NeBIO (2010) Vol. 1(1) Govindapyari et al . 35-41 GENERAL ARTICLE Bryophytes: indicators and monitoring agents of pollution H. Govindapyari, M. Leleeka, M. Nivedita and P. L. Uniyal Department of Botany, University of Delhi, Delhi – 110 007 Author for correspondence: [email protected], [email protected] Received: 17 September 2009; Revised and Accepted: 2 January 2010 ABSTRACT Bryophyte proves to be a potential bio-indicator of air pollution. The habitat diversity, structural simplicity, totipotency, rapid rate of multiplication and high metal accumulation capacity make bryophytes an ideal organism for pollution studies. The decline and absence of bryophyte populations especially epiphytes is a phenomenon primarily induced by air pollution caused by gaseous and particulate pollutants. Bryophytes are reliable indicators and monitors of air pollution as they are easy to handle and show a vast range of specific sensitivity and visible symptoms to pollutants greatly exceeding that of higher plants. KEY WORDS: Bryophyte, bio-indicator, air pollution, pollutants. Bryophytes are green land plants which lack a • which have the capacity to absorb and retain vascular system and are simple both morpho- pollutants in quantities much higher than those logically and anatomically. The growth potential in absorbed by other plant groups growing in the bryophytes is not as highly polarized as vascular same habitat. These plants trap and prevent plants. Bryophytes grow in a variety of habitats recycling of such pollutants in the ecosystem especially in moist places on soil, rocks, trunks and for different periods of time. Analysis of such branches of trees and fallen log. They obtain plants gives a fair idea about the degree of nutrients directly from substances dissolved in metal pollution. ambient moisture. Some substances are probably absorbed directly from the substrate by diffusion Pollutants through the cells of the gametophyte. Bryophytes are used as reliable indicators of air pollution (Le Pollutants may be gaseous such as carbon Blanc & Rao, 1975). They are exploited as bryo- monoxide (CO), fluorides, hydrocarbons (HC), meters instrument for measuring phytotoxic air hydrogen sulphide (H 2S), nitrogen oxides (NO), pollution. They either independently or together Ozone (O 3), sulphur dioxide (SO 2), aldehydes, lead with lichens can be valuable organisms in develop- and automobile exhaust fumes. NO X and NH 3 are ing an index of atmospheric purity (IAP) which is primary gaseous pollutants which are strongly based on the number, frequency-coverage and phototoxic. SO 2 and NO 2 are readily converted to resistance factor of species. This index can provide strong acids by oxidation and solution in atmo- a fair picture of the long-range effects of pollution sphere as water droplets to form acid rain. The in a given area (Rao, 1982). There are two smoke and SO 2 is produced by the combustion of categories of bryophytes in response to pollution: traditional fuel of automobiles, together with vari- ous metals released into atmosphere by smelting • which are very sensitive to pollution and show and other heavy metal industries. Nitrogen oxides visible symptoms of injury even in the presence have also greatly increased in the cities with the rise of minute quantities of pollutants. This serve as of use of automobiles. Particulate pollutants are good indicators of the degree of pollution and dust, particles of metallic oxides, coal, soot and fly also of the nature of pollutant. ash, cement, liquid particles, heavy metal and 35 NeBIO Vol. 1(1) radioactive materials. Ozone (O 3) is a secondary organisms either individually or in combination of pollutant formed by the action of sunlight on two or more. The common symptoms of injury are nitrogen dioxide and on certain hydrocarbons. It is plasmolysis and chlorophyll degradation in the leaf more phytotoxic than the primary pollutants. NH 3 a cells. SO 2 exposed plants showed brownish spots on pollutant is also being released by intensive animal the chloroplasts and plasmolysis in cells of leaves rearing. Other pollutants are agricultural pesticides which contributed to the ultimate death of the and fertilizers and various forms of aquatic pollu- plants. When plants are exposed to SO 2, it get tion. The air pollutant either in a gaseous state absorbed in the plant tissue which causes degrada- mixed with air or in a liquid state affected by dew, tion of chlorophyll a by increasing the concen- rain, or snow, will be noxious to bryophytes attac- tration of free H+ ions which subsequently displace hed to the bark. the Mg 2+ ions from the chlorophyll molecule, converting it into phaeophytin a. The typical Effect of pollutants on bryophytes response of mosses to SO 2 pollution begin as a loss of colour at the tips of the more exposed leaves and There is an impoverishment of bryophytic commu- this gradually extends down the leaves and down nities in and around cities and industrial areas the shoots until they have lost all the chlorophyll. (Gilbert, 1968).Urban areas comprise a series of Chronic injuries such as growth retardation