Heavy metals and polycyclic aromatic hydrocarbons: Pollution and ecological risk assessment in street dust of Tehran

Journal of Hazardous Materials 227–228 (2012) 9–17

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Heavy metals and polycyclic aromatic hydrocarbons: Pollution and ecological risk assessment in street dust of Tehran Mohsen Saeedi a,b,∗ , Loretta Y. Li b , Mahdiyeh Salmanzadeh a a b

Environmental Research Laboratory, School of Civil Engineering, Iran University of Science and Technology, Narmak, Tehran 16846, Iran Department of Civil Engineering, The University of British Columbia, 6250 Applied Science Lane, Vancouver, British Columbia V6T 1Z4, Canada

a r t i c l e

i n f o

Article history: Received 2 October 2011 Received in revised form 17 April 2012 Accepted 19 April 2012 Available online 8 May 2012 Keywords: Street dust Heavy metal PAH Ecological risk Multivariate analysis

a b s t r a c t 50 street dust samples from four major streets in eastern and southern Tehran, the capital of Iran, were analyzed for metal pollution (Cu, Cr, Pb, Ni, Cd, Zn, Fe, Mn and Li). Hakanson’s method was used to determine the Risk Index (RI) and ecological risks. Amongst these samples, 21 were also analyzed for polycyclic aromatic hydrocarbons (PAHs). Correlation, cluster and principal component analyses identified probable natural and anthropogenic sources of contaminants. The dust had elevated concentrations of Pb, Cd, Cu, Cr, Ni, Zn, Fe and PAHs. Enrichment factors of Cu, Pb, Cd and Zn showed that the dust is extremely enriched in these metals. Multivariate statistical analyses revealed that Cu, Pb, Zn, Fe and PAHs and, to a lesser extent, Cr and Ni have common anthropogenic sources. While Mn and Li were identified to have natural sources, Cd may have different anthropogenic origins. All samples demonstrated high ecological risk. Traffic and related activities, petrogenic and pyrogenic sources are likely to be the main anthropogenic sources of heavy metals and PAHs in Tehran dust. © 2012 Elsevier B.V. All rights reserved.

1. Introduction The growth of population, industrial activities and vehicles in large cities are the major causes of pollution in urban environments. Top soils, roadside and street dusts are among the indicators of environmental urban pollutants [1,2]. Amongst different pollutants, heavy metals and petroleum hydrocarbons are the most harmful to public health and to the environment in urban systems [3–6]. Heavy metals in street dust may originate from anthropogenic sources such as petroleum, diesel and coal combustion, as well as industrial activities [4,7] and natural geochemical processes such as weathering. Heavy metals are not biodegradable and can remain in soil and dust over long periods of time. Human exposure to heavy metals in the urban environment likely occurs through food, drinks and water [8]. Skin contact and hand-mouth contamination could be due to direct exposure to metal-contaminated dust, in particular unintentional uptake by children in playgrounds and city streets [9]. Metal pollutants such as Cd, Cr, Ni and Pb have cumulative effects, causing growth retardation in children, kidney disease, cancer and many other adverse health effects [10].

∗ Corresponding author at: Environmental Research Laboratory, School of Civil Engineering, Iran University of Science and Technology, Narmak, Tehran 16846, Iran. Tel.: +98 9121900228; fax: +98 2177240398. E-mail address: [email protected] (M. Saeedi). 0304-3894/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jhazmat.2012.04.047

Polycyclic aromatic hydrocarbons (PAHs) are mainly released into the urban environment as a result of fossil fuel combustion, motor vehicle emissions, wood and waste burning, painting, asphalt pavement operations and solvent application in small industries and workshops [11]. PAHs with large number of rings cause adverse health effects such as genetic mutations and cancer [10,12]. Benzo[a]pyrene, one of the most hazardous PAHs, is categorized as a probable human carcinogenic substance by the USEPA [13]. Street dust contamination has received much attention in recent years [2,10,11,14,15]. Multivariate analyses, such as cluster and principal component analyses, have been used to identify probable sources of heavy metals and PAHs. De Miguel et al. [16], based on the ward method and principal component analysis, found that high vehicle traffic volumes, building construction and natural resources are probable sources of 25 trace metals in Madrid (Spain) and Oslo (Norway). Ordonez et al. [17] used cluster analysis to distinguish human activities and natural sources as possible origins of 27 metals in an industrial city in northern Spain. Metal contamination in street dust has been studied extensively in developed countries, but data are scarce for developing countries. There are even fewer data available on PAHs contamination in street dust around the world [10,11,18,19]. In recent years, large amounts of atmospheric dusts have been deposited in Tehran, crossing the western borders of Iran. Even though there is no confirmed origin, it is suspected that most of this dust originates from the dry wetlands of southeastern Iraq and the

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Fig. 1. Street dusts sample collection sites. () Samples for metal analysis. () Samples for metal and PAHs analysis.

