. The median total PAH concentrations for Detroit and New Orleans soils are 3,436 µg/kg, and 1,821 µg/kg, respectively, for a ratio of 1.9 for the two the cities. The soil PAH concentrations found in both cities are generally higher than reported in some recent studies about the sources and distribution of soil PAHs (Johnsen et al., 2006; Ye et al., 2006; Zuo et al., 2007; Ping et al., 2007). For example, the mean concentration of total PAHs from 188 soil samples from Tianjin municipal area in China was found at less than 1,000 µg/kg (Ye et al 2006); in Johnsen and coworkers’ study of soils near a motorway north of Copenhagen, Denmark, the total PAHs in diffusely pol-

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G. Wang et al. Table 3 Results Summary for PAH Concentrations (µg/kg) in Detroit Soil Samples Open Space (n = 17) Sample Type PAHs

Foundation (n = 17)

Street Side (n = 52)

Busy Street (n = 20)

Median Average Median Average Median Average Median Average

Naphthalene 1.1 11.7 Acenaphthylene 1.2 1.4 Acenaphthene 9.8 15.6 Fluorene 1.3 3.4 Phenanthrene 55.3 102 Anthracene 7.8 24.1 Fluoranthene 231 447 Pyrene 175 408 Benz(a)anthracene 126 181 Chrysene 110 163 Benzo(b)fluoranthene 174 214 Benzo(k)fluoranthene 117 131 Benzo(e)pyrene 203 212 Benzo(a)pyrene 167 188 Indeno (1,2,3-cd)pyrene 201 205 Dibenz(a,h)anthracene 52.7 63.1 Benzo(g,h,i)perylene 129 141 Tot PAHs 1654 2299

9.8 11.6 7.7 14.5 1.1 1.2 7.0 1.2 12.9 1.2 < 1.2 7.2 7.2 14.5 16.5 1.3 5.5 1.3 5.4 1.3 108 140 185 244 255 23.9 29.8 34.6 49.3 64.7 400 451 689 926 1227 326 366 542 740 967 142 263 312 404 507 152 212 300 411 566 259 286 385 530 750 132 197 250 354 543 212 236 308 384 489 179 217 279 367 476 221 259 348 491 614 65.3 72.3 120 131 169 150 162 216 271 419 2169 2687 3542 4966 6293

14.9 51.8 34.2 62.9 828 193 4389 3436 1697 1738 2527 1218 940 1040 2451 255 966 20900

luted soils more than 3 meters away from road pavement were found in the range of 250 to 430 µg/kg while the average sum of PAHs in soils within 3 meters of pavement was more than 8,000 µg/kg (Johnsen et al., 2006); also in China, a study of thirty top soils in the Yangtze River Delta shows the average concentrations of 15 PAHs at 397 µg/kg, with total PAH concentrations of just two sites exceeding 1,000 µg/kg in (Ping et al., 2007). In Detroit and New Orleans, open space and foundation soil PAHs exhibit lower concentrations than soils bordering residential and busy streets, suggesting that vehicle exhaust contributes to elevated concentrations of PAHs. Furthermore, these results suggest that diffuse pollution accounts for much of the PAH concentration in open space and foundation soils where several times higher concentrations are reported than in urban studies conducted elsewhere. Comparison of PAH Distribution Between Different Census Tracts To compare PAH distributions in different locations of an urban environment, the median and average concentrations of individual and total PAHs are tabulated by city’s census tracts, as shown in Tables 4 and 5. In New Orleans, soil PAH concentrations are found to vary widely between census tracts. For example, soils in three inner city census tracts, CT58, 78, and 92, contain PAH averages of 18,628, 3,498, 10,459 µg/kg, respectively. Soils with PAHs at such levels are considered highly contaminated. However, the average PAH concentrations in three suburban census tracts (CT 17.24, 271, and 306.03) in New Orleans ranged from 819 to 881 µg/kg. Traffic density is higher in the inner city where main traffic

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CT 271 (n = 19)

CT 306.03 (n = 19)

