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The biological effects of ionising radiation on Crustaceans: A review
Neil Fuller, Adélaïde Lerebours, Jim Smith, Alex Ford
To cite this version:
Neil Fuller, Adélaïde Lerebours, Jim Smith, Alex Ford. The biological effects of ionis- ing radiation on Crustaceans: A review. Aquatic Toxicology, Elsevier, 2015, 167, pp.55-67.
�10.1016/j.aquatox.2015.07.013�. �hal-01978333�
AquaticToxicology167(2015)55–67
ContentslistsavailableatScienceDirect
Aquatic Toxicology
jo u r n al h om ep ag e :w w w . e l s e v i e r . c o m / l o c a t e / a q u a t o x
The biological effects of ionising radiation on Crustaceans: A review
Neil Fuller
a, Adélaïde Lerebours
a, Jim T. Smith
b, Alex T. Ford
a,∗aInstituteofMarineSciences,SchoolofBiologicalSciences,UniversityofPortsmouth,FerryRoad,Portsmouth,HampshirePO49LY,UK
bSchoolofEarth&EnvironmentalSciences,UniversityofPortsmouth,BurnabyBuilding,BurnabyRoad,Portsmouth,HampshirePO13QL,UK
a r t i c l e i n f o
Articlehistory:
Received13May2015
Receivedinrevisedform15July2015 Accepted23July2015
Availableonline26July2015
Keywords:
Ionisingradiation Crustacean
Environmentalradioprotection Radionuclide
a b s t r a c t
Historicapproachestoradiationprotectionarefoundedontheconjecturethatmeasurestosafeguard humansareadequatetoprotectnon-humanorganisms.Thisviewisdisparatewithothertoxicants whereinwell-developedframeworksexisttominimiseexposureofbiota.Significantdatagapsformany organisms,coupledwithhighprofilenuclearincidentssuchasChernobylandFukushima,haveprompted there-evaluationofourapproachtowardenvironmentalradioprotection.Elucidatingtheimpactsofradi- ationonbiotahasbeenidentifiedaspriorityareaforfutureresearchwithinbothscientificandregulatory communities.Thecrustaceansareubiquitousinaquaticecosystems,comprisinggreaterthan66,000 speciesofecologicalandcommercialimportance.Thispaperaimstoassesstheavailableliteratureof radiation-inducedeffectswithinthissubphylumandidentifyknowledgegaps.Aliteraturesearchwas conductedpertainingtoradiationeffectsonfourendpointsasstipulatedbyanumberofregulatorybod- ies:mortality,morbidity,reproductionandmutation.Amajorfindingofthisreviewwasthepaucityof dataregardingtheeffectsofenvironmentallyrelevantradiationdosesoncrustaceanbiology.Extremely fewstudiesutilisingchronicexposuredurationsorwildpopulationswerefoundacrossallfourendpoints.
Thedoselevelsatwhicheffectsoccurwasfoundtovarybyordersofmagnitudethuspresentingdiffi- cultiesindevelopingphyla-specificbenchmarkvaluesandreferencelevelsforradioprotection.Based onthelimiteddata,mutationwasfoundtobethemostsensitiveendpointofradiationexposure,with mortalitytheleastsensitive.Currentphyla-specificdoselevelsandlimitsproposedbymajorregulatory bodieswerefoundtobeinadequatetoprotectspeciesacrossarangeofendpointsincludingmorbidity, mutationandreproductionandexamplesarediscussedwithin.Thesefindingsservetoprioritiseareas forfutureresearchthatwillsignificantlyadvanceunderstandingofradiation-inducedeffectsinaquatic invertebratesandconsequentlyenhanceabilitytopredicttheimpactsofradioactivereleasesonthe environment.
©2015TheAuthors.PublishedbyElsevierB.V.ThisisanopenaccessarticleundertheCCBYlicense (http://creativecommons.org/licenses/by/4.0/).
Contents
1. Introduction...56
2. Radiation-inducedmutationincrustaceans...57
3. RadiationimpactsonmorbidityinCrustaceans ... 58
3.1. Radiation-inducedimpactsongrowth&respiration...60
3.2. Theeffectsofionisingradiationonthebehaviour&histopathologyofCrustaceanspecies ... 61
4. TheeffectofionisingradiationonreproductioninCrustaceans...62
5. Radiation-inducedmortalityinCrustaceans...62
6. Conclusions...63
Conflictofinterest...64
Acknowledgements ... 65
References...65
∗Correspondingauthor.
E-mailaddress:alex.ford@port.ac.uk(A.T.Ford).
http://dx.doi.org/10.1016/j.aquatox.2015.07.013
0166-445X/©2015TheAuthors.PublishedbyElsevierB.V.ThisisanopenaccessarticleundertheCCBYlicense(http://creativecommons.org/licenses/by/4.0/).
1. Introduction
Therenewedinterestinnuclearpowerasalowcarbonemis- sion energy source coupled with concern regarding past and potential nuclear accidents dictate that elucidating the impact of radionuclides on the environment is a global issue. Tradi- tionalapproachestoradiological protectionof theenvironment are based on the assumptions that the standards of environ- mental control needed to protect humans would be adequate toprotectotherspecies (Copplestoneet al.,2004;International Commission on Radiological Protection (ICRP, 1977). However thisanthropocentric approachis nolongeracceptedduetothe paucity of information regarding the effects of ionising radia- tion on non-human biota (Pentreath, 1998; Thompson, 1988), the varying sensitivities of different species and developmen- talstagestoradioactivecontaminants(Haggeretal.,2005)and the existence of habitats in which organisms may be exposed todosesabove thepermissiblelimitsfor humans(Copplestone etal.,2001).Assessingthebiologicalimpactofionisingradiation onnon-humanbiotahasbeenidentifiedasanecessaryapproach towardsprotectingandmitigatingtheimpactsoffutureradioac- tivereleaseson theenvironment by a number ofinternational directives(e.g.,ERICAandPROTECT[Howardetal.,2010;Larsson, 2008]).
Thepresenceofionisingradiationintheenvironmentoriginates from both natural and anthropogenic sources. Natural sources includecosmicradiationoriginatingfromoutsidethesolarsys- temandprimordial radionuclidesarisingfromstellarprocesses (Smith&Beresford,2005).Themajorityofanthropogenicradionu- clidesintheenvironmentarederivedfromthreemajorsources:
nuclear weapons testing, nuclear disasters and permitted dis- charges from nuclear reprocessing plants (Aarkrog, 2003). The aquaticenvironment representsan importantsinkfor radionu- clides(Avery,1996),sincethemajorityofdepositionofradioactive wastefromnuclearfacilitiesisin liquidformanddepositionof atmosphericfalloutinoceanecosystemsisapproximatelytwo-fold higherthanin terrestrialsystems(Burton,1975).Radionuclides present in the terrestrial environment may also contribute to radioactivityin aquaticenvironmentsviarun-off. For137Cs and
90Sr,thetwomajorman-madecontributorstoworldwideradi- ation doses (IAEA, 1995), approximately2 and 9% of thetotal landinventorieswillbetransported toaquaticsystems respec- tively via this pathway (Yamagata et al., 1963). However, the bioavailabilityofradionuclidesderivedfromrun-offisoftenlimited by the binding of such radionuclides to particulates and sub- sequentsedimentation(Aarkorg,2003).Furthermore,catchment andsoilcharacteristicshave beendemonstratedtosignificantly impactthemobilityofradionuclidesbythispathway(Smithetal., 2004).
