Distribution, compositional pattern and sources of polycyclic aromatic hydrocarbons in urban soils of an industrial city, Lanzhou, China

Ecotoxicology and Environmental Safety 126 (2016) 154–162

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Distribution, compositional pattern and sources of polycyclic aromatic hydrocarbons in urban soils of an industrial city, Lanzhou, China Yufeng Jiang a,n, Uwamungu J. Yves a, Hang Sun a, Xuefei Hu a, Huiying Zhan b, Yingqin Wu c a

School of Environmental & Municipal Engineering, Lanzhou Jiaotong University, Lanzhou 730070, PR China Chemical Engineering College, Lanzhou University of Arts and Science, Lanzhou 730000, PR China c Key Laboratory of Petroleum Resources Research, Institute of Geology and Geophysics, Chinese Academy of Sciences, Lanzhou 730000, PR China b

art ic l e i nf o

a b s t r a c t

Article history: Received 6 September 2015 Received in revised form 24 December 2015 Accepted 28 December 2015

The level, distribution, compositional pattern and possible sources of polycyclic aromatic hydrocarbons (PAHs) in Lanzhou urban soil of Northwest China were investigated in this study. The total level of 22 PAHs ranged from 115 to 12,100 mg kg
1 and that of 16 priority PAHs from 82.4 to 10,900 mg kg
1. Seven carcinogenic PAHs generally accounted for 6.18–57.4% of total 22 PAHs. Compared with data from those reported about urban areas, PAH contamination in Lanzhou urban soils was moderate. Among different functional areas, higher level of PAHs was found along roadsides and in the industrial district (po 0.01), while lower levels were detected in the commercial, park and residential districts. The composition of PAHs was characterized by high molecular weight PAHs (Z 4 rings), among which fluoranthene, benz[a] anthracene and phenanthrene were the most dominant components. Correlation analysis suggested that low molecular weight PAHs and high molecular weight PAHs originated from different sources and further corroborated that TOC was an important factor in the accumulation of PAHs in soil. Isomer ratios and principal component analysis indicated that PAHs in urban soil derived primarily from emissions resulting from the combustion of biomass, coal and petroleum products. Toxic equivalent concentrations (BaPeq) of soil PAHs ranged from 6.12 to 1302 mg BaPeq kg
1, with a mean of 138 mg BaPeq kg
1. The results suggested that human exposure to those soils which polluted by high concentrations of PAHs through direct ingestion or inhalation of suspended soil particles probably poses a significant risk to human health from the carcinogenic effects of PAHs. & 2015 Elsevier Inc. All rights reserved.

Keywords: Polycyclic aromatic hydrocarbons Urban soil Principal component analysis BaPeq

1. Introduction Given the recent rapid worldwide urbanization, urban environments have become supremely important with regard to human health (Cheng et al., 2014). Urban areas are the most densely populated regions of the world as their industrial and economic activities attract residents, and cities have become the geographic focus of intense resource inputs, energy consumption and waste emissions, which may cause many environmental problems (Luo et al., 2012). Urban soils differ greatly from natural soils as they are more strongly influenced by anthropogenic activities (Peng et al., 2011; Argiriadis et al., 2014). In urban settings, harmful contaminants may be inadvertently released into the atmosphere and then deposited in the soil (Peng et al., 2012; Argiriadis et al., 2014). Thus, the study of urban soils has emerged as an important frontier in environmental research (Luo et al., 2012; Chen et al., 2013; Cheng et al., 2014; Jiang et al., 2014; Vane et al., 2014). Urban n

Corresponding author. E-mail address: [email protected] (Y. Jiang).

http://dx.doi.org/10.1016/j.ecoenv.2015.12.037 0147-6513/& 2015 Elsevier Inc. All rights reserved.

soils are subject to continuous accumulation of contaminants from either localized or diffuse sources (Peng et al., 2011). Typical contaminants include persistent toxic substances (PTSs), such as heavy metals (Luo et al., 2012; Cheng et al., 2014), and persistent organic pollutants (POPs) (Jiang et al., 2009; Chen et al., 2013; Vane et al., 2014). Soil quality in urban environments is of vital importance for local residents because it can affect human health and ecosystems in many different ways (Cachada et al., 2012; Chen et al., 2013). Therefore, special attention should be paid to investigation of these soils. Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous environmental pollutants, primarily derived from anthropogenic sources such as the incomplete combustion of fossil fuels, biomass and coal etc. They are now receiving extensive attention because of their high toxicity, mutagenicity and carcinogenicity with a concomitant impact on human health. PAHs are considered persistent organic pollutant (POP) candidates that merit further investigation for possible early inclusion into the Stockholm Convention on POPs (WWF, 2005). The main sources of these pollutants are industrial activities, traffic emissions and wastes derived from human activities (Argiriadis et al., 2014; Luo et al., 2015).

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155

Fig. 1. Schematic map of sampling sites in urban area of Lanzhou, NW China.

