Heavy Metal Contamination in Roadside Soils and Grasses

FEBUART 2014 – APRIL 2014, Vol. 4, No. 2; 1661-1673.

E- ISSN: 2249 –1929

Journal of Chemical, Biological and Physical Sciences An International Peer Review E-3 Journal of Sciences Available online atwww.jcbsc.org

Section D: Environmental Sciences Research Article

CODEN (USA): JCBPAT

Heavy Metal Contamination in Roadside Soils and Grasses: A Case Study from Dhaka City, Bangladesh H. M. Zakir*, Nahid Sultana and Mousumi Akter Department of Agricultural Chemistry, Faculty of Agriculture, Bangladesh Agricultural University, Mymensingh-2202, Bangladesh

Received: 5 January 2013; Revised: 24 February 2014; Accepted: 28 February 2014

Abstract: The research work was conducted to determine the concentration of heavy metals in roadside soils and grass samples collected from different locations of Dhaka metropolitan city, and to assess their pollution level. The concentrations of metals (Cu, Zn, Pb, Cd and Cr) in roadside soil and common grass (Ageratum conyzodes) samples were determined by using an Atomic Absorption Spectrophotometer (AAS). The pH of all soil samples were slightly acidic to neutral. Average concentration of heavy metals in soil samples were: Pb = 45.68; Cd = 0.38; Cu = 42.34; Zn = 163.28 and Cr = 30.17 µg g-1. The highest concentrations of different heavy metals were found in the samples collected from heavy traffic. In case of grass samples the mean concentrations of Pb, Cd, Cu, Zn and Cr were 3.48, 0.52, 75.04, 103.33 and 32.25 µg g-1, respectively. The average concentration of Cu, Zn and Cr in grass samples collected from different locations of Dhaka metropolitan city were above than the critical toxic levels (20-30, 100 and 5-10 µg g-1, respectively) for most plants. The study revealed that the contamination factor for Pb, Zn and Cd were several times higher compared to Cu and Cr, which indicates that Pb, Zn and Cd were the major pollutants in the roadside soils of Dhaka metropolitan city. Finally, the Igeo calculations of the roadside soils of the study area also revealed moderate pollution level in soils by Pb, Zn and Cd from anthropogenic sources. Keywords: Heavy metals, roadside soil, vegetation, Dhaka city

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INTRODUCTION Pollution of the environment with heavy metals has increased dramatically since the onset of the industrial revolution. Soil pollution by heavy metals, such as cadmium, lead, chromium, copper etc. is a problem of concern. Although heavy metals are naturally present in soil, contamination comes from different sources, and among them heavy traffic is an important source in most of the roadside soils. In recent years, it has been shown that lead levels in soil and vegetation have increased considerably due to traffic pollution, especially from usage of leaded petrol and exhaust combustion. The problem worsens as daily traffic increases. Recently, a report was published, which confirmed that the main source of pollution in urban areas of Bangladesh was traffic using leaded petrol1. Heavy metals can be found generally at trace levels in soil and vegetation, and living organisms. However, these have a toxic effect on organisms at high concentrations. Heavy metal toxicity has an inhibitory effect on plant growth, enzymatic activity, stoma function, photosynthesis activity and accumulation of other nutrient elements, and also damages the root system2. High content of heavy metal in urban roadside soil and plant samples is mostly due to the density of traffic, which is considered one of the major sources of heavy metal contamination, especially of Pb, because people use leaded petrol instead of unleaded petrol, which is expensive3. The lead in roadside soil is mainly found in the form of lead sulfate. Little interest has been focused on the contamination of roadside soil by other heavy metals. But metals, such as Cu, Fe, Zn and Cd are essential components of many alloys, wires, tires and many industrial processes, and could be released into the roadside soil and plants as a result of mechanical abrasion and normal wear4. Dhaka is the capital city of Bangladesh, located on the eastern banks of the Buriganga River. It is dominant in terms of population concentration, economy, trade and commerce, education and administration. The city has a population of about 12 million along with an area of 153.84 square kilometers5, is among the top ten mega cities of Asia. Dhaka has 1868 kilometers of paved roads6, which are connected to the other parts of the country through highway and railway links. With the prediction of a faster urbanization, the city will have to accommodate future influx of population. Flaws in transportation system of Dhaka City are now pronounced as severe traffic congestion and resulting environmental pollution. Therefore, accurate measurements of the heavy metals (Pb, Cd, Cr, Cu and Zn) content in roadside soils are required to assess the potential ecological risk of the city area. There is no systemic research report about the heavy metal pollution in roadside soils and grasses of Dhaka city. Therefore, this study was conducted to investigate heavy metal contamination level in roadside soils and grasses of Dhaka city, Bangladesh as well as to compare the contamination level with those of the established pollution indices. EXPERIMENTAL Site selection and sampling: Soil and Grass samples were collected from 20 selected areas of Dhaka Metropolitan City. Details about the locations are presented in Table 1. Thirty four (34) soil samples were collected at the depth of 0-20 cm from the twenty selected regions for laboratory analysis. Each sample was kept in labeled polythene bag. Then the collected soil samples were carried to the laboratory for physical and chemical analyses. Eleven grass samples [common name: Fulkhori (Ageratum conyzodes) of Compositae family] were collected at 1.0 to 15.0m distance from the roadside of the eleven selected regions of Dhaka city for laboratory analysis (Table 1). Each sample was kept in labeled polythene bag. Then the collected grass samples were carried to the laboratory for chemical analyses with specific marking and tagging. 1662


