Man's 50-percent lethal dose is anybody's guess, but we usually use about 450 roentgens or so. The point is that the mammals are actually very, very low on the sensitivity scale compared to plants.

EFFECT OF SHELTERS

When you think about the survival of people versus the survival of other aspects in the economy, particularly the agricultural economy, whether or not we have shelters makes a big difference. For instance, if you do not shelter the population it is certainly simple and obvious that plant life will survive far beyond any kind of human life or animal life but once you shelter then you will allow plant population to be exposed to tremendous amounts of radiation and then you have to take into account different levels of radiation.

There is a wide spread in the range (up to 200 times). The response of seedlings of various plants also gives indication of considerable variation (20 times).

This brief survey on comparative radiosensitivity should enable one to appreciate the difficulty in assessing total radiation effects. However, for any particular level of nuclear attack the fallout contour patterns should indicate whether the levels of serious consideration for ecological effects are being approached.

As part of the necessary knowledge for handling post-attack problems, the catalog of comparative radiosensitivity will have to be considerably expanded. This knowledge, combined with data on the passage and concentration of isotopes through various food chains may eventually lead to reasonable predictability of radio-ecological effects. In complete detail, this is a long way off. Selectively, for items of great concern (e.g., feed crops, certain insects, etc.) concentrated research should be done in the immediate future.

Very little of this has actually been done. I do not think the essential crops, like wheat, actually have more in the way of a complete radiation profile through all the different stages.

There is a tremendous amount of basic research going on in this field, but not quite from the civil defense point of view, not quite from the possible attack recuperation point of view.

Certain gaps are left and this is the point I am trying to bring out today. These programs have to be given a slightly different orienta

RECONSTITUTION OF LAND AFFECTED BY FALLOUT

Over most of the land (forest, chaparral, grassland), time is the only recourse for reducing radiation to a semblance of its original level. Natural decay of isotopes, leaching and fixation in the soil, and washing away will bring about an eventual return to low levels of radioactivity. There appears to be but one item for man's consideration concerning the radiation level. If reseeding or restocking is to be attempted, the introduced material should be relatively unaffected by the existing and projected radiation profile.

For example for the kind of airplane reseeding that could be done, one would want to know that the residual radiation as it is projected will not essentially do away with the effort of the original reseeding.

The possibility of actively reconstituting land for biologically productive use following radioactive fallout would seem, for economic reasons, to be restricted to croplands. The work of the U.S. Department of Agriculture on this problem is important.

STRONTIUM 90 DECONTAMINATION

In areas where cropland is rendered unfit for growing food for human consumption, Sr90 will probably be the principal contaminant. I might add parenthetically, that the Special Subcommittee on Radiation of the Joint Committee on Atomic Energy under Chairman Holifield has held many hearings on this subject and has been responsible in large part for motivating the large scale effort now in progress toward solution of the Sr9 problem. Where Sr90 reaches significant levels, the initial external dose rate may be 3003,000 roentgen-hour. Work here will have to be curtailed for a considerable period of time until the dose rate gets low enough to be safe for men to enter the area.

This ties in with the need for agricultural surpluses to get us over the early stages before we can go in and do something about agricultural land.

The possible methods for handling the Sro contamination include physical removal of topsoil, removal of Sr90 by cropping, and leaching or fixing the Sr. It is also possible to grow crops that can be contaminated without causing future danger (e.g., cotton, tobacco, etc.).

The nonphysical methods of Sr90 removal are not very promising as yet. Chemical fixation, leaching, and cropping all have serious limitations and further research is called for. For example, leaching of Sr90 from soil requires several tons of gypsum or lime as well as large amounts of water and fertilizer per acre. Cropping would require 10 to 20 successive crops under most favorable conditions to obtain a significantly high percentage of removal.

Some of the Department of Agriculture experiments on physical removal are shown in figure M-6, p. 342 and table M-3, p. 342.

FIGURE M-6.—PERCENTAGE OF DECONTAMINATION BY REMOVAL OF CROPS AND

MULCHES

Treatment

Raking mulch, 10 tons per acre..

Raking mulch, 5 tons per acre_

Raking mulch, 2 tons per acre..

Cutting and removing sod__.

Flail chopping soybeans and some soil, after mowing_

Flail chopping Sudan grass and some soil, after mowing

Mowing soybeans--

Mowing Sudan grass_.

Least significant difference (0.05).

1 Only 1 replicate was available for these treatments. The stated least significant difference therefore does not apply to these values.

TABLE M-3.-Percentage of decontamination by scraping surface soil following various treatments

They indicate that the methods are effective. However, these methods are apparently costly and one problem still remaining is what to do with the radioactive material removed. Burial in ditches near the original site is probably the best solution now available.

I would like to show you some of the results. This was done with barium 140 as the radioactive test object and indicates a percentage of decontamination by removal of crops and mulches, and with a raking, 10 tons to the acre, they were able to accomplish 100 percent removal and various other things that they have done down to 29 percent removal.

Apparently this is not too good a method in that it interferes with the general manner in which farmers actually work their farms. In other words, apparently it is not to the farmer's liking or it is uneconomical to spread these mulches around but, rather, they like to work them into the soil to increase the fertility of the soil.

