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Quality Standards Major Challenge in Setting SO, Standards Is Avoiding the Simplistic Approach
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Paper by:
Discussion by:
Willard Machle, M.D.
H. N. MacFarland, Ph.D. Robert E. Eckardt, M.D.
Dr. Mnclrle is n consirltnnt in indirstrid me dicine ond toxicology 3;n Coral Gables. F 'In.
Dr. MacFnrlond is n professor on the faculty of science at York University in Toronto, Ont.
t may appear superfluous to offer additional data and comment upon the effects of sulfur oxides in the ambient air and the production of illness in the community. The accumulated literature on the subject is a formidable mass of material to be synthesized and tied into the general problems of air pollution. There is no comprehensive conceptual scheme that will enable us to come to grips with 'the overall problem. Perhaps we have permitted ourselves t o be heguiled by a simplistic approach, which tries to relate only sulfur oxides-and one or two other pollutants-to the clinical effects that have been seen from time to time. Early observations of the effects of sulfur dioxide relate largely to therapeutic applications or use as a fumigant. Homer mentioned its uses both in the "Iliad" and the "Odyssey" and there were frequent later references to
the use of sulfur dioxide in the treatment of respiratory and skin diseases in man and animals. The concentrations were not well controlled o r recorded in most instances, and, except for mishaps such as occasional cases of pneumonitis or hemorrhagic pneumonia, adverse effects were not noted. Serious effects from exposure to sulfur dioxide first were reported in industry in 1821, and involved irritative effects of sulfur dioxide used as a bleaching agent. The exposure concentrations must have been staggering, since an 1853 report referred to irritation of the vagina. In our own experience, irrespirable concentrations (over 300 p.p.m.) occurred from time to time, but there was only one in- c _ , ..~.:'.,:. ~ ~ stance 01 ourns 01 me grnirarva. i n one of our earlier studies in industry, where the exposure averaged from 80100 p.p.m. for 3 years, and, later,
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llr. Ecknrdt is the director of Esso Resenrch & Engineering Co.'.s medical research
divi,siori (it Linden, N.J .
20-30 p.p.m. for 5 years, we found an elevated incidence of nasopharyngitis, alteration of the senses of smell and taste, and an increased sensitivity to other irritants. There also was a tendency to fatigue and shortness of breath on exertion. At the time, we thought that these symptoms might result from the increased intake of mineral acid, since the urinary acidity was higher in the exposed group of I O 0 men; however, this was not proven as a cause. The normal daily excretion of mineral acids has been estimated to he approximately 20 meg. The average daily exposure of our subjects would approximately increase this amount one and one-half fold. Experimental observations of exposure to sulfur dioxide have been > z.... :--" numerous an", w i n i e w C A K ~ L L W ~ , quite consistent. As long ago as 1884, Ogata, in experiments upon himself, found that 500 p.p.m. were irrespir~
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ablc. Such an increased sensitivity to inhalation is certainly not very great, since from 200-400 p.p.m. may cause chemical pneumoLia and death in animals with a wide range of sensitivities. At more realistic concentrations, in 1915, Holmes and his coworkers reported on a series of experiments upon 60 subjects. No one in this group detected the presence of 1 p . p m of sulfur dioxide, but 10 p . p m was disagreeable and would probably be a nuisance over long periods of time. We found such concentrations to be objectionable but tolerable, as were 20-30 p.p.m. in our industrial study. T o me, 20 p.p.m. is very uncomfortable, but tolerable; others have reported tolerating 30 p.p.m. I have observed tolerance levels in a variety of situations-refrigerator manufacturing, gasoline treating plants, production of sulfur dioxide and sulfuric acid-and have found a remarkable consistency in responses to the various levels after habituation occurs. Exposures to 10 p . p m gave variable results, depending upon the sensitivity and experience of the subject: 10 p.p.m. may be disagreeable to some subjects and not to others. The threshold limit value for sulfur dioxide recommended for industry is 5 p.p.m., but there is no adequate evidence that this level causes any measurable ill effects. By comparison, the so-called lethal concentration in the London fog was 1.34 p.p.m. Sulfur dioxide and particulates
In the past 10-15 years, there have been a number of studies on the effects of mixtures of sulfur dioxides and solid or liquid aerosols and gases. Valuable information has been obtained on the effect, or lack of effect, of such mixtures in intensifying the irritant effects of sulfur dioxide. To my mind, these studies have led to no useful index of the irritant action of such mixtures as they may occur in real situations of air pollution. This position was supported at the Ninth Air Pollution Medical Research Conference (Denver, Colo.) . Burton reported no effect on pulmonary function in men from the inhalation of sulfur dioxide and sodium chloride aerosols; Battigelli’s experiments with gas-particle mixtures also was inconclusive as far as enhancement of the effect of sulfur dioxide was concerned. Snell did, however, find a progressive drop in peak expiratory flow rates in humans as the concentration of in544 Environmental Science & Technology
