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Atmospheric Environment 40 (2006) 3835–3844

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Trace metal concentrations in streetdusts of Dhaka city, Bangladesh

Faruque Ahmed�, Hiroaki Ishiga

Department of Geoscience, Shimane University, Matsue 690-8504, Japan

Received 8 November 2005; received in revised form 15 January 2006; accepted 3 March 2006

Abstract

Street dust samples were collected from differing areas (industrial—medium traffic density, commercial—high traffic

density, and residential 1 and 2—low traffic density) in Dhaka City, Bangladesh, and their major oxide and trace element

compositions were determined. The results show significant concentrations of Pb, Zn, Cu, Ni, and Cr in the Dhaka dusts,

and some variations among the four sample groups. The samples in the commercial area had Pb concentrations two- to

seven-fold those of the industrial and residential areas. Contents of Zn, Cu, Ni, and Cr in the industrial areas were greater

than those in the commercial and residential areas. Levels of Pb, Cu, Ni, and Cr exceeded the maximum permissible limits

for common soil. Increases in these anthropogenic trace metals in the surface environment can most likely be attributed to

rapid urbanization and industrialization and increased vehicle emissions to the atmosphere. Elevated Zn concentrations in

an industrial area can be ascribed to discharges of industrial activities, while elevated Zn abundances in commercial areas

probably originate from traffic sources. The street dusts contaminated with Cu, Ni, and Cr occur mainly in industrial

areas. However, Pb contamination in the Dhaka dusts is probably caused by Pb particles from vehicle emissions.

r 2006 Elsevier Ltd. All rights reserved.

Keywords: Trace metal; Air pollution; Geochemistry; Dhaka dust

1. Introduction

Trace metals are useful indicators of contamina-tion in surface soil environments. Such elementstend to accumulate in topsoils, and may affectpopulation health if they reach levels such that theyconstitute toxic pollutants. Exposure to lead isamong the most significant yet preventable threatsto human health in the world. Persistent exposure tolead can increase the number of mentally retarded

e front matter r 2006 Elsevier Ltd. All rights reserved

mosenv.2006.03.004

ing author. Tel.: +81852 26 6338;

6469.

ess: frahmed2007@yahoo.com (F. Ahmed).

children in a society and reduce the number ofchildren with superior intelligence (Karim et al.,2000). However, while environmental pollutionfrom vehicle-based lead emissions is decreasing inmost of developed countries, such pollution israpidly increasing and is becoming a significantissue in developing countries (Fakayode and Olu-Owolabi, 2003). Many studies of concentrations ofheavy metals in street dusts in large cities have beenconducted in advanced countries (e.g. Chen et al.,1997; De Miguel et al., 1997; Wang et al., 1998; Liet al., 2001, 2004; Imperato et al., 2003; Sezgin et al.,2003), but little has been done in less developedcountries.

.

ARTICLE IN PRESSF. Ahmed, H. Ishiga / Atmospheric Environment 40 (2006) 3835–38443836

Industrial revolution started in the mid-1800s.Since then, the biogeochemical cycle of inorganiccontaminants (e.g. metals) naturally present in theenvironment has been greatly accelerated by humanactivities (Adriano, 2001). At present, air pollutionhas become a major environmental issue in manynations, including Bangladesh. Total numbers ofvehicles and auto-rickshaws (two-stroke enginedvehicles) in Dhaka City of Bangladesh haveincreased several fold in the last decade. Gaseouswastes in the form of automobile exhaust andfactory chemicals, as well as from primitive forms ofheating are the major sources of air pollution in thecountry. In addition to high population growth(2.2% per year), the rate of urbanization has alsoaccelerated, and is now one of the highest in Asia.Although this rapid urbanization has resulted insevere pollution, environmental conditions have notyet been examined in detail.

