Chemosphere 60 (2005) 542–551 www.elsevier.com/locate/chemosphere

Assessment of heavy metal pollution in surface soils of urban parks in ,

Tong-Bin Chen a,*, Yuan-Ming Zheng a, Mei Lei a, Ze-Chun Huang a, Hong-Tao Wu a, Huang Chen a, Ke-Ke Fan b,KeYuc, Xiao Wu b, Qin-Zheng Tian b

a Center for Environmental Remediation, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, 11A Datun Road, Beijing 100101, PR China b Middle School Affiliated to People’s University of China, Beijing 100081, PR China c Computing Laboratory, Oxford University, Parks Road, Oxford OX1 3QD, UK

Received 29 March 2004; received in revised form 23 December 2004; accepted 24 December 2004 Available online 10 February 2005

Abstract

Assessing the concentration of potentially harmful heavy metals in the soil of urban parks is imperative in order to evaluate the potential risks to residents and tourists. To date, little research on soil pollution in ChinaÕs urban parks has been conducted. To identify the concentrations and sources of heavy metals, and to assess the soil environmental qua- lity, samples were collected from 30 urban parks located in the city of Beijing. Subsequently, the concentrations of Cu, Ni, Pb and Zn in the samples were analyzed. The investigation revealed that the accumulations of Cu and Pb were read- ily apparent in the soils. The integrated pollution index (IPI) of these four metals ranged from 0.97 to 9.21, with the highest IPI in the densely populated historic center district (HCD). Using multivariate statistic approaches (principal components analysis and hierarchical cluster analysis), two factors controlling the heavy metal variability were obtained, which accounted for nearly 80% of the total variance. Nickel and Zn levels were controlled by parent material in the soils, whereas Cu, Pb and, in part, Zn were accounted for mainly by anthropogenic activities. The findings pre- sented here indicate that the location and the age of the park are important factors in determining the extent of heavy metal, particularly Cu and Pb, pollution. In addition, the accumulation of Zn did not appear to reach pollution levels, and no obvious pollution by Ni was observed in the soils of the parks in Beijing. Ó 2005 Elsevier Ltd. All rights reserved.

Keywords: Beijing; Heavy metal; Pollution index; Soil; Urban park

1. Introduction

The mobilization of heavy metals into the biosphere by human activity has become an important process in * Corresponding author. Tel.: +86 10 64889080; fax: +86 10 the geochemical cycling of these metals. This is acutely 64889303. evident in urban areas where various stationary and E-mail address: [email protected] (T.-B. Chen). mobile sources release large quantities of heavy metals

