Actinide Colloids and Particles of Environmental C

ActinideColloidsandParticlesofEnvironmentalConcernClemensWalther*,†andMelissaA.Denecke‡†InstituteforRadioecologyandRadiationProtection,LeibnizUniversityHannover,HerrenhäuserStrasse2,D-30419Hannover,Germany‡InstituteforNuclearWasteDisposal,KarlsruheInstituteofTechnology,P.O.Box3640,D-76021Karlsruhe,GermanyCONTENTS1.IntroductionA2.EnvironmentalActinideParticlesB2.1.ParticlesfromNaturallyOccurringRadio-activeMatterB2.2.“Hot”ParticlesReleasedintheEnvironmentD2.2.1.“Hot”ActinideParticlesfromMilitaryNuclearDevicesE2.2.2.NanoparticlesfromDepletedUranium(DU)E2.2.3.“Hot”ActinideParticlesfromReprocess-ingofNuclearMaterialandAccidentsF2.2.4.Colloid-MediatedTransportH3.Aerosols/SafeguardsI4.SyntheticParticlesK4.1.ReferenceActinideParticlesK4.2.ActinideNanoparticlesinSolutionK4.2.1.DetectionofActinideParticlesinSol-utionK4.2.2.ThoriumColloidsL4.2.3.NeptuniumandUraniumColloidsL4.2.4.PlutoniumNanoparticlesM4.3.Well-DefinedNanoparticlesandClustersN5.ConclusionandOutlookPAuthorInformationPCorrespondingAuthorPNotesPBiographyQReferencesQ1.INTRODUCTIONTheradioecologicalrelevanceofactinideparticles1didnotfirstbecomeamatterofconcernfollowingthenuclearaccidentsatFukushima,Chernobyl,orThreeMileIsland.Publicandscientificattentionwasdirectedtothepotentialhazardsofactinideparticlessoonafterthefirstproductionanduseofactinideelementsinthe1940s.Abovegroundatomicexplosionscausedtremendousamountsofradioactivefalloutwithaconsiderablefractionpresentasparticles,whichwereeasilydispersedoverwidedistances.2Asearlyasthe1950sand1960s,severalstudiesappeareddealingwiththeaerosoltransportmechanismsofradionuclidesingeneral3andactinidesinparticular.4Sourcesofactinideparticlesintheenvironmentotherthannuclearexplosionsandnuclearpowerplantaccidentsarenaturallyoccurringradioactivematterorparticlecontaminantsreleasedfromothermilitaryactivities(e.g.,nuclearsubmarines,ammunition),fromactivitiesrelatedtonuclearpowerproduction(e.g.,miningandfuelfabrication),andalsofromminoroccurrencessuchasnuclearpoweredsatellites.5Suchparticles(nanometer-orsubmicrometer-tomicrometer-sizedparticles)containingactinideelementcontaminants(actinidecontainingparticles)arefoundintheenvironmentinawidevarietyofformsormorphologiesandcompositions,exhibitingvaryingchemistriesandstabilities,forexample,aspureactinideoractinideoxideparticles(referredtoasintrinsicactinideparticles),assingleelementormixedoxides,andassolidsolutionsinvariousphases,tonameafew.Radioactivecontaminantparticlesareoftenreferredtoas“hot”particles(andnotnecessarilylimitedtoactinidecontainingparticles),althoughthisdefinitionisqualitativeanddoesnotsignifyadefinedlevelofradioactivity.Theanalysisoftheisotopecontentofenvironmentalactinidecontainingparticlesgivesinformationconcerningitsorigin.Thisinformationcanalsobeusedforsafeguardsagainstproliferation.Characterizationofthespeciationorchemicalandphysicalstateofactinidesinnano-ormicrometer-sizedparticlescanshedlightontheirpotentialtodissolve,tobetransportedintheenvironment(geo-,hydro-spheres),andtoultimatelybetransferredtotheecosystem(biosphere),whichisessentialforpredictingsafetyofnuclearwasterepositories,evaluatingtheeffectivenessofremediationstrategies,andassessingbioavailabilityandrelatedpotentialtoexertnegativehealtheffects.Heterogeneousactinidecontainingparticlescomprisedofmultiplephases,aswellasdifferentelementsandisotopes,presentachallengefortheiranalysis,character-ization,andpredictionoftheirbehavior.Moderninstrumenta-tiondevelopmentsandstudiesoflaboratoryandreferencesystemsarehelpingresearchersmeetthischallenge.Themorphologyandelementalandisotopiccompositionofactinide(containing)particlescanbeobtainedbyagreatvarietyofexperimentaltechniques,5,6suchaselectronSpecialIssue:2013NuclearChemistryReceived:August16,2012Reviewpubs.acs.org/CR©XXXXAmericanChemicalSocietyAdx.doi.org/10.1021/cr300343c|Chem.Rev.XXXX,XXX,XXX−XXXmicroscopy7(includingtransmissionEM,TEM;8scanningEM,SEM;EMwithsecondaryX-rayspectroscopy,Augerspectros-copy,electronenergylossspectroscopyEELS,etc.),massspectrometry9(includinginductivelycoupledplasmaMS,ICPMS;10acceleratorMS,AMS;11secondaryionMS,SIMS;12electrosprayMS,ESI-MS13),matrixassistedlaserdesorptionMS,MALDI-MS;14resonantionizationMS,RIMS;15thermalionizationMS,TIMS),X-ray-basedmethods16(includingscattering,absorption,emission,(spectro)microscopy),andmanymore.Applicationofsuchstate-of-the-arttechniquestocharacterizenanometer-tomicrometer-sizedparticlesinthesolidstateandinsolution(colloidsandmultinuclearspecies),whichcontainactinideelementsand,hence,ofenvironmentalconcernispresentedbelow.Forareviewofthetechniquesthemselves,thereaderisreferredtorefs5,6.InthisReview,across-sectionofthepresentknowledgeconcerningactinidecontainingparticlesofbothenvironmentalaswellassyntheticoriginispresented.Thesyntheticsystemsserveasreferencematerialandmodelsforunderstandingtheformation,reactivity,andstructureofenvironmentalactinidecontainingparticles.Thereaderisalsoreferredtothefirstbookpublishedcoveringdifferentaspectsofresearchonactinidenanoparticles.17ThisReviewisstructuredaccor