Friday, 22 January 2016


Dr Nitesh Joshi* and Ambika Joshi
*Rizvi college of Arts, Science and Commerce ,Associate Professor in Botany,Mumbai
Jaihind college ,Department of Botany,Associate professor in Botany ,Mumbai.

Air pollution

India is growing fast since the last couple of decades, with every year new cities being added to the list. Compounded with this development the so called peri- urban areas also starts experiencing the unavoidable menace of air pollution. That pollution of any types is harmful to the human beings and the ecosystems in general is now a very well known fact. The problem of  suspended particulate matter is fast increasing with increasing construction activities in the cities. In such a scenario citizens often ask, the questions, how much air pollution is there in the area and what Plants have been often used to clean our environment. Shri Narendra Modis call for an SWACHH ABHYAN falls under this category. Cleaning of our cities lies not only with public discipline but also with plants. Research has thrown light on various aspects showing how plants can efficiently be used to keep our environments clean , so also how these can effectively warn the citizens of a failing or deteriorating environments. Considerable literature is available in the area of plants and pollution. However at a local level and for all practical purposes there are no clear cut guidelines regarding the use of plants as indicators of air pollution or green belt development. The current article highlights on the guidelines for establishments of an national level indicator for monitoring dust and green belt development.

In India several scientists have worked on effects of air pollution and plants. However there is an urgent need to spread this work to make use for general citizens and municipal corporations and horticulturists all over the country. The learned botanists can come to the rescue in such cases . an attempt is made to answer some of these questions over here.
Types and sources of Air pollutants

Plants growing in the ambient environment of urban-industrial area would be exposed to not  only one but to a mixture of many pollutants. According to Rao (1985), the effects of air pollution (gaseous pollutant, acid deposition and particulates) on various levels of ecosystem organization may be summarized as follows:
a) Absorption and accumulation of pollutants in plants and other ecosystem components such as soil surface and ground water.
b) Injury to producers (plants) and consumers (animals) due to pollutant accumulation; for example leaf necrosis in plants and dental fluorosis in animals.
c) Change in number, density and diversity of species and a shift in competition.
d) Loss of stability and reduction in the reproductive ability of species.
e) Degeneration of associations of biotic components.
f) Disruption of biogeochemical cycle.
g) Extension of eroded areas in the landscape.

Plants as Indicators and Biomonitors

Plants are important to maintain ecological balance but they also get affected by air pollution either directly or indirectly.They have been harmonizing nature from the days life appeared on the planet by regulating the concentrations of CO2 in the air and now they are destined to commence a more modern and hazardous role of reducing the quantum of air pollution through adsorption, absorption, accumulation, detoxification and metabolization (Rao, 1980). Bio-indicator may be a plant or an animal which reveals the presence of a substance in its vicinity by showing typical symptoms which can be distinguished from the effects of other natural or anthropogenic stresses (L. Steubing and H. J. Jäger,1982). Being stationary, plants play a very important role in indicating the changes taking place in an environment. Two aspects of Bioindicators in plants are known : Sensitive plants are those which show clear symptoms of pollutant effects even in the lowest concentrations. Accumulator plants are those which readily accumulate specific air polluting substances that can be analysed in the plant material often by physico-chemical methods. This leads to a quantitative determination of  pollution load as that plant then acts a receiver or absorber only, without any injury and is actively involved as a selective capturer of pollutants (Posthumus, 1982).


Different levels of organization of the plant can be used for phytomonitoring, ranging from the single plant (leaf or even plant cell) to the plant association and the ecosystem. Some air pollutants have very low ambient concentrations and are complicated to measure accurately with physical and chemical methods. Plants can accumulate those pollutants to a level that is easier to analyze. Some of the parameters which can be used for phytomonitoring of air quality are Plant growth,Macro characters, micro characters and biochemical characters: The need to use genetically uniform material and uniform culturing practices are also important. Such systems have been used by Chaphekar (1972), Posthumus (1982), Joshi (1990), etc. Standardization of methods is also essential to compare results at different sites, months or years.

