Essay on Environmental Pollutants and Plants

Essay on the impact of environmental pollutants on plants!

The environment we live in is polluted greatly by biological activity. If the equilibrium among the activities of different organisms—plant, animal and micro­organisms is seriously disturbed, new equilibria have to be attained sooner or later but that may not be favourable to man or the plant or animal world. Although pollu­tion has been existent since time immemorial, it has assumed disturbing proportions since the industrial revolution and now it is almost alarming.

Since industries are usually situated in or near the cities, the environment of the cities and suburbs are most polluted. The effect gradually decreases with increase in distance. It has been estimated that Calcutta and Howrah air contains about 5.57 tons of dust, 122 tons of SO₂, 440 tons of CO, 70 tons of oxides of nitrogen and 102 tons of hydrocarbons every day.

The smoke produced by coal and oil combustion and automobile fumes combines with fog to produce the smog characteristic of most cities. Aerosols, which have both solid and liquid components are suspended in air or gaseous environments and quite often contain toxic ingredients which include heavy metals like Zn, Pb, Cu and Fe.

Sewage, agricultural and industrial waste discharges are the main causes of water pollution. Sewage discharges in the Dal lake of Kashmir and Loklak lake of Manipur has resulted in the development of extensive vegetation. The Sagar lake near Hyderabad has been polluted by inorganic effluents. The river Ganges receiving the sewage and industrial discharge from the cities on her banks is now one of the most polluted rivers of the world; the water is even unfit for bathing, not to speak of drinking purposes.

The water of the river Yamuna near Delhi is so polluted that it has to be diluted about 8000-fold to reduce its toxicity below permissible level. Important pollutants for river and oceans include heavy metals, halogenated hydrocarbons, petroleum, artificial radioactivity and litter.

Many of the pollutants mentioned above have mutagenic and carcinogenic pro­perties. Respiratory difficulties, nervous disorders, disabilities of various sorts and several other diseases have been reported. Concentration of population in cities, urbanisation, lack of consciousness of pollution hazards have further helped in the spread of pollution. The pathogens responsible for various diseases of man, viruses, bacteria, fungi and protozoa are multiplying and spreading biological pollution. Much less work has been done with plants.

The industries are producing huge quantities of gases which are escaping into the atmosphere of our earth every day. The gases include CO₂, CO, SO₂, H₂S, NH₃ C₂H₄, oxides of nitrogen and various hydrocarbons. The CO₂ concentration according to some estimates has increased considerably; although this should increase crop pro­ductivity the heat loss due to radiation will decrease, as CO₂ does not allow heat to pass through, resulting in an increase in temperature.

If this increase continues, a day will come when the snow caps on North and South Poles will melt, increasing the sea level to an extent that many coastal cities and low lying areas will be inundated. In­crease in CO₂ levels will also affect respiratory processes in both animals and plants. Carbon monoxide, which is considered to be a poisonous gas, may give rise to several diseases; it is poison for plants also, where it affects the cytochrome system.

The oxides of nitrogen, in addition to their harmful effects react with the ozone of our atmosphere, which provides a protective shield from the lethal and mutagenic ultraviolet radiation coming from the sun? This will affect both plant, animal and microbial life. The application of heavy doses of synthetic nitrogenous fertilizers is encouraging the ac­tivity of nitrifying and denitrifying bacteria; the latter group of microorganisms produces N₂O (in addition to N₂) which is dangerous in this respect.

The jet aircrafts are also discharging considerable quantities of nitrogen oxides into our atmosphere. The hydrocarbons in the exhaust fumes of automobiles and the discharges of petroche­mical industries are causing serious health hazards to men, plants and animals also. The industries are also throwing into our atmosphere, in addition to soot and dust particles, various compounds of metals like lead, mercury, arsenic, cadmium, etc. Plant life, particularly, trees are visibly affected in some parts of the Durgapur region.

Equally dangerous are the discharges from various industries, paper, leather, jute, cotton, iron and chemicals (see Table below). A variety of chemicals used in these in­dustries is thrown into river water as industrial waste. This is seriously affecting aquatic life—both flora and fauna.

During the past decade the aquatic flora of many places have changed. One of the reasons why Hilsa fish is becoming more scarce in the Ganga is pollution of Ganga water, particularly in certain regions and they are migrating to new places. The aquatic flora on which they live are gradually disappearing. Chemical wastes from industries are consumed by fish etc., which ultimately produce toxicity symptoms in man.

The havoc caused by industrial wastes containing mercury in the coastal region of Japan is well known. The oil refineries in our country are also polluting our waters. The various petroleum products float on water and plant life, both in water and on the river banks is seriously affected.

At Haldia tree planting on the strand is posing a problem. Polluted river water is dangerous for drinking and irrigation purposes.

Modern agricultural practices are also adding to pollution hazards. Thus, appli­cation of excessively high doses of fertilizers are encouraging the growth of unwanted plants and algal blooms, which produce organic matter via photosynthesis, and settle at the bottom of tanks and ponds.

Drainage water from agricultural lands contains inorganic salts, which are difficult to remove by conventional procedures and toxic compounds including pesticides used for plant protection purposes. Faulty irrigation of crops is also quite often responsible for salt and alkali accumulation; inadequate drainage leads to increased salinity of ground water.

The extensive use of fungicides, insecticides and agricultural chemicals has created serious problems. Many of the chemicals, though in small quantities, have found their way to human bodies through the crops and vegetables we use. It has been estimated that every one of us is carrying in his adipose tissues about 20 mg. of the insecticide DDT, the use of which has now been banned in many Western countries.