desserts of Iran’s western neighbors. Tehran, experiencing a rapidly growing population, is polluted by heavy traffic, residential heating, small industries and workshops. With severe dry deposition and dust settling in the area, no known study has been conducted nor reported on the environmental quality of the street dust of Tehran. This study primarily examines nine metals (Cu, Pb, Cr, Ni, Cd, Zn, Fe, Mn, Li) and 16 priority PAH pollutants [20] in the street dust of Tehran and their potential health and environmental impact. We comprehensively evaluate metals and PAHs through analysis of 50 street dust samples for metals and 21 samples for PAHs combined with multivariate statistical analysis. The major objectives are to identify probable natural and anthropogenic origins of theses pollutants and to assess the intensity of metal contamination.

campus, located inside the eastern sampling network. This campus covers an area of ∼44 ha with relatively reduced traffic around it and higher plant and tree coverage. Approximately 500 g of dust composite sample were collected at each location indicated in Fig. 1 using a broom and suction from six points at the edge of roads and pavement. Samples for metals analyses were stored in closed polyethylene bags at a temperature <4 ◦ C. The laboratory samples were air-dried at room temperature to a constant weight, and then screened through #10, 35, 60 and 230 (63 ␮m) sieves for particle size analysis. Their mean particle sizes were 18, 22, 49, 11% respectively.

2. Materials and methods

The street dust <63 ␮m which affects human respiratory systems and causes risk to human health [23], was digested according to the USEPA 3050B method [24] using HCl, HNO3 and H2 O2 for total metal analyses. The concentrations of metals (Cu, Pb, Cr, Ni, Cd, Zn, Fe, Mn, and Li) were determined by an Atomic Absorption Spectrometer (Buck Scientific-210 VGP model equipped with Deuterium lamp background correction) according to USEPA7000s series methods [25]. Samples for hydrocarbon analysis were stored in amber glass Teflon-capped containers. Particles <63 ␮m were prepared for analyses according to EPA-3550C-ultrasonic extraction method [26] according to Banger et al. [27]. In brief, samples were extracted with dichloromethane. After sonication for 3 min, samples were allowed to settle; solvent layer was decanted and filtered through a Whatman 41 filter into a glass tube. This step was repeated twice. After the second sonification, the mixture was poured onto the same Whatman 41 filter, both dust and beaker were rinsed with dichloromethane, and the filtrate was obtained. The filtrate from the previous steps was evaporated to about 0.75 ml using nitrogen gas. The liquid sample was transferred to a 1 mL volumetric flask and brought up to the volume using dichloromethane. Deuterated PAHs (naphthalene-d8(d8Nap), acenaphthene-d10(d10-Ace), phenanthrene-d10(d10-Phe), chrysene-d12(d12-Chr) and perylene-d12(d12-Per)) were used as internal standards for quantification just before the injection.

2.1. Study area Tehran is one of the oldest cities of Iran. It covers an area of 730 km2 with a population of 8,791,000 [21]. With a density of ∼11,000 persons km−2 , it is the most densely populated area in Iran and in the Middle East [21]. 2.2. Sample collection and preparation Fall and winter are the rainy seasons in Tehran. Samples were collected in August 2010, the driest month of the year. The prevalent wind direction is west to east [22], the air pollutants and particles tend to settle in the eastern parts of Tehran. In total, 50 samples were collected in different locations in eastern and southern Tehran (Fig. 1), near major pollution sources such as a thermal steam power plant, the major diesel bus terminal of the city and some industrial sources. 14 samples were taken from the southern part and 35 from eastern of Tehran. The eastern sampling points were selected along high-traffic streets and highways of this part of the city. Areas next to gas stations, workshops, factories and any other direct sources of significant pollution were avoided in selecting the sampling locations. One sample was also taken from the central part of the Iran University of Science and Technology

2.3. Chemical analysis

M. Saeedi et al. / Journal of Hazardous Materials 227–228 (2012) 9–17

According to Hanedar et al. [28], PAHs extracts were analyzed by High-Performance Liquid Chromatography (HPLC-Agilent + 1100 Series model) using UV–visible and fluorescence detectors in series. Separation was performed by means of a column with a corresponding guard cartridge. The UV–visible detector is operated at wavelength of 254 nm, and the in-series fluorescence spectrophotometer wavelength is programmed according to the elution time. A gradient elution program was utilized using mobile phases of acetonitrile and distilled deionized water. A flow rate of 1 ml min−1 was maintained at 20 ◦ C; the equilibration time was set at 5 min. The system was calibrated for the 16 EPA target PAHs [20]: Naphthalene (Nap), Acenaphthylene (Acy), Acenaphthene (Ace), Fluorene (Fl), Phenanthrene (Phe), Anthracene (Ant), Fluoranthene (Flu), Pyrene (Pyr), Indeno[1,2,3c,d]pyrene (IND), Chrysene (Chr), Benzo[b]fluoranthene (BbF), Benzo[k]fluoranthene(BkF), Benzo[a]pyrene(BaP), Dibenzo[a,h]anthracene (DBA), Benzo[g,h,i]perylene (BghiP) and Benzo[a]anthracene (BaA). USEPA classifies these PAHs as premier polycyclic aromatic hydrocarbons [29].

