Polycyclic aromatic hydrocarbons (PAHs) in urban surface dust of Guangzhou, China: Status, sources...

Science of the Total Environment 409 (2011) 4519–4527

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Polycyclic aromatic hydrocarbons (PAHs) in urban surface dust of Guangzhou, China:Status, sources and human health risk assessment

Wei Wang a, Min-juan Huang a, Yuan Kang a, Hong-sheng Wang a, Anna O.W. Leung a,Kwai Chung Cheung a, Ming Hung Wong a,b,⁎a Croucher Institute for Environmental Sciences, and Department of Biology, Hong Kong Baptist University, Kowloon Tong, Hong Kong, PR Chinab School of Environmental and Resource Sciences, Zhejiang Agriculture and Forestry University, Linan, PR China

⁎ Corresponding author. Tel.: +852 34117746; fax: +E-mail address: [email protected] (M.H. Wong

0048-9697/$ – see front matter © 2011 Elsevier B.V. Aldoi:10.1016/j.scitotenv.2011.07.030

a b s t r a c t
a r t i c l e i n f o
Article history:Received 24 March 2011Received in revised form 26 May 2011Accepted 13 July 2011

Keywords:PAHsUrban surface dustHealth risk assessmentSource analysisComposition profile

Ninety-six urban surface dust samples collected from Guangzhou, a typical urban center in South China, wereanalyzed for 16 PAHs (2–6 rings). ∑PAHs concentrations in the urban surface dust ranged from 0.84 to12.3 μg/g with a mean of 4.80 μg/g. High molecular weight compounds (4–6 rings) contributed to 62 to 94% of∑PAHs mass in the surface dust samples. Four hotspots with highest ∑PAHs were identified via krigingprediction mapping, representing the highly-urbanized regions: central downtown, highway and industrialarea. Two major origins of PAHs inputs to urban surface dust were identified as vehicle emissions (51.9%) andcoal combustion (26.8%). The 95% UCL of Incremental Lifetime Cancer Risk (ILCR) due to human exposure tourban surface dust PAHs in central South China was 3.03×10−6 for children and 2.92×10−6 for adults.

852 3411 7743.).

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1. Introduction

Polycyclic aromatic hydrocarbons (PAHs) are one of the mostubiquitous classes of anthropogenic organic pollutants found in urbanenvironment such as atmosphere, precipitation, urban surface dust,sediment and soil (Larsen and Baker, 2003). They are released into theurban environment mainly through anthropogenic activities such asvehicle emissions, coal and fossil fuel combustion for power generation,petroleum refining, straw and firewood burning, industrial processing,chemical manufacturing, oil spills and coal tars (Peng et al., 2011).Several PAHs are known carcinogens such as benzo[a]pyrene (BaP) andbenz[a]anthracene (BaA) and some are the precursors to carcinogenicdaughter compounds such as benzo[b]fluoranthene (BbF) (Larsen andBaker, 2003; Dickhut et al., 2000). The toxicity of PAHs includingprobablemutagenic and carcinogenic effectsmay exert potential healthrisk to urban residents (Colombo et al., 2006; Szabová et al., 2008).

PAHs in the urban surface dust are mainly derived from depositionof PAHs containing particulates in the atmosphere and absorption ofemitted PAHs via direct exposure to vehicle exhaust emissions(Martuzevicius et al., 2011; Mostafa et al., 2009). Urban surface dustrepresents a hazardous carrier of organic compounds which bears adynamic relationship with atmospheric aerosol by resuspension intoand redeposition from the atmosphere and should be considered as anair pollutant of concern (Han et al., 2009). In addition, some surface

dust has become a potentially significant pollutant source of PAHs tosurface water, marine sediment, and consequently the food chain(Mostafa et al., 2009) because of the effects of run-off water (Maiet al., 2003). Several projects have studied the concentration anddistribution of PAHs in surface dust (Liu et al., 2007; Dong and Lee,2009; Fang et al., 2004). However, the health risk of surface dustPAH exposure is less understood, especially urban surface dust inurbanized densely populated areas.

Guangzhou, as the economic and culture center of the Pearl RiverDelta region, has an area of 7434 km2 and a population reaching10 million (Li et al., 2006). It is geographically connected with manydevelopedmetropolitan cities in South China, e.g. Shenzhen,HongKongandMacao. Featured by a typical subtropical monsoon climate in SouthChina, it is cool and dry in winter, while wet and hot in summer.However, data concerning PAHconcentrations in the urban surface dustand their potential health risk is limited. The major objectives of thepresent study were to (1) determine the levels and distribution of PAHcompounds; (2) identify potential PAHs sources to those found in urbansurface dust; and (3) examine the human health risks for PAH exposureto urban surface dust via inhalation, ingestion and dermal contact.

2. Materials and methods

2.1. Site description

The central urban area of Guangzhou (113.3°E and 23.2°N) arecomprised of four districts: Tianhe, Liwan, Yuexiu and Haizhu, whilethe suburban area under investigation in this studywas Panyu district.

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4520 W. Wang et al. / Science of the Total Environment 409 (2011) 4519–4527

The population density varied, from 11,931 people km−2 for Tianhe,30,574 people km−2 for Yuexiu, 14,885 people km−2 for Haizhu to12,411 people km−2 for Liwan and 1926 people km−2 for Panyu(Guangdong Statistical Bureau, 2009).

