Status, source and health risk assessment of polycyclic aromatichydrocarbons in street dust of an industrial city, NW China

Yufeng Jiang a,n, Xuefei Hu a, Uwamungu J. Yves a, Huiying Zhan b, Yingqin Wu c

a School of Environmental & Municipal Engineering, Lanzhou Jiaotong University, Lanzhou 730070, PR Chinab Chemical Engineering College, Gansu Lianhe University, Lanzhou 730000, PR Chinac Key Laboratory of Petroleum Resources Research, Institute of Geology and Geophysics, Chinese Academy of Sciences, Lanzhou 730000, PR China

a r t i c l e i n f o

Article history:Received 18 March 2014Received in revised form19 April 2014Accepted 21 April 2014

Keywords:Polycyclic aromatic hydrocarbonsStreet dustPrincipal component analysisHealth risk assessment

a b s t r a c t

The status, source and health risk of street-dust-borne polycyclic aromatic hydrocarbons (PAHs) inLanzhou of Northwest China were investigated. The total level of the 21 PAHs ranged from 1470 to13,700 mg kg�1 and that of the 16 priority PAHs from 1240 to 10,700 mg kg�1. Higher levels of PAHs weremainly distributed in the Chengguan and Qilihe districts at Lanzhou central areas, and the lower levelswere in Anning and Xigu districts. The level of seven potential carcinogenic PAHs generally accounted for35–40 percent of total PAHs, and the PAHs contained two to four rings, mainly phenanthrene, benzo[b]fluoranthene and fluoranthene. The total level of PAHs increased with the decreasing particle size in thestreet dust. The correlation analysis suggested that the total organic carbon (TOC) was only slightlyaffected the PAH accumulation in street dust. The isomer ratios and principal component analysisindicated that the dust-borne PAHs in the dust were derived primarily from the combustion of biomass,coal and petroleum emission. The toxic equivalent concentrations (BaPeq) of dust-borne PAHs rangedfrom 115 to 827 mg BaPeq kg�1, with a mean of 300 mg BaPeq kg�1. The 95 percent upper confidence limitof Incremental Lifetime Cancer Risk due to human exposure to urban surface dust-borne PAHs inLanzhou urban area was 2.031�10�6 for children and 1.935�10�6 for adults.

& 2014 Elsevier Inc. All rights reserved.

1. Introduction

Polycyclic aromatic hydrocarbons (PAHs) as ubiquitous environ-mental pollutants primarily result from the incomplete combustionof predominant anthropogenic sources, especially fossil fuel, biomass,and coal. PAHs are receiving extensive attention because of theiradverse effects on human health including high toxicity, mutageni-city and carcinogenicity. Sixteen parent PAHs have been identifiedby the United States Environment Protection Agency (US EPA) aspriority pollutants, and among them, the potential carcinogenic PAHsinclude benzo[a]anthracene, chrysene, benzo[b]fluoranthene, benzo[a]pyrene, benzo[k]fluoranthene, indeno[1,2,3-cd]pyrene and dibenz[a,h]anthracene. Furthermore, PAHs are considered as persistent organicpollutant (POP) candidates that merit further investigation forpossible early inclusion into the Stockholm Convention on POPs(World Wide Found (WWF), 2005). Therefore, PAHs pollution hasattracted growing attention recently, and numerous investigationsshow that PAHs are ubiquitous in various environmental media

(Chung et al., 2007; Jiang et al., 2009; Lorenzi et al., 2011; Choiet al., 2012; Krugly et al., 2014).

Street dust in urban areas is an indicator of toxic pollutantsdeposited from the atmosphere (Tsai et al., 2004; Wu et al., 2005;Wang et al., 2011). Street dust consists of vehicle exhaust, air-borne sinking particles in air, house dust, soil dust and air- andwind-borne aerosols (Liu et al., 2007; Martuzevicius et al., 2011;Choi et al., 2012), and significantly contributes to urban pollution.PAHs can accumulate in street dust via atmospheric deposition bysedimentation interception and may threaten human health ifreaching the levels of toxic pollutants (Dong and Lee, 2009;Lorenzi et al., 2011; Wang et al., 2011; Choi et al., 2012). Thetightly-packed buildings along with the urban expansion limit aircirculation and thus lead to enhanced PAHs accumulation in streetdust (Kong et al., 2012; Li et al., 2014). Multiple-source materialsespecially pyrogenic and petrogenic sources contribute to PAHaccumulation in street dust. Street dust which contains a complexmixture of petrogenic and pyrogenic PAHs is a key non-pointsource of PAHs (Boonyatumanond et al., 2007; Liu et al., 2007). ThePAH-polluted street dust presents higher health risk to childrenand adults compared with automobile emissions (Wang et al.,2011; Krugly et al., 2014). Street dust is chemically similar to theprimary portion of atmospheric aerosols in some respects, and is

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Ecotoxicology and Environmental Safety

http://dx.doi.org/10.1016/j.ecoenv.2014.04.0310147-6513/& 2014 Elsevier Inc. All rights reserved.

n Corresponding author. Fax: þ86 931 4956017.E-mail address: Jiangyf7712@126.com (Y. Jiang).

Ecotoxicology and Environmental Safety 106 (2014) 11–18

indeed dynamically related to atmospheric aerosols throughre-suspension into and re-deposition from the atmosphere (Roggeet al., 1993; Liu et al., 2007; Li et al., 2014). However, there are fewstudies about PAHs in street dusts.

