||Pollution of the environment has become a major concern during the 20th century as human society has generated an ever increasing variety and quantity of products and wastes, many of which are released into the environment. Land, water and air are all increasingly affected by a range of pollutants including noise, heat, smoke, chemicals, sewage, manure and radioactive isotopes. Once in the environment, many pollutants are diluted, dispersed or broken down into harmless materials, but others may be concentrated or transformed into more damaging forms. Damage caused by pollution may not be immediately obvious, causing comparatively subtle but far-reaching changes in biological communities which are not of obvious importance to humans and their environment. However, the nature of the ecosystem is such that minor fluctuations may be magnified by the interactions between species: for example, the detrimental effect pesticides can have on bird populations. Monitoring pollution pathways and effects is a formidable problem for environmental scientists, but solving pollution problems is more than a technical issue.
Pollution occurs where human activities introduce something into the environment which has harmful effects. The inclusion of harmful effects in the definition means that the concept of pollution is value dependent and hence politically contested. In many cases, values and interests differ: for example, farmers use weedkillers and pesticides and regard the results as beneficial, while conservationists lament the effects on meadow plants or butterflies. In other cases it matters where the substance is: depletion of stratospheric ozone is regarded as a problem, and so is increased low-level ozone. In some cases sulphur dioxide in the air acts as a valuable source of plant nutrients while in others it contributes to acid rain and plant damage. Concentration of pollutants makes a crucial difference: carbon dioxide would not have been regarded as a pollutant a decade ago but now it is involved in one of the most threatening pollution issues. In small quantities, animal manure is beneficial, but in large quantities it can overwhelm the capacity of natural cycles to deal with it. For most chemical pollutants, and even for radioactivity, harmful effects may be difficult to demonstrate at low concentrations so there may be passionate disputes between emitter and affected publics. In many such cases there may be natural sources of the possible pollutant as well as industrial sources so responsibility is difficult to prove. Although governments seem increasingly concerned to regulate pollution, progress is far from simple, which is illustrated by some examples from air, water and land.
Air pollution has changed from a local problem to a global one in the last two centuries. Industrialization caused a huge increase in coal burning for power and in smelting and also involved new chemical processes. Smoke and corrosive gases became serious problems and were subject to regulation by the mid-19th century, but as industry has grown and spread around the world air pollution has usually followed. The use of the internal combustion engine has added to the problems, at first in the form of urban smog but more recently in the regional problem of acid rain. Industrialized areas such as the northeast US and northwest Europe now have such high emissions of sulphur and nitrogen oxides that rain, fog and snow are acidified and lakes and forests are dying. The precise causes of acid rain are still disputed and as a result controls are not strong enough to promise a solution. Acid rain has become an international issue, but ozone depletion is truly global. It was a largely unexpected problem because the cause was a family of chemicals chosen for their safety and stability, and the effect was strongest through a quite unexpected route. The stability of the chlorofluorocarbons (CFCs) was ideal for refrigerators and aerosols, but it allowed them to spread throughout the atmosphere and into the stratosphere where ultraviolet light from the Sun broke them down. The chlorine released proved extremely effective at breaking down ozone, especially in the special conditions of the Antarctic spring, where more than half of the ozone was lost. The surprise at the extent of the damage, plus fear of skin cancer from increased exposure to UV radiation at the surface, has made the international response unusually energetic, but there are still problems in preventing CFC use from spreading into the Third World. The problem of global warming is an even more challenging global issue, because its causes are integral to the nature of modern society.
Water pollution has also spread from the local to affect large rivers, lakes and land-locked seas. Perhaps the most pervasive pollutant is sewage, which is broken down by bacteria which use oxygen and may reduce oxygen levels below that required by previously existing plants, fish and insects. Other pollutants which are not themselves toxic, including nitrates from fertilizers and phosphates from detergents, can provide nutrients which trigger algal growth, again taking up oxygen and in some cases releasing toxins which affect animals. Algal blooms are now beginning to affect the Adriatic and North Seas as well as ponds and lakes. Many industrial chemicals find their way into rivers and coastal waters, whether discharged legally, accidentally or illegally. Occasionally, levels of toxic substances, for example, mercury or cadmium, may be high enough to cause acute poisoning, most notoriously at Minamata Bay in the 1950s where at least 46 people died from eating fish which had absorbed mercury wastes. More commonly, industrial rivers carry a cocktail of pollutants, including heavy metals, solvents and PCBs (polychlorinated biphenyl), at levels sufficient to cause concern but not to be demonstrably harmful. Rivers like the Rhine, which flow through several countries, may be a source of international disputes, as are the seas into which they discharge.
Land pollution occurs in three main ways:
(1) Mining and mineral processing may produce large voids and spoil heaps. These are at least unsightly and spoil has the potential to cause significant pollution. The entry of air and water into spoil heaps may cause weathering processes which transform sulphides into dissolved acid. In turn, increased acidity can dissolve metals, some of which are toxic. For example, in acidified water courses it may be dissolved aluminium which kills fish rather than the acid itself.
(2) The sites of manufacturing plants may become contaminated by raw materials, combustion products and wastes over the years they are running. Any attempt to redevelop the site may encounter asbestos, toxic metals or hazardous solvents.
(3) More pervasive, and often less identifiable, are the problems associated with landfill sites. Many old dumps contain chemical and metal wastes as well as household refuse. Water percolating through such dumps may dissolve toxic materials, producing leachates which contaminate water courses. More pervasive still is the decomposition of organic materials to produce methane, a gas which is explosive when mixed with air and which is a very effective greenhouse gas. Modern landfills can be managed to reduce water percolation and to collect methane for use as a fuel, but many old dumps are unrecorded and potentially hazardous.
Pollution control is partly a matter of improving technology, for example, incineration of domestic waste can solve the problem of methane in landfills, as well as generating useful amounts of electricity, but adoption of improved controls may be costly and may require political pressure. Several different principles have been used or proposed. In the UK, the Alkali Inspectorate relied for decades on the principle of Best Practicable Means, that is the use of methods which would reduce pollution but not put the polluters out of business. More recently this has evolved into the Best Practicable Environmental Option and then the Best Available Technology Not Entailing Excessive Cost. Most European countries have preferred to set Emission Limits for pollutants and the EC has moved toward imposing the same limits across its territory to provide a â€˜level playing fieldâ€™ for competition. The UK, with the advantage of a westerly airflow and rather short rivers, has objected that these limits are unnecessarily tight. A more radical principle of control is currently being discussed. This is the Prevention Principle, which seeks to prevent pollution from ocurring rather than limiting it or coping with the consequences. As this would bear very heavily on industry and face problems of predicting whether or not pollution would occur in particular circumstances its progress will probably be slow. PS
Further reading B. Price, P is for Pollution.