Pollution, whether it be smog in the air, indestructible plastic rubbish washed up on the beach, or the potential effects of too much heat in the atmosphere, affects everyone in one way or another. Strictly speaking, pollution occurs when humans cause changes to the environment by releasing either substances or energy liable to cause hazards to human health, harm to other animals and ecological systems, and damage to physical structures. Large-scale pollution can conveniently be considered to affect three different areas: air, soil and water.
Many of the things that humans do to the environment can cause harm. The most harm, however, is probably caused as a result of pollutants entering the atmosphere; exhaust fumes and chemical processing plants are just two such examples. Potentially the effects of these polluting activities on the air may include temperature changes, effects of gases on heat transmission, effects on the ozone layer, and a change in the composition of the atmosphere. The emission of heat is one very serious threat. It comes from many sources: from burning fuel in our homes; waste heat emissions from vehicles, from cooling systems of power stations and factories and any other heat wasting activity. Its effects are clearly seen in that it makes the air in cities warmer than in the surrounding countryside. The main concern is that the increasing trend in heat generation will affect climate locally and possibly globally. A further threat to our climate is the production of carbon dioxide (CO;). This gas is produced naturally by the respiration of organisms and decomposition of organic matter, although it comprises less than a half per cent of the total composition of air. Much of the carbon dioxide is dissolved in the sea or used by plants, but as a consequence of the world’s growing population and huge need for energy, fuel combustion, which releases carbon dioxide as an end product, is increasing. In fact the gas is now being released faster than it can be removed from the atmosphere. Carbon dioxide is vital to the earth’s climate because it traps heat from the sun which would otherwise be radiated away. The extent of this warming increases as the level of carbon dioxide in the atmosphere rises. At the current rate of release it is thought that the world’s climate could be significantly affected by the year 2000. This would be because of the so-called ‘greenhouse effect’ producing a rise in temperature all over the world. The resultant changes to winds and ocean currents could produce drastic changes to the land, for example some deserts may become converted to arable lands, whereas an area such as the main wheat-growing area in North America could become dry and unusable. World agriculture would have to be totally reorganized to compensate for this change in world climate. A warmer climate may also cause the polar ice to melt, flooding many of the world’s major cities situated at sea level. The final outcome depends on the way in which we derive our energy in the future and thus how much carbon dioxide we release into the atmosphere.
Of more immediate concern is the effect of another gaseous pollutant, sulphur dioxide, resulting from the combustion of oil and coal. Along with nitrogen oxides, sulphur dioxide reacts with water in the atmosphere to form nitric and sulphuric acids. These acids are suspended in air currents and can be swept thousands of miles before falling with rain and snow, a phenomenon known as ‘acid rain’. This not only causes corrosion of building materials such as metals and stonework, but also harms the growth of plants. The effects of acid rain were first identified in the 1960s in Scandinavia, with the death of countless fish in acidified rivers and lakes. The acids reach the lakes directly from rain or by percolating through the soil. This percolation results in toxic chemicals such as aluminium being washed out into the lake, which either kills the fish or leaves them sterile. Much water plant-life is killed, leaving sphagnum moss to grow in their place, which makes a thick green carpet on the bed of the lake. In acidic streams, leeches, snails, flatworms, crayfish and insects gradually disappear, which upsets their natural balance. Acid rain is also thought to contaminate drinking water that is supplied to homes from wells fed by groundwater. Acid rain has also been associated with the death of forests in Europe (80 percent of West German woods are affected), and reduction of crop yields. To combat acid rain, millions of tonnes of lime are applied to soil and lakes which has a neutralizing effect, but this is costly and is just a means of correcting the results of human misuse of the environment.
Much controversy exists over the pollution of the atmosphere by the exhausts of motor vehicles of which lead is a particulary contentious pollutant. This element is added to petrol to improve performance in certain types of engine. Evidence has suggested that high levels of lead in the blood of, for example, city people are associated with fumes from leaded petrol. The resultant effects on health are thought to involve slight mental impairment, behavioural difficulties and learning problems, and possibly a reduction in IQ. The production of lead-free petrol would involve great cost to the oil industry which in some countries has resisted attempts to ban the use of lead in petrol. Most European countries are committed to banning lead in petrol – but not for several years (West Germany is a notable exception).