Combustion of leaded gasoline is the main sourceof lead exposure in large cities, especially in thecapital, Dhaka City. This has led to ubiquitouscontamination of the environment, but very littlemonitoring of air quality has been carried out in thecity area. The Bangladesh Atomic Energy Commis-sion (BAEC) reported that atmospheric Pb concen-tration in Dhaka reached 463 ngm�3 in the dryseason (November 1995–January 1996), one of thehighest levels of lead pollution in the world (Rah-man et al., 1999). The World Bank recentlyestimated that public exposure to air pollution inDhaka causes nearly 15,000 premature deaths and6.5 million cases of illness every year (Hossen,2002). Therefore, comprehensive studies of elemen-tal composition and concentrations in street dustare needed to determine the present situation of theatmospheric environment in Dhaka City.

Atmospheric pollution is one of the major sourcesof heavy metal contamination in soils and roadsidedusts in urban areas. These metals can accumulatein soils from atmospheric deposition by sedimenta-tion, impaction and interception (Li et al., 2001).Accumulations of heavy metals including Pb, Zn,and Cu on urban surfaces arise from vehicleexhausts, industrial discharges, oil lubricants, auto-mobile parts, corrosion of building materials, andatmospheric deposition (Adriano, 2001; Li et al.,2001, 2004). Thus study of road soils could providemore information of air pollution of Dhaka City.The present investigation aims to assess the presentair environmental conditions by determining thetrace metals in the street dusts of Dhaka City. The

possible sources of the trace metals are alsodiscussed in this study.

2. Materials and methods

2.1. The study site—Dhaka City, Bangladesh

Bangladesh is located in the eastern part of southAsia. It is surrounded by India to the west, north,and northeast, by Myanmar to the southeast, andby the Bay of Bengal to the south. Dhaka City, thecapital, is almost in the middle of Bangladesh. Totalarea of the city is about 1500 km2. In 1950, thepopulation of Dhaka City was only 0.43 million(Hossen, 2002). Even in the post-independentperiod (in the 1970s) the city was not overcrowded,and the number of motorized vehicles was small.However, the population has now passed 10 million,with a rate of increase of about 7% per year (Karimet al., 2000). Numbers of vehicles and industries arealso multiplying rapidly, and recent observation ofsmog in the Dhaka area indicates the onset of airpollution (Hussam et al., 2002). Vehicles, especiallytwo-stroke auto-rickshaws (now banned in DhakaCity) and aged trucks and mini-buses are importantfactors for most of the air pollution (Chowdhuryet al., 2000).

In 1986 and 2000, the total numbers of registeredmotor vehicles in Dhaka City were 66,703 and over200,000, respectively (Chowdhury et al., 2000;BRTA, 2002). And at the same time, the numberof two-stroke auto-rickshaws in Dhaka increasedfrom 8092 in 1986 (BRTA, 2002) to about 60,000 in2000 (Chowdhury et al., 2000). Therefore, totalvehicle numbers and auto-rickshaws in Dhaka haveincreased by almost three times and seven times,respectively, in only fourteen years. Consequently,environmental pollution (air, water, and sediment)by lead is now a major problem in Dhaka.

The study areas lie mainly in the central Dhakametropolitan area. The sample sites were subdividedinto four groups to reflect contrasts between commer-cial, industrial, and residential areas with high, me-dium, and low traffic density roads (Fig. 1). The fourgroups are (1) industrial area (IA)—Tejgaon industrialarea, and Old Dhaka City small industrial-cum-residential area (sampling sites 37–39 and 1–4, res-pectively) with medium traffic (500–1500vehicles h�1);(2) commercial area (CA)—Motijheel commercialarea, and commercial-cum-residential areas along themain trunk roads (Fig. 1) with heavy traffic (41500vehicles h�1); (3) residential area 1 (RA1)—other sites

ARTICLE IN PRESS

52

Ziainternationalairport

Azampur

KhilkhetManikdi

Gulshan

Motijheel

Rayerbazar

Old Dhaka City

Tejgaon industrial area

CMH

DOHS

Dhanmondi

Mohammadpur

Manikmiaav

Azimpur

Chakdigun

35

4

36

67

66Botanical

garden

626364

51

57

5554

48 47 45 44 43 42 4146

4039383734

65

61 60 59

5049 53 56

32 31 30 29 28 27 26 25

24

8765

1 2

910111213141516

17 18 19 20 21 22 23

33

70

6968

58

Sampling site

Waterbody

Hazaribag

31km

N

90° 24'

