Nature and Sources of Pollutants

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ADDRESS FOR REPRINTS: Monitoring, U.S. Environmental ington, D.C. 20460.

Office of Research and

Protection Agency,


ensure disposal or reuse of unwanted residues,

and to avoid such hazards as have occurred from combustion, acid mine drainage, and agricultural poisons. We must recognize the essential unity of the environment and its limited capacity to absorb pollutants. We cannot simply transfer pollutants from air to water, or water to soil. We must

under-stand the interaction of environmental contami-nants with each other, as in the production of photochemical smog. Various aspects of

environ-mental effects must be incorporated into the assess-ment of the total impact on health.

We obviously must develop the ability to forecast technologic and sociologic trends. Occasionally, it

may be necessary to settle for a less than desirable environment, as when needs are strategic or control is not feasible or poses an intolerable economic

burden. We have to be aware of variations in sus-ceptibility within the general population, and it should be emphasized that unusual susceptibility may be found in several subgroups in addition to

the fetus and child.

The medical profession must recognize that the

care of individual patients must be joined with con-cern for the general population. The wonders of recent medical progress must be used to the utmost to prevent or postpone coronary heart disease; to reduce the menu of doubtfully useful

pharmaco-logical agents; and, most of all, to identify adverse physiologic changes well before the appearance

of clinical disease.

I close with a restatement of the major thesis of my presentation: prevention of ill health in its

broadest sense should be the objective of environ-mental control. I am tempted to apologize for not limiting myself to the fetus and child and to chemi-cal pollutants. To do so, however, would somewhat

distort an overview by isolating a few among the many elements in the complex relationship of the various compartments of the environment and the population. Alternatively, I hope that I have not confused breadth with diffuseness.


and Sources

of Pollutants

Vaun A. NewiII, M.D.

From the Office of the Administrator, Environmental Protection Agency, Washington, D.C.

Air, water and soil have always been an

admix-ture of chemicals. Some of these chemicals are capable of profound effects on living systems with which they come into contact. Plant and animal life has always depended on natural

transforma-tions continuously recycling high quantities of

chemical substances through the biosphere. Man too has been exposed to and depended upon many of these environmental chemicals since time

im-memorial. Adaptive change has been necessary.

However, a cognitive capability has distinguished man from other living things. This capability has permitted him to develop rapidly and to learn to

use available surrounding resources both to im-prove the quality of his life and at times to

jeopardize it.

In the late 1940s and 1950s, destructive air

pollution episodes occurred in the Meuse Valley, Donora, London, and New York. Thus, seeds of apprehension and fear of air pollution effects were

sown. Such feelings were rekindled by The Silent Spring, the mercury problem, and others.

It is my opinion that the doomsday approach


i.e., doomsday caused by environmental contami-nation per se


is wrong, and, by sane, sensible, and vigorous environmental control action we shall take care of the problems. Many requisites are neces-sary, one being an understanding of the nature

and sources of pollutants.

There are a number of ways to classify pollu-tants, such as by the medium polluted (air, water, or soil), the polluting chemical (organic, inorganic, etc.), the target organisms (people, plants, wild-life), the nature of effects (odors, respiratory

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Fic. 1. Air pollution emissions in the United States, 1968: percentage by weight.

tants, carcinogens, eggshell thinning of birds

ex-posed to “DDT”), or according to the sources


natural or man-made, intensive or extensive, etc.). Each point of view brings with it certain insights

and understanding helpful in learning about the problem. However, there can be no detailed con-sideration of these classifications here.

For our discussion, the environmental pollution problems generally fit into two broad categories: the massive problems of air and water pollution

(intensive pollution) and the more disseminated problems of specific toxic substances (extensive pol-lution). Let us first consider the major air pollu-tants, their sources, and the magnitude of emission.


The number of air pollutants present in our air, considering all physical and chemical

varia-tions, is large. As of now, our ability to identify, measure, and monitor all of these is limited. They

can be either solid, gaseous, or liquid in form. Some are relatively stable in the atmosphere, where-as others change completely and rapidly during their transport through air. The five major air pol-lutants chosen for control were those most in abundance across the country, namely, total par-ticulate matter, sulfur oxides, oxides of nitrogen, carbon monoxides, and hydrocarbons.

