Lead in Vegetation : Contamination of plant due to atmospheric lead was generally considered to be surface phenomenon and largely susceptible to be removed by washing, scrubbing, etc.

The variation in lead content of all the three plant species varied significantly between February and May, 1985 (F-calculated 9.98 is greater than F-Table 5.32). However, there was no significant variation observed among the interaction between location, plant species and season, i.e., February and May, 1985. This suggests that the lead accumulation is influenced by the seasonal changes. Lead particles deposited from ambient air adhered to the surface of the plant parts and were less subject to removal by wind action during winter. Generally there was reduction in the total chlorophyll content of leaves, total biomass production and total leaf area per plant at the five traffic intersections as compared with that of the NPL Nursery (Table 8). Close examination of data on the reduction of chlorophyll, biomass and leaf area revealed that among all the three plant species, growth performance of Eugenia (Jamun) was generally better as compared with that of the other two species.

Assessment of Impact of Autoexhaust Lead Pollution of Plant Species : One of the main objectives of the study is to screen and select the plants by field trials for their suitability to grow along the roadside so that they can serve as immediate filters of autoexhaust pollutants. Quite logically, the choice will fall upon a plant species that would accumulate maximum quantities of lead by all means, while its optimum metabolism would not be in jeopardy. Therefore, percent increase of lead in plants (A) and soil (B) and percent retention of chlorophyll (C) biomass (D) and leaf area (E) were calculated for all the plant species at all the five traffic intersections and the NPL Nursery. The average of the sum (A + B + C + D + E)/5 would thus give a Lead Pollution Tolerance Index (LPTI). Higher LPTI of a plant species would thus suggest its better suitability for lead accumulation by tolerance, and such species could be recommended for plantation along the roadside. Among the three species studied over the period of six months from November, 1984 to May, 1985, at most of the traffic intersections (80%), the maximum value of LPTI was recorded in Eugenia plants followed by Nerium and Alstonia (Table 9). It is therefore, concluded that among all the three species studied, the Eugenia (Jamun) seems to be the

AUTOEXHAUST LEAD

Table 8 : GROWTH PERFORMANCE OF PLANTS* OF DIFFERENT SPECIES COLLECTED FROM DIFFERENT LOCATIONS

S.N.	Location	Traffic  Density Class	ALSTONIA                                       EUGENIA                                               NERIUM
			Total Chlorophll		Biomass		Total Leaf Atea		Total Chlorophyll		Biomass		Total Leaf Atea		Total Chlorophyll		Biomass		Total Leaf Atea
			F	M	F	M	F	M	F	M	F	M	F	M	F	M	F	M	F	M
1.	Delhi Gate	I	268	572	24	37	469	2164	544	491	35	46	933	2144	1195	834	38	55	431	2601
2.	India Gate	II	290	854	34	39	379	1490	438	834	33	28	847	537	642	766	32	40	439	1367
3.	Red Fort	III	588	695	19	38	704	1930	527	442	30	39	1041	2533	749	644	23	53	551	2584
4.	Ashram	IV	276	345	39	22	679	718	380	252	30	27	1249	1419	352	673	26	37	689	1328
5.	Azadpur	V	781	1193	37	34	854	876	553	896	20	32	1043	1494	1060	753	27	32	570	1664
6.	NPL Nursery	s-	910	1397	45	46	1016	2080	598	911	41	53	1034	2060	1233	1307	42	60	333	2326

Table 9 : LEAD POLLUTION TOLERANCE INDEX (LPTI) OF PLANT SPECIES AT DIFFERENT TRAFFIC INTERSECTIONS

Plant Species	Delhi Gate	India Gate	Red Fort	Ashram	Azadpur
ALSTONIA
February            May	88 60	112 56	115 53	126 39	85 59
EUGENIA
February            May	250 167	223 133	303 119	166 187	116 88
NERIUM
February            May	174 105	163 54	223 58	198 100	132 58

most promising one followed by Nerium. The former, a tree species, could be planted along the roadside; while latter, being a shrub, would be suitable for growing in the road-divider channels.

FINDINGS

The general levels of lead in the ambient air at five different traffic intersections are in the range of 185 ng/ m3 to 324 ng/m3, while background concentration at NPL Nursery was 62 ng/m3 (Table 4).

The lead content in soil in the pots of the three plant species at all locations increased in May, 1985 as compared to February, 1985. But this increase was found to be in significant when the data were subjected to the analysis of variance. Lead accumulation in plant (root, shoot, leaf and leaf washing) had significant variation between May and February. It was more in February than in May (Table 7).

Eugenia (Jamun) was found to be suitable for growing along the roadsides. The tree would not only accumulate and adsorb the lead from the autoexhaust but shall also provide shade for human beings and shelter to the birds.

Nerium (Kaner), a dense shrub, is suitable for growing in the road divider channels. The profusely dense leaves on branches can serve as filters of particulate pollutants emitted from the autoexhausts.

FURTHER WORK

Considering the face that the behaviour of plant species under the impact of any specific chemical varies widely and that the duration of investigation on three plant species is very short (only 10 months) and therefore, investigations using a few more plant species have been conducted and published elsewhere12.

ACKNOWLEDGEMENTS

Authors gratefully acknowledge and thank Central Pollution Control Board for its permission to publish this Paper.

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