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Table 1: Details about soil and grass samples collected from different locations of Dhaka city, Bangladesh Locations South Jatrabari Saydabad Matijhil Khilgaon Shahbag Azimpur Sonargaon hotel Kalabagan Mogbazar Satrastarmor Bijoy saroni Mohakhali Agargaon Mirpur-10 Gulshan-1 Soinik club Banani Airport Azampur Abdullahpur

Sample ID 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Type of sample Soil Soil Soil and Grass Soil Soil Soil and Grass Soil and Grass Soil and Grass Soil Soil Soil and Grass Soil Soil and Grass Soil and Grass Soil and Grass Soil and Grass Soil and Grass Soil and Grass Soil Soil

Dry weight of plant sample (g) 9.43 4.72 6.30 5.58 3.15 4.31 3.60 5.56 6.55 11.09 5.22 -

Preparation and analysis of soil samples: The soil sample was placed in a thin layer on a clean piece of brown paper on a shelf in the room and left until it was air dried. Visible roots and plant fragments were removed from the soil sample and discarded. Then the samples were ground and subsequently sieved by using a 2 mm stainless steel sieve. After that each sample was kept in a separate clean polythene bag with appropriate marking for physical and chemical analysis. Soil pH was measured in 1:2.5 soils to water ratio. The suspension was allowed to stand overnight prior to pH determination. Particle size of soil was determined by the hydrometer method7 and organic carbon (OC) was measured by the wet oxidation method of Walkley and Black8. For the determination of total metal concentration, exactly 1.00 g of powdered soil sample was digested with aqua regia (HNO3: HCl = 1: 3). The concentrations of different heavy metals in aqueous solution of soil were determined by using an atomic absorption spectrophotometer (AAS). Mono element hollow cathode lamp was employed for the determination of each heavy metal of interest. Preparation and analysis of grass samples: At first the collected roadside grass samples were washed and sun dried. After then the samples were dried in an electric oven at 600C temperature for about 48 hours and then ground the samples by grinding mill. Then the powdered samples were preserved in polythene bags with appropriate marking for further chemical analyses. Roadside grass sample extract was prepared by wet oxidation method using di-acid mixture9. In this method, exactly 1 g of finely

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ground grass samples were taken into a 250 mL conical flask and 10 mL of di-acid mixture (conc. HNO3: HClO4 = 2:1) was added to it. Then the flask was placed on an electric hot plate for heating at 180-200ºC temperature until the solid particles disappeared and white fumes were evolved from the flask. Then, it was cooled at room temperature, washed with distilled water and filtered into 100 mL volumetric flasks through filter paper (Whitman No. 1). Finally, the volume was made up to the mark with distilled water. The concentrations of different heavy metals in the extract were determined by using an AAS. The instrument was operated at maximum sensitivity with an air-acetylene flame. Lamp current and slit width was used according to the manufacturer’s recommendation. RESULTS AND DISCUSSION Physicochemical Properties of Soil: The results obtained on pH of soils are presented in Table 2. The results indicated that all soil samples were slightly acidic to neutral (pH range was 6.47 - 7.04 with an average value of 6.86). Table 2: Physicochemical properties and particle size distribution of some roadside soils of Dhaka city Sample ID

pH

OM (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Range Mean

6.58 6.68 6.73 7.00 6.76 6.83 6.86 6.84 6.86 6.99 6.88 6.97 6.92 6.93 6.88 6.96 6.47 7.00 7.03 7.04 6.47-7.04 6.86

