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/1.2. 1.4. 6. Effects on embryonic development. Ionizing radiationhas a deleterious effect on developing embryos. The consequencesof damage in the developing embryonal system are amplified in thelater stages of the development and may result in malformation inthe adult stage. If the embryo is irradiated during early development,such malformations may occur in eyes, brain, medulla andalso in kidney and liver. During later embryonic development theirradiation causes abnormalities of the skeleton. When higher dosesare applied, prenatal death ensues. In man the first three monthsof pregnancy during which organogenesis occurs are most importantfor the development of malformations due to irradiation.1.2. 1.4. 7. Lethal effects. Different types of organism have verydifferent radiosensitivities. For mammals the radiosensitivity,expressed as LD 50/30 (survival of 50% of the animals 30 days afterwhole-body irradiation), varies from 400 rads for the guinea pigto 800 rads for the rat. The best estimate for man is around 500 radsafter whole-body irradiation. The individual parts of the human bodyare able to withstand comparatively high radiation doses, a circumstanceof which advantage is taken in therapy.Cold-blooded animals are generally more radioresistant, ascan be seen from Table III. The 50% survival dose for the snail isabout 20 000 rads; for bacteria the dose ranges from several thousandrads up to 50 000 and more. Phage, viruses and some protozoa areeven more radioresistant.There are several possible explanations for this phenomenon.The generally accepted hypothesis of Bergonie and Tribondeau isthat rapidly dividing tissues are generally more sensitive than tissuesin which the mitotic rate is slow. To a certain degree genetic factorsplay a role. For example, different strains of mice have differentradiosensitivity (about ± 30% of the mean quoted above). The sameholds true for bacteria and other m icro-organism s. Lately someexperiments have been performed to prove that certain radioresistantbacteria contain in their cells radioprotectors, while theradiosensitive strains are devoid of them.Another explanation of different radiosensitivity may lie in thecircumstance that some organisms have in their tissue a low oxygentension and that this could account for their higher radiosensitivity(see also section 1.2. 2. 2, role of oxygen).Up to now we have discussed radiosensitivity to whole-body ir radiation. Quite another result is obtained if the radiosensitivity of16
This publication is no longer validPlease see http://www.ns-iaea.org/standards/TABLE III. RADIOSENSITIVITY OF DIFFERENTORGANISMS TO X-RAYS (LDrJV 5 0 'A bsorbed dose (rad)T o m a to bushy stu n t virus 4 5 0 0 0 0B a c te rio p h a g e T 2 4 0 0 00E s c h e ric h ia c o l i B 4 0 0 0D ip lo c o c c u s p n e u m o n ia e 3 0 0 0 0A m o eb a 100 000,Wasp 1 00 0 0 0S n a il 20 0 0 0G o ld fish 850Frog 7 0 0B a t 15 0 0 0M ouse 5 6 0Rat 8 00G u in ea p ig 4 0 0R ab b it 7 0 0H a m ster 8 00D og 2 6 0Burro 3 0 0 (y -r a y s )Sw in e 2 50G o a t 2 4 0M o n k ey 5 4 0M an 4 0 0 (y -ra y s )different tissues is compared. Normal human lymphocytes showabout 15% lethality after a dose of 2 rads. Most human cell linescultivated in tissue cultures have a mean lethal dose of about 50-17
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