Directdisposalofsolidradioactivewasteintothemarineenvi- ronmentwasconductedovera48yearperiodfrom1948to1993, leading to dumping of approximately 85 PBq (1×1015 Bq) of radioactivematerial(IAEA,1999).Themajorityofdumpedwaste waslow levelsolidwastedepositedintheNEAtlanticanddis- posalofreactorsbytheformerSovietUnionintheKaraSea,being 53.4and43.3%oftotaldumpedactivityrespectively(IAEA,1999).
Radiologicalmonitoringofdumpsitesbyanumberoforganisations revealed negligible impacts on overall radioactive contamina- tionandemphasisedthegreaterinfluenceofatmosphericfallout, althoughelevatedradionuclidelevelswereobservedinthevicinity ofsomedumpsites(i.e.,Baxteretal.,1995).
Permittedreleasesfromnuclearreprocessingsitesrepresenta significantsourceofanthropogenicradionuclidestotheworld’s oceans. For example, the Sellafield nuclearspent fuel reproce- ssingsitelocatedinCumbria,UnitedKingdom,generatedaliquid radioactiveeffluentof6.649×105 GBqbetaandgammaemitters
(excludingtritium) over a four yearperiod from 1995to1999 (EuropeanCommission,2001).Suchdischargesaredetectablein mostareasoftheNEAtlanticandintheArcticOcean,represent- ingasignificanttransferofradioactivecontamination(Kershaw&
Baxter,1995).MajorcatastrophessuchastheexplosionattheCher- nobylNPPandtheT ¯ohokuearthquake–tsunamiattheFukushima Dai-ichi NPP led tolarge scale releases of radioactive material into theenvironment (Buesseler et al., 2012). Estimatesof the overall input of 137Cs to the world’s oceans as a consequence oftheChernobylincident are15–20PBq(Aarkroget al.,2003).
Finallytheuseofradioisotopesinmedical,industrialandscien- tificinstitutionsleadstocontaminationofthemarineenvironment typically orders of magnitude lower than other major sources (Aarkrogetal.,2003).
Althoughtheneedforenvironmentalradioprotectionframe- workshaslongbeenestablished,(PentreathandWoodhead,1988;
Pentreath, 1998) a lack of scientific consensus regarding the doses at which significantbiological effects occur(Beresford &
Copplestone,2011)andthedisparitybetweenresultsoflabora- torybasedexposuresandfieldstudies(Garnier-Laplaceetal.,2013) haveprecludedaradiologicalriskassessmentfortheenvironment.
Thisprovidesacontrastwithotheranthropogeniccontaminants wherein protection frameworks and concepts (i.e., the Ecolog- ical Risk Assessment concept) are well developed (Bréchignac, 2003).Anoverviewoftheeffectsofionisingradiationonaquatic invertebrates has previously been carried out by Dallas et al., (2012).Thispaperadoptsa phyla-specificapproach inorderto provideamoredetailedanalysisofeffects,andprioritiseresearch needs for the Crustacea,a group of organisms that have been identifiedas keymodelsforthedevelopmentof environmental radioprotection frameworks (ICRP, 2008).Members ofthe sub- phylumCrustaceaarethedominantcomponentsofglobalaquatic ecosystems and comprise more than 66,000 species (LeBlanc, 2007).Theseorganismsprovideanarrayofcommercialandecolog- icalservicesandareusedbothdirectlyforhumanconsumptionand asafoodsourceforothercommerciallyimportantspecies(Benzie, 2009).Duetotheirubiquityinaquaticenvironmentsandwellchar- acterizedbiology,amarinecrustaceanofthefamilyCancridaehas beenselectedasoneoftheICRP’sreferenceanimals(ICRP,2008).
Referenceorganismswillbeusedasabasistodevelopenviron- mentalradioprotectionmeasures,andareconsideredecologically representativeofaspecifiedgroupofplantsoranimalswithbio- logicalcharacteristicsamenabletostudy(ICRP,2008).Tosupport thedevelopmentofrobust,applicableecologicalbenchmarkval- uesforenvironmentalradioprotectionitisnecessarytoreviewand identifyresearchneedsforradiobiologicalstudiesintheselected referenceorganisms.Thispaperaimstoreviewtheavailablelit- eratureregarding the biological effects of ionisingradiation on thecrustaceansubphylum,drawcomparisonsacrossbiomarkers andassess anygapsinknowledge inthecontextof developing doselevelsforradioprotection.Emphasiswillbeplacedonstudies employingthefourbiologicalendpointsasoutlinedbyCopplestone etal.,(2008)andRealetal.,(2004);mutation,morbidity,reproduc- tivecapacityandmortality.
Thescopeoftheliteraturesearchwaslimitedtoaquaticcrus- tacean species exposed to any form of ionising radiation. The FREDERICAradiation effects database(Availableat http://www.
frederica-online.org) along with other search engines (Google Scholar,ScienceDirectandWebofScience)wasusedasatoolto extractreferencesrelatingtothefourumbrellaendpointsselected inthisreview.TheFREDERICAdatabasecontainsreferencesfrom anumberofEuropeanCommissionfundedprojects(i.e.,EPICand FASSET)from1945to2007.Allreferenceswithinthisdatasetare subjecttoreviewbasedontheadequacyandreproducibilityofthe study(Copplestoneetal.,2008).
N.Fulleretal./AquaticToxicology167(2015)55–67 57
Fig.1.Illustrationoftherelationshipbetweencontaminantexposureandecosystemquality.AdaptedfromJha(2008).Fig.1reproducedwithpermissionfromJha(2008).
2. Radiation-inducedmutationincrustaceans
Forthepurposeofthisreview,amutationisdefinedas“Achange inthechromosomeorgenesofacellwhichmayaffectthestructure anddevelopmentoftheresultantoffspring”(Copplestone,2008).
Chromosomalandgeneticchangeshavebeenpostulatedbyanum- berofauthorstohavesignificantecologicalimplicationsathigher levelsofbiologicalorganisation(SeeFig.1(AndersonandWild, 1994;Depledge,1998;Jha,2008).
Despiteevidencesuggestingtheclastogenic(capacitytocause chromosomal aberrations) and mutagenic potential of ionising radiationobservedinarangeoforganismsincludinghumans(Lucas etal.,1992),fish(AnbumaniandMohankumar,2012;Kligerman etal.,1975;Pechkurenkov,1991)andmolluscs(AlAmrietal.,2012), thereisapaucityofinformationwithintheliteratureregardingthe crustaceansubphylum.Indeed,theFREDERICAdatabasecontain- ingover30,000dataentriescollatedfromanumberofinternational radiationeffectsdirectivescontainsnodataregardingmutationin crustaceanspeciesoverchronicdoserangesof0–>10,000Gy/hr-1 (SeeTable1Copplestoneetal.,2008).Similarly,the2008ICRPpub- licationintroducingtheconceptofreferenceanimalsandplants reportednoavailabledataforchromosomaleffectsincrabspecies (ICRP,2008),reiteratingthelackofstudiesinthisarea.
