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Extent of air pollution in Kandy area, Sri Lanka: Morphological, mineralogical and chemical
characterization of dust
D.S. Samaradiwakara and H.M.T.G.A. Pitawala*
RESEARCH ARTICLE
Highlights
• Chemistry, mineralogy and morphology of natural dust are altered due to the anthropogenic influences.
*Corresponding Author’s Email: apitawala@pdn.ac.lk
Extent of air pollution in Kandy area, Sri Lanka: Morphological, mineralogical and chemical
characterization of dust
D.S. Samaradiwakara1,2 and H.M.T.G.A. Pitawala1,2*
1Postgraduate Institute of Science, University of Peradeniya, Peradeniya, Sri Lanka.
2Department of Geology, Faculty of Science, University of Peradeniya, Peradeniya, Sri Lanka.
Received: 04/12/2020; Accepted: 01/09/2021
https://orcid.org/0000-0001-7483-5922
This article is published under the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0/),
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
RESEARCH ARTICLE
Ceylon Journal of Science 50(4) 2021: 475-486
DOI: http://doi.org/10.4038/cjs.v50i4.7946
Abstract: Dust is one of the most common sources of air
pollution in cities, providing a considerable health risk. Kandy,
Sri Lanka, has been declared as a UNESCO World Heritage Site.
As a result, a study into causes of air pollution in Kandy and its
environs is urgently required. We examined the composition of
dust particles collected from the city and suburbs to determine the
degree of particulate pollution. The abundance of particles and
materials in various phases has previously been quantified in one
dimension in an idealized sphere. The morphological examination
of particulate matter is usually ignored. Eighteen road and thirteen
household dust samples collected in the Kandy Municipal area
were analyzed for elemental concentrations, as well as for
mineralogical and morphological characteristics. Higher Ca, Zn,
and Cu concentrations in the samples indicate anthropogenic
(construction industry and traffic activities) influences on the dust.
Mineralogically, fine and coarse dust fractions are dominated by
clay minerals and quartz with feldspar. The majority of fibrous
materials in dust are coated with secondary matter, resulting in
short suspension duration in the atmosphere and, as a result, a
reduction in the harmfulness of the fibers. In terms of mineralogy,
morphology, and chemical properties, road and household dust
samples are nearly identical. Despite the fact that dust is primarily
derived from soil, its composition has been altered due to
anthropogenic influences such as transportation and construction
activities. As a result, dust containing clay particles can be
regarded of as a fluxing and heavy metal accumulation medium.
Although fibers have minor influence on human health and the
environment, heavy metals have a significant impact. Though
industrial and transportation activities in Kandy are remarkably
low when compared to those in other major cities in Sri Lanka
and megacities around the world, pollution levels in the city
are comparably high. To reduce the vulnerability of the current
pollution condition of the city, appropriate, long-term strategies
for construction and transportation activities are required.
Keywords: Kandy; dust; heavy metals; fibers; urban environment.
INTRODUCTION
Dust is one of the most common air pollutants, derived
from the interaction of solid, liquid, and gaseous materials
produced by both natural and artificial processes (Banerjee,
2003). The decline of air quality in urban areas around the
world has been one of the key challenges in recent decades.
As air quality deteriorates, many emerging countries face
several environmental issues (Bhaskar and Mehta, 2010).
Dust contributes significantly to fine particulate matter
(PM) emissions (Wang et al., 2005; Wang et al., 2011).
Dust is a heterogeneous mixture of organic,
inorganic, and biological particles that come from a variety
of places. Natural sources of dust include weathering,
erosion, and redistribution of adjacent soil, seawater spray,
atmospheric wet and dry deposition, and natural rock
dust. Transportation-related activities such as vehicular
emissions and abrasion-induced wear of tires, brake pads,
and other vehicle parts, as well as industrial and domestic
activities, are the anthropogenic sources of dust (Chang et
al., 2009; Bhaskar and Mehta, 2010; Gupta, 2020). Coal
and other fossil fuel-fired power stations, mining activities,
the cement and lime industries, and construction activities
all contribute to the secondary dust particle formation
process.
After being released into the environment, dust
particles may stay in the air for some time before settling
and accumulating on surfaces. The morphological
characteristics of dust particles, such as size, shape and
aerodynamic diameter; environmental factors, such as
climate, wind speed and direction; and anthropogenic
factors, such as land use patterns and vegetation cover, all
influence dust distribution and behaviour in the atmosphere
(Kim et al., 1998; McDonald and Biswas, 2004; Pereira et
al., 2007; Pey et al., 2008).
