Aqueousphotolysisof6:2fluorotelomersulfonamidealkylbetaine

by

LennartJohnTrouborst

Athesissubmittedinconformitywiththerequirements

forthedegreeofMasterofScience

DepartmentofChemistry

UniversityofToronto

©CopyrightbyLennartJohnTrouborst(2016)

ii

Aqueousphotolysisof6:2fluorotelomersulfonamidealkylbetaine

MasterofScienceDegree,2016

LennartJohnTrouborst

DepartmentofChemistry,UniversityofToronto

Abstract

Theaqueousphotolyticfateof6:2fluorotelomersulfonamidealkylbetaine(6:2

FTAB)wasdeterminedexperimentally.ThePhotoFatesystemwasusedtocomparethe

kineticandmechanisticdifferencesbetweendirectandindirectaqueousphotolysisof6:2

FTAB.Differencesattributabletovaryingaqueouscomponents(nitrate,bicarbonate,and

dissolvedorganicmatter(DOM))wereinvestigated.DOMhadamajorroleinmodulating

thephotolysisrateof6:2FTAB,likelybyattenuatingradicalproductionandquenching

radicalsinsolution.Amechanisticinvestigationfoundthatthemajorintermediateof6:2

FTABphotolysisis6:2fluorotelomersulfonamide(6:2FTSAm),followedby6:2

fluorotelomersulfonate(6:2FTSA),6:2fluorotelomersulfonamidealkylamine(6:2FTAA),

6:2fluorotelomeralcohol(6:2FTOH)and6:2fluorotelomerunsaturatedcarboxylicacid

(6:2FTUCA).Aswell,thesignificantproductionofperfluoroalkylcarboxylicacids(PFCAs)

wasobserved.Ahighmassbalance(51to68mol%recovery)enabledtheproposalofa

degradationmechanismfortheaqueousphotolysisof6:2FTAB.

iii

Acknowledgements

ThankyoutoScotttakingmeonasastudent.Nooneleavesyourlabwithout

appreciatingthevalueofexperimentalworkandchemicalintuition,andI’mgladIcould

learnthatfromyou.Thanksalsotomysecondreader,DerekMuir,andtoFrankWania,for

servingonmycommittee.

ThankstotheMaburygroupfortheirsupportandcamaraderieduringmytenure

here.Inparticular,thankstoLeoYeungforhistirelesstechnicalhelpandenthusiasm.

ThankstoAnne,Keegan,Lisa,andShirafortrainingandsupportingme,andforanswering

mymanyquestions.ThanksalsotoalltheEnvironmentalChemistrystudentsandfacultyat

theUniversityofToronto.Thanksforyourfriendship,constantencouragement,and

indefatigablespirit.

Thisworkowesahighdebtofgratitudetomybestfriendandpartner,Jodie.We’ve

comealongwaysinceIstartedthisthesis,andI’mgladyouwerewithmetheentiretime.

iv

TableofContents

ChapterOne–AqueousPhotolysisandFluorinatedSurfactants 1

1.1 AqueousFilmFormingFoams–ChemistriesandFate 2

1.2 AqueousPhotolysis 5

1.3 StudyGoals 7

ChapterTwo–Aqueousphotolysisof6:2fluorotelomersulfonamide

alkylbetaine9

2.1 Introduction 10

2.2 MaterialsandMethods 13

2.2.1 PhotoFateSetup 14

2.2.2 Analysis 16

2.2.3 StatisticalAnalysis 17

2.3 ResultsandDiscussion 18

2.3.1 Kineticsof6:2FTABphotolysis 18

2.3.2 Productsof6:2FTABphotolysis 21

2.3.3 EnvironmentalImplications 27

ChapterThree–SummaryandConclusions 30

ChapterFour–References 33

ChapterFive–Appendices 38

v

ListofTables

ChapterTwo

Table2.1 CompositionandpHof16syntheticfieldwatersolutions 14

ChapterFive

Table5.1 Massspectralparameters 41

Table5.2 Analytepercentrecoveries 42

Table5.3 Outputofmultiplelinearregression 43

Table5.4 Molar%ofallidentifiedproductsbyindirectanddirectphotolysis 43

vi

ListofFigures

ChapterOne

Figure1.1 6:2fluorotelomersulfonate(6:2FTSA) 4

Figure1.2 6:2fluorotelomersulfonamidealkylbetaine(6:2FTAB) 5

ChapterTwo

Figure2.1 UV/Visspectrumof6:2FTABinwater 15

Figure2.2 Photolysishalf-lifeof6:2FTABinsixteenSFWsolutionsandDI 19

Figure2.3 Meanhalf-livesof6:2FTABinSFWsolutionsaccordingtotheircomposition

20

Figure2.4 Finalproductdistributionafter4daysofphotolysis 22

Figure2.5 Averagetemporalproductionof6:2FTABindirectphotolysisproducts

23

Figure2.6 Proposedaqueousphotodegradationfor6:2FTAB 27

ChapterFive

Figure5.1 Spectroradiometricspectraofthesolarsimulator 41

Figure5.2 Histogramofhalf-livevalues 43

Figure5.3 Temporalproductionoffluorinatedproducts:SFWC 44

Figure5.4 Temporalproductionoffluorinatedproducts:SFWF 44

Figure5.5 Temporalproductionoffluorinatedproducts:SFWG 45

Figure5.6 Temporalproductionoffluorinatedproducts:DI 45

Figure5.7 Finalproductdistributionwithout6:2FTSAm 46

Figure5.8 OECDLRTPtooloutputfor6:2FTSAmwithawaterhalf-lifeof17280hrs

46

Figure5.9 OECDLRTPtooloutputfor6:2FTSAmwithawaterhalf-lifeof200hrs

47

vii

ListofAppendices

AppendixA SupportingInformationforChapterTwo 38

1

ChapterOne

IntroductiontoAqueousPhotolysisandFluorinatedSurfactants

2

1.1AqueousFilmFormingFoams–ChemistriesandFate

Aqueousfilmformingfoams(AFFFs)areusedtofightliquidfuelledfires.When

combinedwithwaterandsprayedonthefire,thefoamcoverstheliquidfuelandlimits

contactwithoxygen,helpingtochokethefire.[1]AFFFsareusedprimarilyinthe

petroleumindustry,aviation,andmilitary,wheresignificantquantitiesofflammable

liquidsareregularlyused.[2]Thefoamconcentratesareamixofhydrocarbonand

fluorinatedsurfactants.Thehydrocarbonsurfactantsprimarilyinteractwiththeorganic

liquid/foaminterface,whilethefluorinatedsurfactantsinteractatthefoam/air

interface.[2]FluorinatedsurfactantsareidealforuseinAFFFssincetheyaremuchmore

thermallystablethantheirnon-fluorinatedcounterparts.Furthermore,fluorinated

surfactantsalsoexhibithighersurfaceactivitythantheirhydrocarbonanalogues,

indicatingthatmuchlesssurfactantcanbeusedtoachievedesiredsurfacetension

reductionorfoaming.[3]ThemajorfluorinatedsurfactantusedformanyyearsinAFFFs

wasperfluorooctanesulfonate(PFOS),apersistentandbioaccumulativechemicalnow

listedonAnnexBoftheStockholmConvention.[2]

However,PFOSwasneverthesolefluorinatedsurfactantusedinAFFFformulations.

MaterialSafetyDataSheetsofAFFFformulations,aswellaspatentliterature,revealedthat

theseproductscontainedadiversegroupofsurfactants:atypicalformulationcontained

approximately1%perfluoroalkylsulfonates(e.g.PFOS)andupto5%amphoteric

fluoroalkylamidederivatives.[2]Thiswasalsoconfirmedwhenastudysimultaneously

investigatedtheaccidentalreleaseofAFFFmaterialinToronto,ONbytraditionalLC-MS

and19FNMR.Theinvestigatorsfoundthattheperfluoroalkylregionofthesamples’NMR

spectraaccountedforasmuchas5timesmorefluorinatedmaterialthanwasidentifiedas

3

targetedanalytes(e.g.PFOS)intheirLC-MSanalysis.[4,5]Furthermore,alater

investigationintotheorganicfluorinecontentofAFFFsfoundthatsimpleLC-MSanalysisof

knownfluorinatedchemicalsfarunderestimatedthetrueconcentrationoforganofluorine

intheformulations.[6]Thisconfirmsthatotherperfluoroalkylsurfactantsarepresentin

AFFFformulationsandarebeingreleasedintotheenvironment.