Distributions of air pollution emissions#{176} in the United States by type and source are shown in Figure 1. By weight, carbon monoxide is the most prevalent pollutant and transportation, particularly the motor vehicle, the most important source. Fuel combustion, solid waste disposal, and industrial processes-all stationary emissions sources-together

equal the emissions from transportation sources. Table I presents a more detailed breakdown of air pollution emission source categories. Estimated

nationwide emissions of air pollutants for the sources mentioned in Figure 1 are detailed in Table II.

Over two thirds of carbon monoxide comes from vehicles, and fuel combustion in stationary sources

accounts for over two thirds of sulfur dioxides. Industrial processes and fuel combustion in

sta-tionary sources also account for two thirds of particulate emissions. Emissions of pollutants, espe-cially particulates, are increasing; but, emissions attributed to transportation and industrial processes have slightly decreased.

Suspended particulates are in themselves

com-plex, and their chemical and physical

characteris-tics are- variable. Selected constituents of a com-posite sample of gross suspended particulates col-lected from urban, near urban, agricultural, and remote air monitoring stations are shown in Table III. The concentration of particulate ranges from a high of lO2jsg/m’ in urban areas to a low of 2lisg/m’ in remote areas. Striking gradients are noted for absolute levels of benzene-soluble

or-* The relationship between emission and ambient air quality must be kept in mind. Emissions are the quantity of pollutants emitted into the air. The ambient air quality is the level of a pollutant actually in the air. When this level is measured where people are, it is a good estimate of the exposure. It represents the summation of contribu-tions from all emitting sources reaching that point. Because ambient air quality estimates exposure, the primary ambient

air quality standard as defined by the Clean Air



I. Combustion of fuels in stationary sources

(a) Power utilities (b) Industries

(c) Commercial and institutional (d) Domestic (apartments or houses) -further classified by fuel used, i.e., distillate fuel oil and natural gas 2. Combustion of fuels in mobile sources

(a) Motor vehicles (cars, buses, trucks) (b) Airplanes

(c) Trains (d) Vessels 3. Solid waste disposal

(a) Incinerators (municipal, industrial and domestic) (b) Open burning (on-site and dumps)

4. Industrial processes (iron and steel, cement mills, petro-chemical, etc.)

5. Evaporation of petroleum products and solvents in general (a) Solvent usage

(b) Storage and marketing of gasoline

ganics, sulfates, and lead. In addition, the

per-centage attributed to nontabled materials, pri-manly carbon or silicon compounds, varied with such constituents accounting for a larger share of the nonurban particulate sample.

Similarly, liquid effluents from industrial and

municipal sources carry pollutants that alter the quality of receiving waters endangering the ex-posed aquatic species as well as making the water unfit for certain uses. These water and air pollu-tion problems are interrelated in that stricter

con-trol on the content of the water effluent may result in increased air pollution emissions, and vice versa.

The more disseminated chemical pollution prob-lems


extensive pollution) are more subtle in na-ture and more difficult to identify and control. Such problems tend to be multimedia in nature, i.e., the air, water, soil, and food are all involved

in the pollutant transport and/or exposure process. The prime interest of this Conference is in the effect of chemical pollutants in the fetus or child. The effects on the child result from exposure

through inhalation or ingestion. This exposure is

similar to that in the adult, though the biological

response may be different. The exposure of the

fetus, however, is dependent upon both the

ex-posure of the mother and the transport of the

chemical and/or its metabolites across the pla-centa. The fetus is exposed to chemicals constantly

present in the mother’s bloodstream from concep-tion until birth.


The environmental sources from which these chemicals arise are many, some of which have already been mentioned (e.g., the residual

chemi-cals in air and water pollution). Another major source is the drugs used to treat or prevent disease.

Other sources are chemicals used to increase food supplies such as growth-stimulating hormones,

anti-biotic drugs, and economic poisons; food additives to improve the color, taste or quality of foods such

as nitrates or synthetic food color dyes; cosmetics, household products, and industrial chemicals such as adhesives, solvents, soaps, detergents, polishes, deodorants, hobby supplies, plastics and synthetic

fibers. Furthermore, as stated earlier, naturally oc-curring chemical compounds can be associated with effects, such as the goitrogens found in

cab-bage and mustard; oxalic acid salts in spinach and rhubarb; cyanide in tapioca, almonds, and lima beans; presser amines in cheese, wines, and fruits;

and teratogenic effects of vitamin A.

