Environ Geochem Health DOI 10.1007/s10653-014-9631-6

ORIGINAL PAPER

Grain-size distribution and heavy metal contamination of road dusts in urban parks and squares in Changchun, China Liu Qiang • Wang Yang • Liu Jingshuang Wang Quanying • Zou Mingying

•

Received: 31 October 2013 / Accepted: 27 June 2014 Ó Springer Science+Business Media Dordrecht 2014

Abstract Due to rapid urbanization and the scarcity of land, most of the urban parks and squares in cities are built close to major roads or industrial areas, where they are subject to many potential pollution sources, including vehicle exhaust and industrial emissions. The aims of this study were to determine the concentrations of selected metals (Pb, Cr, Cu, Ni, Zn, and Cd) in road dusts collected in urban parks and squares in Changchun, China, on June 1, 2013 (International Children’s Day) and to estimate the pollution sources. The mean Pb, Cr, Cu, Ni, Zn, and Cd contents (70.89, 60.30, 43.56, 23.16, 170.80, and 0.3111 mg kg-1 dry weight, respectively) in urban dusts were higher than their corresponding natural background values, particularly Pb, Cu, Zn, and Cd, which had about 2.5, 1.4, 1.9, and 2.6-fold higher levels, respectively. The results of principal component analysis indicated that Cr and Ni concentrations

L. Qiang  W. Yang (&)  L. Jingshuang  W. Quanying Northeast Institute of Geography and Agroecology, Chinese Academy of Sciences, 4888 Shengbei Road, Changchun 130102, China e-mail: [email protected] L. Qiang University of Chinese Academy of Sciences, Beijing 100049, China Z. Mingying CNPC Northeast Refining and Petrochemical Engineering Co. Ltd, JiLin Design Institute, Beijing, China

were mainly of natural origin, while Pb, Cu and Zn were derived from anthropogenic activities, and Cd tended to be from both sources. The geoaccumulation index (Igeo) of these metals in the urban dusts under study indicates that they are uncontaminated with Cr and Ni; uncontaminated to moderately contaminated with Cu and Zn; and moderately contaminated with Pb and Cd. In addition, five particle sizes were analyzed separately for heavy metal concentrations. In all studied areas, there are large differences in the metal-loading percentage of different particle-size fractions among the samples, and the particles in 250–2,000-lm fraction are dominant in the total metal loading. Keywords Road dust  Heavy metal  Geoaccumulation index  Source identification  Particle size fractions  Urban parks and squares

Introduction Urban dust, an important part of the urban environment, is the most pervasive and important factor affecting human health, and its origins are very complex. Urban dust is potentially hazardous to humans due to its small particle size and inherent mobility in windy weather conditions, leading to the possibility of direct and indirect exposure. Direct exposure from dust can occur by inhalation and

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ingestion while indirect exposure results from contact with exposed skin and outer clothing, which in turn can be accidentally ingested (Abrahams 2002). Children are more likely to ingest significant quantities of dust compared to adults because of the behavior of mouthing non-food objects and repetitive hand/finger sucking during outdoor activities (EPA 2011). Components and quantity of urban dusts are environmental pollution indicators, especially in big cities. Environmental contamination by heavy metals is still a serious problem in urban areas due to the constant release of metal pollutants from various industrial operations, traffic emissions, power-generation facilities, fossil-fuel burning, and municipal waste disposal. In urban road dusts, the anthropogenic sources of heavy metals include traffic emission (for example, vehicle exhaust particles, tire-wear particles, weathered street surface particles, brake lining wear particles), industrial emission (power plants, coal combustion, metallurgical industry, auto repair shops, chemical plants, etc.), atmospheric deposited and so on (Ahmed and Ishiga 2006; Amato et al. 2009; Banerjee 2003; Miguel et al. 1997; Han et al. 2006). It has been established that high concentrations of toxic metals in the environment may cause adverse health effects to inhabitants by affecting the central nervous system, and renal and reproductive systems (Papanikolaou et al. 2005; Goyer 1997). Urban road dust is a mixture of mineral constituents, organic matter, and elemental carbon (Amato et al. 2009), and an important media that contains environmental pollutants. Through resuspension-inhalation, hand–mouth ingestion and dermal contact, hazardous pollutants contained in dust can enter the human body and endanger health (Ferreira-Baptista and De Miguel 2005; Soto-Jimenez and Flegal 2011; Zheng et al. 2010). Many studies of heavy metals in urban dust have been carried out (Ahmed et al. 2007; Al-Shayeb and Seaward 2001; Chen et al. 1997; Lu et al. 2009; Ndiokwere 1984; Schwar et al. 1988; Sezgin et al. 2004), while little information is available on heavy metal pollution in road dusts of urban parks and squares located in old industrial bases. The industrial base refers to the city or area with relatively developed and intensive industrial production. As the first heavy industrial base since the establishment of the People’s Republic of China, Changchun has made great contributions to the economic development of China. However, the rapid economic

