Pollution

The cultural definition

The functions of pollution beliefs

Emotional aspects of pollution behavior

BIBLIOGRAPHY

One of the great puzzles in comparative studies of religion has been the reconciliation of the concept of pollution, or defilement, with that of holiness. In the last half of the nineteenth century, Robertson Smith asserted that the religion of primitive peoples developed out of the relation between a community and its gods, who were seen as just and benevolent. Dependent on a sociological approach to religion, Robertson Smith continued always to draw a line between religious behavior, concerned with ethics and gods, and nonreligious, magical behavior. He used the term taboo to describe nonreligious rules of conduct, especially those concerned with pollution, in order to distinguish them from the rules of holiness protecting sanctuaries, priests, and everything pertaining to gods. The latter behavior he held to be intelligible and praiseworthy and the former to be primitive, savage, and irrational—“magical superstition based on mere terror.”

He clearly felt that magic and superstition were not worth a scholar’s attention. But Sir James Frazer, who dedicated The Golden Bough to Robertson Smith, tried to classify and understand the nature of magical thinking. He formulated the two principles of sympathetic magic: action by contagion and action by likeness. Frazer followed Robertson Smith in assuming that magic was more primitive than religion, and he worked out an evolutionary scheme in which primitive man’s earliest thinking was oriented to mechanical ideas of contagion. Magic gradually gave way to another cosmology, the idea of a universe dominated by supernatural beings similar to man but greatly superior to him. Magic thus came to be accepted as a word for ritual which is not enacted within a cult of divine beings. But obviously there is an overlap between nonreligious ideas of contagion and rules of holiness. Robertson Smith accounted for this by making the distinction between holiness and uncleanness a criterion of the advanced religions:

The person under taboo is not regarded as holy, for he is separated from approach to the sanctuary as well as from contact with men, but his act or condition is somehow associated with supernatural dangers, arising, according to the common savage explanation, from the presence of formidable spirits which are shunned like an infectious disease. In most savage societies no sharp line seems to be drawn between the two kinds of taboo…and even in more advanced nations the notions of holiness and uncleanness often touch…[to] distinguish between the holy and the unclean, marks a real advance above savagery. ([1889] 1927, p. 153)

Frazer echoes the notion that confusion between uncleanness and holiness marks primitive thinking. In a long passage in which he considers the Syrian attitude to pigs, he concludes: “Some said this was because the pigs were unclean; others said it was because the pigs were sacred. This…points to a hazy state of religious thought in which the ideas of sanctity and uncleanness are not yet sharply distinguished, both being blent in a sort of vaporous solution to which we give the name of taboo’’ ([1890] 1955, vol. 2, part 5, p. 23).

The work of several modern-day students of comparative religion derives not directly from Frazer but from the earlier work of Durkheim, whose debt to Robertson Smith is obvious in many ways. On the one hand, Durkheim was content to ignore aspects of defilement which are not part of a religious cult. He developed the notion that magical injunctions are the consequence of primitive man’s attempt to explain the nature of the universe. Durkheim suggested that experimentation with magical injunctions, having thus arisen, has given way to medical science. But on the other hand, Durkheim tried to show that the contagiousness of the sacred is an inherent, necessary, and peculiar part of its character.

His idea of the sacred as the expression of society’s awareness of itself draws heavily on Robertson Smith’s thesis that man’s relation to the gods, his religious behavior, is an aspect of prescribed social behavior. It followed, for Durkheim, that religious ideas are different from other ideas. They are not referable to any ultimate material reality, since religious shrines and emblems are only themselves representations of abstract ideas. Religious experience is an experience of a coercive moral force. Consequently, religious ideas are volatile and fluid; they float in the mind, unattached, and are always likely to shift, or to merge into other contexts at the risk of losing their essential character: there is always the danger that the sacred will invade the profane and the profane invade the sacred. The sacred must be continually protected from the profane by interdictions. Thus, relations with the sacred are always expressed through rituals of separation and demarcation and are reinforced with beliefs in the danger of crossing forbidden boundaries. [See the biographies ofDurkheim; Frazer; Smith, William Robertson.]

If contemporary thinkers were not already well prepared to accept the idea that “religious” restrictions were utterly different from primitive superstitions about contagion, this circular distinction between two kinds of contagion could hardly have gone unchallenged. How can it be argued that contagiousness is the peculiar characteristic of ideas about the sacred when another kind of contagiousness has been bracketed away by definition as irrelevant?

This criticism of Durkheim’s treatment of sacred contagion is implicit in Levy-Bruhl’s massive work on primitive mentality (1922). Levy-Bruhl documented a special kind of outlook on the universe, one in which the power to act and to be acted upon regardless of restrictions of space and time is widely attributed to symbolical representations of persons and animals. He himself explained the belief in such remote contagion by the dominance of the idea of the supernatural in the primitive view of the world. And since he would expect “supernatural” to be equated with Durkheim’s “sacred,” he seems to have seen no conflict between his and the master’s views. [See the biography ofLevybruhl.]

We cannot accept Durkheim’s argument that there are two kinds of contagion, one the origin of primitive hygiene and the other intrinsic to ideas about the sacred, because it is circular. If we approach the problem of contagion in Levy-Bruhl’s terms, then the scope of the answer is broadened : there is not simply a residual area of magical behavior that remains to be explained after primitive religious behavior has been understood but rather a whole mentality, a view of how the universe is constituted. This view of the universe differs essentially from that of civilized man in that sympathetic magic provides the key to its control. Levy-Bruhl is open to criticism; his statement of the problem is oversimple. He bluntly contrasts primitive mentality with scientific thought, not fully appreciating what a rare and specialized activity scientific thinking is and in what well-defined and isolated conditions it takes place. His use of the word “prelogical” in his first formulation of primitive thinking was unfortunate, and he later discarded it. But although his work seems to be discredited at present, the general problem still stands. There is a whole class of cultures, call them what you will, in which great attention is paid to symbolic demarcation and separation of the sacred and the profane and in which dangerous consequences are expected to follow from neglect of the rituals of separation. In these cultures lustrations, fumigations, and purifications of various kinds are applied to avert the dangerous effect of breach of the rules, and symbolic actions based on likeness to real causes are used as instruments for creating positive effects.

The cultural definition

If we are not to follow Robertson Smith in treating the rules of uncleanness as irrational and beyond analysis, we need to clear away some of the barriers which divide up this whole field of inquiry. While the initial problem is posed by the difference between “our” kind of thinking and “theirs,” it is a mistake to treat “us” the moderns and “them” the ancients as utterly different. We can only approach primitive mentality through introspection and understanding of our own mentality. The distinction between religious behavior and secular behavior also tends to be misleadingly rigid. To solve the puzzle of sacred contagion we can start with more familiar ideas about secular contagion and defilement. In English-speaking cultures, the key word is the ancient, primitive, and still current “dirt.” Lord Chesterfield defined dirt as matter out of place. This implies only two conditions, a set of ordered relations and a contravention of that order. Thus the idea of dirt implies a structure of ideas. For us dirt is a kind of compendium category for all events which blur, smudge, contradict, or otherwise confuse accepted classifications. The underlying feeling is that a system of values which is habitually expressed in a given arrangement of things has been violated.

This definition of defilement avoids some historical peculiarities of Western civilization. For example, it says nothing about the relation between dirt and hygiene. We know that the discovery of pathogenic organisms is recent, but the idea of dirt antedates the idea of pathogenicity. It is therefore more likely to have universal application. If we treat all pollution behavior as the reaction to any event likely to confuse or contradict cherished classifications, we can bring two new approaches to bear on the problem: the work of psychologists on perception and of anthropologists on the structural analysis of culture.

Perception is a process in which the perceiver actively interprets and, in the course of his interpreting, adapts and even supplements his sensory experiences. Hebb has shown that in the process of perception, the perceiver imposes patterns of organization on the masses of sensory stimuli in the environment (1949; 1958). The imposed pattern organizes sequences into units–fills in missing events which would be necessary to justify the recognition of familiar units. The perceiver learns to adjust his response to allow for modification of stimuli according to changes in lighting, angle of regard, distance, and so forth. In this way the learner develops a scheme or structure of assumptions in the light of which new experiences are interpreted. Learning takes place when new experience lends itself to assimilation in the existing structure of assumption or when the scheme of past assumptions is modified in order to accommodate what is unfamiliar. In the normal process of interpretation, the existing scheme of assumptions tends to be protected from challenge, for the learner recognizes and absorbs cues which harmonize with past experience and usually ignores cues which are discordant. Thus, those assumptions which have worked well before are reinforced. Because the selection and treatment of new experiences validates the principles which have been learned, the structure of established assumptions can be applied quickly and automatically to current problems of interpretation. In animals this stabilizing, selective tendency serves the biological function of survival. In men the same tendency appears to govern learning. If every new experience laid all past interpretations open to doubt, no scheme of established assumptions could be developed and no learning could take place.

This approach may be extended to the learning of cultural phenomena. Language, for example, learned and spoken by individuals, is a social phenomenon produced by continuous interaction between individuals. The regular discriminations which constitute linguistic structure are the spontaneous outcome of continual control, exercised on an individual attempting to communicate with others. Expressions which are ambiguous or which deviate from the norm are less effective in communication, and speakers experience a direct feedback encouraging conformity. Language has more loosely and more strictly patterned domains in which ambiguity has either more or less serious repercussions on effective communication. Thus there are certain domains in which ambiguity can be better tolerated than in others (Osgood & Sebeok 1954, p. 129).

Similar pressures affect the discrimination of cultural themes. During the process of enculturation the individual is engaged in ordering newly received experiences and bringing them into conformity with those already absorbed. He is also interacting with other members of his community and striving to reduce dissonance between his structure of assumptions and theirs (Festinger 1957). Frenkel-Brunswik’s research among schoolchildren who had been variously exposed to racial prejudice illustrates the effects of ambiguity on learning at this level. The children listened to stories which they were afterwards asked to recall. In the stories the good and bad roles were not consistently allocated to white and Negro characters. When there was dissonance between their established pattern of assumptions about racial values and the actual stories they heard, an ambiguous effect was received. They were unable to recall the stories accurately. There are implications here for the extent to which a culture (in the sense of a consistent structure of themes, postulates, and evaluations) can tolerate ambiguity. It is now common to approach cultural behavior as if it were susceptible to structural analysis on lines similar to those used in linguistics (Levi-Strauss 1958; Leach 1961). For a culture to have any recognizable character, a process of discrimination and evaluation must have taken place very similar to the process of language development–with an important difference. For language the conditions requiring clear verbal communication provide the main control on the pattern which emerges, but for the wider culture in which any language is set, communication with others is not the only or principal function. The culture affords a hierarchy of goals and values which the community can apply as a general guide to action in a wide variety of contexts. Cultural interaction, like linguistic interaction, involves the individual in communication with others. But it also helps the individual to reflect upon and order his own experience.

The general processes by which language structure changes and resists change have their analogues at the higher level of cultural structure. The response to ambiguity is generally to encourage clearer discrimination of differences. As in language, there are different degrees of tolerance of ambiguity. Linguistic intolerance is expressed by avoidance of ambiguous utterances and by pressure to use well-discriminated forms where differences are important to interpretation and appropriate responses. Cultural intolerance of ambiguity is expressed by avoidance, by discrimination, and by pressure to conform.

The functions of pollution beliefs

To return to pollution behavior, we have already seen that the idea of dirt implies system. Dirt avoidance is a process of tidying up, ensuring that the order in external physical events conforms to the structure of ideas. Pollution rules can thus be seen as an extension of the perceptual process: insofar as they impose order on experience, they support clarification of forms and thus reduce dissonance.

Much attention has been paid to the sanctions by which pollution rules are enforced (see Steiner 1956, p. 22). Sometimes the breach is punished by political decree, sometimes by attack on the transgressor, and sometimes by grave or trivial sanctions; the sanction used reflects several aspects of the matter. We can assume that the community, insofar as it shares a common culture, is collectively interested in pressing for conformity to its norms. In some areas of organization the community is capable of punishing deviants directly, but in others this is not practicable. This may happen, for example, if political organization is not sufficiently developed or if it is developed in such a way as to make certain offenses inaccessible to police action. Homicide is a type of offense which is variously treated according to the relationship between killer and victim. If the offender is himself a member of the victim’s group and if this is the group which is normally entrusted with protection of its members’ interests, it may be held contradictory and impossible for the group to inflict punishment. Then the sanction is likely to be couched in terms of a misfortune that falls upon the offender without human intervention. This kind of homicide is treated as a pollution.

We would expect to find that the pollution beliefs of a culture are related to its moral values, since these form part of the structure of ideas for which pollution behavior is a protective device. But we would not expect to find any close correspondence between the gravity with which offenses are judged and the danger of pollution connected with them. Some moral failings are likely to be met with prompt and unpleasant social consequences. These self-punishing offenses are less likely to be sanctioned by pollution beliefs than by other moral rules. Pollution beliefs not only reinforce the cultural and social structure, but they can actively reduce ambiguity in the moral sphere. For example, if two moral standards are applied to adultery, so that it is condemned in women and tolerated in men, there will inevitably be some ambiguity in the moral judgment since adultery involves a man and a woman. A pollution belief can reduce the ambiguity. If the man is treated as dangerously contagious, his adulterous condition, while not in itself condemned, endangers the outraged husband or the children; moral support can be mustered against him. Alternatively, if attention is focused on the pollution aspect of the case, a rite of purification can mitigate the force of the moral condemnation.