Each year several thousand new chemicals are




coal, residual or




Source CO Particulate’s SO2 HG J’/02 Total Change



Fuel combustion in

111.5 0.8 1.1 19.8 11.2 144.4 - 1.0

stationary sources Industrial processes Solid waste disposal Miscellaneous

1.8 12.0 7.9 18.2

7.2 14.4 1.4 11.4

24.4 7.5

.2 .2


5.5 2.0 9.2

10.0 .2 .4 2.0

44.3 39.6 1 1.9 41.0

+2.5 +7.3

- 1.0

+ 18.5

Total 151.4 35.2 33.4 37.4 23.8 281.2 +3.2

Percent change +1.3 +10.7 +5.7 +1.1 +4.8

* Computed by the 1969 method from the difference between 1969 estimates and 1968 estimates. The new method results in higher values for 1968 than those computed by EPA for 1968.

Source: The Mitre Corp. MTR-60l3. Based on Environmental Protection Agency data.

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I rban .Nonurban

(2 1 7 Stations ) Proximate (5 ) Intermediate (1 5 ) t Reenote (10 )

zg/cu in Percent ,ug/cu rn Percent g,’cu in J’erce’nt .zg1cu in Percent

Suspended particulates Bcnzcne:solubleorganics .IIlIflOfliUIfl iOfl 102.0 6.7 0.9 -6.6 0.9 45.0 2.5 1.22 -5.6 2.7 40.0 2.2 0.28 ----5.4 0.7 21.0 1.1 0.15 --5.1 0.7

Nitrate ion 2.4 2.4 1.40 3.1 0.85 2.1 0.46 2.2

Sulfatcion 10.1 9.9 10.0 22.2 5.29 13.1 2.51 1.8

Copper Iron 0.16 1.43 0.15 1.38 0.16 0.56 0.36 1.24 0.078 0.27 0.19 0.67 0.060 0.15 0.28 0.71 Manganese Nickel 0.073 0.017 0.07 0.02 0.026 0.003 0.06 0.02 0.012 0.004 0.03 0.01 0.005 0.002 0.02 0.01

Lead 1.11 1.07 0.21 0.47 0.096 0.24 0.022 0.10

* Technically in nonurban areas, but conspicuously influenced by proxilnity to city, i.e., Cape Vincent, N. Y.; Kent County,

Del. ; Washington County, Miss.

t Closer to urban areas, usually with agricultural activity, i.e., Jackson County, Miss.; Humboldt, Calif.

Farthest from large population center, i.e., Glacier National Park, with Pine County, Ne’. Source: Environmental Protection Agency.



developed and new uses are found for existing chemicals. Present legislative authorities regulate some of these chemicals. However, there are many that cannot be regulated under existing authorities; therefore, the Congress, under stimulation from the Council on Environmental Quality has “A Toxic Substance Bill” under consideration.

Screening all new chemicals and keeping those that will cause significant environmental problems out of the environment will be a monumental task. With the existing state-of-the-art of prediction of effects, any such prediction system developed will

be imperfect. Certainly, advances in the state-of-the-art for prediction and toxicity testing will be high on the research priority list.


To give you some idea of the complexity of this

problem, I will review several kinds of information

that need to be assembled and coupled to deter-mine if a new chemical will have a major environ-mental impact. Answers to questions such as those that follow will aid in evaluation.

1. Will the chemical get into the environment? The answer requires a rough-materials balance. What quantity is produced? How leaky is the

pro-duction process? What is the geographic distribu-tion of production points? How will the chemical be used? Will this use be a contained or a disper-sive one? How will the product be disposed? If

by incineration, then the combustion and pyrolysis products must be known. If by sanitary land fill, then the leaching characteristics must be known.

2. WI’ at are the chemical and biological

charac-teristics? This information may in the future be

useful for prediction of toxicity. For now, however, information on such characteristics as solubility,

phase coefficients, etc. will be useful in speculating on routes and rates of movement of the chemical

through the environment. This speculation must include considerations of persistence,

bioaccumula-tion, chemical transformations, and estimates of environmental exposure.

3. What are the dose-response relationships arising from human and environmental exposure? Simple testing procedures need to be used to evaluate

toxicity. Chemicals of low toxicity with little to no environmental exposure need no regulation. However, for compounds of high toxicity or high environmental exposure, much more extensive test-ing must be performed to ascertain dose-response relationships, to assess the environmental impact and determine the need for regulation. It should be carefully pointed out that the quantity of

in-formation necessary to indicate there is an

environ-mental problem usually is much less than that needed to decide on appropriate regulatory action.

