INTERNATIONAL JOURNAL OF ENVIRONMENTAL SCIENCES Volume 7, No 2, 2016
© Copyright by the authors - Licensee IPA- Under Creative Commons license 3.0
Research article
ISSN 0976 – 4402
Exploring the natural combating powers of plant species against air
pollution by assessing their APTI values
Anil Maan1, Ravindra Kumar2
1- Transportation Planning Division
2- CSIR Central Road Research, Institute, New Delhi
[email protected]
doi: 10.6088/ijes.7019
ABSTRACT
The present study throws light on natural combating powers of available flora around us
against air pollution by assessing air pollution tolerance index (APTI) of selected plant
species within and outside CSIR-Central Road Research Institute, New Delhi. The objective
of the study is to analyse and compare the variations of similar parameters over two different
locations i.e. controlled and experimental site and to find a high air pollution tolerant species
of plant betokening of natural tendency of these species to combat against air pollution and to
suggest an alternative approach of tree plantation, green-belt designing to planners and policy
makers. As per the site scenario, five major flora species that is Azadirachta indica,
Eucalyptus globules, Ficus religiosa, Dalbergia sisoo and Eugenia jambolana were the
selected as the plant species for the test. Full mature leaves were collected of almost same
physical features and in same ecological conditions. The fresh leaves were instantly analysed
for the Air Pollution Tolerance index (APTI) parameters namely total leaf chlorophyll, pH of
leaf extract, Ascorbic acid content and Relative water content. The study resulted in
suggesting Ficus religiosa as the most tolerant species followed by Eugenia jambolana.
Keywords: APTI, Chlorophyll, Ascorbic acid, Bio indicators, air pollution, green belt.
1. Introduction
Air is the most important necessity of all living beings on this planet. Clean air constitutes
78% nitrogen gas, 21% oxygen gas and 0.33% carbon dioxide gas and rest is of other gases.
But this natural balance is being deteriorating day by day due to various anthropogenic
activities. Rapid industrialization and increasing number of vehicles on roads has led to
environment degradation. Some of the major pollutants are particulate suspended matter,
oxides of nitrogen, oxides of sulphur, soot particles, Hydrocarbons (Benzene, Methane etc.)
and carbon monoxide. Every living being is affected from air pollution.
Decreasing bird and animal population and its diversity is an indicator of air pollution. In
human’s air pollutants causes diseases of lungs, infection in eyes, nose and throat, decreased
immunity, it causes cancer in different parts of the body, dizziness, headache and irritation in
body, the dust causes choking of nasal passage and throat etc (Curtis et al., 2006; Pope et al.,
2011). In plants oxides of nitrogen causes necrosis and sulphur dioxide causes chlorosis in
trees and plants leaves. Air pollution can directly affect plants via leaves or indirectly via soil
acidification. The dust causes the stomata pores to close which decreases the photosynthesis
activity of the leaves. Photosynthesis is also hindered as the suspended dust in the air
decreases the sunlight intensity reaching the trees’ leaves. Trees growing in polluted
environment tend to have smaller leaves than the trees growing pristine environment.
Received on May 2016 Published on September 2016
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Exploring the natural combating powers of plant species against air pollution by assessing their APTI values
Polluted air makes it difficult for the new trees to grow as they require cleaner and stress less
condition. However, these conditions can be improved by planting more trees and providing
wider and greener belts in industrial, residential and roadside area. Bannett and Hill (In 1973)
have recorded the ability of trees to reduce air pollution. Bernatsky (In 1969) has suggested
that green belts helps to reduce air pollution as plants growing in the air polluted environment
responds and shows significant changes in their morphological, physiological (Dohmen, et al
1990) and biochemistry. Plants provide an enormous leaf area for impingement, absorption
and accumulation of air pollutants to reduce the pollutant level in the environment with
various extents.