Monitoring Dust in a City

Chaphekar, (1995) used leaves of trees like Mangifera indica, Thespesia populnea and Polyalthia longifolia for the estimation of dust fall in 20 different types of localities of Mumbai city in order to monitor airborne dust settling by gravity. They also observed marked reduction in growth of potted plants of Commelina benghalensis transplanted in heavily polluted areas of Mumbai city. Joshi and Joshi (2013) showed that Hyptis suaveolens had high dust capturing capacities among the plants in the city of Mumbai. Recently, Faqih A.G., Joshi N.C. and Joshi A.N. (2014) studied the foliar dust capturing potential of a common plant Pedilanthus tithymaloides growing along road dividers and traffic islands of Mumbai and prepared a foliar dust map of the city based on their study. A co- relation between foliar dust fall and traffic count was found to be positive. Collecting the dust from the leaf and then representing it as dust in gm/m2 is an well accepted method , using either filter paper or crucible.

Further it was observed that:
1. The amount of dust is never constant in the atmosphere. It keeps changing with respect to variations in place, time, season, climate, etc. During the field work it was noticed that foliar dust recorded of various plant species differ at different sites and no plant behaves same at all sites i.e. the plant which is the best dust capturer at one site may be the worse in holding dust at other sites. Hence, each plant behaves independently at various sites without any trend or pattern. This may also because of varying wind speed, humidity, proportion of vehicular and industrial exhausts, etc.

2. In order to determine the best plant for capturing and retaining the atmospheric dust, screening of dust to the plants in a constant system (surrounding) was required. A special dust fumigation chamber was fabricated to analyze the plants under controlled and simulated conditions.

3. A dust chamber is used to explore the dust retention capacities of various trees , shrubs , herbs (Chapekar and Mancharkar, 2007). The plants were screened to dust under controlled (or still) and simulated conditions. The amount of dust was estimated to determine the dust capturing and dust retaining capacities of the plant species. The tendency to hold dust on leaf surface was measured in terms of DRI (Dust Retention Index). Many plants were found to get higher DRI values without fan but some were showing higher DRI values even with fan. The plants that receive and hold more dust without running fan are said to be good dust capturers. 

4. DRI values are percentage values of Dust captured and Dust retained on the foliar surfaces of various species. A list of plant species, herbs, shrubs, trees with their DRI will help in planning the type of plants to be grown along road dividers, residential areas, highways and gardens. Ficus benghalensis L., Ficus benjamina L. var. nuda (Miq.) M. F. Barrett, Lantana Camara L., Mangifera indica L., Muntingia calabura L. Pedilanthus tithymaloides Poit. Trema orientalis (L.) Blume, Ziziphus jujuba Mill.. Ervatamia divaricata (L.), burk with curled leaves, Clerodendrum inerme (L.) Gaertn are some plants with high Dust retention indices. However wind plays an vital role in the dust capturing capacities.

5. Cities in India are undergoing several changes with the introduction of mass rapid transport systems, construction activities of buildings, flyovers and highway renewal. The plants during the study reflected the same with high amounts of dust in areas with constructions activities or around the vicintiy of such areas. Therefore it is suggested to have green belt around road dividers with plants which can be trimmed as well as with high DRI. Plantations with a big canopy alternating with a shorter one are suggested. Ficus benjamina, Pedilanthes tihymalides, Nerium odorum and Bougainvillea species for example.

6. Around industrial areas the situations become complex with several industries placed together. Green belt development in such areas should focus on the utility of the area and the principle should be that the installation factory shouldn’t be seen and the trees should encircle the factory around 50 M.

Choice of plants for roadsides including traffic island should be in accordance with the width of the road. There should be a formation of screen between traffic and roadside residences. The plants should include shrubs and trees, with intermixing of ornamental herbs like Aralia. Another parameter which is important in choice of plant species for green belt development is 'Air Pollution Tolerance Index'. Several agencies and researchers have worked on this area and the data can be used by locals for developemet of green belt. For dust it is also the morphological parameters which play an important role dust retention. Vegetation provides a major filtration and reaction surface which acts to trap particulates. Through sedimentation, particles are usually deposited on the upper surfaces of leaves, particularly the larger particles.