Lanzhou as a rapidly developing city was chosen in this study,because this region is considered as a major work place in thenorthwestern China. Lanzhou contains many workplace segmentssuch as petrochemical complex, smelters, steel and non-steelindustries, construction materials, and chemical plants, etc. Lanz-hou with heavy automobile traffics and large petroleum plants isalso one densely-populated large city in northwest China. Themain fuel in its energy consumption structure is coal, causingserious air pollution in this area. Moreover, Lanzhou is located in avalley with a typical Canyon topography between the northernand southern hills, and thus the specific topography there resem-bles that of a mountain-surrounded valley that traps the dirty airwithin. As a result, the poor air quality in the Lanzhou due to thehigh-level total suspended particles (TSP) and photochemicalsmog (Tang et al., 1985; Jiang et al., 2001; Ta et al., 2004; Gaoet al., 2007; Chu et al., 2008) results in frequent occurrence ofrespiratory diseases, such as asthma and lung cancer (Gao et al.,2007; Pan et al., 2010; Tao et al., 2012; Chen et al., 2013). However,little is known about the PAH pollution in street dust of Lanzhou.The purposes of the present study are to: (1) determine the leveland distribution of PAHs pollution, (2) elucidate the potentialinput sources, and (3) assess the potential health risks of PAHs inLanzhou urban street dust.

2. Materials and methods

2.1. Sampling area description

Lanzhou (35134020″–37107007″N, 102135058″–104134029″E) with a total area of688.9 km2 is the capital of Gansu Province in Northwest China. It has a continentalclimate of the North Temperate Zone, with an annual average temperature of 9.5 1C,relative humidity of 57 percent, and annual rainfall of 327.7 mm. About 50 percentof the annual precipitation (327.7 mm) is centralized during the July-Septemberperiod. Under the topographic effects, the monthly average of the surface windspeed is approximately 0.8 m/s (Ta et al., 2004). About 2.5 million people live in thefour urban districts, including Chengguan district (CG), Qilihe district (QLH), Anningdistrict (AN), and Xigu district (XG). Among them, both Chengguan district andQilihe district have longer history of living and lager population of inhabitants. Theaverage traffic volumes in Chengguan and Qilihe are 2600 and 2333 vehicles per24 h, respectively. Chengguan is a residential-commercial mixed centre of Lanzhou.Anning developed as a suburban area in recent years, with an average trafficvolume of 1206 vehicles per 24 h. Xigu has been an industrial estate of organicpollution for decades (Tang et al., 1985), with an average traffic volume of 1633vehicles per 24 h.

2.2. Dust sampling and preparation

The PAH pollution in urban Lanzhou was assessed using a stratified samplingstrategy and a total of 32 street dust samples were collected in October 2011. Thesampling sites covered the four urban districts, including Chengguang: CG1–CG8,Anning: AN1–AN8, Qilihe: QLH1–QLH8, and Xigu: XG1–XG8 (Fig. 1). At each site,street dusts were collected fromwithin 2 m2 on the road, using polyethylene brush,tray and containers, and samples were collected in polyethylene containers. Thesamples collected at AN2, AN4, CG1, CG5, QLH3, QLH5, XG1 and XG8 were selectedrandomly and divided into four categories depending on particle size measured bylaboratory test sieves: o100 mm, 101–500 mm, 501–1000 mm, and 41000 mm. Thesamples were air-dried at room temperature and crushed after removing stones topass a 100-mesh sieve, and then stored in a refrigerator until analysis. Dust samples(each 1 g) were isolated for measurement of percentage moisture and total organiccarbon (TOC). Dust moisture contents were measured by drying at 105 1C to aconstant weight. After that, these samples were put into a muffle furnace for TOCdetection by measuring their loss upon ignition at 550 1C.

2.3. Reagents and glassware

A composite standard solution with 18 PAHs including naphthalene (Nap),2-methylnaphthalene (2-MNa), 1-methylnaphthalene (1-MNa), 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 of2000 μg mL�1, and a deuterated PAHmixture 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 alsoobtained from Supelco (Bellefonte, PA, USA). A working standard solution containing 21native PAHs and 6 deuterated PAHs was prepared with isooctane before use. Silica gel(100–200 mesh, Qingdao Haiyang Chemical Co., Shandong, China) was activated forabout 16 h at 130 1C and granular anhydrous sodium sulfate was baked at 450 1C for 5 hbefore use. All solvents and chemicals were of analytical grade and redistilled before use.

2.4. Sample extraction, cleanup and analysis

Each sample (10 g) spiked with surrogates (d8-Nap, d10-Acy, d10-Phe, d12-Chr,d12-Pyr and d12-DBA) was mixed with 10 g of anhydrous sodium sulfate and thenSoxhlet-extracted with 200 mL of hexane/acetone (1:1 v/v) for 36 h. The extractswere concentrated by rotary vacuum evaporation and solvent-exchanged tohexane. The concentrated extracts were cleaned up by a silica gel columnchromatography (25 cm�1 cm i.d). The glass chromatographic column, fitted witha Teflon stopcock, was packed from bottom to top with glass wool, 10 g of activatedsilica, and 2 g of anhydrous sodium sulfate. After introduction of the extract, thefirst 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) wascollected. The eluate was concentrated to 1 mL and solvent-changed to isooctane,and then further concentrated to 0.2 mL under a gentle stream of nitrogen beforegas chromatography/mass spectrometry (GC/MS) analysis.