0045-6535/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.chemosphere.2004.12.072 T.-B. Chen et al. / Chemosphere 60 (2005) 542–551 543 into the atmosphere and soil, exceeding the natural emis- the Southeast Suburb. Recently we have undertaken sion rates (Nriagu, 1989; Bilos et al., 2001). In contrast an intensive investigation on heavy metal concentrations to agricultural soils, urban soils, especially that in parks in agricultural and forestry soils of the city (Zheng et al., and residential areas which is not used for food crops, 2003). However, the heavy metal concentrations and may also have a direct influence on public health since subsequent soil pollution levels in BeijingÕs urban parks it can be easily transferred into human bodies (De Mig- remain unknown. The concentrations and pollution lev- uel et al., 1997; Mielke et al., 1999; Madrid et al., 2002). els of soil Cu, Ni, Pb and Zn in urban parks were as- In particular, the ingestion of dust and soil has been sessed to evaluate the environmental quality of the widely regarded as one of the key pathways by which soils in the urban parks and the potential risks to resi- children are exposed to the heavy metals and metalloids dents and tourists. from paint, leaded gasoline, vehicles and local industry (Meyer et al., 1999; Rasmussen et al., 2001). Several researchers have indicated the need for a bet- 2. Materials and methods ter understanding of urban soil pollution (De Kimple and Morel, 2000; Manta et al., 2002), and, indeed, 2.1. Study area increasing research has focused on heavy metals in urban soils (Kelly et al., 1996; Chen et al., 1997; Mielke Beijing city, located in the Northern China, is not and Reagan, 1998). Heavy metals in urban soils may only a quickly developing city, but is also an ancient city come from various human activities, such as industrial with over 1000 years of history and more than 8 million and energy production, construction, vehicle exhaust, urban residents. The city consists of fourteen adminis- waste disposal, as well as coal and fuel combustion trative districts and four counties. In seven central (Komai, 1981; Ikeda and Yoda, 1982; Ritter and Rine- districts, namely Chaoyang, Chongwen, Dongcheng, fierd, 1983; Chon et al., 1995; Wong and Mak, 1997; Fengtai, Haidian, Xicheng and Xuanwu, there are Martin et al., 1998; Li et al., 2001). These activities send approximately 40 main parks (Fig. 1). The 30 parks heavy metals into the air and the metals subsequently investigated in this study are major resort or scenic sites are deposited into urban soil as the metal containing in Beijing that frequently welcome a large number of dust falls. Sakagami et al. (1982) reported that there visitors, including local residents and tourists from was a close relationship between heavy metal concentra- throughout the world. Some of the parks, such as tions in soils and those in the dust falls. Heavy metals in the , , Winter Palace the soils can also generate airborne particles and dusts, and Heaven Temple, were built hundreds of years ago which may affect the air environmental quality (Chen (Table 1). et al., 1997; Bandhu et al., 2000; Cyrys et al., 2003; Gray The seven districts listed above are the majority of et al., 2003). the commercial, industrial and traditional residential Previous studies indicated that the extent of heavy areas of Beijing. The districts of Chongwen, Dongcheng, metal pollution in urban areas varied across time (Pfeif- Xicheng and Xuanwu comprise the older historic center fer et al., 1991) and location (Albasel and Cottenie, district (HCD), while the districts of Haidian in the 1985), and that increased levels of heavy metals in urban northern region, Chaoyang in the eastern region and soil was related to the intensity of human activities and Fengtai in the southern region are the newer districts traffic volume (Zheng et al., 2002). The investigation of and have experienced substantial development over the soil heavy metal concentrations in parks and green areas past 50 years. This study examined parks both within in Seville, Spain, indicated that the concentrations of Pb, the HCD as well as in the other newer regions (Fig. 1; Zn and particularly Cu in the soil often exceeded the Table 1). According to the Beijing Municipal Statistical acceptable limits for residential, recreational and institu- Bureau (2001), the population densities in 2000 were tional sites (Madrid et al., 2002). However, differences 27332 persons/km2 in the HCD and 3337 persons/km2 among cities including population density and industrial outside the HCD. Moreover, although the area of the activities could have a large impact on the findings of HCD comprised only 8.2% of Beijing city, it accounted individual studies. Moreover, little information is avail- for 37.2% of the traffic burden (Jin, 2000). Thus, the able on heavy metal concentrations in soils of urban HCD is a much more densely populated and high traffic parks located in older cities with large populations. region. Beijing, the capital of China, is one of the oldest and most densely populated cities in the world. During the past two decades, research on heavy metal concentra- 2.2. Sampling and analysis tions in the natural and agricultural soils of rural areas has been conducted in Beijing, including surveys of Depending on the area of the parks, 14–30 sub-sam- the background concentrations of soil heavy metals ples of the topsoil (0–5 cm) were collected in each park (CNEMC, 1990) and heavy metal contamination in and mixed thoroughly to get a representative sample. 544 T.-B. Chen et al. / Chemosphere 60 (2005) 542–551

Fig. 1. Sampling sites of soils taken from the urban parks. Full names of the parks listed in Table 1.

Table 1 Brief description of the parks investigated in Beijing Name of parks Abbr. name District History (years) Location (inside or outside the HCD) Area (ha) Forbidden City GUG Dongcheng 596 Inside 72 Heaven Temple TTP Chongwen 582 Inside 270 ZSP Dongcheng 581 Inside 24 Xuanwu Park XWP Xuanwu 538 Inside 7.4 Solar Temple RTP Chaoyang 472 Outside 1 Terra Temple DTP Dongcheng 472 Inside 42.7 Lunar Temple YTP Xicheng 472 Inside 8.1 TRT Xuanwu 307 Inside 59 Winter Palace YMY Haidian 258 Outside 350 JSP Xicheng 251 Inside 23 Summer Palace YHY Haidian 238 Outside 290.8 BHP Xicheng 206 Inside 71 BJZ Xicheng 94 Inside 90 Longtanhu Park LTH Chongwen 50 Inside 120 HLJ Chaoyang 44 Outside 37.5 Liuyin Park LYP Dongcheng 44 Inside 19 Qingnianhu Park QNH Dongcheng 44 Inside 17 YYT Haidian 42 Outside 140.7 Zizhuyuan Park ZZY Haidian 37 Outside 14 Guanyuan Park GYP Xicheng 20 Inside 15 CYP Chaoyang 18 Outside 320 Shuangxiu Park SXP Xicheng 18 Inside 6.4 Tuanjiehu Park TJH Chaoyang 16 Outside 13.8 Rendinghu Park RDH Xicheng 16 Inside 9 Fengtai Park FTP Fengtai 16 Outside 20 Daguan Yuan DGY Xuanwu 16 Inside 13 Beijing Amusement Park BJA Chongwen 15 Inside 40 Wanfangting Park WFT Fengtai 12 Outside 10.6 World Park SJP Fengtai 9 Outside 46.7 Minzu Park MZP Chaoyang 8 Outside 40 T.-B. Chen et al. / Chemosphere 60 (2005) 542–551 545

