Scientific World, Vol. 10, No. 10, July 2012 84
Street dust, particles deposited on road, originates from
the interaction of solid, liquid and gaseous materials
produced from different sources.1 The composition of dust
is very variable, as dust originates from different sources
depending on climate, human activities, soils and rocks of
the surrounding areas, etc.2 Indeed, their components and
quantity are environmental pollution indicators.3 Metals may
be accumulated in dust from atmospheric deposition by
sedimentation, impaction and interception.4 Accumulations
of metals including Pb, Zn, Cd and Cu on road surfaces arise
from vehicle exhausts, industrial discharges, oil lubricants,
automobile parts and corrosion of building materials,
asphalts, road paints, concrete, etc.5
There is ample evidence that street dust is an important
pathway in the exposure of people to toxic elements.6,7 The
intake of dust particles with high concentration of toxic
substances, especially potentially toxic metals, poses a
potential threat to human health.8 For instance, in California,
5–10% of the allergenicity for atmospheric total suspended
particulate matter was attributed to paved road dust
emissions.9 Therefore, the monitoring of such material has
been set as a priority in risk assessment programs in order to
evaluate the risk of inhalation and ingestion of dust for
humans, especially for children.10
As the case with many urban areas, Kathmandu city
also has some vulnerable areas plagued with consistently
higher concentration of pollutants, particularly heavy metal
pollution. For the last decade, the city has been expanding,
including the construction of new buildings and commercial
areas, and an ever increasing number of vehicles. This fastest
growing city with high commercial activities harbors around
3 hundred thousand vehicles and the number is likely to be
doubled in next few years (Office of Traffic Police, Kathmandu
- personal communication). As a consequence, new sources
of potentially toxic metal pollution through dust may be
present. Some major locations of the city such as Kalanki,
Gongabu, Chabahil, Tinkune, Sahidgate, Ratnapark and
Thapathali are considered to be strategically important from
environmental point of view as these locations are densely
populated and also suffer heavy traffic loads and hence may
be used for assessing the environmental status of the
Kathmandu city due to street dust. Therefore, the potential
presence of metals in street dust of these locations and their
distribution according to particle size fractions had to be
Many studies on metal concentrations in street dust
have been conducted particularly in developed countries
with long history of industrialization.11,12,13 Very few studies
have been carried out in developing countries like Nepal.
Besides, very little information is available about the
distribution of metals in different particle size fractions of
the dust. Hence, the objectives of this study were to: (1)
assess the contamination of heavy metals such as Pb, Cu,
Zn and Fe in street dust (bulk sample) from different sampling
locations of Kathmandu city by comparison with reported
results from other cities and (2) investigate the metal
distribution in particle size fractions (three particle sizes) from
street dust of the city.
HEAVY METALS IN BULK AND PARTICLE SIZE
FRACTIONS FROM STREET DUST OF KATHMANDU CITY
AS THE POSSIBLE BASIS FOR RISK ASSESSMENT
Neena Karmacharya* and Pawan Raj Shakya**
*Department of Biology, Padmakanya Multiple Campus, Tribhuvan University, Bagbazar, Kathmandu.
**Department of Chemistry, Padmakanya Multiple Campus, Tribhuvan University, Bagbazar, Kathmandu.
Author for Correspondence: Pawan Raj Shakya, Department of Chemistry Faculty of Science, Padmakanya Multiple Campus Tribhuvan University, Bagbazar, Kathmandu.
Abstract: Street dust has been sampled from eight major locations of Kathmandu city. The samples were separated into three
particle size fractions (<425, 425-600 and >600 μm) and analyzed for Pb, Cu, Zn and Fe using Atomic Absorption
Spectrophotometric method. Results revealed that the bulk samples as well as all particle size fractions under investigation
were found to have the metal abundance order as Fe > Zn > Cu > Pb. However, the trace metal concentrations increased with
the decrease of dust particle size in all samples. About 35-68% of heavy metals were associated with the small particle size
fraction (<425 μm) and this particle size accounted for 64-81% of the total mass of street dust from all locations. The smaller
particle size fraction has a higher heavy metal content, low density, high mobility in runoff, and thus is a higher risk for the
residents of Kathmandu city. From the present study, we conclude that a monitoring plan and a suitable risk assessment are
necessary to evaluate the evolution of metal concentration in dust in order to develop the proper measures for reducing the
risk of inhalation and ingestion of dust for humans and environment.