They act as the scavengers for many air borne particulates in the atmosphere. Plants
sensitivity and tolerance to air pollutants varies with change in pH of Leaf extract, Relative
water content (RWC), Ascorbic acid (A) content and Total Chlorophyll content. Study of
single parameter may not provide a clear picture of the changes induced due to pollution. So
Air Pollution Tolerance Index (APTI) which is based on these parameters has been used to
determine tolerance levels of plant species. These studies provided valuable information for
landscapers and greenbelt designers to select the sensitive as well as tolerant varieties of plant
species for using them to identify the pollution loads of urban/industrial areas, and also to use
the tolerant varieties for curbing the menace of air pollution. Various studies on APTI
(Johnson et al, August 2015, Yan-Ju et al, 2008, Singh S.K. et al, 1991) have confirmed that
the plants with higher APTI values were found to be resistant to air pollution. Indian cities
must have to attain the national ambient air quality standards (NAAQS) and ambient air
quality guideline values set by the World Health Organization (WHO).
To achieve the air quality targets in Delhi city the emissions of SO2, NOx, PM10, and volatile
organic compounds (VOC) should be decreased by 60%, 40%, 50%, and 40% respectively,
on the basis of that in 2015 (Source: Central Pollution Control Board and WHO Reports).A
comprehensive control policy focusing on multiple pollutants and emission sources at both
the local and regional levels has been proposed to mitigate the regional air pollution issues in
Delhi by NGT, MOEF. The options include development of clean energy resources,
promotion of clean and efficient coal use, enhancement of vehicle pollution control,
implementation of Odd and even for private cars to promote car sharing and reduce vehicles
on roads, implementation of synchronous control of multiple pollutants including SO2, NOx,
VOC, and PM emissions, joint prevention and control of regional air pollution and
application of eco-friendly air pollution combaters such as plantation, development of green
belts but unfortunately type of tree plantation in Delhi city is just seen from horticulture point
of view. Which are not helpful in mitigating air pollution Therefore there is need to study the
type of trees which are the best suitable with the help of their APTI values to sustain the clean
air and reduce the air pollution.
2. Material and methods
2.1 Study Area
The present study was undertaken in CSIR-Central Road Research Institute, New Delhi
located at 28.55° N latitude and 77.27° E longitude. The study area was divided into two
parts as shown in below Figure 1 of study area (Source: Google).
1. Experimental site: Near the main gate with high air pollution levels due to heavy
traffic, industrial & commercial activities
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Exploring the natural combating powers of plant species against air pollution by assessing their APTI values
2. Controlled site: Near the playground considered as non-polluted area due to thick belt
of vegetation & no direct exposures to roadside dusts & emissions.
Figure 1: Study Area
2.2 Sample collection
Fully matured leaves in triplicates were collected in morning hours from the selected tree
species of almost same diameter at breast height (DBH) and from the shrubs of almost same
height. Utmost care was taken that the samples from each study site were collected from
plants growing in same ecological conditions. The fresh leaf samples were than analysed for
total leaf chlorophyll, ascorbic acid, leaf extract pH and relative water leaf content. Mature
and healthy leaves of Azadirachta indica, Eucalyptus globules, Ficus religiosa, Dalbergia
sisoo and Eugenia jambolana were collected.
2.3 Sample Analysis
2.3.1 Ascorbic Acid
Ascorbic acid content (expressed in mg/g) was measured using spectrophotemetric method
(Bajaj and Kaur, 1981). 1g of the fresh foliage was put in a test-tube, 4ml oxalic acid –
EDTA extracting solution was added; then 1ml of orthophosphoric acid and then 1ml 5%
tetraoxosulphate (vi) acid added to this mixture, 2ml of ammonium molybdate was added and
then 3ml of water. The solution was then allowed to stand for 15 minutes. After which the
absorbance at 760nm was measured with a spectrophotometer.
2.3.2 Total Chlorophyll
Determination of total chlorophyll was performed according to the methodology described by
Arnon (1949) and calculations were performed in accordance to the below mentioned
equations given by Arnon (1949).