The sample was air-dried, ground, passed through a 3. Results nylon sieve of 100 meshes, and digested with HNO3 and H2O2 using the Method 3050B suggested by Descriptive statistical results are reported in Table 2, USEPA (1996). The concentrations of Cu, Ni, Pb and including the geometric mean and the geometric stan- Zn in the digestion solution were analyzed with a flame dard deviation. Mean values were used when heavy atomic absorption spectrometer (Vario 6, Jena Co. Ltd., metal concentrations had normal distributions and geo- Germany). Standard reference materials, GSS-1 soils, metric mean values were used when heavy metal concen- obtained from Center of National Standard Reference trations had lognormal distributions. We found that Ni Material of China, were inserted for quality assurance levels were comparable with the BC, while Cu, Pb and and quality control (QA/QC) procedures. Satisfactory Zn exhibited higher concentrations than the BC, partic- recoveries were obtained for Cu (91–95%), Ni (103– ularly Cu and Pb, which had about 2- and 1-fold higher 112%), Pb (95–108%) and Zn (95–104%). levels, respectively. The highest concentrations of Cu and Pb, 457.5 and 207.5 mg/kg, found in GUG, the old- 2.3. Statistical treatment est park, were 18- and 6-fold higher than the BC. There- fore, it was evident that Cu and Pb pollution existed in This study employed hierarchical cluster analysis the park soils samples. (HCA) and principal components analysis (PCA) of the Cu, Ni, Pb, and Zn concentrations in the soils. Be- 3.1. Hierarchical cluster analysis (HCA) cause the concentrations of the soil heavy metals varied greatly, the raw data were standardized before HCA. Based on the HCA results, the samples were classified Statistical calculations were also made within each clus- into six clusters using a criteria value of rescaled distance ter to allow for further comparison between clusters. between 5 and 10 (Fig. 2). There were 13 parks in cluster To assess the soil environment quality, a pollution I, 11 parks in cluster II, two parks in clusters III and V, index (PI) of each metal and an integrated pollution and only one park in clusters IV and VI, respectively index (IPI) of the four metals were attributed to each (Fig. 1; Table 3). park. The PI was defined as the ratio of the heavy metal The mean concentrations of heavy metals in cluster I concentration in the study to the geometric means of were higher than those in cluster II (Table 3). Means background concentration (BC) of the corresponding comparison of heavy metal indicated that there were sig- metal of Beijing (Chen et al., 2004). The PI of each metal nificant differences between the two clusters for Pb, Ni was calculated and classified as either low (PI 6 1), mid- and Cu. Notably, 12 of the 13 parks in cluster I were in- dle (1 < PI 6 3) or high (PI > 3). The IPI of the four side the HCD, while nine of the 11 parks in cluster II metals for each park was defined as the mean value of were outside the HCD (Fig. 1). The location of the parks the metalÕs PI, and was then classified as low (IPI 6 1), appears to affect the heavy metal concentrations in the middle (1 < IPI 6 2) or high (IPI > 2). soil samples greatly. The distribution of data was tested with the Shapiro– The samples in clusters III, IV and VI, which were Wilk method (p < 0.05). All statistical treatments men- characterized with longer histories, had much higher tioned above were performed using SPSS and Origin concentrations of Pb compared with those in clusters I Pro software. and II. There were significant differences between the