Urban soil quality may be severely affected by PAH contamination, impairing environmental and human health (Cachada et al., 2012). PAHs can remain in urban soils for a long time, which then may act as a source of further pollution in urban environments (Luo et al., 2012). The typical diffuse pattern of PAH contamination and the proximity of urban soils to humans increase the risk of human exposure through inhalation, ingestion or dermal contact (Peng et al., 2011; Cachada et al., 2012; Chen et al., 2013; Yu et al., 2014). Although there are many studies focused on urban soil pollution, the status, distribution and source of PAHs pollution are different due to different regions, sources and different latitude and longitude (Wilcke, 2007). Therefore, it is necessary to study the soil PAHs pollution in different regions and all these studies will contribute to the regional environmental pollution management and control, especially point-source control of pollution. For these reasons, recognizing the levels, distribution, sources and potential risk of PAHs in urban soils is vitally important. Given recent rapid industrialization and urbanization, environmental pollution, including urban soil pollution, has become a very important issue in China (Cheng et al., 2014). Lanzhou, a major industrial center in northwestern China, is one of the most industrialized and economically significant cities in China and has been subjected to heavy anthropogenic influences as a result of rapid economic development and urbanization. It contains many industrial segments such as petrochemical complex, smelters, steel and non-steel industries, construction material manufacturers, and chemical plants, among others. As the most densely

populated city in northwest China, Lanzhou also has heavy automobile traffic. Coal is its primary fuel source with 6.09 million tons consumption per year, accounting for 62.27% of total energy use (Niu et al., 2011). Moreover, Lanzhou is located in a valley, with typical canyon topography, sandwiched between northern and southern hills that prevent pollutant movement. Previous studies on pollutants in Lanzhou have focused on atmospheric pollutant (Ta et al., 2004; Chu et al., 2008; Pan et al., 2010; Jiang et al., 2014). Our previous study showed that the total level of the 16 US EPA priority PAHs ranged from 1240 to 10,700 mg kg-1 in street dust of Lanzhou City (Jiang et al., 2014). Several studies indicate that poor air quality causes respiratory diseases, such as asthma and lung cancer, in many people (Pan et al., 2010; Tao et al., 2012). However, there is no data on PAH pollution in Lanzhou. The purposes of this study are to: (1) determine the level and distribution of PAHs in Lanzhou urban areas, (2) elucidate the potential input sources, and (3) assess the potential risks of PAHs to residents.

2. Materials and methods 2.1. Study area description Lanzhou (35°34′20′′-37°07′07′′N, 102°35′58′′-104°34′29′′E), with a total area of 688.9 km2, is the capital of Gansu Province in northwest China. It has a North Temperate Zone continental climate, with an annual average temperature of 9.5 °C, relative

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humidity of 57% and annual rainfall of 327.7 mm. About 50% of the annual precipitation (327.7 mm) occurs from July to September. Because of the local topography, the monthly average surface wind speed is approximately 0.8 m/s (Ta et al., 2004). About 2.5 million people live in the four urban districts of Chengguan, Qilihe, Anning and Xigu. For this study the city was classified into five different functional areas representing the main roadsides and park, industrial, residential and commercial districts. Roadside samples were collected within 10 m of major highway and crossroads. Industrial soil samples were collected from greenbelt near the industrial segments such as petrochemical complex, smelters, steel and non-steel industries, construction material manufacturers, and chemical plants. Commercial area consisted of any regional landscape and public squares near commercial center. Samples included in the rest of functional areas (park and residential) were collected in the corresponding areas as their name indicated. 2.2. Soil sampling and preparation PAH pollution in urban Lanzhou was assessed using a stratified sampling strategy with a total of 62 soil samples collected in July 2012, 18 from industrial districts (A1–A18), 15 from main roadsides (B1–B15), 9 from residential areas (C1–C9), 10 from commercial districts (D1–D10) and 10 from parks (E1–E10) (Fig. 1). For each sampling site, 5 sub-samples were taken from the same area (at a depth of 0–15 cm in a 100 m2 area), and mixed thoroughly to form one composite sample. A composite surface soil sample was scooped using a pre-cleaned stainless steel scoop at each site, and each wet sample was filled in aluminum vessels. All the samples were air-dried for one week at room temperature in a storage room separated from the laboratory, sieved through a 1-mm mesh screen after removing stones and residual roots, then sealed in glass bottles and stored at
20 °C until analysis. Soil samples (each 1 g) were isolated for measurement of percentage moisture and total organic carbon (TOC). Soil moisture contents were measured by drying at 105 °C to a constant weight. After that, these samples were put into a muffle furnace for TOC detection by measuring their loss upon ignition at 550 °C. 2.3. Reagents and glassware A composite standard solution with 18 PAHs—naphthalene (Nap), 2-methylnaphthalene (2-MNa), 1-methylnaphthalene (1MNa), acenaphthylene (Acy), acenaphthene (Ace), fluorene (Fl), phenanthrene (Phe), anthracene (Ant), fluoranthene (Flu), pyrene (Pyr), benz[a]anthracene (BaA), chrysene (Chr), benzo[b]fluoranthene (BbF), benzo[k]fluoranthene (BkF), benzo[a]pyrene (BaP), indeno[1,2,3-cd]pyrene (InP), dibenz[a,h]anthracene (DBA), and benzo[g,h,i]perylene (BP)—each at a concentration of 2000 μ g mL
1 and a deuterated PAH mixture standard solution containing d8-Nap, d10-Ace, d10-Phe, d12-Chr, d12-DBA, and d12-Pyr each at a concentration of 2000 μg mL
1 were purchased from Supelco (Bellefonte, PA, USA). Individual solutions of benzo[e] pyrene (BeP), Retene (Ret), perylene (Per) and coronene (Cor) at 200 μg mL
1 were also obtained from Supelco (Bellefonte, PA, USA). A working standard solution containing 22 native PAHs and 6 deuterated PAHs was prepared with isooctane before use. Silica gel (100–200 mesh, Qingdao Haiyang Chemical Co., Shandong, China) was activated for about 16 h at 130 °C and granular anhydrous sodium sulfate was baked at 450 °C for 5 h before use. All solvents and chemicals were of analytical grade and redistilled before use. 2.4. Sample extraction, cleanup and analysis The sample extraction, cleanup and detection method is