Recently,severalmajorinvestigationshaveidentifiedaplethoraofdiverse

surfactantspresentinAFFFformulations.[7–9]ThedominantsurfactantinhistoricAFFF

formulationswasPFOS,whichwasmanufacturedbyelectrochemicalfluorination(ECF),

primarilybythe3MCompany.In20013Mendeditselectrochemicalfluorination,dueto

theenvironmentalconcernsforPFOS,andperfluorooctanoicacid(PFOA).[10]

Subsequently,fluorinatedproductsbasedonthetelomerizationprocesshaveplayeda

largerroleinthechemicalcompositionofrecentAFFFformulations.[7,9]Today,themajor

fluorinatedsurfactantsinAFFFsarefluorotelomer-based.Fluorotelomersurfactants

containaperfluoroalkylchainboundtoanalkylmoiety,whichconnectsthechaintoa

polarheadgroup.Fluorotelomerchain-basedchemicalsarenamedaccordingtothe

numberofperfluorinatedandnon-fluorinatedcarbonatomstheybear.Thus,6:2

fluorotelomersulfonatehasaperfluorohexylmoietyboundtoanethylmoietywitha

sulfonicacid(sulfonateatenvironmentalpH)headgroup,asshowninFigure1.1.Theterm

fluorotelomerderivesfromthetelomerizationprocessbywhichthechainsare

synthesized.[3]

4

Figure1.1:6:2fluorotelomersulfonate(6:2FTSA)

Dependingonthealkylmoietyandtheheadgroupusedinafluorinatedsurfactant,

thechemicalcanexhibitvastlydifferentchemicalpropertiesandsubsequent

environmentalfate.[11]Themainsurfactantsdetectedcanhave:anegativelycharged

carboxylicorsulfonicacidheadgroup,apositivelychargedquaternaryammoniumhead

group,oranamphotericheadgroupsuchasabetaine.[9]Specieswhicharechargedat

environmentalpHarelikelytobewatersolubleandexhibitnopartitioningtothegas

phase.Incontrast,anunchargedneutralspecieswouldbemuchlesswatersolubleandmay

partitionstronglytosolidphasesorvolatilizeintotheatmosphere.Fluorinatedsurfactants

arefrequentlychargedandtheirmainfateisprimarilytotheaqueousenvironment.Dueto

theiruseinfire-fighting,AFFFsaretypicallydrainedintorun-offorsewage,wheretheir

componentsentertheaqueousenvironment.[2]

Fluorotelomer-basedchemicals,unlikeperfluoroalkylacids,containabstractableH

atomsandrelativelyelectron-richCatoms,andthusaremuchmoresusceptibleto

environmentaloxidation.[12,13]Thisreducestheirpersistenceandthereforelimitstheir

bioaccumulationpotential.However,theenvironmentaldegradationbyproductsof

fluorotelomer-basedchemicalsmaypersist.TwoinvestigationsfoundthatthemajorAFFF

component6:2fluorotelomermercaptoalkylamidosulfonate(FTSAS),andits4:2and8:2

analogues,biodegradetoproduceperfluoroalkylcarboxylicacids(PFCAs).[6,14]

5

Perfluoroalkylcarboxylicacidsarehighlypersistentwithnoknownenvironmentally

relevanttransformations,andsomelonger-chaincongeners(7perfluorinatedcarbonsand

greater)areknowntobebioaccumulativeandtoxic.[15]Theuseofvolatilepercursorshas

ledtothedetectionofPFOSandPFOA,globallyinvirtuallyallenvironmental

matrices.[10,16]

Figure1.2:6:2fluorotelomersulfonamidealkylbetaine(6:2FTAB)

Severalinvestigationshaveidentified6:2fluorotelomersulfonamidealkylbetaine

(6:2FTAB),asamajorfluorinatedsurfactantpresentinAFFFformulationsand

groundwatersurroundingUnitedStatesmilitarybases.[7–9]Mostrecently,D’Agostinoand

Maburyfound6:2FTABtobethesecondmostfrequentlydetectedfluorinatedsurfactantin

theiranalysisofAFFFconcentrates.Anotherstudyidentified6:2FTABinsoilsurrounding

anairportinNorwayandattemptedtoassessthephotodegradationof6:2FTAB.[17]

Unfortunately,theirinvestigationwasexperimentallyhinderedandwasunabletocalculate

ahalf-life,proposeacompletemechanism,orquantifymanydegradationproducts.[17]As

azwitterionic(neutral,butbearingapositiveandanegativecharge)fluorinatedsurfactant,

6:2FTAB(showninFigure1.2)hasarelativelyhighwatersolubilityandisexpectedto

primarilypartitiontotheaqueousenvironment.Duetoitsfluorotelomer-basedstructure,

6:2FTABislikelytobesusceptibletooxidationmechanismssuchasindirectphotolysis,

whichmayplayasignificantroleinitsoverallenvironmentaltransformation.

6

1.2AqueousPhotolysis

Aqueousphotolysisisbroadlyseparatedbetweendirectandindirectphotolysis.

Directphotolysisoccurswhentheanalyteofinterestitselfabsorbslightradiationand

undergoesachemicalreaction.Indirectphotolysisoccurswhenlightradiationisabsorbed

byotherspeciesthatchemicallyproduceareactivespeciesthatactsontheanalyteof

interest.Aqueousreactionswithhydroxylradicals(•OH),carbonateradicals(•CO3-),

peroxyradicals(•OOR),orsingletmolecularoxygen(1O2)areallinitiatedphotolytically

andthusareformsofindirectphotolysis.[18]Ifachemicalexhibitsnolightabsorptionin

theactinicspectrum(>290nm),itcannotundergodirectphotolysis.Incontrasthowever,

nearlyallchemicalsarelabiletoindirectphotolysis.Onlythemostrecalcitrantand

persistentchemicalsareknowntobeinerttoindirectphotolyticprocesses(e.g.

perfluoroalkylcarboxylicandsulfonicacids).[19,20]

PriorstudiesinvestigatingthefateofAFFFsurfactantshavefocusedprimarilyon

microbialbiodegradation,sinceAFFFsarelikelytoenterthewastewatertreatmentsystem

andinteractwiththemicrobialactivitythere.However,watersolublesurfactantssuchas

thoseinAFFFsarelikelytobetransportedthroughtheaquaticenvironmentultimatelyinto

surfacewaters.Insurfacewaters,biodegradationtypicallyplaysarelativelyminorrolein

comparisontophotolysis.

Investigationsintothephotolysisofperfluoroalkylandpolyfluoroalkylsubstances

(PFASs)havelargelybeenrestrictedtoremediation-basedstudies.Thesestudiesuse

highlyenergeticfar-UVradiationanduniquephotosensitizerstodegradeallPFASs

includingPFCAs.[21–23]Theseconditionsfarfrommimicthenaturalenvironmentanddo

notelucidatetheenvironmentaltransformationofPFASs.Incontrasttothese,somestudies

7

havesolelylookedatthedirectphotolysisofPFASs.Giventhelackofchromophoresin

mostPFASshowever,theirresultshavefrequentlyindicatedslowphotolysisorcomplete

persistence.[19,20,24]

Realisticenvironmentalaqueousphotolysisisdependentontheconcentrationofa

fewkeyreactivespecies.Inparticular,•OH,carbonateradical(•CO3-),1O2,•OOR,triplet

excitedstatesofdissolvedorganicmatter(3DOM),andhydratedelectrons(e-(aq))haveall

beenidentifiedasreactivetransientsinnaturalwaters.[18]Thesourcesofallthese

transientsarelargelyderivedfromafewmaincomponentsofnaturalwaters:•OHfrom

nitratephotolysis,[25]•CO3-from•OHandHCO3-/CO32-,[26]3DOMfromdirect

photolysis,[27]1O2and•OORfromO2and3DOM,[18,28]ande-(aq)fromDOMoraromatic

carboxylicacidphotolysis.[29,30]

