What are the Effects of Air Pollutions on Plants and Animals?

Air pollution certainly affects crop yields and, in California, crop losses caused by such pollution have been estimated to exceed $ 150 million annually. Studies carried out in England (see Edwards, 1972) have revealed significant reductions in the yields of such plants as radish, lettuce, various flowering annuals and other crops when grown in the more highly polluted parts of big industrial cities than in villages remote from such polluted zones.

The smelting of ores is also known to cause serious damage to vegetation. Pollutant particles some time settle down on leaves of nearby trees and may block the stomatal pores thus affecting gas exchanges, water relations and other physiological processes. Ozone can cause damage to palisade cells which lose water and disintegrate. At levels of 0.02 ppm, it damages tobacco, tomato, bean, pine and other plants (Papetti and Gilmore, 1971).

Peroxyacetyl nitrate attacks spongy mesophyll cells. Fluorides have been found to damage young plants of conifers. Fluorides are cumulative poisons which enter the leaves through stomata, are carried along with the water stream, and are concentrated along the leaf margin. Certain grasses can develop resistance against fluorides.

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Plants have evolved in a gaseous environment. When the composition of this environment exceeds the capacity of plants to tolerate or adapt to the change, some stress is imposed, and the sensitive components of the ecosys­tem start malfunctioning. Guard cells and cuticle are the first to be exposed to the pollutant gas. When the gas reaches inside the leaf, the cell membranes are affected.

Alterations occur in SH/SS ratio. There can be permeability dys­function as well. Free radicals are formed and ion transport can be inhibited and normal functions disrupted. Once within the cell, the pollutant interacts with cytoplasm, organelle membranes and cellular metabolites. Disulphide bonds in proteins can be split up. The overall effect of the above disturbances is that plant growth is impaired and productivity declines.

Plants growing in polluted environment often show symptoms of injury,’ general debility and premature ageing. In temperate countries, alfalfa has bee, found to be susceptible to SO₂ gladiolus to hydrogen fluoride, tobacco to ozone and petunia to photochemical smog. In the tropics, mango (Mangifera indica) has been reported to be especially sensitive to polluted air.

The aerial parts of the trees growing near thermal power stations, brick kilns, steel factories and smelters (habitats polluted with SO₂ and other pollutants) exhibited such symptoms as necrosis of leaves, defoliation of young terminal branches, hardening of floral buds, necrosis of stigmatic surfaces, necrosis of fruit tips, and reduction in fruit size (see Rao, 1972).

Recently the leaves of several plants such as Phaseolus vulgaris, Coleus blumei, Daucus carota, Ficus variegatus and others have been found to be capable of fixing carbon monoxide (Bidwell and Bebee, 1974). Some workers are of the opinion that vegetation can constitute a sort of global sink for air pollutants such as carbon monoxide (see Hill, 1971). The average CO concen­tration in air over major land masses ranges between 0.1 to 1.0 ppm, and Bidwell and Bebee have estimated that about 3 x 10¹⁴ grams of it may be fixed by various plants per year.

Sulphur oxides are highly toxic. Their effects include interveinal necro­ses and yellowing of broad-leaved plants.

Nitrogen oxides cause defoliation, chlorosis, necrotic spots, tip and margin burn, and general growth retardation.

Excessive dusting of plants with particulate matter can clog stomata thereby preventing gas and water exchange. Most plants are insensitive to carbon monoxide levels known to affect man, but at high concentrations, CO produces the following symptoms: leaf curling, ageing, and reduction in leaf size.