Fieldstudieshavesuggestedthatmutationmaybeasensitive endpointof radiation-induced effects incrustaceanspecies. For example,Florouetal.,(2004)assessedchromosomalaberrationsin microfaunacollectedfromgeothermalspringareasontheisland ofIkaria, Greecewhere maximumdoseratesofnatural gamma emittersinsedimentswere9.6mGyyr−1(∼0.001mGy/hr−1).These values are substantially elevated above the reported mean of 0.07mGyyr−1(∼0.008Gy/hr−1)forcoastalsedimentsinGreece (FlorouandKritidis,1992).Anelevatedlevelof cellsdisplaying chromosomeaberrations(3.8%)wasrecordedinpopulationsofthe amphipodcrustaceanMelitapalmata collectedfromtheseareas comparedwithcontrolsites(1.5–1.7%).Theauthor(Florouetal., 2004)attributedthis toincreasednatural doseratesof gamma andnaturalalphaemitters,whichwerealsoincreasedaboveback- ground levels in spring areas (14–26Bql−1 of 222Rn compared with 1.3–7Bql−1 in control areas). These dose values fall sig- nificantlybelow proposedenvironmentalprotectionbenchmark valuesprovidedbyanumberoforganisations(SeeTable2)sug- gestinginductionofsignificantbiologicaleffectsbelowdosesthat are consideredtohave nodeleteriouseffects at thepopulation level. However,thebiotainhabiting geothermalspringhabitats aretypicallyspecies-poorandsubjecttomultiplestressorsinclud- ingelevatedtemperaturesinwinterperiods(Flourouetal.,2004)
Table1
CollationofavailablechronicradiationeffectdataanddatagapswithinthesubphylumCrustacealocatedintheFREDERICARadiationEffectsDatabase.X=availabledata -=nodataavailable.ReproducedwithpermissionofCopplestoneetal.,(2008).
DoseRateRange(Gy/hr−1)
0–50 50–100 100–200 200–400 400–600 600–1000 1000–5000 5000–10,000 >10,000
Morbidity X X – – – X X X –
Mortality – – – – – – – – –
Mutation – – – – – – – – –
ReproductiveCapacity – – – – – – – – –
andextremesofpHandchemicaltoxicants(Dugganetal.,2007).
Thus,theobservedcytogeneticresponseinspringbiotamayhave beenduetothecomplexenvironmentalconditionspresentatthe studysitesasopposedtothedirecteffectsofionisingradiation.
Thishighlightstheinherentdifficultiesinfieldradioecologystud- ies(Salbu,2009)andtheimportanceofquantifyingtheindividual contributionofstressorsinenvironmentswhereabioticpressures mayactsynergistically(Dallasetal.,2012).Theaforementioned paperrepresentstheonlystudyofnaturalcrustaceanpopulations usingmutationasanendpoint.Thepreviouslydiscussedlimita- tionspresentdifficultiesindrawingconclusionsfromthisstudy asobserved cytogeneticeffects cannot bedirectlyattributedto ionisingradiation.
Laboratory studies assessing radiation-induced mutations in crustaceans typically involve acute high doses that are unrep- resentative of environmental exposures. Such studies have demonstratedtheabilityofionisingradiationtoinducechromo- somalaberrationsincrustaceanspecies.Tsytsugina(1998)exposed embryosoftwocrustaceanspecies,IdoteabalticaandGammarus oliviitodosesof0.5–5Gyfromarangeofradionuclidesandchem- icalmutagens (LeadAcetate andChlorophene) and scoredcells onthepresenceofchromosomal abnormalities.Themeannum- berofcellswithchromosomalaberrationsincreasedconcomitant withradiationdose.Furthermore,theauthordescribedcharacter- istictypesofaberrationsproducedbythetwotoxicantswhichmay beusedtodistinguishbetweentheeffectsofindividualstressors.
Forexample,ionisingradiationwasshowntoelicitchromosomal damageintheformofsingleandtwinfragments,whereas,sin- gle and twin bridges were more commonly observed in those embryosexposedtochemicaltoxicants.Thedistributionofaber- rationsbetweencells wasalsofoundtocorrespondtodifferent statisticaldistributionsdependentonthetoxicant,underpinning thepotentialofthismethod.However,thekaryotypeofcrustacean speciesisoftenreportedtobeunamenabletocytogeneticstudy (Salemaa,1985)duetothetypicallysmallsizeandhighdiploid numbersofchromosomes(White,1973).Thismayprecludeappli- cationofthismethodtonaturalpopulations.
Recentapproachestoassessingradiation-induced genotoxic- ityinaquaticinvertebrateshaveinvolvedmonitoringlevelsofthe expressionofgenesthatareinvolvedinDNAdamagerepairpath- ways(AlAmrietal.,2012;Hanetal.,2014a;Hanetal.,2014b;Won andLee,2014).Forexample,Hanetal.,(2014b)exposedcultures oftheintertidalcopepod,Tigriopusjaponicustogammaradiation from137CsandmonitoredmRNAexpressionofthreeDNArepair genes:Ku70(Xrcc6),Ku80(Xrcc5)andDNA-PK.Thesethreegenes areintegraltothenon-homologousendjoining(NHEJ)DNArepair pathwayinvolvedinthedetectionandrepairofradiation-induced doublestrandbreaks(DSBs)(Mahaneyetal.,2009).Expressionof thethreegeneswassignificantlyelevatedwithrespecttocontrols in200Gyexposedorganisms,suggestinginductionofDSBsatthese doselevels(Hanetal.,2014b).Thepotentialofthisapproachasa biomarkerforgenotoxicityincrustaceanspecieswasemphasised byWonandLee(2014)whoreportedadosedependentincreasein mRNAexpressionofthesegenesinanothercopepodspecies,Para- cyclopinanana(SeeFig.2).However,bothofthesestudiesuseddose
Fig.2.Dose-dependentincreaseinmRNAexpressionofthreegenesinvolvedinthe non-homologousendjoiningpathwayforDNArepairingammaradiationexposed culturesofthecopepod,Paracyclopinanana.Fig.2reproducedwithpermissionof Won&Lee(2014).
levelssignificantlyhigherthanthoseencounteredinradioactively contaminated environments (except perhaps in the immediate aftermathofamajornuclearaccident).Furthermore,intheformer study (Han et al., 2014b)gene expressionwas only monitored atdoselevelsof150and200Gy,despiteinductionofsignificant biologicalimpactssuchasareducedfecundityinT.japonicusat three-foldlowerdoselevels(50Gy).Alterationstogeneexpression patternsandmolecularlevelresponsesareoftenreportedtobesen- sitiveindicatorsofcontaminantexposureinaquaticinvertebrate species (Lee et al., 2006). A recent study supported the previ- ousstatement, reportingsignificantDNAalterations in Daphnia magnafollowingexposureto137Csdosesaslowas0.007mGyh−1 usingrandomamplifiedpolymorphicDNA-polymerasechainreac- tion(RAPD–PCR) methods(Parisotet al.,2015).Molecularlevel responseswereevidentatbothlowerdosesandshorterexposure durationsthanotherendpointsincludingmortality,morbidityand perturbationstoreproduction.Giventhesensitivityofmolecular endpointstoionisingradiationobservedinthispublication,itis imperativethata greaternumberofstudiesfocusonmolecular alterationsinrelationtoeffectsathigherlevelsofbiologicalorgani- sationtoconfirmthesefindingswithinthecrustaceansubphylum.