When action is taken on minimal information, the prudent decision (most protective) is made and usually proves to be a more costly one.

Our best efforts need to be put forth in learning to cope with the toxic substance problems, the extensive pollution. Long after the massive prob-lems of air and water pollution are behind us and the major efforts for these media is in air and water resources management, we shall still be beset by the toxic substance problems. Techniques for





DR. ARENA. Dr. Lowe mentioned the problem of

salicylism in children. We have observed a common oc-currence among teen-agers, probably a part of the drug

culture, and greatly influenced by television

advertis-ing, namely, the ingestion of large numbers of aspirin tablets. Often the school nurse, school physician, or private physician first sees these youngsters because they are suffering tinnitus, which frightens them. The prob-lem is well recognized by practitioners, but it has not been well documented in the literature. This morning

we spoke at length of research, but we should not for-get the important role of the practitioner in defining these problems and others in our deliberations here.

DR. LOWE. Dr. Arena’s comment has particular

rele-vance to the role of the American Academy of

Pedi-atrics. We tend to think of research in isolation from

the activities of the practitioner. Environmental issues

help us to focus not only on the key importance of the practitioner as the first line of alert, but also on the

need for interaction between the physician who sees

the patients, and the scientist who is trying to solve environmental problems. The investigator can operate in the laboratory using tissue cultures, cell-free systems,

and isolated organ-perfusion to develop biological

truths. We are dealing today, however, with an inter-action between basic research and applied research, as

at the turn of the century, when challenges were

iden-rifled at the bedside and then referred to the laboratory.

I would hope that one of the benefits of this Conference will be to re-cement an alliance which I visualize as

hay-ing come apart-to be sure that the warning will come loud and clear from the practitioner, and that the

scien-list in the laboratory is responsive to these alerts.

DR. MILLER. The purpose of this Conference is to

sug-gest future actions by the American Academy of Pedi-atrics on behalf of children with respect to chemical

exposures. By coincidence, we have on the platform at

present three people who are among the most

corn-petent anywhere to tell us which health organizations,

Federal or otherwise, are best able to advise on research

pertaining to chemical hazards encountered by the

fetus or child. Dr. Lowe can tell us if it is the National

Institute of Child Health and Human Development (NICHD) where he is the scientific director; Dr. Kotin can tell us if it is the National Institute of Environmental

Health Sciences (NIEHS), which he formerly directed;

and Dr. Newill can tell us if it is the Environmental Pro-tection Agency, where he is the medical director.

DR. NEWILL. All three groups have some

responsi-bility. The Environmental Protection Agency (EPA) is

concerned with the regulatory aspects of the Toxic Sub-stance Act, for example, while such agencies as the Na-tional Institute of Child Health and Human Develop-ment and the National Institute of Environmental Health Sciences will provide scientific information.

DR. LOWE. Dr. Miller’s question is in part operational

and pragmatic, and in part philosophical. There is great weakness inherent in the assignment of responsibility

either to a single agency or to a component of an

agency. There is great strength if we do not subdivide

responsibility but encourage its assumption by various

agencies. For example, one may ask which arm of the

National Institutes of Health (NIH) should be

con-cerned with the issues before us. I have adopted the

atti-tude that both NIEHS and NICHD will assume some

responsibility to the extent that they are able. With

re-gard to intramural programs on teratogenesis in its

tra-ditional form, NIEHS can probably do a better job

than NICHD can. NIEHS has the resources and

per-sonnel and a broad mandate to cover this area.

The philosophical issue is broad and complex. Our

government tends to engage in what I call “brush-fire operations.” It has been consistently reluctant to estab-lish broad national policy where health issues are in-volved. In part this stems from the belief that the less regulation, the better. There is also a problem in coordi-nating agencies among different Cabinet officers. Until

we are convinced, and willing and able, to adopt a more global attitude toward health issues, we are destined to

follow the fragmented or “brush-fire” approach. I do

not see how we can attack air pollution totally separate from other environmental issues. Although some effort has been made at coordination, it has not in my view been entirely successful.

