INTERNATIONAL ATOMIC ENERGY AGENCYVIENNAISBN 9201147058ISSN 10206566The explosion on 26 April 1986 at the Chernobyl nuclear power plant and the consequent reactor fire resulted in anunprecedentedreleaseofradioactivematerialfrom anuclearreactorandadverseconsequencesforthe publicandtheenvironment.Althoughtheaccident occurrednearlytwodecadesago,controversystill surroundstherealimpactofthedisaster.Therefore the IAEA, in cooperation with the Food and Agriculture OrganizationoftheUnitedNations,theUnited NationsDevelopmentProgramme,theUnitedNations Environment Programme, the United Nations Office for theCoordinationofHumanitarianAffairs,theUnited NationsScientificCommitteeontheEffectsofAtomic Radiation, the World Health Organization and the World Bank, as well as the competent authorities of Belarus, theRussianFederationandUkraine,establishedthe ChernobylForumin2003.ThemissionoftheForum was to generate authoritative consensual statements on the environmental consequences and health effects attributabletoradiationexposurearisingfromthe accident as well as to provide advice on environmental remediationandspecialhealthcareprogrammes,and tosuggestareasinwhichfurtherresearchisrequired. This report presents the findings and recommendations oftheChernobylForumconcerningtheenvironmental effects of the Chernobyl accident.Report of theChernobyl Forum Expert Group EnvironmentEnvironmental Consequencesof the Chernobyl Accidentand their Remediation:Twenty Years of ExperienceRADIOLOGICALASSESSMENTREPORTSS E R I E SEnvironmental Consequences of the Chernobyl Accident and their Remediation: Twenty Years of Experience9.9 mm 180 pagesP1239_covI+IV.indd 1 2006-03-30 14:41:37ENVIRONMENTAL CONSEQUENCES OF THE CHERNOBYL ACCIDENT AND THEIR REMEDIATION: TWENTY YEARS OF EXPERIENCEReport of the Chernobyl Forum Expert Group EnvironmentThe following States are Members of the International Atomic Energy Agency:The AgencysStatute was approved on 23 October 1956bytheConference ontheStatute ofthe IAEAheld at United Nations Headquarters, New York; it entered into force on 29 July 1957. The Headquarters of theAgency are situated in Vienna. Its principal objective is to accelerate and enlarge the contribution of atomicenergy to peace, health and prosperity throughout the world.AFGHANISTANALBANIAALGERIAANGOLAARGENTINAARMENIAAUSTRALIAAUSTRIAAZERBAIJANBANGLADESHBELARUSBELGIUMBENINBOLIVIABOSNIA AND HERZEGOVINABOTSWANABRAZILBULGARIABURKINA FASOCAMEROONCANADACENTRAL AFRICAN REPUBLICCHADCHILECHINACOLOMBIACOSTA RICACTE DIVOIRECROATIACUBACYPRUSCZECH REPUBLICDEMOCRATIC REPUBLIC OF THE CONGODENMARKDOMINICAN REPUBLICECUADOREGYPTEL SALVADORERITREAESTONIAETHIOPIAFINLANDFRANCEGABONGEORGIAGERMANYGHANAGREECEGUATEMALAHAITIHOLY SEEHONDURASHUNGARYICELANDINDIAINDONESIAIRAN, ISLAMIC REPUBLIC OF IRAQIRELANDISRAELITALYJAMAICAJAPANJORDANKAZAKHSTANKENYAKOREA, REPUBLIC OFKUWAITKYRGYZSTANLATVIALEBANONLIBERIALIBYAN ARAB JAMAHIRIYALIECHTENSTEINLITHUANIALUXEMBOURGMADAGASCARMALAYSIAMALIMALTAMARSHALL ISLANDSMAURITANIAMAURITIUSMEXICOMONACOMONGOLIAMOROCCOMYANMARNAMIBIANETHERLANDSNEW ZEALANDNICARAGUANIGERNIGERIANORWAYPAKISTANPANAMAPARAGUAYPERUPHILIPPINESPOLANDPORTUGALQATARREPUBLIC OF MOLDOVAROMANIARUSSIAN FEDERATIONSAUDI ARABIASENEGALSERBIA AND MONTENEGROSEYCHELLESSIERRA LEONESINGAPORESLOVAKIASLOVENIASOUTH AFRICASPAINSRI LANKASUDANSWEDENSWITZERLANDSYRIAN ARAB REPUBLICTAJIKISTANTHAILANDTHE FORMER YUGOSLAV REPUBLIC OF MACEDONIATUNISIATURKEYUGANDAUKRAINEUNITED ARAB EMIRATESUNITED KINGDOM OF GREAT BRITAIN AND NORTHERN IRELANDUNITED REPUBLIC OF TANZANIAUNITED STATES OF AMERICAURUGUAYUZBEKISTANVENEZUELAVIETNAMYEMENZAMBIAZIMBABWEENVIRONMENTAL CONSEQUENCES OF THE CHERNOBYL ACCIDENT AND THEIR REMEDIATION: TWENTY YEARS OF EXPERIENCEReport of the Chernobyl Forum Expert Group EnvironmentRADIOLOGICAL ASSESSMENT REPORTS SERIESINTERNATIONAL ATOMIC ENERGY AGENCYVIENNA, 2006IAEA Library Cataloguing in Publication DataEnvironmentalconsequencesoftheChernobylaccidentandtheirremediation:twentyyearsofexperience/reportoftheChernobylForumExpertGroupEnvironment.Vienna:InternationalAtomic Energy Agency, 2006.p.;29cm.(Radiologicalassessmentreportsseries,ISSN1020-6566)STI/PUB/1239ISBN 9201147058Includes bibliographical references.1.ChernobylNuclearAccident,Chornobyl,Ukraine,1986Environmentalaspects.2.RadioactivewastesitesCleanup.I. International Atomic Energy Agency.II. Series.IAEAL0600424COPYRIGHT NOTICEAll IAEA scientific and technical publications are protected by the termsoftheUniversalCopyrightConventionasadoptedin1952(Berne)andasrevisedin1972(Paris).ThecopyrighthassincebeenextendedbytheWorldIntellectual PropertyOrganization(Geneva)toinclude electronicandvirtualintellectualproperty.PermissiontousewholeorpartsoftextscontainedinIAEApublicationsinprintedorelectronicformmustbeobtainedandisusuallysubjecttoroyaltyagreements.Proposalsfornon-commercialreproductionsandtranslationsarewelcomedandwillbeconsideredonacase by casebasis.EnquiriesshouldbeaddressedbyemailtothePublishingSection, IAEA, at sales.publications@iaea.org or by post to:Sales and Promotion Unit, Publishing SectionInternational Atomic Energy AgencyWagramer Strasse 5P.O. Box 100A-1400 ViennaAustriafax: +43 1 2600 29302tel.: +43 1 2600 22417http://www.iaea.org/books IAEA, 2006Printed by the IAEA in AustriaApril 2006STI/PUB/1239FOREWORDThe explosion on 26 April 1986 at the Chernobyl nuclear power plant, which is located 100 km from Kievin Ukraine (at that time part of the USSR), and the consequent reactor fire, which lasted for 10 days, resulted inan unprecedented release of radioactive material from a nuclear reactor and adverse consequences for the publicand the environment.The resulting contamination of the environment with radioactive material caused the evacuation of morethan100000peoplefromtheaffectedregionduring1986andtherelocation,after1986,ofanother200 000people from Belarus, the Russian Federation and Ukraine. Some five million people continue to live in areascontaminatedbytheaccident.Thenationalgovernmentsofthethreeaffectedcountries,supportedbyinternational organizations, have undertaken costly efforts to remediate the areas affected by the contamination,provide medical services and restore the regions social and economic well-being.TheaccidentsconsequenceswerenotlimitedtotheterritoriesofBelarus,theRussianFederationandUkraine, since other European countries were also affected as a result of the atmospheric transfer of radioactivematerial. These countries also encountered problems in the radiation protection of their populations, but to alesser extent than the three most affected countries.Although the accident occurred nearly two decades ago, controversy still surrounds the real impact of thedisaster. Therefore the IAEA, in cooperation with the Food and Agriculture Organization of the United Nations(FAO), the United Nations Development Programme (UNDP), the United Nations Environment Programme(UNEP), the United Nations Office for the Coordination of Humanitarian Affairs (OCHA), the United NationsScientific Committee on the Effects of Atomic Radiation (UNSCEAR), the World Health Organization (WHO)andtheWorldBank,aswellasthecompetentauthoritiesofBelarus,theRussianFederationandUkraine,established the Chernobyl Forum in 2003. The mission of the Forum was through a series of managerial andexpert meetings to generate authoritative consensual statements on the environmental consequences andhealtheffectsattributabletoradiationexposurearisingfromtheaccident,aswellastoprovideadviceonenvironmental remediation and special health care programmes, and to suggest areas in which further researchis required. The Forum was createdas a contributionto the United Nations tenyear strategy for Chernobyl,launched in 2002 with the publication of Human Consequences of the Chernobyl Nuclear Accident A Strategyfor Recovery.Over a two year period, two groups of experts from 12 countries, including Belarus, the Russian Federationand Ukraine, and from relevant international organizations, assessed the accidents environmental and healthconsequences. In early 2005 the Expert Group Environment, coordinated by the IAEA, and the Expert GroupHealth, coordinated by the WHO, presented their reports for the consideration of the Chernobyl Forum. BothreportswereconsideredandapprovedbytheForumatitsmeetingon1820April2005.Thismeetingalsodecided, inter alia, to consider the approved reports as a common position of the Forum members, i.e., of theeightUnitedNationsorganizationsandthethreemostaffectedcountries,regardingtheenvironmentalandhealth consequences of the Chernobyl accident, as well as recommended future actions, i.e., as a consensus withinthe United Nations system.ThisreportpresentsthefindingsandrecommendationsoftheChernobylForumconcerningtheenvironmentaleffectsoftheChernobylaccident.TheForumsreportconsideringthehealtheffectsoftheChernobyl accident is being published by the WHO. The Expert Group Environment was chaired by L. Anspaughof the United States of America. The IAEA technical officer responsible for this report was M. Balonov of theIAEA Division of Radiation, Transport and Waste Safety. EDITORIAL NOTEAlthoughgreatcarehasbeentakentomaintaintheaccuracyofinformationcontainedinthispublication,neithertheIAEA nor its Member States assume any responsibility for consequences which may arise from its use.The use of particular designations of countries or territories does not imply any judgement by the publisher, the IAEA, asto the legal status of such countries or territories, of their authorities and institutions or of the delimitation of their boundaries.Thementionofnamesofspecificcompaniesorproducts(whetherornotindicatedasregistered)doesnotimplyanyintentiontoinfringeproprietaryrights,norshoulditbeconstruedasanendorsementorrecommendationonthepartoftheIAEA.CONTENTS1. SUMMARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11.1. Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11.2. Radioactive contamination of the environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21.2.1. Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21.2.1.1. Radionuclide release and deposition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21.2.1.2. Urban environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21.2.1.3. Agricultural environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31.2.1.4. Forest environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41.2.1.5. Aquatic environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41.2.2. Recommendations for future research and monitoring. . . . . . . . . . . . . . . . . . . . . . . . . . . .41.2.2.1. General. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41.2.2.2. Practical . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .51.2.2.3. Scientific. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .51.2.2.4. Specific recommendations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .51.3. Environmental countermeasures and remediation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .61.3.1. Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .61.3.1.1. Radiological criteria. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .61.3.1.2. Urban countermeasures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .71.3.1.3. Agricultural countermeasures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .71.3.1.4. Forest countermeasures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .81.3.1.5. Aquatic countermeasures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .81.3.2. Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .81.3.2.1. Countries affected by the Chernobyl accident . . . . . . . . . . . . . . . . . . . . . . . . . . . .81.3.2.2. Worldwide. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .91.3.2.3. Research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .91.4. Human exposure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .91.4.1. Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .101.4.2. Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .111.5. Radiation induced effects on plants and animals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .121.5.1. Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .121.5.2. Recommendations for future research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .131.5.3. Recommendations for countermeasures and remediation . . . . . . . . . . . . . . . . . . . . . . . . . .131.6. Environmental and radioactive waste management aspects of the dismantling of the Chernobyl shelter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .131.6.1. Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .131.6.2. Recommendations for future actions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14Reference to Section 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .152. INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .162.1. Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .162.2. Objectives of the Chernobyl Forum. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .162.3. Method of operation and output of the Chernobyl Forum. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .172.4. Structure of the report . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17References to Section 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .173. RADIOACTIVE CONTAMINATION OF THE ENVIRONMENT. . . . . . . . . . . . . . . . . . . . . . . . . . .183.1. Radionuclide release and deposition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .183.1.1. Radionuclide source term. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .183.1.2. Physical and chemical forms of released material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .203.1.3. Meteorological conditions during the course of the accident. . . . . . . . . . . . . . . . . . . . . . . .213.1.4. Concentration of radionuclides in air. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .223.1.5. Deposition of radionuclides on soil surfaces. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .233.1.6. Isotopic composition of the deposition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .253.2. Urban environment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .273.2.1. Deposition patterns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .273.2.2. Migration of radionuclides in the urban environment. . . . . . . . . . . . . . . . . . . . . . . . . . . . .283.2.3. Dynamics of the exposure rate in urban environments. . . . . . . . . . . . . . . . . . . . . . . . . . . . .293.3. Agricultural environment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .293.3.1. Radionuclide transfer in the terrestrial environment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .293.3.2. Food production systems affected by the accident. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .303.3.3. Effects on agriculture in the early phase. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .303.3.4. Effects on agriculture in the long term phase. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .323.3.4.1. Physicochemistry of radionuclides in the soilplant system . . . . . . . . . . . . . . . . .323.3.4.2. Migration of radionuclides in soil. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .333.3.4.3. Radionuclide transfer from soil to crops. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .343.3.4.4. Dynamics of radionuclide transfer to crops. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .363.3.4.5. Radionuclide transfer to animals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .383.3.5. Current contamination of foodstuffs and expected future trends . . . . . . . . . . . . . . . . . . . .403.4. Forest environment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .413.4.1. Radionuclides in European forests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .413.4.2. Dynamics of contamination during the early phase. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .423.4.3. Long term dynamics of radiocaesium in forests. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .433.4.4. Uptake into edible products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .443.4.5. Contamination of wood. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .453.4.6. Expected future trends. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .463.4.7. Radiation exposure pathways associated with forests and forest products. . . . . . . . . . . .463.5. Radionuclides in aquatic systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .473.5.1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .473.5.2. Radionuclides in surface waters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .483.5.2.1. Distribution of radionuclides between dissolved and particulate phases. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .483.5.2.2. Radioactivity in rivers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .483.5.2.3. Radioactivity in lakes and reservoirs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .503.5.2.4. Radionuclides in freshwater sediments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .523.5.3. Uptake of radionuclides to freshwater fish. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .533.5.3.1. Iodine-131 in freshwater fish. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .533.5.3.2. Caesium-137 in freshwater fish and other aquatic biota . . . . . . . . . . . . . . . . . . . .533.5.3.3. Strontium-90 in freshwater fish. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .543.5.4. Radioactivity in marine ecosystems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .553.5.4.1. Distribution of radionuclides in the sea. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .553.5.4.2. Transfers of radionuclides to marine biota . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .563.5.5. Radionuclides in groundwater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .563.5.5.1. Radionuclides in groundwater: Chernobyl exclusion zone. . . . . . . . . . . . . . . . . .563.5.5.2. Radionuclides in groundwater: outside the Chernobyl exclusion zone. . . . . . . .583.5.5.3. Irrigation water. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .583.5.6. Future trends. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .583.5.6.1. Freshwater ecosystems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .583.5.6.2. Marine ecosystems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .603.6. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .603.7. Further monitoring and research needed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .61References to Section 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .624. ENVIRONMENTAL COUNTERMEASURES AND REMEDIATION. . . . . . . . . . . . . . . . . . . . . . .694.1. Radiological criteria. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .694.1.1. International radiological criteria and standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .694.1.2. National radiological criteria and standards. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .714.2. Urban decontamination. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .724.2.1. Decontamination research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .734.2.2. Chernobyl experience . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .734.2.3. Recommended decontamination technologies. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .744.3. Agricultural countermeasures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .754.3.1. Early phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .754.3.2. Late phase. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .774.3.3. Countermeasures in intensive agricultural production . . . . . . . . . . . . . . . . . . . . . . . . . . . . .784.3.3.1. Soil treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .794.3.3.2. Change in fodder crops grown on contaminated land. . . . . . . . . . . . . . . . . . . . . .804.3.3.3. Clean feeding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .804.3.3.4. Administration of caesium binders. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .814.3.4. Summary of countermeasure effectiveness in intensive production . . . . . . . . . . . . . . . . . .814.3.5. Countermeasures in extensive production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .814.3.6. Current status of agricultural countermeasures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .834.3.7. A wider perspective on remediation, including socioeconomic issues. . . . . . . . . . . . . . . .834.3.8. Current status and future of abandoned land. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .844.3.8.1. Exclusion and resettlement zones in Belarus . . . . . . . . . . . . . . . . . . . . . . . . . . . . .844.3.8.2. Rehabilitation of contaminated lands in Ukraine . . . . . . . . . . . . . . . . . . . . . . . . .854.3.8.3. Abandoned zones in the Russian Federation. . . . . . . . . . . . . . . . . . . . . . . . . . . . .864.4. Forest countermeasures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .864.4.1. Studies on forest countermeasures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .874.4.2. Countermeasures for forests contaminated with radiocaesium. . . . . . . . . . . . . . . . . . . . . .874.4.2.1. Management based countermeasures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .874.4.2.2. Technology based countermeasures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .874.4.3. Examples of forest countermeasures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .894.5. Aquatic countermeasures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .904.5.1. Measures to reduce doses at the water supply and treatment stage . . . . . . . . . . . . . . . . . .904.5.2. Measures to reduce direct and secondary contamination of surface waters. . . . . . . . . . . .914.5.3. Measures to reduce uptake by fish and aquatic foodstuffs . . . . . . . . . . . . . . . . . . . . . . . . . .924.5.4. Countermeasures for groundwater. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .934.5.5. Countermeasures for irrigation water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .934.6. Conclusions and recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .934.6.1. Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .934.6.2. Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .944.6.2.1. Countries affected by the Chernobyl accident . . . . . . . . . . . . . . . . . . . . . . . . . . . .944.6.2.2. Worldwide. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .954.6.2.3. Research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .95References to Section 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .965. HUMAN EXPOSURE LEVELS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1005.1. Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1005.1.1. Populations and areas of concern. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1005.1.2. Exposure pathways. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1005.1.3. Concepts of dose. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1015.1.4. Background radiation levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1015.1.5. Decrease of dose rate with time. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1025.1.6. Critical groups. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1025.2. External exposure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1035.2.1. Formulation of the model of external exposure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1035.2.2. Input data for the estimation of effective external dose . . . . . . . . . . . . . . . . . . . . . . . . . . . .1035.2.2.1. Dynamics of external gamma dose rate over open undisturbed soil . . . . . . . . . .1035.2.2.2. Dynamics of external gamma dose rate in anthropogenic areas . . . . . . . . . . . . .1055.2.2.3. Behaviour of people in the radiation field . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1055.2.2.4. Effective dose per unit gamma dose in air. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1065.2.3. Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1065.2.3.1. Dynamics of external effective dose. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1065.2.3.2. Measurement of individual external dose with thermoluminescent dosimeters. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1065.2.3.3. Levels of external exposure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1085.3. Internal dose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1095.3.1. Model for internal dose. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1095.3.2. Monitoring data as input for the assessment of internal dose. . . . . . . . . . . . . . . . . . . . . . .1095.3.3. Avoidance of dose by human behaviour . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1105.3.4. Results for doses to individuals. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1105.3.4.1. Thyroid doses due to radioiodines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1105.3.4.2. Long term internal doses from terrestrial pathways . . . . . . . . . . . . . . . . . . . . . . .1125.3.4.3. Long term doses from aquatic pathways. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1155.4. Total (external and internal) exposure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1165.5. Collective doses. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1185.5.1. Thyroid. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1185.5.2. Total (external and internal) dose from terrestrial pathways . . . . . . . . . . . . . . . . . . . . . . . .1185.5.3. Internal dose from aquatic pathways. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1195.6. Conclusions and recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1195.6.1. Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1195.6.2. Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .121References to Section 5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1216. RADIATION INDUCED EFFECTS ON PLANTS AND ANIMALS . . . . . . . . . . . . . . . . . . . . . . . . .1256.1. Prior knowledge of radiation effects on biota. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1256.2. Temporal dynamics of radiation exposure following the Chernobyl accident . . . . . . . . . . . . . . . .1276.3. Radiation effects on plants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1286.4. Radiation effects on soil invertebrates. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1306.5. Radiation effects on farm animals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1316.6. Radiation effects on other terrestrial animals. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1326.7. Radiation effects on aquatic organisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1326.8. Genetic effects in animals and plants. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1336.9. Secondary impacts and current conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1356.10. Conclusions and recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1376.10.1. Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1376.10.2. Recommendations for future research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1376.10.3. Recommendations for countermeasures and remediation . . . . . . . . . . . . . . . . . . . . . . . . . .138References to Section 6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1387. ENVIRONMENTAL AND RADIOACTIVE WASTE MANAGEMENT ASPECTS OF THE DISMANTLING OF THE CHERNOBYL SHELTER . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1417.1. Current status and the future of unit 4 and the shelter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1417.1.1. Unit 4 of the Chernobyl nuclear power plant after the accident . . . . . . . . . . . . . . . . . . . . .1417.1.2. Current status of the damaged unit 4 and the shelter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1427.1.3. Long term strategy for the shelter and the new safe confinement. . . . . . . . . . . . . . . . . . . .1447.1.4. Environmental aspects. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1457.1.4.1. Current status of the shelter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1457.1.4.2. Impact on air. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1457.1.4.3. Impact on surface water. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1457.1.4.4. Impact on groundwater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1487.1.4.5. Impacts of shelter collapse without the new safe confinement. . . . . . . . . . . . . .1487.1.4.6. Impacts of shelter collapse within the new safe confinement. . . . . . . . . . . . . . . .1507.1.5. Issues and areas for improvement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1517.1.5.1. Influence of the source term uncertainty on environmental decisions . . . . . . . .1517.1.5.2. Characterization of fuel-containing material. . . . . . . . . . . . . . . . . . . . . . . . . . . . .1517.1.5.3. Removal of fuel-containing material concurrent with development of a geological disposal facility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1517.2. Management of radioactive waste from the accident. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1517.2.1. Current status of radioactive waste from the accident. . . . . . . . . . . . . . . . . . . . . . . . . . . . .1537.2.1.1. Radioactive waste associated with the shelter . . . . . . . . . . . . . . . . . . . . . . . . . . . .1537.2.1.2. Mixing of accident related waste with operational radioactive waste . . . . . . . . .1547.2.1.3. Temporary radioactive waste storage facilities. . . . . . . . . . . . . . . . . . . . . . . . . . .1547.2.1.4. Radioactive waste disposal facilities. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1557.2.2. Radioactive waste management strategy. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1567.2.3. Environmental aspects. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1577.2.4. Issues and areas of improvement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1597.2.4.1. Radioactive waste management programme for the exclusion zone and the Chernobyl nuclear power plant. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1597.2.4.2. Decommissioning of unit 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1597.2.4.3. Waste acceptance criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1597.2.4.4. Long term safety assessment of existing radioactive waste storage sites. . . . . .1607.2.4.5. Potential recovery of temporary waste storage facilities located in the Chernobyl exclusion zone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1607.3. Future of the Chernobyl exclusion zone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1607.4. Conclusions and recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1617.4.1. Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1617.4.2. Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .162References to Section 7 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .163CONTRIBUTORS TO DRAFTING AND REVIEW. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16511.SUMMARY1.1. INTRODUCTIONThis report provides an up to date evaluationoftheenvironmentaleffectsoftheaccidentthatoccurred on 26 April 1986 at the Chernobyl nuclearpower plant. Even though it is now nearly 20 yearsaftertheaccident,therearestillmanyconflictingreportsandrumoursconcerningitsconsequences.ForthisreasontheChernobylForumwasinitiatedbytheIAEAincooperationwiththeFoodandAgricultureOrganizationoftheUnitedNations(FAO),theUnitedNationsDevelopmentProgramme(UNDP),theUnitedNationsEnvironmentProgramme(UNEP),theUnitedNationsOfficefortheCoordinationofHumani-tarianAffairs(OCHA),theUnitedNationsScientificCommitteeontheEffectsofAtomicRadiation (UNSCEAR), the World Health Organi-zation(WHO)andtheWorldBank,aswellasthecompetentauthoritiesofBelarus,theRussianFederationandUkraine.ThefirstorganizationalmeetingoftheChernobylForumwasheldon3-5 February2003,atwhichtimethedecisionwastaken to establish the Forum as an ongoing entity ofthe above named organizations.TheChernobylForumwasestablishedasaseriesofmanagerial,expertandpublicmeetingswiththepurposeofgeneratingauthoritativeconsensual statements on the health effects attrib-utabletoradiationexposurearisingfromtheaccidentandtheenvironmentalconsequencesinducedbythereleasedradioactivematerial,providing advice on remediation and special healthcareprogrammesandsuggestingareasinwhichfurtherresearchisrequired.Thetermsofreference of the Forum as approved at the meetingwere:(a) ToexploreandrefinethecurrentscientificassessmentsonthelongtermhealthandenvironmentalconsequencesoftheChernobyl accident, with a view to producingauthoritativeconsensusstatementsfocusingon:(i) Thehealtheffectsattributabletoradiationexposurecausedbytheaccident;(ii) Theenvironmentalconsequencesinducedbytheradioactivematerialreleased due to the accident (e.g. contam-ination of foodstuffs);(iii) Theconsequencesattributabletotheaccidentbutnotdirectlyrelatedtotheradiationexposureorradioactivecontamination.(b) To identify gaps in scientific research relevanttotheradiationinducedorradioactivecontaminationinducedhealthandenviron-mental impacts of the accident, and to suggestareas in which further work is required basedon an assessment of the work done in the pastandbearinginmindongoingworkandprojects.(c) Toprovideadviceon,andtofacilitateimple-mentation of, scientifically sound programmesonmitigationoftheaccidentconsequences,includingpossiblejointactionsoftheorgani-zations participating in the Forum, such as:(i) Remediationofcontaminatedland,withtheaimofmakingitsuitablefornormalagricultural,economicandsociallifeunder safe conditions; (ii) Specialhealthcareoftheaffectedpopulation;(iii) Monitoring of long term human exposureto radiation;(iv) Addressingtheenvironmentalissuespertaining to the decommissioning of theChernobylshelterandthemanagementof radioactive waste originating from theChernobyl accident.TheChernobylForumisahighlevelorgani-zation of senior officials of United Nations agenciesand the three most affected countries. The technicalreports of the Forum were produced by two expertgroups:ExpertGroupEnvironment(EGE)andExpert Group Health (EGH). The membership ofthetwogroupscomprisedrecognizedinternationalscientistsandexpertsfromthethreemostaffectedcountries.Throughtheworkofthesetwogroupsandtheirsubworkinggroups,thetechnicaldocumentswereprepared.TheEGEwascoordinatedbytheIAEAandtheEGHwascoordinated by the WHO.Inallcases,thescientistsoftheEGEandEGH were able to reach consensus on the contentsoftheirrespectivetechnicaldocuments.The2technicalreportswerefinallyapprovedbytheChernobyl Forum itself. This report, on the environ-mental consequences, is published by the IAEA; thereport on the health consequences will be publishedby the WHO.1.2. RADIOACTIVE CONTAMINATION OF THE ENVIRONMENTTheChernobylaccidentcausedalargeregionalreleaseofradionuclidesintotheatmosphereandsubsequentradioactivecontami-nationoftheenvironment.ManyEuropeancountries were affected by the radioactive contami-nation; among the most affected were three formerrepublicsoftheSovietUnion,nowBelarus,theRussianFederationandUkraine.Thedepositedradionuclidesgraduallydecayedandmovedwithinandamongtheenvironmentsatmospheric,aquatic, terrestrial and urban.1.2.1. Conclusions1.2.1.1. Radionuclide release and depositionMajorreleasesfromunit4oftheChernobylnuclearpowerplantcontinuedfortendays,andincluded radioactive gases, condensed aerosolsanda large amount of fuel particles. The total release ofradioactivesubstanceswasabout14EBq1(asof26 April1986),whichincluded1.8EBqof 131I,0.085 EBq of 137Cs and other caesium radioisotopes,0.01 EBqof 90Srand0.003EBqofplutoniumradioisotopes.Thenoblegasescontributedabout50% of the total release of radioactivity.Large areas of Europe were affected to somedegree by the Chernobyl releases. An area of morethan 200 000 km2 in Europe was contaminated withradiocaesium(above0.04MBqof 137Cs/m2),ofwhich 71% was in the three most affected countries(Belarus, the Russian Federation and Ukraine). Thedepositionwashighlyheterogeneous;itwasstrongly influenced by rain when the contaminatedair masses passed. In the mapping of the deposition,137Cs was chosen because it is easy to measure and isofradiologicalsignificance.Mostofthestrontiumandplutoniumradioisotopesweredepositedclose(less than 100 km) to the reactor, due to their beingcontained within larger particles.Muchofthereleasecomprisedradionuclideswithshortphysicalhalf-lives;longlivedradio-nuclideswerereleasedinsmalleramounts.Thusmany of the radionuclides released by the accidenthavealreadydecayed.Thereleasesofradioactiveiodinescausedconcernimmediatelyaftertheaccident. Owing to the emergency situation and theshorthalf-lifeof 131I,fewreliablemeasurementsweremadeofthespatialdistributionofdepositedradioiodine(whichisimportantindeterminingdoses to the thyroid). Current measurements of 129Imayassistinestimating 131Idepositionbetterandthereby improve thyroid dose reconstruction.Aftertheinitialperiod, 137Csbecamethenuclideofgreatestradiologicalimportance,with90Srbeingoflessimportance.Forthefirstyears134Cswasalsoimportant.Overthelongerterm(hundredstothousandsofyears),theonlyradio-nuclidesanticipatedtobeofinterestaretheplutonium isotopes and 241Am.1.2.1.2. Urban environmentInurbanareas,opensurfacessuchaslawns,parks,streets,roads,squares,roofsandwallsbecamecontaminatedwithradionuclides.Underdryconditions,trees,bushes,lawnsandroofsbecamemorecontaminated;underwetconditions,horizontalsurfacessuchassoilplots,lawns,etc.,receivedthehighestcontamination.Particularlyhigh 137Csactivityconcentrationswerefoundaroundhouseswhererainhadtransportedtheradioactivematerialfromtheroofstotheground.The deposition in urban areas in the nearest city ofPripyatandsurroundingsettlementscouldhaveinitiallygivenrisetosubstantialexternalradiationdoses,butthiswaspartiallyavertedbytheevacuation of the people. The deposited radioactivematerialinotherurbanareashasgivenrisetoexposure of the public in the subsequent years andcontinues to do so.Duetowindandrainandhumanactivities,including traffic, street washing and cleanup, surfacecontamination by radioactive material was reducedsignificantlyininhabitedandrecreationalareasduring1986andafterwards.Oneoftheconse-quencesoftheseprocesseshasbeenthesecondarycontaminationofsewagesystemsandsludgestorage areas.Atpresent,inmostofthesettlementssubjected to radioactive contamination, the air doserateabovesolidsurfaceshasreturnedtothepre-accidentbackgroundlevel.Theelevatedairdose1 1 EBq = 1018 Bq (becquerel).3rateremainsmainlyoverundisturbedsoilingardens, kitchen gardens and parks.1.2.1.3. Agricultural environmentIn the early phase, direct surface deposition ofmanydifferentradionuclidesdominatedthecontamination of agricultural plants and the animalsconsumingthem.Thereleaseanddepositionofradioiodineisotopescausedthemostimmediateconcern,buttheproblemwasconfinedtothefirsttwomonths,becauseoftheshortphysicalhalf-life(eightdays)ofthemostimportantiodineisotope,131I. The radioiodine was rapidly transferred to milkatahighrateinBelarus,theRussianFederationand Ukraine, leading to significant thyroid doses tothoseconsumingmilk,especiallychildren.IntherestofEuropetheconsequencesoftheaccidentvaried; increased levels of radioiodine in milk wereobservedinsomecontaminatedsouthernareaswhere dairy animals were already outdoors.Different crop types, in particular green leafyvegetables,werealsocontaminatedwithradio-nuclidestovaryingdegrees,dependingonthedepositionlevelsandthestageofthegrowingseason. Direct deposition on to plant surfaces was ofconcern for about two months.After the early phase of direct contamination,uptakeofradionuclidesthroughplantrootsfromsoilbecameincreasinglyimportantandshowedstrongtimedependence.Radioisotopesofcaesium(137Csand 134Cs)werethenuclidesthatledtothegreatest problems, and after the decay of 134Cs, 137CsremainstocauseproblemsinsomeBelarusian,RussianandUkrainianareas.Inaddition, 90Srcauses problems in the near field of the reactor, butatlongerdistancesthedepositionlevelsweretoolowtobeofradiologicalsignificance.Otherradio-nuclides,suchasplutoniumisotopesand 241Am,either were present at very low deposition levels orwerenotveryavailableforrootuptake,andthereforedidnotcauserealproblemsinagriculture.Ingeneral,therewasaninitialsubstantialreductioninthetransferofradionuclidestovegetationandanimals,aswouldbeexpected,duetoweathering,physicaldecay,migrationofradio-nuclidesdownthesoilcolumnandreductioninradionuclidebioavailabilityinsoil.Particularlyincontaminated intensive agricultural systems, mostlyintheformerUSSR,therewassubstantialreductioninthetransferof 