Nowadays, the air pollution is one of the most serious problems faced by mankind resulting from growing population, increasing density in domestic areas, traffic etc. Air pollution caused by SO2 is rapidly increasing with economic activities both in small and metro cities in India. It is a fact that visible symptoms of injury can be seen on plants due to automobile exhaust pollutants. Air pollutant from automobile exhausts affect vegetation and causes injury by alterations in metabolism, reduction in photosynthesis, foliar necrosis, defoliation and growth reduction. The micrometeology of the areas also plays important role in determining the concentration of air pollutants. The plants usually have little chance for detoxifying the absorbed pollutants due to the lack of sufficient pollution free time and results in assumption of pollutants which damages the plant organs. This article deals with Lichens as biomonitor for automobile exhaust pollutants in Imphal city.
They are a distinct kind of organisms that is one part is fungus (the mycobiont) and another part is alga (the photobiont). Each lichen body or thallus is composed of fungal stands called hyphae which surround trapped algal cells. The fungus derives nutrients from the captive alga without harming it. The alga can produce new cells inside the growing lichen thallus, but it cannot escape to reproduce on its own.
The biomonitor is an organism or a part it that depicts the occurrence of pollutants on the basis of specific changes symptoms, reactions morphological changes or concentrations (market et al, 1997). Biomonitor can be further classified according to their origin into (i) Passive biomonitor in which organisms that occur naturally in the study areas are monitored and (ii) active biomonitor in which the organisms are brought into the research area under controlled conditions for a specific period of time (Market et al, 2003).
Automobile exhaust pollution
The automobile exhaust pollution is a major issue in Imphal city. The sources of automobile exhaust is varied ranging from the condition of the vehicles to the quantity of fuel used. The vehicle used in the public transport system viz, autos, buses, vans, etc. are mostly old exceeding 10 years and are ill maintained.
The fuel used for this public transport systems is of poor quality and often contaminated. These vehicles emit carbon monoxides, oxides of nitrogen, ozone, lead, hydrocarbons, benzene, polyaromatic hydrocarbons, oxides of sulphur particles which are highly polluting substances. During the last two decades, the number of such vehicles has increased tremendously. As a result of which the amount of pollutants may reach alarming proportions in the coming years.
The registration of motor vehicle in Manipur as on 31st March 2015 was 2,49,978 (Truck – 12,709; buses – 13,85; Jeeps – 1,542; Cars – 22,886; Taxis – 4,552, two wheelers – 1,91,838; three wheelers – 14,310 and others 766). Out of the 14,310 three wheelers, 60% of them are in Imphal West and Imphal East Districts which causes alarming automobile exhaust in the Imphal city (Please refer to The Sangai Express – 7 June, 2016).
Sampling and Collection of data
Eight spots (Keishampat Parking, Kangla traffic island, Palace gate, Nitaipat Chuthek traffic island, Khuyathong, Nupa Keithel traffic point, Sagolband parking and Sanjenthong near head post office traffic point) in Imphal city were selected. Two lichen genera viz. Dirinaria and Parmeliawere collected from the dominant trees. The dominant trees in the study rites were Gulmohar, Mango, Peepul, etc. For control, lichen species were collected from unpolluted areas of the Manipur University Campus, Canchipur.
SO2 concentration in Lichens
Determination of sulphur in the form of Sulphate was performed on two Lichen species (Dirinariaconsimilisand Parmeliapraesorediosa) following Cox (1977). The SO2concentration in Dirinariaconsimilis ranges from 0.25µg to 0.29µg. Whereas SO2 concentration of Parmeliapraesorediosa ranges from 0.24 µg to 0.27µg. In both lichen types, SO2concentration yielded less amount when collected both from controlled or unpolluted areas.
The highest SO2 concentration (0.30µg) was found in Dirinariaconsimilescollected from Sanjenthong near head post office traffic point followed by Khuyathong traffic point (.29µg). Parmeliapraesorediosawas more sensitive to SO2 than D. Consimilisas indicated by its absence in some study sites. Some sites have more or less similar patterns of lichen distribution and similar concentration of SO2 was recorded in the lichen body.
It was evident that the distribution of Dirinariaconsimilis was unique among the lichen species studied. It occurs at every site including those trees very near to the road. They were mostly abundant in the Kanglapat area where the Gulmohar trees are abundant. Their sparsity in other areas might be due to the absence of suitable trees rather than SO2 pollution in the air. It was the most tolerant foliose lichen of the sites showing 100% occurrence.
The occurrence of Parameliapraesorediosain the selected sites was more or less irregular and clearly affected by the polluted air from the motor vehicles. In the road areas where the trees were subjected to maximum exposure to automobile exhaust. P. praesorediosawas absent but present very rarely on few areas which were a little distance from the roads (in the range of 5m or more from the road.)
The data obtained during the course of analysis had clearly shown that SO2 content was very high in the lichen samples collected from road side trees (traffic points) in comparison to SO2content present in the lichen samples collected from the control site. The presence of higher concentration of SO2 in the lichen from road side might be due to the entry of SO2 gas through the stomatal opening in the lichen thallus and partly through the absorption by the rhizome. The results of the present survey indicate that auto exhaust emissions were sources of sulphur. There was also variation in the SO2 concentration in lichen specially between the one growing in heavy traffic areas like Kanglapat/BT road and less congestedsite like Sagolband area even though it is a parking area.
As mentioned earlier D.consimiliswas more tolerant of air pollution than Parmeliapraesorediosa. Finding a suitable, sufficiently common species for use as a bioindicatorwas usually problematic because it needs extensive survey. Because of the sensitivity of Parmeliapraesorediosa, it could be used as indicators in maping studies. The absence of Parmeliapraesorediosa might be due to the increase level of air pollutions from the automobile exhaust which has increasing dramatically during the last 2 (two) decades (The Sangai Express, 7th June, 2016). The increase in motor vehicle could be due to the increase in the population by various activities in Imphal city. There is a need arising for studies and data collection on lichens in Imphal city and its suburbs on which we can refer to further research on using lichens as biomonitor of environmental pollution.
Conclusion and Suggestion
Biomonitoring could be employed to detect toxic substances in the environment for their safe disposal control at source. The auto exhaust emission resulting from increasing number of auto vehicles in Imphal city specially at BT Road/Pologround auto parking place are responsible for air pollution in the air and the lichen can be used as biomonitors to indicate thelevel of air pollutants in the Kwairamband Bazar (Imphal city).
The lichen species like Parmeliapraesorediosa could be used as a sensitive tool for the assessment of the degree of atmospheric pollution at a particular area. Introduction of CNG vehicle in place of Diesel being used nowadays to the autos and EURO model engines and time totime monitoring of air quality are suggested before becoming Imphal, a Smart City. The Senior author is former Professor (Higher Academic Grade)/Life Sciences, Manipur University and Former Dean, School of Life Sciences, Manipur University and can be reached at [email protected] and the junior author is Additional Programme Manager, RMSA Chandel District, Government of Manipur.