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burning of coal, which has about 14 to 16 to 20 parts per million in it, and creates a certain amount of lead to the atmosphere.

Now since that time, the concentration of lead in the atmosphere, which has been tested on several different occasions in a very precise manner has been substantially stationary. There has been a slight apparent decrease in recent years presumably as the consequence of changed patterns in the traffic of Cincinnati, of loosening up the congestion and getting a more peripheral traffic flow of automobiles.

The traffic in Cincinnati is definitely easier now than it was, say 5 years ago.

Senator MUSKIE. Have you drawn any conclusions as to whether or not the concentration of lead in the atmosphere attributable to the automobile in Cincinnati has gone up, gone down, or remained stationary?

Dr. KEHOE. I would say from the evidence we have at this point, that it is a little risky to attribute much change to that. What has occurred during this period of time has been within the variability of day to day results.

Senator MUSKIE. So you have a conclusion? Dr. KEHOE. We conclude that there has been no increase. Senator MUSKIE. Let us see if we can generalize that conclusion. Are you saying that the increase in the automobile population of the C'nited States has not in the past and is not likely in the future, given the same quality of gasoline that we now use, to increase the concentrations of lead in the atmosphere?

Dr. KEHOE. I am not drawing any such conclusion, Senator Muskie.

Senator MUSKIE. We have to draw the conclusion. From what you have told us so far about Cincinnati's situation that you believe that the automobile has not added to the concentration of lead in Cincinnati air.

Now I am trying to find out what that means in terms of the United States.

Dr. KEHOE. There would be no question in my mind that if you could move a larger number of vehicles through an American city, you would find more lead in the atmosphere. But we have very nearly reached the point of standstill in some of our cities.

Senator Muskie. I guess I have not driven in those cities. Dr. Kehoe. In consequence of this in some of these this has reached almost a stationary point. Certain areas of Philadelphia, certain areas of Los Angeles, certain areas of New York City.

Senator MESKIE. It seems to me we are constantly building highways that makes it possible for more automobiles to go to the cities.

Dr. Kehoe. Yes. What this results in is a spreading out.
Senator MUSKIE. A spreading out but not a reduction of automo-

Dr. KEHOE. Nor does it mean a reduction in the total lead content in the air. It means that the concentration at particular points where there are people tends to be more widely spread over the community, so that the overall concentration is lower than it would be at a point of such congestion of traflic as to produce a virtual stoppage in its fiow.

Senator MUSKIE. What you have said to me suggests that the concentration in some places would be less and in other places more?

biles in the city?

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Dr. KEHOE. You are quite right.
Senator MUSKIE. We are spreading it out.
Dr. KEHOE. You are quite right.

Senator MUSKIE. You seem to have emphasized the less rather than the more.

Dr. KEHOE. No, I have not except that there is a tendency to distribute the exhausts of motor cars more evenly throughout the entire community, from suburban areas to the center of the city. This tends to decrease the concentration at the center and to increase it in the periphery, so that it becomes more nearly uniform.

Senator MUSKIE. What is the net result to the city? Is it more lead or less lead! You talk about distribution now. How about the net?

Dr. KEHE. This may be more in the total air of the community, but it is less in those areas in which previously it was high, where you find people. So that from the point of view of the person who is exposed

Senator Muskie. Yes, but Doctor, have you ever filled an empty river basin? The lowest spots get filled up first but eventually the high spots get reached. As the water goes up it gets deep enough to drown people.

What you are saying is that in Cincinnati, presumably in other cities, as traffic patterns change because of the construction of new highways and so on it loosens up and tends to spread it.

I am interested in whether or not the level is going up. This is the question I have been driving at for the last few minutes, whether or not your evidence in Cincinnati indicates that the level is going up with the growth in the automobile population.

I still don't have an answer that I can hang on to.

Dr. KEHOE. The level at a particular point up to the present time has not gone consistently upward because the effect on the population has not altered. This raises the question of what will happen in the future. You don't know, and I don't know, and nobody knows, what will happen in the future. This is the thing which has to be known.

Senator MUSKIE. This is a rather mathematical certainty, if we have the same lead content in gasoline, that as the number of automobiles goes up the amount of lead poured into the atmosphere will go up.