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Table 1 Enrichment categories on the basis of EF values [34]. EF Value

Enrichment category

EF < 2 2 ≤ EF < 5 5 ≤ EF < 20 20 ≤ EF < 40 EF ≥ 40

Deficiency to minimal enrichment Moderate enrichment Significant enrichment Very high enrichment Extremely high enrichment

Table 2 Potential ecological risk categories on the basis of RI values [41]. RI values

Ecological risk category

RI < 150 150 ≤ RI < 300 300 ≤ RI < 600 RI ≥ 600

Low ecological risk Moderate ecological risk Considerable ecological risk Very high ecological risk

2.7. Enrichment factors and ecological risks Enrichment factors (EFs) were calculated according to:

2.4. Quality assurance/quality control EF =

(Cx /Cref )sample (Cx /Cref )background

.

(1)

All 50 samples and blanks were analyzed in duplicates for quality assurance/quality control of laboratory analyses. MESS-3 from Institute for National Measurement Standards, National Research Council of Canada (NRC) was used as the standard sediment sample for quality control of metal analyses. The measured concentrations of all metal analyzed were within the published metal contents given by NRC (2000) [30]. For PAHs QA/QC was performed by field and laboratory blanks and standard spiked recoveries. For the analysis of solutions, a standard reference material of house dust (SRM 2585) of the National Institute of Standards and Technology (NIST), USA was used for calibration and analytical control. PAHs were identified relative to internal standards. Recoveries of SRM and internal standards varied from 75% (Pyr) to 133% (Nap).

To determine the metal enrichment in street dusts and probable natural or anthropogenic sources [14]. Here (Cx /Cref ) is the ratio of concentrations of heavy metal to the concentration of a reference metal in the sample and background. In this study, the reference metal was selected based on correlation coefficient analysis and multivariate statistical analyses from metals that are neither likely to be affected by anthropogenic activities nor correlated with heavy metal pollutants. Five different categories defined for EF values are listed in Table 1 [34]. The method of determining ecological risks of heavy metals originally introduced by Hakanson [41] has recently been used in soil contamination studies [42,43]. Hence, the potential ecological risk index

2.5. Statistical analysis

RI =

m 

Er

(2)

i=1

SPSS 18.0 and MVSP software packages were used to perform statistical analyses. Pearson’s correlation coefficient analysis, Cluster analysis (CA) and principal component analysis (PCA) identified the relationship among contaminants in street dusts and their probable sources. The Pearson correlation coefficient measures the strength of relationships between pairs of contaminants within samples. CA and PCA are among the most common multivariate statistical methods widely applied by environmental researchers [31,32]. In recent years these methods have also been used in soil and street dust contamination studies [14,32–35]. CA was used here to evaluate the similarities of metals sources in street dust samples. PCA was also utilized to identify sources, apportioning them to natural vs. anthropogenic sources.

was adopted to assess the degree of metal pollution in Tehran street dusts. Here Er = Tr × Cf and Cf =

Cs Cn

where Cs and Cn are heavy metal sample and background concentrations, respectively. Er is the ecological risk of each element and RI shows the ecological risk of multiple elements. Hakanson [41] defined Tr as a “toxic-response factor” for a given substance and demonstrated this value for Cd, Cu, Pb, Cr, Zn to be 30, 5, 5, 2, 1, respectively. Different RI classifications are delineated in Table 2.

2.6. PAHs ratio analysis 3. Results and discussion In addition to statistical analyses, diagnostic ratios of PAHs were used to distinguish petrogenic and pyrogenic sources of PAHs in street dust of Tehran. In recent studies on soil and dust PAHs contamination such ratios as BaA/(BaA + Chr), IND/(IND + BghiP), Flu/(Flu + Pyr), Phe/Ant, Ant/(Ant + Phe) and BaP/BghiP were used to determine different sources of PAHs [36–40]. In this study ratios of IND/(IND + BghiP), BaA/(BaA + Chr), Flu/(Flu + Pyr) and Ant/(Ant + Phe) were calculated to distinguish PAHs sources [36,38,40].

3.1. Heavy metal and PAH concentrations Table 3 compares the statistical concentration data for metals (in 49 samples) and PAHs (in 21 samples) from Tehran with earth crust contents and background street dust concentrations at the IUST campus. Heavy metal of Cu, Cd, Pb and Zn in Tehran street dust were found to be substantially higher than those of the earth’s crust, indicating that these heavy metals are likely from anthropogenic

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Table 3 Metals, L.O.I. (n = 49) and PAHs (n = 21) contents in street dust and IUST campus samples of Tehran. Contaminanta , b

Cu

Cd

Pb

Cr

Mean Min Max Median St. Dev. Skewness Kurtosis Coefficient of variation Geometric mean IUST campus sample Earth crust content

