This article throws light upon the top three environmental problems with preventive measures.
The top three environmental problems are: (1) Greenhouse Effect and Global Warming (2) Depletion of Ozone and (3) Acid Rain. The global environmental problems along with the environmental sustainability and biotechnology are briefly described below.
Problem # 1. Green House Effect and Global Warming:
The earth receives solar energy from the sun in the form of short wave radiations (mostly visible light). This solar energy is absorbed by the earth’s surface and emitted into the space as long-wave (infra-red) radiations. If the incoming radiations from the sun and the outgoing radiations from the earth are equal, then a good balance between the absorbed and emitted energy by the earth is maintained. But this does not happen.
The incoming short-wave radiations (from the sun) can easily pass through the atmosphere while the outgoing long-wave radiations (from the earth) are partially absorbed by certain gases in the atmosphere. Greenhouse effect refers to the phenomenon of retention of earth’s heat by the atmosphere. The consequence of greenhouse effect is global warming.
Green House Gases:
The gases that cause greenhouse effect are collectively referred to as greenhouse gases (Fig. 60.1). The most important greenhouse gases are carbon dioxide (55%), methane (15%), chlorofluorocarbons (17%), nitrous oxide (6%) and several other gases like carbon monoxide, nitrous oxide, ozone, sulfur dioxide, fluorine, bromine and iodine (7%). The presence of water vapour in the atmosphere in association with greenhouse gases significantly contributes to global warming.
Sources of greenhouse gases:
The important sources of major greenhouse gases are given in the Table 60.1. Fossil- fuel combustion, decomposition of organic wastes, deforestation and industries largely contribute to greenhouse gases. Chlorofluorocarbons (CFCs) are synthetic chemicals widely used in the preparation of refrigerants, solvents and aerosol propellants.
CFCs are dangerous environmental pollutants that significantly contribute to greenhouse effect. The global warming potential of CFCs is around 7,000 in comparison to CO2 taken as 1, methane 11 and nitrous oxide 260.
The relative contribution of total greenhouse gases from the major contributing sources is given here
Fossil-fuel combustion and anaerobic decomposition of organics – 57 %
Chlorofluorocarbons – 17%
Deforestation – 8%
Other – 3%
Effects of greenhouse gases and global warming:
The natural occurrence of greenhouse effect is essential for the existence of life on earth. For instance, it is only due to the presence of CO2 and water vapour, the mean temperature of the earth’s surface is around 17°C. In their total absence, the temperature would have been around -17°C, where life cannot exist. The main problem is the ever increasing concentrations of the greenhouse gases in the atmosphere that are resulting in irreversible and highly dangerous climatic changes.
The effects of global warming contributed by greenhouse gases are listed below:
1. Increase in temperature:
There occurs a general warming up of the atmosphere due to greenhouse gases. It is estimated that the temperature increases by about 0.3°C per decade.
2. Changes in sea level:
Due to a rise in temperature, there occurs thermal expansion of oceans and melting of glaciers, ice sheets and ice caps. The net result is an increase in sea level. It is estimated that during the last 100 years, the average sea level has risen by about 20 cm. As per the present prediction, the sea level is expected to rise by 20-30 cm in the next 2-3 decades. Rise in sea levels may be disastrous to some low-lying areas e.g. Netherlands, Maldives.
3. Water imbalance:
The warmer world would have less water available on the earth and this may lead to water crisis.
4. Crop yield:
Due to a rise in temperature, the agricultural production may be reduced. There may also occur, dislocation of crop lands. Some researchers however, predict that the crop yield may be higher in some areas due to increased availability of CO2.
Some disturbances in the ecosystem and the existence of living organisms may not be ruled out.
6. Human health:
The changing climatic conditions, due to global warming, may adversely affect human health. For instance, the risk of spreading major tropical diseases (malaria, filariasis, schistosomiasis, dengue fever, yellow fever) would be higher.
Measures to Control Green House Effect:
The major contribution of greenhouse gases comes from the developed countries. Thus, with a world’s population of about 15%, these countries contribute to as much as 65% of greenhouse gases. This is mostly because of industrialization and changing life styles of people. It is therefore, natural to expect that the developed countries significantly contribute (finances and resources) for the containment of global warming.
There is a worldwide concern on the alarming impact of global warming due to greenhouse effect. Several steps are being taken at the international and national levels for the protection of environment with particular reference to greenhouse effect.
Some of the important approaches for the management of greenhouse effect with special reference to biotechnology are briefly described:
1. Renewable forms of energy:
The various forms of energy generation (fossil-fuel burning, fuel wood combustion) are intimately linked to the production of greenhouse gases. Switching over to renewable forms of energy (the best being solar source) is highly desirable.
Deforestation is major concern. Growing of plants wherever possible and reforestation are the need of the hour. Plants will take up atmospheric CO2 and generate O2, and thus significantly help to reduce the greenhouse effect.