Table 2 Heavy metal concentrations in the soils of urban parks in Beijing Metal concentration (mg/kg) Distribution type Min. Max. Mean S.D. Geom. M. Geom. S.D. Soils from the investigation of urban parks (Soil samples = 30) Cu 24.1 457.5 71.2 74.7 59.6 1.63 Lognormal Ni 6.10 37.2 22.2 8.70 21.4 1.49 Normal Pb 25.5 207.5 66.2 44.2 55.8 1.76 Lognormal Zn 25.7 196.9 87.6 31.2 82.5 1.44 Lognormal Background concentrations in the soils of Beijing (Chen et al., 2004) Cu 6.00 37.9 19.7 6.30 18.7 1.41 Lognormal Ni 11.0 59.3 27.9 7.90 26.8 1.34 Lognormal Pb 11.5 38.2 25.1 5.10 24.6 1.28 Lognormal Zn 27.9 119.8 59.6 16.3 57.5 1.30 Lognormal 546 T.-B. Chen et al. / Chemosphere 60 (2005) 542–551

higher than the mean concentrations of all parks. GUG was built as an imperial palace about 600 years ago. It is a popular park located in the HCD with the highest population and traffic density in the city, and accommodates a large quantity of visitors every year. All these factors are likely to accelerate accumulation of heavy metals in the soils. Therefore, it seemed that the location of the urban park was a very important factor in determining the soil heavy metal concentrations since the samples collected from inside the HCD had a much greater accumulation of heavy metals. The history of park may also contribute to the increased concentrations of heavy metals in the soils. There were no significant differences between the Zn concentrations of any two clusters, suggesting that human activities have less different influence on Zn levels in the soils.

3.2. Principal components analysis (PCA)

The results of the PCA indicated that Cu, Ni, Pb and Zn concentrations could be reduced to two components, Fig. 2. Dendrogram of hierarchical cluster analysis of heavy which accounted for nearly 80% of the total variance for metal concentrations in urban park soils of Beijing. the data (Table 4). The communalities of variables ran- ged from 75% for Pb to 85% for Ni. All the elements were well represented by two components. Pb concentrations of cluster III and those of clusters I The initial component matrix indicated that Cu and and II. There were only one park in clusters IV and VI Pb were associated, displaying high values in the first and no comparison could be conducted between cluster component (F1). Nickel and Zn showed greater values IV or VI and other clusters. in the second component (F2) and were also partially Cluster V was unique because of its low concentra- represented in F1. The rotation of the matrix eliminated tion of Ni. The Pb concentration was not significantly ambiguities. As shown in Table 4, F1 included Cu and different from that of cluster II, but was significantly dif- Pb, F2 included Ni, and Zn was distributed in both F1 ferent from those of clusters I and III. The samples in and F2. This implies that some of the Cu, Pb and Zn this cluster were taken from the parks at the southern in the soils may originate from similar pollution sources, border of the HCD. Therefore, the concentrations of such as the deposition of aerosol particles emitted by the metals, with the exception of Ni, were similar to that vehicular traffic (Artaxo et al., 1999; Cyrys et al., 2003; in cluster II. Gray et al., 2003), and that the parent materials of the Cluster VI consisted of GUG with the highest Pb and soils may control the concentrations of Ni, and Zn in Cu concentrations, which were about 6- and 3-fold part.

Table 3 Statistics of the clusters in hierarchical cluster analysis (HCA) Cluster No. of samples Means of park history (years) Soil heavy metal concentration (mg/kg) Cu Ni Pb Zn Mean S.D. Mean S.D. Mean S.D. Mean S.D. I 13 197.2 62.9a 14.8 27.1a 4.41 63.1a 26.7 83.0 17.5 II 11 99.5 46.5b 12.7 17.6b 4.25 41.1b 11.6 78.7 23.8 III 2 222.0 74.4ab 23.5 19.5b 6.37 147.0c 13.6 102.5 20.3 IV 1 472.0 74.7 – 37.2 – 136.6 – 80.8 – V 2 161.0 62.7ab 3.66 6.10 – 37.8b 1.8 124.3 102.6 VI 1 596.0 457.5 – 36.6 – 207.5 – 148.5 – * a, b and c showed that there are significant differences between heavy metal concentrations at 0.05 levels. T.-B. Chen et al. / Chemosphere 60 (2005) 542–551 547

Table 4 Total variance explained and component matrices for the heavy metals Total variance explained Factor Initial eigenvalues Extraction sums of squared Rotation sums of squared loadings loadings Total % of Cumulative Total % of Cumulative Total % of Cumulative variance (%) variance (%) variance (%) 1 2.140 53.51 53.51 2.140 53.51 53.51 2.064 51.59 51.59 2 1.126 28.15 81.66 1.126 28.15 81.66 1.203 30.07 81.66 3 0.473 11.83 93.49 4 0.260 6.51 100.00 Component matrix Element Component matrix Rotated component matrix 12 12 Cu 0.917 0.013 0.878 0.265 Ni 0.487 0.780 0.254 0.884 Pb 0.870 0.007 0.835 0.246 Zn 0.553 À0.720 0.729 À0.540 Extraction Method: Principal Component Analysis (PCA).