23°49'

23°47'

23°45'

90° 21'

Zoo

Aricha high way

Rokeyasarani

Railway

Mymensingh road

IACA

RA2RA1

(b)(a)

Bangladesh

Bay of Bengal

SylhetBasinOld

Brahamaputra

FloodPlainGanges

GangesDelta

100 Km0 50

Jessore

MadhupurTract

Chittagong

BarindTract

24°MeghnaFloodPlain

India

Mya

nmar

23°Khulna

Calcutta

90°88° 91°

21°

26° Rangpur

Jam

una

Dhaka

Fig. 1. (a) Map of Bangladesh; (b) sampling sites of street dusts in Dhaka City. Sampling sites 1–64 are in the main city, and 65–70 are in

the outskirts. IA, CA, RA1, and RA2 indicate industrial area, commercial area, residential area 1 in the main city, and residential area 2 in

the outskirts, respectively. The dashed lines indicate IA and CA.

F. Ahmed, H. Ishiga / Atmospheric Environment 40 (2006) 3835–3844 3837

in the main city (Fig. 1) with low (100–500vehicles h�1)and medium traffic densities (500–700vehicles h�1); (4)residential area 2 (RA2)—outside of the main city(sampling sites 65–70) with very low traffic densities(50–100vehicles h�1). However, sample sites in OldDhaka City are on the margin of a small industrialarea, and are strongly affected by the many smallfactories, workshops, and vehicle garages in that area.

2.2. Sampling

Sixty-four road sediment samples (D-1 to D-64)were collected from locations in the main city,

including street intersections, and other six samples(D-65 to D-70) were collected in the northern partof Dhaka City (Fig. 1). Total seventy samples werecollected during the dry season in February 2003.The dust sampling was carried out from pavementedges using a plastic dustpan and brushes. Dustswere not collected adjacent to site-specific pollutionsources, e.g. industries or gasoline stations. About100 g of dust were stored in small self-sealing plasticbags after screening through a 1.0mm mesh nylonsieve to remove extraneous matter such as smallpieces of brick, paving stone, and other debris. Thedust samples were mostly very fine sands, fine silts,

ARTICLE IN PRESSF. Ahmed, H. Ishiga / Atmospheric Environment 40 (2006) 3835–38443838

and clay particles, and are regarded as representa-tive of the environmental materials present inDhaka. Samples D-1 to D-64 were collected fromnear intersections of a rectangular grid (Fig. 1).These sampling sites are in commercial, residential,and industrial with medium to heavy traffic existingroads. The other six sample sites are in residential orgarden districts with very low traffic densities, andserve as baselines for comparison with the samplesfrom Dhaka City proper. Background concentra-tions in typical Tropical Asian soils and likely toexist in common soils are also listed in Table 1 forcomparison.

2.3. Analytical procedures

Approximately 50 g of each sediment sample weredried for 24 h in an oven at 110 1C. The driedsamples were then ground for 20min in anautomatic agate mortar and pestle.

Selected major oxides [TiO2, Fe2O3* (total iron isexpressed as Fe2O3*), CaO, and P2O5], total sulfur(TS), and trace elements (As, Pb, Zn, Cu, Ni, Cr, V,Sr, Zr, U, Br, and I) in the sediments weredetermined by X-ray fluorescence (XRF) in theDepartment of Geoscience, Shimane University,using a RIX-2000 spectrometer (Rigaku Denki Co.Ltd.) equipped with a Rh-anode X-ray tube. Allanalyses were made on pressed powder disks,following Ogasawara (1987). Average errors forthese elements are less than 710%. Analyticalresults for USGS standard SCo-1 (Cody Shale) areacceptable compared with the proposed values ofPotts et al. (1992).