Lametal.devisedasystemtocombinethesemajorcomponentstocreatearich

systemofphotolyticallyproducedtransientstofullysimulateindirectphotolysisinthe

laboratory.[31]TheirPhotoFatesystemcombinesnitrate,bicarbonate,anddissolved

organicmatterindifferentproportionstoproduceabroadsuiteofsyntheticfieldwater

solutionswithdifferinglevelsofradicalproductionandquenching.Overalltheyfoundthat

nitrateandbicarbonatehadthelargestcontributiontophotolysisrates(i.e.via•OHand

•CO3-),andthatDOMwaslargelyresponsibleforthequenchingofradicalsratherthantheir

production,particularlyathighDOMconcentrations.[31]

1.3StudyGoals

Thegoalofthisresearchwastoinvestigatetheaqueousphotolysisofacurrently

usedfluorinatedAFFFsurfactant,6:2FTAB.ThePhotoFatesystemwasusedtoassessits

8

half-lifeinvarioussunlitsurfacewaterconditions.Thissystemwasalsousedtocompare

theeffectsofdifferentradicals,i.e.•OHvs•CO3-,onthehalf-livesandmechanismof6:2

FTABphotolysis.ThePhotoFatesystemalsoallowedthecomparisonofnitrate,

bicarbonate,andDOMontheoverallphotolyticfateof6:2FTAB

AmechanisticstudywasundertakenwithasubsetofPhotoFatesolutionstoidentify

thefluorinatedproductsof6:2FTABphotolysis.Adiversesuiteoffluorotelomerand

perfluorinatedchemicalswerescreenedtofullyconsiderthemechanismbywhich6:2

FTABisexpectedtodegrade.Inparticular,thepotentialproductionofhighlypersistent

PFCAscangiveinsightintotheoverallenvironmentalhazardthat6:2FTABposesinsunlit

surfacewaters.

9

ChapterTwo

Aqueousphotolysisof6:2fluorotelomersulfonamidealkylbetaine

10

2.1Introduction

Aqueousfilmformingfoams,asusedforfightingliquid-fuelledfires,havelongbeen

asourceoffluorinatedsurfactantstotheenvironment.Thefluorinatedsurfactantsusedin

AFFFsarechosenfortheirthermalstabilityandhighersurfaceactivitycomparedtotheir

hydrocarbonanalogues.[2,3]InvestigationsofsitescontaminatedbyAFFFusehave

frequentlyfoundthatthemajorfluorinatedsurfactant(s)analyzedfor(historicallyPFOS),

didnotaccountforthetotalbreadthofPFASspresent.Forinstance,19FNMRanalysisofan

accidentalreleaseofAFFFfoundmuchhigherconcentrationsattributabletoperfluoroalkyl

groupsthanwascalculatedfromtraditionalLC-MSanalysisofthethen-knownPFASs

(PFOS,perfluorohexanesulfonate,andperfluorooctanoicacid).[4,5]Followingthephase-

outofelectrochemicallyfluorinatedmaterialsby3M,theroleofPFOSinAFFFshas

diminishedinfavourofalternativefluorinatedsurfactantssynthesizedby

telomerization.[7]Severalinvestigationshaveuncoveredaplethoraoffluorinated

surfactantscontainingperfluoroalkylchainsofvarylengths(3to15carbons)associated

withvariousdiversepolarheadgroups.[7–9]Manyreplacementfluorinatedsurfactants

arebasedonfluorotelomerchainsratherthanperfluoroalkylchains;6:2fluorotelomer

chainsbeingthemostfrequentlyobserved.[9]Thoughthesesurfactantsarelesspersistent

thantheirperfluoroalkylanalogues,theyhavebeenshowntodegradetoproduce

perfluorinatedacidssuchasperfluoroalkylsulfonicacidsandperfluoroalkylcarboxylic

acids(PFCAs),bothofwhichhavenoknownenvironmentaldegradationpathwaysand

thusarehighlypersistent.[6,12,32–34]Fluorotelomer-basedchemicalsarealsoofpotential

concernbecauseanumberofintermediatesoftheirbiodegradationhavebeenshownto

11

exhibitgreaterproteinbindingandtoxicitycomparedtotheirperfluorinated

analogues.[35,36]

D’AgostinoandMaburydetected6:2fluorotelomersulfonamidealkylbetaine(6:2

FTAB)in4outof10AFFFsamplescollectedfromacrossOntario,Canada.[9]Itwasthe

secondmostfrequentlydetectedclassoffluorinatedsurfactantafter6:2fluorotelomer

mercaptoalkylamidosulfonate(6:2FTSAS).Aswell,6:2FTABhasbeendetectedinsoil

surroundingafire-trainingfacilityinNorway.[17]Thehighwatersolubilityof6:2FTAB

andsimilarsurfactantssuggeststhatoneoftheirmajorenvironmentalsinksmaybein

groundandsurfacewatersneartheirrelease.

Biodegradationoffluorinatedsurfactantscanberelevanttotheiroverall

environmentaltransformationwhentheyarepresentingroundwaterorsoil.Insurface

waterssunlightradiationcanhavealargeeffectontheirdegradation.Photolysismaybe

rapidandcanbethemostsignificantformofdegradationformanyorganics.[37,38]

Environmentalphotolysiscanoccurviaeitherdirectphotolysis,wherethetargetmolecule

absorbslightradiationandundergoesbondcleavage,orindirectphotolysis,wherelight

radiationcanproduceoxidizingradicalswhichsubsequentlyreactwiththemolecule.[18]

Formanymoleculeswithlittleornoabsorptionoflight,indirectphotolysismayrepresent

aprimaryfateinlight-exposedsurfacewaters.[18,31]

Lametal.introducedthePhotoFatesystemtostudythecontributionofindirect

photolysistotheoverallphotolysisofaqueousphaseorganiccontaminants.[31]The

PhotoFatesystemmimicsnaturalsurfacewatersbycombiningtherelevantphotoactive

componentsofnaturalsurfacewatersinsixteendifferentcombinationstoreflectabroad

rangeofenvironmentalconditions.Thecomponentsusedarenitrate,bicarbonateand

12

dissolvedorganicmatter(DOM).Togetherwithmolecularoxygen,thesecomponentsare

knowntophotolyticallyproduceoxidizingspeciessuchashydroxyl(•OH),peroxy(•OOR),

andcarbonate(•CO3-)radicals,singletoxygen(1O2),andtripletDOM(3DOM),amongst

otherspecies.[18,26,28,31,37]

StudiesofthephotolysisofPFASshavetypicallyutilizedphotolyticremediation

usingfar-UVradiationandphotochemicalsensitizers,bothconditionsunlikethosefoundin

environmentalsurfacewaters.[21-23]However,twoenvironmentallyrelevantstudies

havelookedattheaqueousphotolysisof8:2FTOHandperfluoroalkane

sulfonamides.[33,40]Theanalytestestedwereallsusceptibletoindirectphotolysiswith

half-livesoftheorderofdaysorweeksundercontinuoussunlightconditions.Direct

photolysiswasnotobservedforeither8:2FTOHorperfluoroalkanesulfonamideswithin

theirexperimentaltimeframesof150and25hours,respectively.BothstudiesfoundPFCAs

tobemajoridentifiableproductsoftheindirectphotolysis,howeverneithercould

accomplishafullmass-balanceofproducts.

Moeetal.previouslyinvestigatedthebiodegradationandaqueousphotolysisof

Forafac1157(anAFFFformulationwith6:2FTABasthemainfluorinatedsurfactant)in

seawater.[17]Althoughtheydetectedseveralfluorinateddegradationproducts,their

photolysisexperimentswereunabletodetectasignificantdecreasein6:2FTAB

concentrationsoverthecourseof180hrsandthuscouldnotcalculateaphotolytichalf-life.

Unfortunatelytheirinvestigationdidnotprobethepossibilityofdirectphotolysis.Further,

thepresenceofmanyfluorinatedimpuritiesintheformulation,suchasperfluorinated

carboxylicacidsandfluorotelomersulfonates,hinderedafullmechanisticinvestigation.