Keywords: Environment; Heavy metals; Street dust; Kathmandu city.
Scientific World, Vol. 10, No. 10, July 2012
MATERIAL AND METHODS
Study area and sampling
The study sites were located at different places around
the Kathmandu city (Fig. 1), viz., Tinkune, Chabahil, Gongabu,
Kalanki, Thapathali, Sahidgate, Ratnapark and Shivpuri
(control). A total of 24 street dust samples (three samples
from each place) including control were collected during dry
season to avoid rain washing out the heavy metals. The
sampling was carried out by sweeping an area of about 1m2
from the paved roads using a brush and plastic dustpan.
The amount of dust collected from each site was 250–500 g.
In order to avoid re-suspension of the finest particles during
sampling, the sweeping was made slow and collected directly
into the plastic bag. Samples were then taken for analysis.
Precautions were taken to avoid contamination during
sampling, drying and storage. Table 1 shows the description
of all sampling locations of Kathmandu city.
Bulk samples including those of control were oven-
dried at 105 °C for 24 hr to drive out moisture and then passed
through a 2 mm metal free sieve to remove unwanted
fragments and pebbles. The soil pH in bulk samples was
analyzed by using a glass electrode in a 1:1 soil/water
suspension14 and electrical conductivity at room temperature
in a 1:5 soil/water suspension15 on a CON 510 bench
conductivity meter, using a 2-ring stainless steel ultem-body
conductivity electrode (cell constant, K = 1.0) with built-in
temperature sensor. For analyzing particle size distribution,
100 g of each of the bulk sample from the different sampling
locations were separated into three particle size fractions by
using a stack of sieves with the sizes, 600 and 425 μm such
that particle size fractions of >600, 600-425 and <425μm were
obtained. The particle size fractions in the present study
may be categorized as follows: >600 (large size), 600-425
(medium size) and <425μm (small size).
For analyzing heavy metals (Pb, Cu, Zn and Fe) in bulk,
control and particle size fractions, 1 g of each of the dried
samples was digested using 20 mL nitric/perchloric acid at
210°C during 90 minutes. After cooling, 0.1 N HCl was added
to fill a 100 mL volumetric flask16 and the total amounts of
metals were measured by atomic absorption spectrometry
(SOLAAR M5 Dual Automizer, 180-900nm, Thermo Elemental,
UK). All the standard solutions (1000 ppm) for Pb, Cu, Zn
and Fe were certified and obtained from FLUKA AG,
Switzerland. These solutions were diluted carefully to the
required concentrations with double-distilled water. The
instrumental parameters were those recommended by the
manufacturer. Quality assurance of analytical results was
controlled using the reference materials NIST SRM 1648 for
dust. The recovery percentage of metal concentrations from
the reference materials was between 96.3 and 98.1%. In order
to determine the precision of the analytical process, samples
from the sites 1 and 4 (Table 1) were analyzed by three times.
The standard deviation for both samples was calculated to
2.5 and 3.1% respectively and can be considered satisfactory
for environmental analysis. All analyses were performed in
Metal concentration was calculated using the
working formula given below:
Concentration of metal, μ
. of sa
Wt. of dust sample (g)
We used the concentration for undisturbed areas from
the current study as local background (control) metal
contents. The selected undisturbed areas are lands without
evidence of past and current anthropogenic activities and
no signals of disturbances were observed during the
All statistical analyses and data processing in this study
were performed on an IBM-PC computer using Statistical
Package for Social Sciences (SPSS) program. Descriptive
statistics (mean, percentage and standard deviation) were
performed after multi-element analysis. The inter-element
correlation coefficients (r) for street dust samples were
calculated by p<0.05. The contamination ratio for each site
separately for street dust was calculated; Contamination ratio
is the average metal concentration of a site over (:) the metal
concentration of the reference site (control).
