ABSTRACT

One month old plants of Alfalfa were exposed in different parts of Delhi city in May. 1983 and their responses correlated with known levels of air pollution in the city. The study indicates that it can be successfully used as indicator species for assessment of the air quality.

INTRODUCTION

It has become necessary to take urgent steps to improve atmospheric quality in the city of Delhi, which is threatened by the air pollution due to auto-exhaust and industrial emission. The major contributors to the atmospheric emission in Delhi are chemical industries, textile units, thermal power station and increasing number of automobiles. About seven million population also add considerable atmospheric contaminants every day. The emissions include mainly sulphur dioxide, particulates, oxides of nitrogen, carbon monoxide, PAN, PAH, oxigenates etc. depending upon the process involved. Though the intensive monitoring of air quality can not be the top priority, the need of the same is generally agreed. One of the relatively inexpensive way of monitoring air quality is to use plants that are sensitive to air pollutants

(De Sloover & Le Blanc, 1968; Craker et al., 1974, Sochting & Johnsen, 1978; Chaphekar et al., 1989; Varshney, 1985). The present paper deals with efforts made in the similar direction where Alfalfa (Medicago sativa L.) plants where used as indicator plants for the air quality monitoring in the city of Delhi in May, 1983.

MATERIALS AND METHODS

For this experiment Medicago sativa L., plants were raise^d from the certified seeds in plastic pots (alluvial soil, 75% and farm yard manure, 25%), in identical numbers and comparable mode of watering. After the plants were grown till properly established, they were installed at five different locations of various landuse pattern in the city of Delhi. Watering of the plants in the field was done every day. Age of the plants at the time of exposure was 30 days and duration of exposure was 21 days. At the end of exposure period in field, the plants were brought back to the laboratory and studied for shoot length (cm) shoot biomass (mg), (after oven-dried at 100°C±2''C for 24 hrs.) and soluble sulphates in leaves (Tonnies & Bakey, 1953). Ambient air quality measurement was done once in a week for 4 h duration at each location for sulphur dioxide, nitrogen dioxide and suspended particulate matter (APHA, 1977; NEERI, 1978). Lead oxide candles were also installed at all the locations, along with plants, for 21 days to study the atmospheric sulphation rate (NEERI, 1978).

RESULTS AND DISCUSSION

Results obtained are presented in Table 1 and Fig. 1. It is seen that all the three characters, tested, of the Alfalfa plants were affected due to the quality of air at different locations. This indicated the usefulness of these characters {i.e. shoot length, shoot biomass and sulphate in leaves) for the purpose of assessment of the air quality. The relationship of the plant characters with each other in the extent of their responsiveness has also been brought about in terms of their percent decrease (in case of shoot length and biomass) and percent increase (in case of sulphate in leaves) when com-

Table 1 : Characters of plant species and parameters of ambient air quality at different location in the city of Delhi

Location	Plant characters % decrease % increase   API				Air quality parameters
					Microgram per cubic   meter, 4 h average			mg SO3/1OO cm2/day
	Shoot length (A)	Biomass (B)	Soluble SO4 in leaves (C)	D= A+B+C           3  (D)	SO2	No2	SPM	Sulphation rate
D.S.I.D.C. Wazirpur (Roadside-Industrial area)	13	36	203	84	48	29	414	0.83
Najafgarh  (Industrial area)	35	44	291	123	128	36	600	1.91
I. T. 0. (Roadside)	27	36	187	83	62	56	454	1.14
Dr. Mukherjee Nagar (Residential & Commercial)	+2	22	156	59	35	20	304	0.25
J.N.U. Campus  (Clean, Control Location)	0	0	0	0	17	16	150	0.03

pared with the plants installed at the control location (I.e. J.N.U. Campus). It was immediately noticed that while shoot length and biomass were decreased and sulphate content of the leaves increased in the known polluted areas. Additionally, the average of the sum of the percent loss, in case of shoot length and biomass, and percent gain, in case of sulphate content of the leaves, with respect to the plants grown in the control location, was referred to as Air Pollution Index (API). Though the API values may not be the absolute measures of the level of air pollution but when compared to the zero of the control location, they reflected the quality of the air on a quantitative scale. The higher values at location Nos. 1, 2 and 3 also pointed to the high level of pollution of the air.

The comparision of the values of API with the values of sulphur dioxide and sulphation rate in the ambient air showed that correlation between the API and sulphation rate was 0.91 (at 5% level) whereas between sulphate content of leaves and sulphation rate it was 0.95 (at 5% level), however, there was no correlation between API and sulphur dioxide in ambient air.

The inter-relationship between the API and atmospheric sulphation rate and between the sulphate in leaves and sulphur dioxide in air proved the usefulness of Alfalfa plants as suitable indicator plant for the general air quality in the city.

ACKNOWLEDGEMENTS

Authors are thankful to colleagues for their co-operation during the work.

REFERENCES

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