37.7 30.8 36.0 122 149 8.7 12.2 26.0 60.2 67.4 99.0 9.9 14.4 24.2 46.9 68.1 7.2 10.5 1.3 55.9 1689 148 181 655 1045 201 42.4 53.6 134 195 3564 353 465 1440 2242 2965 368 417 1311 1865 1394 213 261 445 696 1592 164 221 517 797 2049 317 348 529 783 1023 175 192 319 491 1039 291 333 564 735 1124 314 346 404 557 1734 391 432 510 710 122 206 214 133 160 782 225 281 362 462 18628 2927 3498 7802 10459

12.3 1.2 < 1.2 1.3 107 1.3 127 82.0 25.2 35.9 74.3 2.2 13.9 1.4 4.3 4.8 3.4 539

19.5 5.1 0.4 1.8 136 5.2 158 115 49.3 65.5 91.1 31.7 27.0 35.1 35.4 4.8 35.4 819

17.2 1.2 < 1.2 1.3 81 3.3 125 109 53.9 74.9 44.7 42.3 37.5 1.4 4.3 4.8 8.0 656

16.5 2.5 2.8 2.1 97 8.2 173 143 79.4 92.5 58.9 53.5 51.0 34.7 14.3 5.2 24.4 867

18.6 1.2 5.0 1.3 126 4.1 174 116 45.7 70.5 19.0 25.4 16.7 1.4 4.3 4.8 3.4 765

27.9 3.3 7.0 8.8 133 7.4 182 145 74.4 103 52.9 48.1 37.9 24.8 5.6 5.3 7.5 881

13.1 1.2 32.4 1.3 723 164 1822 1560 1231 1082 1157 872 748 800 1100 76.4 540 11175

CT 17.24 (n = 19)

Naphthalene Acenaphthylene Acenaphthene Fluorene Phenanthrene Anthracene Fluoranthene Pyrene Benz(a)anthracene Chrysene Benzo(b)fluoranthene Benzo(k)fluoranthene Benzo(e)pyrene Benzo(a)pyrene Indeno(1,2,3-cd)pyrene Dibenz(a,h)anthracene Benzo(g,h,i)perylene Tot PAHs

CT 92 (n = 18)

Median Average Median Average Median Average Median Average Median Average Median Average

CT 78 (n = 19)

Census Tract PAHs

CT 58 (n = 13)

Table 4 New Orleans Soil PAH Concentrations (µg/kg) by Census Tracts (CT)

556 CT 1420 (n = 19)

CT 5004 (n = 12)

CT 5064 (n = 19)

CT 5103 (n = 18)

CT 5264 (n = 19)

12.6 1.1 6.6 15.6 1.2 9.5 18.5 8.9 18.8 1.5 1.3 7.1 196 183 333 47.3 44.5 73.9 958 637 865 851 506 684 398 409 532 466 347 492 549 563 805 350 369 481 407 351 491 393 364 502 546 545 911 99.2 145 173 248 264 412 5149 4410 6305

1.1 4.6 57.1 46.8 1.2 1.4 1.2 33.3 1.2 9.1 18.7 41.8 1.3 3.6 1.3 44.9 200 248 193 325 41.2 59.8 49.6 117 742 1060 609 1130 617 743 458 922 318 418 206 500 389 474 174 446 422 574 253 607 324 421 138 385 250 337 308 496 243 320 251 510 230 480 381 712 15.9 41.1 167 287 191 268 263 415 3950 5125 2990 6522

Median Average Median Average Median Average Median Average Median Average Median Average

CT 1417 (n = 19)