RESULTS AND DISCUSSION
Street dust properties
The pH in the different locations under investigation
was mostly alkaline (Table 2), which may be explained by the
presence of carbonates.17 The small differences among the
locations show the high stability of pH in the dust.
Electrical conductivity (EC) was found to be variable,
ranging from 0.3 dS m-1 in Shivpuri dust (undisturbed area;
control) to 2.8 dS m-1 in Kalanki (Table 2). This shows that
the salt content in dust depends on the location; the highest
salt concentrations in the locations such as Kalanki and
Gongabu dust are likely due to a spill of material rich in salts.18
Fractionation of bulk samples to various particle sizes
revealed that <425 ìm (small size fraction) was the dominant
fraction (64.3–80.6%) into the dust from all locations (Table
2), the highest being found in Chabahil and the lowest in
Fig. 1: Sampling map of the study areas of Kathmandu city
Scientific World, Vol. 10, No. 10, July 2012 86
Table 3: Heavy metals in street dust (bulk sample), mean
(standard deviation; n = 3) “ìg/g” from different cities and
Table 2: Properties of street dust bulk samples (n = 3, mean,
standard deviation) from different sampling locations of
Shivpuri (undisturbed area; control). The amount of the
medium fraction (600-425 μm) ranged from 7.1% (Ratna park)
to 18.3% (Sahid gate), while the occurrence of particles >600
μm (large size fraction) in size varied from 9.5% (Sahid gate)
to 19.7% (Shivpuri; control). The particles with small sizes
are considered a major environmental and health hazard.19
Therefore, the highest risk for humans and the environment
occurs in Chabahil (80.6%) > Ratna park (77.2%) > Kalanki
(76.7%) > Gongabu (74.4%) > Sahid gate (72.6%) > Thapathali
(70.1%) > Tinkune (69.2%) > Shivpuri (control; 64.3%).
Heavy metals in bulk samples
The mean and standard deviation of metal
concentrations and average contamination ratios
investigated in the studied samples, as well as values of
other cities, are presented in Table 3. As might be evident
from the results that the mean concentration of all metals in
Kathmandu city is different and can be ranked by abundance
as follows: Fe > Zn > Cu > Pb. Similar metal abundance order
was obtained in all the locations including control site. The
mean concentration of heavy metals in the Kathmandu dust
(mean of all locations) was 7.2 mg/g for Fe, 62.2 μg/g for Zn,
29.5 μg/g for Cu and 22.3 μg/g for Pb respectively while
those of control were 2.1 mg/g for Fe, 29.9 μg/g for Zn, 15.6
μg/g for Cu and 12.3 μg/g for Pb respectively. Besides, the
metal concentration from all the locations ranged from
2.1(control) - 8.2 mg/g(Ratna park & Sahid gate) for Fe,
29.9(control) – 110.4 μg/g(Ratna park) for Zn, 15.6(control) –
41.9 μg/g(Kalanki) for Cu and 12.3(control) – 43.7 μg/g(Ratna
park) for Pb respectively. Iron was found to be prevalent in
significantly higher level in bulk samples from all locations.
Homady et al.20 also noticed significant accumulation of Fe
from street dust in Jordan which they identified to be due to
vehicle sources, petroleum residue and tyre repair.
Additionally, the high abundance of Fe in nature could be
another source of contamination along with activities related
to mechanical workshops, iron bending and welding of
metals. Moreover, the observed differences in the range of
metals are most likely caused by variation in the sources of
the metals. Acosta et al.21 identified industrial activities and
traffic as the main sources of Pb while Cu was associated
with inorganic fertilizers in agricultural areas, and Zn was
related to recreational, domestic, and commercial sources.