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development in Changchun over the last two decades has led to a significant release of waste into the urban environment and placed great pressure on the local environment, including heavy metals contamination of urban soils, such as Cd, Cu, Pb, and Zn (Guo 2005; Yang et al. 2011a). Parks and squares are used for leisure, sporting, or recreational activities and they are the main places of the outdoor activities for urban residents. However, the heavy metal pollution levels of road dusts in Changchun’s urban parks and squares remain unknown. The purposes of this study were to: (1) determine the concentrations of heavy metals (Pb, Cr, Cu, Ni, Zn, and Cd) in road dusts of urban parks and squares; (2) assess the heavy metal contamination; (3) identify possible sources of trace metals; and (4) study trace metal distribution in different particle size fractions of dusts. In addition, in this study, all the samples were collected on International Children’s Day 2013. On this day, urban parks and squares were very crowded with parents and kids and frequent human activities would increase the risk for exposure to heavy metals in road dusts. Therefore, the study of environmental pollution of urban parks and squares plays an important role in helping people to choose safer areas of activity and protecting human health.

Materials and methods Study site The study site is located in an urban area of Changchun (43°170 –44°50 N, 125°30 –125°340 E), which is the capital of Jilin Province and an important social-economic center of northeastern China located in the hinterland of the Northeast Plain. The city occupies an area of 20,604 km2, with 4,906 km2 classified as urban areas. The climate is dominated by northerly continental monsoons, characterized by long and cold winters and generally short and warm summers. The average annual temperature is 4.8 °C and the highest temperature in summer is 39.5 °C, the lowest temperature in winter is -39.8 °C, and the average annual rainfall is 569.6 mm. The 12 locations (seven public parks and five squares) investigated in this study are major sites in Changchun that frequently welcome a large number of visitors for free and provide opportunities for a wide range of leisure, sporting, and recreational activities. Some of the parks and squares, such as the South Lake Park, South

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Lake Square, Xinmin Square, People’s Square, Peony Park, Victory Park, Children’s Park and Station Square, were built more than 80 years ago (Table 1).

Table 1 Brief description of the parks and squares investigated in Changchun Name (Abbr.name)

Sampling A total of 28 dust samples from 12 different sites (seven parks and five squares) were collected using hand brushing with a plastic brush and plastic collection pan on June 1, 2013 (Fig. 1). Each brush and pan was used only once or cleaned using acetone. At each sampling site, four to six subsamples were taken and then mixed thoroughly to obtain a bulk sample. Care was taken to reduce the disturbance of fine particles and any obvious extraneous matter such as stones and leaves was removed. About 500 g of dust samples was collected and transferred into coded selfsealing polyethylene bags for transport to the laboratory. All of the sample sites were recorded using a hand-held global positioning system.

All the samples were oven-dried at B40 °C for 7 days. The dried samples were screened with a 2-mm plastic sieve to remove large plant parts and gravel-sized material. Further, a portion (200 g) of each sample was sorted into grain-sized fractions of \63, 63–100, 100–150, 150–250, and 250–2,000 lm. These fractions and their descriptive class names (Folk 1974) were: \63 lm (silt and clay), 63–125 lm (very fine sand), 125–250 lm (fine sand), 250–500 lm (medium sand), 500–1,000 lm (coarse sand), and 1,000–2,000 lm (very coarse sand). Particles coarser than 2,000 lm are of limited importance in transporting adsorbed metals in urban systems (Stone and Marsalek 1996; Sutherland and Tolosa 2000) from both a hydraulic and a geochemical point of view. The different-sized fractions were weighed on the day of screening and the coarse fractions ([100 lm) of dust were ground in an agate grinder until fine particles (\100 lm) were obtained to chemical analysis.

