Agro-chemicals and their effects

Agrochemicals-pesticides and weedicides :

A number of chemicals have been developed to kill a variety of pests in order to improve agriculture, forestry, horticulture and water reservoirs.

The most widely used among them are insecticides.

Most of these insecticides are broad spectrum and affect other animals, man and even plants.

They are, hence, also called biocides.

These include:

(i) Organo insecticides: They include DDT, PCB, Aldrin, BHC (benzene hexachloride) etc. Chlorinated hydrocarbons are toxic. Besides being toxic, these pesticides are both persistent and mobile in the ecosystem. The chlorinated hydrocarbons like DDT results in biological magnification.

Organophosphorus compounds (e.g., malathion, parathion) and organocarbamates are degradable but they influence the nervous system.

(ii) Weedicides (Herbicides) : The weedicides or herbicides are usually metabolic inhibitors which stop photosynthesis and other metabolic activities and hence kill the plants.

2. Industrial wastes:

Both solid and liquid wastes of the industry are dumped over the soil.

The wastes contain a number of toxic chemicals like mercury, copper, zinc, lead, cadmium, cyanides, thiocyanates, chromates, acids, alkalies, organic solvents etc.

3. Mine dust:

It is a major source of poilution in mining areas.

Mine dust not only spreads with wind but also spread over a large area during transportation to purification plants.

4. Fertilizers:

Excessive use of chemical fertilizers causes soil deterioration through the decrease in natural bacterial population (nitrogen fixing, nitrifying, etc.) and destruction of crumb structure.

The salt content of the soil is also bound to increase with continuous use of fertilizers.

Case Study of Organic Farming

Integrated organic farming is a cyclical, zero-waste procedure, where waste products from one process are cycled as nutrients for other processes.

This allows the maximum utilisation of resources and increases the efficiency of production.

Ramesh Chandra Dagar, a farmer in Sonipat, Haryana, is doing just this. He includes bee-keeping, dairy management, water harvesting, composting and agriculture in a chain of processes, which support each other and allow an extremely economical and sustainable venture.

There is no need to use chemical fertilisers for crops, as cattle excreta (dung) are used as manure.

Crop waste is used to create compost, which can be used as a natural fertiliser or can be used to generate natural gas for satisfying the energy needs of the farm.

Enthusiastic about spreading information and help on the practice of integrated organic farming, Dagar has created the Haryana Kisan Welfare Club, with a current membership of 5000 farmers.

SOLID WASTE

Solid wastes refer to everything that goes out in trash.

Sanitary landfills were adopted as the substitute for open-burning dumps where in a sanitary landfill, wastes are dumped in a depression or trench after compaction, and covered with dirt everyday.

But these sites are getting filled too and seepage of chemicals, etc., from these landfills pollutes underground water resources.

Anthropogenic solid waste is categorised into three types -(a) bio-degradable, (b) recyclable and (c) the non-biodegradable.

Polyblend, a fine powder of recycled modified plastic, was developed by the company owned by Ahmed Khan in Bangalore.

This mixture is mixed with the bitumen that is used to lay roads.

Blends of Polyblend and bitumen, when used to lay roads, enhanced the bitumen's water repellant properties, and helped to increase road life by a factor of three.

The use of incinerators (burning in presence of O₂ at 900-1200°C) other is pyrolysis (anaerobic burning at 16S0°C) is crucial for disposal of hospital waste.

Irreparable computers and other electronic goods are known as electronic wastes (e-wastes). E-wastes are buried in landfills or incinerated.

Over half of the e-wastes generated in the developed world are exported.

Recycling is the only solution for the treatment of e-wastes, provided it is carried out in an environment-friendly manner.

Developing countries like China, India and Pakistan imports over half of the e-waste generated by developed countries for recovery of metals like copper, iron, silicon, nickel and gold.

RADIOACTIVE WASTES

It is physical pollution of air, water and soil with radioactive materials.

Radioactivity is the property of certain elements (radium, thorium, uranium etc.) to spontaneously emit protons (alpha particles), electrons (beta particles) and gamma rays (electromagnetic waves of very short wavelength) by disintegration of their atomic nuclei.

The elements that give radiation are called radioactive elements.