13

Thepresentinvestigationexaminedtheaqueousphotolyticdegradationof“pure”

6:2FTABusingthePhotoFatesystem.Thekineticsof6:2FTABphotolysiswasdetermined

andtherelativeeffectsofdirectandindirectphotolysiswerecompared.Thefluorinated

products,includingmanymajorfluorinatedacids,werealsomonitored.Usingthis

information,weproposeamechanismbywhich6:2FTABundergoesphototransformation

intheenvironment.Thisinvestigationwasthefirstofitskindtoprobetheaqueous

photolysisoffluorinatedsurfactantsandthereforecanprovideauniqueinsightintothe

overallfateofthesechemicalsintheenvironment.Knowingtheaqueousphotolysisof6:2

FTABalsoprovidesabasisforunderstandingtheaqueousfateofsimilarfluorotelomer-

basedAFFFsurfactants.

2.2MaterialsandMethods

ADOMstockwaspreparedasperEPAmethodOPPTS835.5270,[41]usingAldrich

humicacid(SigmaAldrich).Sodiumbicarbonateandpotassiumnitrate(ACPChemicals)

wereusedtocreateHCO3-andNO3-stocksolutions.ThePhotoFatesystemcombinesthree

concentrationsofnitrate,twoconcentrationsofbicarbonate,andthreeconcentrationsof

DOM,invaryingratiostomakeabroadsuiteofsyntheticfieldwaters(SFWs)thatsimulate

therangeofenvironmentalconditionsinsunlitsurfacewaters.ThePhotoFatesystemuses

sixteendifferentSFWsolutions(denotedasA-PinTable2.1)anddeionizedwater(DI).The

followingfluorinatedanalyteswereobtainedfromWellingtonLaboratories:6:2FTSA,6:2

FTCA,6:2FTUCA,5:3FTCA,andC4toC8PFCAs.Mass-labelledinternal standardsforall

thesechemicals(except5:3FTCA),andforperfluorooctanesulfonate(FOSA),werealso

obtainedfromWellingtonLaboratories.

14

Theanalytes6:2FTAB,6:2FTAA,and6:2fluorotelomersulfonamide(6:2FTSAm),

whicharenotcommerciallyavailable,weresynthesizedinhouseto>99%purityas

describedinD’AgostinoandMabury,andanalyzedusingLC-MS/MS.[42]

Table 2.1: Composition and pH of 16 synthetic field water solutions. Bicarbonate and nitrate are reported in mg/L, DOM in mg C/L

2.2.1PhotoFatesetup

Syntheticfieldwatersolutionswerepreparedinquartzvialswithaspikeof6:2

FTAB(finalconcentration:10or250ppb(20or500nM))toafinalvolumeof10mL.Each

experimentcontainedatleastthreereplicatevials,andupto6or12replicatesas

necessary,oftheSFWsolutionstestedandblankdeionizedwatercontrols.Darkcontrols

wereinglassvialscoveredwithaluminumfoil.Allsamplevialswereweighedafter

samplingand,beforethenextsamplingtime,toppedupwithdeionizedwatertocorrectfor

evaporativelosses.Aquartzplatewasalsoplacedoverallquartzvialsinthesunlight

simulatortominimizeevaporation.

TheSuntestCPSsunlightsimulator(Atlas)emitslightacrosstheactinicspectrum

(290-800nm).Thesolutionswerekeptcoolbyachilledwaterrecirculatorandafan

systemwithinthesimulator.Theinternaltemperatureofthesolutionswasapproximately

A B C D E F G H I J K L M N O P DI

HCO3- 45 300 45 45 300 45 300 300 300 45 45 300 300 45 45 300 –

NO3- 0.5 0.5 0.5 5 5 50 50 50 0.5 5 5 5 5 50 50 50 –

DOM 0.72 7.2 62 7.2 7.2 0.72 0.72 62 62 0.72 62 0.72 62 7.2 62 7.2 –

pH 7.6 8 7.6 7.6 8 7.6 8 8 8 7.6 7.4 8 8 7.6 7.6 8 5.5

15

30-35˚Cduringthephotolysisexperiments.Spectroradiometrywasconductedonthe

sunlightsimulatortoconfirmitsspectralcharacteristicsandassessintensity.Thiswas

donewithaBlack-CometC-50spectroradiometer(StellarNet).Furtherdetailsarelistedin

AppendixA.AportionofthemeasuredspectrumisshowninFigure2.1.UV/Visspectra

weretakenwithaLambda25spectrometer(PerkinElmer).

Figure 2.1: UV/Vis spectrum of 6:2 FTAB in water. Irradiance of the solar simulator is shown on the right-hand axis.

Kinetics-basedexperimentsusingallsixteenPhotoFatesolutions(n=3to12)were

conductedata6:2FTABconcentrationofapproximately10ppb(20nM).Mechanistic

studiesconductedonSFWC,F,G,andDIweredoneatapproximately250ppb(500nM).

Triplicatesofeachsolutionweretested,andoneoutliereach(foundusingGrubbs’test)

fromSFWCandDIwereremoved.Thusallmechanisticdatarepresentsn≥2.

Experimentstocapturevolatile6:2FTOHweredoneusing100mLofsolution(SFW

ForDI)in130mLquartztesttubeswhichweresealedwithrubbersepta.Theseptawere

0.0

0.5

1.0

1.5

2.0

0.000

0.003

0.006

0.009

0.012

0.015

290 310 330 350 370 390

Irrad

ianc

e (W

/m2/

nm)

Abs

orba

nce

Wavelength (nm)

0.1% FTAB Solar Simulator

16

piercedtofitXAD-2cartridgesandasingleXAD-2cartridgewasfittedineachseptum.The

experimentswerespikedtoa6:2FTABconcentrationof~250ppbandirradiatedfor144

hrs.Afterirradiation,priortosamplingoftheaqueousphaseandXADcartridges,the

solutionswerebubbledwithpurifiedhouseairfor24hrs.DetailsoftheXADextraction

protocolandsubsequentGC-MSanalysisaredescribedinAppendixA.Aspikeandrecovery

of5µgof6:2FTOHfromaqueoussolutionsinthesamefashionhada34%recovery.The

relativelypoorrecoverymaybeduetotheuseofoneXADcartridgeforeachsolution,as

spacerequirementsinsidethesunlightsimulatorpreventedtheuseoftwocartridgesin

series.

2.2.2Analysis

Aliquotswerecombinedwithanequalvolumeofmethanolandstoredat-20˚Cprior

toanalysis.LC-MS/MSanalysiswasconductedonaWatersAcquityUPLCcoupledtoa

WatersXevoTQ-Striplequadrupolemassspectrometer.AllsamplesdetectedbyLC-

MS/MSwereinjectedandanalyzedintriplicate.SeparationwasperformedwithanAcquity

UPLCBEHC18column(1.7µm,2.1x75mm,Waters)outfittedwithaWatersVanGuard

BEHC18pre-column(1.7µm).Theelutiongradient,runat0.5mL/min,wasasfollows(A:

10mMammoniumacetateinwater;B:methanol):90%Afor1minute,rampto60%A

from1to2mins,thenrampto75%Bfrom2to5.5mins,thenrampto95%Bfrom5.5to

5.6mins,thenholdat95%Bfrom5.6to6.5mins,returnto90%Afrom6.5to6.6mins,

andholdat90%Bfrom6.6to7.5mins,markingtheendoftherun.Thecolumnwas

maintainedat60˚Cthroughoutanalysis.

17

Allanalyseswereruninmixedpositiveandnegativeelectrospraymode,

dynamicallyswitchingbetweenmodesperion.Massspectralparametersinclude:capillary

voltage1.5kV,sourceoffset50V,nebulizer7.0bar,desolvationtemperature500˚C,cone

flow150L/hr,desolvationflow800L/hr,collisiongasflow0.15mL/min.Nitrogenwas

usedastheconeanddesolvationgas,argonwasusedasacollisiongas.

Asuiteofperfluorinatedandpolyfluorinatedchemicalswerescreenedfor:6:2

FTSA,6:2FTCA,6:2FTUCA,5:3FTCA,andC4toC8PFCAs.Weemployedmass-labelled

internalstandardsforallanalytesexceptforthosesynthesizedinhouse.Mass-labelled

FOSAwasusedasasurrogatefor6:2FTSAm,andsimilarlymass-labelled6:2FTUCAfor5:3

FTCA.Analyteswithinternalstandardsorsurrogateswerequantifiedbyinternal

calibration,thosewithoutwerequantifiedbyexternalcalibration.Massspectralanalysis

parametersforeachanalytearelistedinTable5.1.Spikeandrecoveryexperimentswere

conductedfortheanalytesinSFWsolutionsC,F,andG,andDI,eachintriplicate.No

significantdifferencesinpercentrecoverywereseenforallfoursolutionstested,andthus

thepercentrecoveriesarereportedasanaverageofallfoursolutions.Percentrecoveries

rangedfrom82to125%,andthelimitsofdetectionandquantificationrangedfrom0.01to

0.3ng/mLand0.03and1.0ng/mL,respectively.Analyte-specificpercentrecoveries,limits

ofdetection,andlimitsofquantificationarerecordedinTable5.2.