History (years)

SLP1 Victory Park (SLP)

SLP2

Peony Park (MDP)

Chaoyang Park (CYP)

Fitness area Leisure area (bathing place)

NHP3

Leisure area 80

Changchun Park (CCP)

Leisure area

238

NHP4

Recreation area

NHP5

Leisure area (main entrance)

MDP1

ETP1

80

Leisure area

6.56

Leisure area 80

Leisure area

18.07

ETP2

Recreation area

CYP1

Fitness area

CYP2

LDP1

79

Recreation area

57

Leisure area 77

Leisure area

LDP2

Leisure area

CCP1

Leisure area

CCP2

Area (ha)

23

NHP1

CYP3 Labor Park (LDP)

Leisure area

SLP3

MDP2 Children’s Park (ETP)

Functional area

Recreation area 98

NHP2 South Lake Park (NHP)

Sample analysis Particle-size analysis

Sites

13

CCP3

Fitness area

12.5

65

Leisure area

Station Square (ZQS)

ZQS1

106

Leisure area

1

People’s Square (RMS)

RMS1

80

Leisure area

7

Xinmin Square (XMS)

XMS1

80

Leisure area

2.7

South Lake Square (NHS)

NHS1

80

Leisure area

2.7

WHS1 Cultural Square (WHS)

WHS2

Leisure area 17

Leisure area

WHS3

Leisure area

WHS4

Leisure area

20.5

Chemical analysis A 0.5-g dust subsample was totally digested with HNO3, HClO4, and HF acids to dryness overnight on a

hot plate (EPAC 1997a, b). The residue was solubilized with HCl and diluted to volume. Concentrations of Pb, Cr, Cu, Ni, and Zn in the digestion solution were

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Fig. 1 Location map of the study area and sampling sites of park and square dust from Changchun, China

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determined by flame (air-acetylene) atomic absorption spectroscopy with the exception of the samples for Cd, which were determined by graphite furnace atomic absorption spectroscopy. The national registered standard reference material [GBW 07405 (GSS5)] obtained from the Center of National Standard Reference Material of China was included in chemical analyses. Reagent blanks and analytical duplicates were included to ensure the accuracy and precision of analysis. All the analyses were carried out in triplicate, and the standard deviations were within ±5 % of the mean. The recoveries for the six observed metals were between 90 and 110 %. In addition, to avoid the contamination as far as possible, all chemicals used for metal measurements were guaranteed reagent, and all of the containers used during the analysis procedure were washed with detergent, acid-soaked (5 % nitric acid), and then rinsed thoroughly with deionized water.

Statistical analysis A t test was used to determine if there was a significant difference among the concentration of heavy metals in road dusts from urban parks and squares. The t tests used were comparisons of two independent sets of data at the 99 and 95 % levels of probability. Principal components analysis (PCA) was performed using SPSS 16.0 for Windows in order to aid the classification and characterization of the samples and to provide preliminary indications of associations and sources. PCA with varimax rotation was performed on log-transformed data. The components with eigenvalues [1 are extracted in this study. The contamination levels of heavy metals in urban dusts are assessed by using the geoaccumulation index (Igeo), introduced by Muller (1969), which is calculated using the following equation: Igeo ¼ log2 ðCn =1:5Bn Þ

ð1Þ

where Cn is the measured concentration of the element in environment, Bn is the geochemical background value. In this study, the natural background values of heavy metals in soils of Changchun (Meng and Li 1995) are chosen for calculating the Igeo values. The constant 1.5 is the background matrix correction factor due to lithological variability. The Igeo for each metal is calculated and classified as: uncontaminated

(Igeo B 0); uncontaminated to moderately contaminated (0 \ Igeo B 1); moderately contaminated (1 \ Igeo B 2); moderately to heavily contaminated (2 \ Igeo B 3); heavily contaminated(3 \ Igeo B 4); heavily to extremely contaminated (4 \ Igeo B 5); extremely contaminated (Igeo C 5). To determine how particles of different grain sizes contributed to the overall contamination of the urban dusts, the pollution load percentage was computed for individual sample by combining the concentration data for the grain-size fractions and their mass size percentages. The equation for GSFLoad (loading on a grain size fraction) values was adapted from Sutherland (Sutherland 2003): Ci  GSi GSFLoad ¼ P m Ci  GSi

ð2Þ

i¼1

where Ci is the heavy metal concentration in an individual grain size fraction in mg kg-1, GSi is the mass percentage of that size fraction, and m is the total number of grain size fractions.

