UseofEthylcelluloseToControlChlorsulfuron
LeachinginaCalcareousSoil
´´FRANCISCOFLORES-CESPEDES,ISABELDAZA-FERNANDEZ,´´*´MATILDEVILLAFRANCA-SANCHEZ,ANDMANUELFERNANDEZ-PEREZ
DepartamentodeQuı´micaFı´sica,Bioquı´micayQuı´micaInorga´nica,UniversidaddeAlmerı´a,
LaCan˜adadeSanUrbanos/n,04120Almerı´a,Spain
Downloaded by SHANGHAI NORMAL UNIV LIB on September 9, 2009 | http://pubs.acs.org Publication Date (Web): March 3, 2009 | doi: 10.1021/jf9004093Controlledreleaseformulations(CRFs)havebeenresearchedtoreducethewater-pollutingriskderivedfromtheuseofconventionalformulationsofchlorsulfuron.CoatedchlorsulfurongranuleswereproducedinaWuster-typefluidized-bedequipmentusingtwodifferentamountsofethylcellulose.Thehighestonewasmodifiedbytheadditionofaplasticizersuchasdibutylsebacate.Theencapsulationefficiencyandmorphologicalpropertiesofcoatedgranuleshavingbeenstudied,thechlorsulfuronkineticreleaseinwaterwasstudied.Inaddition,themobilityofchlorsulfuroninacalcareoussoilwasfinallycarriedout.Highencapsulationefficiencywasobtained,beingnearly100%inallcases.SEMpicturesshowahomogeneousfilmincoatedCRFs;thicknessoscillatesbetween23.32µmforthesystempreparedwitha10%ofethylcelluloseand32.61µmforthesystempreparedwitha20%ethylcelluloseplusplasticizer.TherateofchlorsulfuronreleasefromcoatedCRFsisdiminishedinallcasesinrelationtochlorsulfuroncommercialformulation,thelatterbeingcompletelydissolvedin<1h,butittookatleast50daystorelease90%ofchlorsulfuronfromtheformulationcoatedwitha20%ethylcelluloseplusplasticizer.Usingagenericequation,thetimetakenfor50%oftheactiveingredienttobereleasedintowater(t50)wascalculated.Fromtheanalysisofthet50values,itcanbededucedthatthereleaserateofchlorsulfuroncanbemainlycontrolledbychangingthethicknessofthecoatingfilm,bymodifyingthesurfacepropertiesofthecoatingfilm,andbyaddingaplasticizer.MobilityexperimentscarriedoutincalcareoussoilshowthattheuseofcoatedCRFsreducesthepresenceofchlorsulfuronintheleachatecomparedtocommercialformulation.
KEYWORDS:Chlorsulfuron;ethylcellulose;controlledrelease;fluidizedbed;coating
INTRODUCTION
Chlorsulfuron[1-(2-chlorophenylsulfonyl)-3-(4-methoxy-6-methyl-1,3,5-triazin-2-yl)urea]isasulfonylureaherbicideusedasapre-andpostemergentherbicidetocontrolavarietyofweedsoncerealgrains,pastureandrangeland,industrialsites,andturfgrass(1).Chlorsulfuronislikelytobepersistentandhighlymobileintheenvironment.Itmaybetransportedtonontargetareasbyrunoffand/orspraydrift.Degradationbyhydrolysisappearstobethemostsignificantmechanismfordegradationofchlorsulfuron,butissignificantonlyinacidicenvironments(23dayhalf-lifeatpH5);itisstabletohydrolysisatneutraltohighpH.Degradationhalf-livesinsoilenvironmentsrangefrom14to320days(2).Chlorsulfuronisaweakacid(pKa)3.6)withwatersolubilitiesrangingfrom0.587gL-1atpH5to31.8gL-1atpH7.Themobilityofchlorsulfuron(3,4)wasfoundtobeenhancedathighersoilpHand/orrelativelylowerorganicmattercontent,reflectingtheinfluenceofthesesoilpropertiesonherbicideadsorption.Theslowrateofchlorsulfurondegradationcoupledwithitshighpotential
*Correspondingauthor(telephone+34950015961;fax+34950015008;e-mailmfernand@ual.es).
mobilityinsoilssuggestsahighpotentialfortransportbelowtherootzonewithsubsequentmovementintogroundwaters,especiallyinsoilswithshallowgroundwatertables.