Naphthalene 8.9 18.5 1.1 1.4 12.2 Acenaphthylene 5.6 15.4 1.2 36.5 1.2 Acenaphthene 1.2 8.0 17.7 26.7 13.1 Fluorene 1.3 9.9 1.3 40.8 1.3 Phenanthrene 95.6 143 190 718 138 Anthracene 20.0 32.4 26.9 135 29.3 Fluoranthene 152 531 961 4285 692 Pyrene 93.2 419 752 3358 639 Benz(a)anthracene 129 343 419 1445 211 Chrysene 77.3 334 315 1454 267 Benzo(b)fluoranthene 195 454 367 2050 212 Benzo(k)fluoranthene 126 306 282 912 142 Benzo(e)pyrene 254 425 251 605 254 Benzo(a)pyrene 221 383 250 692 202 Indeno(1,2,3-cd)pyrene 226 396 178 1831 219 Dibenz(a,h)anthracene 128 179 5 70 109 Benzo(g,h,i)perylene 154 258 149 707 134 Tot PAHs 1877 3829 3306 17762 3092

Tract PAHs

Census

Table 5 Detroit Soil PAH Concentrations by Census Tracts (CT)

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thoroughfares cross than in suburban areas where vehicles of local residents account for most of the traffic. This marked difference in PAH concentrations in New Orleans soils also suggests that vehicular exhaust is the main contributor to PAHs in city soils. The difference in PAHs between the inner city and suburban communities is not as pronounced in Detroit soils. Average PAH concentrations vary from 3,829 µg/kg for outlying census tract 1417 and 6,522 µg/kg for inner city census tract 5264. The outlying census tracts for the Detroit soil samples are actually located in the small city of Pontiac, Michigan, and the community is not suburban compared to the outlying census tracts in New Orleans. The soil PAH concentrations in Pontiac census tracts are actually comparable to those found in inner city soils of New Orleans. Nevertheless, the results suggest that higher traffic density contributes PAHs to the six Detroit census tracts, resulting overall in higher PAH quantities in Detroit soils than New Orleans soils.

Relative Concentrations of Phenanthrene vs. Anthracene 6000

Phenanthrene

5000

New Orleans y = 5.3591x R2 = 0.9422

4000 3000 2000

Detroit y = 2.9701x R2 = 0.7734

1000 0 0

200

400

600

800

1000

1200

Anthracene

Relative Concentrations of Benz(a)anthracene vs. Chrysene

Benz(a)anthracene

6000 5000

Detroit y = 0.9889x 2 R = 0.9804

4000

New Orleans y = 0.8464x R2 = 0.9772

3000 2000 1000 0 0

1000

2000

3000

4000

5000

6000

7000

Chrysene

Figure 3. Relative concentrations of PAH isomers in New Orleans () and Detroit () soils. The isomer ratios are given as the slopes of the equation y = (isomer ratio)x where y represents the concentrations of phenanthrene, benz(a)anthracene, benzo(b)fluoranthene, or benzo(a)pyrene, and x represents the concentration of anthracene, chrysene, benzo(k)fluoranthene, or benzo(e)pyrene.

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G. Wang et al. Relative Concentrations of Benzo(b)fluoranthene vs. Benzo(k)fluoranthene

Benzo (b)fluoranthene

4000 3500 3000

New Orleans y = 1.5291x 2 R = 0.9722

2500

Detroit y = 1.5059x 2 R = 0.9748

2000 1500 1000 500 0 0

500

1000

1500

2000

2500

Benzo(k)fluoranthene

Relative Concentrations of Benzo(a)pyrene vs. Benzo(e)pyrene 4500

Benzo(a)pyrene

4000 3500

Detroit y = 0.9846x R2 = 0.898

3000

New Orleans y = 0.9181x R2 = 0.8864

2500 2000 1500 1000 500 0 0

1000

2000

3000

4000

5000

Benzo(e)pyrene

Figure 3. Continued

Source Analysis of PAHs in New Orleans and Detroit Soils To investigate sources of PAHs found in soils from New Orleans and Detroit, diagnostic PAH isomer ratios were calculated by plotting the isomer concentrations relative to each other and fitting for the slope of the lines to obtain the average concentration ratios. Figure 3 shows four plots where the concentration of phenanthrene, benz(a)anthracene, benzo(b)fluoranthene, and benzo(a)pyrene are plotted vs. anthracene, chrysene, benzo(k)fluoranthene, and benzo(e)pyrene, respectively. The resulting isomer ratios are summarized in Table 6. PAH isomer ratios have been used to identify different sources that contribute to the PAHs found in environmental samples (Yunker et al., 2002; Dickhut et al., 2000). Known environmental PAH sources include vehicular exhausts, coal-derived emissions, coke manufacturing, heating oil combustion, and wood burning. In urban environments such as New Orleans and Detroit, the major contributors of PAHs are most likely vehicular emission, domestic heating, and industrial emissions from using fossil fuels (i.e. petroleum and coal).


