Journal of Saudi Chemical Society (2013) 17, 315–319
King Saud University
Journal of Saudi Chemical Society www.ksu.edu.sa www.sciencedirect.com
ORIGINAL ARTICLE
Heavy metals contamination in roadside soil near different traffic signals in Dubai, United Arab Emirates Junaid Aslam a b c
a,b,*
, Saeed Ahmad Khan
a,*
, Sheba Haque Khan
c
Dubai Pharmacy College, Al Muhasinah 1 Al Mizhar, P.O. Box 19099, Dubai, United Arab Emirates Department of Biotechnology, Hamdard University, New Delhi 110062, India G.F. College, Department of Chemistry, M.J.P. Rohilkhand University, Bareilly, UP, India
Received 30 March 2011; accepted 27 April 2011 Available online 3 May 2011
KEYWORDS Environmental pollution; Heavy metals; Roadside soil; Traffic density
Abstract The present research was conducted to study heavy metal contamination in roadside soil viz. (i) at sites having more than two traffic signals (ii) roads having only one traffic signal and (iii) roads having no traffic signals. The samples were collected and analyzed for seven heavy metals i.e. cadmium (Cd), lead (Pb), copper (Cu), nickel (Ni), iron (Fe), manganese (Mn) and zinc (Zn) by Atomic Absorption Spectroscopy (AAS) following the acid digestion of the respective soil samples. The range of the metals observed in soil having more than two traffic signals were Cd (0.17–1.01), Pb (259.66–2784.45), Cu (15.51–65.90), Ni (13.31–98.13), Fe (325.64–5136.37), Mn (57.95–166.43), and Zn (91.34–166.43) mg kg 1 respectively. Similarly, the range of metals analyzed in samples collected from the roadside having only one traffic signal were Cd (nd–0.80), Pb (145.95–308.09), Cu (0.82–18.04), Ni (18.29–59.36), Fe (88.51–3649.42), Mn (25.88–147.34) and Zn (8.97– 106.11 mg kg 1) respectively. However, the range of metals at roads having no traffic signals were Cd (0.0–0.57), Pb (8.34–58.20), Cu (2.88–5.81), Ni (3.34–73.80), Fe (55.34–332.81), Mn (2.98–98.73) and Zn (1.23–46.6 mg kg 1) respectively. Cd, Cu, Ni, Fe, Mn and Zn in soil were present within the normal range of background levels, whereas lead was reported in high concentration. The level of lead had a correlation with the traffic density attributing its origin to vehicular exhaust. The values
* Corresponding authors at: Dubai Pharmacy College, Al Muhasinah 1 Al Mizhar, P.O. Box 19099, Dubai, United Arab Emirates. Tel.: +91 9990706557 (J. Aslam). E-mail addresses:
[email protected] (J. Aslam), dr.khan@dpe. edu (S.A. Khan). 1319-6103 ª 2011 King Saud University. Production and hosting by Elsevier B.V. Open access under CC BY-NC-ND license. Peer review under responsibility of King Saud University. doi:10.1016/j.jscs.2011.04.015
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J. Aslam et al. from three different sites of monitoring suggest that automobiles are a major source of the studied metals for the roadside environment. ª 2011 King Saud University. Production and hosting by Elsevier B.V. Open access under CC BY-NC-ND license.