2.2.3StatisticalAnalysis

StatisticalanalysesofthedatawerecarriedoutusingStatistica13(DellInc.).Two-

tailedStudent’st-testswereusedtoindirectphotolysishalf-livestothatofdirect

photolysis,atp≤0.05levelofsignificance.Amultiplelinearregressionwasalsocarriedout

18

tocomparethecompositionofeachindirectphotolysissolutionwithitsphotolysishalf-life

withafunctionoft½=b1[HCO3-]+b2[DOM]+b3[NO3-]+c.Theregressionfunctionhadap-

value<0.01,andanadjustedR2valueof0.51.Furtherdetailsoftheanalysiscanbefound

intheAppendixA.

2.3ResultsandDiscussion

2.3.1Kineticsof6:2FTABphotolysis

Thetargetanalyte,6:2FTAB,wasfoundtobesusceptibletobothdirectandindirect

photolysisinthisinvestigation.Thehalf-lifebydirectphotolysiswas34±18hrs,andthe

photolytichalf-lifebyindirectphotolysiswasobservedtovarybetween14and108hrs

(illustratedinFigure2.2).Overall,8outof16solutionssignificantly(p≤0.05)extended

thehalf-lifeof6:2FTABinsolutionbeyondthatindeionizedwater,whilenonesignificantly

reducedit.Therelativelyrapidindirectphotolysisof6:2FTABiscoherentwithsimilar

resultsforotherPFASs.GauthierandMaburyfoundthehalf-lifeof8:2FTOHbyindirect

photolysistorangebetween30to163hrsusingSFWsolutionsA,F,andOwiththe

PhotoFatesystem.[33]Plumleeetal.foundthehalf-lifeofvariousN-substituted

perfluorooctanesulfonamidesrangedbetween1.7to5.6hrsin10mMH2O2irradiated

solutions.[40]Theyestimatetheenvironmentalhalf-lifeofN-ethylperfluorooctane

sulfonamidoacetatetovaryfrom0.47to4.7x103days,dependingonthesteadystate

concentrationof•OH(10-14to10-18M).Incomparison,thisinvestigationfoundhalf-livesof

14to108hrsfortheindirectphotolysisof6:2FTAB.Theseresultsaremarginallymore

rapidthanthosefor8:2FTOH,butmaybeattributabletodifferencesbetweenlight

sources.

19

Figure 2.2. Photolysis half-life of 6:2 FTAB in sixteen SFW solutions and DI (n ≥ 3). Half-lives marked with * are significantly different (p ≤ 0.05) from deionized water. Error bars represent standard deviations.

Tounderstandwhethersolutioncompositionplayedamajorroleindictatingthe

photolytichalf-lifeof6:2FTAB,amultiplelinearregressionwasconductedusingthe

concentrationsofbicarbonate,DOM,andnitrate.Theresultsofthisanalysisare

summarizedinTable5.3.Thecorrelationcoefficients(±standarderror)ofbicarbonate,

DOM,andnitratewere-0.16(±0.18),0.76(±0.18),and-0.09(±0.18),respectively.Only

thecorrelationcoefficientofDOMwassignificant(p≤0.05),indicatingthatithada

significanteffectinprolongingthephotolytichalf-lifeof6:2FTAB.Avisualillustrationof

thetrendsforeachSFWcomponentisshowninFigure2.3.Eachbarinthefigureisthe

meanhalf-lifeforallofthe16solutionsthatfallunderacertaincategoryoftheir

composition(i.e.themeanhalf-livesofall8solutionswith45ppmbicarbonate,andall8

solutionswith300ppmbicarbonatearethefirsttwobarsinthegraph).TheroleofDOMin

0

20

40

60

80

100

120

A B C D E F G H I J K L M N O P DI

Pho

toly

sis

half-

life

(hrs

)

*

* ** *

*

**

20

slowingaqueousphotolysiswasalsoobservedbyLametal.whofoundthatthemajorrole

ofDOMinthePhotoFatesystemisasalightattenuatororradicalscavenger.[31]As

discussedbelow,themechanisticdifferencesbetweenanyofthedirectandindirect

photolysissolutionsinthisstudywererelativelyminor.Thissuggeststhatthemajorroleof

DOMisnotinradicalquenching,whichwouldcausemajormechanisticdifferences,but

ratherlightattenuation.Arecentinvestigationofdirectaqueousphotolysisof

neonicotinoidinsecticidesfoundthatdepthwithinthewatercolumn,acorollaryforlight

attenuationbyDOM,wasthemajorfactorinreducingtherateofdirectphotolysis.The

authorscalculatedthatatdepthsof8and18cmintheirmesocosmwaters,lightfluxwas

attenuatedby89and98%respectively.[43]Asimilareffectislikelyatplayforthe

photolysisof6:2FTABwheredirectphotolysisthatoccursisbeingattenuatedbythe

highlyabsorbingDOM.

Figure 2.3: Mean half-lives of 6:2 FTAB in SFW solutions according to their composition (concentrations in ppm are shown on X axis). Deionized water control is shown for comparison. Error bars represent standard deviations.

0

40

80

120

45 300 0.5 5 50 0.72 7.2 62 DI

Hal

f-life

(hrs

)

Bicarbonate Nitrate DOM

21

Theaqueousphotolysisof6:2FTABhasbeenassessedinonepriorstudybyMoeet

al.[17]Overthecourseof180hrsofphotolysisinseawater,nosignificantdegradationof

6:2FTABwasobserved.Thisliesincontrasttoourworkwhichfindsthehalf-lifeof6:2

FTABtobeshorterthan110hrsinallsettings.Aswell,theysawlimitedproductionof6:2

FTSAm,amajorphotolyticproductobservedinthisinvestigation.

2.3.2Productsof6:2FTABphotolysis

Foursolutionsweretestedfortheirphotolysisproductdistribution:SFWC,F,andG,

andDI.ThethreeindirectphotolysissolutionsrepresenthighDOMconditions(SFWC),

high•OHconcentrations(SFWF),andhigh•CO3-concentrations(SFWG).Thedistribution

ofproductsinthefouraqueousphotolysissettingsusedinthisexperimentisillustratedin

Figure2.4andTable5.4.ThemajorproductofphotolysisinallsolutionswastheN-

dealkylationproduct6:2FTSAm.Bytheendof4daysofphotolysis,6:2FTSAmaccounted

for46to61mol%ofallphotodegraded6:2FTAB.Itappearstobethefirststable

intermediateofphotolysis.N-dealkylationisknowntooccurviaboth•OHand•CO3-

radicals.

Thetemporalproductionoffluorinatedproductsinallindirectphotolysissolutions

isillustratedinFigure2.5.Asobserved,6:2FTSAmwastheonlyproductweobservedto

peakandbegintodecreaseinconcentrationwithintheexperiment.Thistrendiseven

moreevidentintheSFWsolutionspecifictrendsshowninFigures5.3to5.6.Aswell,early

intheexperiment,6:2FTSAmand6:2FTSAaretheonlyproductsdetectedpriortothe

appearanceofPFCAs.Thisindicatesthat6:2FTSAmislikelythefirststableintermediate

thatphotolyzestoproducelowerfluorinatedproducts

22

Figure 2.4: Final product distribution after 4 days of photolysis (n = 3 for F and G, n =2 for C and DI). Error bars, when visible, represent standard deviations. Distribution of minor products is shown in Figure 5.7.