described in our earlier reports (Jiang et al., 2011, 2014). Each sample (10 g), spiked with surrogates (deuterated PAH mixture), was mixed with 10 g anhydrous sodium sulfate and then Soxhletextracted with 200 mL of hexane/acetone (1:1 v/v) for 36 h. The extracts were concentrated by rotary vacuum evaporation and solvent-exchanged to hexane. The concentrated extracts were cleaned using silica gel column chromatography (25 cm  1 cm i. d). The glass chromatographic column, fitted with a Teflon stopcock, was packed from bottom to top with glass wool, 10 g of activated silica and 2 g of anhydrous sodium sulfate. After introduction of the extract, the first fraction eluted with 25 mL of hexane was discarded, while the second PAH-containing fraction eluted with 35 mL of n-hexane/dichloromethane (3:2 v/v) was collected. The eluate was concentrated to 1 mL and solventchanged to isooctane, and then further concentrated to 0.2 mL under a gentle stream of nitrogen before gas chromatography/ mass spectrometry (GC/MS) analysis. The PAHs were detected on an Agilent 6890 gas chromatograph-5975 mass selective detector (GC–MS) equipped with a DB5 column (30 m  0.25 mm2 i.d., 0.25 mm film thickness), using helium as the carrier gas. The oven temperature program was set as follows: initially at 60 °C with retention for 2 min, heated at 5 °C min
1 to 190 °C and then at 10 °C min
1 to 290 °C. The injector temperature was 280 °C. The MS was operated in electron impact ionization mode with electron energy of 70 eV and the mass range scanning was from 50 to 550 amu under the selected ion monitoring (SIM) mode. The ion source, quadrupole and transfer line were held at 230, 150 and 280 °C, respectively. The sample extracts (each 1 mL) were injected in the splitless mode. Individual PAHs were identified by the selected ions and by comparison of retention time between samples and the standard solution and were quantified using internal calibration. 2.5. Quality assurance/quality control The limit of detection (LOD) for individual PAHs ranged from 0.21 to 0.45 mg kg
1 with a signal-to-noise ratio of 3:1 in the blank sample (n¼ 7). The spike blanks, solvent blank and duplicate samples were analyzed each in sextuplicate, and no interferences were detected. The procedure was also checked for recovery efficiencies by analyzing uncontaminated samples spiked with PAH standards, with an average recovery (n ¼ 5) of 73–116%. In addition, the deuterated PAH surrogate standards were added to all soil samples to monitor procedural performance and matrix effects. Mean surrogate recovery ranged from 78–108%. The variation of PAHs in duplicate was less than 15%. All results were expressed on a dry weight basis. 2.6. Data analysis Statistical analyses including Pearson correlation and principal component analysis (PCA) were performed using SPSS 17.0 (SPSS Inc., USA). PAH levels were log-transformed to achieve normal distribution prior to the statistical analysis. The results revealed the experimental data to be log-normally distributed.

3. Results and discussion 3.1. Levels and distribution of PAHs in urban soil Concentrations of 22 individual PAHs and the sum of 22 PAHs (Σ22PAHs), 16 US EPA priority PAHs (Σ16PAHs) and 7 carcinogenic PAHs (Σ7CarPAHs) in soil samples from different functional areas are shown in Table 1. The 22 target PAHs were detected in all urban soil samples. Total PAH levels (Σ22PAHs) ranged from 115 to

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157

Table 1 Concentrations (mg kg
1 dry weight) of PAHs in soil from different functional groups in Lanzhou urban area (n¼ 62).

Nap 2-MNa 1-MNa Acy Ace Fl Ant Phe Flu Pyr BaA Chr BbF BkF BeP BaP InP DBA BP Cor Per Ret Σ22PAHs Σ16PAHs Σ7CarPAHs

Industrial district (n¼ 18) Min Max Mean

Roadside (n ¼15) Min Max Mean

Commercial district (n¼ 9) Min Max Mean

Park (n¼ 10) Min Max

Mean

Residential district (n¼ 10) Min Max Mean

8.80 1.51 2.22 7.89 19.7 15.3 1.82 39.9 40.4 26.8 27.9 4.52 28.2 1.49 8.94 13.7 9.78 10.7 3.35 1.70 2.35 6.29 468 391 174

7.50 0.350 0.671 3.12 15.8 18.4 16.9 123 109 78.4 67.3 3.54 80.6 2.16 17.8 35.2 18.9 20.8 5.64 0.781 3.72 8.91 765 708 317

6.72 4.54 2.09 2.21 1.74 4.77 4.31 10.8 11.4 2.29 19.5 6.83 8.09 1.43 3.13 10.6 3.62 1.48 1.21 nd 1.08 2.82 274 165 46.8

3.29 nd nd 0.242 0.413 nd 1.23 2.47 2.01 3.06 15.0 1.36 1.47 nd 1.31 3.19 0.745 0.794 1.12 nd nd 2.77 115 82.4 26.9

5.37 3.19 1.77 2.37 5.79 4.32 7.83 22.8 21.1 14.3 30.2 6.35 32.2 1.61 3.22 14.4 13.4 8.27 3.15 0.971 1.08 20.3 574 521 267

4.29 2.78 1.35 1.86 1.58 3.34 0.391 1.68 24.8 3.63 39.4 1.91 45.9 6.31 1.06 3.91 1.24 5.91 3.79 0.743 0.891 2.73 387 350 124

697 188 338 185 1320 645 420 2420 2750 2160 2250 220 557 40.9 211 265 178 195 77.9 96.3 59.6 231 11300 10900 4750

218 38.3 71.8 42.7 247 140 50.6 311 347 270 282 45.1 139 8.56 43.3 61.9 39.6 42.3 14.9 16.3 12.0 49.8 2490 2240 1550

874 195 345 849 1468 799 171 1090 1910 1570 1510 606 628 125 740 768 623 639 255 16.0 192 675 12100 10800 5610

