Safety_Series_025_1968 - gnssn - International Atomic Energy ...

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This publication is no longer validPlease see http://www.ns-iaea.org/standards/100 rads. In Fig. 3 the ranges of doses for different biological effectsin experimental animals are indicated. It is apparent that, amongmammals a great variety of responses exists for different functionsand different tissues.------------------1— — --------r— i— i— ' ' ' |-------------------1---------- --------1 . , . . . j ---------1............................................IMPAIRED FOETAL DEVELOPMENT - IN TR A UTER IN E DEATH■ * ---------------■*------------------------------------------------------------------------------------------------ HIGHER DOSES LETHAL TO MOTHERCATARACT PRODUCTIONHAEMATOPOIETIC DAMAGE f ANIMAL DIES--------------- ------------------------------------------------------------------------------------------------------------------------------------------------ ► < BEFORES TER ILITY U e^ 15 °E‘DECREASE IN LIFE-SPAN A F TE R SINGLE EXF OSURE------------------ -- ----------------------------------------------------------------------» ani MALSSPLEEN AND THYMUS, WEIGHT LOSSRAT INTESTINE. WEIGHT LOSS— m » .MAMMALIANL D 50 RANG EMOUSE BODY. WEIG HT LOSSFAIL TO SURVIVEACUTE EXPOSUREHIGHER DOSES PRODUCENO FURTHER DECREASECIRCULATORY CHANGESIMPAIREDKIDNEY FUNCTIONLIVERDAMAGECNS DAM AGEPANCREATIC"" D a m a g e10 100 1000 10000RONTGENSFIG. 3. Sensitivities o f different organs and functions to ionizing radiation. The dotted linesindicate that an effect at smaller doses is possible [5 ],1.2. 1 .4.8. Shortening of life- span (see also sections 1. 2. 1. 5. 3,1. 3 .2 .2 , 1.3. 2. 3). Experiments with animals have convincinglyshown that even relatively low acute doses of radiation, which donot produce typical radiation sickness, may lead to a reduced lifeexpectancy. The median survival time is shortened with increasedexposure (e.g. life-shortening effect in the mouse varies from about0.5 to 2% of the mean life expectancy for a dose of 100 rads [4]).Practically nothing is known about the lesions shortening life-spanin organisms. Different strains of mice differ in their life-tim eshortenings. There have been attempts made to explain radiation18
This publication is no longer validPlease see http://www.ns-iaea.org/standards/life -s h o rte n in g as a m utational p r o c e s s in som a tic c e lls . At thep resen t tim e it is d ifficu lt to p rovid e a sa tisfa cto ry explanation o fthis phenom enon as it is always c lo s e ly connected with p rob lem s ofsen escen ce which are not w ell understood. Irradiated anim als d e velop som e of the diseases prevalent in the sp ecies e a rlie r than nonirradiatedones and show signs of general early sen escen ce.L ife -sh o rte n in g e ffe cts o f radiation in man have not up to nowbeen dem onstrated. T here is con flictin g evidence am ong m ortalitystudies o f US and B ritish ra d io lo g ists, the m orta lity ra tes in thefo r m e r being sligh tly h igh er than in the g en era l m ale population,probably due to different ra d iologica l p ra ctice s. D oses higher than200 rads o f w h ole-b od y irra d ia tion m ay cau se a life -sh o rte n in g inman, but the effects o f lon g-term , lo w -le v e l irradiations are in thissense uncertain.1 .2 . 1 .4 . 9. Induction o f tu m ou rs. It has been establish ed beyonddoubt that m alignant tum ours m ay be induced by radiation in m osttissu e s after what m ay be a c o n s id e ra b le latent p e rio d . F o r thisrea son , if the a vera g e p eriod fo r the m an ifestation o f the tum ourgenerally exceeds the life-sp a n o f the animal, no effect is observable,because there is no tim e fo r the developm ent of the tum our.R adiation m ay induce m alignant grow th a lso through in d irectm echanism s. Pituitary tum ours may be induced through the ir r a d iation o f the thyroid.In som e experim en ts on the induction o f tum ours in rats thed o s e -e ffe c t rela tion sh ip can be lin e a rly extrapolated to v e ry lowd o se s, assu m ing p ra ctica lly no th resh old . In oth er ex p erim en ts,there are indications that som e kind o f threshold dose exists belowwhich tum ours are not induced during the existin g life -sp a n .1. 2. 1. 5. R elation between dose and effect1. 2. 1. 5. 1. The problem o f threshold d ose. In estim ating probableradiation injury, it is important to con sid er the d ose -e ffe ct relation ship at low d o se s. It is o f in terest to know whether it is feasible toextrapola te from a lin ea r rela tion sh ip to the re g io n o f e x tre m e lylow d oses, i . e . indicating that any d ose, how ever sm all, p rod u cesa p roportion al effe ct. In such a ca se , no threshold ex ists and it isto be exp ected that natural radiation m ay p rod u ce a p ro p o rtio n a leffect. The linear relationship between dose and effect is valid overa wide range fo r v iru ses, b acteria and other unicellular organ ism s.19
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