DR. KOTIN. I think EPA has exclusive responsibility, since basically the decisions involve considerations other than those exclusively scientific. Hazards from DDT or 2,4,5-T, for example, cannot be fully evaluated bccause of the paucity of human biological data. Hopefully, coordination within the government will be achieved in

the future, and will allow continued experimental,

chemical, and epidemiological evaluations prior to


DR. MILLER. Drs. Kotin and Newill in their

presen-tations spoke of environmental hazards in general. They

made no reference specifically to children. NIEHS and EPA do not have personnel who are experienced with

and concerned about fetuses and children. NICHD

does have these personnel and interests. Is there a role

for NICHD regarding the chemical environment of

the fetus and child, especially since Dr. Kotin has said that attention is shifting from microbial problems to the many new chemicals that are being introduced into our


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DR. LOWE. I would like to emphasize the need to dis-tinguish the regulatory responsibility on the one hand and development of scientific data which can lead to good regulation on the other hand. NIH in my view does not have a regulatory function.

Dn. KOTIN. I see no agency other than EPA as the

focal point for all information concerning pollutants, since it is to EPA that Congress turns for enforcement

of regulations and for establishment of criteria and standards. The problem is one of internal Federal

cen-tralization and increased effectiveness.

Dn. BROWN. Dr. Lowe has cleared up one of the

defi-nitions we need to understand better who regulates and

who develops information. I am having difficulty with

the definition of environment. Pediatricians and neo-natologists are certainly creating special environments for their patients, and they are encountering difficulty with regulation of devices used in these environments (e.g., phototherapy and oxygen) . The mother creates an

environment for the baby, and society creates another. Are you really saying the EPA should be equally in-volved in the urban ghetto environment and in the chemical pollution from smoke stacks? We really should define various environments so we can direct our ques-tions and attention more effectively.

One reason for this Conference is that rarely have the fetus or child and their special susceptibility been given special consideration. How can we be assured that pediatricians will be able to contribute scientific data that are not being considered at present?

DR. LOWE. Dr. Brown has brought up a point that needs discussion: who is going to be responsible and perform research to provide the background that EPA

needs before it can act? This is a tangled and difficult story. If NIH were to be assigned the responsibility to develop segments of scientific information to funnel to EPA, we would be increasingly committed to targeted research. Government officials would decide what

proj-ects will receive Federal support. I would be deeply concerned were this practice to increase. Yet, probably this is the only way we can accelerate the pace of de-veloping information needed by government. I am strongly persuaded that the soundest scientific posture is that which leaves maximum initiative to the investi-gator in the hope that his intelligence and commitment will lead him to perceive needs and to bend his effort in the directions that are worthwhile and exciting.

DR. HOLLAND. In his presentation, Dr. Kotin referred to cost-benefit analyses. When this practice is applied to environmentally induced disease, a note of caution should be sounded. One may quickly reach a dead-end, as occurred when we tried to develop a cost-benefit

analysis of the effects of cigarette smoking. We found the benefits of smoking to the nation were great be-cause people did not live as long, and therefore one does not have to pay as much in Social Security bene-fits or retirement pensions. The reduction of life during the productive years fell far short of compensating for the monetary loss incurred by extending life beyond the working years.

In talking about chemical effects I am disappointed that only Dr. Lowe has so far mentioned the importance of cigarette smoking, which is probably the most im-portant environmental agent at this time affecting mor-bidity and mortality.

DR. Kormr. The question of cost versus benefits is

knotty, but I have great faith in the estimated cost on the basis of our calculations. We could reasonably estimate the cost of occupational diseases, and our figure is conservative.

DR. Lowe. I would echo with enthusiasm Dr. Hol-land’s comments about cost-benefit analyses. My pur-pose is not to challenge Dr. Kotin but to imply that the kind of algebra we use involves a number of

assump-tions. We live at a moment in i commercial culture

enthralled with the concept of management. Our only point of reference is the dollar, and this may not be the

proper measure of benefit. Cost involves issues other

than dollars and cents. It involves the enjoyment of life, happiness, and avariety of other measures of well-being.

DR. WEHRLE. Dr. Lowe referred to targeted research. We are concerned about too much targeting, although some is needed particularly with regard to the subject of this Conference. Our major concern is to accumulate data for both the fetus and child. In doing so we en-counter problems that are both ethical and medical-legal. Suits may be brought regardless of who signs consent forms on behalf of the child under 18 years of age. Perhaps Mr. Frank Barton, a lawyer in the AMA’s Environmental Health Unit, would like to describe where we stand in developing the necessary data, be-cause without them it is impossible to take proper

regu-latory action.