Table 1

Concentrations of elements (ppm) in Tropical Asian soils and likely to

References Elements Average values

(Tropical Asia)

Domingo and Kyuma (1983) Zn 66

Cu 33

Ni 22

Ali et al. (2003) Pb NA

Cr NA

P2O5b NA

TSb NA

Ahmed et al. (2002) CaOb NA

NA ¼ not available.aFabis (1987), cited from Sezgin et al. (2003).bConcentrations in wt%.

3. Results

3.1. Major elements

Elemental compositions of the dusts are summar-ized in Table 2. Means and standard deviations ofsamples within each group were calculated. Abun-dances of TiO2 (0.46–0.92wt%), Fe2O3

(2.47–13.41wt%), CaO (1.43–6.47wt%), and P2O5

(0.12–0.48wt%) show considerable variation in thesamples as a whole. Sample D-37 from the Tajgaonindustrial area has an exceptional higher level ofFe2O3 (13.41wt%). TS also shows wide variation inthe dusts (0.06–0.56wt%). The highest contents ofTS (0.56wt%) and P2O5 (0.48wt%) were found inthe CA and IA, respectively. Compared to othergroups, average values of Fe2O3 (5.00wt%) andP2O5 (0.28wt%) are greater in the industrial area(Table 2). The highest concentration of TiO2

(0.92wt%) was found in sample D-66 from RA2,which also had the lowest levels of CaO (1.43wt%),Fe2O3 (2.47wt%), and TS (0.06wt%), and a lowerP2O5 content (0.14wt%), possibly because it wascollected from the Dhaka botanical garden, andconsisted of very fine silty sands. However, theaverage concentrations of TiO2 are quite similarthroughout the four groups in the study areas.

3.2. Trace elements

In this study, abundances of As (3–19 ppm), Pb(19–205 ppm), Zn (44–261 ppm), Cu (7–304 ppm),Ni (16–54 ppm), and Cr (61–203 ppm) showdifferences between the groups of samples from

exist in common soil

Average values

(Bangladesh)

Acceptable

valuesa (common

soil)

Maximum valuesa

(common soil)

68.00 300 300

27.00 50 100

22.00 50 50

23.50 100 100

95.90 100 100

0.11 NA NA

0.06 NA NA

1.49 NA NA

ARTICLE IN PRESS

Table

2

Geochem

icalcompositions(m

ean7standard

deviation)ofstreet

dustsin

DhakaCity,byarea

Area

Majoroxides

andTS(w

t%)

Trace

elem

ents

(ppm)

TiO

2Fe 2O

3CaO

P2O

5TS

As

Pb

Zn

Cu

Ni

Cr

VSr

Zr

UBr

I

IA (n¼

7)

0.637

0.04a

5.007

3.73a

3.017

0.28a,b

0.287

0.10a

0.277

0.09a

772.17a

547

19.2

b1697

71.1

a1057

110a

357

13.6

a1367

35.8

a727

23.1

a1467

14.8

a,b

2117

20.5

b370.27a

17

0.39b

337

6.40a

CA

(n¼

24)

0.667

0.08a

4.037

0.70a,b

3.127

0.64a

0.207

0.03b

0.287

0.08a

873.07a

747

36.4

a1547

42.4

a467

18.7

b267

4.65b

1057

16.9

b687

13.1

a1457

9.57b

2337

29.8

b370.19a

37

2.16a

297

2.24b

RA1

(n¼

33)

0.667

0.09a

3.457

0.41b

3.027

0.80a

0.207

0.06b

0.187

0.06b

570.88b

357

7.78b,c

977

28.8

b227

9.04c

237

4.22b

997

16.9

b647

10.9

a1537

10.9

a2367

39.0

b370.14a

17

0.76b

287

2.20b

RA2

(n¼

6)

0.717

0.12a

3.187

0.47b

2.297

0.48b

0.177

0.02b

0.117

0.04c

470.34b

257

4.81c

657

15.3

b147

6.59c

247

2.50b

777

14.3

c647

6.03a

1417

27.7

b2867

105a

370.20a

17

0.17b

267

0.56b

IA,industrialarea;CA,commercialarea;RA1,residentialarea1in

themain

city;RA2,residentialarea2in

theoutskirts.

a,b,cMeanswithdifferentsuperscriptlettersin

acolumnare

significantlydifferent(po0:05).