The PAHs were detected on an Agilent 6890 gas chromatograph-5975 massselective detector (GC–MS) equipped with a DB-5 column (30 m�0.25 mm i.d.,0.25 mm film thickness), using helium as the carrier gas. The oven temperatureprogram was set as follows: initially at 60 1C with retention for 2 min, heated at5 1C min�1 to 190 1C, and then at 10 1C min�1 to 290 1C. The injector temperaturewas 280 1C. The MS was operated in the electron impact ionization mode withelectron energy of 70 eV and the mass range scanning was from 50 to 550 amuunder the selected ion monitoring (SIM) mode. The ion source, quadrupole andtransfer line were held at 230, 150 and 280 1C, respectively. The sample extracts(each 1 mL) were injected in the splitless mode. The individual PAHs were identifiedon basis of the selected ions and comparison of retention time between samplesand the standard solution. The individual PAHs were quantified using internalcalibration.

2.5. Risk assessment

The exposure risk of environmental PAHs was quantified using incrementallifetime cancer risk (ILCR) based on the U.S. EPA standard models (US EPA, 1991;Chen and Liao, 2006; Peng et al., 2011; Wang et al., 2011). The ILCRs in terms ofingestion, dermal contact and inhalation after exposure to urban surface dust-borne PAHs in different areas of Lanzhou were calculated as follows:

ILCRsIngestion ¼CS�ðCSFIngestion�

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiBW=70ð Þ3

p�IRIngestion�EF�ED

BW�AT�106

ILCRsDermal ¼CS� ðCSFDermal �

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiBW=70� �

3q

Þ � SA � AF� ABS� EF � ED

BW � AT � PEF

ILCRsInhalation ¼CS� ðCSFInhalation �

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiBW=70� �

3q

Þ � IRInhalation � EF � ED

BW� AT� PEF

where CS is the sum of converted PAH levels based on toxic equivalents of BaPusing the toxic equivalency factor (TEF). CSF is carcinogenic slope factor(mg kg�1 day�1)�1, BW is body weight (kg), AT is the average life span (years),EF is the exposure frequency (day year�1), ED is the exposure duration (years),IRInhalation is the inhalation rate (m3 day�1), IRIngestion is the soil intake rate(mg day�1), SA is the dermal surface exposure (cm2), AF is the dermal adherence factor(mg cm�2 h�1), ABS is the dermal adsorption fraction, and PEF is the particle emissionfactor (m3 kg�1). PEF is particle emission factor (m3 kg�1); CSFingestion, CSFDermal andCSFInhalation of BaP were addressed as 7.3, 25, and 3.85 (mg kg�1 day�1)�1, respectively,determined by the cancer-causing ability of BaP (Peng et al., 2011). All the parametersused in these models for children (1 to 6 years old) and adults (7 to 31 years old) werebased on the Risk Assessment Guidance of U.S. EPA and related publications (US EPA,1991; Wang et al., 2011).

2.6. Quality assurance/quality control

The limit of detection (LOD) for individual PAHs ranged from 0.15 to0.41 mg kg�1 with a signal-to-noise ratio of 3:1 in the blank sample (n¼7).The spike blanks, solvent blank and duplicate samples were analyzed each insextuplicate, and no interferences were detected. The procedure was also checked

Y. Jiang et al. / Ecotoxicology and Environmental Safety 106 (2014) 11–1812

for recovery efficiencies by analyzing uncontaminated samples spiked with PAHstandards, with the average recovery (n¼5) of 76 percent to 107 percent. Inaddition, the deuterated PAHs surrogate standards were added to all dust samplesto monitor procedural performance and matrix effects. The mean recoveries ofsurrogates ranged from 69 percent to 112 percent. The variation of PAHs induplicate was less than 15 percent. All results were expressed on dry weight basis.

2.7. Data analysis

Statistical analyses including Pearson correlation and principal component analy-sis (PCA) were performed using SPSS 17.0 (SPSS Inc., USA). The levels of PAHswere log-transformed to achieve normal distribution prior to the statistical analyses conducted.The results revealed the experimental data to be log-normally distributed.

3. Results and discussion

3.1. Levels and distribution of PAHs in street dust

The descriptive statistical of PAHs levels in Lanzhou street dustsare showed in Table 1. The total PAHs levels (Σ21PAHs) were in arange of 1470–13,700 mg kg�1 with a mean of 4630 mg kg�1, andthe sum of the 16 priority PAHs (Σ16PAHs) varied from 1240 to10,700 mg kg�1 with a mean of 3900 mg kg�1. The PAHs levels indust samples significantly varied around the world. The Σ21PAHsin this study was higher compared with urban Bangkok in Thai-land (1.1070.801 mg g�1, Boonyatumanond et al., 2007), GreaterCairo in Egypt (0.045–2.60 mg g�1, Hassanien and Abdel-Latif,2008), and Xincheng of China (1.63–8.99 mg g�1, Zhao et al.,2009). The PAH pollution level was compared to those fromGuangzhou (0.841–12.3 mg g�1, Wang et al., 2011) and Dalian(1.89–17.1 mg g�1, Wan et al., 2006) in China. But PAH pollutionlevel in urban Lanzhou street dust was lower compared withurban Birmingham in UK (12.6–93.7 mg g�1, Smith et al., 1995),northeast England (0.600–46.0 mg g�1, Lorenzi et al., 2011), Ulsanin South Korea (45.8–112 mg g�1, Dong and Lee, 2009), Beijing(0.72–40.5 mg g�1, Zhang et al., 2008) and Shanghai (9.76–32.6 mg g�1, Liu et al., 2007). Compared with these urban areas,

