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EffectofDissolvedOrganicCarbononSorptionofPyrethroidstoSediments L.DELGADO-MORENO,*L.WU,ANDJ.GAN (DepartmentofEnvironmentalSciences,UniversityofCalifornia,Riverside,California92521ReceivedNovember6,2009.RevisedmanuscriptreceivedSeptember20,2010.AcceptedOctober1,2010.) Abstract:Despitetheirstronghydrophobicity,recentstudiesshowedwidespreadoccurrenceofpyrethroidindownstreamsurfacewatersbodies.somepyrethroidshavethepotentialtobioaccumulateorexerttoxiceffectsonaquaticwildlife.PyrethroidsareextremelyhydrophobicwithlogKocfrom5.1to6.0.Thestrongsorptiontothebedsedimentshouldrenderthesechemicalslessmobileafterapplication.however,nostudyhasquantitativelyexaminedtheeffectofDOConsorptionanddesorptionofpyrethroidsandlittleisknownabouttheinfluenceoffactorssuchassourcesofDOCandpreinteractionsbetweenDOCandpyrethroids.thustheobjectivesofthisstudyweretoevaluatetheeffectofDOCofdifferentoriginsonthepartitionofpyrethroidsbetweensedimentandwaterandtounderstandtheinfluencesofpreinteractionsandpropertiesofDOCsolutions.TheresultsfromthisstudymaybeusedtoimprovepredictionofHOCtransportviaprocessessuchasrunoffbyprovidingenvironmentallyrelevantKdvalues. Inthiswork,SolutionsofDOCwerepreparedfromthreesources:(a)theupperlayer(0-25cm)ofacitrusorchardsoil(DOCs).(b)acommercialpottingmix(DOCp)consistingofamixtureofcompostedforestproducts,compostedorganicmatter,pumice,sphagnumpeatmoss,sand,anddolomitelime(pHstabilizer);(c)ayardwastecompostproduct(DOCc).Sorptionofpyrethroidstosedimentwasdeterminedusingtwomethods.Anddesorptionofpyrethroidsfromthesedimentwasmeasuredusingsamplesofthehighestconcentrationfollowingthesorptionexperiment. PresenceofDOCfromthreesourcesat38(2mgL-1intheaqueousphasedecreasedpesticidesorptiontoasedimentby1.7to38.9timesandincreasedtheirdesorptionby1.2to41.4times.Theeffectonpyrethroidsorptiontothesedimentwaslinear.Inaddition,interactionsbetweenDOCandpyrethroids,whentakingplacepriortothecontactwithsediment,decreasedsorptionofsomepyrethroidsevenfurther,implyingthatDOC-pyrethroidcompl