As a result of rapid development in the last few
decades, human activities that lead to changes in dust
distribution in urban areas have resulted in substantial
land use degradation in developing countries (Kim et al.,
2013). Dust poses a serious threat to the health of the
urban population (Bosco et al., 2005). In consideration
of the health effects of dust, there are no safe threshold
limits below which the health effects do not occur (WHO,
2017). After entering the body, both coarse and fine
particles produce health impacts, further, finer particles
are more hazardous since they can penetrate deep into
the lung tissues. (De Costa, 2008; Wang et al., 2016;
Gope et al., 2017). Dust pollution has been linked to an
476 Ceylon Journal of Science 50(4) 2021: 475-486
increase in chronic obstructive pulmonary disease, asthma,
pneumonia, cardio-respiratory disease and respiratory-
related disorders. (Balachandran et al., 2000; Pope and
Dockery, 2006; Brunekreef et al., 2009; Boldo et al., 2011).
Emission sources, atmospheric chemical processes,
and climatic variables all have a role in dust generation and
distribution (Harrison, 2006; Garland et al., 2008). Due
to its complexity, dust can cause a number of chemical
reactions that result in secondary compounds (Chen et al.,
2006). Other contaminants can be carried by dust particles
and physiochemical properties such as the nature, size,
and surface roughness of various minerals and organic
compounds determine their pollutant capability (McBride,
1994; Butte and Heinzow, 2002). Anthropogenic particles
can also combine with mineral components to form unique
combinations, which impact the distribution and behaviour
of dust.
Due to differences in mineral solubility, lead in
galena (PbS) is less accessible than lead in carbonate
(PbCO3) (Casteel et al., 2006). The morphology of dust
particles can be utilized to characterize behaviour, identify
sources, creation mechanisms, climatic conditions,
travel distance from the source and their potential health
consequences (Ličbinský et al., 2010).
The majority of urban environments of Sri Lanka
are densely populated areas with significant levels of
anthropogenic activity. The dispersal of dust is more
affected by unplanned land use patterns and significant
traffic congestion in cities. UNESCO has designated
Kandy as a World Heritage City. As a result, it is essential
to analyze the mode of air pollution in Kandy and its
environs. In comparison to other cities in the country, it
features unique urban and climatological surroundings.
The wind flow and circulation, in particular, differ
from those in other major Sri Lankan cities (Pitawala et
al., 2013). The basin-like and bottleneck geomorphology
of the city operate as obstacles to wind flow, which prefers
to cycle within the metropolitan area. This may result in
an increase in the gathering of air pollutants such as dust
particles and heavy metals, which may stay in the air for
prolonged periods of time due to a lack of space to blow
them out, finally settling in the urban region (Abeyratne and
Ileperuma, 2006; Weerasundara et al., 2017). Despite the
fact that Kandy has a unique environment in comparison to
other cities, only a few studies on dust have been conducted
(Pitawala et al., 2013; Weerasundara et al., 2017).
The morphologic evaluation of particulate matter is
often neglected, despite the importance of dust morphology.
This study is a new approach to understanding air pollution
in the urban environment of Kandy city. Hence, a
comprehensive characterization based on mineralogy and
morphology of dust along with chemical studies has been
carried out to get a better understanding of the possible
sources, distribution patterns and levels of the urban dust.
It would also be useful to introduce appropriate pollution
prevention methods for the long-term development of
urban ecosystems. Therefore, the major objective of the
present study was to understand the factors influencing the
accumulation and distribution patterns of the urban dust,
based on the mineralogical, morphological and chemical
characteristics.
MATERIALS AND METHODS
Study area
The city of Kandy is the second most commercially
important city in Sri Lanka, extending over an area of
26 km2 with an urban population higher than 100,000
(Census, 2012). Kandy lies at an elevation of 500 m
from mean sea level and belongs to the tropical rainforest
climate. The study area has an average annual rainfall
of nearly 1500 mm with an average annual temperature
of 24.5 ℃. The average annual percentage of humidity
is 84.0%. The wind direction and speed are primarily
controlled by the monsoonal conditions (Department of
Meteorology, 2017). However, the wind circulation in the
city is high as it is located in an area that shows a basin-like
morphology which act as a barrier to the movement of the
wind (Weerasundara et al., 2017; Dissanayake et al., 2019).