The use of nuclear energy has two very serious inherent problems.

The first is accidental leakage, as occurred in the Three Mile Island and Chernobyl incidents and the second is safe disposal of radioactive wastes.

It causes mutations to occur at a very high rate.

At high doses, nuclear radiation is lethal and at lower doses, it creates various disorders, the most frequent of all being cancer.

It has been recommended that storage of nuclear waste, after sufficient pre-treatment, should be done in suitably shielded containers buried within the rocks, about 500 m deep below the earth's surface.

Production of nuclear weapons involves the tests of nuclear arms.

These tests produce large amount radioactive elements into the environment and make other materials also radioactive. They include strontium-90, cesium-137, iodine-131 and some others.

The radioactive materials are transformed into gases and fine particles which are carried to distant places by wind.

When rain drops, the radioactive particles fall on the ground, it is called fall out.

Strontium-90 accumulates in the bones, replaces calcium and may cause bone cancer and tissue degeneration in most animals and man.

The operation of a nuclear power plant releases large amounts of energy.

This energy is used in large turbines, which produce electricity.

Wastes from atomic reactors also contain radioactive materials.

The biggest problem is the disposal of these radioactive wastes.

If these wastes are not properly disposed off, can harm the living organisms wherever they may be dumped.

NOISE POLLUTION

The quality of our environment is judged, apart from other factors, by the amount of noise present.

Noise has been defined as "unwanted sounds" which is being "dumped" into the atmosphere to disturb the unwilling ears.

It adversely affects our physiological and mental health.

Noise is measured by a sound meter and is expressed in a unit called decibel (dB).

Any value more than 80 dB causes noise pollution.

Noise becomes unbearable at 140 dB.

The quietest sound that man's ear can detect is known as threshold of hearing.

A noise that hurts one's ears and gives headache is called threshold of pain.

The role of sound vibrations is measured in cycles per second (cps) or hertz (Hz).

The ear is potentially liable to damage, if it receives high intensity noise.

Noise in general is a physical form of pollution.

It has no persistent adverse effects on the life supporting systems but, has direct effects on the recipients.

Moderate conversation = 60 dB

Loud conversation = 70 dB

Scooter = 80 dB

Truck / Bus = 90 dB

Jet aeroplane = 150 dB

Rocket = 180 dB

Zone-wise permissible ambient noise levels (acoustic zoning) are given below. (According to central pollution control board)

I. Sources of Noise Pollution

Noise can either be natural like thundering sound or man made. The main sources of man made noise pollution are:

(i) Annoying and damaging sounds of various industries.

(ii) Defence material like rockets, tanks etc.

(iii) Entertainment sources like record players, radios, cassette players, loud speakers etc.

(iv) Transport automobiles and other vehicles such as trucks, buses etc.

II. Effects of Noise Pollution

Noise causes some serious damaging effects which are briefed as follows :

(i) Diminish hearing. Noise damages the ears, causes temporary or permanent noise induced hearing loss, depending upon the intensity and duration of the noise level. It leads to auditory fatigue and may finally lead to deafness. A sudden loud noise of any explosion may damage the tympanic membrane permanently. Sudden noise is more harmful than the continuous one. Factory workers suffer chronic hearing loss after many years of occupational noise exposure.

(ii) It has adverse effects on thinking and coordination of limbs.

(iii) Noise affects verbal communication on which we depend in all kinds of environment.

(iv) Noise increases blood cholesterol level, causes high B.P., digestive spasm, decreased heart output, defective night and colour vision. It impairs the development of nervous system of unborn babies which leads to abnormal behaviour in later life.

Control of Noise Pollution

Noise pollution can be controlled by following measures :

(i) Green muflur scheme. Trees such as Neem and Ashoka absorb sound vibrations to a great extent. Plantation of these trees on both sides of the roads, around silent zones reduces the menace of noise pollution.

(ii) Sound absorbing material should be used for reducing industrial noise.

(iii) Noise producing agencies should be located far away from residential areas. Vehicular traffic should be directed away from the human dwellings, educational institutions and hospitals etc.

(iv) General awareness should be developed among the people to minimize noise pollution in the environment.

GLOBAL ENVIRONMENT CHANGE

CO₂, CH₄, N₂O and CFCs are radiatively active gases and also called green house gases.