3. RadiationimpactsonmorbidityinCrustaceans
Morbiditycanbebroadlydefinedas“Alossoffunctionalcapac- itiesgenerallymanifestedasreducedfitness,whichmayrender organismslesscompetitiveandmoresusceptibletootherstressors, thusreducingtheirlifespan”(Copplestoneetal.,2008).Definition ofthetermmorbidityvariesbetweenauthorsandencompassesa vastnumberofendpointsincludingperturbationstogrowthrates, behaviouralalterationsandimmunesystemeffects(Copplestone etal.,2004).Inordertomaintainrelevancebothecologicallyand forenvironmentalprotection,anendpointshouldbeamenableto
N.Fulleretal./AquaticToxicology167(2015)55–6759 Table2
NumericalbenchmarkvaluesinGy/hr−1proposedbyanumberofdifferentorganisationsanddirectivesfortheprotectionofpopulationsofarangeofbiota.USDOE=UnitedStatesDepartmentofEnergy.NCRP=NationalCouncil onRadiationProtectionandMeasurements.IAEA=InternationalAtomicEnergyAgency.-=Nodataprovided.AdaptedfromAnderssonetal.,(2008).
DoseLevel(Gy/h−1)
USDOE(1990) NCRP(1990) IAEA(1992) Environment Canada(2003)
FASSET(2003) Larsson,(2004)
ERICA(2007) Beresfordetal.
(2007)
ICRP(2008) UNSCEAR(2008) PROTECT(2009) Andersson,(2008)
FreshwaterOrganisms 400 400 400 – 100 10 – 400 10
Algae – – – 100 – – – – –
Macrophytes – – – 100 – – – – –
BenthicInvertebrates – – – 200 – – – – –
Fish – – – 20 – – – – –
ReferenceTrout – – – – – – 40–400 – –
ReferenceFrog – – – – – – 4–40 – –
MarineOrganisms 400 400 – – 100 10 – 400 –
MarineMammals – – – – – – – – –
DeepOceanOrganisms – – 1000 – – 10 – – –
ReferenceCrab – – – – – – 400–4000 – –
ReferenceFlatfish – – – – – – 40–400 – –
ReferenceBrownSeaweed – – – – – 40–400 – –
TerrestrialOrganisms – – – 100 100 10 – 100 10
Plants – – 400 – – – – – –
ReferencePineTree – – – – – – 4–40 – –
ReferenceWildGrass – – – – – – 40–400 – –
Animals – – 40 – – – – – –
Invertebrates – – – 200 – – – – –
ReferenceBee – – – – – – 400–4000 – –
ReferenceEarthworm – – – – – – 400–4000 – –
Mammals – – – 100 – – – – –
ReferenceDeer – – – – – – 4–40 – –
ReferenceRat – – – – – – 4–40 – –
Birds – – – – – – 4–40 – –
ReferenceDuck – – – – – – 4–40 – –
Table3
SummaryofmorbiditystudiesinCrustacea.HTOrepresentsTritiatedWater.Acuteexposuresaredefinedhereasthoselastinglessthan24h,withchronicexposureslasting overaperiodoftheorganismslifespanandgreaterthan24h
Species DoseRate/Total Dose
LowestObserved EffectDose/Dose Rate(LOEDR)
RadiationSource ExposureDuration ExposureType Conclusion Reference
Pollicipespolymerus7.9,62.5nGy/hr−1, 0.625,6.25and 62.5Gy/hr−1
0.000625mGy/h−1 HTO 32Days Chronic Alteredmoulting
patterns
Abbott&Mix, (1979)
Daphniamagna 0.02,0.11and 0.99mGy/hr−1
0.11mGy/h−1 241Am 23Days Chronic Reductioninbody
mass,Increased respiratorydemand andReductionin offspringfitness
Alonzoetal., (2006)
Daphniamagna 0.3,1.5and 15mGy/hr−1
0.3mGy/h−1 241Am 70Days Chronic Increasedoxygen
consumption, Reductioninbodysize andmassacross generations
Alonzoetal., (2008a)
Artemiasalina 100,200,400and 800Gy
200Gy 6◦Co ∼30–220Minutes Acute Decreaseinrespiration rate
Angelovic&Engel (1968)
Callinectessapidus 40,80,160,320 and640Gy
40Gy 6◦Co ∼11–175Minutes Acute Behaviouralchanges;
reductioninirritability, catatonicstateathigh doses
Engel,(1967)
Daphniamagna 0.41,4.2and 31mGy/hr-1
31mGy/hr−1 137Cs 23Days Chronic Decreasein
mass-specific respirationrate, Reductioninoffspring fitness
Gilbinetal.,(2008)
Nephrops norvegicus
0.5and5Gy 0.5Gy 6◦Co <5Minutes Acute Morphological
aberrations;
deteriorationof cytoplasmand aberrationsin cytoplasmicorganelles
Mothersilletal., (2001)
Daphniamagna 0.007,0.07,0.65, 4.7and 35.4mGy/hr1
4.7mGy/hr−1 137Cs 75Days Chronic Reductionsinbody
lengthandVon Bertalanffygrowthrate
Parisotetal., (2015)
Palaemonetespugio
&Ucapugnax
9.75,19.5,48.75, 97.5,195and 390Gy
9.1Gy 6◦Co 0–20Minutes Acute Alterationstomoulting
patterns
Rees,(1962)
Pacifastacus leniusculus trowbridgii
2.8,5.6,8.4,11.2 and16.8Gy
5.6Gy X-Ray 1Minute Acute Behaviouralchanges;
detectionand avoidanceofradiation source
Rodriguez&
Kimeldorf(1976)
Macrobrachium rosenbergii
3,30,300and 3000mGy
3mGy 6◦Co ∼0–10Minutes Acute Behaviouralchanges;
alterationsto swimmingpatterns;
histologicalaberrations tothegill
Stalinetal.(2013a)
Macrobrachium rosenbergii
3,30,300and 3000mGy
3mGy 6◦Co ∼0–10Minutes Acute Morphological deformations, Decreased hepatosomaticindex
Stalinetal.(2013b)
measurement,specifictothehazardinquestionandappropriate forextrapolationtohigherlevelsofbiologicalorganisation(Ankley etal.,2010;Suter,1990).Thepracticalityofusingmorbidityasan endpointforradiationexposuremaythereforebelimitedduetothe lackofspecificityandmultitudeofeffectsitincludes.Thisisexem- plifiedwithinthecrustaceansubphylum,withadiversearrayof endpoints(SeeTable3forsummary)usedtoassessmorbidity.
3.1. Radiation-inducedimpactsongrowth&respiration
Alonzo et al., (2006, 2008a) investigated the effects of chronic internal exposure to the alpha emitting radionuclide,
241Americium,onthegrowth dynamicsof Daphniamagna. The authorsrecordedasignificantlylowerdrymassandbodylength ofirradiatedspecimensatdosesof∼1.5mGy/hr−1infirstgener- ationorganisms(F0),withsignificantincreasesintheseverityof effectsovergenerations.Forexample,individualsoftheF2genera- tiondisplayeda15%reductionindrymassatdosesof0.3mGy/hr−1
(Alonzo et al., 2008a). A recent study furtherunderpinned the potential of ionisingradiations to perturb growth dynamics in daphnids(Parisotetal.,2015),withreductionsof5and13 %in thegrowth rateof F2generation daphnidsexposed to 4.7 and 35.4mGy/hr−1ofgammaradiation,respectively.Experimentalevi- dencesuggeststhatlargerdaphnidshaveenhanced competitive and resourceexploitation abilityrelative tosmallerindividuals, leadingtoelevatedmortalityin thoseindividuals withreduced competitioncapacity(KreutzerandLampert,1999).Thefinding thatradionuclideexposuremayperturbgrowthdynamicsthere- forehasimportantimplicationsfornaturalcrustaceanpopulation dynamics.