299 54.9 101 116 347 199 63.7 416 486 372 386 96.5 213 20.5 110 138 100 106 38.4 3.11 31.1 121 3820 3370 1590

469 78.9 113 171 240 179 48.1 299 268 202 234 77.4 211 12.1 67.4 97.4 63.7 23.2 71.2 9.43 18.3 94.5 3050 2690 1040

161 56.8 43.1 35.2 48.3 39.1 16.5 85.3 81.0 54.2 84.6 23.5 61.6 2.16 15.1 33.7 21.6 10.4 13.5 2.04 3.27 36.7 1870 1540 612

10.3 7.31 4.52 9.91 24.0 10.3 35.2 50.0 76.3 96.3 89.5 26.0 171 13.2 10.8 60.5 72.3 30.3 16.0 8.03 8.11 45.0 1320 1240 598

215 133 63.0 11.2 8.03 16.8 84.4 160 282 235 316 84.1 646 143 52.5 295 176 279 26.1 21.8 4.71 252 2630 2450 1510

96.1 66.2 34.1 5.49 3.28 7.62 10.4 70.7 101 40.5 114 23.9 170 22.8 7.91 62.1 51.5 49.4 9.05 4.05 1.07 85.3 1040 954 439

nd: not detected; Σ22PAHs: sum of the detected 22 PAHs; Σ16PAHs: um of the US EPA has identified 16 PAHs as priority environmental pollutants; Σ7CarPAHs: sum of BaA, BbF, BkF, BaP, InP, Chr, and DBA.

12100 with a mean of 2590 mg kg
1; the sum of the 16 priority PAHs (Σ16PAHs) varied from 82.2 to 10900 with a mean of 2360 m g kg
1. Higher concentrations of the Σ22PAHs (4 5000 mg kg
1) were detected in soil samples at A2, A3, A5, A7, B5 and B16. These sites were located near the main crossroads (A2, A3, A5 and A7), Lanzhou Petrochemical Enterprises (B5) and Lanzhou Thermal Power Plant (B16) and were greatly affected by emissions from heavy traffic, industrial activities and coal combustion. Lower concentrations ( o500 mg kg
1) were observed in soil samples at C5, D1, D6, D7, D8, E2, E4 and E7—sites mainly collected from sparsely populated areas or outskirts, which less affected by human activities, especially traffic emission. On average, concentrations of Σ16PAHs made up 80.9% of the Σ22PAHs. The concentration of Σ7CarPAHs accounted for 6.18–57.4% of Σ22PAHs. Moreover, BaP, one of the most potent carcinogenic PAHs, varied from 3.19 to 768 mg kg
1 with a mean of 68.2 mg kg
1. The concentration of BaP in Lanzhou urban soil was higher than that in urban soil in Kumasi, Ghana (32.6 7 51.9 mg kg
1; Bortey-Sam et al., 2014). But BaP levels in this study were lower than those in urban soils in Hong Kong (34.0–1414 mg kg
1, Chung et al., 2007) and Beijing (98.4 7209 mg kg
1, Liu et al., 2011). Levels of Σ16PAHs were compared with those in other regions to evaluate the status of Lanzhou urban soil with regard to pollution (Table S1, Supplementary material). PAH concentrations in soil samples from different areas around the world vary remarkably. The concentration of Σ16PAHs in this study was higher than those in urban soils from Chiang-Mai, Thailand (Amagai et al., 1999), Tokushima, Japan (Yang et al., 2002), Kuala Lumpur, Malaysia (Omar et al., 2002), Kathmandu, Nepal (Aichner et al., 2007), Terragona, Spain (Nadal et al., 2007), three cities in Portugal (Cachada et al., 2012), two cities in Italy (Morillo et al., 2007; Orecchio, 2010), Kumasi Metropolis, Ghana (Bortey-Sam et al., 2014), Ulsan, Korea (Kwon and Choi, 2014) and Hong Kong (Chung et al., 2007), Huizhou (Ma and Zhou, 2011), Zhangjiang (Ma and Zhou, 2011) and Hangzhou (Yu et al., 2014), China. Lanzhou has a dense population with heavy traffic and various industrial plants, including smelters, steel and non-steel industries, thermal power

plants, chemical plants, and the second largest petrochemical enterprise in northwest China, all of which may contribute directly to PAH contamination. But PAH levels in Lanzhou urban soil was lower than those in urban soils in Tallinn, Estonian (Trapido, 1999), Glasgow, Scotland (Morillo et al., 2007), three cities in New England (Bradley et al., 1994), New Orleans (Wang et al., 2008) and Detroit (Wang et al., 2008), United States, Moscow, Russia (Nikiforova and Kosheleva, 2011), Bratislava, Slovakia (Musa Bandowe et al., 2011), London, England (Vane et al., 2014) and Beijing (Tang et al., 2005), Ji’nan (Dai et al., 2008), Dalian (Wang et al., 2009), Shanghai (Jiang et al., 2009) and Urumqi (Chen et al., 2013), China. Compared with the data from those reported urban areas, the level of PAHs pollution in Lanzhou urban soil is significantly lower than those in the heavy industrial cities and large cities, such as London, Detroit, Moscow, Tallinn, and Beijing, etc. However, the level of pollution is significantly higher than the non industrial cities or small cities, such as Hanzhou, Ulsan, and three cities in Portugal etc. According to these comparison results, the soil in Lanzhou urban areas is moderately contaminated by PAHs. Soil PAH levels differ significantly (p o0.01) among the five functional districts defined for the study as determined by a oneway ANOVA with a multiple comparison test. Lower levels of PAHs were found in soil samples collected from park (115–1320 m g kg
1) and residential districts (387–2630 mg kg
1) perhaps because these sampling sites are further from the city center with relatively less traffic and industrial activities than other sites and hence lower levels of PAH pollution from human activities. The highest concentration (mean of 3820 mg kg
1) was found in roadside areas, which would corroborate the hypothesis that heavy traffic in metropolitan areas is a major source of urban soil pollution (Rogge et al., 1993; Nielsen, 1996). Meanwhile, the concentration of total PAHs was influenced more by meteorological factors such as wind and rainfall, and soil samples were collected in July, as a city distributed in arid and semi-arid areas in China, the dry season could enhance the input of PAHs caused by resuspension, either mechanically or by wind, of particulate-adsorbed PAHs. Furthermore, higher PAH levels were also detected in