Now, this represents the kind of physical things that were done in that they cut off and scraped the surface of the soil, and they did various things like putting asphalt on it, and they checked the various kinds of things like plowland, discland, seedbeds, and in a general way, the chart just shows that you can get 75 to 85 or 90 percent removal of the strontium 90 or the radioactive material by physically going over this land and scraping it.

So we do have methods for handling this problem, at least, in the essential cropland areas.

SUMMARY OF ECOLOGY PROBLEMS

I have tried to show, in a general way, and in an ecological frame of reference, the types of damage which may occur following a nuclear attack.

The threats of large-scale fires, erosion, and radiation have been pointed out.

Detailed biological and local geographical data must be compiled and then related to particular types and levels of attacks.

Much information exists already and needs only to be collected. How much additional experimental and field research will be needed remains to be seen.

Selective concern for those forms of life most needed for our survival should be examined first. Coincidentally, those forms which may become unmanageably destructive pests, such as insects, rodents, and weeds, should receive early priority for study.

Radioecology is the qualitatively new consideration. The comparative radiosensitivity catalog must be enormously increased.

The combined efforts of land-management experts, engineers, agriculturists, radiobiologists, and others, will be needed to define and handle the complex problems raised by extensive damage to the biosphere from fire, radiation, and the concatenated consequences. Thank you.

Mr. HOLIFIELD. Thank you, Dr. Mitchell.

Any questions, Mr. Roback?

DISTRIBUTION OF STRONTIUM 90

Mr. ROBACK. This discussion of strontium 90 is based on the sup position that the fallout is a homogeneous hazard, that is, that the hazard is the same wherever the radioactive material is deposited. Is that right?

Dr. MITCHELL. It is both homogeneous and nonhomogeneous.

Mr. ROBACK. What I am asking about is this: Isn't it the case that the strontium 90 deposition usually occurs much further away from the point of explosion, as in worldwide or delayed fallout?

Dr. MITCHELL. I would say the bulk of the strontium 90, percentagewise, will come within our local fallout pattern areas.

This would be my impression. And that the subsequent worldwide fallout, coming down much more slowly-well, what would you say the division is, Dr. Hill, between the two?

Dr. HILL. As far as total fallout is concerned, oh, on the order of 80 percent or more would be local fallout, but there is the problem of fractionation which I think Mr. Roback was referring to.

However, the local fallout areas would still be the most substantially contaminated with strontium 90 even so.

Mr. HOLIFIELD. I think the information we had before our Atomic Energy Committee does not quite agree with that.

As I remember, about 75 percent of the fission products went into the stratosphere and only 25 percent was deposited locally. The other 75 percent came down later.

Dr. MITCHELL. Yes; but that would be spread over thousands of unit areas.

Mr. HOLIFIELD. That is right.

Dr. HILL. There are good reasons for that, because most of our shots or a large percentage of our shots were not surface burst, in the test series.

That is the main reason for that.

Mr. ROBACK. Well, Mr. Chairman, I was not referring to total estimates of distribution worldwide as against local fallout, but I was referring to the fact that the composition of the radioactive elements or the radioactive production, you might say, after an explosion is such that not everything is affected the same way.

There are materials which have different volatilities and rates of condensation. Strontium, being highly volatile, condenses more slowly, and since radioactive elements are taken up more efficiently by carrier material (dust and debris) offer condensation from the gaseous state, it could well be that particles which fall far downward or in worldwide fallout contain more strontium than closein fallout. Dr. MITCHELL. Not per unit area, sir, which is what we are interested in.

In other words, even if there were and I do not know what the numbers are some really wide discrimination-let us say, 10 percent coming down in the target area and 90 percent going up into the stratosphere, distributed worldwide-then the amount which would then come back and fall on the United States over the local area, would still be only a small addition per unit area.

In other words, it would be the local fallout problem which would probably determine the effect on our agriculture in that area. For an area that escaped completely and was out of the local fallout area, then the contribution from the strontium in the worldwide distribution would be significant there.

Mr. ROBACK. Is it conceivable in some circumstances that it might be important or less hazardous to do agricultural work closein rather than far away?

Dr. MITCHELL. I cannot conceive of it; no.

Mr. ROBACK. You cannot conceive of it?

Dr. MITCHELL. No.

Mr. ROBACK. We will discuss that at a subsequent point.

Mr. HOLIFIELD. Any other questions?

Mr. ROBACK. No.

Mr. HOLIFIELD. Thank you, sir.

STATEMENT OF DR. JERALD E. HILL, RAND CORP.

Mr. HOLIFIELD. Proceed, Doctor.

Dr. HILL. I will state my background first. I have a B.S. degree from Western Michigan University, an A.M. degree from the University of Michigan, and a Ph. D. degree from the University of Rochester-all in physics.

I taught physics for 7 years. I was a postdoctorate Westinghouse research fellow and a research physicist at research laboratories of the Westinghouse Electric Corp.

I attended the first postdoctorate course in atomic energy at Oak Ridge National Laboratory following World War II and worked as a research physicist there.