The interception and retention of atmospheric particles is highly variable and primarily dependent on: 
1) the size, shape, and surface texture of the Particles, 
2) the size, shape, and surface texture of the intercepting plant part, and 
3) the micro- and ultra microclimatic conditions surrounding the plant. 

For particulate removal, species with high leaf circumference-to-area and surface-to-volume ratios, along with leaf surface roughness may be recommended. It may be concluded that within their limits of tolerance, plants absorb pollutants and to that extent remove air pollutants(Hill,1971). Several worker have published their work in other parts of the world on air pollution and its effects on plants (Manning ,W.J, and Fedder,J.(1980), and Yunus, M. and K. J. Ahmad, (1978) ).

Concept of Green belt 

Green belts are thought to be effective in such scenarios, where green plants form a surface capable of absorbing air pollutants and forming sinks for pollutants. Leaves with their vast areas in a tree crown, absorb pollutants on their surface, thus effectively reduce their concentration in the ambient air. Plants grown in such a way as to function as pollutant sinks, are collectively referred to as green belts (Kapoor, et al, 1996; Onkar, 2006 and S.C Sharma,2009 ). 

Plant scientists favour the development of green belts for use as parks within large urban industrial areas. Most city planners look to the green belt as a park system to provide areas for recreation and simply to break the monotony of the urban complex. Some have stressed the potential screening effect of green belts to remove air pollutants and thus serve to benefit human health. Commonly the green belt as such has been taken as a strip or a piece of land consisting of plants belonging to a few species, may be common or beautifully flowering ones for removal of air pollutants. Many scientist have also suggested the use of green belt, which is rows of trees for reducing pollution originating from industrial operations (Gupta V. K. and R. K. Kapoor, 1992;Hanson & Thorne, 1970; Warren, 1973; Ganguly 1976 and Chaphekar,1995). 

Plant species suitable for green belt 

This new approach has evolved in recent years which aim at growing plants in and around industrial areas and roadsides. And for that, selection of tree species is a task that requires sound knowledge of the plants and their response towards environmental stresses, especially dust fall & emission of gaseous pollutants. Capacity of plants to reduce air pollution is well-known.To check the spread of air pollutants emitted from industrial complexes, it is recommended by many scientists that vegetation be grown around such areas . It is known that plants differ considerably in their response towards pollutants (Rao, 1985). Some are highly sensitive & show immediate injury symptoms while others are hardy and tolerant. Tolerant plant species can function as pollution sinks & therefore a number of environmental benefits can be derived by planting tolerant species. They will help to reduce overall pollution load and make the air free from pollutants and particulate matter. Therefore appropriate selection of tolerant plant species, which can withstand pollution, may result in pollution mitigation. Parameters have been suggested for the choice of plantations of green belts, for e.g. , Air Pollution Tolerance Index (APTI) values, ( Singh and Rao,1983) and Dust Retention Index (DRI) for different plant species have been worked by Chaphekar and Mancharkar, 2007, in Pune. Dust interception capacity of plants depends on their surface geometry, phyllotaxy, and leaf external characteristics such as hairs, cuticle etc., height, and canopy of trees.

Removal of pollutants by plants from air is by three means, namely absorption by the leaves, deposition of particulates and aerosols over leaf surfaces, and fallout of particulates on the leeward side of the vegetation because of the slowing of the air movement (Tiwari, 1994). A comprehensive report is prepared by the Central Pollution Control Board of India on green belt development (C.P.C.B, 2000). The work carried out by this laboratory at Rizvi College , Botany Department financed by the University Grants Commission under the title “Studies on monitoring Suspended Particulate Matter using urban plants and understanding their Green Belt Potentials”, highlighted the importance of roadside plants, to monitor dust and types of plants species effective in reducing dust pollution . Elsewhere also work done by ecology department  of Pune University highlighted the important dust capturing capacities of certain avenue trees and at Institute of Science, Mumbai in the past . Plants like Nerium odorum, Pedilanthes tithymaloides, Ficus benjamina, Bougainvillea spectabliis growing on road dividers all over the country were found to be effective dust retainers.

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