Precambrian metamorphic rocks are underlying the setting
of the Kandy and it is located in the Highland Complex
(HC) of Sri Lanka. The major bedrock types found within
the area comprise biotite and hornblende bearing gneisses,
charnockitic and granitic gneisses as well as calcsilicate
gneiss (Cooray, 1994; Kehelpannala, 2003).
Around 350,000 people are entering to the city in a
daily basis, comprising about 90,000 for employment and
over 60,000 for schools. The total vehicle entry level to city
has increased to 56,000 vehicles per day and has a growth
rate of 5% per annum (Kandy City Transport Study, 2011).
As the city is located in a narrow valley, higher traffic
congestion in the city is observed with high quantity of
vehicles travelling within a small area at a very low speed.
And also, buses are racing on first gear, stopping at all bus
stops for a long time (Premasiri et al., 2012).
Sample collection
A total of 31 dust samples were collected including 18
road dust (R) and 13 household dust samples. Sampling
was done in 2019 during the dry period as the rain fall
results in wash-off process which could lead redistribution
and removal of the available road dust in the surfaces
(Egodawaththa et al., 2007). Road dust samples were
collected within the center of the city and in the surrounding
commercial areas with high traffic intensities where traffic
lights are in the vicinity. Road dust samples were collected
by sweeping the road surface using a plastic brush and
a dustpan and collecting the dust into sealed polythene
sample bags. Household dust samples were collected
from selected residential neighborhoods of the Kandy
urban area. These areas had higher elevations and lower
traffic conditions as compared to the areas where road dust
samples were collected. Dust gathered on window panels
and top of other furniture in abandoned houses was also
collected following the same procedure used to collect road
dust samples. The dustpan and plastic brush were washed
D.S. Samaradiwakara and H.M.T.G.A. Pitawala 477
using methanol after collection of dust at each location to
minimize contaminations.
Chemical, mineralogical and morphological analysis
A portion of dust were first weighted and treated with 70%
hydrogen peroxide (H2O2) for removal of the organic matter
and set aside until the bubbling was over. When there were
no more bubbling, the samples were washed by water and
oven dried for 24 h in 105 ℃. The samples were weighted
and the difference in the weight was taken as the organic
matter content. Organic matter contents were calculated as
weight percentage of the initial dry weight.
Approximately 0.2 g of each sample was accurately
weighed and digested for heavy metal analysis using aqua
regia [3:1 HCl (34%) / HNO3 (69%), v/v]. The extracts were
analyzed by flame atomic absorption spectrophotometry
(AAS-Perkin Elmer, Model 2380) to determine the total
concentrations of Zn, Cu, Ni, Fe, Mn, Pb, Na, K, Ca and
Mg. Calibration control standards were used for the linear
calibration.
Mineralogy of the samples was studied under an
optical reflection microscope (Nikon) at the Mineralogy
Laboratory, Department of Geology, University of
Peradeniya. Magnetic material was separated using a hand-
magnet. The magnetic material content was calculated as a
percentage.
Scanning Electron Microscope (SEM), model Zeiss
EVO LS 15 was used to study the size variations, sorting
of particles, shapes of the particles, surface features and to
detect the presence of fibers. In the sample preparation for
the SEM analysis, samples were placed on carbon plaster to
coat with 20 nm thin layer of gold (Au) and palladium (Pd).
The Energy Dispersive X-ray spectroscopy (EDX) which
was equipped with the SEM was used in the study of
the elemental composition of the appropriate fibers and
magnetic grains and grain surfaces.
Assessment of the heavy metals
Enrichment Factor (EF)
The following equation was used to calculate the EF of the
heavy metals (Kantor et al., 2018).
where, x is the concentration of the element. In the present
study, iron (Fe) was used as the normalizing element,
since Fe has a relatively high natural concentration, and
further, it is not expected to be substantially enriched from
the anthropogenic process and sources (Abrahim and
Parker, 2008). UCC values of elements were obtained from
Rudnick and Gao (2005) for the comparison. The following
classification from Barbieri et al. (2015) is given for the EF
(Table 1).
RESULTS AND DISCUSSION
Organic matter content
Higher organic matter contents in road dust were mainly
found in samples collected near road junctions, areas of high
traffic intensity and areas around traffic lights (Figure 1).