F. Ahmed, H. Ishiga / Atmospheric Environment 40 (2006) 3835–3844 3839

industrial, commercial, and residential areas (Fig.2). The highest contents of Zn (261 ppm), Cu(304 ppm), Ni (54 ppm), and Cr (203 ppm) werefound in the industrial area. However, the highestPb concentration (205 ppm) in the street sampleswas found in the commercial very high trafficdensity area. Compared to other groups, averagelevels of Zn (169 ppm), Cu (105 ppm), Ni (35 ppm),and Cr (136 ppm) are also greater in the industrialarea (Table 2). Concentrations of Sr (85–171 ppm),Br (1–9 ppm), and Zr (165–497 ppm) also showgreater differences among the study sites. Incontrast, V, U, and I abundances vary little betweensamples. The highest concentration of Zr (497 ppm)was again found in sample D-66, which also had thelowest values of Pb (19 ppm), Zn (44 ppm), and Sr(85 ppm), and low Cu (8 ppm) and Ni (21 ppm). Asnoted above, this silty sand sample was collectedfrom a very low traffic density road.

4. Discussion

4.1. Trace metals contamination in street dusts

In this study, the elemental compositions showvariations among the four sample groups. The Pband Zn contents in the dust samples show significanthigher concentrations compared to Bangladeshisurface soil, and CaO, P2O5, and TS also showhigher levels in the road dusts (Tables 1 and 2).Concerning the average values, samples collectedfrom industrial sites have higher concentrations ofZn, Cu, Ni, and Cr than those from commercial andresidential sites (Table 2; Fig. 2). Considering thehigher concentrations of these elements, three mainfactors may be responsible for the contamination ofstreet dusts in Dhaka City. These are emissions,urbanization and industrialization, and domesticwastes. These factors are discussed below.

4.1.1. Emissions

Air pollution in Bangladesh occurs due to thesignificant emissions of toxic matter introduced intothe atmosphere from the use of leaded gasoline anddiesel fuels with high sulfur content. As notedabove, most of the air pollution in Dhaka City iscaused by vehicles, especially two-stroke auto-rickshaws (‘‘baby taxies’’). The two-stroke enginesused in Bangladeshi auto-rickshaws emit 13 timesmore smoke than four-stroke engines of thesame size (Chowdhury et al., 2000), because fuel

ARTICLE IN PRESS

0 50 100 150 200 250

IA

CA

RA1

RA2

Pb (ppm)

*

*

*

* Mean*

(a)

0 50 100 150 200 250 300

IA

CA

RA1

RA2

Zn (ppm)

*

*

*

* Mean*

(b)

0 50 100 150 200 250 300 350

IA

CA

RA1

RA2

Cu (ppm)

*

*

*

* Mean*

(c)

10 20 30 40 50 60

IA

CA

RA1

RA2

Ni (ppm)

*

*

*

* Mean*

(d)

50 100 150 200 250

IA

CA

RA1

RA2

Cr (ppm)

*

*

*

* Mean*

(e)

0 0.1 0.2 0.3 0.4 0.5 0.6

IA

CA

RA1

RA2

TS (wt%)

*

*

*

* Mean*

(f)

Fig. 2. (a)–(f) Summary of concentrations of heavy metals and TS in Dhaka dusts in different areas. IA, CA, RA1, and RA2 indicate

industrial area, commercial area, residential area 1 in the main city, and residential area 2 in the outskirts, respectively. Horizontal lines

give the range, excluding outliers (circles); boxes enclose 50% of the data, and illustrate the 25% quartile, median (vertical bar) and 75%

quartile. Stars ¼ mean. Outliers are defined as the upper or lower quartile 71.5 times the interquartile difference.