1.16 2.58 2.96 2.61 6.19 3.49 2.58 2.46 3.27 2.47 2.61 1.13 3.37 3.20 0.92 1.83 3.88 1.80 1.99 1.32 0.92-6.19 2.59

Particle size distribution (%) Sand Silt Clay 30 46 24 46 44 10 46 54 0 40 48 12 34 38 28 50 34 16 62 34 4 46 38 16 72 20 8 30 40 30 58 36 6 28 40 32 62 32 6 56 34 10 91 10 -1 50 38 12 26 52 22 42 52 6 46 40 14 34 36 30 26-91 10-54 -1 to 32 47.45 38.30 14.25

Textural class Loam Loam Silt loam Loam Clay loam Loam Sandy loam Loam Sandy loam Clay loam Sandy loam Clay loam Sandy loam Sandy loam Sand Loam Silt loam Silt loam Loam Clay loam Sand-Clay loam -

The variation in soil pH in different soils is may be due to degree of decalcification and losses of carbonate minerals for the topsoil to the subsoil10. The amount of organic matter among the sampling 1664


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locations ranged from 0.92 to 6.19 with a mean value of 2.59. The highest organic matter content was found in roadside soils of Shahbag area which was very close to a garbage dumping location. The deposition and decomposition of huge quantities of solid wastes and sewage sludge may be responsible for the organic matter enrichment in this soil. The lowest organic matter content was found in the roadside soils of South Jatrabari area. The variation of organic carbon was due to temperature, rainfall, topography, soil textural class, and soil pH and soil profile. It is evident from Table 2 that soil textural class varied from one location to another location. Among the 20 locations, 07 were loam, 03 were silt loam, 01 were sand, 04 were clay loam and the rest 05 were sandy loam (Table 2). The variation of the textural classes of the roadside soils might be due to the origin of the soil used during road construction, age, weather and others. Heavy Metal Status in Roadside Soils: Total heavy metals concentration of soils collected from different locations of Dhaka metropolitan city are presented in Table 3. The highest amount of Cu and Cr were 53.56 and 70.96 µg g-1, respectively. It is evident from Table 3 that the distribution of Cu and Cr in roadside soils of Dhaka metropolitan area was generally lower than the earth’s crust average. According to Chamon et al.11 the soil collected from Tejgaon industrial area contained 99.7 and 173 µg g-1 Cu and Cr, respectively. Table 3: Heavy metal concentrations in roadside soils collected from twenty selected locations of Dhaka city, Bangladesh Sample ID Heavy metal concentration (µg g-1) Cu Zn Pb Cd Cr 1 48.06 115.83 36.32 0.34 68.62 2 32.61 169.16 38.24 0.32 38.28 3 28.12 115.16 20.14 0.50 20.87 4 53.29 279.45 65.19 0.53 70.96 5 42.68 129.57 46.00 0.46 18.74 6 38.57 163.96 15.03 0.14 13.24 7 50.09 166.05 92.60 0.58 28.14 8 41.17 84.24 42.68 0.38 Trace 9 52.92 103.68 21.50 0.19 25.92 10 43.73 105.46 25.84 0.29 0.23 11 53.13 183.87 104.62 0.67 41.50 12 28.36 183.87 27.48 0.19 31.88 13 53.39 352.35 86.56 0.53 40.89 14 36.79 167.67 37.08 0.38 44.58 15 50.02 241.20 59.59 0.27 23.58 16 39.37 225.75 21.86 0.30 10.90 17 39.30 120.69 56.48 0.43 25.27 18 52.65 146.61 56.35 0.43 36.04 19 40.46 120.30 33.69 0.40 35.68 20 22.21 90.72 26.33 0.24 27.90 Range 22.21-53.39 84.24-352.35 15.03-104.62 0.14-0.67 Trace-70.96 Mean 42.34 163.28 45.68 0.38 30.17 a Earth’s crust average 55.00 70.00 12.50 0.20 100.00 a

Huheey14

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The source of Cu in the roadside soils was indicated by research as being due to corrosion of metallic parts of cars derived from engine wear, thrust bearing, brushing and bearing metals12,13. On the other hand, according to Al-Khashman14, the Cr in roadside soil and dust is associated with the chrome plating of some motor vehicle parts. However, the present study found that the mean concentrations of Cu and Cr in roadside soils of Dhaka city were lower compared with several other cities in the world (Table 4). Table 4: Mean concentration of heavy metals (µg g-1) in roadside dust of several cities in the world City Ammana Bahrainb Birminghamc Londond Manchester e Istanbulf Israelg Greeceh This study (Dhaka City)

