Radiation effects on the population of Belarus after the Chernobyl accident and the prediction of stochastic effects
Jacov E. Kenigsberga, Viktor F. M inenkob
&Elena E. Bug/ova
cTheacciden t at the Chemobyl nuclearpower plant causedan extensive releaseofradioactivityinto the enviro nme n t,and muchof the territory of Belarus wascontaminated byradionuclides.The caesium- 137 fallo ut was highest within a 30-km radins aro und the reacto r.which be camethe "excl usio n zone". As a result of the accident, 23% of Belarus's territo ry wa s polluted by t37Cs with a densityof contam inatio n more than 37 kBq/m2.
Because of this radioactive co ntaminatio n of theenvironmen t,the populationof severalregio ns was expose d to radiation after the accident and received variousdoses.
Different conditions of dose formation during the pos t-accidentperiodenable ustoidentifyvari- ous time period sin the radiation exposure of the Belarusian population. The first involved the ef- fects ofradionuclides with a shorthalf-life.That is whydosesfrom these radionuclides occu rre d dur- inga relativelyshort period (2-3 monthsafter the acciden t). In the first period,one of the prima ry sources of radiation exposure wasiod ine-lSl,The role of externalexposure to theshort-lived radio- nuclides which fell on the soil was consid er ab ly lowe r. The con tri bu tio n s of inhalation of rad io- nuclides and exposure to clo uds of fallout in the totaldose weresmall for the majority of the Bela- rusian population .
Thesecond period is ch a rac te rized bytheinflu- en ce of the long-lived rad io n u clid es which fell on the soil.During this period,the influenceof long- lived radionuclideswascharacterized on thewhole byth e intakeof 137Cswith foo d stuffs (mainlymilk producedin rad io actively-con tam in a ted districts) and by ex ternal gamma-exposure from radio- nuclidesin fallout. Mostofthe stron tiu man d plu- tonium fallo ut landednearthepower plant, on the territory from which people were evacu ated, Be- cause of this, thc role of these radionud ides in dose formation fo r the Bel arusian population is minor.
During these two periods,severalcatego ries in the Belarnsian populat ionreceived dosesof radia-
aProfessor,ResearchInstitute ofRadiationMedicine ,Ministry ofHealth,Minsk,Belarus.
bCandidate in biological science, Research Institute of RadiationMed icine ,MinistryofHeal th.Minsk,Bela rus.
cCandidate in medicalscience, ResearchInstituteofRadiation Med icin e.Ministryof Health.Minsk,Belarus.
58
tion.Differen tdoses andconditio ns of doseforma- tion make it possible to identity othercatego ries among theexp osed population:peoplewh o lived in thecontamin ated territorieswithoutevacuation and rel ocatio n;evacuated peopl e; and radiation workers or "liq u idato rs". The ra n ge of thyroid dosesreceivedand special conditionsofexposure during thefirst periodmentioned above indicate a fourth categ ory of people who were exposed in ch ild hood, especiallyto thyroidirrad iation.
Because of theradiobiologicalcharacte risticsof 1311 and its highaccu m u la tio n in the thyroid,local exposureof thisglan d to a relativelyhigh dose rate occurred.Estimatesof thyroid dosesare based on the results ofdirect dosimetri c investigations car- ried out in May:July1986 on personsliving in con- taminatedareas of Comel,Mogilev an d Brestre- gio ns and in the city of Minsk.
On the basis of these results of more than 250000 direct measurem ents, doses were recon- structedfornearly130 000 persons,of whom30% were children (1).
Thedata analysis sh ows thatthe highestthyroid doses were receivedbyinhabitants of Khoiniki dis- trict, in the Comel region, who were relocated beforeMay5,1986:theaverage dose for adultswas 159 cGy, an d fo r children an djuven iles 310 cGy.
The highestdoses Were received bychildren up to age 7,whoseaverage dosewas 469 cGy.
Thyroid dosesover 1000 cGywere received by nearly 20% of exp o sed children aged between 6 months and 2 years, 11% of children exposed between the ages of 2 an d 7,and 0.6% ofad u lts.
Relocated inhab itants of Bragin distric t and non- reloc a ted inhabitants of Khoiniki, Bragin and Vetkadistrictsreceivedsligh tly smallerdoses.Com- parison of average thyroid doses for adults and persons age d0-18years shows thatdoses received by children an djuven iles Were 3-10 times highe r thanthosefor adults.The greatest differenceswere noted among inhabitan ts of districts from which childrenwe re not relocatedin May1986 .