3. Development of energy-efficient industries:
Attention should be directed for the technological advancement of industries with low energy consumption. And wherever possible, renewable sources of energy should be used.
4. Nuclear power industries:
Cost-effective installation of nuclear power stations is advocated. This will certainly help to solve energy crisis, besides minimizing the greenhouse effect. But care should be taken for a safe disposal of nuclear wastes.
5. Other energy sources:
Generations of energy from different sources that do not produce CO2 are desirable. These include hydroelectric energy, solar energy, wind energy, geothermal energy and tidal energy.
6. Minimal use of CFCs:
Chlorofluorocarbons significantly contribute to the greenhouse effect. They contribute to about 17% of greenhouse gases. CFCs are about 4,000-7,000 times more potent than CO2 in causing greenhouse effect. For these reasons, many environmentalists advocate a halt for the production of CFCs. This is not practicable, since CFCs have become a part of the life system of a modern man. Hence, their minimal use is advocated.
As is evident from the above discussion, the greenhouse effect can be minimized by reducing the addition of CO2, CFCs, methane and nitrous oxide to the environment.
Problem # 2. Ozone Depletion:
Ozone (O3) is a blue coloured gas with a pungent smell. It forms a thick layer in the stratosphere of the atmosphere (16 to 40 km). The concentration of ozone is in the range of 2-8 ppm (parts per million by volume) depending on the distance.
Generation of ozone:
Ozone is produced naturally when oxygen is dissociated by solar ultraviolet radiations (80-240 nm).
(M represents a third body molecule like N2 or O2).
Beneficial affects of ozone:
Ozone is capable of absorbing ultraviolet radiations from the sun (200-300 nm) so that they do not reach the earth and cause health hazards (described later). In this process, ozone dissociation occurs as follows.
Thus, ozone is constantly being generated and destroyed in the stratosphere.
Depletion of Ozone:
There are a number of pollutant gases in the stratosphere-nitric oxide (NO), nitrous oxide (N2O), chlorine (CI) and chlorofluorocarbons (CFCs like chlorofluoromethane or freon) that can react with ozone to produce oxygen. The net result is that the ozone gets depleted in the stratosphere of the atmosphere.
There are three major mechanisms for the destruction of ozone-nitrogen system, hydrogen system and chlorine system.
About 60% of the ozone destruction occurs by nitrogen system. Nitrous oxide (N2O), produced by the microbial action in soils and oceans enters the atmosphere and reaches the stratosphere. Here, in the presence of light, N2O reacts with nascent oxygen (O) to form nitric oxide (NO). The latter is a powerful destroyer of ozone.
Approximately 10% of the ozone is destroyed by hydrogen system. The hydroxyl (OH) group that reacts with ozone is mostly derived from water, and to a lesser extent from methane.
The reactions involving H2O are shown below.
Chlorofluorocarbons (CFCs) and natural chlorine can also destroy ozone to a significant extent. CFCs on dissociation form CI which acts on ozone, as shown below.
Besides the major systems described above, there are several other compounds that can destroy ozone. A group of chemicals namely halons, widely used in fire extinguishers, are important in this regard. The major halons are bromochloroflurocarbons and bromofluorocarbons.
It was in 1987, the first evidence for the depletion of ozone over the entire Antarctic content came to light. This is regarded as ozone hole, and the depletion of O3 was observed between 12 to 24 km altitudes. Later evidence indicated that the occurrence of ozone hole over Antarctic continent is an annual phenomenon, during August and September. The factors for the causation of ozone hole are not clearly known.
The present belief that the chlorine and chlorine radicals are mainly responsible for ozone hole. It is feared that more ozone holes may develop which is highly dangerous.
Effects of Ozone Depletion:
Ozone acts as a filter of ultraviolet radiations from the sun with a result that the hazardous UV rays do not reach the earth. The biologically active UV radiations (UV-B) are in the range of 2.9 × 10-7 nm to 3.2 × 10-7 nm. They are highly sensitive for ozone depletion. UV-B radiations cause several harmful effects to the living (humans, animals, plants) and non-living (materials) systems on earth. Some of them are briefly described.
Effects on human health:
1. The incidence of skin cancer (melanoma) is very high in the population exposed to UV-B radiations. Melanoma is associated with overexposure to sunlight-mostly found in people who spend more time outdoors. It is estimated that with every 1% decrease in ozone layer, there would be an increase of about 3% in the skin cancers of people.
2. UV-B radiations may damage DNA and cause mutations that may result in various types of cancers.
3. Exposure to UV-B radiation is also associated with several other health complications-damage to eyes, decreased immune response, and increased incidence of several infections.
Effects on terrestrial plants:
1. Exposure to UV-B radiations in some plants may result in reduced growth and smaller leaves, with a reduced efficiency of photosynthesis.
2. The quality and quantity of foods are adversely affected.
3. Retardation in the growth of forests.
Effects on aquatic ecosystems:
1. The aquatic life is very vulnerable to UV-B radiations, particularly up to a depth of 20 m in clear waters and a depth of 5m in unclear waters.