2.2. Sampling

There were 96 urban surface dust samples collected in total inAugust 2010 at various locations in Guangzhou (Fig. 1). The samplingsites covered the central region of Guangzhou with an area from23.06N to 23.14N latitude and 113.23E to 133.40E longitude. Thirty-two sampling locations were chosen to represent seven variousfunctional classes designated to reveal the pollution impacts fromvarious human activities: Traffic Area (TR), Central Business District(CB), Residential Area (RA), Mixed Residential and Commercial Area(MRC), Industrial Nearby (IN), Suburban Road (SB) and Park/GreenArea (PG). Traffic Area included major highway and crossroads;Central Business District represented business center and downtown;Mixed Residential and Commercial Area consisted of both theresidential communities and commercial activities; and the samplesfrom the Suburban Road, Residential Area and Park/Green Area werecollected in the corresponding areas indicated by their names.Approximately 20 g of the dust particles accumulated on impervioussurfaces of the pavement and road within a 5-m radius circle werecollected using plastic brushes and dustpans by gentle sweepingmotion to collect fine particulates. After each sampling, brushes anddustpans were cleaned with paper towels. All samples were stored inpaper bags wrapped with solvent-rinsed aluminum foil and thensealed in polyethylene bags (Ziploc) for transport to the laboratory.The samples were then placed in a desiccator to get rid of moisture,sieved (b0.1 mm), and homogenized.

2.3. Extraction and analysis of PAHs

For PAHs analysis, samples (about 2 g) were extracted for 16 h with100 ml acetone/dichloromethane/n-hexane (1:1:1, v/v/v) in Soxhlet

Tianhe

Haizhu

Yuexiu

Liwan

C

Fig. 1. Schematic showing the geographical locality of (A) the Guangdong Province in China;of urban surface dust in Guangzhou City.

apparatus (U.S. EPA, 1996a). The concentrated extract was cleanedup using a florisil column according to the EPA Standard Method 3620B(U.S. EPA, 1996b). Deuterated PAHs [naphthalene-d8 (d8-Nap),acenaphthene-d10 (d10-Ace), phenanthrene-d10 (d10-Phe), chrysene-d12 (d12-Chr) and perylene-d12 (d12-Per)] were used as internalstandards for quantification. The extractswere analyzed for PAHs using aHewlett-Packard (HP) 6890N gas chromatograph (GC) coupled with aHP-5973mass selective detector (MSD) and a 30 m×0.25 mm×0.25 μmDB-5 capillary column (J & W Scientific Co. Ltd., USA) using the EPAStandard method 8270C (U.S. EPA, 1996c). Sixteen US EPA priority 2- to6-ring PAHs were detected by GC with mass spectrometry (GC-MS):Naphthalene (Nap), acenaphthylene (Acy), acenaphthene (Ace), fluor-ene (Fl), phenanthrenes (Phe), anthracene (Ant), fluoranthene (Flu),pyrene (Pyr), benzo(a)anthracene (BaA), chrysene (Chr), benzo(b)fluoranthene+benzo(k)fluoranthene (B(b+k)F), benzo(a)pyrene(BaP), indeno(1,2,3-c,d)pyrene (IcdP), dibenzo(a,h)anthracene (DBA),and benzo(g,h,i)perylene (BghiP). Benzo(b)fluoranthene and benzo(k)fluoranthene co-eluted and therefore were quantified together.

2.4. Quality control

QA/QC was conducted by performing field and laboratory blanks,standard spiked recoveries and GC/MS detection limits. Filter blankswere less than 10% of the sample amount. The relative standarddeviation was below 10% for PAHs. For the analysis of solutions, aninternational standard reference material of house dust (SRM 2585)from the National Institute of Standards and Technology (NIST), USAwas used for calibration and analytical control. PAHs were identified onthebasis of retention times relative tofive deuterated internal standards(d8-Nap, d10-Ace, d10-Phe, d10-Chr, and d12-Per). Recoveries of SRMand internal standards varied from 65% (Pyr) to 149% (Nap).

2.5. Risk assessment

The incremental lifetime cancer risk (ILCR) was developed toquantitatively estimate the exposure risk for environmental PAHs

Hong Kong

Guangdong

Pearl River Delta

A

B

(B) the city of Guangzhou and Pearl River Delta (PRD) region; and (C) the sampling sites

Table 1Parameters used in the incremental lifetime cancer risk assessment.

Exposure variable Unit Child Adult Reference

Body weight (BW) kg 15 61.5 Shi et al., 2011Exposure frequency (EF) d a−1 180 180 Ferreira-Baptista and De Miguel, 2005Exposure duration (ED) a 6 24 USEPA, 2001Inhalation rate (IRinhalation) m3 day−1 10 20 SFT, 1999Dust ingestion rate (IRingestion) mg day−1 200 100 USEPA, 2001Dermal exposure area (SA) cm2 2800 5700 USEPA, 2001Dermal adherence factor (AF) mg cm−2 0.2 0.07 USEPA, 2001Dermal adsorption fraction (ABS) Unitless 0.13 0.13 USEPA, 2001Averaging life span (AT) d 70×365=25,550 70×365=25,550 Ferreira-Baptista and De Miguel, 2005Particle emission factor (PEF) m3 kg−1 1.36×109 1.36×109 USEPA, 2001

4521W. Wang et al. / Science of the Total Environment 409 (2011) 4519–4527

based on the U.S. EPA standardmodels (U.S. EPA, 1991; Chen and Liao,2006; Peng et al., 2011). The following assumptions underlie themodel applied in this study: (1) Human beings are exposed to urbansurface dust through three main pathways: ingestion, inhalation, anddermal contact with dust particles; (2) Intake rates and particleemission can be approximated by those developed for soil particles;(3) Some exposure parameters of people in the observed areas aresimilar to those of reference populations; (4) The total carcinogenicrisk could be computed by summing the individual risks calculated forthe three exposure ways; (5) The cancer risk is assessed based onexposure under a type of land use pattern over the entire lifetime.

