ABSTRACT

In metropolitan areas petrol driven vehilcles are recognised today as the major source of lead pollution. In view of the rise in the number of vehicles on road as well as the Octane value of petrol from "83" to "87" there is logical possibility of increased lead emissim from petrol driven vehicles. Central Pollution Control Board carried out systematic studies over a period of January 1984 to April 1987 in the city of Delhi in order to reassure ourselves with regard to lead contamination of the roadside ecosystem and search of the plant species that help mitigate roadside autoexhaust lead pollution. The present paper deals with the studies carried out during August 1985 to April 1987 which revealed increase of atmoshperic lead concentration, increase of lead in the soil and accumulation of lead in the plant species "posted" at five specifically chosen traffic interesecticns. Alstonia scholaris, Eugenia janbolana and polyalthia longifolia were found quite useful for roadside plantation and there by help In mitigation of lead pollution.

KEYWORDS

Autoexhaust, Lead Pollution. Ecosystem, Roadside Ecosystem.

INTRODUCTION

Lead in the form of alkyl lead compounds is added to improve the antiknock quality of motor spirit and most of it leave engine through exhaust pipe as the particles of lead salts. The amount of lead in Indian gasoline varies from 0.06 to 0.44 gm per liter of motor spirit. In view of the substantial rise in the number of vehicles and also octane value of petrol from "83" to "87" there is logical possibility of increased lead emission from petrol driven vehicles. In the wake of promulgation of pollution control laws, automobile exhaust pollution and its adverse effect on the environment drew more attention of scientists as well as techonologists all over (Smith,1976; Bayliss,1983; Mathur et al.,19e5;C.P.C.B.,1985, Luhar and Patil,1986;Bhatnagar,I988 and many more).

Central Pollution Control Board(Ministry of Environment, Govt.of India) carried out systematic studies over a period of January,1984 to April,1987 in the city of Delhi in order to reassure ourselves with regard to lead contamination of the road side ecosystem and search for the plant species that help to mitigate roadside autoexhaust lead pollution. The present paper deals with the studies carried out during August,1985 to April,1987.

EXPERIMENTAL ARRANGENTS

Anbient air quality monitoring for lead (APHA,1977) at selected five traffic intersections (namely Delhi Gate, India Gate, Red-Fort, Ashram and Azadpur) and at control site i.e the Nursery of National Physical Laboratory (NPL), was done once-a-month in 1985 and generally once in two month in 1986 and 1987, so as to have total fifteen number of observations. Plant species earlier grown properly in the nursery were installed at all the six sites and harvested once in three months for their growth performance Study as below.

Sr.No.	Plant species	Date of installation	Date of Harvest
1.	Alstonia scholaris	Feb., '86	May and Sept.,'86
2.	Eugenia jambolana	Feb., '86	May and Sept.,'86
3.	Polyalthia longifolia	a) Feb., '86	May and Sept.,'86
		b) Sept., '86	Dec.,'86 and Apr.,'87
4.	Populus deltoida	Sept., '86	Dec.,'86 and Apr.,'87
5.	Putranjiva roxburghi	Sept., '86	Dec.,'86 and Apr.,'87

The parameters studied included lead in soil (Jackson,1958),lead in foliage (washed, acid digested and then scrutinised on 'A.A.S'), total leaf area in sq.meter per plant using area-meter and total biomass, in gm. per plant(Mishra,1968).

RESULTS AND DISCUSSION

Lead in the Roadside Air

The results of ambient air quality in regard to lead measured during the study period is presented in Table 1. Comparision of individual results of air borne lead concentrations at various traffic intersections and control location revealed correlation between lead in air and traffic volume. This indicates that automobile exhaust emission is the prominant source of air borne lead in the city of Delhi. It is seen from the results that the levels of lead in ambient air at traffic intersections were higher in winter and monsoon season as compared with that of summer season. A sharp increase in the lead concentration in ambient air at all the five traffic intersections was observed during the present study period of August,1985 to April,1987 as compared with that of the period from January,1984 to June,1985(C.P.C.B., 1985) as below.

Sr. No.	Period	Lead, ng/cu.m, (10-h average, once-a-month)
1.	January,1984 to June,1985	185 (India Gate) to 324 (Red Fort)
2.	August, 1985 to April, 1987	199 (India Gate) to 459 (Red Fort)

Lead in Soil

The base data (Table 2) show that lead in the soil increased in the Sept., 86, when compared with that of May, '86/ Dec.,'86 and Apr., '87 in all the pots of all plant species at all locations. The contamination of soil in the pots is thus evident due to sedimentation of atmospheric emission of autoexhaust lead as well as decomposition of lead-contaminated leaf litter fall.This may adversely affect the useful biological activities in soil (Smith, 1976).

Lead in vegetation

Lead in Plants: Lead content of plants from different locations in May,1986; September,1986; December,1986 and April,1987 are presented in Table 3 indicated higher lead in plants from traffic intersections as compared with that of plants from control location. The response of plant species to lead accumulation varied, however, it was not found related to traffic density. Plant Growth. Generally there was reduction in total leaf area and biomass production of the plant species at different traffic intersections as compared with that of N.P.L.Nursery (Table 4). Growth performance of Polyalthia (Ashok) Eugenia (Jamun) and Alstonia plant species was generally better than the other plant species studied.

Assessment of Impact : Plant species that would accumulate and adsorb maximum quantities of lead by all means without jeopardising its growth and metabolism would be preferable for growing along the roads so as to help mitigate the autoexhaust lead pollution. For this purpose percent increase of lead in plants (A) and soil (B) and percent retention of leaf area (C) and biomass (D) were calculated for all the plants species at all the traffic intersections with respect of N.P.L. Nursery (control site), the average of the sum i.e (A+B+C+D)/4 was designed as an Index of Lead Pollution Tolerance (L.P.T.I.). Higher value of the L.P.T.I. of a plant species would thus suggest its better suitability for lead accumulation and/or adsorption by tolerance. Among all the species studied Polyalthia, Alstonia and Eugenia seem to be the promising ones for their role in mitigation of autoexhuast lead pollution. L.P.T.I. values for all the species studied are presented in Table 5.