137Cstoplantsandanimals,especiallyinthefirstfewyears.However,inthepastdecadetherehasbeenlittlefurtherobviousdecline,andlongtermeffectivehalf-liveshave been difficult to quantify with precision.Theradiocaesiumactivityconcentrationsinfoodstuffs after the early phase were influenced notonlybydepositionlevelsbutalsobysoiltypes,managementpracticesandtypesofecosystem.Themajor and persistent problems in the affected areasoccurinextensiveagriculturalsystemswithsoilswith a high organic content and where animals grazeonunimprovedpasturesthatarenotploughedorfertilized. In particular, this affects rural residents intheformerUSSR,whoarecommonlysubsistencefarmers with privately owned dairy cattle.Inthelongterm, 137Csinmeatandmilk,andtoalesserextent 137Csinvegetables,remainsthemost important contributor to human internal dose.As its activity concentration, in both vegetable andanimalfoods,hasbeendecreasingduringthepastdecadeveryslowly,at37%/a,thecontributionof137Cs to dose will continue to dominate for decadesto come. The contribution of other long lived radio-nuclides, 90Sr,plutoniumisotopesand 241Am,tohuman dose will remain insignificant.1.2.1.4. Forest environmentFollowingtheChernobylaccident,vegetationand animals in forests and mountain areas showed aparticularlyhighuptakeofradiocaesium,withthehighest recorded 137Cs activity concentrations beingfoundinforestproducts,duetothepersistentrecyclingofradiocaesiuminforestecosystems.Particularlyhigh 137Csactivityconcentrationshavebeenfoundinmushrooms,berriesandgame,andthesehighlevelshavepersistedsincetheaccident.Thus, while there has been a general decline in themagnitude of exposures due to the consumption ofagriculturalproducts,therehavebeencontinuedhigh levels of contamination in forest food products,whichstillexceedinterventionlimitsinmanycountries.Thiscanbeexpectedtocontinueforseveraldecadestocome.Therefore,therelativeimportanceofforestsincontributingtotheradiationexposuresofthepopulationsofseveralaffected countries has increased with time. It will be,primarily,thecombinationofdownwardmigrationinthesoilandthephysicaldecayof 137Csthatcontribute to any further reduction in the contami-nation of forest food products.Thehightransferofradiocaesiuminthelichenreindeer meathumans pathway was demon-stratedaftertheChernobylaccidentintheArctic4andsub-ArcticareasofEurope.TheChernobylaccidentledtoconsiderablecontaminationofreindeermeatinFinland,Norway,theRussianFederationandSweden,andcausedsignificantproblems for the Sami people.Theuseoftimberandassociatedproductsmakes only a small contribution to the exposure ofthegeneralpublic,althoughwoodashcancontainhigh amounts of 137Cs and could potentially give risetohigherdosesthanotherusesofwood.Caesium-137intimberisofminorimportance,althoughdosesinthewoodpulpindustryhavetobeconsidered.Forestfiresincreasedairactivityconcentra-tions in 1992, but not to a high extent. The possibleradiological consequences of forest fires have beenmuch discussed, but these are not expected to causeany problems of radionuclide transfer from contam-inatedforests,except,possibly,inthenearestsurroundings of the fire.1.2.1.5. Aquatic environmentRadionuclidesfromChernobylcontaminatedsurface water systems not only in areas close to thesitebutalsoinmanyotherpartsofEurope.Theinitial contamination of water was due primarily todirect deposition of radionuclides on to the surfacesof rivers and lakes and was dominated by short livedradionuclides(mostimportantly 131I).Inthefirstfew weeks after the accident, activity concentrationsindrinkingwaterfromtheKievreservoirwereaparticular concern.The contamination of water bodies decreasedrapidlyduringtheweeksafterfalloutthroughdilution,physicaldecayandabsorptionofradio-nuclidesbycatchmentsoils.Forlakesandreservoirs, the settling of suspended particles to thebedsedimentsalsoplayedanimportantroleinreducingradionuclidelevelsinwater.Bedsedimentsareanimportantlongtermsinkforradionuclides.Theinitialuptakeofradioiodinebyfishwasrapid,butactivityconcentrationsdeclinedquickly,due primarily to physical decay. Bioaccumulation ofradiocaesiumintheaquaticfoodchainledtosignificantconcentrationsinfishinthemostaffectedareas,andinsomelakesasfarawayasScandinaviaandGermany.Owingtogenerallylowerfalloutandlowerbioaccumulation, 90Sractivity concentrations in fish were not a significantcontributortohumandoseincomparisonwithradiocaesium, particularly since 90Sr is accumulatedin bone rather than in edible muscle.In the long term, secondary contamination bywash-off of long lived 137Cs and 90Sr from contami-natedsoilsandremobilizationfrombedsedimentscontinues (at a much lower level) to the present day.Catchments with a high organic content (peat soils)releasemuchmoreradiocaesiumtosurfacewatersthanthosewithmostlymineralsoils.Atpresent,surfacewateractivityconcentrationsarelow;irrigationwithsurfacewateristhereforenotconsidered to be a problem.FuelparticlesdepositedinthesedimentsofriversandlakesclosetotheChernobylnuclearpowerplantshowsignificantlylowerweatheringrates than the same particles in terrestrial soils. Thehalf-life of these particles is roughly the same as thephysical half-life of the radionuclides 90Sr and 137Cs.While 137Cs and 90Sr activity concentrations inthewaterandfishofrivers,openlakesandreservoirs are currently low, the most contaminatedlakes are those few lakes with limited inflowing andoutflowingstreams(closedlakes)inBelarus,theRussianFederationandUkrainethathaveapoormineralnutrientstatus.Activityconcentrationsof137Cs in fish in some of these lakes will remain for asignificanttimeintothefuture.Inapopulationlivingnexttoaclosedlakesystem(e.g.LakeKozhanovskoeintheRussianFederation),consumptionoffishhasdominatedthetotal 137Csingestion for some people.OwingtothelargedistanceoftheBlackandBalticSeasfromChernobyl,andthedilutioninthesesystems,activityconcentrationsinseawaterhave been much lower than in fresh water. The lowradionuclideconcentrationsinthewatercombinedwiththelowbioaccumulationofradiocaesiuminmarinebiotahasledtoactivityconcentrationsinmarine fish that are not of concern.1.2.2. Recommendations for future research and monitoring1.2.2.1. GeneralVariousecosystemsconsideredinthisreporthave been intensively monitored and studied duringtheyearsaftertheChernobylaccident,andthetransfer and bioaccumulation of the most importantlongtermcontaminants, 137Csand 90Sr,arenowgenerally well understood. There is, therefore, littleurgent need for major new research programmes onradionuclidesinecosystems;thereis,however,a5requirementforcontinued,butmorelimited,targetedmonitoringoftheenvironments,andforfurtherresearchinsomespecificareas,asdetailedbelow.Longtermmonitoringofradionuclides(especially 137Cs and 90Sr) in various environmentalcompartmentsisrequiredtomeetthegeneralpractical and scientific needs described below.1.2.2.2. PracticalThe practical needs are to:(a) Assesscurrentandpredictfuturelevelsofhumanexposureandcontaminationoffoodsinordertojustifyremedialactionsandlongterm countermeasures.(b) Informthegeneralpublicinaffectedareasaboutthepersistenceofradioactivecontami-nationinfoodproductsanditsseasonalandannualvariabilityinnaturalfoodproductsgatheredbythemselves(suchasmushrooms,game,freshwaterfishfromclosedlakes,berries,etc.)andgiveadviceondietaryandfood preparation methods to reduceradionu-clide intake by humans.(c) Informthegeneralpublicinaffectedareasaboutchangingradiologicalconditionsinorder to relieve public concerns.1.2.2.3. ScientificThe scientific needs are to:(a) Determinetheparametersofthelongtermtransferofradionuclidesinvariousecosystems and different natural conditions inordertoimprovepredictivemodelsbothforuseinChernobylaffectedareasandforapplicationtopotentialfutureradioactivereleases.(b) Determinemechanismsofradionuclidebehaviour in less studied ecosystems (e.g. theroleoffungiinforests)inordertounderstandthemechanismsdeterminingthepersistenceofradionuclidesintheseecosystemsandtoexplorepossibilitiesforremediation, with special attention to be paidtoprocessesofimportanceforcontributionto human and biota doses.Asactivityconcentrationsinenvironmentalcompartmentsarenowinquasi-equilibriumandchangingslowly,thenumberandfrequencyofsamplingandmeasurementsperformedinmonitoringandresearchprogrammescanbesubstantially reduced compared with the early yearsafter the Chernobyl accident.Thedepositsof 137Csandanumberofotherlong lived radionuclides in the 30 km zone should beusedforradioecologicalstudiesofthevariousecosystemslocatedinthishighlycontaminatedarea.Suchstudiesare,exceptforverysmallscaleexperiments,notpossibleordifficulttoperformelsewhere.1.2.2.4. Specific recommendationsUpdatedmappingof 137CsdepositioninAlbania,BulgariaandGeorgiashouldbeperformedinordertocompletethestudyofthepost-Chernobyl contamination of Europe.Improvedmappingof 131Ideposition,basedbothonhistoricalenvironmentalmeasurementscarried out in 1986 and on recent measurements of129IinsoilsamplesinareaswhereelevatedthyroidcancerincidencehasbeendetectedaftertheChernobylaccident,wouldreducetheuncertaintyin thyroid dose reconstruction needed for the deter-mination of radiation risks.Longtermmonitoringof 137Csand 90Sractivityconcentrationsinagriculturalplantandanimal products produced in areas with various soilandclimateconditionsanddifferentagriculturalpractices shouldbeperformedin thenextdecades,intheformoflimitedtargetresearchprogrammesonselectedsites,todetermineparametersforthemodelling of long term transfer.Studiesofthedistributionof 137Csandplutoniumradionuclidesintheurbanenvironment(Pripyat,Chernobylandsomeothercontaminatedtowns)atlongtimesaftertheaccidentwouldimprove modelling of human external exposure andinhalation of radionuclides in the event of a nuclearor radiological accident or malicious action.Continuedlongtermmonitoringofspecificforestproducts,suchasmushrooms,berriesandgame, should be carried out in those areas in whichforestsweresignificantlycontaminatedandwherethepublicconsumeswildfoods.Theresultsfromsuchmonitoringarebeingusedbytherelevantauthoritiesintheaffectedcountriestoprovideadvice to the general public on the continued use offorestsforrecreationandthegatheringofwildfoods.6In addition to the general monitoring of