Because of the peculiar meteorol ogi cal condi- tions during the firstdaysafter the accident,inhab- ita n ts of Minsk and Gomel, the largest cities in Belarus,wereexposedto131Iradionuclides.Signif- icant differences in average thyroid doses were found inallagegrou ps fortheinhabitants of these cities: the average dose for Gomel ch ild ren ex- posed at agesunder 6 monthswere several times higher than for thecorresp o n d in ggrou p of Minsk Rapp.tnmest.stsust.ssm: mond.,49(1996)
childre n.The averagedoses for ad u lts fro m Comel and Minskwere 11cCyand 1,8cC)'accord ingly.
Analysisofthyroid do ses for the popula ti on of Bela rus as a ,v.hole shows that 2.3% of chil dre n exposed bet ween 6 mon th s an d 2yea rs ofage an d
O.O~~% of ad ults received do ses higher than 1000 cGy (2).
Accordi ng to the levels of thyroid do ses, the grou p mo st exposed to th is typ e of rad ia tion was the ch ild re n.The aggrega te dose fo r children of Bela rus, exposed lip to the age of 6 is 25%ofthe aggregate thyro id do sefo rthe ent ireexp os ed Bcla- rusian pop ula tio n (T able 1).
During the sec ond pe ri od of dose forma- tion, do ses resulted from prolon ged exposure to caes iu m,stro n tiu m an d plutoniu m in ad d iti on to earlierdoses.
The highest do ses were foun d in liqu idat o rs who worke d nea r the power plantin 19H6-19H7,of who m 30%received to taldo sesin the range of50 to 100 mSv,47% from 100 to 250 mS\' and 7.3% more tha n 250 mSv (3).
People who were evacuated from the 30-km zone recei ved doses com parab le with valuesmen- tio nedabove for liquidators.Investiga tionofdo ses fo r more than 1300 evacuees exam ine d in Minsk clinicsduring May:June of1986,shows tha t these dosesvari edbetwee n 1an d850 mS\,. Themajority of the people exami ned (78.5%) received doses in the 5-50mSv range.The do sesfor 12.4%ofthese peopl e exceeded 100IllS Vand fo r 1.5% of the m were in the 250-850 nrSvrange.
Asfordo ses forall the Bela ru sia npo pula tion,it is po ssibl e to con clu de tha t duri ng 1986-} 994 in- habitantsofterri torieswith adensityof1:\iCscon- tamina tion be tween 555 and 1480 kBq/m2proha- blyreceived average totaldoses of 50-60 mS\';for inhabitants of territo ries with a density of 1:l'iCs con taminatio n less than555kBq/m2,the dose was 20-40 ruSv.
Itsho u ldbe emp hasized tha tthe external doses fo r in hab itan tsofco n ta minated districts became visiblystableby19HY-1990.Averageannual inte rn al doses for inhabitan ts of mo st contami nated dis- trictsdecr eased by at least 10times as co mpa red to 1YH6and as aru ledid notexceed0.2-0.;")mS\"(3) .
For the inh abitantsof territorieswith aden sity of ISiCs cont a minatio n less than 185 kBq/m2,in- ternalexp o su re plays aleadingrole in doseform a- tion.In con trast,forinhabita nt s of highlycontam i- nat ed territo ries, the contrib u tio n of the extern al do se to the totaldose value isgrea ter.
On the whole , the values of agg regate doses received hythe Belarusian popula tion du ring the po st-accident periodshow th atexternal do ses arc high e r tha n in ternal (Table1). Doses received by the rural popul at ion were 1.3 an d 1.8tim eshigh e r (for externaland in ternal exp os u re acco rd ing ly) thantho se inthe urb anpopu lation.Nearly60%of do ses received by the rural populat ion of the Re- public and nearly70%ofdosesinitsurhanpopula- tionoccurredin the in hab itants of Come! district.
Stro n ti u m and pluto ni u m radi on u clid es ac- coun tfor no more tha n 5%of totaldo ses.Evalua-
Table 1
Totalradiation doses(Sv perperson) for thepopulation ofBelarus,1986·1994 Tableau1
Dosestotalesderayonnements pourlapopulation du Belarus,1986-1994 (Sievert-personne)
j !
Dose
Externaldose- Dose externe ruralpopulation -
populationrurale Urbanpopulation-
populationurbaine Internal dose-Dose Interne
ruralpopulation - populationrurale Urbanpopulation-
populationurbalne Thyroiddose- Dose alathyroide
total population-
ensemble dela population children0-6years-
enfants de0 a 6ans
Wldnnnstatist.quart..4911996)
Belarus-Belarus
9407 7218
3404 1910
4664 75 117 016
Gomel region- Region de Gomel
5393 4882
1956 1244
315748 80797
59
~':
li I1 ~
' .