Theriskofcontaminationresultingfromrapidrunoffandleachingofhighlysolublepesticidessuchaschlorsulfuroncanbeminimizedthroughtheapplicationofthepesticideincontrolledreleaseformulations(CRFs).Besides,theuseofCRFshasbeneficialeffectsrelatedtothereductionintheamountofchemicalrequiredforpestcontrol,increasedsafetyforthepesticideapplicator,andageneraldecreaseinnontargeteffects(5).
TheparametersthataffectthepropertiesofCRFsdependonthenatureandtypeofpolymerused.DespiteseveralpolymersemployedinCRFsinagriculture,naturalpolymerssuchasstarch,ethylcellulose,lignin,chitosan,andalginatearepreferredoversyntheticpolymersbecauseoftheirnontoxic,low-cost,wideavailability,andbiodegradabilitycharacteristics(6-10).Previousencapsulationstudiesofagrochemicalsusingbio-degradablepolymersandmodifiers(5,6,8)showedthatitwasnecessarytodevelopandoptimizethepreparationofCRFstoencapsulateactiveingredientswithhighwatersolubilityvaluessuchastheherbicidechlorsulfuron.
10.1021/jf9004093CCC:$40.752009AmericanChemicalSociety
PublishedonWeb03/03/2009
ControlofChlorsulfuronLeachingbyEthylcelluloseFigure1.Chemicalstructureofchlorsulfuron.
Table1.CoatingSolutionCompositionforthePreparationofCRGranulesContainingChlorsulfuron
coatingsolutioncomposition
wtofCFECDBSethanolECbDBSbCRgranulesagranules(g)
(g)(g)(mL)(%)(%)
CFEC1020210010CFEC20
20420020CFEC20DBS
20
4
0.45200
20
2.25
aCFEC10,commercialchlorsulfuronformulation,ethylcellulose10%;CFEC20,commercialchlorsulfuronformulation,ethylcellulose20%;CFEC20DBS,commercialchlorsulfuronformulation,ethylcellulose20%,dibutylsebacate2.25%.bBasedontheweightofCFgranules.
ThepurposeofthispaperwastoresearchthepreparationandcharacterizationofchlorsulfuroncoatedCRgranulesusing39anaturalpolymersuchasethylcellulose(EC)andaplaticizer040suchasdibutylsebacate(DBS).Ethylcelluloseisoneofthe0f9mostwidelyusedfilmcoatingsbecauseofthemanyadvantagesj/12itaffordsformulators,suchasgoodfilmformability,excellent01.physical-chemicalstability,andminimumtoxicity(11).Plas-01 ticizeriscommonlyincorporatedwiththepolymericfilm,to:iodchangetheflexibility,tensilestrength,andadhesionproperties | 9oftheresultingfilm(12).DBShasbeenusedinprevious002researchduetoitslipophiliccharacter(13)andalsoduetoa ,3 minimumpollutionpotentialfortheenvironment(14).
hcraInthepresentstudy,CRFswerepreparedbycoatingaM :commercialchlorsulfuronformulationwithethylcellulose.There-)before,coatedchlorsulfurongranuleswereproducedinaWuster-W(typefluidized-bedequipment,usinganethanolicsolutionofEC etaontwodifferentpolymerlevels.ThehighestonewasmodifiedD nbytheadditionofaplasticizersuchasdibutylsebacate.TheoitacharacteristicsoftheCRchlorsulfuronherbicidegranuleswerecilbtested,andkinetic-releaseexperimentswerecarriedoutinwateruPtodeterminethereleasecharacteristicsoftheCRgranules. Besides,mobilityexperimentswerealsoperformedtodeterminetheleachingcharacteristicsofchlorsulfuroninacalcareoussoilfromCRgranulesandthecommercialproduct.