The increased amounts of these gases in atmosphere is affecting the global climate and this phenomenon is known as global climatic change.

I. Green House Gases and Global Warming

(i) Term green house effect was coined by Arrhenius.

(ii) Green house gases trap the long wave radiations. A part of this energy is re-radiated back to the surface of earth. The downward flux of long wave radiation by green house gases is called green house flux.

(iii) The phenomenon of keeping the earth warm due to presence of certain radiatively active gases in the atmosphere is called green house effect, without which the average temperature of earth would have been between -18°C to -20°C rather than present average of 15°C.

Relative contribution of different green house gases to global warming

(iv) The excessive increase in concentrations of these gases in the atmosphere would retain more and more of the IR -radiation (long wave radiations), resulting in enhanced green house effect.

(v) CFC is most effective green house gas (effectiveness is 14,000 times more than CO₂),

Effects of Green House Gases

(a) CO₂ fertilization effect: Increase in atmospheric concentration of CO₂ increases productivity of C₃ plants and decreases rate of transpiration due to partial stomatal closure.

(b) Possible Effects of Global Warming

(i) Increasing of global temperature (increased 0.6°C, most of it during last 3 decades) and more extreme climatic conditions [EI Nino effect].

(ii) Warming of troposphere and cooling of stratosphere and thermosphere.

(iii) Global warming will push tropics into temperate areas and temperate areas towards pole (shifting of climatic zones) and higher altitudes in mountains resulting into changed species distribution.

(iv) Melting of ice caps.

(v) Rising of sea level, changes in rainfall pattern.

Control measures -Reduced deforestation, cutting down use of fossil fuel, planting trees, slowing down population growth.

II. Ozone Depletion

(i) Ozone layer is present in stratosphere at altitude of 23-25 km (conc. 0.3 ppm) and act as shield against UV radiation.

(ii) Large hole has appeared in ozone shield over Antarctica and smaller one over North pole. (Discovered by Farman 1985).

(iii) Ozone is commonly called as chemical weed, 'Bad' ozone is formed in troposphere that harms plants and animals. Good ozone is found in stratosphere as shield.

(iv) ODS: ozone depleting substances -CFC, CH₄, CCl₄, halons and N₂O causes destruction of O₃.

(v) CFC's are most damaging. They release Cl free radicals in stratosphere which destroy O₃.

(vi) Thinning of the ozone-layer results in an increase in the UV-B radiation.

(vii) UV -B damages DNA and mutation may occur. It causes aging of skin, damage to skin cells and various types of skin cancers. A high dose of UV-B causes inflammation of cornea called snow blindness.

(viii) Nowadays CFC's are being replaced by Hydro Fluoro Carbons (HFCs).

DEGRADATION BY IMPROPER RESOURCE UTILISATION AND MAINTENANCE

The lowering of quality, fertility and productivity of land by various factors such as salination of soil, soil erosion, desertification, shifting cultivation and developmental activities etc. is called land degradation. It is caused by five main factors :

(i) Developmental activities:

Many developmental activities such as rapid urbanisation, human settlement, mining, construction of roads, dams, canals, railways, airports, playgrounds, industries cause loss of large areas of fertile and productive land.

(ii) Soil erosion:

It is the removal of top, fertile, mineral rich soil layer by water, floods, wind, ocean waves, glaciers, felling of trees, overgrazing on slopes or some arid soils, over cropping and improper farming techniques etc. It occurs in both wet and arid regions. Roots of grasses are excellent binding material and keep the soil intact and free from soil erosion.

(iii) Desertification:

It is the change of fertile soil into a non productive desert soil. It is due to the shifting of sand dunes by strong winds, or by deforestation, soil erosion or overgrazing in lands sparsely covered by grasses. Many deserts in the world are man-made. Afforestation is the only solution to prevent desertification.

(iv) Shifting cultivation:

In many tribal communities of tropical and subtropical regions of Africa and Asia, it is a practice of slashing, cutting down trees, burning the felled trees and raising crops on the ash formed. This practice is called 'Jhum Cultivation' in north east India. This destroys forests and causes soil erosion.