225.3 68.3 778.3 202.6 149.2 2.05 5.28 0.66 190.1 58.6 50

10.7 9.9 11.1 10.7 0.2 −0.96 1.16 0.02 10.7 11.0 0.2

257.4 64.7 764.9 188.9 158.4 1.42 1.58 0.61 219.8 106.5 14

33.5 15.2 58.0 31.2 11.3 0.58 −0.38 0.33 31.7 23.0 100

a b c

Ni

Mn

34.8 12.6 73.0 31.3 15.1 0.79 −0.16 0.43 31.8 20.7 80

1214.5 721.6 2231.6 1176.3 327.2 0.77 1.17 0.26 1173.4 1101.5 950

Zn 873.2 544.3 1935.2 790.6 274.8 1.66 3.51 0.31 838.5 399.3 75

Fe

Li

L.O.I.c

47935.7 26602.5 96427.3 45145.5 12802.4 1.40 3.47 0.26 46454.6 39338.9 41000

9.5 3.4 16.8 9.1 2.7 0.46 0.05 0.28 9.1 4.1 20

14.8 8.2 22.0 14.6 3.0 0.15 −0.48 0.21 14.5 8.2 –



PAHs

0.33 0.13 1.41 0.23 0.32 2.79 7.59 0.97 0.26 0.43 –

Metals and PAHs are in mg kg−1 and L.O.I. is in %. Number of samples for PAHs: n = 21 and number of samples for heavy metals: n = 49. Loss On Ignition.

sources. Their maximum contents, as well as maximum levels of Cr, Ni and Fe, were detected in samples from the Baghery highhighways in this way side, one of the most heavily traffic-loaded part of Tehran. The maximum concentrations of PAHs were also detected in Baghery highway side dust samples (e.g. sample no. 2). However, a relatively higher concentration of PAHs in IUST cambe indicative pus sample vs. the mean content of other samples may of the existence of other anthropogenic sources of PAHs than Traffic in Tehran. Therefore, these contaminants in this area of study are likely derived from sources related to vehicles. Cd, Mn and Li seem to have other origins since their concentrations in highwayside samples were not among their highest values. However, all of the heavy metals studied (Cu, Cd, Pb, Zn, Ni and Cr) could have various sources in the urban environment. Most could be released into the urban system as a result of vehicle traffic and fossil fuel combustion. So, taking into account that Ni and Cr contents are much lower than for other metals, additional data analyses and statistical tools were deployed to obtain a clearer picture. Although there are no globally accepted sampling and analysis procedures for street dusts, the mean contents of contaminants in street dust are commonly compared for different urban environments. Tehran’s street dust contamination by metals and PAHs in this study are compared to other major cities around the world in Tables 4 and 5. From Table 4, the concentrations of Cd, Mn, Zn and Fe in Tehran street dusts are higher than for other cities, even higher than for major cities in developing countries such as Mutah, Jordan and, Kuala Lumpur, Malaysia. They are also higher than for Kavala, Greece among European countries. The only city with higher concentrations of Cu, Pb and Fe in its street dust is Amman, the capital of Jordan. All metals studied except Cr are much higher than for reference values such as the earth’s crust or background Chinese soil. Note that in Iran, there is still no background or reference recommended value of contaminants for soil and solid media. Iran is less industrialized than many other countries (e.g. Canada, England, Norway and Spain), in terms of population and vehicle volume. Information is also included for some crowded cities in Table 4. London shows lower levels of toxic metals than Tehran. The concentrations of Cd and Zn in Tehran dusts are much higher than for all other cities in the world with which it is compared. This indicates that there may be serious health and environmental impacts related to the uptake of Cd in Tehran. Further investigations are needed. As displayed in Table 5, the concentrations of PAHs in Tehran street dusts are not much higher than for most other cities. However, the levels of some compounds such as acenaphthylene and acenaphthene are much higher than for street dust from Beijing, Zhanjiang, Huizhou and Shanghai. Fluorene, phenanthrene, anthracene, pyrene, chrysene,