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the soil samples from the industrial district (468–11300 mg kg
1)— these sampling sites are located near the second largest petrochemical enterprise in northwest China. Other industries found in urban areas are also key sources of PAHs, such as smelters, steel and non-steel industries, thermal power plants and chemical plants. The spatial variation seen in this study may be accounted for by the fact that there was heavy traffic and more industrial activity in areas with high PAH pollution.

showed a high positive correlation between soil PAHs and TOC (Jiang et al., 2011). To further identify the impacts of TOC on PAH pollution, we applied a Pearson correlation to evaluate the relationship among the individual PAHs and TOC (Table S2, Supplementary material). Soil TOC varied from 1.27% to 8.13%. The correlation analysis indicated that each PAH species (except BkF) was positively correlated with TOC (0.656 Z r Z0.325, p o0.05). Similar results have been reported in previous studies (Tang et al., 2005; Dai et al., 2008; Jiang et al., 2011). This result further corroborated the hypothesis that TOC is a key soil property affecting the fate of POPs in the soil environment (Tang et al., 2005; Dai et al., 2008; Jiang et al., 2011). The correlation coefficient matrix among the individual PAHs showed that nearly all variables were significantly inter-correlated at 0.01 (Table S2, Supplementary material). However, higher correlations (r 40.6) were found for individual PAHs within two groups: compounds with low molecular weight (LMW, 2–3 rings) and compounds with high molecular weight (HMW, Z4 rings). However, the LMW PAHs (2–3 rings) did not correlate well with the HMW group, reflecting the different origins of these two groups. HMW PAHs may have originated mainly from similar sources, namely high temperature pyrolytic sources, while LMW PAHs came from different sources, such as low temperature combustion and petroleum emissions. Regarding correlations between individual PAHs, Table S2 (Supplementary material) shows that some pairs of compounds exhibited significant correlation. The strongest correlations (p o0.01) included Phe and Ant (0.961); BeP and BaP (0.931); BP and InP (0.964); BbF and BkF (0.601) and Pyr and Flu (0.933), suggesting a common source for these pairs of PAHs.

3.2. Compositional pattern of soil PAHs

3.4. Possible sources of PAHs in Lanzhou urban soil

The 22 PAHs studied were divided into three groups based on the number of aromatic rings each contained: 2- to 3-rings, 4-ring, and 5- to 7-ring PAHs. PAH proportions at all sampling sites varied as follows: 4 rings (21.7–65.9%, mean 42.1%), 2–3 rings (8.75– 69.8%, mean 37.9%), and 5- to 7-rings (5.31–55.1%, mean 19.1%) (Fig. 2). The composition and relative abundance of individual PAHs were quite similar, except for a few soil samples collected from roadside and residential areas in which levels of 2- and 3-ring PAHs were relatively higher than in other functional areas. A high percentage of low molecular weight (LMW) PAHs in soils reflects the presence of significant combustion products from low temperature pyrolytic processes, such as biomass burning (Jenkins et al., 1996), and/or petrogenic sources (Ping et al., 2007). It can also indicate recent pollution, since LMW PAHs are more biodegradable and less lipophilic and are not expected to persist or be sorbed as strongly as the high molecular weight (HMW) PAHs (Z 4 rings) (Cai et al., 2007). Generally speaking, most PAHs found in this study were HMW PAHs (Z4 rings), probably because of the higher persistence of these compounds in soils, as well as the tendency of HMW PAHs to accumulate in soils that are close to emission sources (Chung et al., 2007; Liu et al., 2011). For individual compounds, Flu, BaA and Phe were predominant and accounted for 12.5% (1.51–30.9%), 9.74% (1.96–21.4%) and 9.71% (2.11–20.4%) of Σ22PAHs respectively, followed by Nap (2.15–24.3%, mean 9.68%), Pyr (1.45–24.6%, mean 8.39%) and BbF (1.6–19.7%, mean 6.31%).

Generally, the composition patterns of PAHs derived from different sources vary significantly and their characteristic spectra are often used to identify their sources. The usefulness of PAH isomer ratios in source identification has also been extensively proved (Yunker et al., 2002; Cachada et al., 2012; Bortey-Sam et al., 2014; Jiang et al., 2014). A ratio of Ant/(Ant þPhe) o 0.1 indicates a petroleum source, while a ratio 40.1 indicates a dominance of combustion products. A ratio of Flu/(Flu þPyr) o0.4 also indicates a petroleum input source; 0.4–0.5 indicates petroleum combustion sources (especially liquid fossil fuel, vehicle and crude oil); 4 0.5 indicates sources from the combustion of biomass and coal (Yunker et al., 2002). In this study, the ratio of Ant/(Ant þPhe) was between 0.053 and 0.798 (4 of the 62 samples were less than 0.10), and the ratio of Flu/(Flu þPyr) ranged from 0.236 to 0.887 (5 of the 62 samples were less than 0.40, Fig. 3), indicating that the major source was from combustion of biomass, coal and petroleum. A InP/(InP þBP) ratio ofo 0.20 indicates a petroleum source, 40.50 combustion of biomass and coal and 0.20–0.50 liquid fossil fuel combustion (Yunker et al., 2002). A BaP/BP ratio of 40.6 suggests a source of primarily traffic emissions, while a BaP/BP ratio of o0.6 suggested no traffic emissions were involved (Pandey et al., 1999). As shown in Fig. 3, the ratio of InP/(InP þBP) was between 0.159 and 0.892 (48.4% of the 62 samples are larger than 0.50), which also implies a major source contribution from fossil fuel combustion, especially coal and petroleum combustion. Furthermore, the ratios of BaP/BP in most soil samples was greater than 0.6 (64.5% of the 62 samples are greater than 0.60), indicating that PAHs in urban soil were strongly affected by traffic emissions (Fig. 3). To further investigate possible sources of PAH pollution in Lanzhou urban soil, PCA was performed using the correlation matrix of the log-transformed PAH levels. Four principal