MATERIALSANDMETHODS
Chemicals.Thechlorsulfuronusedinthisstudywasacommerciallyavailableformulation(CF),Glean(75%w/w)(DuPontIbe´rica,SL,Barcelona,Spain)suppliedaswaterdispersiblegranules.Itsmolecularformulaandselectedpropertiesareasfollows(1):molecularformula,C12H12ClN5O4S;molecularweight,357.8;meltingpoint,174-178°C;vaporpressure(25°C),3×10-6mPa;watersolubility(25°C),0.587gL-1(pH5),31.8gL-1(pH7);pKa,3.6.ThechlorsulfuronstructureisshowninFigure1.
Thefilm-formingmaterialofpolymercoatingwasethylcellulose(EC)(Ethocel;ethoxycontent,48.0-49.5%;viscosity,9-11cP).ThisproductwassuppliedbyFlukaChemieAG(Buchs,Switzerland).Theplasticizerselectedforthestudywasdibutylsebacate(DBS),(g97%,d)0.936gmL-1),suppliedbyFlukaChemieAG(Buchs,Switzerland).
Formulations.(a)PreparationofCoatingDissolution.Appropriatequantitiesofethylcelluloseandplasticizerwerecombinedanddissolvedinethanol(Table1)toobtaincoatingdissolutionswithtwodifferentpolymerlevelsand,inonecase,withaplasticizer.Thecoatingfilmconsistsof10and20%ethylcellulose,respectively,oftheweightofthecommercialchlorsulfuronformulation(20g).Forthecoating
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Table2.CharacteristicsofCommercialFormulationandControlledReleaseGranules(0.2mm 65.0063.60(1.69)85.5897.8430.26(3.59)CFEC20DBS 63.80 64.01(0.50) 91.41 98.67 32.61(2.05) aTheoreticalchlorsulfuronloading(%))(totalamountofchlorsulfuronusedtopreparetheformulations/totalamountofsolidcomponentsusedintheformulationprocess)×100.bSolidsrecovery(%))(totalamountofformulationrecovered/totalamountofsolidcomponentsusedintheformulationprocess)×100.cValuesinparenthesesrepresentthestandarddeviation. dissolutioncontainingaplasticizer,thecoatingfilmconsistsof20%ECand2.25%DBSoftheweightofthecommercialchlorsulfuronformulation. (b)PreparationofCoatedFormulations.Thecommercialchlor-sulfuronformulation(CF)wassievedtoobtaingranulesbetween0.20and1.0mm,and20gofthisfractionwasloadedintoafluidized-bedcoater(Mini-Glatt,GlattAG,Prattelnl,Switzerland)assembledwithaWusterinsert.Thebedtemperaturewasregulatedto60(2°C.Thegranuleswerepreheatedatthistemperaturefor10min.Coatingdissolutionwasdeliveredbyaperistalticpump(Watson-Marlow,model1B-1003/R)andsprayedintothefluidizedbedviaaspraynozzleattheatomizingpressureof1.2bar.Coatingdissolutionswerepumpedataflowrateof2.5mLmin-1toprepareCFEC10andataflowrateof5mLmin-1forbothCFEC20andCFEC20DBSgranules.Thetotalsprayingtimewasinallcases40min.Thecoatedgranuleswerethendriedinthesameequipmentat70°Cfor10min.Coatedgranulesweresieved,selectingthegranulesofsizebetween0.2and1mm.CoatedGranulesCharacterization.Theactualconcentrationofchlorsulfuroninthegranuleswasdeterminedbydissolving20mgofthegranulesin50mLofmethanolinanultrasoundbathfor15min.Thisledtoacompletedisintegrationofthegranules.Thevolumewasmadeupto100mLwithwater.Theconcentrationofchlorsulfuroninthesolutionwasdeterminedbyhigh-performanceliquidchromatog-raphy(HPLC)usingaBeckmanCoulterInc.,SystemGoldHPLC(Fullerton,CA)equippedwithadiodearraydetectorand32Karatdatastation.TheHPLCoperatingconditionstoanalyzechlorsulfuronweredescribedbyBernaletal.