F. Ahmed, H. Ishiga / Atmospheric Environment 40 (2006) 3835–38443840

combustion is not as efficient in two-stroke engines,as lubricant is mixed with the fuel.

Ali et al. (2003) collected 43 surface soil samplesfrom all over Bangladesh, and found an average Pbconcentration of 23.5 ppm. Average Zn concentra-tions of 68 ppm for Bangladesh and 66 ppm forTropical Asian surface soil were reported byDomingo and Kyuma (1983; Table 1). In this study,concentrations of Pb (av. 74; max. 205 ppm) in thecommercial heavy traffic density area (CA; Table 2;Figs. 2(a) and 3(b)) and concentrations of Zn (av.169; max. 261 ppm) in the industrial medium traffic

density area (IA; Table 2; Figs. 2(b) and 3(a)) ofDhaka are elevated over the levels in Bangladeshsurface and Tropical Asian surface soils. They arealso above average upper continental crust levels(UCC; av. Pb 20 ppm and Zn 71 ppm; Taylor andMcLennan, 1985). The mean and maximum con-centrations of Pb in the CA are about three timesand nine times greater, respectively, than that of themean value for Bangladeshi surface soil. The highestPb value in the Dhaka street dusts is double themaximum permissible level for common soil. There-fore, additional Pb has been contributed to the city

ARTICLE IN PRESS

(b)

0 1

km

0

25

50

75

100

125

150

175

200

0 1

km

90° 26'90° 24'90° 22' 90° 26'90° 24'90° 22'

23°

48'

23°

46'

23°

44'

23°

48'

23°

46'

23°

44'

0

25

50

75

100

125

150

175

200

225

250

(a)

Fig. 3. Geochemical maps of Zn (a) and Pb (b) concentrations (ppm) in street dusts of Dhaka City.

F. Ahmed, H. Ishiga / Atmospheric Environment 40 (2006) 3835–3844 3841

environment, resulting in increased concentrationsin the dusts.

Surveys conducted in differing geological areas(e.g. Chen et al., 1997; De Miguel et al., 1997; Wanget al., 1998; Li et al., 2001, 2004; Fakayode and Olu-Owolabi, 2003; Imperato et al., 2003; Sezgin et al.,2003; many others) indicate that the most importantsource of anthropogenic Pb to street dust is fromgasoline additives. The number of two-strokeengined vehicles in Dhaka City increased by 60%between 1990 and 1996, and had continued toincrease by an annual rate of 20% until 2001 (ICT,2001). As noted above, total vehicle numbers andauto-rickshaws in Dhaka have increased by threetimes and seven times, respectively in fourteen years.The high traffic density commercial area (CA) hasgreater Pb concentrations than IA (medium traffic),RA1 (low and medium traffic), and RA2 (very lowtraffic). The mean and maximum amounts of Pb inCA are about 1.5, 2 and 3 times, and 2.5, 4 and 6.5times greater than the mean and maximum values ofPb in the IA, RA1, and RA2, respectively. Auto-mobile exhaust, especially from two-stroke engines,may thus be the major reason for the significantconcentration of Pb in the Dhaka street dusts.

4.1.2. Urbanization and industrialization

The higher concentrations of Pb, Zn, Cu, Ni, Cr,and TS in the road samples of Dhaka appear to berelated to urbanization and industrialization in the

urban areas. Pb is used in the manufacture ofpesticides, fertilizers, in paints and dyes, and inbatteries and explosives. Therefore, wastes fromthese industries contaminate the environment(Khuda, 2001). Among these industries, a numberof battery factories and printing and dyeing worksare situated in the central part of the study area inthe Tejgaon industrial district. Such operations andother lead product factories (lead products manu-facturing; heating, machining, or spraying leadproducts; smelting or casting lead; removing leadcoatings) are established mainly in the Tongiindustrial areas in north Dhaka, and in theKeraniganj areas on the southern side of DhakaCity. However, these industrial areas are far fromthe sampling sites, and their drainage systems areconnected to different fluvial systems, namely theTongi and Buriganga Rivers, respectively. Conse-quently, there is little possibility that Pb contamina-tion in the dust sediments can be attributed to directsupply from factories.