are habitats with a variety of substrates and moisture seen. Low exposure of plants to hydrogen fluoride regimes and are subject to varying levels of poll- (HF) results in the minimal injury and accumulation ution. Bryophytes occupying certain substrates of fluoride to this plant is low. Once hydrogen appear to more sensitive to air pollution than others. fluoride (HF) is adsorbed on the plant surface, it Bryophytes have been disappearing from urban moves towards the tip of leaves causing a distinct industrial environments because of their sensitivity pattern of injury which remain proportional to the to polluted air. Species diversity in a polluted area exposure. Ozone uptake by the plant species often varies not only with the distance from the source of results in acute injury, premature ageing and pollution but also with the type of substrate. senescence. Bryophytes show impairment of photosynthesis or increased membrane leakage Air pollution inhibits gametangial formation and when subjected to an acute (150 p.p.b) ozone sexual reproduction in bryophytes. They also red- exposure. Several species of Sphagnum species uce photosynthesis by degrading chlorophyll and were found to be chronic to O 3 exposure. Ammonia growth of plants and eventually cause their death. (NH 3) is highly phytotoxic (Greven, 1992). Leaf tip Metals and metalloid are accumulated by bryop- chlorosis is followed by necrosis when plants were hytes from the substratum, wind-blown or in wet exposed to NH 3. Acid rain has two distinct effects deposition. When the metal enters the cell, it like wet deposited acidity and wet atmospheric inhibits the photosynthetic activity. Enzymes and deposition of the nutrients such as nitrogen and membrane are poisoned when a heavy metal gains sulphur. Acidification may damage cell membranes, access to the cell interiors. Mercury is particularly solubilize potentially toxic metals like Al 3+ and toxic low concentration greatly inhibited photosyn- worsen the impact of other pollutants like SO 2 thesis, temporarily increased respiration, reduced (Farmer et al., 1992). Acid rain produces drastic chlorophyll levels and caused loss of intracellular changes in the chemical properties of both K+ from Rhytidiadelphus squarrosus (Brown & epiphytes and their bark substrates by reducing the Whitehead, 1986). It is evidenced that when the pH of stem flow, increasing the proportion of toxic 2- pollution level goes down, the percentage frequency bisulphate (HSO 3 ) ions in stem flow, decreasing of species goes up, which subsequently increases the buffer capacity of the bark, decreasing the the fertility percentage. This situation varies from internal pH of the epiphytes and increasing the species to species depending on the prevailing metal concentration and chlorophyll loss in climatic conditions in the area. Bryophytes die epiphytes. Lead (Pb) pollution is caused by anti- within a short period of time depending on the level knock compounds consisting of tetramethyl lead. of pollution, when transferred along with their Pb contents in the plant correspond to the respective substrates from unpolluted to polluted areas in a traffic intensities and without significant correlation city or around a factory. The pollutants can affect to the lead content of the soil. Aquatic bryophytes 36 NeBIO Vol. 1(1) accumulate heavy metals from contaminated water habitat to habitat under different microclimate to a much greater extent than vascular plants as the conditions. Among mosses the profusely branched metal uptake is less seasonal and partly because and ramifying pleurocarps and the densely packed they can absorb over their entire surface. Uptake of acrocarps are more efficient entrappers and abso- mercury by Jungermannia vulcanicola and rbers of metal particles than the unbranched and Scapania undulata involved the formation of erect acrocarps. Accumulation of mercury is found crystals of HgS in the cell walls of these taxa greater in Dicranum scoparium. Bryophytes are (Satake et al., 1990). Chlorinated hydrocarbons able to concentrate heavy metals in large amounts, may be accumulated by adsorption on to aquatic greatly surpassing the absorbing capacity of bryophytes (Mouvet et al., 1993). Funaria leaves vascular plants. The gametophytes of moss can showed apical necrosis disintegration of chlorop- accumulate iron 5-10 times more readily than the lasts and plasmolysis in their cells and other cellular vascular plants. The concentration of Al, Ba, Cr, abnormalities. Radioactive isotopes get accumu- Cu, Fe, Ga, Ni, Pb, Ag, Ti, Vi, Zn and Zr were lated in bryophytes from the fallout from nuclear higher in bryophytes than those in angiosperms. weapons testing (Burton, 1968). Bryophytes behave The bryophytes are able to concentrate rare earth as perfect sinks for atmospheric deposition of elements. Elements which are rarely founds in other isotopes (Svensson & Liden, 1965). The ionizing plants were found in bryophytes. Bi were found in radiations activate plant cell molecules and thus the thallose liverworts like Conocephalum conicum quicken chemical reactions.