forestproducts,requiredforradiationprotection,moredetailed,scientificallybased,longtermmonitoringofspecificforestsitesisrequiredtoprovideanongoingandimprovedunderstandingofthemechanisms, long term dynamics and persistence ofradiocaesium contamination and its variability. It isdesirabletoexplorefurtherthekeyorganisms,forexamplefungi,andtheirroleinradiocaesiummobilityandlongtermbehaviourinforestecosystems. Such monitoring programmes are beingcarried out in the more severely affected countries,such asBelarusand the RussianFederation, and itis important that these continue into the foreseeablefutureifthecurrentuncertaintiesonlongtermforecasts are to be reduced.AquaticsystemshavebeenintensivelymonitoredandstudiedduringtheyearsaftertheChernobylaccident,andtransfersandbioaccumulationofthemostimportantlongtermcontaminants, 90Srand 137Cs,arenowwellunderstood.Thereis,however,arequirementforcontinued (but perhaps more limited) monitoring ofthe aquatic environment, and for further research insome specific areas, as detailed below.Although there is currently no need for majornewresearchprogrammesonradioactivityinaquaticsystems,predictionsoffuturecontami-nation of aquatic systems by 90Sr and 137Cs would beimprovedbycontinuedmonitoringofradioactivityinkeysystems(thePripyatDniepersystem,theseas,andselectedriversandlakesinthemostaffectedareasandwesternEurope).Thiswouldcontinue the excellent existing time series measure-ments of activity concentrations in water, sedimentsandfish,andenabletherefinementofpredictivemodels for these radionuclides.Althoughtheyarecurrentlyofminorradio-logicalimportanceincomparisonwith 90Srand137Cs, further studies of transuranic elements in theChernobyl zone would help to improve predictionsofenvironmentalcontaminationintheverylongterm(hundredstothousandsofyears).Furtherempiricalstudiesoftransuranicradionuclidesand99TcareunlikelytohavedirectimplicationsforradiologicalprotectionintheChernobylaffectedareas,butwouldaddtoknowledgeoftheenviron-mentalbehaviouroftheseverylonglivedradio-nuclides.FutureplanstoreducethewaterleveloftheChernobylcoolingpondwillhavesignificantimplicationsforitsecologyandthebehaviourofradionuclides/fuelparticlesinnewlyexposedsediments.Specificstudiesonthecoolingpondshouldthereforecontinue.Inparticular,furtherstudyoffuelparticledissolutionratesinaquaticsystemssuchasthecoolingpondwouldimproveknowledge of these processes.1.3. ENVIRONMENTAL COUNTERMEASURES AND REMEDIATIONAftertheChernobylaccident,theauthoritiesintheUSSRintroducedarangeofshorttermandlong term countermeasures to reduce the effects oftheenvironmentalcontamination.Thecounter-measuresconsumedagreatamountofhuman,economicandscientificresources.Unfortunately,there was not always openness and transparency intheactionsoftheauthorities,andinformationwaswithheldfromthepublic.Thiscan,inpart,explainsome of the problems experienced later in commu-nication with the public, and the publics mistrust oftheauthorities.SimilarbehaviourinmanyothercountriesoutsidetheRussianFederation,BelarusandUkraineledtoadistrustinauthoritythat,inmany countries, prompted investigations on how todealwithsuchmajoraccidentsinanopenandtransparent way and on how the affected people canbe involved in decision making processes.TheuniqueexperienceofcountermeasureapplicationaftertheChernobylaccidenthasalreadybeenwidelyusedbothatthenationalandinternationallevelsinordertoimproveprepar-ednessagainstfuturenuclearandradiologicalemergencies.1.3.1. Conclusions1.3.1.1. Radiological criteriaAtthetimeoftheChernobylaccident,welldevelopedinternationalandnationalguidanceongeneralradiationprotectionofthepublicandspecificguidanceapplicabletomajornuclearemergencies was in place. The basic methodology ofthe guidance used in the former USSR was differentfromthatoftheinternationalsystem,butthedoselimits of the radiation safety standards were similar.Thethenavailableinternationalandnationalstandards were widely applied for the protection ofthe populations of the European countries affectedby the accident.7ThescaleandlongtermconsequencesoftheChernobylaccidentrequiredthedevelopmentofsomeadditionalnationalandinternationalradiationsafetystandardsasaresultofchangingradiological conditions.1.3.1.2. Urban countermeasuresDecontaminationofsettlementswaswidelyappliedasacountermeasureinthecontaminatedregions of the USSR during the first years after theChernobylaccidentasameansofreducingtheexternalexposureofthepublicandtheinhalationof resuspended radioactive substances.Decontaminationwascosteffectivewithregardtoreductionofexternaldosewhenitsplanningandimplementationwereprecededbyaremediationassessmentbasedoncostbenefittechniquesandexternaldosimetrydata.Sincetheareashavebeencleanedup,nosecondarycontaminationofcleanedupplotshasbeenobserved.Thedecontaminationofurbanenvironmentshasproducedaconsiderableamountoflowlevelradioactivewaste,which,inturn,hascreatedaproblem of disposal.Numerousexperimentalstudiesandassociatedmodellinghavebeenusedasthescientific basis for developing improved recommen-dationsfordecontaminationoftheurbanenvironment. Such recommendations could be usedintheeventofanyfuturelargescaleradioactivecontamination of urban areas.1.3.1.3. Agricultural countermeasuresCountermeasures applied in the early phase ofthe Chernobyl accident were only partially effectivein reducingradioiodineintakeviamilk, becauseofthelackoftimelyinformationabouttheaccidentand guidance on recommended actions, particularlyforprivatefarmers.Thisledtosignificantradioiodine exposure of some people in the affectedcountries.Themosteffectivecountermeasuresintheearly phase were exclusion of contaminated pasturegrassesfromanimalsdietsandtherejectionofmilk.Feedinganimalswithcleanfodderwaseffectivelyimplementedinsomecountries;however,thiscountermeasurewasnotwidelyappliedintheUSSR,duetoalackofuncontami-nated feeds. Slaughtering of cattle was often carriedout, but it was unjustified from a radiological pointofviewandcausedsignificanthygienic,practicaland economic problems.Severalmonthsaftertheaccident,longtermagriculturalcountermeasuresagainstradiocaesiumand radiostrontium were effectively implemented inallcontaminatedregions;thesecountermeasuresincludedfeedinganimalswithcleanfodderandobligatorymilkprocessing.Thisenabledmostfarmingpracticestocontinueinaffectedareasandresultedinalargereductionindose.Themostimportantpreconditionwastheradiationmonitoringofagriculturallands,feedsandfoodstuffs,includinginvivomonitoringofcaesiumactivity concentrations in the muscle of cattle.Thegreatestlongtermproblemhasbeenradiocaesiumcontaminationofmilkandmeat.IntheUSSR,andlaterinthethreeindependentcountries,thiswasaddressedbythetreatmentoflandusedforfoddercrops,cleanfeedingandtheapplicationofcaesiumbinderstoanimals.Cleanfeedingisoneofthemostimportantandeffectivemeasuresusedincountrieswhereanimalproductshave 137Csactivityconcentrationsexceedingtheactionlevels.Inthelongterm,environmentalradiationconditionsarechangingonlyslowly;however,theefficiencyofenvironmentalcounter-measures remains at a constant level.Theapplicationofagriculturalcounter-measuresinthethreemostaffectedcountrieshassubstantiallydecreasedsincethemid-1990s,because of economic problems. Within a short timethis resulted in an increase of radionuclide contentin plant and animal agricultural products.Therearestillagriculturalareasinthethreecountries that remain out of use. This land could beusedafterappropriateremediation,butatpresentlegal,economicandsocialconstraintsmakethisdifficult.Where social and economic factors, along withradiologicalfactors,havebeentakenintoaccountduringtheplanningandapplicationofcounter-measures,betteracceptabilityofthecounter-measures by the public has been achieved.InwesternEurope,becauseofthehighandprolongeduptakeofradiocaesiumintheaffectedextensivesystems,arangeofcountermeasuresisstillbeingusedforanimalproductsfromuplandsand forests.For the first time, practical, long term agricul-tural countermeasures have been developed, testedandimplementedonalargescale;theseincluderadicalimprovementofmeadows,pre-slaughtercleanfeeding,theapplicationofcaesiumbinders,8and soil treatment and cultivation. Their implemen-tationonmorethanthreebillionhectaresofagriculturallandhasmadeitpossibletominimizetheamountofproductswithradionuclideactivityconcentrationsabovetheactionlevelsinallthreecountries.1.3.1.4. Forest countermeasuresTheprincipalforestrelatedcountermeasuresappliedaftertheChernobylaccidentweremanagementbasedcountermeasures(restrictionsof various activities normally carried out in forests)and technology based countermeasures.Restrictionswidelyappliedinthethreemostaffectedcountries,andpartiallyinScandinavia,includedthefollowingactionsthathavereducedhumanexposureduetoresidenceinradioactivelycontaminated forests and the use of forest products:(a) Restrictionsonpublicandforestworkeraccess,asacountermeasureagainstexternalexposure.(a) Restrictionsontheharvestingoffoodproductssuchasgame,berriesandmushrooms.Inthethreemostaffectedcountriesmushroomsarewidelyconsumed,andthereforethisrestrictionhasbeenparticularly important.(b) Restrictionsonthecollectionoffirewoodbythepublic,inordertopreventexternalexposuresinthehomeandgardenwhenthewoodisburnedandtheashisdisposedoforused as a fertilizer.(c) Alterationofhuntingpractices,aimedatavoidingtheconsumptionofmeatwithhighseasonal levels of radiocaesium.