This approach to pollution allows further applications of Durkheimian analysis. If we follow him in assuming that symbolism and ritual, whether strictly religious or not, express society’s awareness of its own configuration and necessities, and if we assume that pollution rules indicate the areas of greater systematization of ideas, then we have an additional instrument of sociological analysis. Durkheim held that the dangerous powers imputed to the gods are, in actual fact, powers vested in the social structure for defending itself, as a structure, against the deviant behavior of its members. His approach is strengthened by including all pollution rules and not merely those which form part of the religious cult. Indeed, deriving pollution behavior from processes similar to perception comes close to Durkheim’s intention of understanding society by developing a social theory of knowledge.

Pollution rules in essence prohibit physical contact. They tend to be applied to products or functions of human physiology; thus they regulate contact with blood, excreta, vomit, hair clippings, nail clippings, cooked food, and so on. But the anthropologist notes that the incidence of beliefs in physiological pollution varies from place to place. In some communities menstrual pollution is gravely feared and in others not at all; in some, pollution by contact with the dead is feared, in others pollution of food or blood. Since our common human condition does not give rise to a common pattern of pollution observances, the differences become interesting as an index of different cultural patterning. It seems that physiological pollutions become important as symbolic expressions of other undesirable contacts which would have repercussions on the structure of social or cosmological ideas. In some societies the social definition of the sexes is more important than in others. In some societies social units are more rigorously defined than in others. Then we find that physical contact between sexes or between social units is restricted even at second or third remove. Not only may social intercourse be restricted, but sitting on the same chair, sharing the same latrine, or using the same cooking utensils, spoons, or combs may be prohibited and negatively sanctioned by pollution beliefs. By such avoidances social definitions are clarified and maintained. Color bars and caste barriers are enforced by these means. As to the ordered relation of social units and the total structure of social life, this must depend on the clear definition of roles and allegiances. We would therefore expect to find pollution concepts guarding threatened disturbances of the social order. On this, nearly everything has been said by van Gennep. His metaphor of society as a kind of house divided into rooms and corridors, the compartments carefully isolated and the passages between them protected by ceremonial, shows insight into the social aspects of pollution. So also does his insistence on the relative character of the sacred:

Sacredness as an attribute is not absolute; it is brought into play by the nature of particular situations. . . . Thus the “magic circles” pivot, shifting as a person moves from one place in society to another. The categories and concepts which embody them operate in such a way that whoever passes through the various positions of a lifetime one day sees the sacred where before he has seen the profane, or vice versa. Such changes of condition do not occur without disturbing the life of society and the individual, and it is the function of rites of passage to reduce their harmful effects. (Gennep [1909] 1960, pp. 12–13)

Van Gennep saw that rites of transition treat all marginal or ill-defined social states as dangerous. His treatment of margins is fully compatible with the sociological approach to pollution. But van Gennep’s ideas must be vastly expanded. Not only marginal social states, but all margins, the edges of all boundaries which are used in ordering the social experience, are treated as dangerous and polluting.

Rites of passage are not purificatory but are prophylactic. They do not redefine and restore a lost former status or purify from the effect of contamination, but they define entrance to a new status. In this way the permanence and value of the classifications embracing all sections of society are emphasized.

When we come to consider cosmological pollution, we are again faced with the problem unresolved by Lévy-Bruhl. Cosmological pollution is to the Westerner the most elusive, yet the most interesting case. Our own culture has largely given up the attempt to unify, to interpenetrate, and to crossinterpret the various fields of knowledge it encompasses. Or rather, the task has been taken over by natural science. A major part of pollution behavior therefore lies outside the realm of our own experience: this is the violent reaction of condemnation provoked by anything which seems to defy the apparently implicit categories of the universe. Our culture trains us to believe that anomalies are only due to a temporarily inadequate formulation of general natural laws. We have to approach this kind of pollution behavior at second hand.

The obvious source of information on the place of cosmic abnormality in the mind of the primitive is again Levy-Bruhl. Earthquakes, typhoons, eclipses, and monstrous births defy the order of the universe. If something is thought to be frightening because it is abnormal or anomalous, this implies a conception of normality or at least of categories into which the monstrous portent does not fit. The more surprising that anomaly is taken to be, the clearer the evidence that the categories which it contradicts are deeply valued.

At this point we can take up again the question of how the culture of civilization differs from that which Lévy-Bruhl called primitive. Recalling that dirt implies system and that pollution beliefs indicate the areas of greatest systematization, we can assume that the answer must be along the same lines. The different elements in the primitive world view are closely integrated; the categories of social structure embrace the universe in a single, symbolic whole. In any primitive culture the urge to unify experience to create order and wholeness has been effectively at work. In “scientific culture” the apparent movement is the other way. We are led by our scientists to specialization and compartmentalism of spheres of knowledge. We suffer the continual breakup of established ideas. Levy-Bruhl, looking to define the distinction between the scientific and the primitive outlook, would have been well served if he had followed Kant’s famous passage on his own Copernican revolution. Here Kant describes each great advance in thought as a stage in the process of freeing “mind” from the shackles of its own subjective tendencies. In scientific work the thinker tries to be aware of the provisional and artificial character of the categories of thought which he uses. He is ready to reform or reject his concepts in the interests of making a more accurate statement.

Any culture which allows its guiding concepts to be continually under review is immune from cosmological pollutions. To the extent that we have no established world view, our ways of thinking are different from those of people living in primitive cultures. For the latter, by long and spontaneous evolution, have adapted their patterns of assumption from one context to another until the whole of experience is embraced. But such a comprehensive structure of ideas is precarious to the extent that it is an arbitrary selection from the range of possible structures in the same environment. Other ways of dividing up and evaluating reality are conceivable. Hence, pollution beliefs protect the most vulnerable domains, where ambiguity would most weaken the fragile structure.

Emotional aspects of pollution behavior

Pollution beliefs are often discussed in terms of the emotions which they are thought to express. But there is no justification for assuming that terror, or even mild anxiety, inspires them any more than it inspires the housewife’s daily tidying up. For pollution beliefs are cultural phenomena. They are institutions that can keep their forms only by bringing pressure to bear on deviant individuals. There is no reason to suppose that the individual in a primitive culture experiences fear, still less unreasoning terror, if his actions threaten to modify the form of the culture he shares. His position is exactly comparable to a speaker whose own linguistic deviations cause him to produce responses which vary with his success in communicating. The dangers and punishments attached to pollution act simply as means of enforcing conformity.

As to the question of the rational or irrational character of rules of uncleanness, Robertson Smith is shown to have been partly right. Pollution beliefs certainly derive from rational activity, from the process of classifying and ordering experience. They are, however, not produced by strictly rational or even conscious processes but rather as a spontaneous by-product of these processes.

Mary Douglas

[See alsoCaste; Communication; Magic; Myth and Symbol; Rltual.]

BIBLIOGRAPHY

Douglas, Mary 1966 Purity and Danger: A Comparative Study of Concepts of Pollution and Taboo. London: Routledge.

Durkheim, Émile (1912)1954 The Elementary Forms of the Religious Life. London: Allen & Unwin; New York: Macmillan. → First published as Les formes elementaires de la vie religieuse, le systeme totemique en Australie. A paperback edition was published in 1961 by Collier.

Eliade, Mircea (1957) 1959 The Sacred and the Profane: The Nature of Religion. New York: Harcourt. → First published in German. A paperback edition was published in 1961 by Harper.

Festinger, Leon 1957 A Theory of Cognitive Dissonance. Evanston, III.: Row.

Frazer, James (1890) 1955 The Golden Bough: A

Study in Magic and Religion. 3rd ed., rev. & enl. 13 vols. New York: St. Martins, London: Macmillan. → An abridged edition was published in 1922 and reprinted in 1955.

Frenkel-Brunswik, Else 1949 Intolerance of Ambiguity as an Emotional and Perceptual Personality Variable. Journal of Personality 18:108–143.

Gennep, Arnold Van (1909) 1960 The Rites of Passage. London: Routledge; Univ. of Chicago Press. → First published in French.

Hebb, Donald O. 1949 The Organization of Behavior: A Neuropsychological Theory. New York: Wiley. Hebb, Donald O. 1958 A Textbook of Psychology. Philadelphia: Saunders.

Leach, Edmund R. 1961 Rethinking Anthropology. London School of Economics and Political Science Monographs on Social Anthropology, No. 22. London: Athlone.

LÉvi-Strauss, Claude (1958) 1963 Structural Anthropology. New York: Basic Books. → First published in French.

LÉvy-Bruhl, Lucien (1910) 1926 How Natives Think. London: Allen & Unwin. → First published as Les fonctions mentales dans les societes primitives.

LÉvy-Bruhl, Lucien (1922) 1923 Primitive Mentality. Macmillan → First published in French.

Osgood, Charles E.; and Sebeok, Thomas A. (editors) (1954) 1965 Psycholinguistics: A Survey of Theory and Research Problems. Bloomington: Indiana Univ. Press.

Smith, William Robertson (1889) 1927 Lectures on the Religion of the Semites. 3d ed. New York: Mao millan.

Steiner, Franz 1956 Taboo. New York: Philosophical Library.

Pollution

Pollution can be defined as a change in the physical, chemical, or biological characteristics of the air, water, soil, or other parts of the environment that adversely affects the health, survival, or other activities of humans or other organisms. After pollution occurs, the polluted resource is no longer suitable for its intended use. Most pollutants are solid, liquid, or gaseous chemicals created as byproducts of the extractive or manufacturing industries. Pollution can also take the form of excessive heat, noise, light, or other electromagnetic radiation.

Pollution is also a complex political problem and affects people's lives in numerous ways other than health. Determining an acceptable level of pollution is often more of a political problem than a scientific problem. This is especially true when jobs are at stake, as when a manufacturing plant is forced to close or to modify its operations.

Air Pollution

Air pollution is the contamination of air by unwanted gases, smoke particles, and other substances. Air pollution has been around since the beginning of the Industrial Revolution. In the United States, smoke pollution was at its worst in the first half of the twentieth century. The smoke was so thick in the winter in some industrial cities that street lights had to be left on all day. However, air pollution was considered a local problem. The burning of fossil fuels produced the most smoke, so some cities restricted the type of coal that could be burned to hard coal, which burns cleaner than soft coal. More efficient burners were installed and devices were attached to smokestacks to remove soot. Diesel locomotives replaced steam locomotives, which had burned coal or oil to heat the water to make the steam. These changes all led to a gradual reduction in smoke pollution during the last half of the twentieth century.

However, a new type of air pollution, smog, became a problem beginning in the 1940s. Smog is not the same as smoke pollution, although this was not immediately apparent. When Los Angeles had its first major smog attack, it became obvious that some phenomenon other than smoke was responsible. Los Angeles did not burn coal or oil to generate heat or electricity, yet its smog problem worsened. Scientists now know that smog is the result of the action of sunlight on unburned hydrocarbons and other compounds in the air. These unburned hydrocarbons come from the exhaust of motor vehicles with internal combustion engines.

Rapid industrial growth, urban and suburban development, dependence on motor vehicles, construction and operation of large facilities using fossil fuels for generating electricity, production of iron and steel, petrochemicals, and petroleum refining converted what had been a local problem into a regional or national problem. Many areas of the United States now suffer seasonal episodes of unhealthy air, including smog, haze, and acid rain . A wide range of pollutants currently poses an ecological threat in cities all over the United States and in other industrialized nations. Since pollution does not recognize national borders, the problem can spread around the world.

Costs of Air Pollution

The costs of air pollution in the United State are difficult to estimate. The economic benefits from the control of pollution are even harder to estimate. Business and industry bear the direct costs of compliance with regulations designed to control air pollution. Ultimately, consumers bear these costs through increased prices and reduced stock dividends. However, the economic benefits of cleaner air may be returned to the consumer in the form of lower health costs and longer-lasting and more reliable products.

Types of Pollutants and Controls

There are six principal classes of air pollutants: particulate matter (soot), carbon monoxide, sulfur oxides, nitrogen oxides, unburned hydrocarbons, and ozone. Billions of metric tons of these compounds are discharged into the air each year.

Particulates.

Suspended particulate matter such as soot and aerosols, are particulates. These particles of solids or liquids range in size from those that are visible as soot and smoke, to those that are so small they can only be seen through a microscope. Aerosols can remain suspended in the air for long periods and can be carried over great distances by the wind. Most particulates are produced by burning fossil fuels in power plants and other stationary sources. Controlling particulates usually involves washing, centrifugal separation, or electrostatic precipitation.

Particulates are harmful for a number of reasons. Some particles contribute to acid rain. Toxic materials such as lead or mercury can appear as particulates. However, the greatest health risk comes from breathing particulates. Some particles can lodge deep in the lungs and cause inflammation or chronic lung disease.

Carbon monoxide.

Carbon monoxide is a colorless, odorless, flammable, poisonous gas. The incomplete burning of carbon fuels produces carbon monoxide. Carbon monoxide comes largely from motor vehicles, with lesser amounts from other internal combustion engines such as those on lawnmowers and leafblowers, and from open fires and industrial processes. Carbon monoxide emissions can be controlled by more efficient burners or improved combustion chambers. Modern computer-controlled engines with catalytic converters successfully remove most carbon monoxide from automobile exhaust.

Sulfur oxides.

Sulfur oxides are the major contributor to acid rain in the United States. Sulfur oxides include sulfur dioxide, sulfuric acid, and various sulfate compounds. Sulfur oxides are produced when fuel that contains sulfur is burned, or when metal ores are processed. Sulfur oxide emissions in the United States come primarily from plants that use fuels containing sulfur to generate electricity. The best way to reduce sulfur oxide emissions is to use fuels that naturally contain less than 1 percent sulfur, but these fuels are more expensive. Other techniques include removing sulfur from fuels and sulfur oxides from the combustion gases. Removing sulfur from stack gases after fuel is burned is difficult and expensive. However, the byproduct, sulfuric acid, can be sold to recover some of the cost.

