Director Of Laboratory Replies To Questions On Fall-Out

Press, Volume CI, Issue 29851, 18 June 1962, Page 7

Director Of Laboratory Replies To Questions On Fall-Out

Fall-out from nuclear testing has increased the natural level of radioactivity by about 1 per cent., according to Mr G. E. Roth, director of the Dominion X-ray and Radium Laboratory, replying to two correspondents, “L.K.” and “Reaction,” who had written to -“The Press” about the effects of fall-out and radioactivity. “L.K.” said in his letter: Through you I would like to ask Mr G. E. Roth, director of the Dominion Xray and Radium Laboratory, to answer the following. Taking the figure 1 as the normal fall-out before any tests commenced and the figure 10 as the “accepted maximum permissible concentration," what has been the increase up to date since testing started some years ago? Does it now stand at, say, 2.5, 7.9, 9.9, or what? “Reaction’s” letter said: Sir Ernest Marsden says Brazil nuts are extraordinarily radio-active. Over 10 years ago a friend informed me of the discovery that rats would not eat Brazil nuts. It was wondered at the time if they were contaminated by some particularly powerful chemical. Taking the hint, we eat no Brazils in consequence. Were the nuts always radio-active or was the state induced after fall-out began from experiments? We hear that other foods are in similar condition today. Should we not be informed as to which foods are naturally or artificially affected? Persons with any weakness through previous exposure to X-rays require protection from extra dosage. Natural Level Replying to the correspondents, Mr Roth said: “In answer to your correspondent ‘L.K.,’ is must be stated that there was no fall-out before testing commenced; therefore the level of fallout must be taken as zero at that time. ‘‘However, we can take the level of natural radioactivity which existed throughout the lifetime of the last few hundred generations as 1 and say that the present level of environmental radioactivity, as increased by fall-out. is about 1.01, i.e., fall-out has increased the natural level of radioactivity by about 1 per <;ent. This is a very broad over-all global average. “As to the effect of this increase on humans and as to the permissible level of this increase, your correspondent would get a clearer picture if I gave him the figures he wants not merely in terms of the ‘maximum permissible concentration’ of any single radionuclide or of mixed fission products, but in those terms which most

clearly show the ultimate effect on the entire population, i.e., in terms of the ‘genetically significant dose’ of radiation actually received by the population. “If we consider numerical values of the genetically significant radiation dose from natural sources (cosmic rays, radon in air, radiation from the soil or from the walls of buildings, and from naturally occurring radioactive potassium) we find that there are very large variations not only between sea level and higher altitudes but also, for example, between dwelling places at sea level, so that say an indoor worker living at sea level in a wooden house may receive 2.7 radiation units (rem) in 30 years, while in the same locality, living in a brick house, he may receive 3.4 units, and he may receive 4.4 units if living in a concrete or stone dwelling. “The increase in genetically significant radiation received from fall-out at the present level is about 0.03 radiation units in 30 years and is thus still only a very small fraction indeed of the large variations observed in the amount of natural radioactivity in different localities and affecting persons living in different environments. Significant Dose “Even though humans have been exposed for hundreds of generations to widely differing levels of radiation from naturally occurring radioactive substances, so far no evidence could be found that even large variations in natural background radiation have produced statistically significant genetic changes in the population groups exposed to relatively high doses of radiation from natural sources, such as a large population group in India living on highly radioactive thorium sands, or population groups living on high mountain plateaus where they are subject to greatly increased cosmic radiation. “The International Commission on Radiological Protection states that the genetically significant dose to people in a large population should not exceed five radiation units (rem) over a period of 30 years: this refers to the dose received over and above the dose from natural background radiation and the dose received from medical procedures. For the specific example given above for the indoor worker living in a wooden house at sea level this means that the genetically significant dose could be increased from the pre-bomb test background level of

about 2.7 units in 30 years to a limit of about 7.7 units, while in effect the present amount of fall-out would increase the 30 year dose of genetically significant radiation only from about 2.70 to 2.73 units. Brazil Nuts

“The radioactivity of Brazil nuts referred to by your correspondent ‘Reactions’ is almost entirely due to naturally occurring radium and its daughter products which are being selectively concentrated by the Brazil nuts. Many plants and vegetables take up naturally occurring radioactive substances from the soil and this accounts for the minute amounts of radioactive substances which humans throughout the ages have taken into their bodies with their food.

“Since the beginning of the nuclear weapon tests the level of radioactivity in some foods has slightly increased due to the fall-out deposited on soil and plants. An approximate indication of this over-all increase has been given in the reply to the letter by ‘L.K.’ Just as was explained there for the variations of the level of natural radioactivity, there are also large differences in the amount of fall-out not just between different parts of the world (say between the Northern and Southern hemisphere) but even within any one country depending on e.g. whether we measure on high or low lying land, or on different types of soil, or in areas with high or low rainfall. “In no case has the radioactivity in human diet, due to either natural radioactivity or fall-out even remotely approached levels involving a hazard to health. Brazil nuts, the classical example of high natural radioactivity in food, art an extremely small fraction of the diet in New Zealand. There is therefore no need to restrict their use on Account of their radioactivity. In New Zealand the Health Department keeps a close check on possible increases of the level of radioactivity in food,” said Mr Roth.