MR. BARTON. The increase in malpractice claims is of interest to all physicians, especially in California. There is no guarantee that a seemingly adequate informed-consent agreement will protect the physician against legal action and the substantial possibility that the judgment will be rendered against him. Informed con-sent should be in writing and should be as complete as possible. That will not be a guarantee, but it will be far better than an oral or vaguely written agreement. The AMA’s General Counsel has issued statements concerning problems regarding informed consent and

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malpractice. These statements are available on request.


DR. PRESS. Informed consent is an important

corn-ponent of any research. When the patient is a child

or otherwise not competent to give consent, the parents should have the privilege of granting it or denying it after hearing a full explanation of the procedures

in-volved. The American Academy of Pediatrics and the

American Medical Association could make it clear to

their legal representatives that we are against research

on any person without informed consent, but are in

favor of research with such consent as given by the per-son himself or by his legal guardian.

DR. LOWE. The problem is difficult. Our legal

coun-sels at the Department of Health, Education, and Wel-fare and at NIH advise us that there is no legal struc-ture for obtaining informed consent from those who

can-not provide it for themselves. We have developed a

proxy procedure which uses the mother or father, or

both. Actually, this is a social and not a legal

con-venience. We need now to develop a mechanism for

substitute consent, in which society plays a role in

agreeing that it is proper and essential to perform research on a class of persons who cannot themselves

give informed consent and for whom no parent can do


Another problem concerns the right of the mother to

give informed consent for a fetus to whom she has no

commitment, since she has agreed to abortion. The law

looks askance at this mother, and says no one may in-jure a fetus in utero. Willing or unwilling, the mother

may not give consent to any procedure that may

in-jure the fetus that is to be aborted. The need, therefore, is to develop a socially acceptable mechanism to permit proper and much needed research in this area.

My understanding is that no language is available

for a written agreement which will have an exculpa-tory effect. The physician is never excused from any

ad-verse outcome of the treatment he provides. The

pa-tient can proceed against him whether or not informed

consent was given. If the patient thinks he has been damaged, he may go to court.

The concept of research requires an additional kind of consent, namely, the adult patient’s willingness to participate in procedures outside normal health care. There are opinions, though not necessarily statutory law, that suggest the conduct of such research is

ap-propriate when permission has been given by persons competent to understand the nature of their consent. There is apparently no basis for the parent or guardian to provide informed consent for procedures on a child that are not for his direct benefit. We have no adequate legal mechanism for developing information

concern-ing normal processes on the fetus, the child, or the

pop-ulation at large. It is this particular kind of research

activity for which we are being forced to devise a

pro-cedural device. NIH is now deeply involved in doing

just this, but its efforts will be to no avail if contrary legislative activity leads to restrictive laws before NIH can complete its task.

DR. BRENT. The right to perform research on a

corn-ponent of the population for which there is no legal basis available presents a danger. By focusing on this problem as the major issue, we may further jeopardize the shaky position of United States biomedical science. There have been changes in the legislative and

execu-tive branches of government regarding what we as

scientists are requested to do. I am concerned about

defending all that we have done over the decades

re-garding the importance of basic research-the right

way to conduct applied research-the right interaction between the practitioner and the physician-scientist as contrasted with the isolated laboratories of the experi-mental scientist. The increase in goal-oriented research at the expense of basic research is a more serious

prob-lem. There should and can be the opportunity to do

both. Basic research is a resource of a capitalistic so-ciety. The notoriety given to the issue of research on

abortuses, and the lack of notoriety given to the serious

problem of support for biomedical research are

evi-dence that nonscientific influences are setting scientific

priorities and issues-an increasing problem recently.

DR. THOMPSON. In the 1920s, when we were faced with epidemics of communicable diseases, we consid-ered only the professional knowledge of the time, and the public’s acceptance of it. Today, with the greater complexity of chemical versus microbiological aspects of life, sophistication becomes so great that it is difficult

for us to adapt medical practice and research to the

challenges we face. We must find some way through

our professional societies to come to a national

consen-sus about what ought to be done and how, before it is

determined by politicians.

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Vaun A. Newill

Nature and Sources of Pollutants


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