Nitrogen oxides.

Nitrogen oxides are also contributors to acid rain and are a principal component of photochemical smog. Nitrogen oxides primarily result from the high-temperature combustion of gasoline or diesel in internal combustion engines. During combustion, nitrogen in the air chemically combines with oxygen to produce nitric oxide. Much of the nitric oxide is converted to nitrogen dioxide in a chemical reaction promoted by sunlight. Computer-controlled combustion and optimally designed combustion chambers can partially reduce the formation of nitrogen oxides. Special catalytic converters can combine nitric oxide with carbon monoxide and unburned hydrocarbons to produce nitrogen, carbon dioxide, and water.

Unburned hydrocarbons.

Unburned hydrocarbons in air also represent wasted fuel. Gaseous hydrocarbons are not toxic at concentrations normally found in the atmosphere, but unburned hydrocarbons are a major contributor to the formation of ozone and smog. Catalytic converters on automobile engines have substantially reduced the emission of unburned hydrocarbons.

Ozone.

Ozone is a form of oxygen in which the molecule contains three atoms instead of two. Ozone is beneficial when it is high in the atmosphere, but near the surface, ozone can damage rubber and paint as well as damage lung tissue. Ozone is a constituent of smog, and is produced from the reaction of nitrogen oxides with gaseous hydrocarbons in the presence of sunlight. A small amount of ozone is also produced by lightning storms. The control of ozone and other photochemical oxidants depends on the effective control of both nitrogen oxides and gaseous hydrocarbons.

Water Pollution

Water pollution is caused by any chemical, physical, or biological substance that affects the natural condition of water or its intended use. We rarely stop to think about how important a reliable and safe water supply is until it is restricted or damaged. Water pollutants are produced primarily by the activities of humans. Our fresh water supply is under worldwide threat from pollution.

Water in lakes and rivers (surface water) throughout the world must satisfy a wide variety of different needs. Some of these needs partially conflict with others:

• The public wants lakes and rivers preserved in their natural state.
• Lakes and rivers must support a healthy population of fish and wildlife.
• Surface water must be safe for recreational uses such as swimming.
• Many localities depend on surface water for a safe drinking water supply.
• Surface water must be safe for agricultural use.
• Surface water must accommodate a variety of industrial purposes
• Surface water is used to generate power or cool power plants.
• Surface water is counted upon to dilute and transport human and industrial waste.

Because of the complex factors involved, there is no precise definition of water pollution. Instead, the intended use of the water must be considered. Once the intended use of the water is specified, pollutants can be grouped as not permissible, as undesirable and objectionable, as permissible but not necessarily desirable, or as desirable. For example, if water is to be used for wildlife support and enhancement, toxic compounds are not permissible, but oxygen is desirable. If the water is to be converted to steam in a power plant, some toxic materials might be desirable (because they reduce zebra mussel infestations), while excess oxygen that could corrode equipment would be undesirable.

Another method of classifying water pollutants is to distinguish between pollutants that are not altered by the biological processes occurring in natural waters, and those that will eventually break down into other, perhaps less objectionable, compounds. Inorganic chemicals are diluted by water but do not chemically change. Industrial waste often contains this sort of pollutant (for example, mercury). On the other hand, domestic sewage can be converted into inorganic materials, such as bicarbonates, sulfates, and phosphates, by the action of bacteria and other microorganisms in the water. If the water is not too heavily laden with waste, bacteria can break down the waste to safe levels.

Until early in the twentieth century, efforts to control water pollution were directed toward eliminating potential disease-causing organisms, such as typhoid. This led to treatment plants to provide safe drinking water and measures to enhance the natural biological activity of streams and rivers in order to assimilate and break down waste. By the middle of the twentieth century, the focus had shifted to the treatment of chemical pollutants not removed by conventional water-treatment methods.

By the middle of the twentieth century, the situation was changing. Rapidly growing urban areas generated large quantities of waste that had to be processed. Increased manufacturing capacity greatly increased the amount and variety of industrial waste. Commercial fertilizers and pesticides created many new pollution problems. Sewer systems were often unable to keep pace with rapid urban growth. Today, virtually every body of water on Earth has some degree of water pollution. Even the oceans, which were once thought to be able to absorb an unlimited amount of waste, are now showing significant stress due to pollution.

Major Water Pollutants

Water is considered polluted if it contains an amount of any substance that renders the water unsuitable for a particular purpose. The list of substances that may pollute water is very long, and only a few major pollutants can be discussed here.

Organic waste.

Organic waste comes from domestic sewage, agricultural runoff, feedlot operations, and industrial waste of animal and plant origin, such as from a paper mill. Domestic sewage is the largest and most widespread source of organic waste. Industrial organic waste tends to occur in larger quantities at fewer locations. Industries that make food and paper (and wood pulp) produce the largest amounts of industrial organic waste.

Bacteria can efficiently break down organic waste. However, bacterial action also removes oxygen from the water. Because fishes and other forms of aquatic life depend on dissolved oxygen, the bacterial action necessary to break down the waste damages the aquatic environment. If organic waste consumes oxygen at a rate greater than it can be replenished, then anaerobic bacteria dominate the decay process. Anaerobic decomposition by bacteria is smelly and aesthetically unpleasant.

Plant nutrients.

Nitrogen and phosphorus are the two main plant nutrients acting as polluting agents. If plant nutrients get into water, they stimulate the growth of algae and other water plants. When these plants die and decay, they consume oxygen, just like any other organic waste. The excess plant growth caused by fertilization and subsequent build up of dead plant matter is called eutrophication. If the oxygen level drops even a small amount, desirable species of fishes, such as trout and bass, will be replaced by less desirable species such as carp and catfish. If the oxygen level drops low enough, all species of fishes, crayfishes, shrimp, and other organisms may die.

Synthetic organic chemicals.

The water pollution problem causing the greatest concern is the ever-increasing variety of new chemical compounds. Often new compounds are developed and old ones abandoned before their environmental impact is known. Some of these compounds will remain in water for decades, or longer. The presence of these synthetic chemicals adversely affect fishes and other aquatic life. Many researchers think that some synthetic chemicals mimic natural hormones, disrupting growth and reproductive cycles in affected populations.

Inorganic chemicals.

Inorganic chemicals such as mercury, nitrates, phosphates, and other compounds may also enter surface water. Many of these chemicals destroy fish and aquatic life, cause excessive hardness of water supply, and corrode machinery. This adds to the cost of water treatment.

Mercury pollution has been recognized as a serious, chronic, and widespread danger in many waterways. Even very small amounts of mercury can cause serious physiological effects or even death. Because mercury is not normally found in food or water, no organisms have developed the ability to process and excrete mercury. So it collects in tissues until toxic levels are reached. Mercury also undergoes biomagnification . Organisms at higher trophic levels consume a large number of organisms at lower trophic levels. The concentration of mercury becomes progressively higher at higher trophic levels. Predators at the highest trophic levels can accumulate dangerously high levels of mercury in this way.

Radioactive materials.

Radioactive materials are a recent addition to the list of potential water pollutants. Radioactive waste comes from the mining and processing of radioactive ores, from the refining of radioactive materials, from the industrial, medical, and research uses of radioactive materials, and from nuclear-powered reactors. Some radioactive waste still remains from the atmospheric testing of nuclear weapons in the 1940s and 1950s. The two most common radioactive materials found in water are strontium-90 and radium-226.

Oil.

Oil pollution can enter water through bilge flushing, from accidental or deliberate discharge from ships, or from accidental spills of crude oil during transport. Some experts estimate that 1.5 million tons of oil are spilled into the oceans each year. Water polluted by oil greatly damages aquatic life and other wildlife such as birds that depend on the water for food and nesting areas. Waterfowl alighting on oil-covered waters usually become so oil soaked that they are unable to fly. One speck of oil on a bird's feathers can poison the bird if it ingests the oil while preening. Oil destroys much of the aquatic life of oceans. It is particularly damaging to shellfish and other filter feeders . It also damages the small shrimp and other organisms that serve as food for larger fish.

Thermal pollution.

Thermal pollution is caused by the release of heat into the water or air. Electric power plants are a major source of thermal pollution, since they convert only about one-third of fuel energy into electricity. The remaining heat is discharged to the local environment as heated water or air. This can alter the ecological balance of a large area. For example, if warm water is discharged into a lake, the warm water will not be able to dissolve as much oxygen. This may result in more desirable species of fishes being replaced by less desirable species.

Land and Soil Pollution

One of the miracles of technology in the late twentieth century has been the extraordinary ability of agriculture to increase the productivity of croplands to previously unheard of levels. However, this increased productivity requires the heavy use of pesticides and fertilizer. Most pesticides today are designed to decompose very quickly into harmless compounds. Thousands of pesticides are currently in use, and in most cases their agricultural value balances their risks. However, many scientists think that we may be in an unbreakable cycle of having to continually develop new and more potent pesticides to overcome pests that are resistant to older pesticides.

Noise Pollution

Noise pollution is a recently identified source of environmental degradation. The hearing apparatus of living things is sensitive to certain frequency ranges and sound intensities. Sound intensities are measured in decibels. A sound at or above the 120 decibel level is painful and can injure the ear. Noise pollution is present even in the open ocean. Researchers have shown that whales communicate over great distances using low frequency sound waves. Unfortunately, the noise generated by engines and screws of ships falls in the same frequency range and can interfere with the whale's communication.

Light Pollution

Professional and amateur astronomers have recently identified a problem that did not exist a generation ago: light pollution. This form of pollution has spread so widely in the last few decades that many people are only able to see a few of the brightest stars. From many of our big cities, no stars at all are visible. Light pollution is not an inevitable consequence of making our streets and neighborhoods safer. Most light pollution comes from wasted light. At least 75 percent of the sky glow in most cities comes from poorly designed or improperly installed light fixtures. According to a study conducted by the International Dark-Sky Association in 1997, about $1.5 billion per year is spent on wasted light that does nothing to improve security or safety.

Efforts to Control Pollution

Because pollution does not recognize national borders, the solution to many pollution problems requires cooperation at regional, national, and international levels. For example, smokestacks of coal-burning power plants in the United States cause some of the acid rain that falls in Canada.

In the United States, the Environmental Protection Agency (EPA) is charged with enforcing the many and complex laws, rules, executive orders, and agency regulations regarding the environment. The EPA came into being in 1969 with the passage of the National Environmental Policy Act (NEPA). This act also required the filing of environmental impact statements. Almost all government agencies and many businesses are required by law to file these statements, which state the potential harmful environmental effects of such activities as opening new factories, building dams, and drilling new oil wells.

Additional laws to protect the environment were passed in the 1970s and 1980s, including the Clean Air Act, the Safe Drinking Water Act, and the Comprehensive Environmental Response, Compensation, and Liability Act, known as Superfund. Then-president George Bush signed the Clean Air Act of 1990. This new law called for substantial reductions in emissions of all types. The act also added to the list of potentially toxic chemicals that must be monitored by the EPA. The pace of new environmental legislation has waned since 1990, but congress enacted the Food Quality Protection Act in 1996 and the Chemical Safety Information, Site Security and Fuels Regulatory Relief Act in 1999.

see also Habitat Loss; Trophic Level.

Elliot Richmond

Bibliography

Art, Henry W., ed. The Dictionary of Ecology and Environmental Science. New York: Holt, 1993.

Bowler, Peter J. Norton History of Environmental Sciences. New York: Norton, 1993.

Caplan, Ruth. Our Earth, Ourselves: The Action-Oriented Guide to Help You Protect and Preserve Our Planet. Toronto, Canada: Bantam, 1990.

Carson, Rachel. Silent Spring. Boston: Houghton Mifflin, 1994.

Chiras, Daniel D. Environmental Science: Action for a Sustainable Future, 4th ed. Menlo Park, CA: Benjamin-Cummings Publishing Company, 1993.

Franck, Irene M., and David Brownstone. The Green Encyclopedia. New York: Prentice Hall General Reference, 1992.

Harms, Valerie. The National Audubon Society Almanac of the Environment. New York: Putnam Publishing, 1994.

Luoma, Jon R. The Air Around Us: An Air Pollution Primer. Raleigh, NC: Acid Rain Foundation, 1989.

Miller Jr., G. Tyler. Living in the Environment, 6th ed. Belmont, CA: Wadsworth Publishing Company, 1990.

Mott, Lawrie, and Karen Snyder. Pesticide Alert: A Guide to Pesticides in Fruits and Vegetables. San Francisco: Sierra Club Books, 1997.

Newton, David. Taking a Stand Against Environmental Pollution. Danbury, CA: Franklin Watts Incorporated, 1990.

Rubin, Charles T. The Green Crusade: Rethinking the Roots of Environmentalism. New York: Free Press, 1994.

In the United States, concern for the natural condition of water was first expressed in the 1899 Rivers and Harbors Appropriation Act. The measure made it illegal to dump waste into waters used by any kind of vessels, except by special permission.

The 1990 Pollution Prevention Act created a new office in the Environmental Protection Agency, with the mission to help industries limit pollutants.

