OECD GUIDELINES FOR THE TESTING OF CHEMICALS.docx

OECD GUIDELINES FOR THE TESTING OF CHEMICALS.docx

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OECDGUIDELINESFORTHETESTINGOFCHEMICALS

PROPOSALFORANEWGUIDELINE

BioaccumulationinSediment-dwellingBenthicOligochaetes

INTRODUCTION

Sediment-ingestingendobenthicanimalsmaybeexposedtosedimentboundsubstances

（1）.Amongthesesediment-ingesters,aquaticoligochaetesplayanimportantroleinthebottomsoftheaquaticsystems.Theyliveinthesedimentandoftenrepresentthemostabundantspeciesespeciallyinhabitatswithenvironmentalconditionsadversetootheranimals.Bybioturbationofthesedimentandbyservingaspreytheseanimalscanhaveastronginfluenceonthebioavailabilityofsuchsubstancestootherorganisms,e.g.benthivorousfish.Incontrasttoepibenthicorganisms,endobenthicaquaticoligochaetesburrowinthesediment,andingestsedimentparticlesbelowthesedimentsurface.Becauseofthat,theseorganismsareexposedtochemicalsviamanyuptakeroutesincludingdirectcontact,ingestionofcontaminatedsedimentparticles,porewaterandoverlyingwater.SomespeciesofbenthicoligochaetesthatarecurrentlyusedinecotoxicologicaltestingaredescribedinAnnex6.

Theparameterswhichcharacterisethebioaccumulationofasubstanceincludefirstofallthebioaccumulationfactor（BAF）,thesedimentuptakerateconstant（ks）andtheeliminationrateconstant（ke）.DetaileddefinitionsoftheseparametersareprovidedinAnnex1.

Toassessthebioaccumulationpotentialofchemicalsingeneral,andtoinvestigatethebioaccumulationofsubstanceswhichtendtopartitionintoorontothesediments,acompartment-specifictestmethodisneeded

（1）

（2）（3）（4）.

ThisTestGuidelineisdesignedtoassessbioaccumulationofsediment-associatedchemicalsinendobenthicoligochaeteworms.Thetestsubstanceisspikedintothesediment.Usingspikedsedimentisintendedtosimulateacontaminatedsediment.

Thisguidelineisbasedonexistingsedimenttoxicityandbioaccumulationtestmethods

（1）（4）（5）（7）（8）（9）（10）.Otherusefuldocumentsare:

thediscussionsandresultsofaninternationalworkshop（12）,andtheoutcomeofaninternationalringtest（62）.

Thistestappliestostable,neutralorganicchemicals,whichtendtoassociatewithsediments.Bioaccumulationofsediment-associated,stablemetallo-organiccompoundscanalsobemeasuredwiththismethod（13）.Itisnotapplicabletometalsandothertraceelements（12）.

PREREQUISITEANDINFORMATIONONTESTSUBSTANCE

ThereareonlyafewwellestablishedQuantitativeStructure-ActivityRelationships（QSAR）concerningbioaccumulationprocessespresentlyavailable（14）.Themostwidelyusedrelationshipisthecorrelationbetweenthebioaccumulationandbioconcentrationofstableorganicsubstances（expressedaslogKow;seeAnnex1fordefinition）andtheirlipophilicity,respectively,whichhasbeendevelopedforthedescriptionofasubstancepartitioningbetweenwaterandfish.Correlationsforthesedimentcompartmenthavealsobeenestablishedusingthisrelationship（15）（16）（17）（18）.ThelogKow-logBCFcorrelationasamajorQSARmaybehelpfulforafirstpreliminaryestimationofthebioaccumulationpotentialofsediment-associatedchemicals.However,theBAFmaybeinfluencedbylipidcontentofthetestorganismandtheorganiccarboncontentofthesediment.ThereforetheKocisamajordeterminantofthebioaccumulationofsediment-associatedorganiccompounds.

Thistestisapplicableto:

-stable,organicsubstanceshavinglogKowvaluesbetween3.0and6.0（5）（19）;

-superlipophilicsubstancesthatshowalogKowofmorethan6.0（5）;

-substanceswhichbelongtoaclassoforganicsubstancesknownfortheirbioaccumulationpotentialinlivingorganisms,e.g.surfactantsorhighlyadsorptivesubstances

Informationonthetestsubstancesuchassafetyprecautions,properstorageconditionsandanalyticalmethodsshouldbeobtainedbeforebeginningthestudy.Guidancefortestingsubstanceswithphysical-chemicalpropertiesthatmakethemdifficulttotestisprovidedin（21）.Beforecarryingoutatestforbioaccumulationwithaquaticoligochaetes,thefollowinginformationaboutthetestcompoundshouldbeknownwhenavailable:

-commonname,chemicalname（preferablyIUPACname）,structuralformula,CASregistrynumber,purity;

-solubilityinwater[Guideline105;（22）];

-octanol-waterpartitioncoefficient,Kow[Guidelines107,117;（22）];

-sediment-waterpartitioncoefficient,expressedasKoc[Guideline121（22）];

-hydrolysis[Guideline111;（22）];

-phototransformationinwater[（23）];

-vapourpressure[Guideline104;（22）];

-Henry'slawconstant;

-readybiodegradability[Guidelines301AtoF;（22）];

-biodegradationintheaquaticenvironment（Guidelines308and309;（22））

-surfacetension[Guideline115;（22）];

-criticalmicellesconcentration（24）.