1. Introduction
2. Experimental
Heavy metals enlist a relatively large series of elements with specific density over 5 g cm 3 and relative atomic mass above 40. Environmental pollution by metals became extensive with the fillip in mining and industrial activities during the last two centuries. The current worldwide mine production of Cu, Cd, Pb and Hg is considerably huge (Jarup, 2003). These pollutants, ultimately derived from a growing number of diverse anthropogenic sources, have had enormous impact on different ecosystem (Macfarlane and Burchett, 2001; 2002). Fifty-three of the ninety naturally occurring elements are heavy metals (Weast, 1984). Of these, Fe, Mo and Mn are important as micronutrients, while Zn, Ni, Cu, Co, Va and Cr are toxic elements, but have importance as trace elements. Ag, As, Hg, Cd, and Pb have no known function as nutrients, and seem to be toxic to plants and microorganism (Nies, 1999). The majority of the heavy metals are toxic to the living organism and even those considered as essential can be toxic if present in excess. The heavy metals can impair important biochemical process posing a threat to human health, plant growth and animal life (Jarup, 2003; Silva et al., 2005; Ali et al., 2008; Yoshinori et al., 2010). Studies have shown that such pollutants can be harmful to the roadside vegetation, wildlife and the neighboring human settlements (Muskett and Jones, 1980; Khan and Frankland, 1983; Ndiokwere, 1984; Iqbal et al., 1994; Ferretti et al., 1995; Turer and Maynard, 2003; Nakayama et al., 2010). The pollution of soils by heavy metals from automobile source is a serious worldwide environmental issue. These metals are released during different operations of the road transport such as combustion, component wear, fluid leakage and corrosion of metals. Lead, cadmium, copper and zinc are the major metal pollutants of the roadside environments and are released from burning of fuel, wearing out of tyres, leakage of oils, and corrosion of batteries and metallic parts such as radiators etc. (Akbar et al., 2006; Dolan et al., 2006; Baker et al., 2007; Yoshinori et al., 2010). It has also been vastly documented that rapid industrialization, increasing vehicular traffic and application of fertilizers result in the release of large quantities of metals in the biosphere (Motto et al., 1970; Turer and Maynard, 2003). In soil, metal concentration is mainly influenced by the industrial activity or by the application of sewage sludge. However, in urban areas automobile exhaust is one of the potent contributions especially of lead (Fergusson, 1991). The toxicity of lead and its chronic effect on human and its immediate effect on the environment have been extensively studied including deposition and accumulation (Baker and Senft, 1995; Nakayama et al., 2010). Therefore, the present study was undertaken to study the heavy metals (cadmium, lead, copper, nickel, iron, manganese and zinc) contamination in soil near the roadside traffic, to check, whether the heavy metals exist within the range tolerance limit or not.
2.1. Study material Twenty two sites at roadsides covering major areas of Dubai city were selected for sampling of the present study i.e. roadside soil having more than two traffic signals (1–6), roadside soil having only one traffic signal (7–11) and roadside soil from the roads having no traffic signals (12–22). At each point four surface soil samples were collected within 5 m distance. In each case, the surface soil was scraped into a plastic bag using a steel spatula. Samples were air dried and sieved through 2 mm screen. 2.2. Sample preparation One-gram of air dried soil was placed in 50 ml beaker with 5 ml of concentrated nitric acid and heated at 95–100 C for 30 min followed by adding a 5 ml mixture of concentrated nitric and perchloric acid (3:1 v/v) and heated again. After proper digestion, the digest was made up to 50 ml with deionised water. 2.3. Standard preparation Seven heavy metals were selected for the analysis including; Cd, Pb, Cu, Ni, Fe, Mn and Zn. The standard used for the atomic absorption analysis of these metals was multi- elements system, which was prepared from the stock standard (BDH spectrosol, UK) by appropriate dilution with 0.5 N nitric acid. 2.4. Atomic absorption analysis A GBC atomic absorption spectrometer (model, 906) fitted with an eight lamp turret, equipped with a graphite furnace and an auto sampler was employed for the analysis, using Avanta Sigma software. 2.5. Statistic analysis The data on analysis of seven heavy metals at various points near roadside soil were analyzed by one way analyses of variance (ANOVA).Values are means of four replicates from two experiments, and the presented mean values were separated using Duncan’s Multiple Range Test (DMRT) at p P 0.05. 3. Results and discussion In the present study, monitoring on selected heavy metals was carried out in soil especially near the roadside sites. 3.1. Sites having more than two traffic signals Results showed a significant variation of metal concentrations in soils. The maximum and minimum concentration of heavy