POLLUTION

The term "pollution," which carries with it a sense of an impurity, can be defined as a chemical or physical agent in an inappropriate location or concentration. The sources of pollution are varied. Natural sources include those that are not directly under human control, such as volcanoes, which spew forth sulfur oxides and particles; and those people could avoid, such as groundwater with naturally high levels of arsenic, which has caused poisoning in Bangladesh and Taiwan. All human activities have the possibility of polluting the environment by contaminating air, water, food, or soil, The earliest human pollution-control efforts dealt with avoidance of diseases caused by contamination of water and food by human excreta and with the control of smoke from fires used for cooking and heating. Sanitary engineering to manage human wastes remains a central public health need. Indoor air pollution due to the use of wood and fossil fuels in poorly ventilated residences also remains a major source of exposure to pollutants and a cause of respiratory disease in much of the world.

TYPES OF POLLUTION

Pollution production can be considered under the heading of the four major human activity sectors: industry, energy, transportation, and agriculture. With the marked increase in human population and the industrialization of much of the globe has come a whole new set of pollutants. Scientific advances based upon understanding the chemical and physical forces underlying nature have led to new processes and new products that have transformed society and have had a major positive impact on human health. But these industrial activities also result in air and water emissions and contamination of the soil and of food as by-products of the processes involved in manufacture. The products themselves may be the means by which pollutants are distributed to the general population, such as lead poisoning through the use of lead in house paints. In the United States and other more wealthy countries, there recently has been a marked decline in industrial pollution emissions per unit produced. This has come about through regulatory control of emissions and, in part, through the recognition by industry that emissions represent a loss of raw materials or product that is economically advantageous to retain. As developed countries move into the information era, much of the production of textiles and durable goods has shifted to developing countries, not always with the same level of pollution control or protection of the work force. In developing countries, industrial production often occurs in smaller units, such as backyard smelters, which have significant local effects and are more difficult to control.

The energy sector continues to grow rapidly worldwide. There are basically three types of energy sources: the burning of fossil fuels and biomass; nuclear power; and energy derived from natural processes such as the sun, wind, and the flow of water. Energy from fossil fuels results from the conversion of carbon to carbon dioxide, with the least efficient and most polluting fossil fuels reflecting the extent of components other than carbon and hydrogen in the fuel source. The most plentiful fossil fuel is coal, which is also among the most polluting. Coal contains mineral ashes, nitrogen, and sulfur, which produce particulates, nitrogen oxides and sulfur oxides, when coal is burned. The use of high-sulfur coal for electric power generation and for home heating was a dominant cause of major air pollution episodes in London in 1952, Donora, Pennsylvania, in 1948, and the Meuse Valley in Belgium in 1930. Much of the U.S. electric grid is powered by low-sulfur oil. Natural gas, which is a relatively pure hydrocarbon, is increasing in use and is particularly effective as a source of peak electric power during periods of high demand. The combustion of all fossil fuels produces nitrogen oxides, which are a major precursor of ozone and particulates. One form of nitrogen oxide, nitrogen dioxide, is itself a pollutant of concern. Carbon dioxide, the end product of efficient fossil fuel energy production, is a major contributor to global climate change. Reduction in carbon dioxide emissions requires more efficient production, transmission, and use of fossil fuel-derived energy. A switch to other energy sources will also help to reduce emissions.

Nuclear power has the advantage of not producing carbon dioxide or any of the sulfur oxides, nitrogen oxides, or particulates that are associated with fossil fuels. Its major disadvantages are the release of low-level radiation, the need for major water resources for cooling (with attendant ecological challenges), and, most importantly, the small but not absent risk of an uncontrolled nuclear reaction. The worst such example, and the only one in which there were substantial short-term health impacts from the civilian use of nuclear power, occurred in Chernobyl in the former Soviet Union in 1986. The extent of long-term effects due to the radiation that spread widely over Europe and globally is still being evaluated.

Wind and solar energy are expected to increase in use as the costs of fossil fuels increase and as new technology is developed. These are, in essence, free of pollution emissions. Hydroelectric power is a mainstay in some parts of the world, but dams have significant ecological implications and there is a growing movement against them. The most effective means of decreasing energy use is by lessening demand.

The transportation sector worldwide is increasingly dominated by automobile and truck emissions. In the United States there has been a marked decrease in pollutant emissions per mile driven that has been almost counterbalanced by an increase in the number of miles driven. Pollutants from gasoline-powered automobiles include the evaporation of volatile organic compounds and tailpipe emissions such as carbon monoxide, nitrogen oxides, benzene, and polycyclic aromatic hydrocarbons (PAHs). Increased engine efficiency and catalytic converters have been effective in decreasing all but nitrogen oxide emissions. Diesel engines, which in the United States are primarily used on trucks, emit high levels of particulates and PAHs. Two-cycle engines on mopeds and other smaller vehicles are relatively inefficient, with much of the fuel evaporating. This is particularly a problem in developing countries. All internal combustion engines lead to the production of carbon dioxide. Future growth in the use of personal automobiles will be a major threat to global carbon dioxide production unless new engines and power sources are developed. Control of automotive emissions is as much a function of effective planning of transportation systems, including mass transit, as it is of technology. There have been relatively few studies of airport-related pollutant emissions, a segment of transportation that is increasing rapidly.

Agriculture is also a major source of pollution. World population growth has been accompanied by increased crop yields, which have been made possible by heavy use of fertilizers and pesticides. Nitrogenous fertilizers, an important part of the increased yield, result in nitrite contamination of drinking water, to which infants are particularly vulnerable. Nitrogenous fertilizers contribute to oxygen problems in water bodies and to greenhouse gas emissions. Phosphate fertilizers are of concern because of trace amounts of cadmium and other heavy metals that sometimes are part of natural phosphates. Cadmium can be taken up into certain crops, can cause renal toxicity, and is a potential carcinogen.

There are a wide range of pesticides and herbicides that are central to modern agriculture. Each of these is chosen because of its ability to have a biological effect on a plant or insect, and there is always a possibility that the biological effect will extend to humans or to other species. Major problems have been caused by pesticides that persist in the environment, such as heptachlor. This has led to bans on persistent organic pollutants and to testing protocols to avoid developing new ones.

OTHER POLLUTION CATEGORIES

Categorizing pollution in terms of the four sectors of industry, energy, transportation, and agriculture obscures the fact that some of the most important sources of pollution are intersectorial. As just one example, the Aswan High Dam provides Egypt with an important hydroelectric source and is effective in controlling flooding and providing irrigation for agriculture. But by retaining silt it decreases the nutrient load to the Nile Delta, which leads to a much heavier requirement for chemical fertilizers for agriculture as well as loss of sardine and salmon fisheries. The lack of the flushing effect of Nile floods has led to increased salinization of the land and has optimized breeding conditions for snails that carry schistosomiasis, an ancient scourge of this area. Similarly, the use of wood for local energy in developing countries is more than just a potential source of indoor and outdoor air pollution. Loss of forests can lead to soil erosion, flooding, and desertification, and have a negative impact on global climate.

Activities that lead to human development within and across each of these major sectors have the potential for producing a pollution impact that outweighs any benefit. There is, unfortunately, one common human activity that has an enormous environmental impact with no redeeming developmental consequences: war.

Pollutants can also be characterized by chemical or physical class; by use; by industrial source; by whether they are likely to be present in air, water, food, or other media; by the organs they attack or the effects they have; by the laws that control their use; and by whether they present a local, regional, or global problem. All of these categorization schemes are valuable, but none are without its faults. Chemicals have multiple properties and uses, and are able to move across environmental boundaries. Pollution episodes have often come about through an inappropriate focus on only one aspect of a chemical. For example, the 1990 U.S. Clean Air Act required the use of oxygenated fuels, which have chemical characteristics that were thought to be beneficial in decreasing automotive emissions in polluted areas. Yet another chemical characteristics of the most commonly used oxygenate compound, methyl tertiary-butyl ether (MTBE), caused it to be a major groundwater contaminant, a problem that was not foreseen because of an inappropriately narrow focus.

A more holistic approach to environmental pollution is particularly important during the current transition period. Pollution control techniques have been largely successful in dealing with end-of-pipe emissions. Through regulatory command and control of major pollution sources there has been a steady diminution of measured emissions to air and water in developed countries, and an improvement in air and water quality. Yet major problems remain, and in some instances they are getting worse. Two interrelated categories of particular concern are global climate change and pollutants from nonpoint sources.

Our planet maintains itself through a series of feedback loops involving interconnected biological, geological, and physical processes. The science that has enhanced our understanding of these processes has also demonstrated their vulnerability to the increasing dominance of human activities, including the effect of pollutants. One example is the diminution of the stratospheric ozone layer that protects humans against the harmful effects of short-range ultraviolet light. A major source of this diminution is chlorofluorocarbons (CFCs). These compounds were seemingly ideal for refrigeration and a variety of other industrial purposes, in part because they are inert and cause little or no direct biological effects. But this lack of reactivity allows CFCs to persist and rise into the stratosphere where they enter into a reaction that decomposes ozone. An international treaty, the Montreal Protocol, has led to a decrease in this particular threat to the ozone layer. The feedback loops involved in global climate change, including the greenhouse effect which is now warming the earth, are far more complex and less well understood. Further, competitive economic and nationalistic interests have made it more difficult to deal with carbon dioxide and nitrogenous greenhouse gases.

Nonpoint source emissions refer to pollution for which there is no readily obvious target, or source. An example is damage to the Chesapeake Bay due to runoff of nitrogenous fertilizer compounds from farms along the Susquehanna River, including a heavy contribution from farms using natural fertilizing techniques. Agricultural practices and energy and transportation decisions contribute heavily to regional air and water pollution and to global warming.

UNDERSTANDING POLLUTION EFFECTS

A transition is also occurring in our understanding of the health effects of pollutants. It is now recognized that there are subtle health effects of environmental pollutants, such as endocrine disruption and neurobehavioral changes, for which newer toxicological paradigms are being developed. The unraveling of the human genome may provide a better understanding of the role of genetic susceptibility factors in response to pollution.

Understanding the effects of pollutants requires understanding how pollutants change following their release from a source, and how they can have effects many miles from their sources. For example, there are no significant direct emitters of air pollutant ozone. Rather, this major component of oxidant smog is formed in the air through the action of sunlight on a mixture of nitrogen oxides and hydrocarbons coming from many different sources, primarily automobiles. The precursors may have been emitted hundreds of miles upwind of where the ozone is eventually formed. For the northeastern United States, this means that statewide control strategies, which are the major enforcement focus of the U.S. Clean Air Act, are an inadequate approach to a regional issue. Similarly, acid rain and other forms of particulate air pollution can be derived from atmospheric reactions of gaseous sulfur dioxide and nitrogen oxides precursors occurring many hundreds of miles downwind. Agents released into water can also undergo significant changes. For example, methyl mercury, which is far more toxic than elemental mercury, is formed in water through the action of bacteria and makes its way into the food chain. The dumping of inorganic mercury from a single chloralkali plant in Minimata Bay, Japan, led to contamination of fish with methyl mercury and to over a hundred deaths and thousands of people being affected by what is known as Minimata disease. There is also a global air circulation of metals, such as mercury, and of persistent organic pollutants, such as PCBs, which tends to carry these agents toward the arctic where they often bioaccumulate.

Understanding the effects of pollutants on human health requires not only an understanding of the intrinsic hazard of the chemical or physical agent, but also the extent of human exposure. Exposure is often determined by local pathways within a community, such as whether drinking water comes from wells or from surface sources or whether individuals consume vegetables grown in their backyards or brought to market from far away. Individual activities can also alter pollutant intake; exercise, for example, increases respiratory uptake of air pollutants. Health effects due to pollutants are heavily dependent upon susceptibility factors, including age, gender, and genetic predisposition.

MANAGING POLLUTION

A variety of approaches have been developed to manage existing pollution. These include punishment of polluters through regulation, taxation, fines, toxic tort suits, and other disincentives; encouragement of nonpolluting approaches through tax and other incentives; and education of the public. The increased awareness of the potential harmful effects of pollution has had a major impact on industries and on individuals, particularly the young, who have led the way in activities such as recycling. Risk assessment has developed as a useful technique to estimate the risks of environmental pollutants and to establish priorities for environmental control and remediation efforts. These efforts to manage existing pollution are largely a form of secondary prevention in that the pollution already exists and the focus is on lessening the extent or the effects.

Primary prevention of pollution has occurred through approaches that, like any form of primary prevention, are both highly effective and difficult to quantify. The United States National Environmental Policy Act of 1969 was the first major action arising out of the new environmental movement aimed at avoiding unwanted environmental consequences. It contained the requirement that significant newly proposed federal activities have an environmental impact statement prepared in advance, the goal being the incorporation of environmental concerns into all planning processes and the avoidance of those activities that would have an adverse impact. Advances in science have had a significant primary preventive effect, in part through providing assessment tools of use in preventing the development of new harmful products by the chemical industry. As examples, a basic understanding of the role of mutation in cancer and recognition of the structural aspects resulting in the environmental persistence of chemicals have led the chemical industry to detect and quickly drop out of its development programs those new chemicals that are mutagens or are likely to persist in the environment. The Precautionary Principle is basic to public health practice, but is also now being advocated as a form of primary prevention of environmental pollution.

Control of the more challenging insidious pollutant effects related to the health of the planetary biosphere and to nonpoint sources cannot depend solely upon standard command and control regulatory approaches. Central to avoiding significant long-term consequences to health and the environment is the development of innovative pollution prevention and control strategies, including emissions trading, taxation of consumption and international compacts; better targeting of controls through improved scientific understanding of the processes involved; and a more informed public.