The following models were widely used to evaluate the ILCR interms of ingestion, dermal contact and inhalation:

ILCRsIngestion =CS × CSFIngestion ×

ffiffiffiffiffiffiffiffiffiffiBW70

� �3q� �

× IRIngestion × EF × ED

BW × AT × 106

ILCRsDermal =CS × CSFDermal ×


� �3q� �

× SA × AF × ABS × EF × ED

BW × AT × 106

ILCRsInhalation =CS × CSFInhalation ×


� �3q� �

× IRInhalation × EF × ED

BW × AT × PEF

where CS is the sum of converted PAHs concentrations based on toxicequivalents of BaP using the Toxic Equivalency Factor (TEF) listed inTable 2 (μg/kg) (Nisbet and LaGoy, 1992). CSF is carcinogenic slopefactor (mg kg−1 day−1)−1, BW is body weight (kg), AT is the average

Table 2Summary of measured PAHs in urban surface dust of Guangzhou (μg/g).

Compounds Abbreviation Aromatic ring TEFa

Naphthalene Nap 2 0.001Acenaphthylene Acy 3 0.001Acenaphthene Ace 3 0.001Fluorene Fl 3 0.001Phenanthrene Phe 3 0.001Anthracene Ant 3 0.01Fluoranthene Flu 4 0.001Pyrene Pyr 4 0.001Benz(a)anthracene BaA 4 0.1Chrysene Chr 4 0.01Benzo(b+K)fluoranthene B(b+k)F 5 0.1Benzo(a)pyrene BaP 5 1Indeno(1,2,3-cd)pyrene IcdP 5 0.1Dibenz(a,h)anthracene DBA 6 1Benzo(g,h,i)perylene BghiP 6 0.01

LMW PAHsc

HMW PAHsd

ΣPAHse

a PAHs toxic equivalency factor with respect to BaP (Nisbet and LaGoy, 1992).b Standard deviation.c Low molecular weight 2–3 ring PAHs.d High molecular weight 4–5 ring PAHs.e Total PAHs concentration.

life span (years), EF is the exposure frequency (day year−1), ED is theexposure duration (years), IRInhalation is the inhalation rate (m3 day−1),IRIngestion is the soil intake rate (mg day−1), SA is the dermal surfaceexposure (cm2), AF is the dermal adherence factor (mg cm−2 h−1), ABSis the dermal adsorption fraction, and PEF is the particle emission factor(m3 kg−1). CSFingestion, CSFDermal and CSFInhalation of BaP were addressedas7.3, 25, and3.85 (mg kg−1 day−1)−1, respectively, determinedby thecancer-causing ability of BaP (Peng et al., 2011). Other parametersreferred in the model for children (1–6 years old) and adults (7–31 years old) were based on the Risk Assessment Guidance of U.S. EPAand related publications, shown in Table 1.

2.6. Data analysis

The ordinary Kriging interpolation analysis, based on Sphericalmodel to construct the filled contour map of ∑PAHs, was applied tovisualize the spatial distribution of data using ArcGIS 9.3 software.Principal component analysis (PCA) and other statistical analyseswere carried out with SPSS 16.0 and Origin 8.0.

3. Results and discussion

3.1. Characterization of PAHs

Concentrations of ∑PAHs (sum of the 2–6 ring PAHs) in urbansurface dust of Guangzhou city varied from 0.84 to 12.30 μg/g with anaverage of 4.80 μg/g, as shown in Table 2. This result indicated thatPAHs tend to accumulate in dust particles, which could be used as an

Mean Minimum Maximum Median SDb

0.14 0.00 3.14 0.07 0.400.03 0.01 0.14 0.03 0.020.01 0.00 0.04 0.01 0.010.03 0.00 0.11 0.02 0.020.52 0.10 1.65 0.47 0.320.04 0.01 0.12 0.04 0.020.90 0.16 2.06 0.83 0.420.56 0.09 1.69 0.54 0.260.21 0.03 0.65 0.19 0.100.52 0.08 1.29 0.50 0.240.62 0.10 1.57 0.60 0.270.24 0.04 0.54 0.23 0.110.40 0.06 1.05 0.38 0.170.09 0.01 0.28 0.09 0.040.48 0.08 1.05 0.46 0.190.78 0.17 4.21 0.68 0.574.02 0.66 8.72 3.92 1.624.80 0.84 12.30 4.57 2.00

Table3

Effect

offunc

tion

altype

onindividu

alPA

Hco

ncen

trations

inurba

nsu

rfacedu

st.