(d) Fire prevention, especially in areas with largescaleradionuclidedeposition,aimedattheavoidanceofsecondarycontaminationoftheenvironment.However,experienceinthethreemostaffectedcountrieshasshownthatsuchrestrictionscanalsoresultinsignificantnegativesocialconse-quences,andadvicefromtheauthoritiestothegeneralpublicmaybeignoredasaresult.Thissituationcanbeoffsetbytheprovisionofsuitableeducational programmes targeted at the local scaleto emphasize the relevance of suggested changes inthe use of some forest areas.It is unlikely that any technology based forestcountermeasures(i.e.theuseofmachineryand/orchemicaltreatmentstoalterthedistributionortransferofradiocaesiumintheforest)willbepracticable on a large scale.1.3.1.5. Aquatic countermeasuresNumerous countermeasures were put in placein the months and years after the accident to protectwatersystemsfromthetransferofradionuclidesfrom contaminated soils. In general, these measureswere ineffective and expensive and led to relativelyhighexposuresoftheworkersimplementingthecountermeasures.Themosteffectivecountermeasurewastheearlyrestrictionofdrinkingwaterabstractionandthechangetoalternativesupplies.Restrictionsontheconsumptionoffreshwaterfishhaveprovedeffective in Scandinavia and Germany; however, inBelarus,theRussianFederationandUkrainesuchrestrictions may not always have been adhered to.It is unlikely that any future countermeasurestoprotectsurfacewaterswouldbejustifiableinterms of economic cost per unit of dose reduction. Itisexpectedthatrestrictionsontheconsumptionoffishwillremaininafewcases(inclosedlakes)forseveral more decades.Futureeffortsinthisareashouldbefocusedon public information, because there are still publicmisconceptionsconcerningtheperceivedhealthrisks due to radioactively contaminated waters andfish.1.3.2. Recommendations1.3.2.1. Countries affected by the Chernobyl accidentLongtermremediationmeasuresandcountermeasuresshouldbeappliedintheareascontaminatedwithradionuclidesiftheyareradio-logically justified and optimized.Membersofthegeneralpublicshouldbeinformed,alongwiththeauthorities,abouttheexisting radiation risk factors and the technologicalpossibilitiestoreducetheminthelongtermviaremediation and countermeasures, and be involvedin discussions and decision making.Inthelongterm,remediationmeasuresandcountermeasuresremainefficientandjustifiedmainlyintheagriculturalareaswithpoor(sandyandpeaty)soils,wherehighradionuclidetransferfrom soil to plants can occur.9Particularattentionmustbegiventoprivatefarmsinseveralhundredsettlementsandtoabout50intensivefarmsinBelarus,theRussianFederationandUkraine,whereradionuclideconcentrationsinmilkstillexceedthenationalaction levels.Amonglongtermremediationmeasures,radicalimprovementofpasturesandgrasslands,aswellasthedrainingofwetpeatyareas,ishighlyefficient.Themostefficientagriculturalcounter-measures are pre-slaughter clean feeding of animalsaccompaniedbyinvivomonitoring,applicationofPrussian blue to cattle and enhanced application ofmineral fertilizers in plant cultivation.Restrictingharvestingbythepublicofwildfoodproductssuchasgame,berries,mushroomsandfishfromclosedlakesmaystillbeneededinareaswhereradionuclideactivityconcentrationsexceed the national action levels.Adviceshouldcontinuetobegivenonindividualdiets,asawayofreducingconsumptionofhighlycontaminatedwildfoodproducts,andonsimplecookingprocedurestoremoveradioactivecaesium.It is necessary to identify sustainable ways ofmaking useofthemostaffectedareas,butalsotorevivetheeconomicpotentialofsuchareasforthebenefitofthecommunity.Suchstrategiesshould take into account the associated radiationhazard.1.3.2.2. WorldwideTheuniqueexperienceofcountermeasureapplicationaftertheChernobylaccidentshouldbecarefully documented and used for the preparationofinternationalandnationalguidanceforauthoritiesandexpertsresponsibleforradiationprotection of the public and the environment.Practicallyallthelongtermagriculturalcountermeasuresimplementedonalargescaleincontaminatedlandsofthethreemostaffectedcountries can be recommended for use in the eventoffutureaccidents.However,theeffectivenessofsoilbasedcountermeasuresvariesateachsite.Analysis of soil properties and agricultural practicebeforetheapplicationofcountermeasuresistherefore of great importance.Recommendations on the decontamination oftheurbanenvironmentintheeventoflargescaleradioactivecontaminationshouldbedistributedtothemanagementofnuclearfacilitiesthathavethepotentialforsubstantialaccidentalradioactiverelease(nuclearpowerplantsandreprocessingplants) and to authorities in adjacent regions.1.3.2.3. ResearchGenerally,thephysicalandchemicalprocessesinvolvedinenvironmentalcounter-measuresandremediationtechnologies,bothofamechanicalnature(radionuclideremoval,mixingwithsoil,etc.)orofachemicalnature(soilliming,fertilization,etc.),ortheircombinations,areunderstood well enough to be modelled and appliedinsimilarcircumstancesworldwide.Muchlesswellunderstoodarethebiologicalprocessesthatcouldbeusedinenvironmentalremediation(e.g.reprofilingofagriculturalproduction,bioremedi-ation, etc.). These processes require more research.Animportantissuethatrequiresmoresocio-logicalresearchistheperceptionbythepublicoftheintroduction,performanceandwithdrawalofcountermeasuresintheeventofanemergency,aswell as the development of social measures aimed atinvolving the public in these processes at all stages,beginning with the decision making process.There is still substantial diversity in the inter-national and national radiological criteria and safetystandardsapplicabletotheremediationofareasaffectedbyenvironmentalcontaminationwithradionuclides.TheexperienceofradiologicalprotectionofthepublicaftertheChernobylaccidenthasclearlyshowntheneedforfurtherinternationalharmonizationofappropriateradio-logical criteria and safety standards.1.4. HUMAN EXPOSUREFollowingtheChernobylaccident,bothworkersandthegeneralpublicwereaffectedbyradiationthatresulted,orcanresult,inadversehealtheffects.Inthisreportconsiderationisgivenprimarilytotheexposurepatternsofmembersofthegeneralpublicexposedtoradionuclidesreleased totheenvironment.Informationon dosesreceivedbymembersofthegeneralpublic,boththoseevacuatedfromtheaccidentareaandthosewholivepermanentlyincontaminatedareas,isrequired for the following health related purposes:(a) Substantiationofcountermeasuresandremediation programmes;10(b) Forecastofexpectedadversehealtheffectsandjustificationofcorrespondinghealthprotection measures;(c) Information for the public and the authorities; (d) Epidemiologicalandothermedicalstudiesofradiation induced adverse health effects.Theresultsofpost-accidentenvironmentalmonitoring indicate that the most affected countrieswere Belarus, the Russian Federation and Ukraine.MuchoftheinformationondosesfromtheChernobyl accident relates to these countries.Therewerefourmainmechanismsfordeliveringradiationdosetothepublic:externaldosefromcloudpassage,internaldosefrominhalationofthecloudandresuspendedmaterial,externaldosefromradioactivematerialdepositedonsoilandothersurfaces,andinternaldosefromthe ingestion of food products and water. Except forunusualcircumstances,thelattertwopathwayswerethemoreimportant.Externaldoseandinternaldosetendedtobeapproximatelyequallyimportant,althoughthisgeneralconclusionissubjecttolargevariation,duetotheshieldingafforded by buildings and the soil from which cropswere grown.Estimatesofdosestoindividualmembersofpopulationgroupswerebasedonmillionsofmeasurementsofconcentrationsofradioactivematerialinair,soil,foods,water,humanthyroidsandthewholebodycontentsofhumans.Inaddition,manymeasurementsweremadeoftheexternalgammaexposurerateoverundisturbedanddisturbedfields,andexternaldosestohumansweremeasuredwithindividualthermoluminescentdosimeters. Thus the resultsof estimated dosesarefirmlybaseduponmeasurementsandtendtoberealistic rather than conservative.AsthemajorhealtheffectoftheChernobylaccidentforthegeneralpublicwasanelevatedthyroidcancerincidenceinchildrenandadoles-cents,muchattentionhasbeenpaidtothedosimetryofthethyroidgland.Theassessmentofthyroiddosesresultingfromtheintakeof 131Iisbasedontheresultsof350000humanmeasure-mentsandafewthousandmeasurementsof 131Iinmilk performed in Belarus, the Russian Federationand Ukraine within a few weeks of the accident.Dosestohumanswerereducedsignificantlybyanumberofcountermeasures.Officialcounter-measuresincludedevacuationandrelocationofpersons,theblockageofcontaminatedfoodsupplies,theremovalofcontaminatedsoil,thetreatment of agricultural fields to reduce the uptakeofradionuclides,thesubstitutionoffoodsandtheprohibitionoftheuseofwildfoods.Unofficialcountermeasuresincludedtheself-initiatedavoidance of foods judged to be contaminated.1.4.1. ConclusionsThecollectiveeffectivedose(notincludingdosetothethyroid)receivedbyaboutfivemillionresidents living in the areas of Belarus, the RussianFederationandUkrainecontaminatedbytheChernobylaccident(137Csdepositiononsoil>37 kBq/m2)wasapproximately40 000manSvduring the period 19861995. The groups of exposedpersonswithineachcountryreceivedanapproxi-mately equal collective dose. The additional amountof collective effective dose projected to be receivedbetween 1996 and 2006 is about 9000 man Sv.Thecollectivedosetothethyroidwasnearly2 106 man Gy, with nearly half received by personsexposed in Ukraine.Themainpathwaysleadingtohumanexposurewereexternalexposurefromradio-nuclides deposited on the ground and the ingestionofcontaminatedterrestrialfoodproducts.Inhalation and ingestion of drinking water, fish andproductscontaminatedwithirrigationwaterweregenerally minor pathways.Therangeinthyroiddoseindifferentsettlementsandinallagegendergroupsislarge,betweenlessthan0.1Gyandmorethan10Gy.Insomegroups,andespeciallyinyoungerchildren,doseswerehighenoughtocausebothshorttermfunctionalthyroidchangesandthyroidcancerinsome individuals.Theinternalthyroiddosefromtheintakeof131Iwasmainlyduetotheconsumptionoffreshcowsmilkand,toalesserextent,ofgreenvegetables;children,onaverage,receivedadosethatwasmuchhigherthanthatreceivedbyadults,becauseoftheirsmallthyroidmassesandconsumptionratesoffreshcowsmilkthatweresimilar to those of adults.Forpopulationspermanentlyresidingincontaminated areas and exposed predominantly viaingestion,thecontributionofshortlivedradio-iodines(i.e. 132I, 133Iand 135I)tothyroiddosewasminor (i.e. about 1% of the 131I thyroid dose), sinceshort lived radioiodines decayed during transport ofthe radioiodines along the food chains. The highestrelative contribution (2050%) to the thyroid dosestothepublicfromshortlivedradionuclideswas11receivedbytheresidentsofPripyatthroughinhalation;theseresidentswereevacuatedbeforethey could consume contaminated food.Both measurement and modelling data showthattheurbanpopulationwasexposedtoalowerexternaldosebyafactorof1.52comparedwiththeruralpopulationlivinginareaswithsimilarlevelsofradioactivecontamination.Thisarisesbecauseofthebettershieldingfeaturesofurbanbuildingsanddifferentoccupationalhabits.Also,astheurbanpopulationdependslessonlocalagricultural products and wild foods than the ruralpopulation,botheffectiveandthyroidinternaldosescausedpredominantlybyingestionwerelower