the PAH pollution level in Lanzhou was lower than the globallyreported data in street dust. The total level of seven carcinogenicPAHs (ΣCar-PAHs) ranged from 628 to 4640 (mean 1680) mg kg�1,accounting for 35–40 percent of Σ21PAHs. Among the carcinogenicPAHs, BbF, Flu and BaP were the most abundant in dust samples.BaP was detected in all samples at level of 20.1 to 373 (mean120) mg kg�1. The higher levels of BaP (4100 mg kg�1) weredetected at Qilihe and Chengguan, indicating that the heavytraffics and human activities remarkably contributed to the highlevels in these sampling sites where several main highways andcommercial centre are situated.

The road dust PAH pollution levels are slightly different amongthe four districts in Lanzhou (Fig. S1, Supplementary material). Thelower levels of PAHs were observed in Anning (1470–6710 mg kg�1) and Xigu (1570–6140 mg kg�1). The reason may bethat Anning as an intensive cultural and educational area is faraway from the city center and it has relatively small traffictransport and private car occupancy, which indicate less sourcecontribution of PAH pollution from human activities. Xigu as theindustry-intensive area is located with the largest petrochemicalenterprises in Northwest China. In addition, some industries arekey sources of PAHs, such as smelters, steel and non-steelindustries, thermal power plants, and chemical plants. However,the results about PAH levels in the road dust of Xigu were not highas expected, probably because Xigu is located in the upwind ofLanzhou, the polluted particles were rapidly transferred by windto other districts, but the transfer mechanism should be furtherstudied. Qilihe as the national trade and rail transportation huband a rapidly developing area has a higher level of PAH pollutionin street dust (2050–9420 mg kg�1). The reason may be that thedomain of urbanization with more emission sources, such asincreasing traffic and prosperous population, contributed to PAHpollution in Qilihe. The highest PAH level was detected in the dustsamples from Chengguan (2090–13,700 mg kg�1), which is thecommercial-residential mixed zone, and the financial, politicaland trade center in Lanzhou with high population density and

Fig. 1. Schematic map of street dust sampling sites in the urban area of Lanzhou.

Y. Jiang et al. / Ecotoxicology and Environmental Safety 106 (2014) 11–18 13

heavy traffic volume. Chengguan is distributed in the downwind ofLanzhou which is located in a valley between northern andsouthern hills. However, west and north-west winds prevail inLanzhou. This Canyon topography prevents the transfer of pollu-tants out of Lanzhou. Therefore, the combination of heavy trafficemission and specific topography greatly increased the contents ofPAHs in Chengguan.

3.2. Compositional pattern of dust PAHs

According to the number of aromatic rings, the 21 PAHs weredivided into three groups, representing 2- to 3-ring, 4-ring, and5- to 7-ring PAHs. The proportions of PAHs at all sampling siteschanged in the order as: 2–3 rings (20.6–57.4 percent), 4 rings(25.4–41.5 percent), and 5- to 7-rings (17.5–51.4 percent) (Fig. 2).However, the proportions of 2–3 rings PAHs were relatively higherin Qilihe and Anning, and four sampling sites are in the downwindmuch closer to major petroleum industrial plants, indicating thatPAHs in these areas probably originated from atmospheric deposi-tion. Interestingly, relative contents of high-molecular-weight(HMW) PAHs at Chengguan and Xigu were the highest, with morethan 50 percent of Σ21PAHs, probably related with the heavytraffic source and coal combustion there. For individual com-pounds, Phe, BbF and Flu were the predominant and accountedfor 16.4 percent (1.5–33 percent), 12.9 percent (6.3–19.0 percent)and 12.1 percent (7.5–17.6 percent) of Σ21PAHs, respectively,followed by BaA (2.5–15.0 percent, mean 9.3 percent), Pyr (4.5–11.6 percent, mean 8.1 percent) and Nap (1.6–16.6 percent, mean5.8 percent).

3.3. Size distribution of PAHs in street dusts

The size distribution of airborne particles may affect the distribu-tion pattern of a toxic chemical. According to particle size of dustsamples (Table S1, Supplementary material), the results suggestedthat the predominant size group was 101–500 mm, and their frac-tions ranged from 31.9 to 53.2 percent. The second most dominantsize group was 501–1000 mm, and the range of their fractions was23.2–34.2 percent. The mass fraction of the street dusts that had thelargest particle sizes was the lowest (7.10–23.7 percent).

Table1The concentration (mg kg�1) of individual PAHs and total toxic equivalent concentrations of PAHs (mg BaPeq kg�1) in street dust in urban area of Lanzhou, Northwest of China.