,
;I·I
tionsofstro ntium during the post-a ccident years showthat for inhabitanLs ofthe Minskdistrict,the average adso rbed do ses to redbon e marrowwere 4.5010-' Cl'per yea r;5.5010-' Cl'pe r yearforinhab- itants of th e Mogilevdistrict (4); (5.6-6.5) 010-' Cl' pe r yea r for inhabitants of the Gorn el district in 1986-19 89; an d 1.250J(~'Cl'per yearforthe same grou p in 1990-1993 (5).
It is well-known that radiatio n exposure may cause development of different conse que nces de- pending on level sofdose.Evaluati on of dosesre- cei ved by the Belarusian population due to the Cherno byl accident show no evid en ce tha t could lead to deterministic conse quences of radiation expo sure..
During health examinations of the evacuated population, nodeterministic effec ts werefound, in particular, no depr ession of the blood system.
Among people with doses between 250 an d 850 mSv there were no cases of modification in bloodindicators connected with suchdoses.
Accordin gto the dos esreceived bycertainex- posedcatego ries ofthe Belarusian population.it ispossibleto pred ictthede velopm entof diffe rent stochasticco nseque nces of exposure.On the ba- sis of well-known risk coe ffici en ts (6, 7, 8, 9)pre- dictions of radiation consequences for different categ o ries of expose d persons in Belaru s were made (Table 2).
Evaluatio nof theexpec tedrate ofgen eticdisor- dersfo r the firstgenerati on ofdescendan tsofthe expose d population shows that among these
people it ispossibl e to expect the development of up to200 cases ofrad iatio n -ind ucedgeneticdisor- ders.. Taking into account that the spo ntaneo us rateof hereditarydiseasesis 36000to46 000cases pe r IOclivebirth s(7) an d thebirthrate fo rBelarus was 140 000 ch ildre n perre a r (10),the incr ease of gene tic disord ersdue to radiatio nsho uld not ex- ceed 0.1%pe r year.
The total radiationexposure due to the Cher- nobylaccid en t may cause 10.9 cance r deaths per 105 persons in additio n to the spontaneous rate which accounts for nearly0.09%of the current annualcance r mortality rate.
The possible frequ en cyofthyroidcance rcases among childrenexposed underthe ageof6 ycars is 191.2 cases per 10"ch ild re n for the en tire Repub- Iic. The highest predi cted thyroid cancer inci- den cerate among childrenexpo sed in the Gomel regionis812 casesper10
r ,
individuals.Among the Bclarusianliq u idatorswho worked atthe powerplant andin30-kmzone aroundit in 1986-1987 ,notmore than 250casesof fatalcance rs arc ex pec ted. This is a conserva tive estimate be- cause da ta on the life expectancy of liquid atorsis not available.
Among the evacuees, there may be nearly 100 cases of fa ta lcanc e r. Itisunderstandablethat the abovevaluesare lowin compariso n tosponta- neous levelsoffatalcance rand it willbe ,"erydiffi- cult to evaluate the increase of fatal cance r inci- den ce caused byChernobylexp osure forthe cate- goriesof liquidators andevacuees..
Table2
Predictionofthe stochasticconsequencesof exposure duetothe Chernobylaccident forselectedcategories ofthe Belarus population
Tableau2
Prediction des eflets stochastiques deI'expositionauxrayonnements dus
a
I'accidentde Tchernobylpourcertainescategories dela populationduBelarus
Category ofexposedpeople- Categoriede personnesexposees
Belaruspopulation- Populationde Belarus
Childrenunder age6- Enfantsde moinsde6ans
Liquidators,1986-1987- Personnelchargede laremiseenetat
en1986-1987 Evacuees- Personnesevacuees
60
Type ofstocbasnceffect- Typed'effetstocnasnque
Geneticdisorders - Troubles genetiques
Fatalcancer - Cancerfatal
Thyroid cancer - Cancerdelathyroide Fatalcancer - Cancerfatal
Fatal cancer- Cancerfatal
Expectedvalue- Valeurattendue
200cases in firstgeneration ofdescentants-200casdans la premiere generationdedescendants
10.9cases per105persons- 10,9caspour105personnes 191.2casesper105persons- 191,2caspour105personnes
240cases -240cas
120cases-120cas
Rapp.tttmest:statisf.sand.mond.,49(1996)
Summary
Evaluation of conditionsof exposureduring the post- acc identperiod make s it possibletoide ntifylWOperiods inthe radiation exposureofBelarus'spop ulation.As a result of our investigations we obtained data about doses for four different categori es in the exposed popu lation:peop le who livedin thecontaminated terrl- fories without evacuation and relocation; evacu ated' people; cleanup workers ("liquidators"); and people who were exposed inchildhood,especiallyfor thyroid exposure.