Heavy metals contamination in roadside soil near different traffic signals in Dubai metals ranged from Cd (0.17–1.01), Pb (259.66–2784.45), Cu (15.51–65.90), Ni (13.31–98.13), Fe (325.64–5136.37), Mn (91.34–166.43) and Zn (72.40–170.27 mg kg 1) respectively. The highest concentration of Cd, Pb, Cu, Ni, Fe, Mn and Zn were found at 2, 3, 1, 4, 3, 3 and 2 sample points, whereas, the lowest concentration was observed at 6, 1, 3, 1, 1, 6 and 5 points. Table 1 summarized the mean value of each heavy metal concentration at five points. 3.2. Sites having only one traffic signal Similarly, here also a significant variation among the metals concentrations was noticed. The concentration of the heavy metals ranged from Cd (nd–0.80), Pb (145.95–308.09), Cu (0.82–18.04), Ni (18.29–59.36), Fe (88.51–3649.42), Mn (25.88–147.34) and Zn (8.97–106.11 mg kg 1) respectively. The values indicate that, among the heavy metal Fe was present in high concentration; however, it was in the range of background level. Whereas, Cd, Pb, Cu, Ni and Mn were present relatively in low concentrations. The maximum concentration of the Cd, Pb, Cu, Ni, Fe, Mn and Zn were analyzed from 9, 8, 11, 7, 7, 7, 8 and 8 sample points, while the lowest concentration was found at 11, 11, 7, 11, 11, 11, 11 and 11 points. Moreover, Cd was not detected at point 10. Table 2 showed a comparative account of various analyzed heavy metals at six different points. 3.3. Sites have no traffic signals The maximum and minimum concentration of studied heavy metals ranged from Cd (nd–0.93), Pb (8.34–113.26), Cu (nd– 5.81), Ni (nd–73.80), Fe (nd–332.81), Mn (nd–102.58) and Zn (1.23–46.6 mg kg 1) respectively. The highest concentrations of the metals were found at 13 (Cd), 21 (Pb), 18 (Cu), 21 (Ni), 19 (Fe), 21 (Mn) and 13 (Zn) sample points, whereas,
Table 1
317
the lowest concentration was observed at 17 (Cd), 19 (Pb), 12 (Cu), 22 (Ni), 22 (Fe), 15 (Mn) and 22 (Zn) points. Cd, Cu, Ni, Fe and Mn were not detected at some sampling points. Table 3 summarized the mean values of analyzed heavy metals at eleventh point. In the present investigation, analysis of selected heavy metals was carried out at three sites, the highest concentration was found at sites having more than two traffic signals; however, most of the elements were within the range of normal background levels except lead. These results agreed with the observation previously studied (Roth and Hornung, 1977; Peterson and Alloway, 1979; Basco et al., 1984; USEPA, 1988; McGrath and Loveland, 1992; Kiekens, 1995; Olendrzynski et al., 1995; Aksoy and Sahin, 1999; Tahir et al., 2007; Yoshinori et al., 2010; Nastja, 2011). In the last decades, considerable attention has been directed towards lead in the roadside environments as a result of its widespread use as an anti-knocking agent in gasoline (Davies and Hololmes, 1972; Wheeler and Rolfe, 1979; Hafen and Brinkmann, 1996; Turer and Maynard, 2003). In the present study only lead was present at considerably high concentrations. It was observed that the lead concentration in roadside soil was not only dependent on traffic density but also on the traffic signals. The lead in the samples of soil collected from the sites having more than two traffic signals, i.e. the bigger sites having traffic signals to every approaching road, was high as compared to the samples collected from the sites having one or no traffic signal. Lead concentration was different in soil collected from the sites of high traffic density without and with traffic signals. The values of lead concentration in the samples of high traffic density (without signals) were found mostly 200 mg kg 1 of lead in samples collected from the sites of almost same traffic density but with signals. This may be, because every vehicle consumes more fuel when it starts from
Heavy metal concentration (mg kg 1) of roadside soil at round about having more than two traffic signals.