PAHs concentration (mg kg�1) TEFc Carcinogenic groupd BaPeqe (mg BaPeq kg�1)

Mean SDa Min Max Mean SD Min Max

Nap 317 341 47.5 1190 0.001 2B 0.317 0.341 0.047 1.192-MN 140 139 19.6 568 0.001 3 0.078 0.081 0.010 0.3331-MN 77.9 81.2 9.60 333 – D – – – –

Acy 22.5 30.1 0.261 152 0.001 3 0.023 0.030 0.001 0.152Ace 11.8 10.9 0.563 42.6 0.001 3 0.012 0.011 1E-3 0.043Fl 100 87.8 20.4 376 0.001 3 0.100 0.088 0.021 0.376Ant 53.1 54.3 10.5 225 0.01 3 0.531 0.543 0.105 2.25Phe 794 516 8.88 2070 0.001 3 0.794 0.516 0.009 2.07Flu 561 310 152 1230 0.001 3 0.561 0.311 0.152 1.23Pyr 197 245 30.7 1250 0.001 3 0.378 0.216 0.083 0.869Ret 378 216 82.8 869 – D – – – –

BaA 394 183 152 819 0.1 2B 39.5 18.3 15.2 81.9Chr 172 132 57.0 601 0.01 2B 1.72 1.32 0.574 6.01BbF 582 347 195 1640 0.1 2B 58.2 34.7 19.5 164BkF 18.5 13.4 4.34 57.8 0.1 2B 1.85 1.34 0.434 5.78BeP 271 138 114 696 0.01 3 2.71 1.38 1.14 6.96BaP 120 75.0 20.1 373 1 1 120 75.0 20.1 373Per 47.1 32.4 14.1 150 0.001 3 0.047 0.032 0.014 0.153InP 205 114 75.3 618 0.1 2B 20.5 11.4 7.53 61.9DBA 47.6 24.8 13.5 144 1 2A 47.6 24.8 13.5 144BP 158 127 24.3 575 0.01 3 1.58 1.27 0.243 5.75Cor 9.86 6.64 ndb 27.9 0.001 0.010 0.007 nd 0.028∑CarPAHsf 1680 824 628 4640 – – 290 157 110 807∑16PAHsg 3900 1960 1240 10,700 — — 294 159 112 817∑PAHsh 4630 2700 1470 13,700 – – 300 160 115 827

a SD¼Standard deviation.b nd¼not detected.c TEF: Toxic equivalence factors (data from Nisbet and LaGoy (1992), US EPA (1991),, (1993), Collins et al. (1998), Malcolm and Dobson (1994), and Tsai et al. (2004)).d 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.e BaPeq: Toxic equivalent data based on TEF value of individual PAHs.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 ΣPAHs: Sum of the individual detected PAHs.

0.00 0.25 0.50 0.75 1.00

0.00

0.25

0.50

0.75

1.00 0.00

0.25

0.50

0.75

1.00

5-7 Rings

ANCGQLHXG

4Rin

g

2-3 Rings

Fig. 2. Triangular diagram of percentage concentration for the 22 PAHs in dustsamples.

Y. Jiang et al. / Ecotoxicology and Environmental Safety 106 (2014) 11–1814

The average levels of PAHs in the four size fractions (o100 mm,101–500 mm, 501–1000 mm, and 41000 mm) of the 12 dustsamples collected from the four districts are shown in Fig. S2(Supplementary material). The results indicate that the levels ofdust-borne PAHs increased with the decreasing particle size.In particular, the distribution patterns of the PAH levels as afunction of size changed in similar trends. The association of smallparticles with high PAH level can be explained from severalreasons. First, the dusts composed of small-size particles can bedirectly produced from vehicular and industrial activities (Duongand Lee, 2011). Furthermore, the relatively larger available surfacearea per unit mass facilitates the deposition of PAHs near roadsurfaces, and thus, small-size particles have a higher PAH adsorp-tion rate compared to larger particles (Deletic and Orr, 2005).In addition, the lower densities and a greater proportion of organicsand clay minerals allow facilitate the adsorption of PAHs.

3.4. The relationship between ∑21PAHs and total organic carbons(TOC)

TOC is a key property influencing POPs in polluted particles,such as soil, sediment, and TSP (Chen et al., 2005; Tang et al.,2005). TOC is a dominant factor for sorption, sequestration andfate of POPs in particles. Our previous study presented a highpositive correlation between PAHs and TOC in soil (Jiang et al.,2009). To further identify the effects of TOC on PAH pollution, weevaluated the relationship between the PAH levels and TOC in dustsamples using Pearson correlation (Table S2, Supplementarymaterial). The contents of dust TOC varied from 11.0 to 71.4 g kg�1.The analytical results indicated that individual PAHs in dustsamples were not well correlated with dust TOC. Evidently, TOCaffected the distribution of PAHs only in surface soil, but not instreet dust, probably because more than 60 percent of organicmatters in soil are homogeneous humic substances (Senesi, 1992).However, dust is a mixture of atmospheric aerosol, sands, asphalt,tire, and soil participles, and the origins of its organic matters indust are complex (Takada et al., 1990). Thus, soil and dust havedifferent physical and chemical properties, and the organic mat-ters in dust are less homogeneous than in soil, suggesting that TOCdid not largely affect the PAH distribution in dust as in soil.

The correlation coefficient matrix among the individual PAHsreflected that nearly all variables were significantly inter-correlated at level 0.01 (Table S2, Supplementary material). How-ever, the higher correlations represented by r-value (r40.6) werefound in individual PAHs between two groups, low-molecular-weight (LMW, 2–3 rings) compounds group and high-molecular-weight (HMW, Z4 rings) compounds group. However, the LMWPAHs (2–4 rings) did not correlate well with the HMW group,which reflected the different origins of these two groups. Thiscould be explained by the high atmospheric mobility of LMWcompounds, which may have been transported from remote areavia atmospheric transportation (Chung et al., 2007). As semi-volatile organic compounds, the PAHs vapor pressure determinedthe vapor-particle partitioning of compounds, representing theavailable fraction for long-range atmospheric transport and phasetransfer into dust-borne organic pollutions (Agarwal et al., 2009).