The higher contents of Pb concentrated in thesurface sediments may have been transported by air-borne supply from the use of leaded gasoline andthe increased number of two-stroke engine vehicles,which accelerated air pollution in Dhaka City(Rahman et al., 1999; Karim et al., 2000; Hossen,2002). Accumulation of Pb, Zn, Cu, Ni, and Cr inBangladeshi roadside soils was also observed byMoslehuddin et al. (1998), possibly due to the

ARTICLE IN PRESSF. Ahmed, H. Ishiga / Atmospheric Environment 40 (2006) 3835–38443842

intensive vehicle traffic in Dhaka City and sur-rounding areas. In addition, high Zn concentrationsobserved in some soil samples in that study werealso ascribed to industrial discharge.

Table 3 compares the results for Dhaka from thiswork with other studies conducted by Wang et al.(1998), De Miguel et al. (1997), and Sezgin et al.(2003) in London, Oslo and Istanbul, respectively.The Pb and Zn levels in London are far greater thanthose reported in the other three cities. This mayreflect a strong historical influence of high trafficdensity and industrial activity and hence greatercontamination of urban environment in London.Pb, Zn, and Cu levels in Dhaka are also lower thanthose in Oslo and Istanbul, indicating compara-tively lower traffic flows. However, in the presentinvestigation, concentrations of Pb (av. 74; max.205 ppm) in the high traffic density area and Znconcentrations (av. 169; max. 261 ppm) in theindustrial area are well above those of averages inthe surface soils of Bangladesh and Tropical Asia.Concentrations of Cu, Ni, and Cr (average 105, 35,and 136, and maximum 304, 54, and 203 ppm,respectively) in the industrial area (Table 2; Figs.2(c)–(e)) are also much greater than those ofBangladesh surface soils (av. 27, 22, and95.90 ppm, respectively; Domingo and Kyuma,1983, and Ali et al., 2003) and Tropical Asian soils(av. Cu 33 and Ni 22 ppm; Domingo and Kyuma,1983). The highest values of Cu, Ni, and Cr, andeven the average values of Cu and Cr detected in IAalready exceed the maximum permissible limits forcommon soil. In IA, the highest values observed forCu and Cr are triple and double the maximumpermissible levels for common soil.

Concentrations of Pb, Zn, Cu, Ni, Cr, and TS inthe street dusts in the four areas (IA, CA, RA1, andRA2) show variable minimum, mean and maximumlevels (Table 2; Fig. 2). Pb and TS in the CA havethe highest mean and maximum values among the

Table 3

Comparison of mean concentrations (ppm) of heavy metals in

street dusts from London (Wang et al., 1998), Oslo (De Miguel et

al., 1997), Istanbul (Sezgin et al., 2003), and Dhaka (this study)

Metals London Oslo Istanbul Dhaka

Pb 897 180 185 74

Zn 1866 412 447 154

Cu 300 123 122 46

Ni NA 41 30 26

NA ¼ not available.

areas. In contrast, IA samples have the highestlevels of Cu, Ni, and Cr, suggesting a commonsource for these metals in that area. Average levelsof Ni are similar in CA (high traffic density), RA1(low and medium traffic density), and RA2 (verylow traffic density). These features indicate thattraffic is not the main source of these metals in thedusts, and that Pb and TS in the dusts originatefrom a different source than Cu, Ni, and Cr.

Additional Cu, Ni, and Cr therefore seem to besupplied to urban sediments from industrial activ-ity. The high contents of Pb may originate mainlyfrom automobile emissions, because the amounts ofPb in CA are 4IA, even though Pb could besupplied to road soils from industrial emissions.Maximum Zn content is higher in the IA, butminimum, median, maximum and mean levels donot differ significantly between IA and CA,although they are two to three times higher in thesetwo groups than in RA1 and RA2 (Table 2;Fig. 2(b)). Elevated Zn concentrations at theuppermost road soils in industrial areas can beascribed to discharges from metal processingindustrial activities. Elevated Zn contents in hightraffic density areas may originate from trafficsources, such as wear and tear of vulcanized vehicletires, and corrosion of galvanized automobile parts(Li et al., 2001, 2004). Adriano (2001) also reportedthat corrosion of galvanized steel is a major sourceof Zn emission in the surface environment. Fromthese features it can be inferred that high accumula-tions of trace metals and TS in the street dusts areprobably caused by anthropogenically derivedinputs to the Dhaka environment.