Adachi and Tainosho22 from their studies on the morphology
Table 1: Description of different sampling locations of
and chemical composition of heavy metals embedded in tyre
dust and traffic related materials, concluded that tyre dust is
a significant pollutant, especially as a source of Zn in the
If the results from this study are compared with those
reported in other cities (Table 3), the high variability in metal
concentrations in the dust is clear, indicating that the
interplay of sources of metals, human habits, populations,
etc. of each city determines the metal concentration in dust
samples.23,24 But in the absence of knowledge regarding
activities or characteristics of the sampling sites in the various
cities or countries, comparison of data recorded and
comments on the causes of the differences between metal
levels may be unjustified. However, the results from this study
revealed that the mean levels of Zn, Cu and Pb were found to
be significantly lower than the reported values of various
cities (Table 3). The Fe value could not be compared due to
unavailability of the reported values of Fe of other cities. In
addition, taking into account the concentration of metals in
Shivapuri (undisturbed area) and after calculating average
contamination ratio (ACR), we can conclude that the street
dust from the Kathmandu city is contaminated by Fe (ACR =
Scientific World, Vol. 10, No. 10, July 2012
3.4), Zn (ACR = 2.1), Zn (ACR = 1.9) and Pb (ACR = 1.8).
Moreover, a positive correlation between Pb and Cu (r =
0.783, p<0.05), Pb and Zn ((r = 0.813, p<0.05) and Zn and Cu
(r = 0.879, p<0.05) (Table 4) could indicate a common source
of the metals in the street dust of the Kathmandu city.
The contamination ratio in street dust from different
sampling locations is also presented in Table 5. It can be
concluded from the results that all the locations under study
are severely contaminated by Fe. However, the contamination
ratios of Zn, Cu and Pb were found to be variable among the
locations probably due to interplay of sources of metals as
discussed earlier. Furthermore, among the different locations,
Ratna park suffered the highest contamination of Fe, Zn and
Pb by the ratio of 3.9, 3.7 and 3.6 respectively. Similarly, Sahid
gate also suffered from the highest contamination of Fe (3.9)
whereas the highest contamination ratio of Cu (2.7) was found
in Kalanki dust.
Heavy metals in particle size fractions
Table 6 shows the heavy metal concentrations in three
particle size fractions. All the particle size fractions are
enriched in metals; however, the effect of particle size is
different among the locations and metals concerned. It was
found that the concentration of heavy metals embedded into
the dust increased with the decrease of particle size.
Accordingly, the distribution of Fe, Zn, Cu and Pb in all the
sampling locations was found to increase with the decrease
of the particle size as follows:
large size (>600 μm) < medium size (600-425 μm) < small
size (<425 μm)
In all the three fractions, the mean concentrations of
the metals can be ranked by their abundance in the order as
Fe > Zn > Cu > Pb. The metal ranking is similar to those of the
bulk samples. A careful analysis of the data (Table 6) revealed
that particles with size <425 μm contributed alone in a range
of about 35-68% to the total concentration for all metals. For
particles with sizes 600-425 μm, this was about 18-39% and
for >600 μm size, the contribution reached to 7-32%.
For Pb, Ratna park dust showed 27.9, 33.4 and 75.5 μg/
g in large, medium and small size fractions respectively, all
the values being comparatively higher to those of the other
locations. For Cu, 28.0 and 87.6 μg/g were recorded as the
highest values respectively for large and small size fractions
from Ratna park dust whereas Kalanki recorded 48.1 μg/g as
the highest concentration for medium size fraction. As for
Zn, it was also from Ratna park dust that recorded the highest
values of 170.3 and 101.5 μg/g respectively for small and
medium size fractions whereas large size fraction from Kalanki
dust measured the highest value (44.7 μg/g). In case of Fe
content, Ratna park dust recorded 10.4 mg/g for small size
fraction, Sahid gate recorded 8.4 mg/g for medium size
fraction and Kalanki recorded 7.0 mg/g for large size fraction;
all the values being comparatively higher to other locations.
For small size fraction, Ratna park dust reported a
comparatively higher concentration of the metals.
The results of the present study are in agreement with
the study conducted by Fergusson and Ryan25 who also
found the increasing concentrations of heavy metals such
as Cd, Pb, Cu, Zn, Mn and Fe with decrease in size of the
street dust particles from cities like London, New York, Halifax,
Christchurch, Kingston etc. Duong et al26 while studying
the street dust from the Ulsan of Korea, also found that the
concentrations of metals such as Cd, Cu, Pb and Ni increased
with decrease in the size of dust particles.