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Table 6 PAH Ratios Calculated from Average PAH Concentrations in New Orleans and Detroit Soils Samples/PAH source New Orleans soils (n = 107)a Detroit soils (n = 106)a Vehicular emissionb Catalyst equippedc Gasoline enginesd Diesel enginec Diesel engined Coal/coke ovenb Wood burningb Smeltersb

Phe/Ant

BaA/Chr

BbFL/BkFL

BaP/BeP

5.36

0.85

1.53

0.92

2.97

0.99

1.51

0.98

0.53

1.26

0.88

8.00

1.00

1.45

0.95

2.27

0.77

1.29

0.24

7.60 2.49

0.73 1.61 1.11 ± 0.06 0.79 ± 0.13 0.60 ± 0.06

1.07 1.95 3.70 ± 0.17 0.92 ± 0.16 2.69 ± 0.20

0.50 1.48 1.48 ± 00.3 1.52 ± 0.19 0.81 ± 0.04

a. This work b. Dickhut et al., 2000. c. Rogge et al., 1993. d. Khalili et al., 1995.

Characteristic isomer ratios have been reported for PAHs released from various pollution sources such as vehicular emission (Rogge et al., 1993), coke manufacturing (Dickut et al., 2000), and wood burning (Khalili et al., 1995; Rogge et al., 1998) and have been compiled by Dickhut et al. (2000). As shown in Table 6, the ratio of phenanthrene/anthracene in PAHs originating from vehicular exhaust has been reported to vary in the range of 2-8 (Rogge et al., 1993; Khalili et al., 1995). Other studies show that PAHs from pyrolytic sources typically have a phenanthrene/anthracene ratio 10 ratio indicates a dominance of petrogenic origin for the PAHs (Sicre et al., 1987; Budzinski et al., 1997; Baumard et al., 1998). The average phenanthrene/anthracene ratio calculated for both Detroit (phenanthrene/anthracene = 2.97) and New Orleans (phenanthrene/anthracene = 5.36) soil PAH thus strongly indicates vehicular emission as the dominant source. Table 6 shows other isomer concentration ratios such as benz(a)anthracene/chrysene (BaA/Chr), benzo(b)fluoranthene/benzo(k)fluoranthene (BbFL/BkFL), and benzo(a)pyrene /benzo(e)pyrene (BaP/BeP) that can also indicate pyrolytic or petrogenic origin of the PAHs (Rogge et al., 1993; Dickhut et al., 2000). The average BaA/Chr ratios were found to be 0.85 for New Orleans soils and 0.99 for Detroit samples, which are within the range for PAH data from vehicular exhaust. However, the BaA/Chr ratio in PAHs from wood burning and coke oven is not sufficiently different from PAHs emitted by fuel combustion to make it a definitive indicator for PAH origins. The BbFL/BkFL ratio varied widely in PAHs from different sources. Thus, the calculated BbFL/BkFL ratio of 1.53 for New Orleans and 1.51 for Detroit is consistent with range of BbFL/BkFL ratio found for PAHs from

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Table 7 2002 Demographic, Vehicle Travel and Fuel Consumption per Area in Detroit, MI, and New Orleans, LA

Population Metro Area Population Density Freeway DVT Arterial Street DVT Total DVT Total DVT/Area 2002 Fleet Fuel Efficiency Annual VT/Area Fuel/Day Annual Fuel Annual Fuel/Area

SI units

Detroit

New Orleans

km2 Persons/km2 km travel/day km travel/day Total km/day DVkmT/km2 km/liter km/km2 Calculated liters/day Liters/year Liters/km2