Cu 177 466.9 155 113 38.1 60.4 42.7 42.34

Zn 358 151.8 534 680 653 156 82.2 137.8 163.28

Pb Cd 236 1.7 697.2 72 48 1.6 1030 3.5 265 99.3 87.4 0.27 359.4 0.2 45.68 0.38

Cr 144.4 42.4 193.2 30.17

Digestion HCl+HNO3 HCl+HNO3 HClO+4HNO+3H2SO4 HCl+HNO3 HNO3 HCl+HNO3 HCl+HNO3 HClO+4HNO+3H2SO4 HCl+HNO3

Al-Khashman15; bAkhter and Madany16; cCharlesworth et al.,17; dSchwar et al.,18; eRobertson et al,19; fGuney et al.,20; gSwaileh et al.,21; hChristoforidis and Stamatis22. a

Roadside soils and dust are the potential source of metals for people living in urban communities. Total Zn and Cd concentrations in roadside soil samples varied with a range from 84.24 to 352.35 and 0.14 to 0.67 µg g-1, respectively. The mean values of Zn and Cd were 163.28 and 0.38 µg g-1, respectively which were more than twice compare to the average Earth’s crust values (Table 3). The Zn anomaly in roadside soils could have been deposited by the wear and tear of vehicle bodies with common galvanizing of steel surfaces. According to Elik 23, higher concentration of Zn and Cd in heavy traffic zones indicates that fragmentation of car tires is a likely source of these metals. Other possible sources of Zn in relation to automobile traffic are: wearing of brake lining, losses of oil and cooling liquid and wearing of road paved surface24. Furthermore, Ni and Cd could also be traced to electroplating, and cadmium to tyres. The Cd is released as a combustion product in the accumulators of motor vehicles or in carburetors13. Cadmium is now most commonly encountered in Cd-Ni battery production, although it continues to be used in paints as well as in plastic production where it is an effective stabilizing agent25. The range of the median value of Cd in roadside soils and dust samples world-wide has been examined as being 0.5-4.0 µg g-1 26. However, the present study revealed that the mean concentrations of Zn and Cd in roadside soils of Dhaka metropolitan city were still higher compared with some other cities of the world (Table 4). The roadside soil and dust could have received pollutants emanated from the vehicular traffic. The significant amount of Pb in the soil is likely to have derived from vehicle exhaust fumes laden with Pbrich aerosols. Once deposited in the soil, the Pb can become quite immobile and hence it can accumulate over the years. The results on total Pb content of soils from twenty selected areas of Dhaka metropolitan city have been presented in Table 3. The highest Pb concentration of soils was 104.62 µg g-1, which was recorded at Bijoy Saroni, while the lowest content was 15.03 µg g-1 found at Azimpur. The mean value of Pb was 45.68 µg g-1, which was almost four times higher than the Earth’s crust average (Table 3). Lead pollution in the environmental samples including soil, dust, sediments and natural water comes from 1666


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combustion of gasoline that contains tetraethyl lead as an anti-knocking agent 27. The Pb is converted to PbO and PbO2 which is then transformed into volatile PbCl2, PbBr2 and PbBrCl by the addition of dichloro- or dibromomethane to the gasoline. Therefore, Pb compounds emit into the atmosphere from vehicle exhaust gases using Pb added petroleum products24. The present study also revealed that Pb levels in roadside soils of Dhaka city were low yet compared with several other cities in the world (Table 4). Heavy Metal Status in Roadside Grasses: The total heavy metals concentration obtained from roadside grasses of Dhaka city has been shown in Table 5. The highest concentrations of Cu and Cr were found in the sample collected from Kalabagan and Mirpur-10, respectivley. Copper concentration in roadside grasses ranged from 66.30 to 85.20 µg g-1 and the mean value was 75.04 µg g-1, which is above than the critical toxic level for most plants. Normal content of Cu in plants ranges from 2 to 20 µg g-1 but in most plants the normal Cu content is in a narrower range of 4 to 12 µg g-1. Robson and Reuter 28 explained that there are different tolerance ranges for plants but a critical toxic level of Cu is in the range of 20 to 30 µg g-1 for most plants. Chromium concentration in roadside grasses ranged from 15.72 to 41.76 µg g-1 with a mean value of 32.25 µg g-1. Critical levels of Cr for the plants are 5-10 µg g-1 29, and this study results revealed that the investigation area runs a risk of Cr pollution in grass samples (Table 5). Table 5: Heavy metal concentrations in roadside grasses collected from eleven selected locations of Dhaka city, Bangladesh Locations Matijhil Azimpur Sonarga Hotel Kalabagan Bijoy sarani Agargaon Mirpur-10 Gulshan-1 Soinik club Banani Airport Range Mean Critical toxic level for plants a