Bernard D. Goldstein

(see also: Acid Rain; Airborne Particles; Ambient Air Quality [Air Pollution]; Ambient Water Quality; Arsenic; Automotive Emissions; Benzene; Carcinogen; Chlorofluorocarbons; Clean Air Act; Clean Water Act; Climate Change and Human Health; Ecosystems; Emissions Trading; Endocrine Disruptors; Environmental Impact Statement; Exposure Assessment; Groundwater; Human Genome Project; Lead; Mercury; National Environmental Policy Act of 1969; Nuclear Power; PCBs; Persistent Organic Pollutants [POPs]; Pesticides; Precautionary Principle; Radiation, Ionizing; Risk Assessment, Risk Management; Sulfur-Containing Air Pollutants [Particulates]; War )

Bibliography

United Nations Environment Programme (1999). Global Environment Outlook 2000—UNEP's Millennium Report on the Environment. London, UK: Earthscan Publications Ltd.

World Health Organization (1992). Report of the WHO Commission on Health and Environment. Geneva: Author.

pollution control Pollutants in groundwaters, surface waters (rivers, lakes, and oceans), and the atmosphere are introduced into the environment as a result of many industrial activities. After release these pollutants can be affected by physical, chemical, and biological processes. Mathematical models that are used to attempt to predict the mobility of pollutants by accounting for all three processes are generally referred to as ‘fate and transport models’. The majority of processes that affect the fate and transport of elements can be described by rate equations which show that the rate of pollutant reduction is a first-order process. This means that the rate (R) is directly related to the concentration of the pollutant ([A]) times a rate constant (k): R = k[A]. Few processes are second-order, in which the rate of pollutant reduction also depends on the concentration of a second chemical ([B]) that is present in nature: R = k[A][B].

In this context, physical processes are transport processes; they include sorption, volatilization, diffusion, and advection (horizontal flow). Chemical processes are solubility (chemical equilibria), oxidation and reduction (redox), hydrolysis, hydration, and photolysis. Biological processes are primarily biotransformation, biodegradation, and bioaccumulation. It is important to understand the transport processes for toxins because of their effect on living things. We therefore also need to understand the toxicology of each pollutant.

Transport processes

Transport processes can result in the direct dilution of the contaminant as a result of retardation, diffusion, or dispersion.

Sorption refers to the interaction of dissolved constituents (solute) with mineral surfaces in groundwater. The solute is generally a charged ion which can be adsorbed to the surface (see adsorption), absorbed into the surface, or undergo ion exchange with ions in the mineral. Adsorption results from mineral surfaces having a surface charge in aqueous solutions, the charge being pH-dependent. In general, mineral sur-faces are positively charged in acidic waters (low pH) and negatively charged in alkaline waters (high pH). As a result, positively charged metal ions (e.g. Pb²⁺) adsorb to mineral surfaces at intermediate to high pH. When these ions diffuse away from the mineral surface into the structure of the mineral because of concentration gradients, the process is referred to as absorption, not to be confused with adsorption. Dissolved ions can also exchange with ions already present in the structure of a mineral. This process is generally referred to as ion exchange, and is particularly important for minerals such as zeolites and clay minerals which have loosely bound cations in channels or interlayers within their structure. These loosely bound ions generate charge balance with the negatively charged structural units composed of silica, aluminium, and oxygen. For minerals that have ion-exchange properties, the maximum amount of inter-layer or channel ion ex-change with dissolved solids is generally referred to as the ion-exchange capacity.

Sorption of inorganic ions is related to the concentration of the dissolved constituent, the surface area of the minerals, and the pH of the solution. Sorption is generally described by adsorption isotherms, which show the amount of a chemical adsorped as a function of pH or some other chemical variable.

Sorption of organic molecules is primarily on to organic compounds in sediments. Their sorption is hence related to the amount of organic material present and whether the organic compound is hydrophobic (has low water solubility) or hydrophylic (has high water solubility). Hydrophylic organic compounds have low adsorption coefficients and a low bioaccumulation factor (see biogeochemistry). It follows that hydrophobic organic compounds have high adsorption coefficients and high bioaccumulation factors.

Volatilization of organic chemicals from water to the atmosphere is particularly important for chemicals that have high vapour pressures and low water solubilities. Organic vapour production is experienced, for example, at filling stations, where obnoxious petrol odours are usually prevalent. In contrast, many of us are familiar with the pleasant smell of a good whisky or brandy, which also results from the volatilization of certain organic molecules.

Volatilization is a first-order rate process and is an important control on the composition of the upper layers of surface waters and groundwaters. Deep down within fluids or aquifers volatilization is not an important transport process.

Diffusion occurs when solutes move under the influence of thermal-kinetic energy down a concentration gradient. Diffusion continues until the concentration gradient is absent.

The diffusion constant varies as a function of temperature, falling by about 50 per cent upon cooling from 25 °C to 5 °C. Diffusion is a relatively slow process and is not of major importance unless water flow is extremely slow. Over geological timescales, however, diffusion can be an important process.

When dissolved solids are carried along with the flowing groundwater, the process is called advective transport or convection. The amount of solute that is transported is a function of its concentration in the groundwater and the quantity of the groundwater flowing. Groundwater can move at rates that are both greater and less than the average linear velocity. This is caused by differences in pore size, the tortuosity of pore channels, and the differential velocity of fluid across pores caused by drag resulting from the roughness of pore surfaces. Differences in velocity cause mixing to occur along the flow-path. This mixing is called mechanical dispersion, and it results in dilution of the solute at the advancing edge of the flow. The magnitude of dispersion is largest in the longitutinal direction of the flow; the dispersion in the transverse direction of the flow is roughly 10 per cent of the longitudinal dispersion. Dispersion is usually described with the advection–dispersion equation. This equation describes the change in concentration with respect to time in one, two, or three dimensions. In general, dispersion calculations do not take account of any retardation processes and are thus worst-case calculations. Reactive transport modelling is a relatively new area of research, which, because of its complexity, is actively pursued by few research groups at present.

Chemical processes

Chemical processes involve a variety of chemical reactions which affect the concentration of dissolved constitutents along the flow-path. Minerals dissolve in water in a similar way to sugar in a cup of coffee or tea. However, mineral solubility is, in general, very low under the near-neutral pH conditions typical of natural aquatic systems. The amount of a mineral that can dissolve (its solubility) depends on the pH of the water, the temperature, the pressure, and, for elements that have more than one oxidation state (e.g. iron, Fe²⁺ and Fe³⁺), on the amount of oxygen in the water. Mineral solubilities are known from experiments from which thermodynamic data have been derived. In order to use these data it is necessary to assume that the system has reached equilibrium. This takes a very long time (years or decades) at ambient temperatures, but a very short time at high temperatures (a matter of seconds or hours at 1000 °C). Polluted waters at ambient temperatures may not have reached thermodynamic equilibrium. However, by assuming equilibrium conditions it is possible to predict how the system will react in the future; such calculations are therefore of great value for the geochemist when evaluating the effect of chemical reactions on the fate of pollutants in groundwater.

Evaluating chemical equilibria in groundwater systems is done either in terms of solubility or by inferring an alteration from a primary mineral (unstable at ambient conditions) to a secondary mineral (stable at ambient conditions). These mineralogical reactions, whether solubility or alteration reactions, are generally described as proton (H⁺) transfer reactions. Oxidation–reduction reactions are generally referred to as electron (e⁻) transfer. The solubility of calcite (calcium carbonate, CaCO₃) can be simply described by the following reaction:CaCO₃(s) + 2H⁺ = Ca²⁺ + H₂CO₃(aq).

This reaction shows that in dissolving CaCO₃ there is a transfer of 2H⁺ for each Ca²⁺ and that the solubility is dependent on pH (H⁺ concentration).

Similarly, the weathering of feldspar (KAlSi₃O₈) to form kaolinite (Al₂Si₂O₅(OH)₄), one of the most common weathering reactions on the Earth's surface, can be described by 2KAlSi₃O₈ + 2H⁺+ 9H₂O = Al₂Si₂O₅(OH)₄ + 2K⁺ + 4H₄SiO₄(aq).


This reaction also requires the transfer of protons, that is, one H⁺ for each K⁺. Such reactions can be illustrated on activity–activity diagrams on which are plotted the effective concentration (activity) of dissolved ions.

Oxidation and reduction reactions can be described either in terms of oxygen transfer or of electron transfer. For example, the oxidation of the mineral magnetite, (Fe(II)Fe(III)₂O₄), to form the mineral haematite, (Fe(III)₂O₃), can be represented by the equation2Fe₃O₄ + 0.5 O₂ = 3Fe₂O₃

or by2Fe₃O₄ + H₂O = 3Fe₂O₃ + 2H⁺ + 2e⁻.

These reactions are thus dependent on the amount of oxygen in the system, which can also be represented by the dependence of pH (activity of H⁺) and the pe (activity of e⁻). In this respect the solubility of minerals can be shown on pe–pH diagrams which describe the solubility of the minerals as a function of pe and pH.

It will be apparent from the preceding discussion that minerals dissolve in water and the mineralogy of the groundwater reservoir will be reflected by the water composition. The composition of the groundwater in turn plays an import-ant role in determining the concentration of pollutants in groundwater.

The effect of chemical equilibrium reactions can be calculated where thermodynamic data are known. These data are generally commonly available for inorganic species. However, the effects of organic ligands (molecules or ions bonded together) on the amounts of dissolved metals (or metal– organic complexes) in water are still poorly characterized and are therefore the subject of active research.

Oxidation of organic chemicals occurs as a result of reaction with oxidants formed during photochemical processes in natural waters. These oxidants include singlet oxygen and alkylperoxyl radicals (monovalent aliphatic hydrocarbon radicals containing O₂₋ groups). The oxidation process in thus a second-order rate process.

Reduction in anaerobic environments occurs by both inorganic and biological processes. An example of such a reduction process is the replacement of a chlorine atom for a hydrogen atom on industrially produced organochlorine chemicals. Rate expressions for this process are still poorly defined for organic chemicals. Oxidation and reduction of inorganic chemicals depend solely on the amount of oxygen in the system.

Hydration is important for some organic chemicals. In this process carbonyl compounds form hydrates which have different properties from those of the parent (unhydrated chemical + water = hydrated chemical). Rate expressions for this process are not well known at present.

Hydrolysis of organic compounds results in the introduction of a hydroxyl group (−OH) into the chemical structure, commonly with the loss of a functional group (−X), RX + H₂O = ROH + H⁺ + X⁻.

This process is a first-order rate reaction. Some organic chemicals show a pH-dependent elimination reaction. These are second-order rate processes in which the hydrolysis reaction is dependent on the concentrations of H⁺ or OH⁻.

Photolysis is important for organic chemicals in surface waters and in the atmosphere. It occurs when chemicals are bombarded by light of wavelengths of more than 290 nm (ozone filters out shorter wavelengths). Photochemical transformations can occur by direct or indirect photolysis.

Direct photolysis takes place if the chemical absorbs light and then undergoes a transformation reaction from an ‘excited state’. These transformations include rearrangement, dissociation, and oxidation. The rate of a photolysis reaction is a first-order process.

Indirect photolysis occurs when substances naturally present in aquatic environments absorb sunlight to form excited chemical species or radicals, which then react with the pollutant chemical. Indirect photolysis is thus a second-order rate process.

Biological processes

Biological processes involve enzyme-catalysed transformation of chemicals and the build-up of chemicals in the food chain.

Organisms require energy, carbon, and other fundamental inputs from the environment for their growth and maintenance. In life they manufacture enzymes which may transform or biodegrade contaminants that have been introduced into the environment. By far the most important biodegradation processes in aquatic and soil environments are carried out by microbes.

The biodegradation rate is a function of microbial biomass and the concentration of the chemical under given environmental conditions. Micro-organisms use the chemical substrate (the substance acted upon by an enzyme) as an energy source. In doing so the biomass is increased. Biodegradation rates, are therefore a function of cell growth rate. If an organic compound is used by a micro-organism as a sole source of carbon, the specific growth rate of the organism is a function of the concentration of the compound.

In the environment, where cell concentration, X, is relatively large, and pollutant concentration is low, microbial populations will not change significantly when the chemical is consumed. The degradation rate under these conditions is thus a ‘pseudo’-first-order process. The first-order rate equation can be used under conditions where micro-organisms become acclimatized to the chemical and can actively use it. The acclimatization period is required to induce the organisms to produce necessary enzymes, to develop biodegradation organisms by mutation, to increase the number of microbes to substantial levels, and to use the diauxic (other readily metabolized) substrates. This acclimatization period cannot generally be ignored when a chemical is newly introduced into an uncontaminated environment.

Some pollutants may be biotransformed only when another organic compound is present to serve as a carbon energy source. This phenomenon is known as co-metabolism and is a second-order rate process. Mathematical expressions for such transformations are still poorly defined.

Bioaccumulation of chemicals in living species is especially important for hydrophobic chemicals which can be partitioned into fat and lipid tissues. Bioaccumulation also occurs where inorganic chemicals are partitioned into bones (which are composed of the mineral hydroxyapatite) and bone marrow. Bioaccumulation is usually evaluated in terms of the bioconcentration factor (BCF), which is equal to the concentration of the chemical in tissue (C_t on a dry weight basis) normalized to the concentration of the chemical in water (C_w); BCF = C_t/C_w.

Bioconcentration data are complicated by the fact that the concentration of a chemical is usually higher in the fatty tissues of the species than in leaner tissues. The rate of uptake and the time for attainment of equilibration in various organs (and species) also depends on the route of uptake (e.g. whether it is part of the diet or is absorbed through the skin). There is a correlation between the BCF and how hydrophobic the organic chemical is.