Metal partitioning as a function of particle size is very
important for soil-bound potentially toxic metals.27 The
preferential partitioning of metals to the small particle size
fractions in all locations and for all metals is shown in Table
6. Such a pattern is usually attributed to the increase in the
specific surface area and concomitant increase in the
proportion of reactive substrates28 with negative charges
associated with these fine particles.29
Most of the studies about risk assessment of metal
focus on the concentration of metals in bulk soil/dust
samples, and most of them are located in a specific soil use.
However, this work shows the distributions of metals from
three particle size fractions (>600, 600-425 and <425 μm) from
8 locations including undisturbed area and the results of
this work show that street dust particles in all locations
showed concentrations of metals higher than those found in
undisturbed area. The results indicated a preferential
partitioning of metals to small particle size fractions in all
cases. The accumulation in the small size fractions was higher
when the metals had an anthropogenic origin. Therefore, we
recommend that risk assessment programs include monitoring
of heavy metal concentrations in dust where each land-use
is separately evaluated. The finest particle fractions should
be examined explicitly and separately given in order to apply
the most efficient measures for reducing the risk for humans
and the environment of the Kathmandu city.
The street dust from different sampling locations in
Kathmandu city has an alkaline pH probably due to a high
amount of carbonates. Its electrical conductivity is very
variable. Fractionation of bulk samples into three particle
sizes revealed that the percentages of particles considering
a major environmental and health hazard (<425 μm) were:
Chabahil (80.6%) > Ratna park (77.2%) > Kalanki (76.7%) >
Gongabu (74.4%) > Sahid gate (72.6%) > Thapathali (70.1%)
> Tinkune (69.2%) > Shivpuri (control; 64.3%).
Bulk samples as well as all particle size fractions in all
locations were found to be enriched for all metals having the
metal abundance order as Fe > Zn > Cu > Pb. The average
contamination ratio (ACR) in the Kathmandu dust for Fe,
Zn, Cu and Pb were 3.4, 2.1, 1.9 and 1.8 respectively. The
mean metal concentrations in all the locations were found to
be higher than those found in undisturbed area. However,
these values were found to be significantly lower than those
of the reported values of other cities. Among the metals
analyzed, Fe was found in significantly higher level in all
It was found that the trace metal concentrations
increased with the decrease of dust particle size fractions.
About 35-68% of heavy metals were associated with the small
particle size fraction (<425 μm) and this particle size accounted
for 64-81% of the total mass of street dusts. This contribution
is comparatively higher than any other particle size under
investigation. For small size fraction, Ratna park dust reported
Scientific World, Vol. 10, No. 10, July 2012 88
a comparatively higher concentration of the metals. Results
from other locations were found to be variable.
From the present study, we conclude that a monitoring
plan is necessary to evaluate the evolution of metal
concentration in dust in order to develop the proper measures
for reducing the risk of inhalation and ingestion of dust for
humans and environment of the Kathmandu city. In addition,
the concentration of all metals in the dust is markedly affected
by the land use, associated with the metal sources. Therefore
we think that a suitable risk assessment should evaluate
specifically each use and avoid mixing samples from different
Table 4: Interelement correlations for street dust bulk
samples from the study area.
Element Pb Cu Zn Fe
Cu 0.783 1.000
Zn 0.813 0.879 1.000
Fe 0.368 0.465 0.532 1.000
High significance by p<0.05 are in bold.
We are grateful to University Grants Commission,
Nepal for research grant. Nepal Environmental and Scientific
Services (NESS), Thapathali is also highly acknowledged
for technical assistance in conducting AAS analyses.
1. Banerjee, A.D.K. 2003. Environ. Pollut. 123: 95–105.
2. Amato, F., Querol, X., Johansson, C., Nagl, C. and Alastuey, A.
2010. Sci. Total Environ. 16: 3070–3084.
3. Yongming, H., Peixuan, D., Junji C. and Posmentier, E. 2006.
Sci. Total Environ. 355: 176–186.