Heavy metal concentration (µg g-1) Cu Zn Pb 66.30 86.70 2.64 75.60 108.90 3.42 73.80 101.40 2.40 85.20 119.10 3.18 77.21 120.20 2.50 78.60 122.10 2.16 75.30 116.70 5.40 80.10 77.70 5.16 74.70 97.20 5.70 67.20 90.30 1.80 71.40 96.30 3.96 66.30- 85.20 77.70- 122.10 1.80-5.70 75.04 103.34 3.48 a b 20-30 100 -

Cd 0.42 0.72 0.60 0.48 0.41 0.30 0.54 0.36 0.72 0.42 0.78 0.30-0.78 0.52 -

Cr 15.72 29.46 31.62 35.34 30.79 35.82 41.76 36.06 36.30 23.34 38.58 15.72- 41.76 32.25 5-10c

Robson and Reuter 28; bRauna et al. 30 & cCicek and Koparal29

Metal concentration in plant samples differs according to its availability in soils, similarly soil metal contents differs according to the soil type and pollution sources. Zinc concentration in roadside grasses of Dhaka city ranged from 77.70 to 122.10 µg g-1 and the mean value was 103.34 µg g-1. Zinc has limited mobility in the plant and it can be accumulated in the root system when Zn has been added to the soil3. The clearest effect of Zn excess is reduction of root growth for the low tolerant plant. According to Rauna

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et al.30 a critical toxic level of Zn for plants is 100 µg g-1, which is exceeded by the mean value obtained from the present study (Table 5). The highest concentration of Pb was found in the sample collected from Soinik Club. Lead concentration in roadside grasses ranged from 1.80 to 5.70 µg g-1 and mean value was 3.48 µg g-1. Researchers3,31,32,33 were notified that heavy metal content was higher in roadside soil and plant samples collected near a main road. The concentration of Cd in roadside grasses ranged from 0.30 to 0.78 µg g-1 with the mean values of 0.52 µg g-1. The highest concentration of Cd was found in grass sample collected from Airport area. The main source of environmental Cd pollution is the ferrous steel industry. In addition, vehicle wheels, mineral oils and usage of waste mud may introduce Cd into the soil and these increase Cd levels of the plants34. The acceptable level of Cd in agriculture is around 3.0 µg g-1 and generally is lower than 0.1 µg g-1 in the soil29. ASSESSMENT OF POLLUTION LEVEL Index of Geoaccumulation (Igeo): A geoaccumulation indexing (Igeo) approach was used to quantify the degree of anthropogenic contamination, and to compare the different metals in soils and sediments35. This quantitative check of metal pollution in soils was proposed in the form of an equation defined as the index of geoaccumulation, as follows: Igeo = log2 (Cn/ 1.5 × Bn) Where, Cn is measured concentration of trace metal in the soil, and Bn is the geochemical background for the same element which is either directly measured in precivilization soils of the area or taken from the literature (average shale value described by Turekian and Wedepohl36). The factor 1.5 is introduced to include possible variations of the background values that are due to lithologic variations. The geoaccumulation index (Igeo) introduced by Muller35 was also used to assess heavy metal pollution in roadside soils of Dhaka metropolitan city. Table 6 shows the geoaccumuation index, which includes seven grades. It includes various degrees of contamination above the background value ranging from unpolluted to extremely polluted soil quality. The highest grade (class six) can be reflected 100-fold enrichment above the background values37. Table 6: Measure of metal pollution in aquatic sediments and solid waste by using geoaccumulation index Index of Geo- accumulation Igeo Class Designation of soil or sediment quality 10 – 5 6 Extremely polluted 4–5 5 Strongly/ extremely polluted 3–4 4 Strongly polluted 2–3 3 Moderately/ strongly polluted 1–2 2 Moderately polluted 0–1 1 Uncontaminated/ moderately polluted 0 0 Unpolluted The calculated Igeo for heavy metals of roadside soils of Dhaka city, and their corresponding contamination intensity are illustrated in Figure 1. The Igeo values for Cu and Cr exhibited zero class, indicating unpolluted soil quality. The values for Cd, among the 20 locations of Dhaka city, 6 sites exhibited Igeo class 1, indicating uncontaminated/ moderately polluted soil quality by Cd. Similarly, in 1668


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case of Zn, among the locations 11 sites showed positive values (0 < I geo < 2), that means Igeo class 1-2, indicating moderately polluted soil quality. Considering Pb, among the 20 locations of Dhaka city, 65% sampling sites exhibited Igeo class 1-2, indicating moderately polluted soil quality by Pb. Finally, the I geo calculations for roadside soils of Dhaka metropolitan city revealed moderate pollution level in soils by Pb, Zn and Cd from anthropogenic sources.