Environmental fate and transport

In evaluating the most important fate process for a given contaminant it is important to pinpoint the processes that have the shortest half-lives (t_½), that is, the time required for the removal of one-half of the initial concentration of the chemical. As for radioactive decay, the half-life of a chemical can be calculated if the rate constants (k₁, k₂, k₃, etc.) are known: t_½ = 0.693/(k₁+k₂+k₃).

When considering the fate and transport of contaminants in the environment, each pollutant has to be evaluated individually. The heavy metal lead and the lubrication fluids known as PCBs (polychrorinated biphenyls) provide good examples. Lead is an important pollutant in mining areas where sulphide minerals (such as galena, PbS) are mined, and in many industrial contexts such as metallurgy, paints, and permanent magnets. PCBs were the miracle fluids, used widely in the western world in transformers, turbines, and vacuum pumps for their high thermal stability and dielectric properties. They were also used as plasticizers in paints, plastics, resins, inks, etc. PCBs were used until it became known that they are both highly toxic to most forms of life and are very stable in the environment.

The dominant mechanism controlling the fate of lead is adsorption. Precipitation of lead sulphate (PbSO₄), lead carbonate (PbCO₃), and lead sulphide (PbS) minerals and bioaccumulation are also important. At low pH values, adsorption and precipitation are not nearly as effective in removing lead from solutions as at higher pH. Lead is therefore much more mobile in acidic waters (such as mine drainage) than at higher pH values. In alkaline and near-neutral waters, removal of lead by adsorption and precipitation occurs relatively quickly. Lead causes genetic changes, foetal malfunctions, and bowel cancer in humans. It is well known that lead causes irreversible retardation in the development of children, especially those exposed to leaded car exhausts. Lead accumulates in bone, because it can partition for calcium in the bone-forming mineral apatite.

Adsorption and volatilization dominate the environmental dynamics of PCBs in natural waters. PCBs do, however, adsorb only to organic compounds within groundwater reservoirs. PCBs can be desorbed from sediments, causing a continuous source of contamination. Dissolved PCBs move with the bulk water flow. PCBs cause growth inihibition and reductions in population in a range of species from algae to birds. In humans PCBs cause cancer of the kidneys and the liver and are known to be mutagens (i.e. capable of changing inheritable characteristics), teratogens (i.e. capable of causing malformation), and act as hormone mimickers.

K. Vala Ragnarsdottir

Bibliography

Moore, J. W. and and Ramamoorthy, S. (1984) Heavy metals in natural waters. Springer-Verlag, New York.
Moore, J. W. and and Ramamoorthy, S. (1984) Organic chemicals in natural waters. Springer-Verlag, New York.

Pollution

BIBLIOGRAPHY

Pollution is the contamination of the natural environment by one or more substances or practices. Most pollution is an externality—an unintended by-product—of the use of energy and other products that have become central to industrial society. As a consequence, pollution is very difficult to eliminate, because doing so requires change in people’s use of these central products and systems. The automobile, for example, is the single most important component of the transportation systems of Western industrial economies, yet it is also a major source of air and water pollution, toxic wastes, and noise.

Pollution of vital “common resources” such as air and water is an especially challenging problem. Because these resources are owned by society as a whole and cannot be divided among individuals, their use is often regarded as being free. The benefits to the individual of using common resources (for instance, disposing of chemical wastes by dumping them in a river) are frequently tangible and immediate (in this case, avoiding the expense of proper disposal), whereas the costs of such use are typically longterm, intangible, and paid by the community as a whole (in the form of polluted water). Thus, it appears to be rational for an individual to make maximum use of common resources, even at the risk of their overuse and eventual destruction.

The single most important cause of pollution, especially in industrial societies, is the use of fossil fuels in cars, industries, and homes. Fossil fuels include petroleum, coal, natural gas, and uranium. Major forms of air pollution, such as global warming, acid rain, depletion of the stratospheric ozone layer, and airborne toxic chemicals, all result at least in part from the incomplete burning of fossil fuels. The main piece of legislation governing air pollution in the United States is the Clean Air Act Amendments (CAAA), first passed in 1970 and amended several times, most notably in 1990. The guiding principle of the CAAA was to require that industrial expansion incorporate efforts to reduce air pollution. Market-based incentives have been added to the CAAA, particularly in the 1990 acid rain title, and are considered by many economists and policymakers to be more effective and more politically palatable than the traditional command-and-control approach to pollution control.

Fossil fuels cause water pollution as well, in the form of oil spills, industrial emissions, and acid rain. Congress passed the Federal Water Pollution Control Act in 1972 to restore the integrity of U.S. waters, and the Safe Drinking Water Act in 1974, giving the Environmental Protection Agency (EPA) the power to set standards for drinking water quality, which are implemented by the states. These legislative initiatives have had demonstrable though partial success, though many aspects of water pollution control, such as the protection of wetlands, remain highly controversial and limited.

Toxic chemical wastes became an important issue in environmental policy soon after the tragedy of Love Canal, an area of Niagara Falls, New York, where the Hooker Chemical Company transferred ownership of some land to the local government for the building of a school. Hooker Chemical had previously dumped massive quantities of hazardous chemicals in the area, and families living nearby began to be alarmed by an unusually high incidence of illnesses and birth defects. The Superfund program, passed in 1980 and reauthorized in 1986, has been the most far-reaching and expensive legislative effort to clean up toxic wastes on land that has been abandoned by its owners. The program has a significant number of drawbacks, however, including the facts that a substantial amount of Superfund money has been spent on lawsuits rather than on remediation of sites, the number of sites cleaned up is a small proportion of the total proposed for cleanup, and the program has slowed almost to a standstill since the 1990s.

Another serious pollution problem stems from the use of artificial radioactivity for the development and testing of nuclear weapons as well as for the production of electrical power. Although nuclear power plants do not emit the same levels of air pollutants that coal and oil-fired power plants do, radioactive substances such as uranium and plutonium are powerful poisons. Meltdowns and near-meltdowns of nuclear plants (such as the Chernobyl disaster in 1986 in Ukraine) have sharply discouraged the use of nuclear power in the United States, as has the inability to create completely inviolable, long-term storage for nuclear wastes.

In addition, pollution problems and loss of habitats have contributed to the extinction of many species of plants and animals. The Endangered Species Act (ESA) of 1973 established a series of regulations to protect endangered and threatened species and the ecosystems on which they depend. The ESA generally has been considered to be successful; conflicts between requirements of the ESA and projects proposed by developers were effectively resolved during most of the act’s existence. However, in recent years the property rights movement has taken strong exception to the continued enforcement of the ESA.

Other forms of pollution are less commonly recognized. One is indoor air pollution. As people work to bring down the high cost of heating and cooling by weatherproofing their homes, the atmosphere in these more airtight homes is more easily contaminated by pollutants such as cigarette smoke and toxins given off by carpeting, paneling, and household chemicals. Another, less commonly recognized form is light pollution: the excessive use of artificial light that brightens the dark sky, interfering with the work of amateur astronomers and harming nocturnal wildlife and other ecosystems. A third, noise pollution, refers to excessive noise levels, typically in urban and industrial areas, which not only disrupt people’s lives and work but also raise blood pressure and stress levels, cause hearing loss, and interfere with the natural feeding, breeding, and migration cycles of animals.

Desertification—the encroachment of desert-like conditions into semidesert land—has been identified in large areas of Asia, Africa, and North America. The use of wood rather than oil or coal for fuel leads people in many developing nations to cut trees on a large scale; this often leads to disastrous flooding because tree roots can no longer hold topsoil in place when the rainy season comes. The burning of agricultural lands to clear dead vegetation, a common practice among farmers in many nations, can cause clouds of soot to move across neighboring nations.

Many of the most common forms of pollution have substantial economic impacts. Increases in air pollutants such as sulfur dioxide and urban ozone affect human health, causing or worsening conditions such as asthma, emphysema, and lung cancer. The resulting costs of medical treatment and shortened life expectancy affect a nation’s productivity. Those who usually suffer are often the most vulnerable members of society: the elderly, the sick, the poor, and the very young. The environmental justice movement charges that the burden of pollution-caused health problems tends to fall most heavily on dis-advantaged groups because these groups are least able to mobilize politically to demand pollution control. In more affluent areas, NIMBY (“not in my backyard”) groups often have been successful at preventing the siting of incinerators, waste dumps, and other environmental hazards that can undermine property values in their neighborhoods.

Cleaning up pollution is very expensive as well. The EPA estimated that the provisions of the CAAA have cost $523 billion to implement between 1970 and 1990 (U.S. Environmental Protection Agency 1997). Some economists and political leaders regard this as unproductive spending, in that these expenditures do not help the businesses spending the money produce more goods. According to the 1997 EPA study, however, during this time period the application of the CAAA saved 205,000 American lives and provided between $6 and $50 trillion in economic benefits. Spending on pollution control goes in part to fund the manufacture of pollution control equipment, which adds to economic growth.

Pollution levels in the United States generally have improved as a result of the pollution-control policies of the past thirty years. Recycling and “precycling” (developing methods of manufacture that produce smaller amounts of waste) have reduced the production of solid wastes in many communities. The amount of lead (a neurotoxin) recorded in the air and in human blood samples is substantially down from 1970 levels, in large part because of the removal of lead from gasoline, due to the CAAA. Some international agreements have been effective, such as the Montreal Protocol (1987), which appears to have stabilized the problem of depletion of the stratospheric ozone layer. The improvement has been uneven, however. Urban ozone levels remain a substantial problem for most big cities in the United States. Global warming (Gore 2006) poses an extremely serious risk to the planet, and pollution problems are worsening rapidly in many industrializing nations, such as China and India.

SEE ALSO Disaster Management; Environmental Kuznets Curves; Externality; Global Warming; Love Canal; Pollution, Air; Pollution, Noise; Pollution, Water; Regulation; Toxic Waste; Transportation Industry

BIBLIOGRAPHY

Caldwell, Lynton K. 1996. International Environmental Policy. 3rd ed. Durham, NC: Duke University Press.

Gore, Al. 2006. An Inconvenient Truth. DVD, Paramount Home Entertainment.

Hardin, Garrett, and John Baden, eds. 1998. Managing the Commons. Bloomington: Indiana University Press.

Rosenbaum, Walter A. 2004. Environmental Politics and Policy.6th ed. Washington, DC: CQ Press.

U.S. Environmental Protection Agency. 1997. Benefits and Costs of the Clean Air Act: Retrospective Study—1970 to 1990. Available from http://www.epa.gov/air/sect812/retro.html.

Marjorie Randon Hershey

pollution is the introduction of substances and energy in concentrations that result in harm to the marine environment and its fauna and flora. But see also environmental issues.

Dumping.

Disposal of waste and raw sewage into the sea from ships and land became commonplace in the 19th and 20th centuries. At the time it provided a relatively cheap and very effective way of keeping the land clean and, following the construction of the sewage systems that discharged wastes either into rivers or the sea, the health of city-dwellers improved immensely. Sea water was thought to be effective in cleansing human waste and killing the pathogens, but after the Second World War (1939–45) it became clear that eating contaminated fish and shellfish from polluted water created a serious health risk, and even swimming in the sea could be hazardous and was linked to poliomyelitis.

At the end of the Second World War there was a major problem of what to do with large quantities of redundant munitions and toxic chemical agents. The solution, which seemed innocuous at the time, was to dispose of them in the sea. Similarly, when the newly emerging nuclear industries started to generate large quantities of dangerous radioactive waste, this too was dumped in the deep ocean. The first of the campaigns by Greenpeace led to banning of the disposal of radioactive waste in the sea and eventually to a complete reappraisal of marine dumping and a tightening of international regulations.

Once the relevant annexe of the 1978 International Convention for the Prevention of Pollution from Ships, known as MARPOL, came into force, throwing and discharging most wastes from ships was also banned. All wastes now have to be off loaded in port, and the oceans are awarded greater protection from dumping of industrial waste than is afforded to the land or the atmosphere.

Toxic Chemicals.

Marine ecosystems do have a limited capacity to cope with low levels of naturally occurring toxic chemicals. Organisms that take up some pollutants like heavy metals (e.g. mercury and lead), either directly from the water or via their food, can regulate their contents to some extent. Once the pollutant is absorbed into the body it may be excreted or converted into a non-toxic form and stored in the liver or in fatty tissues. However, if a predator eats prey containing such detoxified pollutants, it too absorbs and stores the pollutant and so it accumulates—a process known as biomagnification. Top predators tend to accumulate high concentrations of the pollutants in their tissues, and humans are, of course, the ultimate top predator. For example, in the Faeroe Islands the traditional hunt for pilot whales has been abandoned because the whales are too heavily contaminated with heavy metals and PCBs (polychlorinated biphenyls) to be safe to eat.

Chemical industries continue to synthesize many thousands of novel substances each year. Many of these are specifically designed to be toxic and persistent. Ecosystems have no built-in ability to deal with novel substances, and so they have the potential to cause chronic long-term problems. Intensive agriculture, aquaculture, and industry all have high demands for chemicals that will boost production, control pests, and limit corrosion. The high cost of such chemicals favours the selection of persistent substances, which reduces the number of applications. The problems accruing from the synthesis and use of such novel substances were first recognized with DDT. Post-war, this was the most effective insecticide, particularly successful in controlling malaria-carrying mosquitoes and agricultural pests. However, DDT accumulated in body fat and interfered with the laying down of eggshells in birds, including seabirds; populations of many charismatic species declined catastrophically. This was the first indication of a much greater environmental disaster as DDT residues were found to be accumulating not only in Antarctic species but also in human tissues, which persuaded governments to curb its manufacture and use.