4. Li, X., Poon, C.S. and Liu, P.S. 2001. Appl. Geochem. 16:
5. Adachi, K. and Tainosho, Y. 2005. Appl. Geochem. 20: 849–
6. Ferreira-Baptista, L. and De Miguel, E. 2005. Atmos. Environ.
7. Sammut, M.L., Noack, Y., Rose, J., Hazemann, J.L., Proux,
O., Depoux, M., Ziebel, A. and Fiani, E. 2010. Chemosphere.
8. Faiz, Y., Tufail, M., Tayyeb, M., Chaudhry, M.M. and Naila-
Siddique, N. 2009. Microchem. J. 92: 186–192.
9. Miguel, A.G., Cass, G.R., Glovsky, M.M. and Weiss, J. 1999.
Environ. Sci. Technol. 33: 4159–4168.
10 . Government of Canada. 2001. In Order Adding Toxic Substances
to Schedule 1 to the Canadian Environmental Protection Act,
Canada Gazette, 135: 1–8.
11 . Tokalýoglu, S. and Kartal, S. 2006. Atmos. Environ. 40: 2797–
12. Lu, X., Wang, L., Lei, K., Huang, J. and Zhai, Y. 2009. J.
Hazard. Mater. 161: 1058–1062.
13 . Christoforidis, A. and Stamatis, N. 2009. Geoderma. 151: 257–
14. Soil Survey Staff 2004. In Soil Survey Laboratory Methods
Manual, Version No. 4.0, USDA NRCS, Soil Survey
Investigations Report No. 42, U.S. Govt. Print. Office,
15. Acosta, J.A., Faz, A., Kalbitz, K., Jansen, B. and Martinez-
Martinez, S. 2011. J. Environ. Monitoring. 13: 3087-3096.
16. Risser, J.A., Baker, D.E. and Westerman, R.L. 1990. In Soil
Testing and Plant Analysis, Soil Sci. Soc. Amer. Spec. Publ. 3,
Madison, WI, 3rd edn, pp. 275–298.
17. Yaalon, D.H. 1997. Catena. 28: 157–169.
18 . Fuente, D., Chico, B. and Morcillo, E. 2006. Port. Electrochim.
Acta. 24: 191–206.
19. Homolya, J. 1999. In Particulate matter (PM2.5) Speciation
Guidance Document, January 21, DRAFT 131, U.S. EPA.
20 . Homady, M., Hussein, H., Jiries, A., Mahasneh, A., Al-Nasir, F.
and Khleifat, K. 2002. Environ. Res. 89: 43-49.
21 . Acosta, J.A., Faz, A.and Martinez-Martinez, S. 2010. Environ.
Monit. Assess. 169: 519–530.
22. Adachi, K. and Tainosho, Y. 2004. Environ. Int. 30: 1009-
23. Stone, M. and Marsalek, J. 1996. Water, Air, Soil Pollut. 87:
24 . De Miguel, D., Llamas, J., Chacoon, E., Berg, T., Larssen, S.,
Røyset, O. and Vadset, M. 1997. Atmos. Environ. 31: 2733–
25. Fergusson, J.E. and Ryan, D.E. 1983. Sci. Total Environ. 34:
26. Duong, T.T.T., Lee, B.K., Dong, T.T.T., Jeong,U., Kim, A.
and Lee H.K, 2006. Strategic Technol. 213-215.
27. Wang, X., Qin, Y. and Chen, Y. 2006. Environ. Geol. 50:
28. Sutherland, R.A. 2003. Environ. Pollut. 121: 229–237.
29 . Acosta, J.A., Faz, A., Arocena, J.M., Debela, F. and Martinez-
Martinez, S. 2009. Geoderma. 149: 101–109.
Table 5: Contamination ratio in street dust from different
Table 6: Heavy metal concentrations (ìg g"1) in particle size
fractions from street dust of different sampling locations of
Kathmandu city; mean (standard deviation; n = 3).