Dr. KEHOE. In the total atmosphere, yes.

Senator MUSKIE. Yet the value you have given us with respect to Cincinnati suggests, as you have presented it, that this is not inevitable!

Dr. Keuoe. It is not inevitable, no, if you change the characteristiesif, for example, you could bring more air into this and sweep

it out, the concentration would be low.

Senator MUSKIE. How do you bring more air into the city?

Dr. KEHOE. I am not trying to do that. I say if you could. This is hypothetical. If you could move the air more rapidly it would get more rapidly diluted.

If you then distributed the vehicles so that they are more widely and more uniformily distributed the high results will come down, the lowest results will go up.

The qnestion then will be what is the critical concentration which becomes dangerous for any man anywhere?

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Senator Muskie. With your chief maximum distribution then the level will start to go up, or will it?

Dr. KEHOE. The level of the total atmosphere will go up but what happens to it at any particular point depends on the manner of its distribution.

Senator MUSKIE. So that with respect to Cincinnati the conclusion must still be regarded as tentative and inconclusive!

Dr. KEHOE. With respect to the future, yes.

Senator MUSKIE. It cannot be taken to justify any conclusion as to any city, any other city?

Dr. ŘEHOE. Yes and no. Senator Muskis. That is a very uncertain answer. Dr. KEHOE. Well, what one deals with in this situation, Mr. Muskie, are the probabilities. The recent survey of Philadelphia, Cincinnati, and Los Angeles have shown so many characteristics of this situation that are very nearly identical, that we have not a leg to stand on to believe at the present time that any one of these is particulary unique in this regard.

Senator Muskie. As to your testimony with respect to Los Angeles, for example—now Los Angeles has done a tremendously effective job of eliminating stationary sources of pollution.

Yet our testimony just this week is that we have had a recurrence of smog in Los Angeles because of the growth of the automobile population notwithstanding the control of stationary sources.

So, all of our evidence is in the testimony up to now is that the automobiles are raising the level of pollutants in the air. Now your testimony this morning is that we do not need to expect that with respect to lead in Cincinnati and now I am so asking you to try to generalize that with respect to Los Angeles and other cities.

Dr. KEHOE. All right. There are spots in Los Angeles at certain times of the year in which the values are relatively high. When, however, these are looked at in a cross-sectional way the difference between Cincinnati and Los Angeles is of the order of 1.4 in Cincinnati and to 2.2 or 2.3 in Los Angeles.

Senator Muskie. I agree but that is not relevant to my question. Dr. KEHOE. I am trying. Senator Muskis. The question is, can we expect again the amount of lead in the atmosphere to go up as the automobile population grows?

The evidence in Los Angeles is that pollution from automobiles generally not specifically tied to lead is going to go up. I am wondering if the lead is going to go up with the rest of it.

Dr. KEHOE. I think it is very likely that it is. I think where it goes up will depend on a number of circumstances which would have to be investigated in order to give you the answer.

What I have been saying in this, Mr. Muskie, quite consistently for 30 years is that we must know what we are talking about before we talk

Senator Muskie. Now that is a point on which we can agree.
Dr. Prindle's testimony yesterday with reference to the studies in
Cincinnati, Philadelphia, and Los Angeles, included this statement :

The average concentration of lead in all samples collected in each city was
1.4 micrograms per cubic meter of air-a microgram being a millionth of a gram
80 these are very small amounts we are dealing with-in Cincinnati, 1.6 in Phila.

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delphia and 2.5 in Los Angeles. The samples taken in heavy vehicular traffic were considerably higher. 14 micrograms per cubic meter in congested traffic on Cincinnati streets, and 25 micrograms per cubic meter on the Los Angeles Freeway.

Now let me ask you this question, Doctor. How do the figures you have given us with respect to Cincinnati relate to vehicular traffic as against outside of the vehicular areas of the city?

Dr. KEHOE. Many of these observations that were made with respect to vehicular traffic were made in Cincinnati by our own group. Consequently the statement there is true.

The point with respect to human exposure, which is the big problem here, is that there are really not very many people who spend much of their lifetime on a freeway.

They go to work and they return home, but they don't spend days on it except for certain individuals who drive trucks, who drive delivery wagons, using these in the course of their normal work, and who therefore spend considerable time on them.