3.3. Statistical results Table 5 Statistical results of pollution index (PI) of heavy metals in the According to the location, all parks investigated were urban park soils of Beijing classified into two groups: the parks inside the HCD PI Number of samples (group I) or the ones outside the HCD (group II). The Min Max Mean Low Middle High Cu concentration for group I was significantly greater than that for group II (p < 0.01). Cu 1.29 24.47 3.81 0 14 16 Ni 0.23 1.39 0.83 20 9 0 Based on the history of their establishment, the parks Pb 1.04 8.43 2.69 0 21 9 were classified into two groups: the parks with a history Zn 0.45 3.42 1.52 4 25 1 < 100 years (class A) and the parks with a history > 100 years (class B). There were significant differences be- tween two classes (p < 0.01). There were significant correlations between the his- The PIs of Cu and Pb were much higher since all of tory of the parks and the concentrations of Cu (correla- the 30 samples contained medium to high PIs, ranging tion coefficients: 0.580, p < 0.01) and Pb (correlation from 1.29 to 24.47 for Cu and from 1.04 to 8.43 for coefficients: 0.628, p < 0.001). Pb. These data indicate that the Cu and Pb pollution All results listed above made the basis of discussion is widespread in the urban parks of Beijing. Further- later. more, there were 16 parks with high PIs for Cu and nine parks with high PIs for Pb, which accounted for about one-half and one-third of all of the parks investigated 3.4. Assessment of the environmental quality for the in this study, respectively. The maximal PIs were 24.47 soils of urban parks for Cu and 8.43 for Pb. Thus, it is very likely that many of the urban parks in Beijing are highly polluted with Cu The PIs, calculated according to the BC of heavy met- and Pb. als, varied greatly across the different metals (Table 5). The IPIs of all parks varied from 0.97 to 9.21 with an Nickel and Zn exhibited lower values, ranging from average of 2.21 (Table 6). There was only one park with 0.23 to 1.39 and from 0.45 to 3.42, respectively. For Ni, an IPI < 1, 15 parks with an IPI between 1 and 2, and 14 the mean PI was 0.83 and all of the samples had low or parks with an IPI > 2. In particular, the GUG demon- mid-level PIs, indicating that the concentration of Ni in strated an IPI of 9.21, indicating the presence of serious the soil samples were comparable with the BC of Beijing heavy metal pollution. Approximately one-half of the and there was no obvious pollution of Ni in the park soil parks investigated had high pollution levels. Thus the samples. The mean PI for Zn was 1.52, but only one sam- soil quality of BeijingÕs urban parks has clearly been im- ple was classified as high PI, indicating an absence of pacted, particularly those parks visited by large crowds problematic Zn pollution of soils in Beijing parks. of people, such as GUG, BHP and YYH. 548 T.-B. Chen et al. / Chemosphere 60 (2005) 542–551