0.00

1.00

Park Residential Roadside Industrial Commercial

0.75

0.50

0.50

0.25

0.75

1.00 0.00

in g

5 -7

Ri

4R

ng

0.25

0.25

0.50

0.75

0.00 1.00

2-3 Ring Fig. 2. Triangular diagram of percentage concentration for the 22 PAHs in Lanzhou urban soil (n¼ 62).

3.3. Correlation analysis Persistent organic pollutants (POPs) frequently bind with soil organic matter because of their hydrophobicity so total organic content (TOC) could have an important impact on POP soil residues (Tang et al., 2005; Dai et al., 2008). Our previous study

Petroleum

0.9

Petroleum Combustion Grass/Wood/Coal Combustion

0.8

Ant/(Ant+Phe)

0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 0.0

0.2

0.4

0.6

0.8

1.0

Petroleum Grass/Wood/Coal Combustio n

Y. Jiang et al. / Ecotoxicology and Environmental Safety 126 (2016) 154–162

Flu/(Flu+Pyr) Petroleum

Petroleum Combustion

Grass/Wood/Coal Combustion Traffic source

1.4 1.2

0.8 0.6

No traffic source

BaP/BP

1.0

0.4 0.2 0.0 0.0

0.2

0.4

0.6

0.8

1.0

InP/(InP+BP) Fig. 3. Cross plot for the isomeric ratios of (a) Ant/(Ant þ Phe) vs. Flu/(Flu þPyr), and (b) BaP/BP vs. InP/(InP þBP) in Lanzhou urban soil. Table 2 Results of factor analysis with varimax rotation on PAHs in urban soil of Lanzhou, NW China. Rotated Component Matrix Component

Nap 1-MNa 2-MNa Acy Ace Fl Ant Phe Flu Pyr Ret BaA Chr BbF BkF BeP BaP InP DBA BP Per Cor Eigen value % of Variance Cumulative %

1

2

3

4

0.191 0.050 0.116 0.063 0.149 0.234 0.184 0.201 0.379 0.386 0.177 0.701 0.931 0.814 0.692 0.912 0.932 0.919 0.745 0.924 0.758 0.861 11.2 55.6 55.6

0.455 0.055 0.171 0.589 0.369 0.386 0.734 0.846 0.701 0.702 0.434 0.373 0.263 0.177 0.108 0.254 0.291 0.311 0.239 0.308 0.092
0.018 3.68 16.7 72.3

0.501 0.838 0.756 0.549 0.644 0.612 0.156 0.176 0.133 0.150 0.131 0.079 0.170 0.225 0.124 0.104 0.155 0.172 0.103 0.160
0.030 0.121 2.55 11.6 83.9

0.238 0.177 0.122 0.007
0.023 0.020 0.167 0.142 0.140 0.072 0.789 0.154 0.102 0.274 0.161 0.223
0.041 0.027 0.169 0.036 0.434 0.053 1.25 5.67 89.5

components PC1, PC2, PC3 and PC4 with eigenvalue 41 were extracted and explained 55.6%, 16.7%, 11.6% and 5.67% (89.5% in total) of the total variance in urban soil, respectively (High loading variables are presented with bold numbers in Table 2). PC1 was characterized by high loadings of PAHs with five to six