Theproductionof6:2FTSAmwasalsoreportedbyMoeetal.asaresultof

photolysis.[17]Thechemicalpropertiesof6:2FTSAmarelikelycomparabletoits

perfluoroalkylanalogue,perfluorooctanesulfonamide(FOSA)andthusitwillexistasa

neutral,semi-volatilespeciesunderenvironmentalconditions.Experimentstocapture

volatile6:2FTOHwerealsoscreenedfor6:2FTSAm,butfoundrelativelylowquantities(<

1mol%),comparedtoitsaqueousphaseconcentration.Since6:2FTSAmisexpectedtobe

aneutralunchargedspeciesatenvironmentalpH,itwillexhibitvolatilizationintothe

atmosphere.SimilartoFOSA,6:2FTSAmmaybesusceptibletolong-rangetransportand

couldbeaprecursortoPFCAsthroughatmosphericoxidation.

0

25

50

75

100

C F G DI

mol%ofp

hotolyzedFTAB

6:2FTAA 6:2FTSAm6:2FTSA 6:2FTUCAPFHpA PFHxAPFPeA

23

Figure 2.5: Average temporal production of 6:2 FTAB indirect photolysis products. Error bars represent standard deviations. Values are averaged for SFW C, F, and G.

Tounderstandthelong-rangetransportpotentialof6:2FTSAm,itwasassessed

usingtheOECDoverallpersistenceandlong-rangetransportpotentialtool(availablefrom

http://www.oecd.org/exposure/povlrtp).[44]Briefly,thetoolassessesthreeglobalscale

compartments(air,water,andsoil)andpredictstransportandoverallfatebetweenthese.

Thelargestofthesevalues,typicallyinair,arereportedasameasureoflong-range

transportpotential.TheinputsforthetoolwerefoundusingEPISuite4.11.Themodelled

EPISuitevalueswere:logKAW0.683,logKOW3.97,andthehalf-livesinair,water,andsoil

were28.6hrs,17280hrs,and34560hrs,respectively.Basedonthepossibledegradation

of6:2FTSAmobservedinthisinvestigation,afasterhalf-lifeinwaterof200hrswasalso

24

proposed.ThecompleteoutputsforbothscenariosareshowninFigures5.8and5.9.For

bothwaterhalf-lifevalues,thetoolpredictedthecharacteristictraveldistanceof6:2

FTSAmintheatmospheretobe594km,anditstransportefficiencytobe0.0003%.The

factthatthesevalueswereconsistentbetweenbothwaterhalf-lifevaluesindicatesthe

strongeffectoftheaircompartmentinlimitingthetransportof6:2FTSAm.Theoverall

persistencewas124dayswithahalf-lifeinwaterof17280hrs,or11dayswithahalf-life

inwaterof200hrs.Thelowcharacteristictraveldistanceandtransportefficiencyboth

indicatethat6:2FTSAmistoorapidlydegradedintheatmospheretotravelonaglobal

scale.ThoughitislikelyasourceofPFCAstotheatmosphere,therangeof6:2FTSAmlimits

theirreachtowith500to1000kmofthe6:2FTSAmemission.Furthermeasurementsof

thephysicalpropertiesandenvironmentaldegradationsof6:2FTSAm(e.g.half-lifeinair)

mayaffecttheoutputofthismodelhowever.

Thesecondmajorproductofindirectphotolysiswas6:2FTSA.Figure5.7showsthe

finalproductdistributioninallfoursolutionsoftheminorfluorinatedproducts(i.e.

excluding6:2FTSAm).Bytheendoftheexperiment,6:2FTSAaccountedfor4.0to5.9mol

%ofphotodegraded6:2FTAB.Itmaybeproduceddirectlyfrom6:2FTAB;although,since

after1dayofphotolysisitrepresentsonly2.7%ofknownproducts(averageforSFWC,F,

andG),itmaybederiveddirectlyfrom6:2FTSAm.Thebiodegradationof6:2FTSAtoform

6:2FTCA,6:2FTUCA,andPFCAs(C6andlower)hasbeendocumentedinthe

literature.[45,46]

Thephotolyticproductionof6:2FTAAwasprimarilyviadirectphotolysis.Bythe

endofourexperiment,6:2FTAAaccountedfor2.6mol%ofproductsbydirectphotolysis,

butonly0.06mol%byindirectphotolysis.Thestrongbiasfor6:2FTAAproductionby

25

directphotolysismayprovideameanstoassesstherelativeeffectsofdirectandindirect

photolysis.Thelackof6:2FTAAinindirectphotolysismaybeduetooneormorefactors.

Firstly,•OHand•CO3-radicalsmaynoteasilydealkylatethequarternarynitrogenatomin

6:2FTAB.Thisisunsurprisingasbothcarbonateandhydroxylradicalsreactwithelectron-

richatoms,andthebetainegroupwithquarternarynitrogenandcarboxyliccarbonare

electron-deficient.Additionally,6:2FTAA,withtwoelectron-richnitrogenatoms,maybe

moresusceptibletofurtheroxidationfrom•OHand•CO3-andwouldhavealowersteady-

stateconcentrationunderindirectphotolysisconditions.Coincidentwiththisinvestigation,

D’Agostino&Maburyhavefoundthat6:2FTAAbiodegradestoproduce6:2FTSAm,6:2

FTOH,6:2FTCA,6:2FTUCA,5:3FTCA,andPFCAs.[42]

Aminorintermediateobservedinallsolutionswas6:2FTUCA.Itaccountedfor0.05

to0.12mol%of6:2FTABproductsafter4daysofindirectphotolysis.Fluorotelomer

unsaturatedcarboxylicacidshavebeendetectedinthephotolysisof8:2fluorotelomer

alcohol(8:2FTOH).[33]BothFTCAsandFTUCAsareenvironmentallylabilecompounds

andreadilydegradetoproduceshorter-chainPFCAs.[32,47]Thelackofdetectionof6:2

FTCAmaybetheresultofitsrelativeinsensitivitytoelectrosprayionizationmass

spectrometry(LOD:0.2ng/mL).TheobservationofPFHpAasamajorproductinall

solutionsimpliesthepresenceof6:2FTCA.

Thoughphysicalrequirementslimitedthecollectionofvolatilesduringmost

experiments,twophotolysisexperiments(SFWFandDi)wereconductedwithsealed

quartzvialsandXAD-2cartridgestocapture6:2FTOH.Wetargeted6:2FTOHbecauseit

hasbeendetectedinthedegradationsimilarfluorotelomerchemicalsincluding6:2FTSAS

and6:2FTSA.[6,46]SolutionFwaschosenofthethreemechanisticsolutions(C,F,andG)

26

becauseitexhibitedthefastesthalf-life,andthereforewouldhavethebestdetectionlimit

forintermediates.After6daysofphotolysis,6:2FTOHwasdetectedinthecartridge

extractsofbothSFWFandDI,attributableto0.85mol%and0.82mol%(recovery

corrected)ofphotolyzed6:2FTAB,respectively.Thisisindicativeof6:2FTOH’sroleasa

minorintermediateintheoverallphotodegradationof6:2FTAB.Thisisinlinewithother

experimentsthathavefoundthatFTOHsareintermediatesinthedegradationof6:2

FTSA,[46]6:2FTSAS,[6]6:2FTAA,[42]and6:2fluorotelomermono-anddisubstituted

polyfluoroalkylphosphates.[48]Also,FTOHsareknownprecursorsto6:2FTCA,6:2

FTUCA,andPFCAs.[12,33,49]However,sincetheproductionof6:2FTOHwaslowinthese

experiments,itlikelydoesnotaccountforthe32to49mol%ofmissing6:2FTAB

photolysisproducts(Figure2.4).Anapproximatelyequalamountof6:2FTSAmwas

detectedas6:2FTOHinthesameXADextracts.However,no6:2FTAAwasdetected.All

told,capturedspeciesinthegasphasedidnotaccountformorethan1to2mol%of

photolyzedFTABintheseexperiments.