Wind is the main natural factor of the transportation of dust
particles and consequently, road junctions act as a barrier
to smooth wind flow. Therefore, dust that transport with
wind tends to deposit in the vicinity of the junction. Vehicle
movement is one of the main factors that contribute the
production of road dust. The shearing action between the
tyre and the road surface creates loose materials that are
then transported into the air by the turbulence caused by the
movement of vehicles. Vehicles are subjected to constant
starting and stopping with breaks in locations with high
traffic intensities or traffic signals, resulting in increased
shearing activity and intensive dust particle formation. The
organic materials in the dust produced by such actions are
concentrated with tyre materials, road particles such as
bitumen and soil organic matter. The turbulence created
by movement of vehicles would not be adequate to lift
and transport the generated coarse dust particles since the
momentum of vehicles is minimal. Thus, the organic stuff
in road dust formed by shearing will be deposited in situ.
Organic materials made up of functional groups, such as
COO-, would create complexes with heavy metals that are
more bioavailable than the metal itself (Alloway, 1995).
The organic matter content of road dust in the study area
(Table 2) is higher than that of road dust in the Colombo
metropolitan area (CMA), Sri Lanka (Herath et al., 2015),
Delhi, India (Shandilya et al., 2013), West Midlands,
United Kingdom (Shilton et al., 2005) and Manchester,
England (Robertson et al., 2003).
Magnetic material content
Samples with high concentrations of magnetic material
were typically found in samples obtained from major
highways with heavy traffic congestion (Figure 2). This
suggests that there is a correlation between magnetic
material abundance and traffic congestion (Spassov et al.,
2004). The sample location closest to the railway station
Table 1: Detection limits of the heavy metals in AAS.
Element Detection Limit (mg L-1)
Pb 0.029
Cu 0.004
Mn 0.011
Zn 0.002
Ni 0.004
Table 2: EF categories (Barbieri et al., 2015).
Value Soil dust quality
EF < 2 Deficient to minimal enrichment
2 < EF < 5 Moderate enrichment
5 < EF < 20 Significant enrichment
20 < EF < 40 Very high enrichment
EF > 40 Extremely high enrichment
478 Ceylon Journal of Science 50(4) 2021: 475-486
has higher concentrations of magnetic materials. High
magnetic material concentration samples were typically
found in those obtained from main highways with heavy
traffic congestion (Figure 2). This indicates that there is
a relationship between magnetic material abundance and
traffic congestion (Spassov et al., 2004). The sample location
closer to the railway station has higher concentration of
magnetic material. According to Moreno et al. (2015) the
high value obtained in this area is mostly attributable to the
creation of magnetic material in the abrasion of sliding and
wear at the brake-rail wheel and rail wheel-rail interfaces.
The high turbulence caused by train movement is mainly
responsible for particle transport. Corrosion of trains that
have been stationary for a long time may also result in high
concentrations of magnetic material.
Chemical characteristics
Calcium (Ca), followed by Fe, is the most abundant
element in both road and domestic dust samples. In both
types of samples, the heavy metal concentrations are in the
following order: Zn > Mn > Cu > Ni > Pb. Except for Cu, all
heavy metals are higher in road dust than in residential dust
(Table 3). In both road and residential dust, key element
concentrations change in the order Ca > Fe > Mg > K > Na.
Iron (Fe), Cu and Zn concentrations are higher in residential
dust than in road dust.
Despite the low concentrations of Na, Mg, K and Mn
(Table 3), they are comparable with the background values,
and can be considered as derived from natural processes.
The concentrations of these metals are low due to the mixing
Figure 1: Map showing the distribution of organic materials in the study area.
Figure 2: Map showing the distribution of magnetic materials in the study area.
D.S. Samaradiwakara and H.M.T.G.A. Pitawala 479
of other materials derived from anthropogenic sources.
Even though Fe is found in low concentrations compared
to the background levels, high anthropogenic influence can
be attributed to the presence of magnetic materials in the
dust. However, Ca shows higher enrichment with respect
to the background levels (Table 3). The presence of high
Ca concentrations may be due to the construction process,
as destruction of existing structures can release enormous
amounts of dust into the environment (Guttikunda and
Goel, 2013).
Zinc (Zn), Cu, Ni and Pb can be considered as
anthropogenically derived metals as they have much higher
measured concentrations compared to the background
values (Table 3). There must be anthropogenic inputs of
these metals to possess such higher levels of concentrations
in the road and household dust. It indicates that chemical
composition of the naturally derived dust has been altered
due to the anthropogenic influence.