4.1.3. Domestic wastes

Contents of P2O5, CaO, and TS are also elevatedin the street dusts of Dhaka City. Compared toother groups, average P2O5 concentration is greaterin the industrial area. In this study, concentrationsof P2O5, CaO, and TS (av. 0.21, 2.99, and 0.21wt%,respectively) are two- to threefold greater thanaverage Bangladesh surface soil (av. 0.11, 1.49, and0.06wt%, respectively). The sources of P2O5 andCaO in the dust samples are mainly domesticwastes, especially from illicit dumping of residentialgarbage and abattoir wastes onto roads andfootpaths, and into drains. As noted above, a largeindustrial zone (Tejgaon industrial area) is situatedin the central part of the study site. Concentrationsof elements including Zn and phosphorus are highin soils and wastewaters influenced by the wastes

ARTICLE IN PRESSF. Ahmed, H. Ishiga / Atmospheric Environment 40 (2006) 3835–3844 3843

and effluents from factories in this industrial zone(Mondol et al., 2002). Phosphorus concentrationsabout three times greater than those of normal,uncontaminated soils was also reported in theirstudy.

The primary sources of anthropogenic emissionsof SO2 for Dhaka in winter were computed byKarim et al. (2000), using fuel consumption andemission factors. Their results suggested the mainsources were vehicles (55.8%), the brick manufac-turing industry (28.8%), and other industries(10.5%). Khuda (2001) also reported that SO2 wasa sulfur contributor, which also accounted for airpollution, and originated mainly from the combus-tion of sulfur-rich fossil fuels. This element can becarried or washed away by rain and/or by wind, andbe deposited in surface sediments. In this way,atmospheric SO2 can mix with road soil. Atmo-spheric emissions of SO2 are thus a likely source ofhigher contents in TS in the Dhaka dusts.

Considering the above discussion, it is reasonableto propose that a combination of anthropogenicemissions (Pb, Zn, and SO2) and the effects ofurbanization and industrialization (Zn, Cu, Ni, andCr) are major possible causes for the contaminationof street dusts in Dhaka City.

5. Conclusions

Our present results suggest that increases inanthropogenic Pb, Zn, Cu, Ni, and Cr in streetdusts in Dhaka City can most likely be attributed torapid development, increased vehicle emissions tothe atmosphere, and to the lack of sophisticatedmanagement of wastes and effluents from factories.Pb pollution in the street dusts is likely caused by Pbparticulate from vehicle emissions. The road dustsare also contaminated with Zn, Cu, Ni, and Croriginating mainly from industry. Although con-tamination is not as severe as in cities with longerhistories of urbanization such as London, Oslo, andIstanbul, levels in Dhaka still exceed maximumpermissible values in soils. Therefore, managementprograms such as planned reduction of lead andsulfur contents from fuel, improved treatmenttechniques for the wastes and effluents of industries,and reduction of contaminants from atmosphericsources should be implemented by government tominimize pollution of the environment in DhakaCity. Such action would also improve air quality inthe city.

Acknowledgments

The authors thank Professor Yoshihiro Sawadaof Shimane University for access to the XRFfacilities, to Ms. Mika Hibata of Shimane Uni-versity for her help with the graphics in Fig. 3, andto Md. Mostafizur Rahman of Rajshahi University,Bangladesh for his cooperation in sampling.Dr. Barry Roser of Shimane University is acknowl-edged for his constructive review, which improvedthe manuscript considerably. The Dhaka CityCorporation Authority gave permission to collectsamples for this research.

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