Safety in the Use of ChemicalsChapter 3The Environmental Impact of Chemicals |
Chemicals released into the air, water or soil endanger not only the health and well being of local populations; some of them may cause problems of global proportions. |
Life on the planet earth -- the only inhabitable one we know of -- is sustained by a series of delicate balances created by the complex interaction of physical and chemical forces which help to renew and nourish life. Many man-made materials and human activities are now threatening the health of the planet and its inhabitants. The problem with the use of many chemicals is that their impact may not become evident immediately or to people in the geographical vicinity where they are released.
Some effects of chemicals are so subtle and intertwined with natural phenomena that it is difficult to point an accusing finger at a specific chemical or process. The environmental impact of chemicals can be classified into certain categories, some of them of local, other of global scale.
Water pollution
Water, essential for the life of man and many organisms, may become polluted as a result of numerous human activities. Polluted water can have detrimental effects on animals, plant life and humans themselves.
Fresh water pollution
A major consequence of the discharge of untreated industrial and urban sewage into the waterways is the depletion of the oxygen content of the water. Oxygen is essential for water organisms, including fish, and most plant species. If materials of biological origin (like paper, pulp, edible oils) are discharged into water, anaerobic (without oxygen) bacteria will proliferate, resulting in foul odours and toxic wastes. Most chemical like heavy metals, pesticides, and polychlorinated biphenyls (PCBs) are toxic to plankton and may enter the food chain by being absorbed by fish and ultimately end up in human food.
Ground water pumped by hand pumps or from wells is used in most parts of the world for drinking purposes. There have been incidents of ground water pollution by waste from industrial and urban discharges, resulting in grave public health problems. Some common types of chemical wastes produced by industrial activities and their impact on the freshwater ecosystems and humans are given in Table 3.1.
Table 3.1 Some typical water pollutants and their impact on the ecosystem and human health
| Polluant | Activity/process from which generated | Impact on ecosystem/human health |
| Heavy metals:
- Chromium - Mercury |
Leather tanneries, electroplating
Chloralkali plants, gold extraction |
Human carcinogen
Toxic to plants, may be accumulated by fish and enter the human food chain, may cause brain damage in humans |
| Acids and alkalis
(e.g., sulphuric, hydrochloric acids, caustic soda, etc.) |
Chemical, pharmaceutical, textile, metal fabrication, fertilizer factories and as a result of oxidation of sulphur and nitrogen oxides in the atmosphere | Change in the pH of the waterways, resulting in alterations in the pattern of vegetation and the whole ecosystems of lakes and streams. In the case of nitrates, eutrophication (too much growth of vegetable matter) and resulting decay may render the lakes 'dead'. |
| Pesticides (especially chlorinated) | Depletion from treated fields, crops, etc. | Potential to cause long-term effects on human health by accumulating in fish. |
| Inorganic salts:
- Cyanides - Sulphites - Sulphides |
Electroplating
Paper and pulp manufacture Tanneries |
May poison the waterways and render them useless for agricultural and domestic consumption |
| Dyes and colorants | Textile and leather industry | Cause offensive colours, some are suspected human carcinogens |
Untreated waste water from tanneries contains a number of toxic chemicals which have long-term ecological and public health risks
Marine pollution
We often read in the newspaper headlines of a spill of petroleum or toxic chemicals from a tanker. Accidental or deliberate spills or dumping of toxic chemicals in the marine environment contribute about 10 percent of the pollution of the sea. It is estimated that every thousandth barrel of oil produced in the world (or 3.2 million tonnes out of the total world production of 3.2 billion tonnes of oil per year) ends up in the sea.
On the other hand, land-based sources like industrial and urban sewage contribute about 70 percent of marine pollution. Many fish and molluscs are known to accumulate certain toxic chemicals in their bodies. Fish are now found with enormous concentrates of DDT in their bodies. A number of chemicals have long lives and continue to persist in the marine environment for a long time. Estuaries are particularly sensitive to the effects of toxic chemicals.
Soil pollution
In many countries urban and industrial waste is dumped into large land-fill sites without consideration of geography, soil texture, the water table or potential seeping into ground water which might be used for drinking. Waste from some industries, like those producing alkaline salts, affects the fertility of the soil by making it salty. Solid wastes and liquids seeping into the soil from liquid waste sources render it unsuitable for human habitation. This is causing serious problems in many countries of the world, where land sources are already very limited because of urban sprawl and increasing populations. The phosphate fertilizers used in agricultural activities also seep into the soil and clog the waterways.
Air pollution
| Urban air pollution caused by automobiles and industrial sources can cause and aggravate many respiratory and health problems. |
The air we breathe can be contaminated by a number of sources, most related to industrial, transport and household activities. Most pollution in urban areas comes from the burning of fuels in the engines of automobiles. The concentration of pollutants in a particular area may vary according to such climatic factors as ambient temperature, wind speed and direction, humidity, atmospheric pressure, and the vegetation in the area. Many pollutants like nitrogen oxides and polycyclic aromatic hydrocarbons (PAHs) react in the presence of humidity and light to produce smog, which can be seen hanging like a pall on most cities.