3.5. Possible sources of PAHs in street dust

Generally, the composition patterns of PAHs derived fromdifferent sources vary significantly. The characteristic spectra ofPAHs composition are often used to identify their sources and theusefulness of PAH isomer ratios in source identification has beenextensively proved (Budzinski et al., 1999; Yunker et al., 2002;Wang et al., 2011).

The ratio of Ant/(AntþPhe) o0.1 indicates the source ofpetroleum, while a ratio 40.1 indicates a dominance of combus-tion. In the present study, the ratio of Ant/(AntþPhe) was between0.04 and 0.97, which indicates a dominance of combustion. More-over, a ratio of Flu/(FluþPyr) o0.4 stands for the petroleum inputsource, 0.4–0.5 for petroleum combustion (especially liquid fossilfuel, vehicle and crude oil), while 40.5 for combustion of biomassand coal (Yunker et al. 2002). The ratio of Flu/(FluþPyr) rangedfrom 0.42 to 0.67 (Fig. 3), which implies the major contributionfrom combustion of biomass and coal. The ratio of InP/(InPþBP)o0.20 stands for a petroleum source, 40.50 for the combustionof biomass and coal, and 0.20–0.50 for liquid fossil fuel combus-tion. The ratio of BaA/(BaAþChr) o0.2 stands for petroleum,0.2–0.35 for petroleum combustion (especially liquid fossil fuel,vehicle and crude oil), and 40.35 for combustion of coal, grassand wood (Yunker et al., 2002). In the present study, the ratio ofInP/(InPþBP) was between 0.45 and 0.87, and the ratio of BaA/(BaAþChr) ranged from 0.37 to 0.80, indicating that PAHs in streetdust from Lanzhou were derived primarily from combustion ofbiomass and coal (Fig. 3).

For further investigations of possible sources of PAH pollutionin Lanzhou street dust, PCA was performed using the correlationmatrix of the log-transformed PAH levels. Three principal compo-nents PC1, PC2 and PC3 with eigenvalue 41 were extracted, andexplained 43 percent, 28 percent and 23 percent (94 percent intotal) of the total variance in dust, respectively (Fig. 4).

PC1 was characterized by high loadings of PAHs with five toseven rings, which are typical markers of coal and petroleum

Fig. 3. Cross plot for the isomeric ratios of Ant/(AntþPhe) vs. Flu/(FluþPyr), andBaA/(BaAþChr) vs. InP/(InPþBP) in Lanzhou street dust.

Y. Jiang et al. / Ecotoxicology and Environmental Safety 106 (2014) 11–18 15

combustion. BaA, Chr, BeP, and BaP are markers of coal combustion(Simcik et al., 1999; Larsen and Baker, 2003), while BbF and BkF aremarkers of fossil fuels combustion (Rogge et al. 1993). BaA and Chroften result from the combustion of both diesel and natural gas(Rogge et al., 1993; Khalili et al., 1995). InP, BP, BeP and BaP areassociated with traffic emission (Sadiktsis et al., 2012). Per isformed from non-specific precursor materials by biogenic

transformation processes, and it also originates from combustionsources in surface soil (Silliman et al., 1998). Thus, PC1 reflectedthe contribution of coal and petroleum combustion to the origin ofPAHs. PC2 was loaded by Phe, Ant, Flu, Pyr, and Ret (Fig. 4). LMWPAHs, such as Phe, Ant, Flu, Pyr, indicate the presence of significantcombustion products from low-temperature pyrogenic processes(Jenkins et al., 1996). An extensive investigation about the atmo-spheric PAH sources in Los Angeles indicated that the Phe, Ant, Flu,and Pyr were mainly produced from wood combustion (Duval andFriedlander 1981). Ret is a marker of wood combustion (Simciket al., 1999; Larsen and Baker, 2003). Thus, PC2 represents thesource of wood combustion. PC 3 was loaded by Nap, Ace, Acy, Fl,1-MNa, and 2-MNa (Fig. 4). Alkylate PAHs and LMW PAHs areusually emitted from petroleum and its products, and purified oilproducts (Steinhauer and Boehm, 1992). Among them, Nap Ace, Acy,and Fl indicate the coke oven origin and accounted for the majorityof the mass in the coke oven, highway tunnel and gasoline enginesamples (Duval and Friedlander, 1981; Khalili et al., 1995; Simciket al., 1999). 1-MNa and 2-MNa are associated with petroleum(Yunker et al., 2002). Thus, PC3 represents petroleum emission.

As one major industrial center in the Northwest China, Lanz-hou's energy consumption heavily relies on coal. On the otherhand, like many other cities in north China, coal is heavily used forhome heating in the 5-month winter. The large amount ofconsumption in both industrial and domestic sectors makes coalthe primary contributor to PAHs in the local environment. Lanzhouis also one major densely-populated city in Northwest China withheavy automobile traffics and large petroleum industrial plants,and thus petroleum emission is also a major contributor of PAHpollution. The PCA results in combination with diagnostic ratios

Fig. 4. Factor loadings plots from factor analysis on various PAHs in street dustfrom Lanzhou.

