were to be more completely documented, it might explain some of the striking rise in the prevalence of chronic respiratory diseases which has been observed recently.

The best indication of all of the chronic effects of air pollution is undoubtedly provided by the statistics on chronic bronchitis in Great Britain (19). There, the disease is the third leading cause of death and the leading cause of disability.

In the United States there has been increasing acceptance of the view that a group of chronic respiratory diseases in this country, comprising emphysema, chronic bronchitis, bronchiectasis, and "other chronic interstitial pneumonia," is similar to the chronic bronchitis syndrome observed in Great Britain and that the apparent differences reported in the two countries may merely reflect differences in medical diagnostic criteria and terminology in patients with cases of differing severity and degree of infection.

We are aware that in the United States no evidence has been produced to demonstrate that air pollution is an etiologic agent for the emphysema syndrome. Nonetheless, there is an ever-mounting accumulation of evidence linking the two. Well known is the phenomenal rise of deaths from emphysema in the American population as a whole since 1950 (20). One may, with considerable certainty, ascribe part of the increase to the increasing acceptance of this classification as a cause of death, which in turn is due to the increasing discussion of chronic respiratory disease in the medical literature. Nevertheless, we have no reservation in stating that part, perhaps most, of the sevenfold increase in the frequency of this diagnosis as a cause of death is due to the greater prevalence of the disease.

One reason for assuming an air pollution factor as a cause of emphysema is the urbanrural comparison of mortality in the United States. Certainly, when the age-adjusted urban rates are double the rural rates, there would appear to be some factor which is directly related to residence in cities. Attention has been drawn previously to the fact that smoking differences among males, by residence, are relatively small and presumably do not account for the urban-rural ratio found for

emphysema (21). The well-documented greater pollution of urban atmospheres as compared with rural points to a possible causal relationship.

It is recognized, of course, that there may also be an occupational exposure factor. The records of the Social Security Administration show that emphysema is the second leading cause of disability among male workers 50 years of age and older (22). It is clear that the evaluation of the role of air pollution in the increase in mortality from emphysema will have to take account of the occupational history of the decedent as well as his smoking habits.

Because of the increased interest in chronic respiratory diseases there has been a growing awareness of the need to inform people of the importance of certain symptoms. Accordingly, the National Tuberculosis Association has announced its intention of conducting a campaign during the spring of 1963 to alert people to the significance of "shortness of breath" and "chronic cough" (23). It is quite possible that people become so accustomed to these symptoms that they pay little attention or attach no importance to them. An increasing amount of data on the prevalence of emphysema and chronic bronchitis should be forthcoming as this educational campaign progresses.

In order to learn more about the long-term effects of air pollution, it was found necessary to conduct extensive field studies on selected populations. In 1959 the Division of Air Pollution of the Public Health Service, in cooperation with the Pennsylvania Department of Health, the Pennsylvania Electric Co., and others, undertook a study of two small communities in Pennsylvania, Seward and New Florence (24). The study had the elements of a natural laboratory setting inasmuch as the towns were virtually identical demographically. These towns, inhabited by about 1,000 persons each, are approximately 4 miles apart, with a soft-coal-burning electric power plant between them. The prevailing wind pattern was such that the town of Seward was subject to much higher levels of air pollution than New Florence. Thus, for the period of the study, the level of dust fall in Seward was three times that of New Florence, the level of sulfation was seven times as high, and the level of SO, was

at least nine times as high. Nevertheless, the SO, level in Seward was below that generally found in London (25).

The purpose of the study was to determine the long-term effects of low concentrations of air pollutants. An attempt was made to include the entire adult population of both sexes 30 years old and over. In addition to X-rays, the study used the long Medical Research Council questionnaire, with slight revisions, chiefly in terms of a much more detailed work-experience history. A battery of pulmonary function tests, including the body plethysmograph, was administered to the study group. The analysis, which was scheduled for completion in the summer of 1962, takes into account such variables as smoking and occupational and residence exposure of the townspeople.

In the preliminary report, one significant finding was that the average airway resistance (measured by the body plethysmograph) was higher in Seward than in New Florence even after differences in height and age were taken into account.

A curious finding was that the male population of the polluted area was almost 1 inch shorter than that of New Florence. One would rightfully hesitate to attribute this difference in height to the difference in the environment. Yet this possibility should not be dismissed arbitrarily because of its apparent implausibility. One may only say that differences of this sort would have to be documented in many other communities before we could accept the hypothesis that the stature of the inhabitants was related to exposure to air pollutants rather than to ethnic or socioeconomic differences.

Since this study was completed, considerable effort has been made by the industry to reduce the pollution in the area. A restudy some time in the future might prove of considerable interest in evaluating the possible benefits of such reduction in pollutant levels as may have been achieved.

The long-term effects of the Donora disaster have also been studied in the United States (26). The resurvey of Donora 10 years after the disastrous smog of 1948 has shown that the persons who became ill during the outbreak have had a less favorable morbidity and mortality experience than the persons who were

not affected in 1948. While it is true that those who became ill were probably less healthy to begin with than those who did not, it is quite likely that chronic effects due to unusually high levels of air pollution have been manifested in the affected group. Further, it is possible that repeated exposure to air pollution, even at very low levels, may have contributed to the longterm unfavorable experience.

The responsibility of air pollutants for the increasing frequency of lung cancer in the United States is at the moment a matter of some disagreement. Authoritative quantitative estimates of the role of air pollution as an etiologic agent do not exist, and only informed guesses can be made. Nevertheless, it is our thesis that, without decrying the importance of cigarette smoking as a factor, air pollution is also an important etiologic agent. This is not a novel idea. The World Health Organization report on lung cancer mentioned a number of possible etiologic agents and noted the prominence of air pollution in the list (27). Once again the sharp urban-rural differential in mortality rates for this disease is manifested. Also, lung cancer mortality rates appear to be related to the size of the urban area, the larger areas having the higher age-standardized mortality ratios.

many and varied sources in every category, industrial, residential, municipal, and automotive, and makes necessary a wider range of research activities than in many other countries.

In summary, we in the United States are devoting considerable time and effort to this important question: Does longtime exposure to low concentrations of air pollution result in adverse health effects? Our preliminary answer, based on both laboratory and epidemiologic studies, is yes. The evidence as yet is only qualitative; much more will have to be done before the necessary quantitative answers are found on which to base rational control standards. Hopefully, with the data the Public Health Service is able to collect and that amassed by researchers in Europe and throughout the world, this goal can be attained.

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