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Safety_Series_025_1968 - gnssn - International Atomic Energy ...

Safety_Series_025_1968 - gnssn - International Atomic Energy ...

This publication is no

This publication is no longer validPlease see http://www.ns-iaea.org/standards/The e ffe ctiv e h a lf-life is the p ro p e r m eans of ex p re ssin g theduration of contam ination by a certain radion u clide. The p h ysicalh a lf-life fo r caesiu m -137 is 33 y ea rs, and this circu m stance mightseem to designate caesiu m -1 3 7 as a dangerous radion u clide. Butsin ce it is v e ry rapidly excreted , its effectiv e h a lf-life is only25 days and th e r e fo r e it is c la s s ifie d as m o d e ra te ly d a n g e rou s .E ffective h a lf-life is only one fa ctor for the evaluation of m aximump erm issible dose. Among others, the critica l organ is of prim eim p orta n ce. H ere the con cen tration o f the radion u clide, the rateof elim ination, the im portance of the organ or tissue fo r the functiono f the organ ism , its ra d iosen sitiv ity etc. a re fa ctors which shouldbe c o n s id e re d .1.4.5. Factors modifying the absorption and elimination ofradionuclidesThe therapy for radioactive poisoning is b asically a ph arm acolog ica l problem which is in many resp ects sim ila r to acute p oison ­ing with som e m etals. It su ffices here to mention only som e generalp rin cip les of decontam ination. It is vital to lim it the deposit ofradioactive substances in the cr itic a l organs by rapid and p rop erlyd irected m easu res of a ssistan ce.In ca ses w h ere a ra d ioa ctiv e su bstan ce has a lrea d y been in ­corp ora ted in the organ ism , it is even m ore n ece ssa ry than in theca se o f fir s t aid to take into accou nt the nature o f the ra d io a ctiv em a te ria l absorbed and to treat the patient a cco rd in g ly .The aim of internal decontam ination is to a ccelera te the e lim ­ination of ra d ioactiv e m a terial at the stage o f acute o r ch ron icpoisoning, as the case may be. It is to be rem em bered that the greatm ajority of radioactive elem ents, when once absorbed, are elim in ­ated only gradually by natural p r o c e s s e s . It is, for example, p ra ctica l­ly im p o ssib le to rem ov e radium from the body once se v e ra l w eekshave elapsed follow in g in gestion . A ll attem pts to brin g about as p e e d ie r elim in ation o f an absorb ed ra d ioa ctiv e m a teria l m ay bereg a rd ed as based on the follow in g p rin cip le s :(1) Taking advantage of the corresp on d en ce of the m etabolismo f the radioelem en t with a related elem ent in the patient (e.g.stron tium and ca lciu m );(2) Taking advantage of the discrim ination made by the organismbetw een a ra d ioa ctiv e elem ent and a c h e m ica lly rela ted but non ­ra d io a ctiv e elem ent; and5 0

This publication is no longer validPlease see http://www.ns-iaea.org/standards/(3) The u tiliza tion o f c o m p le x -fo r m in g su b sta n ce s.EDTA is rela tiv ely to x ic and in sm a ll d oses induces h y p o ca l-caem ia. It is th erefore adm inistered in the form of CaEDTA whichis not m etabolized and is rapid ly elim inated in the urin e, w h ereasthe ca lciu m is to a certa in d e g re e exchanged fo r oth er m e ta b o licion s. F o r som e elem ents like plutonium, thorium , yttrium and ther a r e earth s the ch elatin g agent d ie th y le n e -tria m in e -p e n to a ce ta te(D TPA) has proved su p erior to the CaEDTA. P rolonged treatm entwith DTPA effectiv ely rem oves part of deposited plutonium.1.4.6. Effects o f absorbed radionuclidesThe radiotoxic effect of radioisotopes on the organism is a co m ­plex function which depends on a variety o f physical fa ctors, one ofthe m ost im portant of which is the physical h a lf-life of, and thestrength and type o f radiation emitted by, the isotope. The chem icaltoxicity o f the isotop e is a lso som etim es im portant. F o r uraniumits toxicity as an elem ent must be considered in relation to its radioactivep rop erties. With regard to the organism , too, a whole serieso f b io lo g ica l fa cto rs are in volved, such as the m ode of entry o f thera d ioa ctiv e m a teria l, the site o f its d ep osition and the rate o f itselim ination. A nother im portant fa cto r is the age and the assum edrem aining life -sp a n o f the org a n ism .E a rly effectsIn experim ental anim als early effects have been observed afteradm inistration o f lethal d oses of ra d ioactive m a teria ls. They appeared7-10 days after exposure and included m ostly haematopoieticsym ptom s of acute radiation d isea se. There have been observationso f early effects in man after accidental intake of radioactive m aterial(e.g. the acciden tal exposu re of 103 lu m in ou s-dial painters to 90Srinvolved urinary excretion and early haem atological effects as w e ll).Late effectsL ong-term effects follow ing ingestion of sm all amounts of internalem itters m ay be a seriou s p rob lem . The in ciden ce of lungca n cer am ong S chneeberg and Jachym ov uranium m in ers is at least50% h igher than that in the g en era l population. O ther data fro mC olorado Plateau and the St. L aw rence region also strongly suggest51

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