Centralbu

sine

ssdistrict

Mixed

reside

ntialan

dco

mmercial

area

Reside

ntialarea

Trafficarea

Indu

strial

area

Park/green

area

Subu

rban

road

Sampleno

.21

1512

249

99

Mea

nMed

ian

Max

Mea

nMed

ian

Max

Mea

nMed

ian

Max

Mea

nMed

ian

Max

Mea

nMed

ian

Max

Mea

nMed

ian

Max

Mea

nMed

ian

Max

Nap

0.39

0.07

0.00

–3.14

0.06

0.03

0.00

–0.17

0.10

0.12

0.00

–0.19

0.09

0.09

0.01

–0.22

0.12

0.11

0.06

–0.29

0.04

0.04

0.00

–0.08

0.04

0.04

0.00

–0.09

Acy

0.04

0.04

0.01

–0.09

0.03

0.03

0.01

–0.04

0.03

0.02

0.01

–0.06

0.04

0.04

0.01

–0.08

0.05

0.04

0.02

–0.14

0.01

0.01

0.01

–0.02

0.02

0.01

0.01

–0.03

Ace

0.01

0.01

0.00

–0.02

0.01

0.01

0.00

–0.02

0.01

0.01

0.00

–0.02

0.02

0.01

0.00

–0.04

0.01

0.01

0.00

–0.03

0.01

0.01

0.00

–0.02

0.00

0.00

0.00

–0.01

Fl0.02

0.02

0.00

–0.05

0.03

0.03

0.00

–0.05

0.03

0.02

0.01

–0.07

0.04

0.03

0.02

–0.11

0.05

0.03

0.02

–0.10

0.02

0.02

0.01

–0.02

0.01

0.01

0.00

–0.03

Phe

0.46

0.39

0.22

–1.07

0.53

0.53

0.21

–0.75

0.60

0.41

0.16

–1.58

0.60

0.56

0.27

–1.65

0.73

0.58

0.37

–1.33

0.19

0.17

0.14

–0.25

0.24

0.24

0.10

–0.43

Ant

0.04

0.04

0.01

–0.08

0.04

0.04

0.01

–0.06

0.03

0.03

0.01

–0.09

0.05

0.05

0.02

–0.11

0.05

0.04

0.02

–0.12

0.02

0.02

0.01

–0.02

0.02

0.01

0.01

–0.03

Flu

1.02

0.91

0.46

–2.06

0.93

0.85

0.60

–1.52

0.74

0.66

0.22

–1.51

1.05

0.96

0.67

–2.05

1.21

1.09

0.64

–1.80

0.33

0.32

0.28

–0.39

0.48

0.42

0.16

–0.80

Pyr

0.66

0.54

0.29

–1.69

0.57

0.57

0.37

–0.77

0.44

0.39

0.12

–0.81

0.67

0.64

0.40

–1.20

0.72

0.73

0.42

–1.10

0.20

0.20

0.18

–0.23

0.29

0.30

0.09

–0.47

BaA

0.27

0.25

0.12

–0.43

0.19

0.18

0.09

–0.36

0.13

0.13

0.04

–0.24

0.26

0.25

0.12

–0.44

0.26

0.20

0.12

–0.65

0.09

0.09

0.09

–0.10

0.10

0.11

0.03

–0.15

Chr

0.55

0.54

0.32

–0.96

0.61

0.62

0.31

–0.88

0.35

0.27

0.11

–0.96

0.61

0.58

0.43

–0.83

0.77

0.64

0.50

–1.29

0.25

0.25

0.24

–0.25

0.25

0.22

0.08

–0.40

B(b+

k)F

0.72

0.69

0.43

–1.45

0.65

0.62

0.29

–1.06

0.44

0.41

0.12

–0.84

0.74

0.75

0.57

–0.98

0.81

0.74

0.41

–1.57

0.25

0.25

0.24

–0.26

0.33

0.35

0.10

–0.52

BaP

0.31

0.32

0.16

–0.50

0.22

0.22

0.12

–0.33

0.17

0.17

0.05

–0.30

0.31

0.30

0.18

–0.50

0.29

0.27

0.17

–0.54

0.11

0.10

0.10

–0.13

0.12

0.13

0.04

–0.20

IcdP

0.49

0.48

0.26

–0.85

0.38

0.38

0.21

–0.53

0.28

0.28

0.08

–0.52

0.49

0.46

0.37

–0.71

0.47

0.39

0.24

–1.05

0.15

0.15

0.14

–0.15

0.22

0.27

0.06

–0.33

DBA

0.12

0.12

0.06

–0.20

0.08

0.08

0.04

–0.13

0.07

0.06

0.02

–0.12

0.12

0.11

0.07

–0.17

0.12

0.12

0.06

–0.28

0.04

0.04

0.04

–0.04

0.05

0.06

0.01

–0.07

BghiP

0.58

0.58

0.29

–0.86

0.46

0.47

0.25

–0.61

0.34

0.34

0.10

–0.61

0.60

0.57

0.41

–0.94

0.58

0.58

0.31

–1.05

0.18

0.18

0.18

–0.19

0.26

0.32

0.08

–0.36

ΣPA

Hs

5.69

5.17

3.63

–12

.30

4.79

4.64

2.83

–5.96

3.77

3.67

1.09

–7.05

5.24

5.52

3.84

–8.59

6.23

5.93

4.12

–9.68

1.87

1.86

1.66

–2.10

2.45

2.39

0.84

–3.54

LMW

PAHs

0.97

0.62

0.26

–4.21

0.69

0.70

0.25

–1.01

0.80

0.67

0.24

–1.87

0.71

0.82

0.38

–2.12

1.01

0.95

0.54

–1.74

0.29

0.27

0.18

–0.40

0.33

0.28

0.17

–0.57

HMW

PAHs

4.72

4.47

3.02

–8.60

4.09

4.06

2.26

–5.23

2.97

3.00

0.85

–5.88

4.53

4.59

3.42

–6.65

5.22

4.66

3.43

–8.72

1.59

1.59

1.48

–1.70

2.12

2.19

0.66

–2.98

a The

numbe

rof

surfacedu

stsamples

indifferen

tfunc

tion

alarea

s.


indicator of urban environmental pollution. The highest ∑PAHsconcentration was found in the pavement surface dust from thebustling commercial street where the high concentrations of PAHsmay have resulted from the accumulation of PAHs from the emissionsof slow moving vehicles and the limited dispersion of pollutants(Dong and Lee, 2009).