The most poisonous gas present in the environment is carbon monoxide, and is again produced by motor vehicles. In confined places like a tunnel or a garage it may be inhaled to such an extent that it builds up in the bloodstream, which may subsequently block the transport of oxygen to the body’s tissues. For someone with cardiac or respiratory problems this can prove dangerous.
Other pollutants from vehicles include hydrocarbons and nitrogen oxides which can interact to form oxidants such as ozone that seriously damage plants and also create a smoglike effect such as that seen hovering permanently over Los Angeles. Higher up in the atmosphere, the exhaust emissions of aircraft are cause for concern. High-speed aircraft which fly in the stratosphere produce emissions that react with the ozone layer. The main fear is that a weakening of the ozone layer, which screens out ultraviolet radiation from the sun, will allow more of these harmful rays through, which may, in turn, cause an increase in the incidence of in skin cancer.
When nitrogen fertilizers used by farmers are washed into streams by rain, a massive overgrowth of algae can occur. Plants at the bottom of the stream die because of the lack of light, and these plants along with the algae are decomposed by bacteria. This uses up the oxygen dissolved in the water, resulting in foul-smelling lifeless water. This is called eutrophication and is most serious in lakes and slow-flowing rivers. The process needs phosphates as well as nitrates, and these are often supplied through sewage effluent. In some areas drinking water may be contaminated with nitrates, the result of nearby sewage and agricultural products which seep through the soil, and can cause methaemoglobinaemia in young infants – a condition in which the body cannot carry enough oxygen to the tissues. The rise of nitrate concentration in drinking water has caused concern because of the suggestion that nitrates can be converted by the gut into N-nitrosamines and cause stomach cancer. Effluents from chemical plants, such as cadmium, can cause heart, kidney, and lung damage and possibly cancer. Cadmium is often found in domestic sewage, which prevents its use as an ag-ricutural fertilizer. In some countries fish, and the people who eat them, are occasionally poisoned because of the presence of mercury in the sea. Oil is a common pollutant from ships and tanker spillages at sea. It is hazardous to seabirds and wildfowl because the oil clogs their wings and destroys their buoyancy and waterproofing. Beaches can be ruined as a result of being covered with oil slicks.
Soil and land pollution
Land pollution can include rubbish tips, dumped poisonous chemicals, thrown away rubbish, and abandoned cars. On a less obvious level, pesticides are a major source of pollution. They can harm the creatures that ingest or live near sprayed crops, and are thought to be the cause of many cases of allergic reactions. Supporting this is the finding that the condition of people who are allergic to pesticides and who live near regularly sprayed crops, often improves when they move to an area which is pesticide-free. The use of some pesticides, such as DDT, has been banned or restricted because of the harmful effect they have on some animals. The herbicide 2,4,5-T, which contains the highly toxic chemical dioxin, has been linked to cancer and birth defects in cases in which the mother has been exposed to the substance.
Some people consider that excessive noise is a pollutant (acoustic pollution). Heavy lorries in cities and low-flying aircraft can make life unpleasant for people who are continually exposed to this type of noise. Nuclear power – regardless of impressive safety records – must, by its very nature, pose a risk to the environment. Although safety precautions are normally stringent, there is growing public concern that they are not tough enough. The accidents in North America at Three Miles Island and Chernobyl in the Soviet Union, where there was a substantial release of radioactive materials, served to inflame public fears. Even so, the problem of nuclear waste storage has not yet been adequately solved. Whatever the likely effects – long- or short-term – of all these different pollutants, it is clear that humans must take care of the world and consider carefully what effects these pollutants are having. In practice, we must act as individuals to minimize litter and wastage of raw materials. The more people appreciate the problems and take positive action to solve them, the more chance we have of preserving our environment.