(15).Themobilephaseusedwasanacetonitrile/aqueoussolutionofH3PO4(0.1%w/w)(pH2.2)mixture40:60ataflowrateof1mLmin-1;chlorsulfuronwasanalyzedatitsmaximumabsorptionofwavelength,227nm,byinjectingavolumeof50µL.Separationbyisocraticelutionwasperformedona150×3.9mmNova-PakLC-18bonded-phasecolumn(Waters,MilliporeCorp.).Theresultsofpercentchlorsulfuronloadingandencapsulationefficiency(EE)werecalculatedusingeqs1and2.TheseresultsareshowninTable2. practicalchlorsulfuron(wtofchlorsulfuronloading(%)CR) granules wtofCRgranules )×100 (1) encapsulation(efficiencypracticalchlorsulfuron(%)) loading theoreticalchlorsulfuronloading )×100 (2) ThemorphologicalandstructuralsurfaceofcoatedgranuleswasexaminedwiththeaidofaHitachiS-3500-Nscanningelectronmicroscope(SEM)attherequiredmagnificationatroomtemperature.Thegranulesweresettledonbrassholdandsputteredwithathincoatofgoldundervacuum.Theaccelerationvoltageusedwas10kVwithsecondaryelectronimageasadetector.Toexaminetheinternalmorphologyofthepolymericfilms,coatedgranuleswerecarefullycutwiththeaidofachisel,andtheircrosssectionswerephotomicro-graphed.Thethicknessofthepreparedfilmswasmeasured.Eachfilmsamplewasmeasuredat10differentpoints. Downloaded by SHANGHAI NORMAL UNIV LIB on September 9, 2009 | http://pubs.acs.org 2858J.Agric.FoodChem.,Vol.57,No.7,2009Flores-Ce´spedesetal. Figure2.Scanningelectronmicroscopicphotographsofchlorsulfurongranules(0.2mm WaterReleaseKinetics.Foreachsample(tworeplicates),anaccuratelyweighedquantityofgranulescontainingabout8mgofchlorsulfuronwasaddedto500mLofNa2HPO4/NaH2PO4buffer(pH8.2)andplacedintostopperedconicalflasks.Flasksweremaintainedinathermostatedbathat25(0.1°C.Atdifferenttimeintervals,aliquotsof0.5mLwereremovedfordeterminationofchlorsulfuron,and0.5mLoffreshbufferwaslateraddedtotheflaskstomaintainsinkingconditions. SoilMobilityExperiments.Thesoilusedwasacalcareoussoil(CalcareousRegosol)withapHof8.7,previouslydescribedbyFlores-Ce´spedesetal.(16)andrepresentativeofsoilsfromtheAlmerı´aarea(southeasternSpain). Thecolumnsweremadeusingapolyvinylchloride(PVC)pipe(4.4cminternaldiameter,24cmlength)andapplying2mmthicksiliconeridgesaroundtheinsideofthecolumnat5cmincrementstominimizeboundaryflow(17).Nylonmeshwithaneffective60µmporediameterandlinedwithalayerofwool-lookingfiberglasswassealedtothebottomofeachcolumntopreventdisplacementofthesoilfromthecolumnsandminimizethedead-endvolume(18).Eachcolumncontained,fromthebottomtothetop,soil(20cm)andalayerofacid-washedsand(1cm).Thesoil,screenedthrougha2mmsieve,wasaddedtothecolumninsmallincrementstominimizeparticlesizesegregation,obtainingafinalbulkdensityof1.53gcm-3.Thisbulkdensityresultedinaporevolumeofapproximately100mL.Priortoapplicationoftheherbicidetreatments,thecolumnsweresaturatedwithdistilledwaterviacapillarityandthenlefttobedrainedfor1day.Thepesticidetreatmentswereappliedatarateof7mgofaikg-1.Eachpesticidetreatmentwasappliedtoduplicatesoilcolumns.Theformulationswereuniformlydistributedonthesoilsurface.Afterthat