PAHs levels in surface dust varied greatly in different functional areas(Table 3). The mean concentrations of ∑PAHs decreased in the fol-lowing order of land uses: Industrial NearbyNCentral Business DistrictNTraffic AreaNMixed Residential and Commercial AreaNResidentialAreaNSuburban RoadNPark/Green Area. However, the differences inconcentrations of PAHs in the groups of Industrial Nearby, Traffic Areaand Central Business Area (at p≤0.05) were not significant. Theindustrial release and vehicle emissions might have enhanced ∑PAHsin urban surface dust. This finding was similar to the reports of PAHsdistribution in the road dust of Ulan, Korea (Dong and Lee, 2009) andThailand (Boonyatumanond et al., 2007).

The mean level of ∑PAHs in this study was relatively higher thanthose in the United Kingdom (0.002 mg/kg), Norway (0.0069 mg/kg),Canada (0.0011 mg/kg), Australia (0.0033 mg/kg) and Greater Cairo,Egypt (0.045–2.61 mg/kg) (Hassanien andAbdel-Latif, 2008), but lowerthan those of Taiwan (65.8 mg/kg at traffic site), Birmingham, UK(12.56–93.70 mg/kg) and Ulsan, Korea (11.8–245 mg/kg) (Fang et al.,2004; Dong and Lee, 2009). However, it is clear that the measured∑PAHs in central Pearl River Delta (PRD) in the present study fellwithin relatively low range, in comparison with other studies in Chinaand Asia (Taiwan, Fang et al., 2004; Shanghai, Liu et al., 2007; Korea,Dong and Lee, 2009). The reasonmight be due to the typical subtropicalmonsoon climate in South China, characterized by hot and rainyweather during the sampling period. In addition, the contaminationlevel would also vary with the frequency of city pavement cleaning.

3.2. PAH geographic distribution

The spatial distribution of ∑PAHs is shown using a kriging map(Fig. 2). Four sections with hotspots isolated by the predictedmapping plot coincided with the proximity of PAH sources geograph-ically. Section A was near the pedestrian street and downtown. Thiscommercial district exhibited the predominant impact of humanacitivities on PAHs contamination. Section B was located in the traffic-busy area of the South China Highway Route, Guangzhou Main Road,Huangpu Main Road and Guangzhou Bridge which represented themajor sources of PAHs from traffic emission. Section C showed thehighest ∑PAHs concentrations in the southeastern part of Tianhethat is attributed to the industrial establishments in this district, suchas the Pearl River Oil Refinery and Chebei Wharf. While Section D,located in the commerical and residential area, represented themixedcontribution from human activities. Relatively low levels of ∑PAHsweremeasured at the southern part of Haizhu district (Fig. 2), as therewas nomajor pollution sources in this region and the decreasing trendreflected the possible transport of PAHs from the city center.

3.3. PAHs composition profile

As shown in Fig. 3, Flu, Chr, B(b+k)F, Phe, IcdP and BghiP were themajor compounds. These PAHs species were indicators of combustion(Hwang et al., 2003). This PAH profile was similar to those measuredin street dust of Bangkok, Thailand (Boonyatumanond et al., 2007),Taichung, Taiwan (Fang et al., 2004) and Kuala Lumpur, Malaysia(Omar et al., 2002). In general, PAHs in urban surface dust had acommon characteristic with high molecular weight PAHs (HMWPAHs) (4–5 rings) contribution (62% to 94%), revealing a pyrogenicorigin (Zakaria et al., 2002).

The PAH fingerprints for Traffic Area, Suburban Road and MixedResidential and Commercial Area were similar, with a relatively highercontribution of 5–6 ring PAHs, suggesting that those locations share

Fig. 2. Spatial distribution of PAHs in urban surface dust of Guangzhou (A, B, C and D were the sections isolated with the high-polluted hot spots in Kriging mapping).


a common source of vehicle emission (Larsen and Baker, 2003).Furthermore, this result was consistent with the PAHs speciation ingasolinevehicle soot enrichedbyhighmolecularweight PAHs, revealinga dominant influence of gasoline vehicle release (Boonyatumanondet al., 2007). The samples from Residential Area contained a relativelyhigher abundance of Phe, indicating a heavy impact of coke ovencombustion (Duval and Friedlander, 2004).

3.4. Correlations between individual PAHs

The correlation efficient matrix among the individual PAHs as wellas ∑PAHs reflected that nearly all of the variables were significantlycorrelated with one another at the 0.01 level, besides Nap (Table 4).However, the higher correlations represented by r-value (rN0.8) wereobserved only among HMW compounds group, which is simulta-neously and significantly (pb0.01) correlated with ∑PAHs. In mostcases, low molecular weight (2–3 rings) group did not correlatewell among the compounds and with the HMW group. The poorcorrelation 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 locationsvia atmospheric transportation (Chung et al., 2007). As semi-volatileorganic compounds, the property of PAHs vapor pressure determinedthe compounds vapor-particle partitioning, representing the availablefraction for long-range atmospheric transport and phase transfer intodust organic pollutions (Agarwal et al., 2009).

Functional areas

0% 20% 40% 60% 80% 100%

CB

MRC

RA

TR

IN

PG

SB

Nap Acy Ace Fl PheAnt Flu Pyr BaA ChrB(b+k)F BaP IcdP DBA BghiP

Fig. 3. Composition profile plot of PAHs in surface dust from seven functional areas.