benzo[k]fluoranthene, benzo[a]pyrene, dibenzo[a,h]anthracene, benzo[g,h,i]perylene, and indeno[1,2,3-c,d]pyrene in Tehran street dusts exceed those of Huizhou. Benzo[k]fluoranthene and Phenanthrene concentrations in Tehran are greater than in Zhanjiang. Concentrations of all 16 PAH except Benzo[b]fluoranthene in Tehran dusts are larger than their counterparts in street dusts of Seoul, South Korea. Fossil fuel combustion and the lower quality of petrol used in Tehran are likely to be among the factors contributing to the high release of PAHs. 3.2. Correlation coefficient analysis Pearson’s correlation coefficients are presented in Table 6 for metals and PAHs in 21 street dust samples of Tehran. Significant positive correlations were found for some elemental pairs; Cu–Pb, Cu–Cr, Cu–Ni, Cu–Zn, Cu–Fe, Cu–PAHs, Pb–Cr, Pb–Ni, Pb–Fe, Pb–Zn, Pb–PAHs, Cr–Ni, Cr–Fe, Ni–Fe, Zn–Fe and Fe–PAHs. Li, Mn and Cd show no significant positive correlation with any of the other contaminants studied. These results indicate that Cu, Pb, Cr, Ni, Zn, Fe and PAHs, which are significantly positively correlated, likely originate from common anthropogenic sources. Cadmium, found at high concentrations in all samples, seems also to have anthropogenic sources, but not the same ones as for the other contaminants. This indicates that there might be a different source for Cd other than local anthropogenic sources such as traffic and urban industries. Since none of contaminants were strongly correlated with Mn or Li, metals likely to have natural origins, it can be inferred that the major sources of the metals studied are anthropogenic. Mn and Li are only correlated to each other with a moderate correlation coefficient (0.339). So they are probably reasonable metals to be selected as reference elements for further enrichment factor calculations. 3.3. Cluster analysis Cluster analysis based on Pearson’s correlation coefficients for the similarities between the variables was used to show the dendogram of contaminant concentrations in street dust samples of Tehran (Fig. 2). This method employs linear correlation coefficients as a similarity measure. The highest similarities are clustered/linked first, and variables connected only if they are highly correlated. After two variables are clustered, their correlations with all the other variables are averaged. The CA results for the contaminants studied indicate six clusters: (1) Cu–Fe–Pb; (2) Cr–Ni; (3) Zn; (4) PAHs; (5) Cd; (6) Mn–Li in terms of similarities. However, cluster 1 is moderately associated with clusters 2, 3 and 4, leading to a main cluster named A in Fig. 2. This indicates that the contaminants comprising cluster A (Cu, Fe, Pb, Cr, Ni, Zn and PAHs) may have some common anthropogenic sources. In addition, some of the Cu, Fe, Pb, Cr and Ni in street dusts seem to derive partly

M. Saeedi et al. / Journal of Hazardous Materials 227–228 (2012) 9–17

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Table 4 Mean concentration of heavy metals in street dusts of Tehran (n = 49) and other selected cities (mg kg−1 ). City

Cu

Tehran (this study) IUST campus (this study) Ammana Birminghamb Kuala Lumpurc Londond Mutahe Madridf Oslof Ottawag Kavalah Background-values of heavy metals in soils of Chinai Heavy metal concentration in the earth’s crustj a b c d e f g h i j

Mn

Zn

225.3 58.6

Cd 10.7 11.0

257.4 106.5

Pb

Cr 33.5 23.0

Ni 34.8 20.7

1214.5 1101.5

873.2 399.3

47935.7 39338.9

9.5 4.1

249.6 466.9 35.5 155.0 69.0 188.0 123.0 188.0 172.4 26.7

1.1 1.6 2.9 3.5 1.3

18.3

16.3 41.1

144.6

401.0 534.0 344.0 680.0 132.0 476.0 412.0 184.0 354.8 68.8

5370.6

1.7

1.4 0.6 0.2 0.1

976.0 48.0 2466.0 1030.0 143.0 1927.0 180.0 68.0 386.9 19.4

1790.0 26000.0 5362.0 19300.0 51452.0 25660.0

9.0

50

0.2

14

153.0

59.0 232.4 49.3

1.7 44.0 41.0 19.0 67.9 26.6

136.0 362.0 833.0 534.0

100

80

950

61.0

688.0

75

Fe

Li

–

–

41000

20

Ø (␮m) <63 <63 <200 <63 <63 <500 <63 <100 <100 100–250 <63 –

–

[10]. [5]. [44]. [45]. [7]. [16]. [46]. [35]. [47]. [48,49].

Table 5 Mean concentration of PAHs in Tehran street dusts and other selected cities (mg kg−1 ). PAHs

Tehran (this study)

Kumasia

Ammanb

Beijingc

Zhanjiangd

Huizhoud

Shanghaie

Seoulf

Naphthalene Acenaphthylene Acenaphthene Fluorene Phenanthrene Anthracene Fluoranthene Pyrene Benzo[a]anthracene Chrysene Benzo[b]fluoranthene Benzo[k]fluoranthene Benzo[a]pyrene Dibenzo[a,h]anthracene Benzo[g,h,i]perylene Indeno[1,2,3-c,d] pyrene

0.002 0.048 0.041 0.008 0.070 0.006 0.013 0.020 0.010 0.020 0.004 0.005 0.006 0.015 0.030 0.027

41.7 99.3 111.2 8.9 12.9 5.4 16.2 15 13.8 33.6 ND 45.7 27.9 ND 47 ND

1.2 NDh – 0.17 4.75 – 1.98 2.05 1.54 4.31 1.55 0.21 0.15 0.35 1.74 0.10

0.094 0.007 0.009 0.039 0.109 0.017 0.155 0.098 0.042 0.105 0.085 0.030 0.094 0.005 0.031 0.002

0.006 0.004 0.002 0.019 0.050 0.026 0.064 0.044 0.056 0.029 0.115 0.003 0.055 0.050 0.069 0.050

0.005 0.0005 0.017 0.002 0.018 0.001 0.018 0.011 0.011 0.006 0.021 0.002 0.005 0.001 0.007 0.007

0.028 ND 0.010 0.019 0.13 0.028 0.259 0.22 0.124 0.127 0.177 0.072 0.181 0.059 0.144 0.118

0.004 0.0004 0.005 0.004 0.001 0.003 0.005 0.002 0.002 0.0003 0.003 0.002

a b c d e f g h

Background soil concentration of PAHs in urban soils in USAg

0.2–166 0.145–147 0.169–59 0.251–0.64 15–62 0.3–26 0.165–0.22 0.9–47 8–61

[11]. [10]. [18]. [38]. [3]. [19]. [50]. Not detected.