Results and discussion Trace metal concentrations of road dusts in urban parks and squares Descriptive statistics of heavy metal concentrations of road dusts in urban parks and squares, as well as background values of Changchun topsoil (Meng and Li 1995), which are considered to be the reference values, are presented in Table 2. The concentrations of Pb (30.79–172.89 mg/kg), Cr (12.33–100.47 mg/kg), Cu (2.73–94.24 mg/kg), Ni (7.41–42.39 mg/kg), Zn (59.49–248.45 mg/kg), and Cd (0.0723–0.9707 mg/ kg) in urban dusts of Changchun varied greatly. The mean concentrations of heavy metals analyzed (except for Cr and Ni) were significantly higher than their corresponding natural background values, particularly Pb, Cu, Zn, and Cd, which had about 2.5, 1.4, 1.9, and 2.6-fold higher levels, respectively, and decreased in the order of Zn [ Pb [ Cr [ Cu [ Ni [ Cd. According to the statistics, the concentrations of heavy metals (Pb, Cr, Cu, Ni, Zn, and Cd) in road dusts of parks were comparable with the squares. The results of the t test show that there was no statistical difference between the parks and squares with the p values of Pb

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Environ Geochem Health Table 2 Heavy metal concentrations in the dusts of urban parks and squares in Changchun

Metal

Minimum (mg/kg)

Maximum (mg/kg)

Mean (mg/kg)

SD

Median (mg/kg)

Pb

30.79

172.89

69.12

31.26

59.86

Cr Cu

12.33 2.73

100.47 80.90

59.28 37.82

18.87 17.17

62.43 39.44

BC (mg/kg)

Parks

Ni

7.41

42.39

23.08

7.39

23.10

Zn

59.49

248.45

169.26

49.63

177.30

Cd

0.0723

0.9707

0.3250

0.1936

0.3205

Squares Pb

35.41

112.29

75.30

22.17

77.36

20.46

Cr

30.78

72.81

62.86

13.57

66.80

50.17

Cu

15.68

94.24

57.91

26.38

56.04

17.96

BC background concentrations in the soils of Changchun (Meng and Li 1995)

Ni

15.20

29.56

23.37

4.46

22.72

23.07

Zn

85.50

225.99

174.66

57.01

203.52

59.47

Table 3 Concentrations of heavy metals in urban road dusts in the cities from China (mg/kg)

City

Pb

Cr

Cu

Ni

Zn

Cd

Reference

Hong Kong

181.00

–

173.00

–

1,450.00

3.77

Li et al. (2001)

Guangzhou

240.00

159.30

176.00

78.80

586.00

2.41

Duzgoren-Aydin et al. (2006)

Xi’an Shanghai

230.52 294.90

167.28 159.30

94.98 196.80

– 83.98

421.46 733.80

– 1.23

Han et al. (2006) Shi et al. (2008)

Hangzhou

202.16

51.29

116.04

25.88

321.40

1.59

Zhang and Wang (2009)

53.53

54.28

94.54

43.28

294.47

1.17

Wei et al. (2009)

Cd

Urumqi Baoji Wuhan Xianyang Beijing Changchun

0.1223

408.41

0.4535

–

0.1230

0.2819

123.17

48.83

715.10

–

Lu et al. (2009)

85.5

64.1

58.4

25.8

313.35

–

Yang et al. (2011a)

77.30

135.63

132.17

69.54

375.38

0.13

Shi et al. (2013)

201.82

69.33

72.13

25.97

219.20

0.64

Du et al. (2013)

70.89

60.30

43.56

23.16

170.80

0.31

Present study

(0.46), Cr (0.31), Cu (0.13), Ni (0.22), Zn (0.42), and Cd (0.54). It is a common practice to compare mean concentrations of trace metals in urban dusts from different cities. Compared to average concentrations in urban dusts from other cities, especially old industrialized and larger cities in China (Table 3), average concentrations of heavy metals in Changchun urban dusts were lower. The data in Table 3 also indicate that the pollution of heavy metals is widespread in urban road dusts in China, particularly Pb, Cu, Zn, and Cd. The highest concentrations of Pb and Cu were found in Shanghai, which had about 3.2- and 3.5-fold higher levels than Changchun, respectively, and the highest concentrations of Zn and Cd found in Hong Kong were