Inthepreviousstudy(Alonzoetal.,2008a),oxygenconsump- tionofD.magnawaselevatedabovecontrolsatalldoses,suggesting anincreaseinmetabolicexpenditureinducedbyradiationstress.
Exposureoforganisms tostressorsand adverseconditionsmay resultinreallocationofmetabolicenergytowardsmaintenanceand leadtoreducedenergyinvestmentperoffspring(Baillieuletal.,
N.Fulleretal./AquaticToxicology167(2015)55–67 61
2005).Thiswasreflected by a reduced resistancetostarvation recordedinneonatesderivedfrom0.02mGy/hr−1 exposedadult daphnids(Alonzoetal.,2006).Itisofnotethatthisdoseratefalls belowthevalueof∼0.4mGy/hr−1providedbyanumberoforga- nisationsbelowwhichnodeleteriouspopulationleveleffectsare predictedtooccurinaquaticorganisms(SeeTable2)byanorderof magnitude.Arecentstudy(SarapultsevaandGorski,2013)further suggesteddeleteriousimpactsonneonatesrelatingtometabolic perturbations.Followingparentalexposuretoacutegammadoses of100and1000mGyfromCobalt-60,a∼20%decreaseinthemean lifespanofnon-exposedfirstgenerationD.magnaoffspringwas demonstrated.
Anotherstudyof Daphniamagnaexposed tochronicgamma irradiationfrom137Csreportedcontrastingresultstotheafore- mentioned study (Alonzo et al., 2008a) of decreased oxygen consumptionwithincreasingdose(Gilbinetal.,2008).D.magna receivinggammadoseratesof 31mGy/hr−1 displayeda signifi- cantlylowermass-specificrespirationrate,comparedwithdose ratesof0.3,1.5and15mGy/hr−1allelicitinganincreaseinrespira- tionratefollowingAmericium-241(analphaemitter)exposurein thestudyofAlonzoetal.,(2008a).Whilstthelownumberofrepli- cates(n=6)recognisedbytheauthorinthestudyofGilbinetal., (2008)maypreventcomparisonacrossstudies,thisunderpinsthe importanceofaccountingfordifferingradiationsourcesandthe correspondingvariabilityinrelativebiologicaleffectiveness(RBE).
ThetermRBEwascoinedin1931(FaillaandHenshaw,1931)to accountforthevariabilityinbiologicaleffectobservedwithdose, doserateandtypeofradiation(Valentin,2003).RBEincreasesas afunctionofLETwithhighlinearenergytransfer(LET)sourcesof radiation,e.g.,alphaemitters,typicallymoreeffectiveateliciting biologicaldamageinexperimentalsystemsthanlowLETradiation, i.e.,gammaandbetaraysreachingamaximumat∼100keV/m (HallandHei,2003;UNSCEAR,1996).Thismaybeusedtoaccount forthedifferentresponsesofD.magnainthesetwostudies.
Thevariabilityinbiologicaleffectrelatingtothegivenradiation sourceisexemplifiedbyastudyofmorbidityinthegoosebarnacle, Pollicipespolymerus,whichrecordedalteredmoultingpatternsat extremelylowbetadosesof0.62Gy/hr−1(AbbottandMix,1979).
Theradiationsourceemployedinthepreviousstudywastritiated water(HTO),aradionuclidethatisdischargedintogroundwater systemsfromnuclearoperations(Jaeschkeetal.,2011;Jhaetal., 2005).Despitetherelativelylowenergy emissionofbetaparti- clesfromHTO(average betaenergy of5.73±0.03keV(Pillinger et al.,1961), thenature and behaviourof this radiation source withinorganismshasledtosignificantconcernovertheRBEof theradionuclide(Bridges,2008;LittleandLambert,2008).Ithas beendemonstratedthatHTOmaybeirreversiblyincorporatedinto organiccompoundswithinorganisms(TakedaandKasida,1979) andthereforemayproducea biologicaleffectdisparatewithits emissioncharacteristics.Inaddition,theauthorsoftheaforemen- tionedstudyonPollicipespolymerus(AbbotandMix,1979)stated thatcalculateddoseswereexclusiveofbackgroundradiationwhich wasnotquantified.Thishighlightstheimportanceofrobustquan- tificationofreceiveddoseinradiobiologystudies(Pentreath,2009).
3.2. Theeffectsofionisingradiationonthebehaviour&
histopathologyofCrustaceanspecies
Ionisingradiationhasbeendemonstratedtoinducebehavioural changesinanumberofcrustaceanspeciesincludingcrabs(Engel, 1967), prawns (Stalin et al., 2013a) and crayfish (Rodriguez and Kimeldorf, 1976). Alterations to behavioural patterns are fundamental in environmental risk assessments since these perturbationsmayariseasanadaptivemechanismtochroniccon- taminantexposureandhavethepotentialtoalterspecies–species interactions(Dell’Omo,2002).Theavailableliteratureregarding
behaviouralimpactsofradiationinvolvesmostlyacuteexposures tohighdosesofradiation(Engel,1967;RodriguezandKimeldorf, 1976),withthemagnitudeofbehaviouralchangescorrelatingwith doselevels.Forexample,Engel(1967)assessedtheimpactofboth chronic and acuteradiation exposures onthebehaviour of the bluecrab,Callinectessapidus,ahighlyaggressiveandcannibalistic species(Bushmann,1999).AreductioninaggressivenessofCall- inectessapidusspecimenssubjecttosingleacuteirradiationswith
6◦Codosesfrom40to640Gywasobserved,whilsthigherdoses induceda catatonicstate.Continuousexposurestolowerdoses (0.72,1.64&6.53Gy/d−1)for70daysinducedcessationoffeed- ingandabnormalbehaviouralpatternsdeviatingfromthenormal pugnacious natureofC. sapidus,withtheextentofbehavioural effects relating to dose. Whilst the receiveddose remains sig- nificantly higher than estimates of the highest external doses infreshwatersystemsimmediatelyaftertheChernobylaccident ([4.2–8.3mGy/hr−1frombottomsediments]Kryshevetal.,2005), the findingthat prolongedexposures may perturb behavioural patterns has implications for contaminated areas where radia- tionlevels remainelevatedoverlong time scales.Furthermore, limited datasuggestsinduction of behaviouraleffects atlower, environmentallyrelevantdoses.Stalinetal.,(2013a)demonstrated behaviouralchangesincludingalterationstoswimmingpatterns inthegiantfreshwaterprawn,Macrobrachiumrosenbergiiatacute gammadosesof3mGy.