Table 6 Pearson’s correlation coefficient for metals and PAHs concentrations of street dusts in Tehran (n = 21). Cu Cu Cd Pb Cr Ni Mn Zn Fe Li PAHs

1.000 −0.126 0.785 0.658 0.648 −0.235 0.680 0.879 −0.169 0.603

Cd 1.000 −0.262 −0.312 −0.353 0.212 0.132 −0.337 −0.240 −0.018

Pb

1.000 0.677 0.536 −0.158 0.531 0.748 −0.274 0.478

Cr

1.000 0.788 −0.262 0.429 0.710 −0.008 0.205

Ni

1.000 −0.404 0.341 0.669 0.186 0.360

Mn

Zn

1.000 0.239 −0.119 0.339 −0.325

1.000 0.591 −0.120 0.336

Fe

1.000 −0.156 0.642

Li

PAHs

1.000 −0.493

1.000

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Fig. 2. Dendogram of elemental concentrations in the urban dusts of Tehran (n = 21). Table 7 The rotated component matrix for data of metals in street dusts of Tehran (n = 50). Element

Cu Cd Pb Cr Ni Mn Zn Fe Li Eigenvalue % of variance explained % of cumulative

Component

Communalities

1

2

3

0.89 −0.12 0.87 0.87 0.79 −0.32 0.61 0.89 0.20 4.33 48.15

0.05 −0.08 −0.12 −0.15 −0.26 0.84 0.25 0.08 0.63 1.30 14.50

−0.10 0.83 −0.04 −0.16 −0.14 0.12 0.43 −0.01 −0.40 1.03 11.46

48.15

62.65

74.11

0.80 0.70 0.77 0.81 0.71 0.83 0.62 0.81 0.61

Extraction method: principal component analysis. Rotation method: varimax with kaiser normalization. Rotation converged in five iterations.

from sources other than those of PAHs and Zn. Li and Mn in cluster C appear to have originated mainly from natural sources (e.g. local soil). 3.4. Principal component analysis PCA analysis was performed for the metal contents of all 50 dust samples and combined with Kaiser normalization. Principal factors, extracted from the variables with eigenvalues >1, were selected. The rotated component matrix is presented in Table 7. As expected, three factors were acquired. Principal factors >0.6 are underlined in each column. The first column contains Cu, Pb, Cr, Ni, Zn and Fe with factors >0.6, so they are mainly derived from common sources. Mn and Li appear in the second column, indicating that they originated from the same origins. Finally Cd with a factor >0.8 is in the third column, with its sources differing from the other materials. It appears that factors 1 and 3 are from anthropogenic resources and human activities, whereas factor 2 might be from natural origins. The relations among the contaminants based on the first three principal components are illustrated in Fig. 3 in a threedimensional representation that agrees with the metal results in Fig. 2. 3.5. PAHs ratio analysis Ratios of BaA/(BaA + Chr) vs. IND/(IND + BghiP), Ant/(Phe + Ant) vs. Flt/(Flt + Pyr) and BaA/(BaA + Chr) vs. Flt/(Flt + Pyr) were used to distinguish other sources of hydrocarbons. These ratios may characterize potential PAHs emission sources. Amount of ratio Flu/(Flu + Pyr) <0.4 indicates petroleum, between 0.4 and 0.5 shows liquid fossil fuel combustion, while a ratio <0.5 is the indicator of biomass and coal combustion sources [36]. Ratio of Ant/(Phe + Ant) <0.1 reveals petroleum while a ratio >0.1 implies combustion sources. BaA/(BaA + Chr) <0.2 and IND/(IND + BghiP) <0.2 are

Fig. 3. PCA results in three-dimensional space: plot of the first three principal components loading (n = 50).

