to consider any future potential threat to the public health in this matter on the background of a body of data which will serve as a baseline for comparison.

Incidentally, there has been reference-this is additional oral information-there has been reference to 11 high values found in that survey. I should like to report to you that those values were considered by me to be pure chance phenomena that in a statistical distribution of values which begin on the low side and which taper out into the high side. The results on those men who are available at the present time, which consist of four people in Cincinnati and three people in California, have been rechecked. The results, in this instance, as could more or less be predicted, came right back then into the normal range. All of the results fortuitously turned out to be quite low, on the low side of the mean value rather than high.

Senator MUSKIE. Let me ask you this. In the statement, simply to give you the opportunity to emphasize what you have said, you say that on the basis of the study in Philadelphia, Los Angeles, and Cincinnati, the reliability of the current information on the lead content of the atmosphere of cities was established beyond further question. That is a pretty strong statement for a scientific man to make unless he means it.

Dr. KEHOE. I mean it very definitely, sir.

Senator MUSKIE. You can anticipate no variations from the findings in these three cities and any other place in the United States at any time in the future that would raise a real question?

Dr. KEHOE. My statement does not refer to the future.
Senator MUSKIE. You say beyond further future question.

Any question that would be raised would have to be in the future, with reference to the point in time that that study is made.

Dr. KEHOE. I spoke specifically of current information. I shall speak of the future a little later.

Senator MUSKIE. So that there is further question if you think in terms of further as referring to the future.

Dr. KEHOE. There is this question, yes. But the question at this point in our discussion is completely open. I am not anticipating the future at this point.

Senator MUSKIE. Still, Doctor, let me clarify this further. Your next sentence says it is now possible to consider any future potential threat to the public health in this matter on the background of a body of data which will serve as a baseline for comparison.

That would seem to suggest that your baseline even as to the future is not going to move.

Dr. KEHOE. That was not the intention. There is now a baseline with which one can compare future observations. One of the primary purposes of this investigation which was emphasized by the Surgeon General and his advisory committee was that there were not enough data distributed over a wide enough number of American cities so as to provide a baseline by which to determine future trends.

Is there, in other words, a future danger from the ever-increasing numbers of automobiles, from the increased use of leaded gasoline, from the increased distribution of lead in the atmosphere from any and all sources?

The hygenic issue, at this time, relates to the total pattern of the concentration of lead, from all sources, in the respired air of persons in the general population, in conjunction with the quantities ingested with their food and beverages and any other material that is swallowed. The mere abundance of lead in the human environment is not of itself a threat to mankind, nor in the final analysis is the mere presence of lead within the anatomical structure of man.

Abundance is a nonquantitative term, and the outcome of the absorption of lead into the human tissues-the internal media of the body, depends upon its rate and extent, and upon the physiological mechanisms which are involved in its entrance and exit, its systemic and cellular distribution, and in the metabolic processes in the tissues, including also, the elimination of absorbed lead from the body, and the extent of the accumulation, if any, in the body with time.

The natural environment of mankind is such that lead is taken into the human body in virtually all food and beverages and in the respired air. The many usages to which lead is put in modern industrial society, one of which is involved in the present discussion, have increased the amounts which the average man ingests and inhales, with the result that somewhat more than natural quantities of lead enter into the metabolic processes of his body.

The quantities are small but not insignificant. The food consumed by an adult in the United States contains lead in amounts which range from less than 0.1 milligram to 4.0 milligrams, occasionally more, per day. The higher and lower values mentioned occur infrequently, the larger proportion of the daily quantities grouping themselves regularly and closely around the mean value which is somewhat less than 0.3 milligrams per day.

The quantities taken in daily with the inspired air are not so well defined, since they must always be calculated. The quantities appear to range between 0.015 to 0.09 milligrams per day, and as in the case of the intake in food, the average in any situation is much nearer the low value than the high.

The maximum quantities of lead absorbed into the body from that taken into the alimentary and respiratory tracts of the average man may be estimated on the basis of experimental evidence which shows that somewhat less than 10 percent, of that ingested (swallowed) and somewhat less than 50 percent, of that inhaled, are absorbed.