Fewstudieshaveconsideredtheimpactsofionisingradiation onmorphologicalandhistologicalparametersincrustaceans.Stalin etal.,(2013a,b)demonstratedinductionofhistologicalandmor- phologicalaberrationsincludingswollenandnecroticlamellaein the gill,deformations of the uropod, and discolouration of the abdomeninM.rosenbergiioveradoserangeof3–3000mGy(Stalin etal.,2013a),withthemagnitudeofeffectsrelatingtodose.Iwasaki (1973)adoptedahistologicalapproachtoassessgammaradiation- inducedeffectsinoogoniaandoocytesofthebrineshrimp,Artemia salina. A dose-dependent increase in cellulardeformations and thenumber ofpyknoticcells (celldegradationcharacterisedby chromatincondensation)wasrecordedoverahighdoserangeof 250–3000GyfromCobalt-60.Furthermore,Mothersilletal.,(2001) recordedperturbations tocytoplasmicorganellesinhematopoi- etic cultures of Nephrops norvegicus at gamma doses of 0.5Gy.
Deformationsincludedabnormalmitochondrial-roughendoplas- mic reticulum complexes at 0.5Gy, progressing to complete disintegration ofthecellular cytoplasmatdoses of 5Gy. Struc- turalperturbationstothegilllamellaeofcrustaceanshavebeen recorded in response toa number of toxicants (Li et al.,2007;
SaravanaBhavanandGeraldine,2000)andmayultimatelyimpair gillfunctioning(Tamseetal.,1995)leadingtoasphyxia.Future studiesshouldconsiderhistologicalimpactsonthecrustaceangill usingchronic,environmentallyrelevantradiationdosesinorder tocorroboratethisfinding.Adecreaseinthehepatosomaticindex ofM.rosenbergiiwasalsoobservedasaconsequenceofradiation exposure(Stalinetal.,2013b)whichmayprovidefurtherevidence thatradiationelicitsalterationstoenergybudgetssincechangesto theHSImayreflectmobilizationandutilizationofenergyreserves (Sánchez-Pazetal.,2007).
Behaviouralanalysisofcrustaceanspeciesexposedtoionising radiationhasreliedlargelyuponanecdotalvisualobservationsover adefinedtimeperiod(Stalinetal.,2013a).Thisapproachissub- jecttoanumberoflimitationsincludingalackofteststandards (Kaneetal.,2004),alowsensitivitycomparablewithvideo-based behaviouralanalysersandthepotentialfor individualbias.Fur- thermore, the available studies have employed acute radiation exposureswhichmayinducedifferentbehaviouraleffectstoequiv- alentdosesdeliveredoverlongertimescales(Solomonetal.,2009).
Futurestudies shouldcouple chronic,environmentally relevant exposuredurationswithahigh-throughputbehaviouraltracking
system.Suchsystemsminimisebiasbyprovidingsensitive,reliable recordingsofsmallanimalbehaviourundercontrolledconditions.
4. Theeffectofionisingradiationonreproductionin Crustaceans
Reproductive endpoints are frequently the subject of eco- toxicologicaland environmentalrisk assessments studies since perturbationstoreproductionmayimpactuponthelong-termsur- vivalofaspeciesandhencealterecosystemdynamics(Anderson andWild.,1994;Dallasetal.,2012).Alargenumberofpublica- tionshavefocusedonradiation-inducedeffects onreproductive parametersinaquaticinvertebrates,withthereporteddoselevel atwhichsignificanteffectsoccurvaryingbyatleasttwoorders of magnitude (Harrison and Anderson, 1996). This remarkable variabilityis exemplified withinthecrustaceansubphylum; for exampleAlonzoetal.,(2008a,b) recordedadelayedbroodpro- ductioninD.magnaexposedto15mGy/hr−1overa23dayperiod (totaldoseof0.345Gy),however10Gywasneededtoelicitadelay in thereproduction ofthe marinecopepod, Paracyclopinanana (WonandLee,2014).Differencesintheexposureduration,spe- cificradionuclideandendpointemployedprecludedevelopment ofageneralised‘doselimit’forreproductiveeffectsincrustacean species.Oneofthepriorityareasforfutureresearchinradioecol- ogyisassessingtheconsequencesofmultigenerationalradiation exposure.ThiswasidentifiedintheresearchagendaoftheStrat- egyforAlliedRadioecology(STAR)group(Hintonetal.,2013)on thebasisthatexposuresacrossgenerationshavelongbeenafocus inhumanradiobiologyandepidemiologystudies(Dubrovaetal., 2000;Koturbashetal.,2006;Nomura,1988),butcomparatively ignoredinnon-humanbiota.Radiation-inducedperturbationsto reproductiveparameters maybeparticularlyrelevant in multi- generational exposure scenarios, since such perturbations may alterpopulationdynamicsandthesubsequentabilityofoffspring toadapttoenvironmentalstressors(Alonzoetal.,2008b;Lynch, 1989,1992).
Theavailableliteraturewithinthecrustaceansubphylumsug- geststhepresence of effects overmultiple generations (Alonzo et al., 2008a;Plaire et al., 2013; Massarin et al., 2010; Parisot etal.,2015;SarapultsevaandGorski,2013).Alonzoetal.,(2008a) and Massarinet al.,(2010) recordedan increase in themagni- tudeofdeleteriouseffects acrossgenerations inDaphniamagna exposedtochronicalphairradiationandchronicwaterborneura- niumexposure,respectively, withsevereimpactstofitnessand reproductioninindividualsoftheF2 generation.Incontrast,the multigenerationalstudyofParisotetal.,(2015)reportedadegree ofrecoveryinF1generationdaphnidsandareducedradiosensi- tivityrelative totheparentalgenerationacrossboth lethaland sub-lethalendpoints(mortalityandfecundity,respectively).Differ- entialradiosensitivitybetweendevelopmentallifestageshasbeen widelyrecordedwithinthecrustaceansubphylum,demonstrated incopepods(Bardilletal.,1977)andArtemiaspecies(Metallietal., 1961).Theauthors(Parisotetal.,2015)hypothesisedthatacumu- lative radiation dose may be necessary to elicit compensatory mechanisms such as DNA repair, accounting for the differen- tialradiosensitivitybetweengenerations.Studiesofradionuclide exposeddaphnidsusingRAPD–PCRmethodshaveindicatedtrans- missionofDNAdamagefromadultfemaledaphnidstoprogeny acrossgenerations(Parisotetal.,2015;Plaireetal.,2013).Thismay bemediatedbyanepigeneticmechanism,ashasbeenproposed forthetransmissionofeffectsinD.magnaexposedtoarangeof chemicaltoxicants(Vandegehuchteetal.,2010)causingalterations togeneexpressionacrossgenerations.Furthermolecularstudies arenecessarytoelucidatethismechanism.Giventheincreasein magnitudeofreprotoxicandtheassociateddeleteriouseffectson
populationdynamics(Alonzoetal.,2008a,2008b)observedover generations,itisimperativethatfuturestudiescontinuetoadopt amultigenerationalapproachasstudiesderivedfromsinglegen- erationexposuresmayunderestimaterisk(Massarinetal.,2010).