indicative of petrogenic and petroleum sources. When BaA/(BaA + Chr) is between 0.2 and 0.35 and IND/(IND + BghiP) is between 0.2 and 0.5 combustion of liquid fossil fuels are sources of PAHs. On the other hand, when both ratios exceed 0.5 coal, grass and wood are likely to be the major sources [36,38,40]. The results for these ratios are illustrated in Fig. 4. As can be seen, PAHs in Tehran street dust may originate from combined petrogenic and pyrogenic sources. According to Fig. 4, a mixture of petrogenic and pyrogenic sources, mostly petroleum and petroleum combustion, are expected for PAHs in this study. The ratios analysis results are in common agreement with cluster and correlation coefficient analyses indicating common sources for PAHs and metals. While PAHs originate mainly from petrogenic and pyrogenic sources, based on CA and correlation coefficients those sources are only partly responsible for metals in the dust of Tehran. 3.6. Enrichment factors In recent published works, EFs have been calculated using a recommended reference value [7,51] or background values of elements from previous studies [14,52]. In Iran there are no official recommended reference elemental values. Since this is the first study of Tehran dust contamination, there are also no historical or background elemental concentrations reported for the area. In this study metal contents in earth crust were therefore used as background values in calculating EF as in earlier work [6,31,33,53,54]. Eq. (1) reference metals are frequently Fe, Al, Li. Alternatively, one could use any other metal believed to have no or minimal anthropogenic sources in the area. The statistical analyses (correlation coefficients, CA and PCA) indicate that the sources of Mn, Li and Cd differ from the other elements studied. Both Mn and Li have been previously applied as reference metals by earlier researchers. Li has also been used as a normalizing element [44,55]. Hence, in the present study, EFs were based on both Mn and Li as reference metals. Results are presented in Table 8. With Mn as the reference metal, the heavy metals most likely to cause risk in Tehran dust samples are in order Cd > Pb > Zn > Cu. If Li is taken as the reference element, the order is the same. The EF values of Cd and Pb are substantially higher than for the other

M. Saeedi et al. / Journal of Hazardous Materials 227–228 (2012) 9–17

15

Table 8 Summary of the results of EFs for Tehran dust samples. EF

Cd Cu Cr Fe Ni Pb Zn

Li as reference metal

Mn as reference metal

Mean

Max

Min

St. Dev.

Median

Mean

Max

Min

St. Dev.

Median

126.2 10.2 0.8 2.7 1.0 42.6 27.0

310.4 51.2 1.9 8.1 3.2 189.4 65.7

62.3 2.4 0.4 0.9 0.4 8.2 14.2

45.5 8.1 0.4 1.2 0.6 32.1 13.2

118.0 8.5 0.7 2.4 0.8 32.2 23.3

44.8 3.9 0.3 1.0 0.4 15.9 9.8

72.5 13.3 0.7 2.0 1.0 47.5 34.0

21.8 0.7 0.1 0.4 0.1 3.1 4.3

11.8 2.9 0.2 0.4 0.2 11.6 5.1

43.8 2.7 0.2 0.8 0.3 11.3 8.5

and Ni show lower levels of enrichment from minimal to moderate. Copper enrichment shows a wide range of values, from minimal to moderate enrichment, based on Mn as reference, and from moderate to extreme with Li as reference. Overall, Tehran street dust is highly contaminated with Pb, Cd, Zn and Cu. Although Ni and Cr are derived mostly from the same source as Pb, Cd, Zn and Cu, they are not highly enriched in the dust, indicating that their emissions are less than for the other metals. Fig. 5 shows that using Li as reference metal to calculate EF led to greater enrichments compared with Mn is the reference metal. 3.7. Probable source identification Correlation coefficients and multivariate statistical analyses used to identify possible sources of heavy metals and PAHs demonstrated similar results. Based on the results of statistical and ratio analyses and EFs probable emission origins can be identified:

Fig. 4. Plot of the ratios of: (A) Ant/(Ant + Phe) vs. Flu/(Flu + Pyr), (B) BaA/(BaA + Chr) vs. Flu/(Flu + Pyr), and (C) BaA/(BaA + Chr) vs. IND/(IND + Bghip) in Tehran street dust samples.

metals. Heavy metals with maximum EF values >10 (Cd, Pb, Cu and Zn in this study) are believed to derive from human activities [34]. Substantially higher values indicate high enrichments and probable higher risks of the corresponding metals. Fig. 5 depicts the EF results for metals in Tehran street dust with Li and Mn as reference metals. Although the orders of the enrichment level of metals vary depending on whether Mn or Li is taken as the reference metal, it is clear that the median and range of enrichments of Pb, Cd and Zn are quite high in both cases. According to Fig. 5 and the enrichment criteria in Table 1, EFs of Cd, Pb and Zn are significant, very high and Tehran street dust is extremely highly enriched by these metals. Cr