These are the people we need to look at and these are the people we have looked at.

Senator MUSKIE. Dr. Prindle yesterday and the Surgeon General made a distinction between clinical effects from exposure to lead, as to which he felt there was a pretty good body of data, and low level, subclinical exposure over long periods of time, as to which he said we have very unsatisfactory data.

Now do your certainties on this point relate to both kinds of exposure or both kinds of results?

Dr. KEHOE. Yes; rather more, I should say, than either Dr. Prindle or the Surgeon General. I am not accusing them here of ignorance or drawing a long bow. These gentlemen know this problem as well as I do and they are concerned about it. The point of the matter is that we have shown quite clearly in the industrial situation that if you lower the concentration of lead in the atmosphere to a certain point, if you will prevent exposure of the individual to a certain point, you will not find lead poisoning.

Senator MUSKIE. How about the effects which both of these doctors have clearly said they draw no conclusions about and which they say have not been established ?

Dr. KEHOE. Mind you, I realize the difference between the industrial population and the general population. Our evidence comes very strongly from industrial population. If you will maintain the conditions which we now describe as being safe in industry, men continue to work in this industry all their working lives and at no time do they develop lead intoxication.

We have observations on personnel in industrial plants now over a period of 30 years in which there has been no case of poisoning, no shortening of life, no evidence of any subclinical injury that we can detect in this population, as differentiated from a normál population, that is to say, a population working in the same kind of job without lead.

Now this is not, in the strictly scientific sense, absolute proof. But 30 years of observation is pretty good evidence, which I don't think one discards readily.

Senator MUSKIE. Well, the committee cannot discard readily the apparent conflict between your testimony and that of the Surgeon

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General. So I want to be sure I understand the difference in your
points of view. As I understand from your testimony you have sug-
gested that up to a point the accumulation of lead in the body is
harmless?
Dr. KEHOE. That is right.
Senator MUSKIE. You draw the line just below the lead poisoning?
Dr.KEHOE. Considerably below.

Senator MUSKIE. Does medical opinion agree that there are no harmful effects and results from lead ingestion below the level of lead poisoning!

Dr. KEHOE. I don't think that there would be a complete agreement on this at the present time. I don't think that many people would be as certain about this as I am at this point. Senator Muskie. But you are certain? Dr. Kehoe. Not certain about it. I am only saying these are the probabilities, and we still have observations yet to make. It so happens that I have had more experience in this field than anybody else alive.

Senator MUSKIE. You agree that two men with the same experience could disagree as to the conclusion?

Dr. KEHOE. I don't think there is any doubt among the people who are experienced in the industrial situation, I don't think there is any doubt at all, that if you meet the criteria for safety that now exist in his relationship, you can confidently expect that you will have no cases of lead poisoning. I say, none.

Senator MUSKIE. Let me repeat the question so that I can be sure as to where your certainty lies. I asked: Does medical opinion agree that there are no harmful results from lead ingestion below the level of lead poisoning?

Dr. KEHoe. No; there is no consensus of opinion on this point.
There will not be for a long time to come.

Senator MUSKIE. Are you certain on that point, yourself?

Dr. KEHOE. It is entirely possible to postulate that somewhere, scmetime, within the universe of the population, you will find indiriduals who are so especially susceptible to lead that, under the conditions that exist in the rest of the population, that these people will be singled out and poisoned. Senator MUSKIE. That is a pretty minimal risk as you describe it. Does the medical profession as a whole regard the risk as minimal as you do?

Dr. KEHOE. There are a very considerable body of people at the present time who believe as I do on this. These are people who have had experience with the specific problem.

Senator MUSKIE. In Dr. Prindle's statement yesterday he said this:
In the occupational health field when blood levels reach point zero six mil-
ligrams per hundred grams of blood the worker is normally removed from an
environment in which lead exposure can occur. Concentrations of .08 milligrams
of lead or more per one hundred grams of blood are associated with toxic lead
poisoning, the clinical type that Dr. Stewart described. I would point out the
small difference between .06 milligrams or six parts per ten million and eight
parts per ten million is not a very marked margin of safety.
Would you agree with that?
Dr. Kevoe. I would agree with that. In a general way I would
agree this is a small margin, but in terms of analytical methods

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