Table 6 Integrated pollution index (IPI) of heavy metals in the urban park soils of Beijing High (IPI > 2.0) Middle Low (1.0 < IPI 6 2.0) (IPI 6 1.0) Park IPI Park IPI Park IPI GUG 9.21 QNH 1.99 SJP 0.97 BHP 3.54 BJZ 1.85 RTP 3.09 SXP 1.73 GYP 2.76 FTP 1.67 JSP 2.71 WFT 1.67 YHY 2.69 LTH 1.66 DTP 2.44 YMY 1.65 Fig. 3. Mean concentrations of heavy metals in the soils: ZSP 2.39 CYP 1.55 classified in terms of the location of parks inside or outside the DGY 2.29 HLJ 1.53 HCD. Concentrations of Ni and Zn are arithmetic mean values XWP 2.24 MZP 1.52 within the normal distribution. Others are geometric mean TTP 2.18 RDH 1.50 values within the lognormal distribution. YTP 2.18 TRT 1.47 BJA 2.11 TJH 1.40 Table 7 LYP 2.01 YYT 1.37 Numbers of the parks attributed with high PIs or IPIs classified ZZY 1.03 with location and history Numbers Location History 4. Discussion Inside Outside <100 P100 the HCD the HCD yrs yrs In this study, the assessment of the soil environment Total numbers 18 12 18 12 quality suggests that heavy metal pollution in the park No. of high PIs 14 2 5 11 soils may be related to the location and the history of for Cu the parks. Different locations are associated with differ- No. of high PIs 7227 ences in the density of traffic and human activities. The for Pb age of the parks affected the heavy metal deposition No. of high IPIs 12 2 4 10 found in the soils samples. It is also true that the older parks are more well-known and attract greater numbers of tourists, which is obviously accompanied by a greater tant factors in determining the accumulation of heavy amount of traffic. metals in urban soils (Albasel and Cottenie, 1985). The research performed in Seville, Spain (Madrid et al., 4.1. Location of the parks and the heavy metal 2002) indicated that the concentrations of Pb, Zn and, concentrations particularly, Cu in the soils from major parks and green areas closer to the historic center often exceeded the According to the location, all parks investigated were acceptable limits for residential, recreational and institu- classified into two groups: the parks inside the HCD tional sites. The results of another study found that the (group I) or the ones outside the HCD (group II). The soils from the center of Rostock, Germany had higher mean values of the four heavy metals in the parks of metal contents than did the soils from the outskirts of group I were all much greater than those in the parks the town (Kahle, 2000). Therefore, the higher concentra- of group II (Fig. 3). The Cu concentration for group I tions of heavy metals in the HCD of Beijing may be was significantly greater than that for group II. In addi- interpreted as being directly related to heavy human tion, 14 of 16 parks with high PIs for Cu were inside the activities, such as traffic. The location of a park is clearly HCD, while seven of nine parks with high PIs for Pb one important factor determining the extent of heavy were inside the HCD (Table 7). Of the14 parks with high metal accumulation, particularly of Cu and Pb, in urban IPIs, only two were outside the HCD. Therefore, in this park soil. study park location was related to the amount of heavy Based on location, parks with similar development metal accumulation found in the soil samples, particu- history (<50 years) were classified into two groups: larly for Cu and Pb. parks inside or outside the HCD. Comparison of the The HCD of Beijing is the oldest urban region of the means showed that the parks inside the HCD had mark- city. The traffic intensity in HCD is 4.1 times greater edly higher Cu concentrations than those outside the than that in the districts outside the HCD (Jin, 2000). HCD. Large differences in heavy metal concentrations Commercial and traffic activities are known to be impor- in the soils, especially of Cu and Pb, were seen among T.-B. Chen et al. / Chemosphere 60 (2005) 542–551 549 the soil samples from parks at different locations with a 4.3. Analysis of the pollutant sources similar development history. It is important to note that TRT and BJA, which are located in regions with a The concentrations of Cu and Pb in the soils samples shorter urbanizing history (at the southern HCD border from most of the urban parks of Beijing exceeded the and near the Fengtai district), had lower heavy metal corresponding BC and, indeed, serious soil pollution concentrations than did other parks in the HCD. was found in some parks. Anthropogenic sources may contribute to this elevation of Cu and Pb concentrations 4.2. History of the parks and the extent of pollution in the soils. In fact, Cu and Pb soil pollution appears to be readily affected by anthropogenic factors (Artaxo Based on the history of their establishment, the parks et al., 1999; Martin, 2001; Gray et al., 2003). were classified into two groups: the parks with a history Atmospheric deposition of heavy metals, including < 100 years (class A) and the parks with a history > 100 Cu and Pb, is considered to be a significant factor in soil years (class B). As shown in Fig. 4, the mean concentra- pollution (Martin, 2001; Nicholson et al., 2003). In tions of Cu and Pb in class B were approximately 1.5 woodlands this pollution is increased by 33–259%, and 2 times as high as those in class A, respectively. depending on the