3.5. Ratio analysis

The isomer ratios of Ant/(Ant+Phe), BaA/(BaA+Chr), Flu/(Flu+Pyr) and IcdP/(IcdP+BghiP) were used to distinguish betweenpetrogenic and pyrolytic sources (Zhang et al., 2006). The ratio ofAnt/(Ant+Phe)b0.1 suggested a petroleum source, while a ratioN0.1reflected combustion. Meanwhile, Flu/(Flu+Pyr)b0.4 indicatedpetroleum, between 0.4 and 0.5 implies liquid fossil fuel combustion,and a ratioN0.5 is the characteristic of biomass and coal combustion(Yunker et al., 2002). IcdP/(IcdP+BghiP) and BaA/(BaA+Chr) maycharacterize the nature of potential PAH emission sources that IcdP/(IcdP+BghiP)b0.2 and BaA/(BaA+Chr)b0.2 are indications ofpetroleum and petrogenic sources. When BaA/(BaA+Chr) fallsbetween 0.2 and 0.35 and IcdP/(IcdP+BghiP) between 0.2 and 0.5,the PAHs usually come from petroleum combustion (liquid fossil fuel,vehicle and crude oil combustion). When IcdP/(IcdP+BghiP)N0.5and BaA/(BaA+Chr)N0.5, it strongly indicated the contribution ofcoal, grass and wood (Yunker et al., 2002).

As shown in Fig. 4, the ratios of Flu/(Flu+Pyr) were generallyabove 0.5 while ratios of Ant/(Ant+Phe) were lower than 0.1,suggesting a mixed source of coal combustion and traffic emission(Yunker et al., 2002). This result agreed with the conclusion thatvehicular traffic and coal combustion are major contributors of atmo-spheric PAHs in Guangzhou City (Li et al., 2006) and was consistentwith the sources of PAHs in urban surface dust in central Shanghaiareas (Liu et al., 2007). In addition, values of IcdP/(IcdP+BghiP) ratiovaried between 0.42 and 0.49 while BaA/(BaA+Chr) varied between0.17 and 0.40, revealing vehicular traffic emissions as the main source(Yunker et al., 2002). This supported the result from a previous studythat vehicles were the dominant source of particulate PAHs in thecities of the Pearl River Delta (Bi et al., 2003).

3.6. Principal component analysis

Three principal components (PC1, PC2 and PC3) had beenextracted and collectively represented more than 86.2% of the totalvariance of ∑PAHs in the urban surface dust (Fig. 5A). PC1 (51.9% oftotal variances) was predominated by 5–6 ring PAHs, including DBA,IcdP, BghiP, BaP, B(b+k)F, BaA and Acy, representing vehicle-relatedsources (Larsen and Baker, 2003; Dong and Lee, 2009). The highscores of PC1 were found for T8, I1, C6, C7, C2, T2, T5 and T6 samplinglocations (Fig. 5b), which were located in Central Business District,Traffic Area and Industrial Nearby, reflecting vehicle emission of theseareas.

image of Fig.�3

Table 4Correlation coefficients (r) among the concentrations of individual PAHs and ΣPAHs in the dust samples.

Nap Acy Ace Fl Phe Ant Flu Pyr BaA Chr B(b+k)F BaP IND DBA BghiP LMW PAH HMW PAH ΣPAH

Nap 1.00Acy 0.30** 1.00Ace −0.02 0.45** 1.00Fl 0.10 0.58** 0.55** 1.00Phe 0.10 0.37** 0.36** 0.76** 1.00Ant 0.19 0.79** 0.43** 0.84** 0.62** 1.00Flu 0.22* 0.65** 0.37** 0.70** 0.77** 0.73** 1.00Pyr 0.16 0.52** 0.36** 0.53** 0.70** 0.58** 0.92** 1.00BaA 0.18 0.78** 0.35** 0.39** 0.27* 0.70** 0.65** 0.67** 1.00Chr 0.18 0.62** 0.29** 0.54** 0.46** 0.69** 0.73** 0.76** 0.69** 1.00B(b+k)F 0.27* 0.68** 0.32** 0.39** 0.39** 0.59** 0.72** 0.82** 0.81** 0.89** 1.00BaP 0.24* 0.79** 0.49** 0.38** 0.30** 0.65** 0.67** 0.69** 0.91** 0.63** 0.80** 1.00IcdP 0.31** 0.80** 0.36** 0.38** 0.33** 0.67** 0.68** 0.71** 0.90** 0.75** 0.89** 0.93** 1.00DBA 0.30** 0.82** 0.34** 0.35** 0.25* 0.66** 0.61** 0.63** 0.92** 0.68** 0.83** 0.95** 0.96** 1.00BghiP 0.24* 0.75** 0.42** 0.44** 0.39** 0.69** 0.68** 0.72** 0.84** 0.76** 0.84** 0.90** 0.96** 0.94** 1.00LMW PAH 0.78** 0.51** 0.26* 0.59** 0.70** 0.58** 0.67** 0.57** 0.35** 0.45** 0.47** 0.41** 0.48** 0.42** 0.46** 1.00HMW PAH 0.25* 0.75** 0.39** 0.56** 0.57** 0.74** 0.89** 0.91** 0.85** 0.88** 0.94** 0.87** 0.91** 0.86** 0.90** 0.58** 1.00ΣPAHs 0.43** 0.76** 0.39** 0.62** 0.66** 0.76** 0.91** 0.90** 0.79** 0.84** 0.89** 0.82** 0.87** 0.82** 0.86** 0.75** 0.97** 1.00