4,040,000 3678 1098 52.5 × 106 80.4 × 106 132.9 × 106 36,123 10.5 13.2 × 106 12.7 × 106 4,618.4 × 106 1,256,000

1,090,000 816 1336 9.2 × 106 13.3 × 106 22.5 × 106 27,572 10.5 10.1 × 106 2.1 × 106 782.1 × 106 958,000

DVT = Daily Vehicle Travel. VT = Vehicle Travel. Sources: TTI Urban Mobility, 2007; U.S. Department of Transportation, 2004.

vehicular exhaust (1.07 – 1.95), rather than PAHs from wood burning (0.47 – 0.92) or coke ovens (3.70). Finally, the BaP/BeP ratio for New Orleans and Detroit was 0.92 and 0.98, respectively, resembling the ratio of BaP to BeP emitted by vehicle exhaust (Rogge et al., 1993; Khalili et al., 1995; Dickhut et al., 2000). Comparison of Vehicle Travel in Detroit and New Orleans Table 7 illustrates the population, population density, vehicle travel, vehicle travel per area, calculated fuel consumption, and fuel consumption per area for Detroit and New Orleans during 2002 (TTI, 2007; U.S. DOT, 2004). Comparison of the vehicle travel and gasoline consumption per area indicates the realities behind the deposition of PAHs in the soils of Detroit and New Orleans. In 2002, annual vehicle km’s traveled per km2 was 13.2 × 106 and 10.1 × 106 , respectively, for Detroit and New Orleans, or a ratio of 1.3. Calculated annual liters of fuel consumption per km2 is 1,255,695 and 958,450 for Detroit and New Orleans, respectively, and exhibits the same ratio between the two cities. These quantities are averages for the entire city. The average total PAH concentration of Detroit soils is 7,843 µg/kg, compared to 5,100 µg/kg for New Orleans soils, with a ratio of 1.5. Thus, the vehicle travel data for the two cities are consistent with levels of PAH contamination observed in this study, providing further evidence that PAHs in Detroit and New Orleans urban soils are mainly pyrolytic in origin.

Conclusion From the concentrations of 17 PAHs in 106 soil samples from the city of Detroit and 107 soil samples from New Orleans, it was found that for both cities, soils near busy streets contained the largest PAH concentrations, followed by, in decreasing order, soils from residential street side, foundation, and open space. Overall the PAH concentrations in Detroit


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soils are about 50% higher than in New Orleans, indicating a higher level of PAH contamination in Detroit. This finding is supported by the differences of annual travel and fuel use per area, which is larger in Detroit than in New Orleans. For PAH source analysis, isomer ratios of phenanthrene/anthracene, benz(a)anthracene/chrysene, benzo(b)fluoranthene/benzo(k)fluoranthene, and benzo(a)pyrene/ benzo(e)pyrene are calculated. The ratios are characteristic of PAHs originating from pyrolytic sources such as vehicular emissions. While these diagnostic ratios of PAHs provide only qualitative information about the source contributions to PAH contamination, our results indicate that the most important source of PAHs is likely fuel combustion in vehicles. This is further supported by the general trend observed in this study of higher PAH concentrations at sampling sites near heavier traffic.

Acknowledgement Funding for the research was provided by ATSDR/MHPF through grant numbers U50/TS 473408-04 and U50/TS 473408-05 and in part by DoE through grant number DE-FC0490AL66158