metal. Lead deposition in particular There were significant differences between two classes. is greatly influenced by vehicle emissions and the intro- In addition, among the 12 parks in class B, 10 had high duction of Pb into gasoline (Blake and Goulding, IPIs overall, 11 parks had high PIs for Cu, and 7 had 2002). This study focused on a region with a high density high PIs for Pb (Table 7). These findings indicate that of traffic and human activities, associated with higher most of the parks in class B have been polluted with levels of airborne heavy metals. This in turn may affect heavy metals, particularly with Cu and Pb. Further- the soil environmental quality via subsequent atmo- more, the parks in class B accounted for the majority spheric deposition. Although petrol with lead additives of the parks with high PIs or IPIs overall. There were has been banned in Beijing for several years, lead pollu- also significant correlations between the history of the tion may continue to affect the soil environment for parks and the concentrations of Cu and Pb. years to come. Vehicle emissions and other human activities may The normal activity and deterioration of vehicles on contribute to the accumulation of heavy metals, such the roads can emit heavy metals into the air, especially as Cu and Pb, in soils (Pfeiffer et al., 1991; Blake and Cu (Ritter and Rinefierd, 1983; Martin et al., 1998). Goulding, 2002; Zheng et al., 2002). In this study, the Thus, the various traffic densities can influence the older and more tourist-appealing parks appear to suffer amount of Cu emitted by local vehicles. Application of the highest amount of human traffic, which in turn may Pb- and Cu-containing house paints may also contribute elevate Cu and Pb pollution levels of soils in the parks. to Pb and Cu pollution levels (Alloway and Ayres, 1997; Other reports have found that the extent of pollution Wells et al., 2000). The age of the dwelling is also impor- varied with age and was more serious in the historic area tant in determining the heavy metal concentrations in of the city (Pfeiffer et al., 1991; Madrid et al., 2002). the surroundings (Tong, 1998; Rieuwerts et al., 1999). Taken with our findings, it is evident that the history Therefore, the high concentrations of Cu and Pb in the of the parks should be another factor related to the in- older parks might be related to the discharge of heavy crease of the heavy metal concentrations in the soils. metals contained in the paints in the region. In general, influences between air and soil pollution are mutual. Just as the atmosphere can transfer a large amount of heavy metals into urban soils through precipi- tation (Carey et al., 1980; Ritter and Rinefierd, 1983; Pa- tel et al., 2001), soil dust can also contribute to the concentrations of heavy metals in the air (Chen et al., 1997). Consequently, airborne particles and soil dust containing elevated heavy metal concentrations may en- ter and harm the human body through breathing and ingestion (Chen et al., 1997). Substantial evidence indi- cates that blood Pb concentration is correlated with that in oneÕs environment (McMichael et al., 1985; Bellinger et al., 1990). Fig. 4. Mean concentrations of heavy metals in the soils: In the present study, soil concentration of Zn was classified in terms of the history of the parks. Concentration of also found to be correlated with the level of human Ni is an arithmetic mean value within the normal distribution. activities (Artaxo et al., 1999; Cyrys et al., 2003; Gray Others are geometric mean values within the lognormal et al., 2003). Although the Zn concentration in the urban distribution. park soils may be influenced by anthropogenic activities, 550 T.-B. Chen et al. / Chemosphere 60 (2005) 542–551 it appears to be largely related to the parent materials of Alloway, B.J., Ayres, D.C., 1997. In: Chemical Principles of the soils since Zn was distributed in F1 and F2 in the re- Environmental Pollution. Blackie Academic and Profes- sults of PCA. Zinc accumulation in park soil was rela- sional, London, p. 17. tively low compared to that of the soil background Zn Artaxo, P., Oyola, P., Martinez, R., 1999. Aerosol composition concentration in Beijing soils. With respect of the pollu- and source apportionment in Santiago de Chile. Nuclear Instruments and Methods B 150, 409–416. tion levels of Cu and Pb, the pollution extent of Zn was Bandhu, H.K., Sanjiv, P., Garg, M.L., Singh, B., Shahi, J.S., much lower. Mehta, D., Swietlicki, E., Dhawan, D.K., Mangal, P.C., We did not find Ni pollution in the soil samples of the Singh, N., 2000. Elemental composition and sources of air urban parks. The soil concentration of Ni is mainly pollution in the city of Chandigarh, India, using EDXRF attributable to the parent materials in the soil (Pierce and PIXE techniques. Nuclear Instruments and Methods B et al., 1982; Chen et al., 1999; Zupan et al., 2000). In this 160, 126–138. study, the Ni concentrations in the park soil samples Beijing Municipal Statistical Bureau (compiled), 2001. Beijing were comparable with the background Ni concentration Statistical Yearbook. China Statistics Press, Beijing, in Beijing soils. p. 72. Bellinger, D., Leviton, A., Slowman, J., 1990. 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