Likewise the manufacture of PCBs (polychlorinated biphenyls), once widely used as lubricants and coolants, was halted in 1977, when they were found to be accumulating in both man and animals. By the time their manufacture was banned about 2 million tonnes had been synthesized, most of which still exist today as they are highly stable. About a third is in waste stores and the rest is out there contaminating the environment.

The use of TBTs (tributyltins) in antifouling paints was so effective at controlling fouling organisms that they were rapidly and widely adopted. Soon their devastating impact as hormone disruptors was discovered; marine animals turned into sterile sexual intermediates, and some think reductions in human sperm counts have a similar cause. TBTs have largely been phased out, but they are so persistent that many harbours and yacht basins still have substantial traces of TBTs in their sediments, which are inhabited by very aberrant faunas.

Atmospheric Disruption.

Marine pollution is not all about direct impacts, it also involves the disruption of environmental processes. For example chorofluorocarbons (CFCs), once widely used as refrigerants, are inert in sea water and have no direct effect on the ocean life. But high in the earth's atmosphere, they lead to the breakdown of the ozone layer, which normally shields the surface of the earth from the damaging effects of the full intensity of the ultraviolet light coming from the sun. Once a hole appears in the ozone layer marine plants and animals are exposed to the full intensity of UV radiation. The productivity of the Southern Ocean has probably been reduced by more than 10%. It may also have contributed to the increasing prevalence of coral bleaching in coral reefs. It is estimated that it will take over 50 years for the ozone hole finally to return to normal. Also, the increase of greenhouse gases in the atmosphere, particularly carbon dioxide from the burning of fossil fuels, is threatening to cause climate change that will disrupt the global ecosystem, including the oceans, in an unpredictable manner.

Garbage.

Marine garbage, some thrown from or washed off ships, but most being carried in by rivers and blown into the sea from land, is not only unsightly but also causes real environmental problems. It accumulates in slicks where it becomes a major cause of premature death in turtles (see marine reptiles) through their mistaking plastic bags that block their guts for the jellyfish they feed on. Three hundred albatross chicks examined on the Pacific island of Midway, about as far as one can get from ‘civilization’, all had plastic items in their stomachs.

Inputs of some pollutants can be reduced by cleaning up our rivers and ground waters, and stopping direct discharges from land and ships. But controlling the inputs that arrive via the atmosphere will be much harder. The switch to unleaded fuel for vehicles has substantially reduced the lead entering the oceans from the atmosphere. Now anthropogenic radioactivity adds less than 1% to the natural background levels of radiation.

Oil Pollution.

Another source of pollution is the foundering of large vessels carrying damaging cargoes. The effects of massive oil spills after notorious tanker disasters, such as the Torrey Canyon and the Exxon Valdez, have been well publicized and have resulted in considerable improvements in navigation, ship safety, and routeing that have curtailed the frequency of such accidents. However, human error ensures the risks can never be eliminated while we continue to transport materials around the oceans and exploit seabed minerals. The only sure way to stop marine pollution is to cease the manufacture, use, and transportation of the major pollutants, but so long as the human population continues to grow, marine pollution problems will continue.

Bibliography

Clark, R. , Marine Pollution (1997).
Website on PCBs: www.atsdr.cdc.gov/tfacts17. html

M. V. Angel

Pollution control

Pollution control is the process of reducing or eliminating the release of pollutants (contaminants, usually human-made) into the environment. It is regulated by various environmental agencies that establish limits for the discharge of pollutants into the air, water, and land. A wide variety of devices and systems have been developed to control air and water pollution and solid wastes.

Air pollution control

Methods of air pollution control can be divided into two categories: the control of particulate (pronounced par-TIK-you-let) emissions and the control of gaseous emissions. The term particulate refers to tiny particles of matter such as smoke, soot, and dust that are released during industrial, agricultural, or other activities. Gaseous emissions are industrial products such as sulfur dioxide, carbon monoxide, and oxides of nitrogen also released during various manufacturing operations.

Particulate control. Methods for particulate control tend to operate on a common principle. The solid particles are separated from the gases in which they are contained by physical procedures such as passage through a settling chamber. A settling chamber is a long, wide pipe through which gases from a manufacturing process are allowed to flow. As these gases slow down in the pipe, the solid particles settle out. They can then be removed from the bottom of the pipe.

A cyclone collector is another device for removing particulates from stack gases. The gases are fed into a rotating cylindrical container.

Centrifugal forces (the forces that move things away from the center of rotation) send solid particles in the gas outward against the walls of the container. They collect there briefly, then fall to the bottom of the container. Gases from which the particles have been removed then escape from the top of the container.

Gaseous emissions. Many different methods are available for removing unwanted gases, most of which are acidic. Scrubbers are smokestack devices that contain a moist chemical such as lime, magnesium oxide, or sodium hydroxide. When gases escape from a factory and pass through a scrubber, they react with the moist chemical and are neutralized. From time to time, the scrubbers are removed from the smokestack, cleaned, and replaced.

Another method for controlling gaseous emissions is by adsorption. Activated charcoal is charcoal that has been ground into a very fine powder. In this form, charcoal has the ability to adsorb, or adhere to, other chemicals. When unwanted gases flow over activated charcoal on the inside of a smokestack, they are adsorbed on the charcoal. As with scrubbers, the charcoal is removed from time to time, and a new lining of charcoal is installed in the smokestack.

Water pollution

Methods of controlling water pollution fall into three general categories: physical, chemical, and biological. For example, one form of water pollution consists of suspended solids such as fine dirt and dead organisms. These materials can be removed from water by simply allowing the water to sit quietly for a period of time, thereby allowing the pollutants to settle out, or by passing the water through a filter. (The solid pollutants are then trapped in the filter.)

Chemical reactions can be used to remove pollutants from water. For example, the addition of alum (potassium aluminum sulfate) and lime (calcium hydroxide) to water results in the formation of a thick, sticky precipitate. When the precipitate begins to settle out, it traps and carries with it solid particles, dead bacteria, and other components of polluted water.

Biological agents can also be used to remove pollutants from water. Aerobic bacteria (those that need oxygen to survive) and anaerobic bacteria (those that do not require oxygen) attack certain chemicals in polluted water and convert them to a harmless form.

Solid pollutants

Solid pollutants consist of garbage, sewage sludge, paper, plastics, and many other forms of waste materials. One method of dealing with solid pollutants is simply to bury them in dumps or landfills. Another approach is to compost them, a process in which microorganisms turn certain types of pollutants into useful fertilizers. Finally, solid pollutants can also be incinerated (burned).

Taking on pollution: a global attempt

While artificial chemicals have improved the quality of life around the world, they have also posed a threat to the health of people and wildlife. In late 2000, in an effort to control the effect of toxic global pollutants, the United Nations Environment Program organized a meeting to draft a treaty to restrict the production and use of twelve persistent organic pollutants (POPs), especially those used as pesticides. The twelve toxic chemicals cited, which environmentalists have called the "dirty dozen," include eight pesticides (aldrin, chlordane, DDT, dieldrin, endrin, heptachlor, mirex, and toxaphene), two types of industrial chemicals (hexachlorobenzene and polychlorinated biphenyls or PCBs), and two types of industrial byproducts (dioxins and furans). These toxic pollutants were chosen not because they are the most dangerous, but because they are the most widely studied. Since it is still widely used in Africa to control malaria, DDT was given a special exemption: it can be used in those countries until replacement chemicals or strategies can be developed and put into place. One hundred and twenty-two nations (including the United States) agreed to the treaty. Before it can take effect, however, at least fifty of those nations must also ratify it.

Possible future approach to cleaning up pollution

The cost of cleaning up tens of thousands of toxic sites on factory grounds, farms, and military installations is staggering. In the United States, that amount may soon exceed $700 billion. So far, the main approach has been to dig the polluting chemicals out of the ground and transport them to a landfill. However, after a decade of research, scientists in the early twenty-first century found that hundreds of species of plants, along with the fungi and bacteria that inhabit the ecosystem around their roots, seek out and often break down chemical molecules that can harm most other life. For example, there are sunflowers that capture uranium, ferns that thrive on arsenic, clovers that eat oil, and poplar trees that destroy dry-cleaning solvents. Research into using plants as pollution sponges must continue, but early reports of their helping to clean up pollution were promising.

[See also Acid rain; Pollution ]

POLLUTION

The contamination of the air, water, or earth by harmful or potentially harmful substances.

The U.S. environmental movement in the 1960s emerged from concerns that air, water, and soil were being polluted by harmful chemicals and other toxic substances. During the industrial revolution of the nineteenth century, the mass production of goods created harmful wastes, much of which was dumped into rivers and streams. The twentieth century saw the popular acceptance of the automobile and the internal combustion engine, which led to the pollution of the air. Rapidly expanding urban centers began to use rivers and lakes as repositories for sewage.

Land pollution involves the depositing of solid wastes that are useless, unwanted, or hazardous. Types of solid waste include garbage, rubbish, ashes, sewage-treatment solids, industrial wastes, mining wastes, and agricultural wastes. Most solid waste is buried in sanitary landfills. A small percentage of municipalities incinerate their refuse, while composting is rarely employed.

Modern landfills attempt to minimize pollution of surface and groundwater. They are now located in areas that will not flood and that have the proper type of soil. Solid wastes are compacted in the landfill and are vented to eliminate the buildup of dangerous gases. Hazardous wastes, including toxic chemicals and flammable, radioactive, or biological substances, cannot be deposited in landfills, and the management of these wastes is subject to federal and state regulation. The federal government's Resource Conservation and Recovery Act (42 U.S.C.A. § 6901 et seq.) is a comprehensive regulatory statute that creates a "cradle to grave" system of controlling the entire hazardous waste life cycle.

Nuclear wastes are especially troublesome. Congress passed the Nuclear Waste Policy Act of 1982 (42 U.S.C.A. §§ 10101–226), which directed the department of energy to formally begin planning the disposal of nuclear wastes and imposed most of the costs of disposal on the nuclear power industry. Since 1986 the Department of Energy has been unsuccessful in finding an acceptable site. Yucca Mountain, Nevada, is the only place earmarked for a site study.

Solid waste pollution has been reduced by recovering resources rather than burying them. Resource recovery includes massive systems that burn waste to produce steam, but it also includes the recycling of glass, metal, and paper from individual consumers and businesses. The elimination of these kinds of materials from landfills has prevented pollution and extended the period during which landfills can receive waste.

Land pollution also involves the accumulation of chemicals in the ground. Modern agriculture, which has grown dependent on chemical fertilizers and chemicals that kill insects, has introduced substances into the soil that kill more than pests. For many years the chemical DDT was routinely sprayed on crops to control pests. It was banned when scientists discovered that the chemical entered the food chain and was harming wildlife and possibly humans.

air pollution is regulated by the federal government. The Clean Air Act was originally enacted in 1970 and was extensively amended in 1977 and again in 1990 (42 U.S.C.A. §§ 7401–7626; Pub. L. No. 95-95 [1977 amendments]; Pub. L. No. 101-549 [1990 amendments]). Under its provisions, every stationary and mobile pollution source must comply with emission standards as a means of cleaning up the ambient air quality in the area. This has meant that automobile emission control systems have been created and improved to meet more stringent air quality standards. Coal-burning electric power plants have been required to install filtration systems on their smokestacks, and manufacturing facilities have had to install equipment that "scrubs" polluted air clean.

water pollution has existed longer than any other type of pollution. Depositing liquid and solid wastes in rivers, streams, lakes, and oceans was convenient and inexpensive for a company or municipality, but it eventually destroyed the ecosystems found in the water. Many large rivers became nothing more than sewers. Most troubling was the polluting of groundwater, creating serious health hazards for those people who drank water containing toxic substances.