The present study reveals that Kandy has higher
concentrations of Zn, Cu, Fe and Mn (Table 4). The elements,
Zn and Cu, in road dust could be derived mostly by vehicular
emissions (Charlesworth and Lees, 1998; Al-Khashman,
2007). Even though Colombo and other megacities in
the world have significantly higher traffic activities,
industries, construction activities and population density,
concentrations of Zn, Pb and Cu in dust are comparably
lower than those of Kandy city (Table 4 and 5). The
atmospheric deposition shows comparable values with the
Table 3: Organic matter and magnetic material contents in the road and household dust.
Sample type
Organic matter content Magnetic material content
Maximum Minimum Mean Maximum Minimum Mean
Road dust 29.06% 4.63% 15.04% 5.89% 2.41% 4.25%
Household dust 21.60% 8.26% 15.50% 6.75% 3.48% 4.79%
Table 4: Concentrations of major and heavy metals (mg/kg) of samples studied.
Major metals Road dust Household dust Background
Range Average Range Average
Mg 5,160 - 12,182 8,909 6,876 - 11,301 8,547 11,000
Na 772 - 2,213 1,202 428 - 1,962 1,140 26,500
K 1,323 - 6,032 3,113 2,501 - 6,035 4,364 13,000
Fe 27,772 - 50,074 36,704 29,991 - 63,052 40,347 86,000
Ca 20,879 - 127,596 50,706 22,768 - 107,949 45,164 27,200
Heavy metals
Pb 15 - 126 49 22 – 72 40 25
Cu 235 - 447 319 299 – 409 352 11
Mn 403 - 724 541 451 – 578 507 800
Zn 236 - 1,557 775 406 – 3065 783 68
Ni 252 - 364 305 245 – 330 300 50
Table 5: Comparison of mean concentrations (mg kg-1) of heavy metals in dust in different cities in Sri Lanka.
Study Area Type Zn Cu Pb Fe Mn
Pitawala et al., 2013
Colombo Household 18.1 2 2.3 32000 191
Kandy Household 738.9 29.8 3.5 39000 145.9
Herath et al., 2015 Colombo Road 476 174 71 29268 689
Priyadarhana et al., 2015 Colombo
suburbs Road 284.01 101.86 34.39 NA NA
Weerasundara et al.,
2018 Kandy Atmospheric
deposition 1116.9 123.6 234.4 13774.9 273.6
This study
Kandy Road 775 319 49 36704 541
Kandy Household 1113 352 40 40347 507
480 Ceylon Journal of Science 50(4) 2021: 475-486
dust samples, proving atmospheric deposition contribution
to the presence of heavy metals of dust in the study area
(Table 4). It also proves that the suspended particles only
disperse over the urban area and deposit within the city
itself due to the basin-like geomorphology of the area.
However, the suspended dust particles in the Colombo city
may disperse over a large area and reduce the concentration
of accumulation with the wind flow and the higher wind
velocities due to its geographical location near the coast
(Pitawala et al., 2013).
Sources of heavy metals
As Zn is used as a vulcanization agent in vehicle tyres
(Alloway, 1990), the higher wearing rate and corrosion
rates in high-temperature tropical areas, such as Kandy,
may contribute to the high Zn content in the dust (Li et al.,
2001). Furthermore, due to the morphological conditions
of the study area, the sharp bends and steep slopes of
roads may exacerbate tire wear (Pitawala et al., 2013).
Usage of Zn in alloys, parchment papers, glass, dry cell
batteries and electrical apparatus may also contribute to the
higher content of Zn in household dust (Adriano, 1986).
Moreover, food wastages containing higher levels of Zn
would contribute to higher levels of Zn in the dust.