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0.2763

0.0863

7.5- and 11.2-fold higher than Changchun. The findings presented here show that Changchun has less environmental pollution of heavy metals in urban dusts relative to the other cities in China, even though it is the first heavy industrial base since the establishment of the People’s Republic of China. Assessment of the degree of metal contamination in road dusts The mean values of Igeo decrease in the order of Pb [ Cd [ Zn [ Cu [ Cr [ Ni (Fig. 2). The Igeo ranges from 0.0 to 2.49 with a mean value 1.11 for Pb, -2.61 to 0.42 with a mean value -0.40 for Cr, -3.30 to 1.81 with a mean value 0.45 for Cu, -2.22 to

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0.29 with a mean value -0.64 for Ni, -0.58 to 1.48 with a mean value 0.86 for Zn, -0.84 to 2.91 with a mean value 1.06 for Cd. The mean Igeo of Cr and Ni is lower than 0, which it is uncontaminated. Cu and Zn have mean Igeo between 0 and 1, indicating uncontaminated to moderately contaminated, while Pb and Cd, with their mean Igeo higher than 1, were classified as moderately contaminated. The data indicate that the pollution of Pb, Cr, Cu, Ni, Zn, and Cd is widespread in road dusts of urban parks and squares in Changchun. The Igeo values for Cr and Ni indicate that the urban road dusts are lowly contaminated by the two metals, but the contamination levels of Pb and Cd in road dusts are high. The sites of NHP5 and CYP1 show the highest Igeo values for Pb and Cd in the main entrance of South Lake Park and the fitness area of Chaoyang Park, respectively. A high concentration of Pb in the road dust is closely associated with the heavy traffic in the main entrance of park, and atmospheric deposition is possibly the main source of Cd in the fitness area. Appropriate measures should be taken to effectively control heavy metal levels in the parks and thus protect human health.

Fig. 2 Geo-accumulation index of heavy metals in urban road dust of park and square in Changchun

According to the pollution levels of road dusts in parks and squares, all metals investigated were classified into three groups: low health risk (Cr and Ni), medium health risk (Cu and Zn), and high health risk (Pb and Cd). Though some elements such as Cu and Zn are essential nutrients, heavy metal pollutants in contaminated road dusts can have a serious impact on human health. For urban parks and squares, the direct risks of heavy metals in recreation areas, leisure areas, and fitness areas are especially significant taking into consideration inhalation, oral ingestion, and dermal exposure. Based on the total metal contents in urban park dusts, at some sites there were risks to human health, especially for children. For example, the recreation areas are the most popular place for children in parks, but the road dusts in recreation areas of Victory Park, South Lake Park, and Children’s Park in the present study were moderately contaminated by Pb, thus appropriate measures are badly needed for protecting children’s health when they are playing in the recreation area of parks. Distribution of heavy metals in particle-size fractions of road dusts The particle-size fraction of 250–2,000 lm (42.9 %) was the most abundant in the urban road dusts of Changchun, followed by the fractions of 63–100 lm (19.4 %), 100–150 lm (18.2 %), and 150–250 lm (14.7 %). The finest fraction (\63 lm) accounted for only 4.7 % of the total road dusts (Table 4). The variations of heavy metal concentration with the size fractions are shown in Fig. 3. It can be seen that the variation patterns of Pb, Cr, Cu, Ni, Zn, and Cd in the urban dust are different. Three elements (Cr, Ni, and Zn) showed higher concentrations in the fine particles (\63 lm). Unlike coarse particles, fine particles have larger available surface area and surface energy, and they have a higher adsorption rate for metals compared to larger particles (Duong and Lee 2009). The fine particles bearing toxic elements may be transported for long distances to the outside of the study area because

Table 4 Average mass fractions of different particle sizes Grain size (lm)

250–2,000

150–250

100–150

63–100

\63 0.4–13.7

Range (%)

17.7–75.0

9.0–23.7

4.0–35.3

5.3–38.0

Mean (%)

