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.