2. Harmful effects have been observed in fishes, crabs, shrimp and zooplanktons.
3. There occurs a reduction in the photosynthetic efficiency of phytoplankton.
Measures to Control Ozone Depletion:
The only effective way of controlling ozone depletion is the complete elimination of the factors responsible for it. As already described oxides of nitrogen, chlorofluorocarbons and halons largely contribute to ozone destruction. These are the environmental pollutants and reduction in their production/utilization will largely help to control ozone depletion.
Problem # 3. Acid Rain:
The normal rain water is slightly acidic with a pH in the range of 6-7. This acidity is contributed by the naturally occurring CO2 which gets dissolved in the rain water to form carbonic acid.
CO2 + H2O → H2CO3
The lowest pH of the normal rain is around 5.6.
When the pH of the rain water is less than 5.5, it is considered as acid rain. This acidity is predominantly contributed by two acids namely sulfuric acid and nitric acid and to a lesser extent by hydrochloric acid and organic acids.
Development of Acid Rain:
As the industrialization world over increases, there is an increase in the environmental pollution by oxides of sulfur and nitrogen. These gaseous pollutants are light and they can be carried away (from the site of production) to hundreds and thousands of kilometers by the winds. Thus, the export of the acid forming pollutants may occur from one region to another region and from one country to another country. For this reason, acid rain is a global problem.
The following reactions summarise the formation of acid rain from the oxides of sulfur (SOx) and oxides of nitrogen (NOx).
In the development of acid rain, there occurs diffusion of SO2, and diffusion of HNO3 gas into the cloud particles/droplets.
Effects of Acid Rain:
Acid rain disturbs the environment. The actual effects of acid rain depends on the degree of the acidity and the nature of the environment-aquatic, terrestrial, human population and materials. Some of the important aspects are described.
Effects on aquatic environment:
The aquatic system is very sensitive to acid rain. With periodical falls of acid rains, the lakes become more and more acidic:
1. The fishes and other aquatic organisms including microorganisms are very sensitive to pH. At a pH below 4, most of them die.
2. The serving fishes contain high concentrations of toxic metals such as mercury, aluminium, lead and zinc (these metals find their entry into lakes by leaching of surrounding rocks by acid rain).
Effects on terrestrial environment:
1. Acid rain damages forests and all forms of vegetation.
2. Soil acidification, due to acid rain, may lead to necrosis of leaves.
3. Plants also accumulate several toxic metals e.g. aluminium, cadmium, mercury, lead.
Effects on human health:
1. Sulfuric acid of acid rain is very dangerous, as it causes breathing problems.
2. The toxic metals (Cd, Zn, Hg, Cu, Al) liberated from rocks and soils by acid rain may ultimately reach the human body through plants and animals through food chain or drinking water. The toxic effects of these metals on humans are well known.
Effects on materials:
The acid rain causes deterioration of buildings, marble rocks, limestone’s etc. Thus, acid rains have become a big threat to preservation of monuments and cultural heritages throughout the world.
Measures to Control Acid Rain:
The most effective measure to control acid rain is to drastically reduce the production of acid- forming gases i.e. the industrial emission of oxides of sulfur and nitrogen should be minimized.
Some measures have been taken to reduce the SO2 emission into atmosphere-desulfurification of the fuels used in industries, recovery of SO2 as H2SO4.
More concrete measures need to be taken globally for effective control of acid rain.
Environmental Sustainability and Biotechnology:
The various aspects of environment and their impact on earth with special reference to human beings have been described. Some of the important global environmental. Despite the occurrence of a complex and sometimes dangerous alterations in the environment, the life processes should go on, normally as far as possible. Environmental sustainability broadly deals with the sustenance (support and maintenance) of the environment to continue life on earth in a normal way.
Biotechnology significantly contributes to environmental sustainability.
There are three different approaches in this regard:
1. Pollution protection:
Environment can be protected from pollution by using renewable raw materials, recycling the processes, appropriate methods for degradation of wastes.
2. Pollution clean-up:
This can be done by employing biotechnological methods for cleanup of oil spills, detoxification of contaminated soils, and purification of water supplies.
3. Pollution control:
Once pollution has occurred, biotechnological methods can be used for control. For instance, heavy metals can be recovered from polluted water. It is a fact that the various activities of humans are exceeding the sustainable capacity of the earth. Increased industrialization and urbanisation are adversely affecting the environment (with heavy pollution).
The biotechnologists are expected to improve the existing biological, chemical and various other industrial processes to make them environmental friendly. They should develop integrated systems which are efficient, controllable and clean. It is the duty of the environmental biotechnologists to achieve a maximum global environmental safety.
This is a new environmental technology concept. International Organisation for Biotechnology and Bioengineering in 1994 defined Eco-Tech as follows: “Embedding technology into ecosphere and human culture by using the whole range of biodiversity in a holistic and low-invasive way in order to achieve benefits for humankind obeying ecological principles”.