A number of respiratory and heart-related disorders like asthma, chronic bronchitis and increased likelihood of cardiac diseases are caused or worsened by air pollution. Even rural areas are not immune to air pollution. Biomass fuels (like wood, sawdust, animal dung, crop residues, leaves and agricultural wastes), which are often used in rural areas for heating and cooking purposes, burn inefficiently, resulting in dense smoke containing carbon monoxide, oxides of nitrogen, PAHs, aldehydes, benzene, phenol, cresol and a host of other toxic chemicals. Most often, it is the women and children in the households who are exposed to these pollutants, which can cause serious respiratory and cardiac problems, in addition to cancer in some cases.
Dense smoke emitted from the chimney of a brick kiln results from inefficient burning of coal and contains toxic gases and aerosolssuch as sulphur dioxide, tar, carbon particles, PAHs, benzene, etc.
Global environmental problems caused by chemicals
The use or production of certain chemicals over a long period has resulted in unforeseen consequences, some of global proportions. Many seemingly harmless chemicals have caused indirect damage to human health and to the climate.
Acid rain
When oxides of sulphur and nitrogen are emitted by industrial or vehicular sources, their impact is not merely local. They can be transported over long distances through the air. While airborne, they undergo chemical reactions in the presence of water and oxygen (which are abundant in the atmosphere), transforming them to acids (sulphuric acid in the case of sulphur dioxide and nitric acid in the case of oxides of nitrogen). These acids fall on the ground with the rain, resulting in the lowering of pH (increasing the acidity) of lakes, rivers and other water bodies.
Sometimes the soils also become acidic. The micro-organisms and vegetation growing in the water need special pH conditions. When the pH alters, the pattern of vegetation and the micro-organisms change, which often results in the death of fish that cannot survive on the altered vegetation. Many lakes in Europe and North America have been rendered "dead" as a result of acid rain.
Acids from the atmosphere also fall on the leaves of crops and trees, causing damage to them as well. Some forests have been badly damaged because of the effects of acid deposits and the pollutants coming from motor vehicle exhausts. The acid in the air also causes damage to stone and metal structures. One example is the tarnishing of the famous Taj Mahal in Northern India by acidic fumes caused by industrial emissions in the area.
Damage to the ozone layer
Ozone is a gas constantly being produced and destroyed in the upper parts of the atmosphere called the stratosphere. It is wrapped around the globe like a thin layer and performs vital functions for us. It absorbs the harmful waves of ultraviolet (UV) radiation from the rays of the sun, so that the light which reaches us does not have harmful levels of ultraviolet waves.
UV radiation can cause extensive damage to crops and can cause skin cancer and eye cataracts, and lessen immunity to human diseases. It also damages plastics and paints. It can disturb the food chain in the marine environment. Once released in the atmosphere, certain chemicals like chlorofluorocarbons (CFCs) reach the stratosphere and destroy ozone molecules by chemical reaction.
These chemicals are used in our daily activities as carrier fluids in spray cans, fire extinguishers, as coolants in refrigerators and air conditioners, as blowers in the manufacture of plastic foams, and as cleaning agents in electronics. Also carbon tetrachloride, used as a degreasing and cleaning solvent, has been found to cause harm to the ozone in the stratosphere. Although a world-wide moratorium has been adopted which bans production of such chemicals after 1999, the damage already done may take a long time to repair.
Climate change
Did you ever think why some summer plants and flowers can grow even in the winter in greenhouses? It is possible because of the glass panes or plastic sheets which are fitted outside the greenhouse. These materials let the energy from sunlight to get in but do not allow all of it to return to the atmosphere. Thus the temperature inside increases, creating the conditions for the summer plants to grow in winter.
This phenomenon of allowing energy in and not letting all of it go back out is called the greenhouse effect. A similar role to that played by the glass or plastic sheets in a green house is now being carried out by certain chemicals released by industrial and agricultural activities and sometimes by natural phenomena. The earth re-emits most of the energy it receives from the sun in the form of infrared radiation. Certain gases in the atmosphere, like carbon dioxide, methane, CFCs and oxides of nitrogen, absorb and retain some of the energy re-emitted by the earth, and global warming is the result.
Where do these chemicals come from? Carbon dioxide is produced when carbon-containing fuels (most flammable materials contain carbon) are burned. The advent of the industrial revolution during the last 150 years has resulted in an explosive increase in carbon-dioxide emissions. Methane can come from oil exploration, the petrochemical industry, paddy fields and cattle. Nitrogen oxides are released by motor vehicle exhausts, fertiliser plants and degradation of nitrogen fertilisers.
Although it is very difficult to say how much damage has been done so far, it is estimated that if the current trends in release of greenhouse gases continue, the temperature of the earth will rise by 3 C° by the middle of twenty-first century. This may seem insignificant, but taken globally it means massive changes in the climate, a rise in the water level in oceans, the melting of glaciers at the poles, severe droughts and desertification in some areas, floods and typhoons, and the inundation of some entire countries (like the Maldives) and areas. The result may be food shortages in certain areas and crop failures, which may lead to starvation. This is not a very rosy future for the next generations. We must do something now to stem the release of greenhouse gases into the atmosphere.
Exercise
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