(v) Salination of Soil:

Increase in the concentration of soluble salts in the soil is called salination. Origin or development of saline soil depends upon following factors:

(a) Poor Drainage of Soil: Salts dissolved in irrigation water accumulate on the soil surface due to inadequate drainage especially during flood.

(b) Quality of Irrigation Water: The ground water of arid (dry, barren having not enough rainfall to support vegetation) regions are generally saline in nature. The irrigation water may be itself rich in soluble salts and add to salinity of soils.

(c) Excessive use of basic fertilizers: Excessive use of alkaline fertilizers like sodium nitrate, basic slag, etc may develop alkalinity in soil.

(d) Saline nature of parent rock materials: If soil develops from saline nature of parent rock materials, soil would be saline.

Control of degradation : Degradation can be checked by the following measures :

(i) Reforestation and plantation of grassess can check soil erosion, floods and water logging.

(ii) Crop rotation and mixed cropping improve fertility. It would increase production, which would support large population.

(iii) Salinity of the soil can be checked by providing adequate drainage.

(iv) Desertification can be checked by artificial bunds or covering the area with suitable soil binding vegetation.

DEFORESTATION

It is the conversion of forested areas to non-forested ones. It is estimated that almost 40 per cent forests have been lost in the tropics, compared to only 1 per cent in the temperate region.

At the beginning of the twentieth century, forests covered about 30 per cent of the land of India. By the end of the century, it shrunk to 19.4 per cent, whereas the National Forest Policy (1988) of India has recommended 33 per cent forest cover for the plains and 67 per cent for the hills.

Trees are axed for timber, firewood, cattle ranching and for several other purposes. Slash and burn agriculture, has also contributed to deforestation.

One of the major effects of deforestation is increased carbon dioxide concentration in the atmosphere. It also causes loss of biodiversity due to habitat destruction, disturbs hydrologic cycle, causes soil erosion, and may lead to desertification in extreme cases.

Reforestation is the process of restoring a forest it may also occur naturally in a deforested area.

Case Study of People's Participation in Conservation of Forests

A Bishnoi woman of Khejarli village, Jodhpur, Rajasthan named Amrita Devi showed exemplary courage by hugging a tree.

Amrita Devi Bishnoi Wildlife Protection Award - for individuals or communities from rural areas that have shown extraordinary courage and dedication in protecting wildlife.

Chipko Movement. It is movement which was initially meant for protecting trees but not meant for preservation of environment including habitat and wildlife. Chipko movement was born in March 1974 in Gopeshwar in Chamoli district. The movement has two leaders, Chandi Prasad Bhatt of Gopeshwar and Sunder Lal Bahugana of Silyara in Tehri region. A similar movement was undertaken by Paudurang Hedge in the South. It is known as appiko movement.

Government of India in 1980s has introduced the concept of Joint Forest Management (JFM) so as to work closely with the local communities for protecting and managing forests.

ENVIRONMENTAL LAWS FOR CONTROLLING POLLUTION

Important legislations directed at the protection of environment in India are listed below:

(i) The Environment (Protection) Act, 1986

(ii) The Insecticide Act, 1968

(iii) The Water (Prevention and Control of Pollution) Act, 1974

(iv) The Air (Prevention and Control of Pollution) Act, 1981 (Amended in 1987 to include noise as an air pollutant.)

International Initiatives for Mitigating Global Change

The long-term challenge of stabilising the atmospheric concentrations of greenhouse gases requires that global emissions be significantly lowered than what they are today.

In 1987, many countries signed the Montreal Protocol (effective in 1989) at Montreal (Canada), a landmark international agreement to protect the stratospheric ozone by agreeing to limit the production and use of ozone-depleting substances, phasing out of ozone-depleting substances and helping the developing countries to implement use of alternatives to CFCs.

The United Nations Conference on Environment and Development (UNCED, Earth Summit), held at Rio de Janeiro, Brazil in 1992, established the principles for reducing greenhouse gas emission.

The Kyoto Protocol, approved by a follow-up conference held in Kyoto, Japan, during December 1997, has specified the commitments of different countries to mitigate climate change.

This protocol requires countries to take appropriate measures to reduce their overall greenhouse gas emissions to a level at least 5% below the 1990 level by the commitment period 2008-2012.