Sample number
Cd
1 2 3 4 5 6
*
Pb a
Cu e
0.91 1.01a 0.71b 0.72b 1.00a 0.17c
284.92 259.66f 2784.45a 1051.07b 519.95c 443.83d
Ni e
15.51 19.73cd 22.48c 65.90a 25.75b 16.29de
Fe e
13.31 21.56d 98.13a 71.59b 52.78c 51.46c
Mn c
2493.27 3425.92b 5136.37a 3582.42b 701.85d 325.64e
Zn e
91.34 166.43a 107.26b 57.95e 75.25d 108.36b
72.40e 112.42d 129.41b 119.96c 170.27a 114.39d
* Values are mean of four replicates. Mean within each column with same superscript are not significantly different at p P 0.005 level according to Duncan’s multiple range test (DMRT).
Table 2
Heavy metal concentration (mg kg 1) of roadside soil from the roads having only one traffic signal.
Sample number 7 8 9 10 11 *
Cd **
Pb a
0.79 0.66b 0.80a nd* 0.44c
Cu b
246.99 308.09a 145.95d 248.99b 201.04c
Ni a
18.04 14.98b 7.23c 7.52c 0.82d
Fe a
59.36 27.73d 48.47b 43.07c 18.29e
Mn a
3649.42 3425.92b 1457.45c 3312.82b 88.51d
Zn b
125.67 147.34a 52.00d 86.20c 25.88e
71.06b 106.11a 47.48c 39.15d 8.97e
nd = Not detected. Values are mean of four replicates. Mean within each column with same superscript are not significantly different at p P 0.005 level according to Duncan’s multiple range test (DMRT). **
318 Table 3
J. Aslam et al. Heavy metal concentration (mg kg 1) of roadside soil from the roads having no traffic signals.
Sample number 12 13 14 15 16 17 18 19 20 21 22
Cd **
0.51b 0.93a 0.54b 0.55b 0.42c 0.39c 0.57b * nd nd nd nd
Pb
Cu
Ni
Fe
Mn
Zn
30.06c 58.20b 9.09fg 10.75f 13.40e 29.00e 19.22d 6.92h 8.34g 113.26a 12.21e
0.94d 5.81a 2.69c 3.58b 2.88c 3.49bc 5.76a nd nd 3.77b nd
15.24d 16.88d nd nd nd nd nd 49.34b 22.66c 73.80a 3.34e
177.79d 279.93b nd nd nd nd nd 332.81a 277.77b 263.92c 55.34e
7.02d 102.58a nd 2.98f 3.04ef 4.66e nd 39.86b 15.21c 98.73a 6.14d
1.49h 46.6a 2.09g 2.93e 5.62d 5.16d 3.67e 6.50c 3.34e 41.2b 1.23h
*
nd = Not detected. Values are mean of four replicates. Mean within each column with same superscript are not significantly different at p P 0.005 level according to Duncan’s multiple range test (DMRT). **
zero, whereas at certain speed the fuel consumption and therefore at the signals, the amount of exhaust coming out from the same number of vehicles will be higher, resulting in greater contamination. The high concentration of lead from automobile has been reported previously by numbers of workers (Foner, 1987; Gratani et al., 1992; Bahemuka and Mubofu, 1999; Renberg et al., 2000; Yaman et al., 2000; Andrews and Sutherland, 2004; Finster et al., 2004; Yakupoglu et al., 2008; Yoshinori et al., 2010). It has also been confirmed that, load on heavy metal contents in topsoils and their variability depend upon the traffic density and the distance (Motto et al., 1970; Bai et al., 2008; Nakayama et al., 2010). Earlier, a number of studies have been carried out on the uptake of heavy metals by various plant species growing near the road junction and roundabouts (Peterson and Alloway, 1979; Lepp, 1981; Page et al., 1981; Nasu and Kugimoto, 1984; De Temmerman and Hoenig, 2004; Lacatusu et al., 2009; Yoshinori et al., 2010; Nastja, 2011). Heavy metals concentration in soils collected from roadside roundabouts and traffic signals were higher as compared to the background levels. The highest concentrations were detected in the samples collected from the roadside soil at round about having more than two traffic signals and there was a trend of gradual decrease in the metal contents with the increasing of the distance.
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