INTRODUCTION:

The air we breathe has not only life supporting properties but also life damaging properties. So, it is our duty to protect our environment by evaluating it continuously, which is done by biomonitoring of plants. No plant has been uniformly distributed around the globe; likewise, no particular region in the world has been reported to lodge all the plants of the plant kingdom. The diversity of plant distribution depends on interaction of a plant with its surrounding.¹Interaction and establishment of plants in any area also depends upon the sensitivity or resistance of plants to air pollutants.²Government college of Engineering is situated on the Bangalore National Highways in Salem. The city is surrounded by a natural amphitheatre of hills formed by the Nagaramalai to the north, the Jeragamalai to the south, the Kanjanamalai to the west and Godumalai to the east. It is divided by the Thirumanimuthar in the main division.³ In the selected site, there were approximately 2000 plants. Salem city lies at the base of Yercaud hills. The geographical location of city is 11.669437A N. latitude and 78.140865A E. longitude.

It has an average elevation of 278 meter. Salem`s climate has maximum temperature is 37.9Â°C and minimum temperature is 20Â°C.The Government engineering college campus is situated in NH-47,6 km from the Salem city.Since,the selected site is located in NH-7 Bangalore Highways, it is unavoidable to regulate the vehicle transportation as it is a busy Highways. Hence, an attempt has been initiated to biomonitor the environment by analyzing APTI of plant species present. Air pollution tolerance index has also been used widely to rank plant species in their order of tolerance to air pollution.⁴The efficiency of plants in absorbing pollutants is such that it can produce clean air.⁵Bernatsky⁶has suggested that green belts might help to reduce air pollution.Plants growing in the air polluted environment responded and showed significant changes in their morphology and biochemistry.

MATERIALS AND METHODS:

Sample collection

The study was carried out during Feb, 2013. The collected leaf samples from different plants located at Government College of Engineering, Salem, Tamil Nadu, India were brought to the laboratory for morphological measurements as well as for APTI analysis.⁷For this, components such as pH, Relative water content,⁸Ascorbic acid,⁹Chlorophyll, carotenoid content¹⁰ of the leaves were studied in order to identify the tolerance level of plants to air pollution.

The formula for APTI is APTI = A (T+P) + R /10

Where,

A=Ascorbic acid (mg/g)

T= Total Chlorophyll (mg/g)

P= pH of leaf extract

R=Relative water content of leaf extract (%).

RESULTS AND DISCUSSION:

Morphological measurements

Morphological measurements of plant leaves studied from the experimental site are exhibited in Table.1.

The length of the leaf was high for Borassus flabellifer and leaf width was found to be lower when compared to Tectona grandis. The leaf length was medium for Theobroma cacao having width of 4.2cm.Similarly, the weight of the leaf was found to have significant changes when weighed with dust and after cleaning the dust. According to the results obtained, the accumulation of dust was more on leaf surface which indicates the polluted environment in the selected site. Plants are continuously exposed to the environment absorb, accumulate and integrate pollutants impinging on their foliar surfaces and show visible or subtle changes depending on their sensitivity level.¹¹Reduction in leaf surface area causes less contact with environmental pollutants, specially air pollutants and improves resistance of plants against pollution.¹²

Air pollution tolerance index analysis

APTI was analysed by studying the leaf pH, Ascorbic acid, Total chlorophyll, Relative water content. The results of APTI studied and the individual components involved in APTI analysis are depicted in Fig1 to Fig.5. Variation in carotenoid content of the leaves was documented in Fig.6.

Table.1 Morphological Measurements of herbal plants from selected site

S.No	Medicinal Plants	Leaf length(cm)	Leaf width(cm)	Leaf weight with dust (mg)	Leaf weight without dust (mg)
1	Spathodea campanulata	10.5	2.0	0.097	0.096
2	Nerium indium	8.0	2.5	0.185	0.183
3	Magifera Caesia	13.4	1.4	1288	1280
4	Ceiba Speciosa	8.5	4.4	0.463	0.462
5	Ficus Religosia	14.5	5.3	1064	1062
6	Manilkara Zapota	7.2	3.4	0.608	0.604
7	Ficus Benghalensis	10.4	5.5	o.747	o.746
8	Azadirachta indica	13.4	2.4	0.117	0.116
9	Polyalthia Longifolia	12.4	2.8	0.370	0.368
10	Psidium Guajava	9.0	4.4	0.605	0.603
11	Borassus flabellifer	32	3.0	1690	1686
12	Nerium oleander	9.5	1.2	0.631	0.630
13	Acacia Arabica	5.0	1.4	0.119	0.116
14	Madhuca longifolia	4.0	2.5	0.066	0.065
15	Ocimum sanctum	3.5	2.0	0.102	0.101
16	Tectona grandis	12.4	6.7	0.778	0.776
17	Cupressus sempervirens	9.5	4.0	0.382	0.380
18	Calotropis gigantea	7.0	4.5	0.658	0.656
19	Frangipani	13.6	4.0	1.615	1.612
20	Moringa oleifera	2.6	1.4	0.042	0.041
21	Albizia amara	8.3	1.2	0.104	0.103
22	Tamarindus indica	8.2	1.5	0.562	0.560
23	Mangifera indica	13.4	2.4	1036	1032
24	Theobroma cacao	23.5	4.2	2739	2736
25	Rhus lancia	6.0	2.6	0.110	0.108
26	Bambusa bambos	18.8	2.5	0.44	0.42