haled sulfur dioxide was increased. A 14% drop was noted in unacclimatized men inhaling 5 p.p.m. of sulfur dioxide. No increase in effect was seen with addition of a saline aerosol. We are, therefore, left without consistent relationships between these two components of air pollution. The conversion of sulfur dioxide to sulfuric acid is affected by a number of variables, among them temperature, humidity, time, and the presence of catalytic metal aerosols. Conversion rates under controlled or observed conditions range rather widely in the reports. These interactions of components can create highly variable situations. Duration of the anticyclonic conditions appears to be an important parameter. as was observed at Donora, London. and elsewhere. This factor, with accompanying humidity, could increase the oxidation of sulfur dioxide. but there is inadequate data on the rates of such occurrence. And, while such a process may be going on, there also is an indeterminate amount of fall-out of sulfuric acid droplets and an accumulation of other pollutants under the inversion. Serious attacks are being made upon this problem, and it is hoped that these studies will be continued on an expanded scale. Air pollution indices and indicators
A great deal of effort has been expended to establish indices to be used as guidelines in the regulation of air pollution that is considered to have reached undesirable levels. In some urban areas, such attempts have met with little success; in others-such as Chicago and San Francisco-considerable progress appears to have been made. Most of the indices proposed have been limited by oversimplified monitoring of a very complex phenomenon. The use of concentrations of sulfur oxides and particulates is common but has not always been satisfactory in general application. It also has been suggested that carbon dioxide levels are an indicator of carbon monoxide. oxides of nitrogen, and sulfur dioxide levels. This information may be useful in urban areas where large amounts of fossil-fuels are burned, but of limited value in nonmunicipal areas where large amounts of single pollutants are discharged. Mathematical models have been applied to specific point sources and types of pollutants, but studies by Marsh in Reading, England, d o not
support the feasibility of such schemes. A 1967 publication by Middleton, director of the National Center for Air Pollution Control, compares the levels of air pollution in 65 metropolitan areas of population of 40,000 or more. Each pollution component included (suspended particulates, gasoline hydrocarbons, and sulfur dioxide) was given a coefficient of severity, between 2 and 65. The basis for these assignments is not clear to me, and Middleton carefully states that many factors must be considered before comparing the areas. The report recognizes that air pollution is not the same from place to place, nor from time to time in the same place, and-most important-the kind of data available is not always the most desirable. This brings us to the recognition that the use of simple indices such as sulfur dioxide and particulates, or sulfur dioxide alone, are not adequate. In many circumstances, they tend to obscure rather than clarify the complex nature of air pollution. Air pollution control boards in New York and Chicago have singled out sulfur dioxide or the sulfur content of fuels as criteria and have proposed limits on the sulfur content of fuels. They have done so without regard to the absence of any data that sulfur oxides alone, in the concentrations encountered in the air of cities, is capable of producing any illness or harm to health. This is a delusive and simplistic attack o n air pollution. Where do we go from here? A great amount of effort is being applied to epidemiological studies. These certainly should be continued, especially with respect to diseases assumed to be modified by pollution of the ambient air. Such studies have not been too fruitful in the past-largely, I think, because reasonable hypotheses of cause do not yet exist (as in pulmonary emphysema), or because inadequate indices, such as sulfur dioxide concentration, have been used to measure gross pollution levels. The application of epidemiologic methods also has limitations in identification of specific components causing disease. Comparative correlation studies of communities differing in magnitude of pollution, as measured by some index or other, becomes very complex when we realize the multifactorial causes involved in air pollution. Much more experimental data are needed to resolve the role of potentially harmful
pollutants and to develop comparative stochastic models for testing hypotheses. The epidemiology of air pollution will be aided by more extensive laboratory observations on the components of air pollution, and their effects under realistic experimental conditions.