References Baumard, P., Budzinski, H., and Garrigues, P. 1998. Polycyclic aromatic hydrocarbons in sediments and mussels of the western Mediterranean Sea. Environ. Toxicol. Chem. 17, 765–776. Budzinski, H., Jones, I., Bellocq, J., Pierard, C., and Garrigues, P. 1997. Evaluation of sediment contamination by polycyclic aromatic hydrocarbons in the Gironde estuary. Mar. Chem. 58, 85–97. Dickhut, R.M., Canuel, E.A., Gustafson, K.E., Liu, K., Arzayus, K.M., Walker, S.E., Edgecombe, G., Gaylor, M.O., and MacDonald, E.H. 2000. Automotive sources of carcinogenic polycyclic aromatic hydrocarbons associated with particulate matter in the Chesapeake Bay region. Environ. Sci. Technol. 34, 4635–4640. Iqbal, J., Gisclair, D., McMillin, D.J, and Portier, R.J. 2007. Aspects of petrochemical pollution in southeastern Louisiana (USA): pre-Katrina background and source characterization. Environ. Toxicol. Chem. 26, 2001–2009. Johnsen, A.R., De Lipthay, J.R., Reichenberg, F., Sorensen, S.J., Andersen, O., Christensen, P., Binderup, M., and Jacobsen, C.S. 2006. Biodegradation, bioaccessibility, and genotoxicity of diffuse polycyclic aromatic hydrocarbon (PAH) pollution at a motorway site. Environ. Sci. Technol. 40, 3293–98. Kavouras, I.G., Koutrakis, P., Tsapakis, M., Lagoudaki, E., Stephanou, E.G., Von Baer, D., and Oyola, P. 2001. Source apportionment of urban particulate aliphatic and polynuclear aromatic hydrocarbons (PAHs) using multivariate methods. Environ. Sci. Technol. 35, 2288–2294. Khalili, N.R., Scheff, P.A., and Holsen, T.M. 1995. PAH source fingerprints for coke ovens, diesel and gasoline engines, highway tunnels, and wood combustion emissions. Atmosph. Environ. 29, 533–542. Krauss, M., and Wilcke, W. 2003. Polychlorinated naphthalenes in urban soils: analysis, concentrations, and relation to other persistent organic pollutants. Environ. Pollution, 122, 75–89. Larsen, R.K. III, and Baker, J.E. 2003. Source apportionment of polycyclic aromatic hydrocarbons in the urban atmosphere: a comparison of three methods. Environ. Sci. Technol. 37, 1873–1881. Madrid, L., Diaz-Barrientos, E., and Madrid, F. 2002. Distribution of heavy metal contents of urban soils in parks of Seville. Chemosphere 49, 1301–1308. Manta, D.S., Angelone, M., Bellanca, A., Neri, R., and Sprovieri, M. 2002. Heavy metals in urban soils: a case study from the city of Palermo (Sicily), Italy. Sci. Total Environ. 300, 229–243. Mielke, H.W., Wang, G., Gonzales, C.R., Le, B., Quach, V., and Mielke, P.W. Jr. 2001. PAH and metal mixtures in New Orleans soils and sediments. Sci. Total Environ. 281, 217–227.

