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/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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