,1cmofacid-washedsandwasaddedtothetopofthecolumn.Next,thecolumnswereelutedwithapproximately1000mLofdistilledwaterbyusingaWatson-Marlowmodel1B-1003/Rperistalticpumpwithaflowrateof4mLh-1.Theleachatewascollectedinfractionsofabout100mLeveryday.Aliquotsweretakenfromtheleachates,thenpassedthrough0.45µmPTFEfilters,andfinallyinjecteddirectlyintheHPLCsystem.Attheendoftheleachingprocedure,thecolumnswereallowedtodrainfor24h.Thesoil,acid-washedsand,andgranuleswereremovedfromthecolumns.Eachsamplewasdriedatroomtemperatureandhomogenized.Subsamplesofeachwereextractedinconicalflasks,placedinashakingbathfor24hwithamethanol/water(80:20)mixture,andanalyzedbyHPLC,asdescribedabove.TheherbicidecontentofCFEC10,CFEC20,andCFEC20DBSweredeterminedbydissolvingthegranulesin50mLofmethanolinanultrasoundbathfor15min.Thevolumewasmadeupto100mLwithwaterandanalyzedbyHPLC.RESULTSANDDISCUSION CoatedGranulesCharacterization.Characteristicsofcon-trolled-releasegranules(0.2mm Itcanbeobservedthatthevaluesofencapsulationefficiency(EE)rangebetween97.84%forthesystemCFEC20and101.79%forthesystemCFEC10.Thesedatahighlighttheefficacyofthemethodusedfortheencapsulationofchlor-sulfuron.FortheformulationCFEC10,theEEvalueobtainedindicatesthattheherbicidecontentinthegranulesisslightlyhigherthanthetheoreticalcontent,suggestingaminimalsolidslossduringtheformulationprocess. SEMpictures(Figure2)showauniformandintactcoatingofethylcelluloseandplasticizer.Inpanelse-hofFigure2(magnification×500)agradualdisappearanceofthewrinkledaspectoftheexternalsurfaceisobservedfromCFtoCFEC20DBSgranules. Thecrosssection(Figure3)showstheporouscorestructurewithafineandcoherentfilmattheboundaryinthecoatedformulations.Thethicknessofthecoatingmaterial,coveringtheherbicidegranule,wasestimatedusingSEMphotographs.Thethicknessofthecoatingfilm(Table2)variedbetween23.32µmforthesystemCFEC10and32.61µmforthesystemCFEC20DBS. Asexpected,thehighestamountofECinthecoatingdissolutionappliedforthesystemCFEC20increasesthethick-nessofthemembraneinrelationtothesystemCFEC10.ThepresenceoftheplasticizerinthesystemCFEC20DBSleadstoaslightincreaseinthefilmthicknesscomparedtothesystemCFEC20. WaterReleaseKinetics.TheeffectsofethylcellulosepercentageonthereleasebehaviorofchlorsulfuronareshowninFigure4.Percentagesinethylcellulosecoatingaside,theseformulationsproduceadiminishingprocessofreleaseoftheactiveingredientinrelationtothecommercialformulation.Asanexample,100%ofchlorsulfuronisreleasedin<1hfortheCF;meanwhile,about35daysisnecessarytoreleasethesameactiveingredientpercentageforCFEC20.ThisfigurealsoshowsthattheinfluenceofethylcellulosepercentageappearsclearlydefinedbymeansofthetwoCRsystemsCFEC10andCFEC20.ThehighestquantityinpolymeroftheCFEC20formulationcausesapronounceddelayinreleaserateinrelationtoCFEC10.OnlyaslightdecreaseinchlorsulfuronreleaseratefromthesystemCFEC20DBSisobservedinrelationtothesystemCFEC20. ControlofChlorsulfuronLeachingbyEthylcelluloseJ.Agric.FoodChem.,Vol.57,No.7,20092859 Downloaded by SHANGHAI NORMAL UNIV LIB on September 9, 2009 | http://pubs.acs.org