42.9

14.7

18.2

19.4

4.7

SD

14.3

3.6

8.3

7.7

2.9

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they are easily resuspended, and they can mix with local polluted particles and pollute the environment around parks and squares. So the source of dust is considered to be a significant factor in determining the

concentrations of heavy metals in road dusts in urban parks and squares. Other element concentrations in different size fractions were not so regular, but all the highest concentrations still occurred in medium-sized

Table 5 Total variance explained and component matrix for heavy metals in the urban dust Component

Initial eigenvalues

Rotation sums of squared loadings

Total

Variance (%)

Cumulative (%)

Total

Variance (%)

Cumulative (%)

Total

Variance (%)

1

3.144

52.394

52.394

3.144

52.394

52.394

2.845

47.412

47.412

2

1.635

27.257

79.651

1.635

27.257

79.651

1.934

32.239

79.651

3

0.822

13.705

93.356

4

0.221

3.677

97.033

5

0.138

2.295

99.328

6

0.040

0.672

100.000

Metal

Cumulative (%)

Extraction sums of squared loadings

Component matrix PC1

Rotated component matrix PC2

PC1

PC2

Pb

0.858

0.254

0.881

Cr

-0.427

0.842

-0.008

0.944

Cu

0.927

0.320

0.972

-0.126

Ni

-0.568

0.755

-0.172

0.929

Zn

0.869

0.408

0.960

-0.021

Cd

-0.536

0.151

-0.413

0.374

Extraction method: principal component analysis

Fig. 3 Distribution of heavy metal concentration in the size-fractioned urban dust

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-0.154

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particles (100–150 and 150–250 lm). This observation is in contrast to some other studies which have suggested that smaller particles tend to contain higher element concentrations (Adgate et al. 1998), but is in agreement with the recent study of Bosco et al. (2005). Unlike fine particles, medium-sized particles are closer to the ground when being transported by winds, and thus tend to be more localized in the area where they originate (Han et al. 2008). Consequently, heavy metals entrained by medium-sized particles in urban dust have a potential for long-term contamination with relatively small mobility. In order to determine the relative contribution of each particle size to the overall metal loads of the samples, we calculated the metal load percentage of each individual sample. The proportions of metal loadings in different size fractions of road dusts of Pb, Cr, Cu, Ni, Zn, and Cd were presented in Fig. 4. In the present study, the amount of metals accumulated in particles of \100 lm contributed about 15.3–22.1 % for 63–100 lm and 4.7–5.8 % for \63 lm of the overall metal loads in the dusts, respectively. The maximum loading percentage of the particle fractions (250–2,000 lm) accounts for 39.5–46.1 % of the total loading with the most abundant in urban road dusts. Generally, particles with a grain size of\100 lm can be easily re-suspended by wind erosion or the action of human feet (Hunt et al. 2006; Laidlaw and Filippelli 2008). In addition, particle fractions of this size tend to adhere more efficiently to human hands than coarser ones (Siciliano et al. 2009; Yamamoto et al. 2006). So

Fig. 4 The loadings of trace metals in different particle-size fractions of urban dust

these results revealed that the small particles (\100 lm) in road dusts from urban parks and squares in Changchun made little contribution to the heavy metal pollution. Identification of heavy metal sources Principal component analysis was performed for the dataset of urban dusts so as to explore the relationship between the six metals as variables, and to assign related variables into principal components. In the analysis, two principal components were considered, which account for over 79 % of the total variance (Table 5), and the eigenvalues of two extracted factors were higher than 1. The rotated component matrix indicated that Pb, Cu, and Zn were closely associated, displaying high values in the first component (PC1). As shown in Table 5, Cr and Ni showed greater values in the second component (PC2) and Cd was also partially represented in PC1. The results imply that Pb, Cu, Zn, and Cd can be defined as anthropogenic components and may originate from similar pollution sources such as the precipitation of aerosol particles released by traffic and industrial activities (Artaxo et al. 1999; Chen et al. 2005; Gray et al. 2003; Mico et al. 2006), and that the parent material and pedogenic processes may control the concentrations of Cr and Ni and Cd in part. According to the results of the PCA, some of the Pb, Cu, and Zn in the dusts may originate from similar pollution sources. Pb, Cu, and Zn in all urban dusts from Changchun are obviously higher than the background values, which suggest their anthropogenic sources. Lead and its compounds in road dusts may be released from contaminated soil near lead refineries and waste sites and from lead-containing paint. Atmospheric deposition is the main source of Pb (Dach and Starmans 2005), such as industrial production and traffic activities. Vehicle emissions have been considered to be the principal source of Pb in urban environment, which has been verified by many related studies (Chen et al. 2010; Duzgoren-Aydin et al. 2004). Historically, lead compounds (lead tetraethyl (C2H5)4Pb) were added as antiknock agents in petrol prior to their cessation in the UK in 1999 (Barlow 1999). Although the use of leaded petrol had been banned in China since 2000, the content of Pb in urban soil still reflects a significant degree of historical Pb contamination and the long half-life of Pb in soil