Table 2Concentrations of PAHs (Cs) and results for ingestion (Ing), dermal (Derm), inhalation (Inh) and total cancer risks for street dust from Lanzhou urban area, Northwestof China.

Exposure pathway CSn Child Adult

Ingestion Dermal contact Inhalation Cancer risk Ingestion Dermal contact Inhalation Cancer risk

LanzhouMean 301 7.40 E�07 9.22 E�07 1.44 E�10 1.66 E�06 5.78 E�07 1.03 E�06 4.48 E�10 1.64 E�06Min. 115 2.84 E�07 3.54 E�07 5.50 E�11 6.38 E�07 2.22 E�07 3.94 E�07 1.72 E�10 6.16 E�07Max. 827 2.04 E�06 2.54 E�06 3.95 E�10 4.57 E�06 1.59 E�06 2.82 E�06 1.23 E�09 4.41 E�06UCL(95 percent) 362 8.92 E�07 1.11 E�06 1.73 E�10 2.03 E�06 6.97 E�07 1.24 E�06 5.04 E�10 1.94 E�06LCL(95 percent) 238 5.88 E�07 7.32 E�07 1.15 E�10 1.32 E�06 4.59 E�07 8.14 E�07 3.56 E�10 1.27 E�06

CGMean 424 1.04 E�06 1.30 E�06 2.03 E�10 2.06 E�06 8.16 E�07 1.45 E�06 6.33 E�10 2.27 E�06Min. 188 4.64 E�07 5.19 E�07 8.99 E�11 1.04 E�06 3.62 E�07 6.43 E�07 2.81 E�10 9.69 E�07Max. 827 2.04 E�06 2.54 E�06 3.95 E�10 4.57 E�06 1.59 E�06 2.82 E�06 1.23 E�09 4.41 E�06UCL(95 percent) 599 1.47 E�06 1.57 E�06 2.86 E�10 3.04 E�06 1.15 E�06 2.05 E�06 8.93 E�10 3.20 E�06LCL(95 percent) 250 9.61 E�07 1.03 E�06 1.19 E�10 2.00 E�06 4.08 E�07 8.53 E�07 3.73 E�10 1.33 E�06

ANMean 209 5.23 E�07 6.52 E�07 1.01 E�10 1.17 E�06 4.08 E�07 7.25 E�07 3.17 E�10 1.13 E�06Min. 115 2.84 E�07 3.54 E�07 5.51 E�11 6.38 E�07 2.22 E�07 3.94 E�07 1.72 E�10 6.16 E�07Max. 366 9.02 E�07 1.12 E�06 1.75 E�10 2.03 E�06 7.04 E�07 1.25 E�06 5.46 E�10 1.95 E�06UCL(95 percent) 289 6.16 E�07 8.83 E�07 1.37 E�10 1.50 E�06 5.53 E�07 9.81 E�07 4.29 E�10 1.54 E�06LCL(95 percent) 137 4.93 E�07 4.20 E�07 6.54 E�11 8.50 E�07 2.63 E�07 4.69 E�07 2.05 E�10 7.32 E�07

QLHMean 289 7.11 E�07 8.86 E�07 1.38 E�10 1.60 E�06 5.55 E�07 9.86 E�07 4.31 E�10 1.54 E�06Min. 116 2.86 E�07 3.57 E�07 5.55 E�11 6.42 E�07 2.23 E�07 3.97 E�07 1.73 E�10 6.20 E�07Max. 548 1.35 E�06 1.68 E�06 2.62 E�10 3.03 E�06 1.05 E�06 1.87 E�06 8.17 E�10 2.93 E�06UCL(95 percent) 390 9.60 E�07 1.20 E�06 1.859 E�10 2.16 E�06 7.49 E�07 1.33 E�06 5.81 E�10 2.08 E�06LCL(95 percent) 188 4.62 E�07 5.76 E�07 8.99 E�11 1.04 E�06 3.61 E�07 6.41 E�07 2.81 E�10 1.00 E�06

XGMean 264 6.50 E�07 8.10 E�07 1.26 E�10 1.46 E�06 5.07 E�07 9.02 E�07 3.94 E�10 1.41 E�06Min. 167 4.11 E�07 5.13 E�07 7.97 E�11 9.24 E�07 3.21 E�07 5.70 E�07 2.49 E�10 8.91 E�07Max. 355 8.75 E�07 1.09 E�06 1.70 E�10 1.97 E�06 6.83 E�07 1.21 E�06 5.30 E�10 1.90 E�06UCL(95 percent) 324 7.99 E�07 9.96 E�07 1.55 E�10 1.80 E�06 6.78 E�07 1.11 E�06 4.84 E�10 1.79 E�06LCL(95 percent) 204 5.01 E�07 6.24 E�07 9.70 E�11 1.13 E�06 3.13 E�07 6.95 E�07 3.04 E�10 1.01 E�06

n CS is the sum of converted PAHs concentrations based on toxic equivalents of BaP using the toxic equivalency factor (TEF, mg BaPeq kg�1).

Y. Jiang et al. / Ecotoxicology and Environmental Safety 106 (2014) 11–1816

revealed that wood, and coal combustion, and petroleum emissionwere probably the main sources of dust-borne PAHs in Lanzhoubased on the PAHs source fingerprints reported from internationalliteratures.