Publication Date (Web): March 3, 2009 | doi: 10.1021/jf9004093×90)(a),surfacemorphologyofCFEC10granule(magnification×500)(d),CFEC20granule(magnification×90)(b),surfacemorphologyofCFEC20granule(magnification×500)(e),CFEC20DBSgranule(magnification×90)(c),andsurfacemorphologyofCFEC20DBSgranule(magnification×500)(f). Figure3.Scanningelectronmicroscopicphotographsofcrosssectionforcoatedchlorsulfurongranules(0.2mm Mt )1-e(-kt)M0 whereMt/M0isthereleasedfractionattimet(days)andkisthedissolutionrateconstant(days-1). Thekvaluesandcorrelationcoefficientswereobtainedbyapplyingthemodeltopredictthereleaserate,usingthenonlinearcurve-fittingutilityofSigmaPlotsoftware(version9.0,SystatSoftware,Inc.).ThesevaluesarepresentedinTable3. TherewasverygoodcorrelationofthereleaseprofilesofCRchlorsulfurongranuleswiththeempiricalequation,thecorrelationcoefficient(r)being>0.99. Thevaluesofkrangedfrom0.108forCFEC20DBSgranulesto10.98forCFgranules.Thetimerangetorelease50%ofchlorsulfuron,t50,wascalculatedforthegranulesusingconstantsfromTable3.Thevaluesrangedfrom0.06dayforCFgranulesto6.41daysforCFEC20DBSgranules.Thevariationorderis Figure4.CumulativereleaseofchlorsulfuronfromEC-coatedgranules intowater(errorbarsrepresentthestandarddeviationoftworeplicates). CF 2860J.Agric.FoodChem.,Vol.57,No.7,2009Table3.ConstantsfromFittingtheEmpiricalEquationMt/M0)1-e(-kt) toReleaseDataofChlorsulfuronintoStaticWaterCRgranulesk(days-1)rt50(days)CF10.98(0.945a0.9900.06CFEC100.379(0.0190.9931.74CFEC20 0.124(0.0050.9945.59CFEC20DBS 0.108(0.004 0.991 6.41 aThesevaluesrepresentthe95%confidencelimits. Table4.PercentagesofChlorsulfuronRecoveredfromtheGranules,Soil,andLeachates chlorsulfuronrecovered CRgranulesinsoil(%)inleachate(%) ingranules(%) total(%)CF0.00100.000.00100.00CFEC107.6589.961.7899.39CFEC20 16.8173.448.1898.43CFEC20DBS 18.87 63.62 17.25 99.74 withoutplasticizer,CFEC10andCFEC20,weseethatthevalueoft50ishigherinthesystemwithasuperiorethylcellulose39percentage(CFEC20).Thisisbecauseofahighercoating040thickness.Otherstudieshavefoundthatt50inthedeliveryof0f9coatedfertilizersislineallyincreasedwithcoatingthickness(11,14).j/12Theadditionofplasticizerinthecoatingprocessproduces01anincreaseoft50values;thiscanbeduetohigherhomogeneity,.01 lessporosity,andmorehydrophobicityofthecoatingfilmin:iodtheCFEC20DBSformulation(20).Besides,thecoatingfilmis | 9thickerintheCFEC20DBSformulationthanineitherthe002formulationsofCFEC10orCFEC20. ,3 MobilityofChlorsulfuroninSoilColumns.Theamountshcrofchlorsulfuronrecoveredinsoil,leachate,andgranulesreferredaMtothetotalamountofherbicideappliedintheexperimentsare :)bindicatedinTable4. eWAscanbeseen,100%oftheherbicidewaspresentinthe( etleachatewhenchlorsulfuronwasappliedasCF.ThepresenceaD ofthishighamountofchlorsulfuronintheleachatewasexpectednoitaccordingtoitsrelativelyhighsolubilityinwater(31.8gL-1aciat25°C,pH7)andthelowvalueofKow(0.10)(1),whichlbuPmeansapotentialmobilitycapacityinsoil.Whenchlorsulfuron