123

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(Yang et al. 2011b). In addition, Pb compounds are also used as anti-wear agents in lubricant oils for engines (Mang and Dresel 2007). The normal activity and deterioration of vehicles on the roads can emit Cu into the air (Martin et al. 1998; Ritter and Rinefierd 1983). Copper compounds, for example, are used in lubricants as anti-wear agents by providing a protective layer on engine surfaces to reduce friction and prevent damage due to continuous rubbing between engine parts. Cu is also used in Cubrass automotive radiators due to its high corrosive resistance and high thermal conductivity (Yang et al. 2011b) and is often used in car lubricants (AlKhashman 2007). It can be released to the urban environment as a result of wear of the automobile’s oil pump or corrosion of metal parts which come into contact with the oil (Lu et al. 2010). The wear and tear of vulcanized vehicle tires and corrosion of galvanized automobile parts were the main sources of Zn in urban dust (Adachi and Tainosho 2004; Lu et al. 2010; Smolders and Degryse 2002). The presence of Zn in tire treads is a direct result of its use (as zinc oxide) as an activator during the rubber vulcanizing process (Smolders and Degryse 2002). In addition, Zn compounds are among the alternatives added into lubricant oils (Mang and Dresel 2007). Thus the higher concentrations of Zn were found in the sample sites with heavy traffic density and old residential with lots of consumption residues. According to earlier discussions, parent material and pedogenic processes partly controlled the amounts and distribution of Cd. However, environmental pollution by Cd has been rapidly increasing in recent decades as a result of the rising consumption of cadmium in industrial production and traffic activities (Charlesworth et al. 2003; Johansson and Westerlund 2001). Traffic pollution is the main source of Cd and it is mainly from the aging of automobile tire wear, gasoline, and car body wear and so on, and brake lining wear can also cause Cd pollution (Weckwerth 2001). We did not find Cr and Ni pollution in the dust samples of the urban parks and squares. The concentrations of Cr and Ni are mainly attributable to the parent materials in the dusts. In the present study, the Cr and Ni concentrations in the road dusts from urban parks and squares in Changchun were comparable with their background values of Changchun topsoil (Meng and Li 1995).

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Conclusions It is concluded that a significant degree of metal pollution exists in some road dusts within the parks and squares of Changchun, particularly for Pb, Cu, Zn, and Cd. The calculated Igeo of the analyzed heavy metals was in the order of Pb [ Cd [ Zn [ Cu [ Cr [ Ni. The high Igeo values indicate that there was considerable Pb, Cu, Zn, and Cd pollution. Two main sources of different heavy metals in road dusts from urban parks and squares in Changchun were identified according to PCA. Pb, Cu, Zn, and Cd can be defined as anthropogenic components and may originate from similar pollution sources such as the precipitation of aerosol particles released by traffic and industrial activities, and that the parent material and pedogenic processes may control the concentrations of Cr and Ni and Cd in part. There are large differences in the metal loading percentage of different particle-size fractions among the samples from the study areas. Overall, particles in the 250–2,000 lm fraction are dominant in the total metal loading and the small particles (\100 lm) in park and square dust of Changchun made little contribution to the heavy metal pollution. These findings will facilitate the characterization of contamination of urban dusts and are significant from an environmental-management perspective, especially for the control of urban park and square contamination. Acknowledgments The authors acknowledge the support of the Knowledge Innovative Program of The Chinese Academy of Sciences (KSCX2-YW-N-077), National Natural Science Foundation of China (41071056), and Strategic Priority Research Program of Northeast Institute of Geography and Agroecology, Chinese Academy of Sciences.

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