Cu

Zn

Pb

Cd

Cr

3 2

Igeo index value

1 0 -1 -2 -3 -4 1

2

3

4

5

6

7

8

9

10 11 12 13 14 15 16 17 18 19 20

Sampling sites Figure 1: Geoaccumulation index (Igeo) of heavy metals in roadside soil samples collected from different locations of Dhaka metropolitan city Pollution load index (PLI): Pollution load index (PLI) is a multi-metal approach, which has been introduced by Tomlinson et al.38 for an overall assessment of soil quality with respect to heavy metal concentrations. According to Tomlinson et al.38, PLI describes the quality of a site in terms of easily understood by the non-specialist and which can be used to compare the pollution status of different sites. The PLI for a single site is the nth root of n number of multiplied together contamination factor (CF) values. The CF and PLI for a single site can be obtained as follows: CF = CMetal concentration/ CBackground concentration of the same metal, and PLI for a site = nth √CF1 × CF2. . . × CFn While computing the contamination factor (CF) for pollution load index (PLI) of soils of the studied region, average shale value for each heavy metal described by Turekian and Wedepohl,36 were considered as background concentration values. The concept of a baseline is a fundamental issue to the formation of 1669


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a PLI38. The PLI values ranged from 0.32-1.74 for soil samples collected from 20 locations of Dhaka metropolitan city (Figure 2). The index as presented provides a simple, comparative means for assessing a site quality: a value of zero indicates perfection, a value of one that only baseline levels of pollutants are present, and values above one would indicate progressive deterioration of the site quality38. However, out of 20 locations, total 11 sites had the value >1.0 indicates pollution load in the respective sites. The PLI can provide some understanding to the public of the area about the quality of a component of their environment, and it can indicate the trends over time and area. In addition, it also provides valuable information and advice for the policy and decision makers on the pollution level of the area.

2.0

PLI

1.8

Baseline value

1.6

PLI value

1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 1

2

3

4

5

6

7

8

9

10 11 12 13 14 15 16 17 18 19 20

Sampling sites Figure 2: Pollution load index (PLI) of heavy metals in roadside soil samples collected from different locations of Dhaka metropolitan city. CONCLUSION The present study reveals that among the studied heavy metals the contamination factor for Pb, Zn and Cd were several times higher compared to Cu and Cr, which indicates that Pb, Zn and Cd are the major pollutants in the roadside soils of Dhaka metropolitan city. Out of 20 locations, total 11 sites have PLI value >1.0 indicate pollution load in the respective sites of the city. Similarly, the Igeo calculations of the roadside soils of the study area also reveal moderate pollution level in soils by Pb, Zn and Cd from anthropogenic sources. On the other hand, the mean value of Cu, Zn and Cr in roadside grass samples obtained from the present study is exceeded the critical toxic levels. The present study results show that heavy metal levels in roadside soils of Dhaka city are low yet compared with several other cities in the world, but if it is continued, the magnitude of heavy metals pollution in the city area will increase to intolerable limits and this may have severe impact on the environment. Although there are environmental 1670


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protection laws and regulations now, but have not been strictly implemented by the Department of Environment, Bangladesh. So, it is necessary to identify the origin and potential sources of heavy metals in the study area and accordingly City Corporation or Government of Bangladesh will have to take necessary initiative to minimize pollution level in the city area. ACKNOWLEDGEMENT This work was supported by the Ministry of Science and Technology, Government of the People’s Republic of Bangladesh under Special Allocation for Science and Technology for the financial year 201213; Research Grant no. # 39.009.006.01.00.042.2012-2013/ES-23. REFERENCES 1.

2. 3.

4. 5.

6. 7. 8.

9. 10. 11.

12. 13. 14. 15.

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* Corresponding author: H. M. Zakir; Department of Agricultural Chemistry, Faculty of Agriculture, Bangladesh Agricultural University, Mymensingh-2202, Bangladesh

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