FOREWORD 



Although man has always been exposed to some radiation from naturally- 

 occurring radionuclides in his environment, and although the food he consumes has 

 always carried some small burden of radioactivity, the coming of the "Atomic Age" 

 has already brought with it a rise in the level of radiation to which man is exposed 

 and the appearance of some new sources of radiation that did not in the past consti- 

 tute a part of the natural background. The latter has been tacitly accepted as being 

 of no great concern, even though the level of exposure may vary widely from place 

 to place. The testing of nuclear weapons has resulted in the appearance in man's 

 environment the world over of radionuclides not formerly present. 



Man's exposure to radiation is in part external— from the materials aroimd 

 him — but it is also in part internal, by reason of the ingestion of food and water 

 having some radioactive components and the inhalation of radioactive particulates 

 or gases in the atmosphere. The effects, if any, on the well-being of the individual 

 "depend upon the radiation dose (and dose rate) delivered to various tissues and upon 

 the radiosensitivity of the tissues. " 



This report deals with some of the early steps in the sequence of events that 

 transfers radionuclides in the environment to the tissues of man in what has come 

 to be referred to as the "food chain. " The food chain of man is not inherently more 

 complicated than those of other organisms that are herbivorous or carnivorous. 

 There is, however, the difference that man has considerable freedom of selection 

 and, at least in industrialized countries, subsists on foods, fresh or processed, 

 derived from diverse and often remote locations. The dietary exposure of man to 

 radionuclides is therefore a most complex question that can be approached realisti- 

 cally only by examining the principles involved in the various steps of the food chain. 



Recognizing the fact that the human diet is derived from the soil directly or 

 indirectly through animals, the Committee sought to have prepared a comprehensive 

 review of the fate of fallout radionuclides in cultivated soils and their transfer to 

 or incorporation in crop plants growing thereon. This report is essentially a dis- 

 cussion of the principles involved and makes no attempt at evaluation of hazards to 

 man, which have been discussed elsewhere in reports prepared by the related Com- 

 mittees on Pathological Effects and Genetic Effects of Atomic Radiation. 



A. G. Norman, Chairman 

 Committee on Effects of Atomic Radiation 

 on Agriculture and Food Supplies 