**Correlation is significant at the 0.01 level (2-tailed).*Correlation is significant at the 0.05 level (2-tailed).


PC2 (26.8% of variance) had high loading values of Phe, Flu, Fl and Pyr,whichwere typicalmarkers for coal combustion. Flu and Pyr aremarkersfor coal combustion (Larsen and Baker, 2003), while Phe and Fl areindicators of coke oven origin (Duval and Friedlander, 2004). Thus, PC2indicated the source of coal and coke combustion. From the distributionof sampling locations, high scores of PC2 were observed at R2, I2, I3 and

0

A

B0.5

Fig. 4. Cross plot for the isomeric ratios of: (A) Ant/(Ant+Phe) vs. Flu/(Flu+Pyr), and(B) BaA/(BaA+Chr) vs. IcdP/(IcdP+BghiP) in surface dust samples.

Fig. 5. Plot with PC1 and PC2 from principal component analysis. (A) Factor loadings of16 PAHs on two components, and (B) factor scores of sampling locations on the PC1 andPC2 (C-CB, M-MRC, T-TR, R-RA, I-IN, P-PG, and S-SB).


T3, mainly located near the Industrial Nearby and Residential Area,indicatingpotential origins of industrial coal consumptionandhouseholdcooking or heating, while PC3 (24.1% of variance) was heavily weightedby Nap, reflecting an incomplete combustion related source (Jiang et al.,2009; Dong and Lee, 2009). The scatter plot (Fig. 5B) clearly demon-strated that the locations in Park/Green Area and Suburban Road wereslightly polluted with PAHs, with negative scores for PC1 and PC2.

3.7. Health risk assessment

This is thefirst study that assessed thepotential cancer risk of humanexposure to urban surface dust PAHs of different functional areas. TheILCRwas taken as an ensign to identify the age-specific potential cancerrisks in the study of human exposure to environmental PAH pollutionsources (Peng et al., 2011; Chen and Liao, 2006). Dependingon the ToxicEquivalence Factor (TEF) and carcinogenic slope factor (CSF), a prob-abilistic risk assessment framework was applied to estimate riskincurred from exposure routes of inhalation, ingestion and dermalcontact (Table 5). The cancer risk levels via dermal contact and ingestion

Table 5Risk of cancer due to human exposure to PAHs via urban surface dust.

Child

Exposure path ways CSa (μg/kg) Ingestion Dermal contact Inhalation

Total sitesmean 4.70E+02 1.16E-06 1.44E-06 2.24E-11min 7.56E+01 1.86E-07 2.32E-07 3.61E-12max 1.17E+03 2.87E-06 3.58E-06 5.56E-11UCL(95%) 5.48E+02 1.35E-06 1.68E-06 2.61E-11LCL(95%) 4.50E+02 1.11E-06 1.38E-06 2.15E-11

Central business district (CB)Mean 5.95E+02 1.47E-06 1.83E-06 2.84E-11Min 3.24E+02 7.97E-07 9.93E-07 1.54E-11Max 9.52E+02 2.34E-06 2.92E-06 4.54E-11UCL(95%) 6.93E+02 1.71E-06 2.13E-06 3.31E-11LCL(95%) 4.97E+02 1.22E-06 1.53E-06 2.37E-11

Mixed residential and commercial area (MRC)Mean 4.36E+02 1.07E-06 1.34E-06 2.08E-11Min 2.20E+02 5.42E-07 6.76E-07 1.05E-11Max 6.23E+02 1.53E-06 1.91E-06 2.98E-11UCL(95%) 4.94E+02 1.22E-06 1.52E-06 2.36E-11LCL(95%) 3.78E+02 9.32E-07 1.16E-06 1.81E-11

Residential area (RA)Mean 3.33E+02 8.21E-07 1.02E-06 1.59E-11Min 9.86E+01 2.43E-07 3.03E-07 4.71E-12Max 5.96E+02 1.47E-06 1.83E-06 2.85E-11UCL(95%) 4.14E+02 1.02E-06 1.27E-06 1.98E-11LCL(95%) 2.52E+02 6.21E-07 7.75E-07 1.20E-11

Traffic area (TR)Mean 5.74E+02 1.41E-06 1.76E-06 2.74E-11Min 3.86E+02 9.51E-07 1.19E-06 1.84E-11Max 8.69E+02 2.14E-06 2.67E-06 4.15E-11UCL(95%) 6.63E+02 1.63E-06 2.03E-06 3.16E-11LCL(95%) 5.18E+02 1.28E-06 1.59E-06 2.47E-11

Industrial nearby (IN)Mean 7.60E+02 1.87E-06 2.33E-06 3.63E-11Min 3.18E+02 7.83E-07 9.76E-07 1.52E-11Max 1.17E+03 2.87E-06 3.58E-06 5.56E-11UCL(95%) 7.75E+02 1.91E-06 2.38E-06 3.70E-11LCL(95%) 3.84E+02 9.45E-07 1.18E-06 1.83E-11

Park/green area (PG)Mean 2.32E+02 5.71E-07 7.12E-07 1.11E-11Min 1.85E+02 4.56E-07 5.69E-07 8.85E-12Max 2.22E+02 5.47E-07 6.82E-07 1.06E-11UCL(95%) 2.48E+02 6.11E-07 7.62E-07 1.18E-11LCL(95%) 1.55E+02 3.81E-07 4.75E-07 7.39E-12