3.6. Risk assessment of PAHs in street dust

PAHs are of great concern owing their documented carcino-genicity and endocrine disruptive activity (Davis et al., 1993).To compare and quantify the toxic potency of dust samples, weused toxic equivalence factors (TEFs) to calculate the toxic equiva-lent concentrations (BaPeq) of dust-borne PAHs (Table 1). Thecarcinogenic potency of 16 PAHs was estimated using the totalBaPeq (sum of 16 PAH BaPeq). In this study, the total BaPeq ofdetected PAHs in dust samples was in the range of 113-824 mg BaPeq kg�1, with a mean of 297 mg BaPeq kg�1, and thetotal BaPeq of 16 PAHs in dust samples was in the range of 112–817 mg BaPeq kg�1, with a mean of 294 mg BaPeq kg�1. The totalBaPeq of 7 carcinogenic PAHs was close to that of 16 PAHs,suggesting that the 7 carcinogenic PAHs were the major contribu-tors to total BaPeq in dust samples. The contribution of PAHs to thetotal BaPeq decreased in the order as: BaP (40 percent)4BkF(19 percent)4DBA (16 percent)4 BaA (13 percent)4 InP(6.8 percent). The total BaPeq of 16 PAHs in street dust of Lanzhouwas compared to that in road dust from Ulsan, Korea (Dong andLee, 2009), and was lower compared with Tianjin (Wu et al., 2005)and Shanghai, China (Liu et al., 2007).

Depending on TEF and carcinogenic slope factor (CSF), weestimated the risks incurred from exposure routes of inhalation,ingestion and dermal contact using a probabilistic risk assessmentframework. The results suggested that the cancer risk levels viadermal contact and ingestion ranged from 10�7 to 10�6 in all dustsamples, which were 103 to 105 times higher than that viainhalation (10�9 to 10�11) (Table 2). Therefore, inhalation ofsuspended particles through mouth and nose was negligiblecompared with other two routes. Our results were similar to thoseobtained after exposure to heavy metals and PAHs in street dust(Ferreira-Baptista and De Miguel, 2005; Wang et al., 2011).

The cancer risk levels via ingestion were within the same orderof magnitude (10�7 to 10�6) as those via dermal contact, indicat-ing that ingestion and dermal contact greatly contributed to thecancer risk for both children and adults (Table 2). However, therisk of direct ingestion for children was significantly higher(po0.01) than that for adults, because the children were the mostsensitive subpopulation owing their hand-to-mouth activity,whereby polluted dust can be readily ingested (Meza-Figueroaet al., 2007). In addition, with the children's lower body weight,the PAHs intake by a child is believed to be greater than that by anadult. Thus, the health risks for children exposed to urban dust-borne PAHs are considerably greater than those of adults (Wanget al., 2011). Compared to children, the dermal contact was thepredominant exposure route for adults that induced a relativelyhigher risk (with 95 percent UCL of 1.24�10�6), followed by theingestion pathway (with 95 percent UCL of 7.00�10�7). Adulthealth risk due to dermal contact was significantly higher(po0.01) compared with children. This finding was similar tothe human cancer risk resulting from PAHs exposure in urban soilsin Beijing (Peng et al., 2011) and in urban dust in Guangzhou,China (Wang et al., 2011), which could be explained by the largerdermal exposure area and longer exposure duration for adults(Wang et al., 2011).

ILCR of 10�6–10�4 indicates potential risk under most regula-tory programs, ILCRr10�6 denotes virtual safety, and ILCR410�4

indicates a high risk (Chen and Liao, 2006; Wang et al., 2011). In thepresent study, the 95 percent confidence intervals for ILCRs of totalcancer risk for both children (2.03�10�6) and adults (1.94�10�6)

were higher than the baseline acceptable risk (1�10�6) (Maertenset al., 2008), indicating a moderate carcinogenic risk. The resultsindicate that the risk of exposure to dust-borne PAHs is pervasivefor local residents in Lanzhou.

4. Conclusions

Polycyclic aromatic hydrocarbons (PAH) in street dust samplesfrom the urban area of Lanzhou were analyzed together with totalorganic carbon (TOC), as well as some PAH source diagnostic ratiosand principal component analysis (PCA). The total levels of thesum of 16 EPA priority PAHs and 21 analyzed PAHs ranged from1240 to 10,700 mg kg�1, and from 1470 to 13,700 mg kg�1, respec-tively. The levels of PAHs in street dust from Lanzhou were alsocompared to the data from different regions and countries. Thehighest PAH levels were detected in dust samples from Chengguandistrict, which is the commercial-residential mixed zone with highpopulation density and heavy traffic. Generally, the PAHs werecomposed of two- to four-ring PAHs, and the dominant compo-nents were Phe, BbF and Flu. The total concentration of PAHsincreased with decreasing particle size in the street dust samples.The correlation analysis suggested that TOC was only slightlyaffected the accumulation of PAHs in street dust. The specificisomer ratios and PCA indicated that PAHs in the studied areaswere derived primarily from combustion of biomass and coal, andpetroleum emission. The carcinogenic potency of 16 PAHs and ILCRalso showed that the risk of exposure to urban surface dust-bornePAHs was pervasive for local residents in Lanzhou.

Acknowledgments

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

Appendix A. Supplementary material

Supplementary data associated with this article can be found inthe online version at http://dx.doi.org/10.1016/j.ecoenv.2014.04.031.

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