Consumption of crabs collected from rice fields receiving very high doses of pes­ticides caused unusual paralytic attacks in man. The agricultural use of seed dressing by mercury and industrial effluents resulted in the accumulation of mercury in fish and birds resulting in the thinning of eggs. Several cases of poisoning have also been reported in green house cultivations in Japan.

Many of the chemicals are not easily decomposed and are deposited in our soils to be carried by rain water to various regions. Burying of industrial water in the soil reduces water pollution but it is no solution since sooner or later it will be carried into river or sea water. Some of them may be reabsorbed by plants. The soil microbial life is also affected.

The extensive use of antibiotics in food processing, fodder and crop protection has contributed to the selection of microorganisms resistant to these antibiotics. Intensive cultivation of the so-called high-yielding cultivars, developed in foreign countries, where common pathogens of our country are non-existent, is replacing our less-yielding but relatively resistant cultivars and crop epidemics are becoming common. De­velopment of the Nagarjuna sagar dam in Andhra Pradesh has increased molyb­denum concentration of soil to such an extent that cereals like sorghum are experien­cing toxic conditions.

Air and other pollutants quite often lead to chlorosis, decreased photosynthesis and necrosis. Particulate matter containing magnesium and lime decrease crop yield, smoke soot suppresses growth, sulphuric acid droplets with moisture, blacken leaf surfaces and automobile fumes cause lead injury in crops. Lethal effects of pollutants on aquatic flora lead to a decrease in oxygen concentration of water, resulting in asphyxia of fish an other aquatic fauna.

The radioactive wastes from nuclear power plants cause radiation hazard to both plants and animals, whether buried in the soil or dumped in the sea. The radio­active fall-out from atomic or hydrogen bomb explosions are polluting air, land and water. ⁹⁰Sr which is usually present in such fall-outs is absorbed by plants which are used as fodder for cattle and the milk of such cattle contains the ⁹⁰Sr which ultimately replaces Ca in our bones becoming a potential carcinogenic source.

Sharma has suggested that induction of plants resistant to pollution may be very rapid, particularly when they are exposed to acute and chronic pollution hazards. The range of tolerance of the plant species may enlarge enabling them to survive in a polluted situation. This is of special ecological significance and plants showing such capability may be used effectively as indicators and pollutant scavengers.

Plants are also helping considerably in reducing the pollution hazards. Thus, the relatively higher CO₂ content of our atmosphere is gradually replaced by O₂ via pho­tosynthesis. A 50 ton tree may produce 1 ton O₂ per year. Many harmful gases are also absorbed by plants.

Soot dust particles (in India 40% of air pollutants are dust par­ticles) and industrial wastes in the particle form—including compounds of heavy- metals are collected by leaf surfaces—the total area of which is considerable. Many trees collect 1-5 gm dust per m- leaf surface. As they absorb various polluting substances from soil and water, they reduce their concentrations in the environment.

Some plants are particularly remarkable in this respect e.g., water hyacinth which has been found to grow luxuriantly in polluted water in several places, as it can remove many toxic com­pounds including metals, and the alga Porphyra, which accumulates Ru. But plants are probably suffering as much from pollution of our air, water and soil as animals do. Several microorganisms are now used for detoxification of water.

The products of de­gradation may even be useful in some cases—microorganisms capable of producing hydrocarbons which may be used as fuel or for utilising hydrocarbon—producing energy and food etc. will be particularly useful in this respect. Some plants introduced in this country have helped in the biological control of certain pests Eradication of alternate hosts of pathogens may also eliminate certain diseases.

Some plants may cause pollution themselves. The fungal spores and pollen grains of many plants are responsible for allergic diseases, particularly respiratory ones. The Cause of hay fever and several types of asthma has been traced to pollen grains. Grass pollen grams are particularly remarkable in this respect, but many other plants are equally dangerous. Plants like Parthenium which are multiplying rapidly are highly toxic and so are several other poisonous plants.

Seeds of Argemone mexicana which are used as adulterants of mustard seeds contain toxic principles. Many plants produce the so called allelochemicals which inhibit the growth of other plants. Since this is done on a large scale for establishment of a community, their implications are quite serious for plant life. The chemicals include abscissic acids, phenolics, alkaloids, terpenes and a variety of substances. Many bacteria and fungi produce toxins. Aflatoxin produced by Aspergillus flavus is posing a serious problem.

Pollution thus, is causing a serious problem, in as much as it is upsetting the eco­logical balance. While industrialization cannot be avoided, the polluting agents, whatever be their source, have to be identified and inactivated as far as possible. Fortu­nately people have become conscious of pollution hazards now and scientists in many countries of the world, including India, are studying the extent of various types of pollution and carrying on research for formulation of remedy measures to check or reduce pollution in our environment.

Meanwhile if pollution is to be controlled, it is essential that antipollution acts are strictly enforced, environmental education is encouraged in schools and colleges, agricultural and industrial wastes are adequately recycled and afforestation and tree planting are pursued intensively.

Use of bio-fertilizers and biological control methods, establishment of bioshpere reserves, conservation of resources in the Himalayas, Arunachal Pradesh, Himachal Pradesh etc., utilization of biomass as a source of energy, conservation of flora and fauna and social forestry are some of the other measures which have been suggested for the control of pollution in our country.