The federal Clean Water Act (CWA) was originally enacted in 1972 and then amended in 1977 and 1987 (33 U.S.C.A. §§ 1251–1387; Pub. L. No. 95-217 [1977 amendments]; Pub. L. No. 100-4 [1987 amendments]). The CWA seeks to eliminate the "discharge of pollutants into navigable waters," to make water safe for people to fish and swim in, and to end the "discharges of toxic pollutants in toxic amounts." The CWA seeks to accomplish these goals through a variety of regulatory strategies.

cross-references

Environmental Law; Environmental Protection Agency; Land-Use Control; Solid Wastes, Hazardous Substances, and Toxic Pollutants.

pollution An undesirable change in the physical, chemical, or biological characteristics of the natural environment, brought about by human activities. It may be harmful to human or nonhuman life. Pollution may affect the soil, rivers, seas, or the atmosphere (see air pollution). There are two main classes of pollutants: those that are biodegradable (e.g. sewage), i.e. can be rendered harmless by natural processes and need therefore cause no permanent harm if adequately dispersed or treated; and those that are nonbiodegradable (e.g. heavy metals (such as lead) in industrial effluents (see heavy-metal pollution) and DDT and other chlorinated hydrocarbons used as pesticides), which eventually accumulate in the environment and may be concentrated in food chains. Other forms of pollution in the environment include noise (e.g. from jet aircraft, traffic, and industrial processes) and thermal pollution (e.g. the release of excessive waste heat into lakes or rivers causing harm to wildlife). Recent pollution problems include the disposal of radioactive waste; acid rain; photochemical smog; increasing levels of human waste; high levels of carbon dioxide and other greenhouse gases in the atmosphere (see greenhouse effect); damage to the ozone layer by nitrogen oxides, chlorofluorocarbons (CFCs), and halons; and pollution of inland waters by agricultural fertilizers and sewage effluent, causing eutrophication (see eutrophic). Attempts to contain or prevent pollution include strict regulations concerning factory emissions, the use of smokeless fuels, the banning of certain pesticides, greater use of renewable energy sources, restrictions on the use of chlorofluorocarbons, and the introduction, in some countries, of catalytic converters to cut pollutants in car exhausts.

pol·lute / pəˈloōt/ • v. [tr.] contaminate (water, air, or a place) with harmful or poisonous substances: the explosion polluted the town with dioxin | [as adj.] (polluted) exposure to polluted air. ∎ fig. defile; corrupt: a society polluted by racism. DERIVATIVES: pol·lu·tant / -ˈloōtnt/ adj. & n. pol·lut·er n. ORIGIN: late Middle English: from Latin pollut- ‘soiled, defiled,’ from the verb polluere, based on the root of lutum ‘mud.’

pollutant A substance that enters the environment or becomes concentrated within it, and that will, or may, harmfully affect human life or that of desirable species. Pollutants are by-products of human activity (compare ALLELOPATHY) and the term embraces noise and the release of substances at temperatures markedly higher than those of the receiving media.

pollutant Any substance, produced and released into the environment as a result of human activities, that has damaging effects on living organisms. Pollutants may be toxic substances (e.g. pesticides) or natural constituents of the atmosphere (e.g. carbon dioxide) that are present in excessive amounts. See pollution.

pollutant A by-product of human activities which enters or becomes concentrated in the environment, where it may cause injury to humans or desirable species. In addition to chemical substances, the term also embraces noise, vibration, and alterations to the ambient temperature.

pollute render impure. XIV. f. pollūt-, pp. stem of L. polluere, f. *por- PRO-1 + base of lutum mud.
So pollution XIV. — (O)F. pollution or late L. pollūtiō, -ōn-.

pollution The defiling of the natural environment by a pollutant. Compare ALLELOPATHY.

POLLUTION

POLLUTION. SeeAir Pollution ; Noise Pollution ; Water Pollution .

pollution The defilement of the natural environment by a pollutant.

pollutant •abeyant, mayn't •ambient, circumambient •gradient, irradiant, radiant •expedient, ingredient, mediant, obedient •valiant • salient • resilient • emollient •defoliant • ebullient • suppliant •convenient, intervenient, lenient, prevenient •sapient •impercipient, incipient, percipient, recipient •recreant • variant • miscreant •Orient • nutrient •esurient, luxuriant, parturient, prurient •nescient, prescient •omniscient • insouciant • renunciant •officiant • negotiant • deviant •subservient • transient •affiant, Bryant, client, compliant, defiant, giant, pliant, reliant •buoyant, clairvoyant, flamboyant •fluent, pursuant, truant •affluent • effluent • mellifluent •confluent • circumfluent • congruent •issuant • continuant • constituent •lambent • absorbent •incumbent, recumbent •couchant • merchant • hadn't •ardent, guardant, regardant •pedant •appendant, ascendant, attendant, codependent, defendant, descendant, descendent, intendant, interdependent, pendant, pendent, splendent, superintendent, transcendent •antecedent, decedent, needn't, precedent •didn't • diffident • confident •accident • dissident •coincident, incident •oxidant • evident •improvident, provident •president, resident •strident, trident •co-respondent, correspondent, despondent, fondant, respondent •accordant, concordant, discordant, mordant, mordent •rodent •imprudent, jurisprudent, prudent, student •couldn't, shouldn't, wouldn't •impudent •abundant, redundant •decadent • verdant • infant • elephant •triumphant • sycophant • elegant •fumigant • congregant • litigant •termagant • arrogant • extravagant •pageant •cotangent, plangent, tangent •argent, Sargent, sergeant •agent • newsagent • regent •astringent, contingent, stringent •indigent • intelligent • negligent •diligent • intransigent • exigent •cogent •effulgent, fulgent, indulgent •pungent •convergent, detergent, divergent, emergent, insurgent, resurgent, urgent •bacchant • peccant • vacant • piquant •predicant • mendicant • significant •applicant • supplicant • communicant •lubricant • desiccant • intoxicant •gallant, talent •appellant, propellant, propellent, repellent, water-repellent •resemblant •assailant, inhalant •sealant • sibilant • jubilant •flagellant • vigilant • pestilent •silent •Solent, volant •coolant • virulent • purulent •ambulant, somnambulant •coagulant • crapulent • flatulent •feculent • esculent • petulant •stimulant • flocculent • opulent •postulant • fraudulent • corpulent •undulant •succulent, truculent •turbulent • violent • redolent •indolent • somnolent • excellent •insolent • nonchalant •benevolent, malevolent, prevalent •ambivalent, equivalent •garment • clement • segment •claimant, clamant, payment, raiment •ailment •figment, pigment •fitment • aliment • element •oddment •dormant, informant •moment • adamant • stagnant •lieutenant, pennant, subtenant, tenant •pregnant, regnant •remnant • complainant •benignant, indignant, malignant •recombinant • contaminant •eminent •discriminant, imminent •dominant, prominent •illuminant, ruminant •determinant • abstinent •continent, subcontinent •appurtenant, impertinent, pertinent •revenant •component, deponent, exponent, opponent, proponent •oppugnant, repugnant •immanent •impermanent, permanent •dissonant • consonant • alternant •covenant • resonant • rampant •discrepant • flippant • participant •occupant • serpent •apparent, arrant, transparent •Arendt •aberrant, deterrent, errant, inherent, knight-errant •entrant •declarant, parent •grandparent • step-parent •godparent •flagrant, fragrant, vagrant •registrant • celebrant • emigrant •immigrant • ministrant • aspirant •antiperspirant • recalcitrant •integrant • tyrant • vibrant • hydrant •migrant, transmigrant •abhorrent, torrent, warrant •quadrant • figurant • obscurant •blackcurrant, concurrent, currant, current, occurrent, redcurrant •white currant • cross-current •undercurrent •adherent, coherent, sederunt •exuberant, protuberant •reverberant • denaturant •preponderant • deodorant •different, vociferant •belligerent, refrigerant •accelerant • tolerant • cormorant •itinerant • ignorant • cooperant •expectorant • adulterant •irreverent, reverent •nascent, passant •absent •accent, relaxant •acquiescent, adolescent, albescent, Besant, coalescent, confessant, convalescent, crescent, depressant, effervescent, erubescent, evanescent, excrescent, flavescent, fluorescent, immunosuppressant, incandescent, incessant, iridescent, juvenescent, lactescent, liquescent, luminescent, nigrescent, obsolescent, opalescent, pearlescent, phosphorescent, pubescent, putrescent, quiescent, suppressant, tumescent, turgescent, virescent, viridescent •adjacent, complacent, obeisant •decent, recent •impuissant, reminiscent •Vincent • puissant •beneficent, maleficent •magnificent, munificent •Millicent • concupiscent • reticent •docent •lucent, translucent •discussant, mustn't •innocent •conversant, versant •consentient, sentient, trenchant •impatient, patient •ancient • outpatient •coefficient, deficient, efficient, proficient, sufficient •quotient • patent •interactant, reactant •disinfectant, expectant, protectant •repentant • acceptant •contestant, decongestant •sextant •blatant, latent •intermittent •assistant, coexistent, consistent, distant, equidistant, existent, insistent, persistent, resistant, subsistent, water-resistant •instant •cohabitant, habitant •exorbitant • militant • concomitant •impenitent, penitent •palpitant • crepitant • precipitant •competent, omnicompetent •irritant • incapacitant • Protestant •hesitant • visitant • mightn't • octant •remontant • constant •important, oughtn't •accountant • potent •mutant, pollutant •adjutant • executant • disputant •reluctant •consultant, exultant, resultant •combatant • omnipotent • impotent •inadvertent •Havant, haven't, savant, savante •advent •irrelevant, relevant •pursuivant • solvent • convent •adjuvant •fervent, observant, servant •manservant • maidservant •frequent, sequent •delinquent • consequent •subsequent • unguent • eloquent •grandiloquent, magniloquent •brilliant • poignant • hasn't •bezant, omnipresent, peasant, pheasant, pleasant, present •complaisant • malfeasant • isn't •cognizant • wasn't • recusant •doesn't

pollute •acute, argute, astute, beaut, Beirut, boot, bruit, brut, brute, Bute, butte, Canute, cheroot, chute, commute, compute, confute, coot, cute, depute, dilute, dispute, flute, fruit, galoot, hoot, impute, jute, loot, lute, minute, moot, mute, newt, outshoot, permute, pollute, pursuit, recruit, refute, repute, root, route, salute, Salyut, scoot, shoot, Shute, sloot, snoot, subacute, suit, telecommute, Tonton Macoute, toot, transmute, undershoot, uproot, Ute, volute •Paiute • jackboot • freeboot • top boot •snow boot • gumboot • marabout •statute • bandicoot • Hakluyt •archlute • absolute • dissolute •irresolute, resolute •jackfruit • passion fruit • breadfruit •grapefruit • snakeroot • beetroot •arrowroot • autoroute

pollution •ashen, fashion, passion, ration •abstraction, action, attraction, benefaction, compaction, contraction, counteraction, diffraction, enaction, exaction, extraction, faction, fraction, interaction, liquefaction, malefaction, petrifaction, proaction, protraction, putrefaction, redaction, retroaction, satisfaction, stupefaction, subtraction, traction, transaction, tumefaction, vitrifaction •expansion, mansion, scansion, stanchion •sanction •caption, contraption •harshen, Martian •cession, discretion, freshen, session •abjection, affection, circumspection, collection, complexion, confection, connection, convection, correction, defection, deflection, dejection, detection, direction, ejection, election, erection, genuflection, imperfection, infection, inflection, injection, inspection, insurrection, interconnection, interjection, intersection, introspection, lection, misdirection, objection, perfection, predilection, projection, protection, refection, reflection, rejection, resurrection, retrospection, section, selection, subjection, transection, vivisection •exemption, pre-emption, redemption •abstention, apprehension, ascension, attention, circumvention, comprehension, condescension, contention, contravention, convention, declension, detention, dimension, dissension, extension, gentian, hypertension, hypotension, intention, intervention, invention, mention, misapprehension, obtention, pension, prehension, prevention, recension, retention, subvention, supervention, suspension, tension •conception, contraception, deception, exception, inception, interception, misconception, perception, reception •Übermenschen • subsection •ablation, aeration, agnation, Alsatian, Amerasian, Asian, aviation, cetacean, citation, conation, creation, Croatian, crustacean, curation, Dalmatian, delation, dilation, donation, duration, elation, fixation, Galatian, gyration, Haitian, halation, Horatian, ideation, illation, lavation, legation, libation, location, lunation, mutation, natation, nation, negation, notation, nutation, oblation, oration, ovation, potation, relation, rogation, rotation, Sarmatian, sedation, Serbo-Croatian, station, taxation, Thracian, vacation, vexation, vocation, zonation •accretion, Capetian, completion, concretion, deletion, depletion, Diocletian, excretion, Grecian, Helvetian, repletion, Rhodesian, secretion, suppletion, Tahitian, venetian •academician, addition, aesthetician (US esthetician), ambition, audition, beautician, clinician, coition, cosmetician, diagnostician, dialectician, dietitian, Domitian, edition, electrician, emission, fission, fruition, Hermitian, ignition, linguistician, logician, magician, mathematician, Mauritian, mechanician, metaphysician, mission, monition, mortician, munition, musician, obstetrician, omission, optician, paediatrician (US pediatrician), patrician, petition, Phoenician, physician, politician, position, rhetorician, sedition, statistician, suspicion, tactician, technician, theoretician, Titian, tuition, volition •addiction, affliction, benediction, constriction, conviction, crucifixion, depiction, dereliction, diction, eviction, fiction, friction, infliction, interdiction, jurisdiction, malediction, restriction, transfixion, valediction •distinction, extinction, intinction •ascription, circumscription, conscription, decryption, description, Egyptian, encryption, inscription, misdescription, prescription, subscription, superscription, transcription •proscription •concoction, decoction •adoption, option •abortion, apportion, caution, contortion, distortion, extortion, portion, proportion, retortion, torsion •auction •absorption, sorption •commotion, devotion, emotion, groschen, Laotian, locomotion, lotion, motion, notion, Nova Scotian, ocean, potion, promotion •ablution, absolution, allocution, attribution, circumlocution, circumvolution, Confucian, constitution, contribution, convolution, counter-revolution, destitution, dilution, diminution, distribution, electrocution, elocution, evolution, execution, institution, interlocution, irresolution, Lilliputian, locution, perlocution, persecution, pollution, prosecution, prostitution, restitution, retribution, Rosicrucian, solution, substitution, volution •cushion • resumption • München •pincushion •Belorussian, Prussian, Russian •abduction, conduction, construction, deduction, destruction, eduction, effluxion, induction, instruction, introduction, misconstruction, obstruction, production, reduction, ruction, seduction, suction, underproduction •avulsion, compulsion, convulsion, emulsion, expulsion, impulsion, propulsion, repulsion, revulsion •assumption, consumption, gumption, presumption •luncheon, scuncheon, truncheon •compunction, conjunction, dysfunction, expunction, function, junction, malfunction, multifunction, unction •abruption, corruption, disruption, eruption, interruption •T-junction • liposuction •animadversion, aspersion, assertion, aversion, Cistercian, coercion, conversion, desertion, disconcertion, dispersion, diversion, emersion, excursion, exertion, extroversion, immersion, incursion, insertion, interspersion, introversion, Persian, perversion, submersion, subversion, tertian, version •excerption