Radiolabelledtestsubstancescanfacilitatetheanalysisofwater,sedimentandbiologicalsamples,andmaybeusedtodeterminewhethermetabolitesidentificationandquantificationshouldbemade.Themethoddescribedherewasvalidatedinaninternationalringtest（62）for14C-labelledcompounds.Iftotalradioactiveresiduesaremeasuredthebioaccumulationfactor（BAF）isbasedontheparentcompoundincludinganyretainedmetabolites.Itisalsopossibletocombineametabolismstudywithabioaccumulationstudybyanalysisandquantificationofthepercentageofparentcompoundanditsmetabolitesinsamplestakenattheendoftheuptakephaseoratthepeaklevelofbioaccumulation.Inanycase,itisrecommendedthatBAFcalculationbebasedontheconcentrationoftheparentcompoundintheorganismsandnotonlyontotalradioactiveresidues.

Inadditiontothepropertiesofthetestsubstance,otherinformationrequiredisthetoxicitytotheoligochaetesspeciestobeusedinthetest,preferablyanLC50forthetimenecessaryfortheuptakephase.Preferenceshouldbegiventotoxicityvaluesderivedfromlong-termstudiesonsublethalendpoints.Ifsuchdataarenotavailable,anacutetoxicitytestunderconditionsidenticalwiththebioaccumulationtestconditionsmayprovideusefulinformation.

Anappropriateanalyticalmethodofknownaccuracy,precision,andsensitivityforthequantificationofthesubstanceinthetestsolutions,inthesediment,andinthebiologicalmaterialmustbeavailable,togetherwithdetailsofsamplepreparationandstorageaswellasmaterialsafetydatasheets.Analyticaldetectionlimitsofthetestsubstanceinwater,sediment,andwormtissueshouldalsobeknown.Ifa14C-labelledtestsubstanceisused,thespecificradioactivity（i.e.Bqmol-1）andthepercentageofradioactivityassociatedwithimpuritiesmustalsobeknown.Thespecificradioactivityofthetestcompoundshouldbeashighaspossibleinordertodetecttestconcentrationsaslowaspossible（12）.

Informationoncharacteristicsofthesedimenttobeused（e.g.originofsedimentoritsconstituents,pHandammoniaconcentrationoftheporewater（fieldsediments）,organiccarboncontent（TOC）,particlesizedistribution（percentsand,silt,andclay）,andpercentdryweight）shouldbeavailable（7）.

PRINCIPLEOFTHETEST

Thetestconsistsoftwophases;theuptake（exposure）phaseandtheelimination（post-exposure）phase.Duringtheuptakephase,wormsareexposedtosedimentspikedwiththetestsubstance,toppedwithreconstitutedwaterandequilibratedasappropriate（12）.Groupsofcontrolwormsareheldunderidenticalconditionswithoutthetestsubstance.

Fortheeliminationphasethewormsaretransferredtoasediment-water-systemfreeoftestsubstance.Aneliminationphaseisnecessarytogaininformationontherateatwhichthetestsubstanceisexcretedbythetestorganisms（19）（20）.Aneliminationphaseisalwaysrequiredunlessuptakeofthetestsubstanceduringtheexposurephasehasbeeninsignificant（e.g.thereisnostatisticaldifferencebetweentheconcentrationofthetestsubstanceintestandcontrolworms）.Ifasteadystatehasnotbeenreachedduringtheuptakephase,determinationofthekinetics–BAFk,uptakeandeliminationrateconstant（s）–maybedoneusingtheresultsoftheeliminationphase.Changeoftheconcentrationofthetestsubstancein/onthewormsismonitoredthroughoutbothphasesofthetest.

Duringtheuptakephase,measurementsaremadeuntilBAFhasreachedaplateauorsteadystate.Bydefault,thedurationoftheuptakephaseshouldbe28days.Practicalexperiencehasshownthata12to14-dayuptakephaseissufficientforseveralstable,neutralorganicsubstancestoreachsteady-state（7）（9）（10）.

However,ifthesteadystateisnotreachedwithin28d,theeliminationphaseisstartedbytransferringexposedoligochaetestovesselscontainingthesamemediumwithoutthetestsubstance.Theeliminationphaseisterminatedwheneitherthe10%levelofsteadystateconcentrationoroftheconcentrationmeasuredinthewormsonday28oftheuptakephaseisreached,orafteramaximumdurationof10d.Theresiduelevelinthewormsattheendoftheeliminationphaseisreportedasendpoint,e.g.asNon-eliminatedresidues（NER）.Thebioaccumulationfactor（BAFss）iscalculatedpreferablybothastheratioofconcentrationinworms（Ca）andinthesediment（Cs）atapparentsteadystate,andasakineticbioaccumulationfactor,BAFKastheratiooftherateconstantofuptakefromsediment（ks）andtheeliminationrateconstant（ke）assumingfirst-orderkinetics.Ifasteadystateisnotreachedwithin28days,calculateBAFKfromtheuptakerateandeliminationrateconstant（s）.ForcalculationseeAnnex2.Iffirst-orderkineticsarenotapplicable,morecomplexmodelsshouldbeemployed（Annex2andreference（26））.

Ifasteadystateisnotachievedwithin28days,theuptakephase