The totaldoses for these categories in different time periods wereanalysed.Evaluationof doses received by the Belarusianpopulation due to theChernobyl acci- dent shows no evidenceof doses, thatcould leadto the deterministic consequences of radiationexposure.For all exposedgroups we made predictionsabout different typesofstochasticconsequencesof exposure.
R esume
E"el des rayonnemenls sur la population du Bl1larus a la suile de I'accident de
Tchernobyi . etprl1diclion des e"els stochastlques
L'evaluation des conditions de I'exposition durant la parioda consecuuve
a
I'accident permel de relever deuxperiod esdansI'exposition auxrayonnementsde la populationduBelarus.A la suitedes enquetes que nous avons effecluees,nous avonsoblenu des don- nees relativesauxdosespourquatre categories dilfe- rentesde populationsexposees:la populationquivivait surlesterritoires contarnlneset quin'a pas eteevacuee et reloqee ailleurs;la popu lationevacuee;le personnel charge delaremise enelat(.I iquidateurs·);etlesper- sonnes qui ant ete exposees dansleur enfance,notam- mentencequi concerneI'expositiondela thyrolde.IWdhl1tJsralist,quarr.,49(1996)
On a analyse I'ensemb le desdoses pour ces categories
a
differentespenodes.L'evaluatlon des doses recues par la popu lation bielorussea
cause deI'accid ent de Tchernobyl montreuneabsence de dosessusceptibles d'entralner les conseque ncesdeterministes de l'expo- sition aux rayonnements.Pourtous les groupesexpo- sesnous avons fait despred ictionssurlesdifferents types d'elfets stoch astiques de I'exposition.References/References
1. Gavrilin, J.I.etal.lntern'llIrradiationof thethyroidin the re sidents of regions contaminated with radio n uclldesin Belarus.Ml'dical mdiolngy.6:15-20 (1993).
2. Ga"Tilin, J.l. et al. IJan icttl.ultic.-s and result s of det e rm iuauou of the in ternalra diation dose to the thvr oid for111(' popnlan on ofcontaminated regionsof Ikiam". Vn:lnik"Aml,.",ii.M,.,liri,ukirllNnulcSS.m.2:3543 (1Wl).[in Russianonly]
3..Kaakov,V.S.etal.RndioecobJgicalJ#ualionmlklnl1Uafterthe C1U"fTl11bj1luridtml.ml'rliro-bialngirolt'01LJI'(/'WN",and srinllific ba sic IIfmMJumfor rtulinlionprolt't1ionofP"",u.Min~k.1991, p.5.
4. Mikhalch nlko.V.C.etal.ContentCif!Iotnm tium-90 in (he bodyof the in ha bitan ts ofMin:\l and Magilcv rc.ogion~.
l.4mvookhm"," i,lYInnui.50:39-41(1991).(inRll...eianonl)'}
5. Pogodin. R.I. rtat Conlm l ofslronliu,,,.90andist1Wfw.J,of p1ulfmiruninlh,bott)ofi,,/,abilllll/Jof{'.om"rrgion.SLirnlifi,...
/Jrnrliralll.l/J'rlSo/lh,hMllhJ1rr5m.'nlirmcif/JnJ!JI"suJlrmlfromIh, a.mlObylnail/mL~fogilev.199-1. pp91-9'1.
6. bu/u('JitmoftllJnutJmnrrrby;onUingrndin.um,.lUemnmmd,u;mJ ofiM NnuolUJICouruilonIlndiauonl'roIn1ion nndMfflSumnn,/.
NCRP Report - BO,lIcthoda,t985,p.55.
7. Beir,V.J1rtllJh 1!«IJ o/~j.nJ"'olullJ lltllt"1JolwnUinK rud;aJ;01I.
WiUhingl onDC. Natio nalAnldr myPm "1990.
B. UNSCEAR. Strurrnandf:l!m.1 of1000;n ng llndinlimJ. I99J
I~10IhI e;,,,nnlAJvmbly. wilhStit-,,'ijieA'mtxn.New York.
UN,199~.pp'rl!J.SO-l.
9. Rrrommn,dnli01Uof'''' In/"'f nlWr,al Cmn",;uumon Radioklgitnl ProI«Iion.1990.lnl cnlation alCcrumlssiononRad iologi cal Protection.Publ icatio n60.199 J.
10. I.azyuk.C.I.etal.Dynamics ofhereditarypashologies in Bclarusand theChemobyl acciden t,7111'CNnlOl,tarribnl:
""J;ml(u pmJ.199~.pp167·182.
61
,I
tI