Studieswithinthe crustaceansubphylumareheavilybiased towardfemalereproductivesuccess,withtypicalendpointsinclud- ingproductionofneweggs(WonandLee,2014),hatchabilityof eggs(Iwasaki,1964;Sellarsetal.,2005)eggmass(Alonzoetal., 2006, 2008a) and time of hatching (Gilbin et al., 2008). Com- paratively,radiation-induced effectsonmalefertilityhavebeen ignored.Totheauthor’sknowledgenostudyhasdirectlyrecorded theimpactsofionisingradiationonmalefertility.Spermarecon- sideredsensitivetotheinfluenceofxenobioticstressorsincluding ionisingradiation(Fischbeinetal.,1997;LewisandFord,2012;
Marquesetal.,2014).Thisisattributedtotheirlackofinherent defencesystemssuchasantioxidantenzymesandDNArepaircom- parablewithotherbiologicalsystems(Trappetal.,2014).Anumber ofstudieshaveconfirmedthesensitivityofspermtoanthropogenic radionuclides.FollowingtheChernobylcatastrophe an elevated incidenceofspermmorphologicalabnormalitiesandperturbations tospermatogenesiswasobservedinliquidatorsexposedtodoses ofupto0.25Gy(Cheburakov andCheburakova,1992;Fischbein etal.,1997).Furthermorelaboratorystudiesofplaice,Pleuronectes platessa,have demonstrated thatchronicexposures toenviron- mentallyrelevantlowdosesofgammaradiation(0.24mGy/hr−1) aresufficienttocauseasignificantreductioninspermnumberin theseorganisms(Knowles,1999).Experimentalevidenceinaquatic invertebrateshassuggestedthatreductionsinspermnumbersmay havesubsequenteffectsathigherlevelsofbiologicalorganisation.
Thisisexemplified byDunn etal.,(2006),who recordeda 55%
reductioninthesizeoffreshwateramphipod(Gammarusduebeni) broodsaftermatingwithmalesdisplayingaspermcountreduction of56%(LewisandFord,2012).Couplingtheecologicalrelevance ofperturbationstospermparameterswiththeknownsensitivity ofsperm,itisimperativethatfuturestudieswithintheCrustacea includetheseendpointswithinradiobiologicalstudies.
5. Radiation-inducedmortalityinCrustaceans
Despitetherecenttrendtowardsstudiesusingchronicexpo- suresofsub-lethaldoses,theavailableliteratureofradiationeffects incrustaceansremainsdominatedbymortalitystudies.Thisdata isoftenusedtocalculatelethaldose(LD50)values(Dallasetal., 2012)inordertoderivehierarchiesofradiosensitivityacrosstax- onomic groups (Blaylock et al., 1996; Harrison and Anderson, 1996).LD50valuesaretraditionallyusedinecotoxicologicalstud- iestodeterminetheecologicalrisktospecies(Starketal.,2004) andhavealsobeenemployedinordertodeterminenoobserved effectconcentration(NOEC)values(Garnier-Laplaceetal.,2006) toinformradioprotectionandregulatoryefforts.However,many studieshavehighlightedthegreatersensitivityandecologicalrel- evanceofreproductiveendpointsinradiationstudiescompared withmeasurementsofadultmortality(Garnier-Laplaceetal.,2006;
Jonesetal.,2003;UNSCEAR,2008).Thiswasfurtheremphasised byAlonzoetal.,(2008b)whofoundthatanincreaseinindividual mortalityhadareducedeffectonD.magnapopulationgrowthrel- ativetoperturbationstotworeproductivebiomarkers(SeeFig.3).
Incontrast,Starketal.,(2004)recordedthatwithinsomespecies stress-inducedindividualmortalityhadagreatereffectonintrinsic populationincreasethanperturbationstoreproductivecapacity.
Mortalityhasthepotentialtoaltertheagedistribution,deathrate anddensity ofapopulation(UNSCEAR,2008).Furthermore,the derivationofLD50valuesisnecessarytoelucidateagivenspecies sensitivitytoradiationandtodetermineappropriatedoselevelsto employinlaboratoryradiobiologystudies.Thisservestoreiterate
N.Fulleretal./AquaticToxicology167(2015)55–67 63
Fig.3.PredicteddelayinpopulationgrowthrelativetogenerationtimeinDaphniamagnapopulationsexposedtoalpharadiationdeterminedusingsinglegenerationmodels.
Theeffectsofincreasedmortality,fecundityreductionsanddelaysinreproductiveprocessesattheendpointlevelaremodelled.ReproducedwithpermissionofAlonzoetal., (2008b).
theimportanceofincludinganumberofendpointsinradioecol- ogystudiesandthatinsomecasesderivationoflethaldosedata remainsrelevant.
Withinthecrustaceansubphylum,thedoseatwhichmortality occursdisplaysremarkablevariability(Dallasetal.,2012).Recent workusingtheharpacticoidcopepodTigriopusjaponicusdemon- stratedtoleranceofexternalgammaradiationdosesofupto600Gy, withmortalityonlyoccurring5daysaftercessationofexposure (Hanetal.,2014).Thisiswithinthesameorderofmagnitudeas somebacteriaandprotozoanspecies,groupsconsideredamongst themostradioresistantorganisms(Copplestoneetal.,2001).Fur- thermore,uponirradiationofdryeggmasses,Iwasakietal.,(1971) demonstratedextremeradioresistanceinArtemiasalinanaupliiof upto2780Gyonedayafterhatching.However,Artemiacystsdis- playremarkableresistancetoarangeofstressors(MacRae,2003) attributedtotheirgreatlyreducedmetabolicanddevelopmental activitypriortohatchingandtherefore arenotconsideredrep- resentativeofothercrustaceanspecies.Conversely,Rees(1962) reporteda30dayLD50of∼15Gyinthegrassshrimp,Palaemon- etes pugiowhichis withintheupperbounds ofradiosensitivity of some mammalian species (Blaylock et al., 1996). There are manyproblemsassociatedwithusinglethaldosedatatocompare radiosensitivityacrossorganisms.Forexample,thereisalackof standardisationofthedurationusedtocalculatelethaldosedata varyingfrom4days(Hanetal.,2014)to40days(Engel,1973)which maygreatlyinfluencethefinalvalue.Forchemicaltoxicants,this parameterhasbeenstandardisedinpublishedguidelinesfortests usingDaphniaspecies(OECD,2004),enablingdirectcomparisons ofLD50valuesacrossstressors.Radiobiologicalstudieswouldben- efitfromadoptingasimilarapproachinordertoaidcomparative ability.