a. Based on PAHs ratio analyses and multivariate statistical analyses, main sources of PAHs in dust samples of the study area are the anthropogenic sources including petroleum production and other industry and fossil fuel combustion including vehicular emissions. b. The high EF values for Cu, Cd, Pb and Zn suggest that anthropogenic sources are the major sources of these elements. Significantly positive correlation and similarities of Ni and Cr with these four metals also indicate that Ni and Cr are also partly derived from the same sources, but in smaller quantities. Although Ni and Cr may have common sources with other metals, the Efs for Ni and Cr indicate minimal to moderate values, so that these elements might also arise from natural sources. c. Moderate to high correlations and similarity of PAHs with Cu, Pb, Cr, Ni, Zn, Fe suggest that a major common source of these metals is as the same as for PAHs, i.e. fossil fuel combustion. Major fossil fuels being combusted in Tehran are petrol, burned by vehicles. From the ratio results, in addition to fossil fuels (in common with heavy metals), PAHs may have other petrogenic and sources such as petrol, coal, grass and wood. The maximum concentrations of metals and PAHs were found in dust samples from Baghery highway, one of the most heavily traveled urban roads in Tehran. However, because the similarity is no more than moderate, those metals and PAHs might also have different anthropogenic origins. For instance, Cr, Cu, Zn and Fe can originate from corrosion of alloys used in vehicle components, vehicle covers or other metallic surfaces and materials [10,14]. Significant positive correlations and similarity of Fe with those metals could indicate that iron-containing materials and surfaces are sources of heavy metals Cu, Zn, Cr and Ni in Tehran dust. Previous studies [2,16] have suggested that the main sources of Pb in street dusts are fuel additives and combustion. d. As noted by Wei et al. [14], cadmium is used in batteries, plastic and building materials. In the Tehran sampling area, there were many administrative and residential buildings and auto service

16

M. Saeedi et al. / Journal of Hazardous Materials 227–228 (2012) 9–17

Fig. 5. Boxplot of enrichment factors for metals in the street dust samples of Tehran.

Table 9 The potential ecological risk indices (RI) of street dusts from different sampling zones in Tehran. Sampling location

Baghery highway Esteghlal street Hengam street Resalat street IUST campus The mean of eastern parts South terminal

Mean value of Er

Ecological risk

Cu

Cd

Pb

Cr

Zn

RI

40.5 26.5 15.2 16.4 5.8 23.9 17.8

1601.6 1596.2 1618.8 1602.0 1647.0 1613.0 1601.3

179.1 86.1 60.0 74.6 38.1 100.1 67.7

0.9 0.8 0.6 0.6 0.5 0.7 0.5

14.9 10.4 10.1 9.4 5.3 11.4 12.6

1837.0 1720.0 1704.7 1703.0 1696.7 1748.9 1699.9

workshops. Therefore, erosion and abrasion of tires, car batteries and building materials might be major sources of Cd. However, in view of the high risk and toxic effects of Cd and its high concentration in all samples, it is probable that Cd has a major source outside of Tehran. Further investigations on the origins and effects of cadmium in the study area are clearly warranted. e. Mn and Li mainly originated from natural sources like soils. f. To be able to evaluate dusts reaching Tehran from neighboring countries and to determine the effect of those dusts on the concentrations of the pollutants studied in Tehran, samples of incoming dust, as well as samples of dust from and the desserts and dried wetlands of neighbor countries need to be analyzed. 3.8. Ecological risk To gain a better image of Tehran street dust pollution and related risks, Table 9 presents ecological risks of Tehran street dust based on Hakanson’s approach (Eq. (2)). From these results and the criteria presented in Table 2, all sampling locations show very high ecological risks. Baghery highway shows the maximum RI value and ecological risk of the dust samples. The lowest ecological risk is for the sample from the Iran University of Science and Technology (IUST) campus. As mentioned above, this sampling location is relatively far from major streets and traffic, protected by trees from direct effects of particles and traffic emissions. Hence, the vast green areas of the university campus and the distance between this sampling site and surrounding streets account for the lower ecological risk of these samples. This also supports the contention that vehicular traffic is the major local source of dust contamination. However, the dust sample from the university campus still shows a high risk level, indicating origins other than traffic or other localized sources, presumably due to transportation and precipitation of contaminated particles. Thus the transport of contaminated particles from other regions (e.g.

Very high Very high Very high Very high Very high Very high Very high

western Iran, dry wetlands and deserts of neighboring countries) should be investigated through extensive sampling and analysis of surficial soils, as well as airborne suspended particles. 4. Conclusions • Metal concentrations in Tehran street dust are higher than for other major cities around the world. • Correlation coefficients, CA and ratio analyses results suggest that PAHs and metals (Cu, Pb, Zn and to some extent Ni and Cr) have some common anthropogenic origins. • PAHs in Tehran street dusts have both petrogenic and pyrogenic sources. • EFs and ecological risk of Cd, Pb, Cu and Zn are extremely high in Tehran dust. • Cd content in all dust samples is alarmingly high. Enrichment levels and ecological risk of Cd are also substantial, indicating high severity of Cd pollution in Tehran. At the same time, statistical analyses indicate that Cd does not have a local anthropogenic source. These facts suggest the need for more comprehensive investigation of Cd in the city and of Cd transport into Tehran via airborne particles. • Although local pollution sources are contributing to Pb, Cu and Zn, and, to a lesser extent, Ni and Cr, probable external origins for these metals need to be investigated. • While the dust sample from the relatively isolated IUST campus showed the least ecological risk of all samples analyzed, even this sample was in the category of “very high” ecological risk. This indicates external sources of airborne metal-loaded particles from outside Tehran. • Traffic and other related activities, such as abrasion of tires and asphalt pavement, in addition to oil, old buildings and workshops, were identified as the main local sources of contamination. In view of the high enrichment of metals (particularly Cd and Pb),

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