by a factor of two to three in the urban thanin the rural population.Theinitialhighratesofexposuredeclinedrapidly due to the decay of short lived radionuclidesandtothemovementofradiocaesiumintothesoilprofile.Thelattercausedadecreaseintherateofexternaldoseduetoincreasedshielding.Inaddition,ascaesiummovesintothesoilcolumnitbinds to soil particles, which reduces the availabilityofcaesiumtoplantsandthustothehumanfoodchain.Thegreatmajorityofdosefromtheaccidenthas already been accumulated.Personswhoreceivedeffectivedoses(notincludingdosetothethyroid)higherthantheaverage by a factor of two to three were those wholived in rural areas in single storey homes and whoate large amounts of wild foods such as game meats,mushrooms and berries.Thelongterminternaldosestoresidentsofrural settlements strongly depend on soil properties.Contributions due to internal and external exposurearecomparableinareaswithlightsandysoil,andthecontributionofinternalexposuretothetotal(external and internal) dose does not exceed 10% inareaswithpredominantlyblacksoil.Thecontri-butionof 90Srtotheinternaldose,regardlessofnatural conditions, is usually less than 5%.Thelongterminternaldosestochildrencausedbyingestionoffoodcontainingcaesiumradionuclides are usually lower by a factor of about1.11.5 than those to adults and adolescents.Bothaccumulatedandpredictedmeandosesinsettlementresidentsvaryintherangeoftwoordersofmagnitude,dependingontheradioactivecontaminationofthearea,predominantsoiltypeandsettlementtype.Intheperiod19862000theaccumulateddoserangedfrom2mSvintownslocated in black soil areas up to 300 mSv in villageslocatedinareaswithpodzolsandysoil.Thedosesexpectedintheperiod20012056aresubstantiallylowerthanthedosesalreadyreceived(i.e.intherange of 1100 mSv).If countermeasures had not been applied, thepopulationsofsomeofthemorecontaminatedvillagescouldhavereceivedlifetime(70years)effectivedosesofupto400mSv.Intensiveapplicationofcountermeasuressuchassettlementdecontaminationandagriculturalcountermeasureshassubstantiallyreducedthedoses.Forcomparison,aworldwideaveragelifetimedosefromnaturalbackgroundradiationisabout170 mSv,withatypicalrangeof70700mSvinvarious regions of the world.Thevastmajorityoftheapproximatelyfivemillion people residing in the contaminated areas ofBelarus,theRussianFederationandUkrainecurrently receive annual effective doses of less than1mSv(equaltothenationalactionlevelsinthethreecountries).Forcomparison,aworldwideaverageannualdosefromnaturalbackgroundradiation is about 2.4 mSv, with a typical range of 110 mSv in various regions of the world.The number ofresidents of the contaminatedareasinthethreemostaffectedcountriesthatcurrently receive more than 1 mSv annually can beestimated to be about 100 000 persons. As the futurereductionofboththeexternaldoserateandtheradionuclide(mainly 137Cs)activityconcentrationsin food is predicted to be rather slow, the reductionin the human exposure levels is also expected to beslow(i.e.about35%/awithcurrentcounter-measures).Based upon available information, it does notappearthatthedosesassociatedwithhotparticleswere significant.TheassessmentoftheChernobylForumagrees with that of UNSCEAR [1.1] in terms of thedose received by the populations of the three mostaffected countries: Belarus, the Russian Federationand Ukraine.1.4.2. RecommendationsLargescalemonitoringoffoodstuffs,wholebodycountingofindividualsandprovisionofthermoluminescentdosimeterstomembersofthegeneralpublicarenolongernecessary.Thecriticalgroupsinareasofhighcontaminationand/orhightransferofradiocaesiumtofoodsareknown.Representativemembersofthesecriticalgroupsshouldbemonitoredwithdosimetersforexternal12doseandwithwholebodycountingforinternaldose.Sentinel or marker individuals in more highlycontaminatedareasnotscheduledforfurtherremediationmightbeidentifiedforcontinuedperiodicwholebodycountingandmonitoringforexternaldose.Thegoalwouldbetofollowtheexpectedcontinueddecreaseinexternalandinternaldoserateandtodeterminewhethersuchdecreasesareduetoradioactivedecayaloneortofurther ecological elimination.1.5. RADIATION INDUCED EFFECTS ON PLANTS AND ANIMALSThebiologicaleffectsofradiationonplantsand animals have long been of interest to scientists;infact,muchoftheinformationontheeffectsonhumanshasevolvedfromexperimentalstudiesonplantsandanimals.Additionalresearchfollowedthedevelopmentofnuclearenergyandconcernsaboutthepossibleimpactsofradioactivereleasesintotheterrestrialandaquaticenvironments.Bythemid-1970s,alargeamountofinformationhadbeen accrued on the effects of ionizing radiation onplants and animals.The Chernobyl nuclear accident in April 1986occurred not in a desert or ocean but in a territorywithatemperateclimateandflourishingfloraandfauna. Both acute radiation effects (radiation deathof plants and animals, loss of reproduction, etc.) andlongtermeffects(changeofbiodiversity,cytogeneticanomalies,etc.)havebeenobservedinthe affected areas. Biota located in the area nearesttothesourceoftheradioactiverelease,the30kmzoneorChernobylexclusionzone(CEZ),weremostaffected.Asaresult,inthisareapopulationandecosystemeffectsonbiota,caused,ontheonehand,byhighradiationlevels,and,ontheotherhand, by plant succession and animal migration duetointraspecificandinterspecificcompetition,haveoccurred.TheplantandanimalconditionsintheCEZchangedrapidlyduringthefirstmonthsandyearsaftertheaccidentandlaterarrivedataquasi-stationary equilibrium. At present, traces of adverseradiation effects on biota can hardly be found in thenearvicinityoftheradiationsource(afewkilometresfromthedamagedreactor),andontherest of the territory both wild plants and animals areflourishingbecauseoftheremovalofthemajornatural stressor: humans.1.5.1. ConclusionsRadiationfromradionuclidesreleasedbytheChernobyl accident caused numerous acute adverseeffectsinthebiotalocatedintheareasofhighestexposure(i.e.uptoadistanceofafewtensofkilometresfromthereleasepoint).BeyondtheCEZ,noacuteradiationinducedeffectsonbiotahave been reported.The environmental response to the Chernobylaccident was a complex interaction among radiationdose,doserateanditstemporalandspatialvariations, and the radiosensitivities of the differenttaxons.Bothindividualandpopulationeffectscausedbyradiationinducedcelldeathhavebeenobserved in plants and animals as follows:(a) Increasedmortalityofconiferousplants,soilinvertebrates and mammals;(b) Reproductive losses in plants and animals;(c) Chronicradiationsyndromeinanimals(mammals, birds, etc.).Noadverseradiationinducedeffectshavebeenreportedinplantsandanimalsexposedtoacumulative dose of less than 0.3 Gy during the firstmonth after the radionuclide fallout.Followingthenaturalreductionofexposurelevelsduetoradionuclidedecayandmigration,populationshavebeenrecoveringfromtheacuteradiationeffects.Bythenextgrowingseasonaftertheaccident,thepopulationviabilityofplantsandanimalssubstantiallyrecoveredasaresultofthecombined effects of reproduction and immigration.Afewyearswereneededforrecoveryfromthemajorradiationinducedadverseeffectsinplantsand animals.TheacuteradiobiologicaleffectsobservedintheChernobylaccidentareaareconsistentwithradiobiologicaldataobtainedinexperimentalstudiesorobservedinnaturalconditionsinotherareasaffectedbyionizingradiation.Thusrapidlydeveloping cell systems, such as meristems of plantsandinsectlarvae,werepredominantlyaffectedbyradiation.Attheorganismlevel,youngplantsandanimalswerefoundtobethemostsensitivetotheacute effects of radiation.Geneticeffectsofradiation,inbothsomaticand germ cells, were observed in plants and animalsintheCEZduringthefirstfewyearsaftertheaccident.BothintheCEZandbeyond,differentcytogeneticanomaliesattributabletoradiationcontinuetobereportedfromexperimentalstudies13performedonplantsandanimals.Whethertheobservedcytogeneticanomalieshaveanydetrimental biological significance is not known.The recovery of affected biota in the CEZ hasbeen confounded by the overriding response to theremovalofhumanactivities(e.g.terminationofagriculturalandindustrialactivitiesandtheaccompanying environmental pollution in the mostaffected area). As a result, the populations of manyplants and animals have expanded, and the presentenvironmentalconditionshavehadapositiveimpact on the biota in the CEZ.1.5.2. Recommendations for future researchIn order to develop a system of environmentalprotectionagainstradiation,thelongtermimpactof radiation on plant and animal populations shouldbe further investigated in the CEZ; this is a globallyunique area for radioecological and radiobiologicalresearch in an otherwise natural setting.Inparticular,multigenerationalstudiesofradiationeffectsonthegeneticstructureofplantandanimalpopulationsmightbringfundamentallynew scientific information.Thereisaneedtodevelopstandardizedmethods for biotadose reconstruction, for examplein the form of a unified dosimetric protocol.1.5.3. Recommendations for countermeasures and remediationProtectiveactionsforfarmanimalsintheevent of a nuclear or radiological emergency shouldbe developed and internationally harmonized basedonmodernradiobiologicaldata,includingtheexperience gained in the CEZ.Itislikelythatanytechnologybasedremediationactionsaimedatimprovingtheradio-logical conditions for plants and animals in the CEZwould have adverse impacts on biota.1.6. ENVIRONMENTAL AND RADIOACTIVE WASTE MANAGEMENT ASPECTS OF THE DISMANTLING OF THE CHERNOBYL SHELTER1.6.1. ConclusionsTheaccidentaldestructionofunit4oftheChernobylnuclearpowerplantresultedinextensiveradioactivecontaminationandthegeneration of large amounts of radioactive waste inthe unit, the Chernobyl nuclear power plant site andthesurroundingarea(CEZ).ConstructionoftheshelterbetweenMayandNovember1986wasaimedatenvironmentalcontainmentofthedamagedreactor,reductionofradiationlevelsonthesiteandthepreventionoffurtherreleaseofradionuclides off the site.The shelter was erected in an extremely shortperiod of time under conditions of severe radiationexposureofpersonnel.Asaresult,themeasurestakentosavetimeandreducedoseduringtheconstructionledtoimperfectioninthenewlyconstructedshelteraswellastoalackofcompre-hensive data on the stability of the damaged unit 4structures.Inadditiontouncertaintiesonstabilityat the time of its construction, structural elements