Comparatively,theeffectsofchronicradiationdosesonmor- talityincrustaceanshavebeenunderrepresented.Marshall(1966) exposed25populationsofDaphniapulextoexternalgammaradia- tionovera55weekperiodfor18.5hadaywithdosesrangingfrom 0to∼5.1Gy/d−1.Atthethree highestdoselevels(∼5.1Gy/d−1,
∼4.8Gy/d−1 and∼4.36Gy/d−1)populationscrashedandbecame extinct,whichtheauthorattributedtoanincreaseinindividual deathrateapproachingtheupper limitof thesustainablebirth rate.Othermonitoredparameters suchasthe% ofaborted eggs andembryoswereshowntoincreaseatdoselevelsbelowthose leadingtoextinction,reiteratingthegreatersensitivityofrepro- ductiveendpointscomparabletomortality.Parisotetal.,(2015) corroboratedthesefindings,reportingaslightbutnon-statistically significantincreaseinmortalityin137CsexposedD.magnaatadose
rateof35.4mGy/h−1,withsub-lethalimpactsoccurringatmuch lowerdoseratesof0.007mGyh−1.Engel(1967)exposedbluecrabs, Callinectessapidus,toacutedoses(maxiumof180minexposure)of gammaradiationfrom6◦Cooveratotaldoserangeof40–640Gy atadoserateof219Gy/hr−1.Theauthoralsocontinuallyexposed C.sapidustodoseratesof0.032,0.073and0.29Gy/hr−1overa70 dayperiod.Followingacuteexposurea30-dayLD50of510Gywas recorded.Incontrast,crabssubjectedtoatotalaccumulateddose of∼460Gyatthedoserateof0.29Gy/h−1 overa70dayperiod displayed100% mortality.Althoughthedifferencein total dose precludesusefulcomparison,thegreatersensitivityofC.sapidus followingcontinuousexposureunderpinstheimportanceofthe exposuredurationindeterminingbiologicalimpactinradiobiology studies.Doseratehasbeenreportedtobeanimportantfactorin determiningbiologicaleffectsacrossarangeoforganismsinclud- inginsects(Russelletal.,1958),humans(Elmoreetal.,2006)and rodents(Russelletal.,1959).Forexample,Shimadaetal.,(2005) demonstratedadoseratedependencyoftransgenerationalmuta- tionfrequenciesinspermatogonialstemcellsofMedaka,Oryzias latipes.Theauthorsexposedmalemedakatoan80TBq137Cssource atdoseratesof3Gy/minand9500Gy/min,andrecordedalower mutationfrequencyateachtotaldose(1.9,3.2and4.75Gy)inthe 3Gy/mingroup.
6. Conclusions
Despite numerous international directives and decades of researchintothebiological effects ofradiation,significantgaps inourknowledgestillremain.Althoughcurrentresearchtrends indicateanincreaseinthenumberofpublicationsusingenviron- mentallyrelevant radiationsourcesand durations(Dallasetal., 2012), asignificantdisparitybetweenthenumberof acuteand chronicstudiespersists.ThisisexemplifiedwithintheFREDER- ICAradiationeffectsdatabase.Withinthisdatabase,64%ofthedata pointswereobtainedfollowingacuteradiationexposures,with36%
following chronicexposures.Furthermore,theavailable chronic dataisheavilybiasedtowardsfish,mammalsandterrestrialplants withascarcityofdataevidentinthecrustaceansubphylum(See Table1(Copplestoneetal.,2008).Anothermajorlimitationisthe discrepancybetweentheavailabledataforlaboratorytoxicitytests comparablewithfieldstudies.Themajorityoffielddataisheavily biasedtowardssmallmammals(Bakeretal.,1996;Beresfordetal., 2008;Chesseretal.,2000),fish(Dallasetal.,1998;Jonssonetal., 1999; Sugg etal., 1996Jonssonet al., 1999;Sugg et al.,1996), plants (Kovalchuket al., 1998, 2000; Syomovet al., 1992)and
Fig.4.Summationoftheavailablechroniceffectdatawithinthecrustaceansubphylumacrossfourendpoints;mortality,morbidity,reproductionandmutation.Thelowest observedeffectdoserate(mGy/h−1)isusedonalogarithmicscale.ThebandofdoseratesselectedbytheICRP(2008)DCRLforthereferencecrabisindicatedby.
birds(Bonisoli-Alquatietal.,2010;Galvánetal.,2014;Hermosell etal.,2013).Comparatively,themajorityoffieldstudiesregarding crustaceancommunitiesexposedtoradionuclidesarefocusedon bioaccumulationofradioactivematerials (Marzano etal., 2000) relatingtotrophic transfer,or calculatingestimates ofreceived doses(Murphyetal.,2011;Batlleetal.,2014).
A summary of the available chronic effect data and the corresponding lowest observed effect dose rate (LOEDR) in crustacean species is shown displayed in Fig. 4. From the limited available data, a tentative hierarchy of radiosensi- tivity in the four endpoints can be derived as follows:
mutation>reproduction>morbidity>mortality.Whilstitmustbe reiteratedthatthisisbasedonextremelylimiteddata(twodata pointsformutation,seeFig.4),thismaychallengetheassump- tionthatreproductionisthemostsensitiveendpointofradiation exposureinnon-humanbiota(UNSCEAR,2008).Responsesatthe molecularlevel,i.e.,alterationstogeneexpression,arefrequently recordedtobesensitiveindicatorsoftoxicantexposureacrossa rangeof organisms(See Section2).Although recentcrustacean radiobiology studieshave demonstrated a shift towardsuse of molecularlevelendpoints(SeeSection2(Hanetal.,2014b;Parisot etal.,2015;WonandLee,2014)),theuseof‘ecotoxicogenomics’
(theintegrationofgenomictechniquesinresponsetoenvironmen- taltoxicantexposure(Iguchietal.,2007))hasbeenafocusofstudies ofothertoxicantsIEendocrinedisruptorsforalmostadecade(Seo etal.,2006).Theobservedsensitivityofmutationasanendpoint observedinthispaperhighlightstheneedtoexploittheadventof cheaperandmoreaccessiblemolecularanalysesinordertovali- datetheusefulnessofmutationasanendpointandevaluatethe potentialofthesetechniquesastoolsinenvironmentalradiopro- tectionandradioecology.Itisimportanttonotethatestablishing linkagesbetweengeneexpressionanalysesandendpointsofhigher levelsofbiologicalorganisationsuchasreproduction,survivaland developmentremainsasignificantchallengeinapplyingecotox-
icogenomicstoecologicalriskassessments(Miracleand Ankley, 2005).Furthermore, transcriptional changes do not necessarily elicitabiologicaleffectwithinagivenorganism(Schirmeretal., 2010).Whilstthisapproachoffershugepotential,untilclearexper- imentallinkscanbedrawnbetweenalterationstogeneexpression patterns and effects at higher levels of biological organisation, monitoringendpoints withclearecologicalimplicationssuchas reproduction,developmentandgrowthremainsimportant.
Inconclusion, thisreviewhassummarized theavailablehis- toricandcurrentliteraturepertainingtoradiation-inducedeffects inanecologicallyrelevantandmodelsubphylum.Sucheffectsare observedoverawiderangeofdoseratesandexposuresources, and could conceivably have ecological consequences for biota chronicallyexposedtoelevatedlevelsofradionuclides.Atpresent howeverthereislimitedpopulationleveldataforaquaticorga- nismsinhabitingchronicallycontaminatedareas.Indeed,astudy oftheabundanceanddiversityofmacroinvertebratecommunities ateightChernobylaffectedlakes(Murphyetal.,2011)foundno evidenceofradionuclidecontaminationimpactingtheecological statusofthewaterbody,andrecordedthehighesttaxonrichness atthemostcontaminatedlake(estimatedtotalexternaldosesof 30.7Gy/hr).Clearly,furtherstudiesathigherlevelsofbiological organisationarenecessarytoelucidatethepotentialecologicalcon- sequencesoftheeffectsoutlinedinthisreview.Finally,thisreview hashighlightedthepersistentpaucity ofdataacrosscommonly usedendpointsinthecrustaceansubphylumand identifiedkey gapsintheliteraturetoenhanceresearchwithinthefield.These datagapsmustbeaddressedinordertoenhancetheefficacyofthe subphylumCrustaceaasareferencepointfortheoptimisationand developmentofenvironmentalradioprotectionframeworks.
Conflictofinterest
Theauthorsdeclarenoconflictofinterest.