ThethreemajorPFCAsproducedbythephotolysisof6:2FTABwerePFHpA,PFHxA,

andPFPeA.PFHpAisconsistentlythemostabundantPFCAproduct,andPFHxAandPFPeA

wereofasimilarconcentrationinmostcases.Analogously,GauthierandMaburyidentified

perfluorononanoicacid(PFNA)asaproductoftheaqueousphotolysisof8:2FTOH,

proceedingviathe8:2FTCAintermediate.[33]Likewise,theproductofPFNAfrom8:2

FTCAhasalsobeenobservedinrainbowtrout.[50]PFHpAisknowntobederivedfrom6:2

FTCAviametabolicdegradationinrathepatocytes.[47]PFHxAandPFPeAhavebeen

identifiedasterminalproductsintheenvironmentaldegradationofseveral6:2

fluorotelomerchemicalsincluding6:2FTSAS,6:2FTSA,and6:2FTOH.[6,14,45,46,51,52]

27

Figure 2.6: Proposed aqueous photodegradation for 6:2 FTAB. Double arrows indicate that a reaction occurs in multiple steps. Only 6:2 FTCA, in the dashed box, was not observed in this study. Reactions observed previously are numbered as follows: 1) Marchington [46] 2) Liu et al. [53] 3) Martin et al. [47] 4) Wang et al. [45]

2.3.3EnvironmentalImplications

Thisinvestigationhasfoundthat6:2FTABphotolyzesrapidlyinsunlitaqueous

environmentswithahalf-livesof14to108hrs.Underrealday/nightcyclesthisisroughly

equivalentof1to9days.Spectroradiometricmeasurementsofthesunlightsimulatorwere

comparedtospectralirradiancedataontwodatesin2015toestimatetheapproximate

intensityofthesolarsimulator.DetailsofthisaregiveninAppendixA.Overall,thesolar

simulatorintensitymeasuredbeneathourquartzsamplecoverfallssomewherebetween

28

nooninJuneandmidafternooninNovember.Thusthehalf-livesinthesolarsimulator

underestimatetheenvironmentalhalf-livesinsunlitsurfacewatersattheheightof

summer,butmayoverestimatetheminwinter.

Thisisrapidincomparisontobiodegradationhalf-livesofsimilarPFASs.There

appearstobenosignificantdifferencebetweenhigh•OHandhigh•CO3-environments.

Bothconditionsproducesignificantquantitiesof6:2FTSAmand,ultimately,substantial

quantitiesofPFCAs.Aswell,nosignificantdifferencesinphotolytichalf-liveswere

observedbetween•OHand•CO3-conditions.Duetothehigherselectivityof•CO3-,its

steadystateconcentrationsare2to3ordersofmagnitudelarger.[31]If6:2FTABreacts

similarlywithbothradicalspecies,asindicatedbythepoortrendbetweenHCO3-orNO3-

concentrationsandphotolysishalf-life,itsenvironmentalphotolysisislikelydominatedby

reactionswith•CO3-ratherthan•OH.Thisassessmentof•OHvs•CO3-mayequallyapplyto

otherphotolysisstudiesthatinvestigatechemicalsbearingelectronrichsulfurornitrogen

functiongroups.Forinstance,thoughPlumleeetal.[40]assessedthehalf-lifeofN-

substitutedperfluorooctanesulfonamideswithrespectedto•OH,theirtrueenvironmental

aqueousphotolysismay,like6:2FTAB,bedominatedby•CO3-.Insuchcases,photolytic

half-livesbasedsolelyonthesteady-stateconcentrationof•OHmayoverestimatethehalf-

livesoftheanalytesinrealaqueoussettings.

Thefindingthat6:2FTSAmmakesupthemajorityof6:2FTABphotolysisproducts

hasimplicationsforthebroaderclassoffluorotelomersurfactants.Manyfluorotelomer

surfactantsuseanN-substitutedsulfonamideoraminegroupchemistry.Insunlitsurface

waterswithsignificantsteadystateconcentrationsof•OHor•CO3-,itappearsthatN-

dealkylationtoproduceaneutralprimarysulfonamideoramineisamajorpathway.Itis

29

possiblethatindirectphotolysisoffluorotelomersurfactantsmaybeanindirectsourceof

neutral,semi-volatilefluorotelomerspeciestotheaqueousenvironment.Althoughthis

studyfoundonlysmallamountsoffluorotelomerspeciesinXADextracts(<2mol%),there

maybemorevolatilizationinrealsurfacewaterswithlongertimetopartition,more

surfacearea,andmoreeffectiveheadspace.Therelativepartitioningofthesechemicals

maybeofinterestduetotheirvolatility,potentialforatmospherictransport,andultimate

oxidationtoPFCAs.

Bytheendofourphotolysisexperiments,upto2.3mol%of6:2FTABwas

convertedtoPFCAs.However,nearlyalltheotherphotolyticproducts(6:2FTSA,6:2FTOH,

6:2FTUCA,6:2FTAA)areknowntobePFCAprecursorsintheenvironment.Furthermore,

thepresentstudyalsoidentifiesthat6:2FTSAmislikelytobeaPFCAprecursor,aswellas

apotentiallysusceptibletolongrangetransport.Perfluoroalkylcarboxylicacidsareof

concernduetotheirextremepersistenceandsubsequentdetectioninavastarrayof

environmentalmatrices.Thisinvestigationhasconfirmedthehypothesisthat

fluorotelomersurfactantsareasourceofPFCAstotheenvironment,andthattherateof

transformationofPFASstoPFCAscanbequiterapidinsunlitsurfacewaters.

30

ChapterThree

SummaryandConclusions

31

Thisinvestigationprobedtheaqueousphotolysisofafrequentlyusedfluorinated

surfactant,6:2FTAB.SincesimilarPFASswithhydrocarbonheadgroups(e.g.8:2FTOH)

aresusceptibletoindirectphotolysis,6:2FTABwasexpectedtobesusceptibletoindirect

photolysis,ifnotdirectphotolysisalso.Aswell,becauseitbearsafluorotelomertail,itwas

expectedtoproducepolyfluorinatedandperfluorinatedproductsincludingPFCAs.

Itwasfoundthat6:2FTABwassusceptibletobothdirectandindirectphotolysis.

Thehalf-lifebyindirectphotolysisrangedfrom14to108hrs,and34±18hrsbydirect

photolysis.Themajorfactoraffectingphotolysishalf-lifewasidentifiedasdissolved

organicmatter,whereincreasingconcentrationsslowedthephotolysisof6:2FTAB.Under

realisticenvironmentalconditions,thehalf-lifeof6:2FTABinsunlitsurfacewatersisofthe

orderof1to9days.Itwasfoundtoreactrapidlywith•CO3-,aswellas•OH,duetoit

bearinganelectron-richN-substitutednitrogenatom.Sincethesteady-state

concentrationsof•CO3-aremuchhigherinnaturalwatersthan•OH,[18]theindirect

photolysisof6:2FTABwillbemediatedprimarilybyreactionswith•CO3-.

Mechanistically,thisinvestigationidentifiedeightfluorinatedproductsof6:2FTAB

photolysis.Thisincludethelittlestudied6:2FTAAand6:2FTSAm,aswellasknownthe

knownfluorotelomerspecies6:2FTSA,6:2FTOH,and6:2FTUCA.Aswell,theproduction

ofthreePFCAs,PFHpA,PFHxA,andPFPeA,wasobserved.Combined,theseproducts

accountedfor51to68mol%ofphotolyzed6:2FTAB,andprovidedthemeanstopropose

anoverallmechanismfor6:2FTABphotolysis.Theprimarysulfonamide,6:2FTSAmwas

themajorproductdetectedinallsolutions,representingtheinitialN-dealkylationreaction.

Themajordistinctionbetweensolutionswasobservedbetweendirectandindirect

photolysissettings,where6:2FTAAwasdominantunderdirectphotolysisconditions.This

32

islikelyduetoitsincreasedreactivitywithoxidizingradicalsinindirectphotolysis

solutions.Allthenon-PFCAproductsdetectedinthisexperimentareknownorsuspected

environmentalprecursorstoPFCAs.Thus,thoughPFCAsaccountedfor1.0to2.3mol%of

products,theiryieldisexpectedtoincreaseastheprecursorsdegrade.Ultimatelythis

investigationfoundthatthough6:2FTABisaless-persistentalternativetosurfactantssuch

asPFOS,itappearstobeasourceofsimilarlypersistentPFCAstotheenvironment.

33

ChapterFour

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38

ChapterFive

Appendices

39

AppendixA–SupportingInformationforChapterTwo

5.1MaterialsandMethods

5.1.1GC-MSmethod

AllsamplesdetectedbyGC-MSwereinjectedandanalyzedinduplicate.Analysisof

6:2FTOHwasdoneusinganAgilent7890AgaschromatographcoupledtoanAgilent

5975CinertXLEI/CIMSDinpositivechemicalionizationwithmethaneasareagentgas.