The sources of copper (Cu) in the road dust could
be corrosion of metallic parts of cars derived from engine
wear, thrust bearing, brushing and bearing metals (Al-
Khashman, 2007). Contamination of Cu in the household
dust is influenced by the general condition of the house
such as, distance from the road, level of traffic and cleaning
habits (Ibanez et al., 2010). The main source of Pb could be
pigments present in paints. The white and the yellow lines
marked on the road using paint are subjected to intense
alteration of conditions in the study area due to the tropical
climate. In addition, vehicles tend to cross white lines with
higher friction in sharply curved bends may cause higher Pb
value in the area. Another potential source of Pb pollution in
the environmental samples including dust is the combustion
of gasoline that contains tetraethyl lead as an anti-knock
agent (Tuzen, 2003). Although leaded gasoline is not being
used, at present, in Sri Lanka, Pb released when it was used
earlier is still in the sediments and is circulated within the
Kandy area because of its basin-like morphology. Also,
the Pb levels may have been influenced by the usage of
lead-based paints which consist of lead chromate (yellow
pigments) and other Pb pigments. Further, Ni pollution on
local scale is caused by emissions from vehicle engines that
use nickel gasoline and by the abrasion and corrosion of Ni
from vehicle parts (Al-Kashman, 2007).
Assessment of heavy metal levels
When considering at the overall distribution of heavy
metals, samples collected from heavily trafficked places
(R4, R8, R11 and H4), the main bus station (R14), train
station (R15) and an abandoned construction site (H3)
indicate higher values of all heavy metals (Figure 3).
EF (enrichment factor) values, which are used to
evaluate anthropogenic input and pollution degree, reflect
the degree of heavy metal pollution in an area (Yang et
al., 2016). Higher EF values of all the heavy metals were
identified in R7, R8, R11, R14, R15, R18, H3 and H4
sample locations (Figure 4). These locations are in places
with high traffic congestions. Heavy metals, which have
EF > 10, were always believed to derive from human
activities (Yang et al., 2016).
Highly significant Pearson correlation values
(> 0.6) were found between Cu and Zn, Cu and Pb, Pb and
Ni, and, Zn and Pb. All these correlations between sample
locations and between heavy metals show that the origin of
the metals in the investigated area is highly related to the
transport activities.
Mineralogical characteristics
Modal mineralogical analyses of coarse fraction of dust
(> 75 µm) reveal that the samples are dominated by quartz
(36%) and opaque minerals (Figure 5). Minor amounts
of calcite are also present, which may be either naturally
derived or secondary products from construction materials.
The fine fraction of the dust samples is dominated by clay
minerals.
Mineralogy of the soils of the study area differs from
the underlying bed rocks since the ferromagnesian minerals
except mica have been subjected to intense weathering
due to tropical climatic conditions (Pohl and Emmerman,
1991). Despite the presence of iron oxide minerals of
the bed rocks as accessory minerals, their content in the
dust is relatively high. It may be due to their resistance
Table 6: Comparison of mean concentrations (mg kg-1) of heavy metals in dust in mega cities of the world.
Study City Pb Zn Cu
Wang et al., 1998 London 897 1866 300
Nazzal et al., 2014 Toronto 182.8 232.8 162.2
Chattopadhyay et al., 1999 Sydney 389 657 147
Suryavanshi et al., 2016 Delhi 120 284 191
Kim et al., 1998 Taejon 52 214 57
This study Kandy 49 775 319
D.S. Samaradiwakara and H.M.T.G.A. Pitawala 481
to weathering. However, some iron fragments from the
metallic materials also appeared as iron oxide minerals.
There is no significant difference in the
mineralogical composition between the two different dust
samples (Figure 5). This indicates that the factors including
geographical location, land use, nature of traffic and
antecedent during the dry period affect the composition of
dust particles (Amato et al., 2011). However, the mineral
composition of the dust samples does not depend on their
location.
Anthropogenic influence on the percentage of the
mineral and other inorganic solids in both types of samples
is not considerable, and both types of samples may have
derived from soil of the basement of the area (Xie et al.,
2000). The modal percentage of the minerals of the samples
is in the range of 70% to 85% and they are common rock
forming minerals of the study area. Most of these particles
are covered by fine dust particles rich in organic matter
that have been released from anthropogenic sources. Poor
sorting, high degree of angularity in the particles, presence
Figure 3: Maps showing the distribution of heavy metals (Zn, Ni, Pb and Cu) in the study area.
Figure 4: Variation of EFs of different heavy metals in the both road and household dust samples studied.
482 Ceylon Journal of Science 50(4) 2021: 475-486
of fresh or slightly weathered feldspar and chlorite suggest
that the dust samples have been transported for short
distances.
Morphological characteristics
According to SEM investigations (Figure 6), dust particles
are in a variety of sizes and shapes. The dust particles of all
types of samples are covered by surface coatings (Figure 6A).
