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FU?$DMIBJTALCONSIDERATIONS IN DETERMTNTNC STGNIFTCANT Division of Biology and Medicine t The radioactivity of tiportan:e in sea water following an atomic explosion at altitude near sea levei is principally due to fission products f’Yomthe bomb which, with other materials, condense into small particles and fall into the sea. Some of this material will be retained in upper layers of water in solution, in suspension, or associated with organic matirids. Radioactivity induced by the radiation fkom the bomb will be relatively un- @a*t, largely because of the extreme rapidity with which it is reduced ,. Fish living and feeding in waters containing radioactive materials will,..,,, accumulate some of these materials in the various tissues of their bodies and on exposed surfaces such as the skin and gills. Observed levels of activity ti sea water are tQO low to produce any harmful effects on the fish or on their food supply. Tn this connection, it may be observed that the levels of radiation required to produce observable effects on lower forms of lfle are generally much greater than for humans, and that the limits of radiation exposure considered acceptable for humans over periods of many years are much .. lower than those which would be acceptable for short periods of *. The best guide that w have available for limitation of radioactivity in food and water is National Bureau of Standards Handbook 52, which contains recommendations of the National Committee on Radiation Protection limiting the qumtities of radioactive material in the body. ‘l’hemxhm pe*ssible concentrations in water, expressed as microcuries per gr~3 reco~ended fi Table 3 of this handbook are considered to be applicable also to food. Tn setting these concentrations, it is assumed that they spply to the entire water supply of the individual (including the water contained in the food that he eats), and it is assumed that these values may be maintained throughout the remainder of his life. The figures given in Handbook 52, based largely on occupational exposure, are considered adequate at the present time, since no one is exposed to radioactive materials at considerable fractions of these values throughout his early life. The possibility of a general.increase in environmental levels of radioactivity from the widespread use of atomic energy for industria3 purposes has led to consideration of the desirability of using lower levels for lifetime environmental exposure. These levels might be as low as one-tenth of those acceptable for occupational exposure to radiation or to radioactive materials. US DOE ARCHIVES
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In tiew of the above considerations we centrations of -ious radioisotopes in the would limit the average contotal food and water supply of members of non-occupational groups tc one-tenth of the values given in Table 3, NBS Hsndbook 52. As far as the welfare of a person eating a radioactive fish is concerned, the amount of radioactivity permitted over a period of several weeks or months9 if uniformly mixed at this concentration through the total food and wat,erintake, could be taken in a single eating of fish with no significant difference h effect. However9 tince meth~s of handling and distributing food make it impractical to determine the average concentration of radioactivity in tidividual diets~ for administrative reasms it is desirable to reject individual fish or other items of food which contain levels of radioactivity materially above the accepted maximum permissible Since it is sometimes impractical to detect every item which rejected on this basis~ it is worth observing that occasional failure to detect tidividual items at much higher levels would not be expected to raise the a= levels of radioactivity in the diets of tiditidual consumers above maximum permissible levels. For short periods of time the radioactivity in the diet may be much higher than the values discussed above without effects on the consumer. Attached are copies of Bulletin TB-11-8, issued December 19S2 by our Federal. civil Defense Agency, suggesting total.activities in water and fo~ SuPplies which, it is believed, could be accepted for short periods of time in complete Stice it is impractical under field conditions to determine the concentrations and the radioisotopic composition of radioactive materials on or in fish or other items of food$ one needs some practical criterion for rapid screening of items requiring further examination from those which almost oertainly meet established standards. ?tastApril$ as a result of conversations with the Federal Food and Drug Administration and other federsl agencies$ the Division of Biology and Medicine of the United States Atomic Energy Commission suggested thata as a teuporary standard$ individual fish be accepted if the aroma %radiation$ measured S cm from the surface of the fish9 does not excee 0.1 mill.iroentgenper hour. Tn terms of the response of G+ survey instruments commonly used in the United States3 this corresponds to from 300 to 600 counts per minute with the tube shielded ~ exclude beta radiation. This value was based on the following assumptions (1) The radioactivity had been deposited on the outside of the fish after the fish was taken from the water; (2) When processed for food, all of the radioactivity deposited on the outside of the fish would be retained in the outer two inches (3] The radiation is measured a% about two weeks after the explcsion from which the radioa.ctiwitycame;
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(4) The composition of the radioactive material at the time of measuremw nublished in Volume 9 of Nucleonics2“Fission Prcdu;;t Decay Ratesz . (~] The gammaradiation received by the counter from the surface of the fish is as great as would be received from material of the same actitity per unit area spread on a plane circular disc 20 cm in radius; (This assumption makes the problem amenable to normal methods of computation. The actual response of the instrument will depend on the size of the fish. This is one of the limitations on accuracy inherent in a practical method of field monitoring.) (6) The level of radioactivity, measured in microcuries per gram of fish, M distributed as assumed in (2) above$ should not exceed the value coquted for this mixture of radioisotopes on the basis of the recommendations given in NBS Handbook 52. Examination of the relative maxinum permissible concentrations of the fission products concentrating in various body tissues show that at lb days or later the tissue receiving the highest radiation dose from the in~,estionof the radioactivity till be the bone. Nearly all of the dose to the tine is due the respective concentrations of these radioisotopes in residual fallout material are about 3.8%$ 0.03% and 13.S~~ while the respective maximum permissible concentrations in water listed in Ta e 3 of Handbook $?2 measured concs:tration of the moss or total fission product activity in t~e total. supply of food and water which would reeult in the ingestion these materials at the maximum rate permitted under the recommendations of Handbook 52. (h the basis of assumption (2) above this would correspond to ~ microcuries per square centimeter of surface. On the basis of assunqtion (S) above~ it is estimated that this would result h a radiation level of about 0.1 mil.liroentgen per hour at S cm from the surface. (This is cozqmted & the use of integral calculus, using the following additional.information% The average gamma ener~ emitted per disintegration from this material is approximately 0~3~ fl~ion electron volts. The intensity of the ear-maradiation at a distance r tiom a where I is measured in mre/hr$C is measured in microcuries~ r is measured in centimeters, and E is the average gamma energy per disintegration measured in millions of electron volts.) Since the conclusion of the recent series of veapons tests in the Pacific Proving Grounds~ any radioactive material which might be acquired by fish in
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this tictiity would be acquired before the fish are tdcen from the water. Thus far, we have been unable to obtain any fish with sufficient radioactivity from this source to permit an approximate emptiical &termination of the external radiation level which would correspond to maximum permissible average concentrations in food and water discussed above. However$ on the basis of the uptake of the various fission products & fish under other conditions, of 0.1 milliroentgens per hour at ~ cm is unnecessarily restrictive for this fission products which may be permitted on the outside of the fish after they are taken from water are relatively unimportant in considering the radioactivity which may be permittad in the flesh of the fish~ stice these radioisotopes are not retained in the flesh. The radioisotopes taken up by the flesh, of which CS137 is an examples have very much higher permissible concentrations in food and water~ of the order of 1 x 10-3 microcuries per milliliter. Fi’oma fish weighing so to 100 pounds$ the gamma radiation from a maximumperndssible concentration of these radioisotopes fi the flesh is estimated to be several milliroentgens per hours measured at a distance of S centheters from the fish. The actual. radiation level will, of course, depend upon the size of the fish.