Discussion MacFarland: Dr. Machle has put his finger very neatly on some of the key problems in this vexing field. The older literature and modern observations verify that exposure to sulfur dioxide by itself is not harmful in concentrations up to a few p.p.m. We are faced with reconciling this with the observation that some people die in air pollution disasters where the concentrations scarcely exceed one p.p.m. The hypothesis of synergistic effects with other smog components was advanced many years ago. As Dr. Machle says, such evidence as is available leads to no consistent picture of synergism between sulfur dioxide and aerosol systems, except at unrealistically high concentrations. Dr. Machle also remarked on the complex and changing composition of polluted air, and the utility of measuring a single component as a pollution index. The fallacies inherent in this simplistic approach are all too evident. It is appalling that practically all of the data on urban sulfur dioxide levels have been obtained by a procedure notably lacking in specificity for sulfur dioxide. We could spend several sessions identifying the deficiencies in analyses of polluted atmospheres, and only conclude that we have only the fuzziest ideas as to what the causative agents of health effects on human population may be. As Dr. Machle indicated, a great deal more work must be done on the health effects of pollutants-work falling in the areas of epidemiological studies, comparative correlation studies, and realistic experimental studies. One other topic I would like to comment on is the basis on which to control air pollution. As Dr. Machle points out, we merely delude ourselves if we approach this complex problem in a simplistic fashion. The National Air Pollution Control Administration seems to be wedded to the idea that pollution abatement be based on standards established for the quality of ambient air. This presupposes that if we knew the composi-
tion of polluted air, we could state what effects on health would ensue from exposure to such air. Unfortunately, we are not in a position to make such an assumption. Even if we had the temerity to make this assumption, we would still be forced back into considering the problems of relating ambient air composition to sources of emission and the effects of topological and meteorological factors on the dissemination of pollutants. Our inability to follow this whole line of approach is exceedingly apparent. We cannot control ambient air and its composition; we can, within the limits of present technology, control emission sources. The missing link in the chain is the tie-up between emission sources and the ultimate composition of the ambient air. Even the best diffusion models that we have, applied to the simplest situation, do not enable use to predict with precision the composition of ambient air. Let us admit, then, that our knowledge in all the major areas of concern-emission sources, dissemination phenomena, health effects-is extremely rudimentary. Let us do the best we can with existing control technologies, while continuing the multidisciplinary studies that may enable us to control air pollution on a scientifically sound basis. Eckardt: Dr. Machle’s review of the present knowledge concerning sulfur oxides clearly points up a dilemma. On one hand, concentrations of sulfur oxides necessary to produce serious effects in animals or humans are far in excess of those presently found in polluted air. On the other hand, serious effects have been produced during air pollution episodes at concentrations that are a fraction of those required to produce effects from the pure gas. The answer may be that something other than sulfur oxides is producing the effects, or that sulfur oxides have a synergistic effect with other pollution constituents. Many air pollution experts believe the latter to be the case, with particulates the materials exerting this synergistic effect. Some support for this concept is the work of Amdur and her associates at Harvard-as mentioned by Dr. Machle-who found that effects could be produced in guinea pigs by a combination of sulfur dioxide and aerosols, whereas either by itself would produce no such effect at comparable concentrations. Further support arises from the observations in
London in 1952 and 1962. Only onetenth the number of deaths occurred in 1962 as had occurred in 1952, yet the sulfur oxides concentration was higher in 1962. One difference was a markedly lower particulate concentration than in 1952. Everyone would like neat, clean, scientific criteria for sulfur oxides, as well as other pollutants, from which standards for the ambient air could be derived. From these, emission standards could be calculated from diffusion models. Unfortunately, however, the criteria are not clear, as pointed out by Dr. Machle; even the diffusion models are not as well established, scientifically, as many would have us believe. Diffusion models are influenced by stack height, number of stacks, wind direction and velocity, temperatures, and other things. Since we do not have such criteria, our approach to standards will have to be partially subjective rather than strictly objective. Value judgments and decisions will have to be made. We shall have to use the data we have, recognize their limitations, and make re-evaluations as new data are accumulated. Thus, the American Petroleum Institute itself is spending several million dollars per year, and in cooperation with the Automobile Manufacturers Association and the National Air Pollution Control Administration, is devoting several more million to develop new data. We believe that each situation should be analyzed independently. The air pollution problems of Los Angeles are different from those in New York City, which, in turn, may be quite different from those in, say, Atlantic City. Each solution must be handtailored to each problem, and technological feasibility as well as costs must enter all discussions. Air pollution abatement is expensive-costs go up exponentially, not linearly, with degree of control. Obtaining the maximum benefits from money expended will require the best brains in government, industry, and universities. We may not be able to go all the way in one step. As technology advances and cost reductions in the f u ture are achieved, we may be able to obtain more control that is possible today. In the meantime, as Dr. Machle has suggested, we should continue the pursuit of scientific criteria, so that we can examine what we have done and where we are: to see if our initial subjective evaluation was adequate. Volume 3, Number 6, June 1969 545