Where, DX = Absorbance of the extract at the wavelength Xnm, V = Total volume of the
chlorophyll solution (ml) and W = Weight of the tissue extracted (g)
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2.3.3 pH of leaf extract:
To determine the pH of leaf extract, 5g of the fresh leaves was homogenized in 10ml
deionised water. Then leaf extract was centrifuged at 2500 rpm for 10 minutes, and the
supernatant was collected to determine the pH with the help of a digital pH-meter.
2.3.4 Relative water content (RWC) in %
Relative water content (in %) was calculated on the basis of the method described by Singh et
al, 1991 and below equation (3) betokens that
Where,
RWC = Relative water content, FW = Fresh weight, DW= Dry weight, TW= Turgid weight
2.3.4 Air Pollution Tolerance Index (APTI)
To calculate Air Pollution tolerance Index, Ascorbic acid, Total Chlorophyll, pH of leaf
extract & relative water content (in %) were used and calculated as per Singh S.K. et al, 1991
mentioned in Equation (5).
Where,
A stands for the ascorbic acid in mg/g
T stands for the total chlorophyll in mg/g
P stands for pH of leaf sample
R stands for is relative water content in %
2.3.5 Gradation of APTI values
Based on APTI values the plants were conveniently grouped as follows (Mary Esther Cynthia
Johnson et al, 2015).
(i) 10.5 - 8.5 as Tolerant species
(ii) 8.4 – 5.0 as Intermediate species
(iii) Less than 5.0 as Sensitive species
3. Result, Discussion and Comparison
3.1 Results
Ascorbic acid content was found to be minimum 3.5 mg/g (dry weight) in Eucalyptus
globules (Table 1) and maximum 7.95 mg/g in Ficus religiosa (Table 1). On an average the
ascorbic acid was found to be 5.25 mg/g in non-polluted area (Table 1) lesser than the
polluted area which is 5.65 mg/g (Table 1). Total Chlorophyll content was found to be
minimum 1.02 mg/g in Azadirachta indica (Table 1) and maximum 2.45 mg/g in Ficus
religiosa (Table 1). On an average, in polluted area, the chlorophyll content was 1.59 mg/g
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Exploring the natural combating powers of plant species against air pollution by assessing their APTI values
(Table 1) and the corresponding value in the non-polluted area was 2.00 mg/g (Table 1). The
value of pH varied from 5.84 in Eucalyptus globules (Table 1) being the lowest to 7.89 in
Ficus religiosa (Table 1) being the highest. On an average the pH of leaf extract was found to
be 6.79 in polluted area (Table 1) lower than the polluted area which is 6.99 (Table 1).
Relative water content (in %) varied from 58.4 in Azadirachta indica (Table 1) which was
the lowest to 82.3 in Ficus religiosa (Table 1) which was maximum. The average relative
water content of the trees in the controlled area was found to be 71.60 (Table 1), slightly
higher than those of trees in polluted area which is 64.66 (Table 1).
Table 1: Ascorbic acid, Total chlorophyll, pH of Leaf extract, RWC (%) and APTI values of
different trees at different locations of study area
Name of the
Tree Species
Ascorbic
Acid
(mg/g)
E*
C#
Total
Chlorophy
ll
(mg/g)
E*
1.0
2
C#
pH of Leaf
extract
APTI
C#
E*
C#
1.62 6.94 7.01 58.40
68.10
10.03
10.57
1.96 5.84 6.02 64.10
70.20
8.95
9.81
2.45 7.56 7.89 75.80
82.30
15.38
16.17
E*
C#
Relative
Water
Content
(RWC)%
E*
Azadirachta
indica
5.26 4.36
Eucalyptus
globulus
3.50 3.60
Ficus religiosa
7.95 7.68
Dalbergia
sissoo
5.18 5.05
1.9
8
2.10 7.07 7.15 59.50
61.10
10.64
10.78
Eugenia
jambolana
6.37 5.56
1.4
6
1.89 6.50 6.90 65.50
76.30
11.62
12.52
1.2
2
2.2
5
Where, E*: Experimental (Polluted Site); C#: Control (Non-polluted Site)
3.2 Discussion
When the plants are exposed to any physical, chemical, or biological stress, ascorbic acid
content increases as an adaptive mechanism. Therefore, higher the ascorbic acid content,
more is the tolerance potential of plant to the stress. Figure 2 shows the Ascorbic Acid of the
leaves at experimental and control location. The chlorophyll content signifies its
photosynthetic activity as well as the production of plant biomass. It is also dependent on the
species, age of the leaf, environmental conditions, and air pollution levels. The plants
sensitive to air pollution will have lower chlorophyll concentration.