Both6:2FTOH(m/z365.0)anditsinternalstandard,13C4-6:2FTOH(m/z369.0),were

detectedbyselectedionmonitoringwithadwelltimeof50ms.Splitless1µLinjections

weredoneviaanautosampler.AnAgilentDB-1701column(30m×0.25mm×0.15μm)

wasusedforchromatography.Theovenprogramwasasfollows:aninitialtemperatureof

50°Cwasheldfor2minutes,thenrampedto150˚Catarateof12°Cperminute,andfinally

raisedto250˚Catarateof30°Cperminute.Heliumwasusedasacarriergasataflowrate

of1.2mLperminute.Theinlettemperaturewas250°CandtheMSDtransferlinewas

280°C.

5.1.2StatisticalAnalysis

Themultiplelinearregressionthatwasperformedassumesanormaldistributionof

dataforitsanalysis.ThetruedistributionisillustratedinFigure5.2.Thedistributiondoes

notcohereentirelywithatypicalnormaldistribution,whichmaylimitthescopeofthe

regressionperformedonthedata.However,transformationsofthedatawereunsuccessful

inproducinganormalizeddataset.Non-parametricmultiplelinearregressionwas

conducted(usingtheRsoftwarepackage(version3.2.3)withtheloessfunction)and

40

indicatedthatofthethreecomponents(bicarbonate,DOM,andnitrate),thatonlyDOMwas

asignificantcontributortothemodelatp<0.1levelofconfidence.

5.1.3SpectroradiometryandComparisontoTorontoSunlight

Spectroradiometricmeasurementsweretakenusing10msintegrationtimeand20

scanswereaveragedtoproducespectra.Figure5.1illustratestwospectratakeninsidethe

solarsimulatorandbeneathourquartzsamplecover.Asacomparison,spectralirradiance

ontworepresentativedaysinToronto,ON,Canadaisshown.Theirradiancewascalculated

usingthe“QuickTUVCalculator”fromtheNationalCentreforAtmosphericResearch

(available:http://cprm.acom.ucar.edu/Models/TUV/Interactive_TUV/).Theparameters

were:Lat:43.662˚,Long:-79.399˚,overheadozonecolumnwas300Dobsonunits,the

surfacealbedowas0.1,andthegroundelevationwas0km.TheJunedatawasfromJune

30,2015at12PMEST,andtheNovemberdatawasfromNovember18,2015at3PMEST.

TheintegratedspectralirradianceinW/m2isshownforeachtrace.Thesimulatorappears

tooutputradiationcloselymatchingthatofsummertimeintensesunlight,butitisslightly

attenuatedbyourquartzsamplecover.

41

5.2TablesandFigures

Figure 5.1: Spectroradiometric spectra of the solar simulator with and without a quartz sample cover. Solar radiation spectra from June and November shown in dashed traces

Table 5.1: MS parameters for each analyte. * indicates the quantifiying transition, where applicable

Analyte ESI Mode MRM Transition(s)

Declustering Potential (V)

Collision Energy (V)

6:2 FTAB + 571.2>440.0 571.2>104.1*

90 90

28 28

6:2 FTAA + 513.0>440.0* 513.0>58.1

90 90

28 28

6:2 FTSAm - 426.2>346.2 426.2>406.2*

-22 -22

-28 -8

13C8-FOSA - 506.0>78.0 -66 -28 6:2 FTSA - 427.0>81.0 -38 -28

13C2-6:2 FTSA - 429.0>81.0 -38 -28 6:2 FTCA - 377.0>293.0 -10 -10

0.0

1.0

2.0

3.0

4.0

5.0

6.0

250 350 450 550 650

Irrad

ianc

e (W

/m2 /n

m)

Wavelength (nm)

Solar Simulator Beneath quartz plate June sunlight November sunlight

352 W/m2

795 W/m2

830 W/m2

533 W/m2

42

13C2-6:2 FTCA - 379.0>294.0 -10 -10 6:2 FTUCA - 357.0>293.0 -10 -10

13C2-6:2 FTUCA - 359.0>294.0 -10 -10 5:3 FTCA - 341.0>236.9 -46 -12 PFHpA - 363.0>319.0 -30 -10

13C4-PFHpA - 367.1>322.0 -30 -10 PFHxA - 313.2>269.0 -26 -6

13C2-PFHxA - 315.0>270.0 -26 -6 PFPeA - 263.0>219.0 -24 -8

13C5-PFPeA - 268.1>223.0 -24 -8 PFBA - 212.9>168.9 -30 -11

13C4-PFBA - 216.9>171.9 -30 -11

Table 5.2: Average percent recoveries (from SFW C, F, and G, and DI; ± standard deviation) and limits of detection and quantification for each analyte.

Analyte Percent recovery LOD (ng/mL) LOQ (ng/mL)

6:2 FTAB 105 ± 4 0.02 0.07

6:2 FTAA 82 ± 3 0.02 0.07

6:2 FTSAm 96 ± 7 0.02 0.07

6:2 FTSA 120 ± 13 0.05 0.2

6:2 FTUCA 115 ± 14 0.01 0.03

6:2 FTCA 112 ± 7 0.2 0.7

5:3 FTCA 110 ± 4 0.03 0.1

PFHpA 118 ± 13 0.03 0.1

PFHxA 125 ± 15 0.03 0.1

PFPeA 119 ± 14 0.03 0.1

PFBA 124 ± 20 0.3 1

43

Figure 5.2: Histogram of half-life values (in hrs)

Table 5.3: Output of multiple linear regression for half-life as a function of bicarbonate, DOM, and nitrate concentrations

Standarized Coefficient (b*)

(± standard error) Raw Coefficient (b) (± standard error) p-value

Intercept (c) n/a 45.5 ± 11.8 0.00222

HCO3- (b1) -0.156 ± 0.180 -0.03727 ± 0.0431 0.404

DOM (b2) 0.757 ± 0.180 0.8138 ± 0.194 0.00125

NO3- (b3) -0.0892 ± 0.180 -0.1198 ± 0.242 0.630

Table 5.4: Molar % of all identified products by indirect and direct photolysis. Averages of all trials ± standard deviations, are reported; n.d. indicates non-detection

C (n=2) F (n=3) G (n=3) DI (n=2) 6:2 FTAA 0.22 ± 0.2 0.011 ± 0.014 n.d. 2.6 ± 0.9

6:2 FTSAm 53 ± 24 61 ± 6 45 ± 9 47.1 ± 1.5

6:2 FTSA 4.0 ± 0.3 5.2 ± 1.2 5.9 ± 1.4 0.62 ± 0.10

6:2 FTUCA 0.12 ± 0.03 0.052 ± 0.014 0.056 ± 0.008 0.03 ± 0.2

PFHpA 1.1 ± 0.5 1.3 ± 0.3 0.52 ± 0.04 0.50 ± 0.04

PFHxA 0.3 ± 0.2 0.5 ± 0.3 0.08 ± 0.03 0.02 ± 0.02

PFPeA 0.47 ± 0.09 0.49 ± 0.12 0.37 ± 0.07 0.048 ± 0.008

∑ products 59 ± 24 68 ± 5 53 ± 8 51 ± 2

0

1

2

3

4

<14 14-33 33-51 51-70 70-89 89-108

Num

bero

fvalue

s

44

Figure 5.3: Temporal production of fluorinated products: SFW C. Error bars are standard deviations

Figure 5.4: Temporal production of fluorinated products: SFW F. Error bars are standard deviations

45

Figure 5.5: Temporal production of fluorinated products: SFW G. Error bars are standard deviations

Figure 5.6: Temporal production of fluorinated products: DI. Error bars are standard deviations

46

Figure 5.7: Final product distribution, as shown in Figure 2.4, but without 6:2 FTSAm, to show minor products (n=3 for F and G, n=2 for C and DI). Error bars are standard deviations.

Figure 5.8: OECD LRTP tool output for 6:2 FTSAm with a water half-life of 17280 hrs.

0

2

4

6

8

10

C F G DI

mol%ofp

hotolyzedFTAB

6:2FTAA6:2FTSA6:2FTUCAPFHpAPFHxAPFPeA

47

Figure 5.9: OECD LRTP tool output for 6:2 FTSA, with a water half-life of 200 hrs.