Fig.1 Leaf ascorbic content

Fig.2.Leaf total chlorophyll content

Fig.3.Leaf pH content

Fig.4.Leaf relative water content

Fig.5.APTI of selected plants

Fig.6.Leaf carotenoid content

The Air Pollution Tolerance Index was high for Bambusa Bambos, Borassus flabellifer, Mangifera indica, Acacia Arabica, Albizia amara whereas low APTI was observed in Magifera caesia, Spathodea campanulata. The APTI of Madhuca longifolia, Ocimum sanctum, Theobroma cacao, Polyalthia longifolia were moderate. The increase or decrease in air pollution tolerance index depends on the internal components such as ascorbic acid, total chlorophyll, pH, relative water content. Ascorbic acid content was found to be high in Madhuca longifolia, Bambusa bambos, Manilkara religiosa, Acacia arabica whereas it was found to be very low in Nerium oleander. Ascorbic acid is a strong reductant activates many physiological and defense mechanism and its reducing power is directly proportional to its concentration. ¹³pH of most of the plants was found to be alkaline whereas Magifera caesia, Moringa oleifera showed acidic pH. Scholz and Reck¹⁴have observed that the leaf pH is reduced by acidic pollutants and the decline is more pronounced in sensitive species. This shift of cell sap pH towards the acid side could decrease the efficiency of conversion of hexose sugar to ascorbic acid is pH dependent i.e the activity is more at higher pH and less at lower pH. Hence, pH on the higher side could provide tolerance in plants against pollutants as reported by Agarwal.¹⁵The total chlorophyll content was higher in Moringa oleifera, and low in Spathodea campanulata, Nerium indium, Spathodea campanulata, Magifera caesia, Ceiba speciosa, Ficus religiosa, Manilkara religiosa, Ficus benghalensis. Pollution a stress factor reduces chlorophyll content.¹⁶Chlorophyll content of plants signifies its photosynthetic activity as well as the growth and development of biomass. It is well evident, that chlorophyll content of plant varies from species to species, age of leaf and also with the pollution level as well as with other biotic and abiotic conditions.¹⁷The decrease in foliar chlorophyll concentration in plants might be due to the destruction of chlorophyll,¹⁸reversible swelling of thyllakodis,¹⁹Inhibition of RuBp carboxylase.²⁰Low chlorophyll content in winter season might be due to the high pollution level, temperature stress, low sunlight intensity and short photoperiod. Similarly, High carotenoid content was observed in Acacia Arabica, Borassus flabellifer, Nerium indium while it was low for Manilkara religiosa. Relative water content recorded for Theobroma cacao, Ceiba speciosa, Polyalthia longifolia was very high when compared to Azadirachta indica. According to Lakshmi et.al ²¹ plants having APTI value in the range of 30-100 were tolerant to pollution and APTI value in the range of 17-29 were intermediate to pollution and below 16 and upto 1 are sensitive and value less than 1 are very sensitive. Implying this in to our results, no plants were found to be very sensitive to pollution. Among the 26 plants selected, most of them were found to be intermediate and in tolerance to pollution.

CONCLUSION:

The plants with higher air pollution tolerance index were found to be resistant and also act as a bioaccumulator for air Pollutants. It is suggestible that the plants having intermediate APTI value in the present investigation can be employed in abatement and control of air pollution. In addition, plants are highly significant as they are of high medicinal value. So, it is better to grow more plants where we live.

ACKNOWLEDGEMENT:

Authors are thankful to Honorable Vice Chancellor Dr. K. Muthuchelian, Periyar University, Registrar Dr. K. Angamuthu Periyar University for their support and Dr. P. Nazni Head, Department of Food Science, Dr. T. Poongodi Vijayakumar, Department of Food Science for providing UV Spectrophotometer for the analysis and also Head, Department of chemistry in rendering timely help.

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Received on 12.03.2013 Modified on 25.03.2013

Research J. Pharm. and Tech. 6(5): May 2013; Page 537-543