Calculations based on these percentages indicate that about 0.03 milligram may be absorbed daily from the alimentary tract, while quantities ranging from 0.007 to 0.045 milligram and averaging between 0.02 and 0.03 may be absorbed daily from the respiratory tract. As is clear from this, there is less likelihood of the absorption of lead day to day from the air, that is, the quantity is less, than the quantity which is likely to be absorbed from the alimentary tract.

Therefore the food and drink side of this environmental picture is still the more important side.

Evidence obtained by corresponding means has demonstrated that the quantities of lead eliminated from the body daily by the average man are substantially equivalent to those taken in.

Thus the lead which is evacuated with the feces, daily, is only slightly less than that in the food and beverages. That which is excreted in the urine ranges from somewhat less than 0.01 milligram to

about 0.08 milligram per day, and averages approximately 0.03 milligram per day. The total output of lead in the feces and urine, over a period of months, usually exceeds slightly the intake in the food and beverages, thereby indicating, indirectly, that the magnitude of that absorbed in the respiratory tract of persons investigated in Cincinnati is not less than 0.02 milligram per day.

Senator MUSKIE. Doctor, you have been giving us figures that come from the Philadelphia studies?

Dr. KEHOE. NO. These have come from very carefully carried out, balance experiments on human subjects in the Kettering Laboratory. Senator MUSKIE. As of what date?

Dr. KEHOE. Beginning in 1939 and extending to the present time. They are still going on. At the time, back in 1939, we gave up any hope of understanding this problem unless we carried out balance experiments on human beings which would tell us the sources of lead, the manner in which it enters into the body, the manner in which it gets out of the body, and what is the relationship between intake and output under ordinary normal conditions and under conditions that exist in industry or whenever there is an unusual exposure.

These experiments have demonstrated facts about the physiology of the behavior of lead in the human body that we could not have learned by any other means.

Senator MUSKIE. The question I was getting at is that since these studies extend over a period of two or three decades do you have any data as to whether or not the amount taken into the body each day has increased over that period?

Dr. KEHOE. The evidence, so far as Cincinnati is concerned-in our experimental subjects have been in Cincinnati in the Kettering Laboratory-this does not apply to other cities specifically, but in a general way it does-the evidence is that over the period of the last 30 years there has been very little change, if any, but the change has been downward, if any, rather than upward.

There has not been an increase in the intake of lead by the citizens of Cincinnati, as represented by our experimental subjects.

Senator MUSKIE. What is the nature of the samplings you take in Cincinnati?

Dr. KEHOE. The sampling is very meticulous. These experimental subjects collect exact duplicates-as exact as can be obtained by intelligent young men exact duplicates of everything eaten and drunk during the period of observation, every item of food that passes their lips, every item of drink including cocktails and Coca-Cola must be in the duplicate sample for analysis.

These men also collect every sample of feces every day, every drop of urine that is passed every day, and this is subject to analysis day by day, as the experiment goes on, so that we have had day-by-day observation on experimental subjects for as long, in one instance, as 41% years.

Senator MUSKIE. With respect to intake, have you had samples over that period, intake from the air as well as intake—

Dr. KEHOE. We know the content of lead in the air in the Kettering Laboratory in which these subjects spend their day. We know also what is the lead content of the atmosphere in which they live, so that by calculation we can get at this. It is quite fair to say that over the

period beginning in 1947 there has been little or no change in the atmospheric conditions in respect to lead in Cincinnati.

Here again if there has been a change there has been a diminution. Senator MUSKIE. You are talking about the lead content in the air. How about the amount of lead that is taken in from the air by human beings?

Dr. KEHOE. First of all we carried out experiments that relate to the intake and output in the food and have increased quantities taken by mouth. In 1949 we began experiments on inhalation dealing with known concentrations of lead in the atmosphere while following the intake and output of lead in the food and beverages; we investigated the response of subjects to low levels of lead in the atmosphere, as to higher levels that approached those of industrial establishments.

One of the things we were most concerned about, and have been over the years, is to get at the question of a standard which can be applied to industry that will demonstrate certainly and without any question of doubt, whether the situation under which a man works is safe or whether it is dangerous.