As a result, the fibrous nature of some particles has been
changed (Figure 6B). The surface coatings of the particles
may have occurred due to the high atmospheric humidity
that can increase adhesiveness of the particle surface due to
the capillary effect (Kollensperger et al., 1999). Capillary
water can retain in particles, and it will tend to attract
and react with finer particles forming the surface coating.
Fibers of household dust have lower surface coating, than
those in road dust samples. It may be due to low capillary
water in such type of dust. The SEM / EDX data showed
the presence of high C and O in the fibrous materials and
on the surface coating indicating the organic origin of the
Figure 5: Average percentages of mineralogical and anthropogenic components of (A) road and (B) household dust samples.
Figure 6: SEM image of (A) porous nature of the surface coating of the fibers in the road dust samples, (B) surface coated cloth fibers
which the fibrous nature has been disappeared, (C) fracturing of the surface of a fiber in the sample, (D) the aggregate which contain
the materials derived from biological materials; roots and pollen.
D.S. Samaradiwakara and H.M.T.G.A. Pitawala 483
fibers. Irregular anhedral and subhedral mineral particles
and clusters of particles (Figure 6D) may have originated
from natural sources (Furutani et al., 2011) and the
aggregates may have formed due to adhesive and cohesive
nature of water. However, particles having smooth surfaces
(e.g. mica) contain lower content of coating compared to
those having rough surfaces. The reason for this may be the
adhesion forces that are higher on rough surfaces than on
flat surfaces (Shi et al., 2015). Naturally derived particles
tend to have smooth surfaces, while particles derived from
anthropogenic processes have a rough surface. Therefore,
naturally derived particles have lower thickness of
surface coating while anthropogenically derived particles
have thick surface coating. Particle aggregates could be
identified as the particles that were cemented together
by cementing materials such as organic matter, calcite or
salt (Meza-Figueroa et al., 2016). Some aggregates were
bound together by fibrous grains. These aggregates were
concentrated with fibers, mineral particles, anthropogenic
particles and some particles with a biological origin
(Figure 6D).
In addition to the porous nature of the surface of the
particles (Figure 6A), breaking of the mineral grains were
observed through their cleavage planes (Figure 6C). This
indicates a low level of stress during the collision between
grains, grains and roads and grains and vehicles. Further,
the surfaces of fine grains have been subjected to abrasion.
The surface coatings of the flat and smooth surface particles
are lower than that of the rough surface particles.
CONCLUSIONS
Characterization of particles of both household and road
dusts of the Kandy urban area indicates that both types do
not differ much in terms of mineralogy, morphology and
chemical composition. Concentrations of Ca, Cu and Zn
are significantly higher than the background levels. High
concentrations of Ca indicate that construction activities
of buildings contribute much to the chemical composition
of dust. The particles in the atmosphere are deposited
after short residence time and transportation due to the
wind circulation of the urban area. The tendency for the
suspension of fibrous materials gradually decreases due to
the coating of finer particles observed on their surfaces.
Even though dust is primarily originated from soil,
it had been altered by anthropogenic and natural processes,
such as traffic emissions, construction processes, and
wearing and weathering of man-made materials. Further,
dust particles can be considered as a fluxing agent and
storing sites of heavy metal, as they consist of considerable
amount of clay minerals derived from the soil. Alteration
processes, such as, incorporation of the heavy metals and
formation of the surface coating turns the primary particles,
into secondary particles.
Natural conditions, mainly the underlying geology
and climatic conditions, have masked the anthropogenic
influence on the chemical, mineralogical morphological
characteristics of both road and household dust in the
Kandy urban environment. Therefore, interpretation of the
dust pollution processes in the area by human interaction is
complicated.
In the development projects for Kandy, measures
should be taken to reduce the traffic congestion within the
city as well as the number of vehicles entering the city, to
improve the quality of life in urban population and city
dwellers, and to build a sustainable city.
RECOMMENDATION
Plastics and microplastics were identified to be the most
common sources of fibrous materials in the dust studied.
Future research on microplastics in dust should be
conducted to gain a better understanding of the current
state of air pollution and its impact on human health.
ACKNOWLEDGEMENT
The authors are grateful for the financial support from
National Research Council (grant no. NRC AB 19-004)
under the under the funds of Ministry Industry and Trade,
Russia.
DECLARATION OF CONFLICT OF INTEREST
The authors declare no conflicts of interest in preparing this
article.
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