wasappliedasEC-coatedCRformulations(CFEC10,CFEC20,andCFEC20DBS),theamountofactiveingredientrecoveredintheleachateswaslowerthanthatobtainedincolumnstreatedwithcommercialproduct(89.96forthetreatmentwithCFEC10granules,73.44%forthetreatmentwithCFEC20,and63.62%forthecolumnstreatedwithCFEC20DBSgranules,respectively).TheseresultsclearlyhighlighttheefficiencyofECformulationsinreducingtheleachingofchlorsulfuronincomparisontocommercialformulation.SeveralresearchershavereportedthattheuseofCRFsreducestheleachingofpesticideinsoilcolumns(21,22).ThechlorsulfuronrecoveredinsoilandgranulesisincreasedfromCFtoCFEC20DBSinthefollowingorder: CF Thetotalpercentageoftotalchlorsulfuronrecovered(soil+granules+leachate)isnearly100%inallcases.Thisisso Flores-Ce´spedesetal. Figure5.ChlorsulfuronrecoveredintheleachatefromEC-coated granules:(a)breakthroughcurves;(b)cumulativepercentagecurves(errorbarsrepresentthestandarddeviationoftworeplicates). becauseofthebasicpHofthesoilused(pH8.7),wherenodegradationisexpectedtooccurasdeducedfromitsphysical-chemicalproperties. ThebreakthroughcurvesandcumulativechlorsulfuronleachedfromsoilcolumnstreatedwithcommercialchlorsulfuronandECcoatedgranules(CFEC10,CFEC20,andCFEC20DBS)areshowninFigure5.Significantdifferenceswerenotedintheleachingpatternsoftheformulationsresearched.Therankingoftheformulationstestedintermsofpercentageleachedwasasfollows: CF>CFEC10>CFEC20>CFEC20DBS Forthecommercialgradeproduct,chlorsulfuronwasfirstspottedintheleachateatapproximately0.10L(firstporevolume).Theamountofleachedchlorsulfuronincreasedsteadilyovertimetoapproximately100%ofthetotalappliedbythetimeofthefifthcolumnleachatesample.FortheCRFs,asmootherlixiviationprofilecanbeappreciated,whichindicatesthattheuseofCRFsreducesleachingofchlorsulfurontoaveryacceptablelevelduringtheentireprocessoftheexperimentcomparedtothecommercialproduct. Conclusions.Controlledreleaseformulationsofchlorsulfuronhavebeenobtainedbycoatingacommercialproductwithabiodegradablepolymersuchasethylcellulose.Nearly100% Downloaded by SHANGHAI NORMAL UNIV LIB on September 9, 2009 | http://pubs.acs.org ControlofChlorsulfuronLeachingbyEthylcellulose encapsulationefficiencywasobtained.UniformandintactfilmswereobservedincoatedgranulesbySEM. ThereleaserateinwatercanbecontrolledmainlybyadjustingthethicknessofthecoatingfilmandbymodifyingthesurfacepropertiesofthecoatingfilmbyaddingaplasticizersuchasDBS. MobilityexperimentsinsoilshowthattheuseofcoatedCRFsreducesthepresenceofchlorsulfuronintheleachate.Thiscanbeusefultopreventthepollutingenvironmentalriskderivedfromtheuseofchlorsulfuronmainlyinsoils,astheonestudiedhere,withaloworganiccarboncontentandhighpH,wherethisherbicideshowsagreaterpotentialtocausegroundwaterpollution. LITERATURECITED (1)Tomlin,C.ThePesticideManual;BritishCropCouncil:Surrey, U.K.,2002. 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ReceivedforreviewOctober31,2008.AcceptedFebruary10,2009.ThisresearchwassupportedbyMECProjectAGL2007-62598/AGR,cofinancedbyFEDER. JF9004093 Downloaded by SHANGHAI NORMAL UNIV LIB on September 9, 2009 | http://pubs.acs.org 因篇幅问题不能全部显示，请点此查看更多更全内容