The differentiation of these two in industry is absolutely imperative to industrial control. So that our first work dealt with this in relation to industrial exposure. During the last 5 years, our work has been concerned specifically with lead of the order of magnitude of that which now occurs in the general ambient atmosphere, and with somewhat larger concentrations which might conceivably be found to occur later.

Senator MUSKIE. Have you taken samples from people who have a particularly heavy exposure to lead in the air, traffic policemen, service station attendants, and so on?

Dr. KEHOE. Yes, we have done this systematically over a period of a good many years. So there is a body of data available on this matter in Cincinnati, a body of data that has been published.

The information is available in these records, from the first obtained, up to that obtained by methods now in use, so that comparable data have been obtained since 1937 and 1938.

Senator MUSKIE. It is your conclusion that in 1937 to the present time, on the basis of that data, that there has been no increase in the amount of lead taken in from the atmosphere by traffic policemen, by attendants at service stations or by the average motorist?

Dr. KEHOE. There is not the slightest evidence that there has been a change in this picture during this period of time. Not the slightest. Senator MUSKIE. Is there evidence that assures you that there has been no change?

Dr. KEHOE. Evidence obtained in an effort to find the one thing about it that we have been concerned about in this situation, and for a good many years have studied; this is that there might be somewhere, sometime, some combination of strange circumstances that would put the lead content of the food and drink high at the same time that the air was high, and that under these circumstances we might find an individual, a group of individuals, or a population in a particular area, like that of an industry, in which there was an undue exposure and in which there would be real risk.

We have looked systematically for such groups for the last 15 years and we have failed, utterly, to find them. This is why we began

to study garage mechanics many years ago, because of two things. First of all, the garage mechanic, in the very nature of his work, has a heavier exposure to the exhaust gas of automobiles than most people do, so much so that a fair number of these men in cold weather go home in the evening with a carbon monoxide headache, which means undue exposure to exhaust gases.

These men however have further occupational exposure to lead by virtue of the fact they do a little body work on cars, a little body painting, some repair work of a variety of kinds; they handle greases, and they sometimes repair storage batteries, which are lead containing; and these men also get unconscionably dirty as we all know. They crawl around on the floor under automobiles. Their clothes are dirty, their hands are dirty, they smoke cigarettes, they eat sandwiches in their place of work. These men have a measurable degree of exposure to lead, as is demonstrated quite clearly by the fact that they are differentiated from filling station employees, refinery workmen, traffic policemen, and postmen who pound the streets, by a barely significant elevation of the excretion of lead in their urine.

This group, and this group only, of the people that we have looked at, have shown a statistically different output of lead from the people in the general population.

This, I may say, is the mildest degree of occupational exposure that we have found, in which there is a certain statistical differentiation in the intake and output of lead and yet without lead poisoning. Lead poisoning in the garage mechanic is essentially nonexistent unless he carries out a specific job such as that of decarbonizing motors, throughout all or most of his workdays, continuously.

Senator MUSKIE. Over the past 30 years I assume there has been a tremendous growth in automobiles and in the amount of traffic in Cincinnati. and yet as I understand it, you say that there has been no increase in the concentration of lead in the ambient air?

Dr. KEHOE. That is a fact.

Senator MUSKIE. Over that period of time?

Dr. KEHOE. This is a fact. There has been a change downward, since the period of the Second World War when we had difficulty in Cincinnati getting the kind of coal we would like to have, and getting it burned in the way we would like to have it. Cincinnati has a very large coal-burning industrial and household problem.

During this period we had to take the coal that could be obtained, and there was definitely an easy going policy with respect to smoke abatement because of the times.

In 1945 this whole situation was changed and in the period immediately following this the lead content of the atmosphere of Cincinnati went significantly downward.

Senator MUSKIE. What you have just said is that the decrease in the concentration in the atmosphere is due to better control of stationary sources of air pollution?

Dr. KEHOE. That is right.

Senator MUSKIE. Do you draw any conclusions as to what has happened to concentrations of air attributable to the automobile over that period of time?

Dr. KEHOE. All this meant was that there was a significant amount of the air pollution in Cincinnati yielding lead that was due to the