159

rings. BaA, Chr, BeP, and BaP are markers of coal combustion (Simcik et al., 1999; Larsen and Baker, 2003), while BbF and BkF are markers of fossil fuel combustion (Rogge et al., 1993). BaA and Chr often result from the combustion of both diesel and natural gas (Rogge et al., 1993; Khalili et al., 1995). InP, BP, BeP and BaP are associated with fossil fuel combustion (Sadiktsis et al., 2012). Per also originates from combustion sources (Silliman et al., 1998). Cor is a marker for high temperature combustion and traffic emissions (Nielsen, 1996). Lanzhou’s energy consumption relies heavily on coal; like many other cities in northern China, coal is heavily used for home heating in the 5-month winter. The large amount of coal consumption in both industrial and domestic sectors makes it the primary contributor of PAHs in the local environment. Lanzhou is a densely populated city with heavy automobile traffic and a large petrochemical complex, and thus petroleum combustion is also a major contributor of PAH pollution. In fact, coal and petroleum contributed 38.0% and 60.7% of the total fossil fuel consumption of Lanzhou, respectively (Niu et al., 2011). Thus, PC1 reflected the contribution of fossil fuel combustion to the origin of PAHs. PC2 was loaded by Nap, Acy, Phe, Ant, Flu and Pyr (Table 2), which are markers of the coking process of industrial manufacturing in China (Mu et al., 2013). Ace, Acy and Fl indicate a coke oven origin and accounted for the majority of the mass from coke ovens (Khalili et al., 1995; Simcik et al., 1999). Flu and Phe are also indicators for coking sources (Simcik et al., 1999). Coke ovens are operated in the non-ferrous industrial complex in Lanzhou so the sampling sites near this complex could be contaminated by coke oven gas as well as coke fly ash. Thus, PC2 can be considered an indicator of coking industry emissions. PC3 was loaded by Nap, Ace, Acy, Fl, 1-MNa and 2-MNa (Table 2). Alkylate PAHs and LMW PAHs are usually emitted from petroleum and its byproducts as well as purified oil products (Steinhauer and Boehm, 1992). Among them, Ace, Acy and Fl accounted for most of the mass in highway tunnel and gasoline engine samples (Duval and Friedlander, 1981; Khalili et al., 1995; Simcik et al., 1999). Nap and Alkylate Nap are associated with unburned fossil fuel-derived PAHs (Yunker et al., 2002): Lanzhou Petrochemical Enterprises is the biggest oil refinery and petrochemical plant in northwest China. Due to its river valley location and an industrial structure dominated by the petrochemical industry, pollution in Lanzhou has had the dubious distinction of being most severe in the recent half century (Niu et al., 2011) and likely accounts for PAHs of petroleum origin. PC4 contributed 5.67% of the total variance and showed high concentrations of retene, an indicator of wood burning (Ramdahl, 1983). Factor 4 was selected to represent wood burning sources of urban soil PAHs in Lanzhou. The PCA results, in combination with diagnostic ratios, suggested that coal and petroleum combustion were probably the main sources of urban soil PAHs in Lanzhou, based on PAH source fingerprints reported in the international literature. 3.5. Comparison with soil criteria or guidance Some environmental criteria or guidance for PAHs in soil were released by the Netherlands’ Ministry of Housing, Spatial Planning, and the Environment (Ministry of Housing Spatial Planning and Environment, 2000), the Danish Environmental Protection Agency (EPA) (DEPA, 2002), and the Canadian Council of Ministers of the Environment (CCME, 2010), for assessing risk at contaminated sites, setting clean-up goals and monitoring remediation efforts. Data from this study was compared with the standards set in the Netherlands (1000 mg kg
1, sum of 10 PAHs including NaP, Phe, Ant, Flu, BaA, Chr, BkF, BaP, InP and BP, Chung et al., 2007) and soil quality criteria recommended by the Danish EPA (1500 mg kg
1 of sum of Flu, B(b þk)F, BaP, DBA and, InP, DEPA 2002). Twenty one of

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62 (33.8%) soil samples were above the target value set in the Netherlands guidelines; 10 out of 62 (16%) samples had levels exceeding the Danish guidelines (100 mg kg
1 of BaP and DBA respectively); 11.3% were above the guideline values for soil quality criteria, based on both chronic and ecotoxicological effects, recommended by the Danish EPA (DEPA, 2002). The most contaminated samples, with levels above the guideline values, were collected in the roadside and industrial districts. Guideline values of 9 PAHs (including Nap, Phe, Pyr, BaA, BbF, BkF, BaP, InP and DBA) in soil for different land uses (e.g., residential/park, commercial and industrial areas) were proposed by the CCME (CCME, 2010). No PAH guideline values for roadside soil were available, so the guideline values for park/residential area soil was used. For individual compounds, only BaA and Pyr had high concentrations based on the target value; these were measured at three sampling sites collected from roadside, park/residential and commercial areas. The most contaminated samples were collected at A8 (Pyr 1570 mg kg
1 and BaA 1510 mg kg
1), B3 (Pyr 1290 mg kg
1 and BaA 1180 mg kg
1) and B15 (Pyr 1320 mg kg
1 and BaA 1290 m g kg
1), all of which greatly exceeded the recommended Canadian limits for both residential and general use. Thus, human exposure to these PAHs polluted soil particles through direct ingestion or inhalation into the body over a long period probably poses an adverse health effect to human health from the carcinogenic effects of PAHs. 3.6. Risk assessment of PAHs in urban soil PAHs are of great concern due to their documented carcinogenicity and endocrine disruptive activity (Davis et al., 1993). To

compare and quantify the toxic potency of soil samples, toxic equivalence factors (TEFs) are used to calculate toxic equivalent concentrations (BaPeq) of soil PAHs. The carcinogenic potency of PAHs was estimated by the total BaPeq (sum of 7 carcinogenic PAH BaPeq, 16 PAH BaPeq and 20 PAH BaPeq). In this study, the total BaPeq of 20 PAHs in soil samples ranged from 6.12 to 1302 m g BaPeq kg
1, with a mean of 138 mg BaPeq kg
1. The total BaPeq of 7 carcinogenic PAHs was approximately that of 22 PAHs and 16 PAHs (Table 3), suggesting that 7 carcinogenic PAHs were the primary contributors to the total carcinogenic potency of PAHs in the soil samples. The contribution of different PAHs to the total BaPeq decreased in the following order: BaP (59.5%) 4DBA (16.0%) 4 BbF (11.0%) 4InP (5.7%) 4BaA (4.3%) 4Chr (2.2%). The total BaPeq of 16 PAHs in Lanzhou urban soil was lower than that in urban soil in Shanghai, China (424 mg BaPeq kg
1, Jiang et al., 2009), Palermo, Italy (151–4291 mg BaPeq kg
1, Orecchio, 2010), Lisbon, Portugal (229 mg BaPeq kg
1, Orecchio, 2010) and Sydney, Australia (440 mg BaPeq kg
1, Nguyen et al., 2014), but higher than that in Kumasi, Ghana (1.24–188 mg BaPeq kg
1, Bortey-Sam et al., 2014), Viseu, Portugal (229 mg BaPeq kg
1, Orecchio, 2010) and Terragona, Spain (124 mg BaPeq kg
1, Nadal et al., 2004). But, Canadian Soil Quality Guidelines for commonly occurring parent PAHs for the protection of environmental and human health provide PAH guidelines based on the PAHs’ carcinogenic effects (CCME, 2010). These guidelines indicate a safe BaPeq value of 600 m g kg
1 based on an incremental life time cancer risk of 10
6 (The incremental lifetime cancer risk (ILCR) was adopted to quantitatively estimate the exposure risk for environmental PAHs based on the U.S. EPA standard models, US EPA, 1991, 1993) for eight carcinogenic PAHs including BaA, BaP, BbF, BkF, Chr, DBA, InP and BP.