Suburban road (SB)Mean 2.42E+02 5.97E-07 7.44E-07 1.16E-11Min 7.56E+01 1.86E-07 2.32E-07 3.61E-12Max 3.57E+02 8.78E-07 1.09E-06 1.70E-11UCL(95%) 3.20E+02 7.88E-07 9.83E-07 1.53E-11LCL(95%) 1.64E+02 4.05E-07 5.05E-07 7.85E-12

a The sum of converted values of PAHs based on toxic equivalents of BaP using the Toxic

pathway ranged from 10−7 to 10−6 in all the dust samples, while themean cancer risk via inhalation was 10−10 to 10−12; about 103 to 107

times lower than that through ingestion and dermal contact. This wasalso observed in a study of exposure to heavy metals in street dust ofAngola (Ferreira-Baptista andDeMiguel, 2005). Therefore, inhalation ofresuspended particles through mouth and nose was almost negligible,when compared with the other routes.

In the case of children, the cancer risk levels via ingestion waswithin the same order of magnitude (10−7 to 10−6) as throughdermal contact, indicating that both ingestion and dermal contactgreatly contributed to the cancer risk for children. However, therisk value of direct ingestion for children was significantly higher(pb0.01) than the corresponding risk of ingestion for adults. Themostsensitive subpopulation is young children because of their hand-to-mouth activity, whereby contaminated dust can be readily ingested(Meza-Figueroa et al., 2007). In addition, with the lower body weightof children, the PAHs intake (mg/kg-bodyweight/day) of a child isbelieved to be greater than that of an adult. Furthermore, earlydevelopment of organ, nervous, and immune systems could probably

Adult

Cancer risk Ingestion Dermal contact Inhalation Cancer risk

2.60E-06 9.04E-07 1.60E-06 7.01E-11 2.51E-064.18E-07 1.45E-07 2.58E-07 1.13E-11 4.03E-076.44E-06 2.24E-06 3.98E-06 1.74E-10 6.22E-063.03E-06 1.05E-06 1.87E-06 8.17E-11 2.92E-062.49E-06 8.65E-07 1.54E-06 6.71E-11 2.40E-06








Equivalency Factor (TEF) (Nisbet and LaGoy, 1992).


enhance the carcinogens sensitivity in children (Maertens et al., 2008).Thus, the hazard health risk for children exposed to urban dust PAHs arethought to be considerably greater than that of adults. Compared tochildren, the dermal contact appeared to be the predominant exposureroute that induced a relatively higher risk (with 95%UCL of 1.87×10−6)for adults, followed by the ingestion pathway. Adult health risk due todermal contact was significantly higher (pb0.01) than that for children.This finding was similar to the human cancer risk resulted from PAHsexposure in urban soils of Beijing, China (Peng et al., 2011),which couldbe explained by the higher values of dermal exposure area (SA) andexposure duration (ED) of adults.

Under most regulatory programs, an ILCR between 10−6 and 10−4

indicated potential risk, where the virtual safety was denoted with anILCR of 10−6 or less and a potentially high risk was estimated by anILCR of greater than 10−4 (Chen and Liao, 2006). In the present study,the 95% confidence intervals for ILCRs of total cancer risk for bothchildren and adults were higher than the baseline value of acceptablerisk (one cancer case per million people) (Maertens et al., 2008),indicating a moderate potential carcinogenic risk. This showed thatthe risk due to urban surface dust PAHs exposure was pervasive forresidents in Guangzhou city. The highest ILCR was found in theIndustrial Nearby, followed by the Central Business District, while thelowest in the Park/Green Area. The variation of ILCRs of total cancerrisk among the seven functional urban areas indicated the greateffects of PAH emission sources on health risk levels. This result wassimilar to the influence of local PAHs releases (mobile and stationaryemissions) on the carcinogenic risk due to PAHs in PM10 in Korea (Vuet al., 2011). Furthermore, the high levels of ILCR of 10−5 was foundfor children in some more sensitive land uses such as residential areanear the industrial ozone and central business area. This should not beoverlooked because these are places where children often play andare densely populated.

4. Conclusion

In spite of the typical subtropical monsoon climate in summer, PAHsrepresented widespread and highly-accumulated organic pollutants inthe urban surface dust of Guangzhou city.∑PAHs ranged from 0.84 to12.3 μg/g with an average of 4.80 μg/g in urban surface dust collectedfrom central Guangzhou areas. About 62%–94% of PAH mass wascontributed by high molecular weight PAHs, suggesting a combustionorigin. The contamination levels varied in different functional groups,with high PAH contamination observed in Central Business District,Traffic Area and Industrial Nearby while low levels in Residential Area,Park/Green Area and Suburban Road. Vehicle emission and coalcombustion were the primary sources of PAHs in urban surface dustin central Guangzhou. The spatial distribution of PAHs clearly showedthat thepotential hotspotswith highest∑PAHs significantly correlatedwith the local human activities, such as commercial downtown,highway traffic and industrial processes. Risk assessment based on theIncrement Life Time Cancer Risk (ILCR) model for environmental PAHswas conducted to for the first time evaluate the human cancer riskassociated with urban surface dust. The estimated 95% confidenceinterval of the ILCRs revealed that urban surface dust PAHs exposurewould result in lifetime cancer risks that are pervasive and moderatefor children and adults. However, exposure to higher levels of PAHsfound in some sensitive areas yielded risks to children that could behigher than 1×10−5.

Acknowledgments

This research was financially supported by the Research GrantsCouncil of the University Grants Committee of Hong Kong (HKBU260209). We thank the graduate students from Sun Yat-sen Universityfor assistance in field work.

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