vv, .Letty it ~eiet " wee Pinte 6 DeenaRad MLR oe oe : . Maa BTN de deg te : - . sy . Ad abdAstle pentabob EbhO AN Be tel in Mtr aI a 8 neBatch TOXICOLOGY OF RADIONUCLIDES svANNARD ipesiae PU Gh lived oC aibans Uy Han. Shuca owis devoted fo studies on this aspect. Some “yp ceaamon form, are so insoluble thet thes . abienk tO mar IN SUENLivent GUANIEY CALepe ' aed wound (206, 207). Other nuctides may semapism or vector in the ecosystem. Ultimate a whether or not this critical step is involved 4+ of several thousund are net uncommon az eapended in identivving critical pathways ‘sshody versus air-soi-plant-cow-milk-body. air abserption of many auclides ts sufficiently 4 to make ihe first ine “critical pathway ” ver, this is not the critical pathway if milk ot :3 this event, the critical pathway mayinstead in. the Orient, and the resultant intake maybe .tromof critical nuctides (209, 211). The isotopic . with the type of reactor and the time of opera-rocessing facility than for a reactor. Thus, the vey be the same for different types of operation. 1 ossibilitv of an undetected critical pathway or _-n&. for example, was not appreciated until syoon to it (212). The primary likelihood for “. environments, especially oceanic (213, 214), ny fuet cvcles ' > role of time, since isotopes of importance in .. ificant later on. Indeed. if times are long, avuve waste disposal, some very unexpected : evaluation of potential hazard (18). iewturs to be considered in the instance of a “tn the paper by Feldt (215). a euusms.—Quite apart from the movement “stem to man is the possibility of deleterious ‘Pies importance fo man in proportion to the < .cusystem or as a member of a food cnatn. suv demenstrated in highly contaminated t Oar Lake at Oak Ridge. Hundreds of revere Hosensdivity «f aninals, plants, soem. sthut ds a tropical rainforest. While DP te ath sen -lavaiy oF Gosufers Ja ditverces in sonsrtivigs ar difterert nek OFgalsd. was yet appeaicd WORES PoGRION In a ccossshim to megete * Ad an eaee attAe netancareaeel heheieta wah . tenth renIESERSEE ETT coRE ye a4 pte. ‘SaneMgt @petty fue, hongpared s 1 espa “ae wht AL ge be Ree pa Gee dbo TUT Studie Whats Led Veiled Loe There are some findmes that clearly need further explanation. For taam. ic, Polikarpov (227) reports from extensive studigs with marine and fresher: g fish exes thathetehing ov larvae js reduced ween at $O 7 pO! bof certamisetoy es. Also, the oceanic environment is so vast that we cannet el fall confidens ae have any more than begun the study of iis radiozcology (2131) Tt is heped a subsequent review can devote special attention ta some of these probleins. SPECIAL PROBLEMS Tritiun and transmutation.—Entering the body as witiated water, tritium (*H) distributes as body water and anyradiation eifects produced are comparable io Whole tody irra tiation. When i enters in organi. forra. particwarly os . label for nucleic acid precursars, it may be incorporated into vital structures such as DNA, This later ..as led to much concern that its effects, especially genetic and carcinogenic. might be much greater than the calculated radiation dose would predict. That such concern was largely unfounded was shown by Bena & Feinendegen (218) in 1966. But the concern has continued in both scientific and lay circles and has becomepart of the ‘‘ nuclear power controversy.” A full re-examination of all aspects of the problem was presented by Bond (219). His conclusion is that in higher organisms, at least, all effects of tritium can be uccounted by the radiation dose delivered and have the same radiobiological meaning as a similar dose from X or alpha rays of the same dose pattern. Also just recently the ICRP (220) and NCRP (140) have revised an earlier recommendation that a quality factor of 1.7 be applied in calculating rem duses for tritium and other very low energyelectrons or photons. Thefactor has bezn returned to 1.0. One of the flaws in the earlier reasoning seems to have been the misc nderstanding that the range of the beta particle even frorn a low-energy source such as tritium is actually long compared to the cross-section or other reasonable measure of DNAas a target. No special local deposition of energy should be expected except for Brage-Gray considerations. A residual concern is the so-called transmutation effect (change of parent atom to one of different atomic number, usually plus local recoil and excitation energy). Re-examination of this possible effect not only for 3H but for other incorporated isotopes, e.g., ?7P, shows (218, 221) that a transmutation etfect does exist sometimes in eukaryouc cells but not in prokaryotic cells except under special circumstances. These special circumstances involve specitic molecular arrangements such as cytosine tritiated in the five pasition and incorporated into DNA of growing cells (222). Since considerable effort must be 2vrer Jed te - produce such labelling and incorporation it can be conchided that transmutation efecto tay a rutaor role, if any, im prokaryotic culls. Cahill & Yuile (223) have recently described effects of continueus ep tsurs “© tritiahG Water on pregnant rats. The calcuiated radialcn dose wos roid 0,3--30.0 rads day. The higher doses produced microgncephaly, steritj, siuuluing, PETERTeetheneeemEoF tes CATSMET y % Uae pA a the 8 Bae SebBet: tHE A most tangoenee “ahhaene foe orge a TTS MELE ry i 4, + Lae sew Lass ae ‘smh phelps 8 eee! 7 oR woe ' Ba TEM a eee Pb aye kt oe tha ytt, Taye ee BPte ENE Lelebiney. F she ry" omtoaeat ee ES time gee Some Sitatry