Table 3 Total toxic equivalent concentrations of PAHs (mg BaPeq kg
1) in urban soil of Lanzhou, NW China. Compound

Nap 2-MNa 2-MNa Acy Ace Fl Ant Phe Flu Pyr BaA Ret Chr BbF BkF BaP BeP Per InP BP DBA Cor ∑CarPAHsf ∑16PAHsg ∑20PAHsh a

TEFa

0.001 – 0.001 0.001 0.001 0.001 0.01 0.001 0.001 0.001 0.1 – 0.01 0.1 0.1 1 0.01 0.001 0.1 0.01 1 0.001 – – –

Carcinogenic groupb

2B – 3 3 3 3 3 3 3 3 2B – 2B 2B 2B 1 3 3 2B 3 2A – – – –

Target valuesc (mg kg
1)

5000 – – – – – – 5000 – 1000 1000 – – 1000 1000 1000 – – 1000 – 1000 – – – –

BaPeqd (mg BaPeq kg
1) Mean

SDe

Min

Max

0.184 – 0.0483 0.0494 0.169 0.0974 0.0355 2.18 0.249 0.185 21.0 – 0.446 13.2 1.13 68.2 0.432 0.0119 4.89 0.419 23.7 0.00657 132 136 138

0.206 – 0.0412 0.120 0.291 0.155 0.0629 3.73 0.465 0.371 37.4 – 0.872 15.2 2.54 113 1.02 0.0273 8.67 0.899 48.1 0.0151 201 205 206

7.51E
4 – nd 1.40E
4 2.33E
4 4.11E
4 nd 0.00351 0.00201 0.00229 1.50 – 0.0068 0.147 nd 0.183 nd nd 0.319 0.00212 0.485 nd 5.47 5.93 6.12

0.874 – 0.195 0.850 1.47 0.799 0.421 24.2 2.75 2.16 225 – 6.06 64.7 14.3 768 7.39 0.192 62.3 6.39 279 0.0963 1270 1290 1300

TEF: Toxic equivalence factors ( data from Nisbet and LaGoy, 1992, USEPA, 1991, Collins et al., 1998, Malcolm and Dobson, 1994, USEPA, 1993, and Tsai et al., 2004). 1: cacinogenic to humans; 2A: probably carcinogenic to humans; 2B: possibly carcinogenic to humans; 3: not classifiable as to its carcinogenicity to humans; D: inadequate information to assess carcinogenic potential. c Target values represent criteria for residential/parkland uses imposed by CCME (2010). d BaPeq: Toxic equivalent data based on TEF value of individual PAHs. e SD ¼ Standard deviation. f Σ7CarPAHs: Sum of BaA, BbF, BkF, BaP, InP, Chr, and DBA. g Σ16PAHs: Sum of the US EPA has identified 16 PAHs as priority environmental pollutants. h Σ20PAHs: Sum of the individual detected PAHs. b

Y. Jiang et al. / Ecotoxicology and Environmental Safety 126 (2016) 154–162

The BaPeq of eight carcinogenic PAHs for urban soil samples in Lanzhou had a range of 5.64 mg BaPeq kg
1 to 1318 mg BaPeq kg
1, with a mean value of 133 mg BaPeq kg
1. Among 62 urban soil samples, 16 had concentrations above the safe value (600 m g BaPeq kg
1). Therefore, special attention should be paid to these sampling sites owing to potential risk to human health through direct or indirect contact with these soils.

4. Conclusions Polycyclic aromatic hydrocarbons (PAH) in soil samples from the urban area of Lanzhou were analyzed together with total organic carbon (TOC), as well as some PAH source diagnostic ratios and principal component analysis (PCA). The total levels of the sum of 16 EPA priority PAHs and 22 analyzed PAHs ranged from 82.4 to 10900 mg kg
1 and from 115 to 12,100 mg kg
1, respectively. PAH contamination in Lanzhou urban soils is moderate compared with other cities around the world. Among different functional areas, the highest levels of PAHs were found in roadside and industrial districts, and the lowest concentrations were detected in residential, commercial and park districts. Generally, PAHs were dominated by higher molecular weight PAH (Z4 rings) homologues, which accounted for about 62.1% of total PAHs in urban soil, the dominant components being Flu, BaA and Phe. Correlation analysis suggested that TOC affected the accumulation of PAHs in urban soil. Specific isomer ratios and PCA indicated that PAHs in the study areas were derived primarily from combustion, especially coal and petroleum combustion. The carcinogenic potency of PAH compounds in Lanzhou urban soil were found to be insignificant at present levels. However, human exposure to those soils which polluted by high concentrations of PAHs through direct ingestion or inhalation of suspended soil particles poses an adverse health effect to human health from the carcinogenic effects of PAHs.

Acknowledgments This work was financially supported by the National Natural Science Foundation of China (41363008) and the National Natural Science Foundation of China (21067005).

Appendix A. Supplementary material Supplementary data associated with this article can be found in the online version at http://dx.doi.org/10.1016/j.ecoenv.2015.12. 037.

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