Figure 2 shows the Total Chlorophyll of the leaves at experimental and control location. The
leaf extract pH was observed to be in the neutral range. This facilitates the conversion of
hexose sugar to ascorbic acid in leaves (Escobedo et al., 2008) and thus increases the tolerant
nature of the plants. Figure 2 shows the pH of the leaf extract at experimental and control
location. Water content within a plant body helps to maintain its physiological water balance
and under stress conditions such as drought or air pollution, the transpiration rate reduces due
to air pollution, thus suction of minerals from soil and supply of nutrients to roots does not
take place. Therefore RWC is an important parameter with respect to APTI. It affects the
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Exploring the natural combating powers of plant species against air pollution by assessing their APTI values
overall biochemical activity. Figure 2 shows RWC of the leaves at experimental and
controlled sites.
Figure 2: Ascorbic Acid, Total Chlorophyll, pH and RWC (%) of the leaves at experimental
and controlled sites
The values of APTI were slightly higher at controlled site as compared to the experimental
site. Figure 3 shows the APTI values at experimental and controlled sites and respective
mean.
Figure 3: APTI of different trees at experimental location, control location and their mean
Thus Among these plants Ficus religiosa was found to be the most tolerant and Eucalyptus
globulus was found to be the least tolerant (From Table 1) and all others were moderately
tolerant (From Table 1).
3.3 Comparison with different case studies performed on APTI (in Indian Scenario)
Till date many studies on APTI have already been done like Air Pollution Tolerance Index of
Plants in Varanasi City done by Singh S.K. et al, 1991. Likewise, APTI values in research
paper Anticipated Performance Index of some tree species considered for green belt
development in and around an urban area: A case study of Varanasi city done by Prajapati et
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Exploring the natural combating powers of plant species against air pollution by assessing their APTI values
al, 2008. Similarly, Air pollution tolerance index values of certain plants of Hyderabad city
done by Johnson et al, 2015. The list is endless which advocates the importance of APTI. In
our study area if we talk about the air quality of Delhi it is one of the most polluted cities
(CPCB reports). This is alarming enough to find out the all possible ways to curb out the air
pollution. So we also attempted to depict the importance of the same in Delhi city. In Figure
3 if we examine minutely it clearly shows that the values of APTI in different case studies of
same tree species was found to be higher. This clearly indicates that the air quality of Delhi
city is worst in comparison to other case studies which are compared in Figure 3. This
advocates our case study and emphasizes for more such studies to be done in future Below
Figure 4 shows a comparison of APTI values of same tree species in different case studies.
Figure 4: Show a comparison of APTI values of same tree species in different case studies
4. Conclusion
Based on the results obtained, it was observed that most of the trees were found to be tolerant
and in most of the tree species ascorbic acid levels at experimental sites were found to be
higher betokening of induced stress conditions and adaptive mechanisms in form of relatively
less RWC (%), more acidic leaf extract and lower chlorophyll content in comparison to
controlled sites due to continuous and direct exposure of experimental tree species to air
pollution. That clearly indicates the working out of adaptive mechanisms, exploring the
natural combating powers of tree species against air pollution. However this is an indicative
and limited study in this context, it further needs more rigorous research to explore different
impact scenarios like size of the tree, water intake to sustain, ever-green or not, suitability in
terms of geography etc. before concluding the most tolerant species (only on the basis of
APTI) to be the fittest one for planners, policy makers or green-belt designers.
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