562

G. Wang et al.

Mielke, H.W., Gonzales, C.R., Powell, E.T., and Shah, A. 2002. Natural and anthropogenic processes that concentrate Mn in rural and urban environments of the lower Mississippi River Delta. Environ. Res., 90 (2), 157–168. Mielke, H.W., Gonzales, C., Powell, E., and Mielke P.W. Jr. 2005. Changes of multiple metal accumulation (MMA) in New Orleans soil: preliminary evaluation of differences between Survey I (1992) and Survey II (2000). Int. J. Environ. Res. Public Health, 2(2), 84–90. Murakami, M., Nakajima, F., and Furumai, H. 2005. Size- and density-distributions and sources of polycyclic aromatic hydrocarbons in urban road dust. Chemosphere. 61, 783–791. Pengchai, P., Nakajima, F., and Furumai, H. 2005. Estimation of origins of polycyclic aromatic hydrocarbons in size-fractionated road dust in Tokyo with multivariate analysis. Water Sci. Technol. 51, 169–175. Ping, L.F., Luo, Y.M., Zhang, H.B., Li, Q.B., and Wu, L.H. 2007. Distribution of polycyclic aromatic hydrocarbons in thirty typical soil profiles in the Yangtze River Delta region, east China. Environ. Pollution, 147, 358–365. Richter, B.E., Jones, B.A., Ezzell, J.L., Porter, N.L., Avdalovic, N., and Pohl, C. 1996. Accelerated solvent extraction: a technique for sample preparation. Anal. Chem. 68, 1033–1039. Rogge, W.F., Hildemann, L.M., Mazurek, M.A., and Cass, G.R. 1993. Sources of fine organic aerosol. 2. Noncatalyst and catalyst-equipped automobiles and heavy-duty diesel trucks. Environ. Sci. Technol. 27, 636–651. Rogge, W.F., Hildemann, L.M., Mazurek, M.A., and Cass, G.R 1998. Sources of fine organic aerosol. 9. Pine, oak, and synthetic log combustion in residential fireplaces. Environ. Sci. Technol. 32, 13–22. Sanders, M., Sivertsen, S., and Scott, G. 2002. Origin and distribution of polycyclic aromatic hydrocarbons in surficial sediments from the Savannah River. Arch. Environ. Contam. Toxicol. 43, 438–448. Sicre, M.A., Marty, J.C., Saliot, A., Aparicio, X., Grimalt, J., and Albaiges, J. 1987. Aliphatic and aromatic hydrocarbons in different sized aerosols over the Mediterranean Sea: occurrence and origin. Atmos. Environ. 21, 2247–2259. TTI Urban Mobility. 2007. Travel information for Detroit and New Orleans were obtained from the 2007 Annual Mobility Report. Texas Transportation Institute, Texas A & M University System, College Station, TX. http://mobility.tamu.edu/ums/congestion data/central map.stm [Accessed 15 November 2007]. Takada, H., Onda, T., Harada, M., and Ogura, N. 1991. Distribution and sources of polycyclic aromatic hydrocarbons (PAHs) in street dust from the Tokyo Metropolitan area. Sci. Total Environ. 107, 45–69. U.S. DOT. 2004. Summary of Fuel Economy Performance. Department of Transportation, Washington, DC, NHTSA, NVS-220. U.S. EPA. 1993. Provisional Guidance for Quantitative Risk Assessment of Polycyclic Aromatic Hydrocarbons, EPA/600/R-93/089. Vrana, B., Paschke, A., and Popp, P. 2001. Polyaromatic hydrocarbon concentrations and patterns in sediments and surface water of the Mansfeld region, Saxony-Anhalt, Germany. J. Environ. Monit. 3, 602–609. Wang, G., Lee, A., Lewis, M., Kamath, B., and Archer, R. 1999. Accelerated solvent extraction and gas chromatography/mass spectrometry for determination of polycyclic aromatic hydrocarbons in smoked food samples. J. Agr. Food Chem. 47, 1062–1066. Wang, G., Mielke, H.W., Quach, V., Gonzales, C., and Zhang, Q. 2004. Determination of polycyclic aromatic hydrocarbons and trace metals in New Orleans soils and sediments. Soil and Sediment Contamination, 13, 313–327. Wang, Z., Chen, J., Qiao, X., Yang, P., Tian, F., and Huang, L. 2007. Distribution and sources of polycyclic aromatic hydrocarbons from urban to rural soils: a case study in Dalian, China. Chemosphere, 68, 965–971. Ye, B., Zhang, Z., and Mao, T. 2006. Pollution sources identification of polycyclic aromatic hydrocarbons of soils in Tianjin area, China. Chemosphere 64, 525–534.


400

405

563

Yunker, M.B., Macdonald, R.W., Vingarzan, R., Mitchell, R.H., Goyette, D., and Sylvestre, S. 2002. PAHs in the Fraser River basin: a critical appraisal of PAH ratios as indicators of PAH source and composition. Org. Geochem. 33, 489–515. Zhang, X.L., Tao, S., Liu, W.X., Yang, Y., Zuo, Q., and Liu, S.Z. 2005. Source diagnostics of polycyclic aromatic hydrocarbons based on species ratios: a multimedia approach. Environ Sci Technol. 39, 9109–9114. Zuo, Q., Duan, Y.H., Yang, Y., Wang, X.J., and Tao, S. 2007. Source apportionment of polycyclic aromatic hydrocarbons in surface soil in Tianjin, China. Environ. Pollution, 147, 303–310.