UC Irvine UC Irvine Previously Published Works Title Chemical kinetics of multiphase reactions between ozone and human skin lipids: Implications for indoor air quality and health effects. Permalink https://escholarship.org/uc/item/82933277 Journal Indoor air, 27(4) ISSN 0905-6947 Authors Lakey, PSJ Wisthaler, A Berkemeier, T et al. Publication Date 2017-07-01 DOI 10.1111/ina.12360 Peer reviewed eScholarship.org Powered by the California Digital Library University of California Received:10June2016 | Accepted:30November2016 DOI: 10.1111/ina.12360 ORIGINAL ARTICLE Chemical kinetics of multiphase reactions between ozone and human skin lipids: Implications for indoor air quality and health effects P. S. J. Lakey1 | A. Wisthaler2 | T. Berkemeier1 | T. Mikoviny2 | U. Pöschl1 | M. Shiraiwa1,3 1MultiphaseChemistryDepartment,Max PlanckInstituteforChemistry,Mainz, Abstract Germany Ozonereactswithskinlipidssuchassqualene,generatinganarrayoforganiccom- 2 DepartmentofChemistry,UniversityofOslo, pounds,someofwhichcanactasrespiratoryorskinirritants.Thus,itisimportantto Oslo,Norway quantifyandpredicttheformationoftheseproductsunderdifferentconditionsinin- 3DepartmentofChemistry,Universityof California,Irvine,CA,USA doorenvironments.Wedevelopedthekineticmultilayermodelthatexplicitlyresolves masstransportandchemicalreactionsattheskinandinthegasphase(KM-SUB-Skin). Correspondence M.Shiraiwa,DepartmentofChemistry, It can reproduce the concentrations of ozone and organic compounds in previous UniversityofCalifornia,Irvine,CA,USA. measurementsandnewexperiments.Thisenabledthespatialandtemporalconcentra- Email:[email protected] tionprofilesintheskinoilandunderlyingskinlayerstoberesolved.Uponexposureto Funding information ~30ppbozone,theconcentrationsofsqualeneozonolysisproductsinthegasphase Max-Planck-Gesellschaft;MaxPlanck GraduateCenterwiththeJohannes andintheskinreachuptoseveralppbandontheorderof~10mmolm−3.Depending Gutenberg-UniversiätMainz(MPGC) onvariousfactorsincludingthenumberofpeople,roomsize,andairexchangerates, concentrationsofozonecandecreasesubstantiallyduetoreactionswithskinlipids. Ozoneanddicarbonylsquicklyreactawayintheupperlayersoftheskin,preventing themfrompenetratingdeeplyintotheskinandhencereachingtheblood. KEYWORDS dicarbonyls,kineticmodeling,ozone,respiratoryirritants,skinirritants,squalene 1 | INTRODUCTION Interactions of O3 with skin lipids are important for indoor air quality, including O3 concentration and deposition in an indoor en- 11–13 Peoplespendonaverage90%oftheirtimeindoors.Indooraircanbe vironment. ThereactionofO3withskinoilshaspreviouslybeen more polluted than outdoor air and the World Health Organization investigatedinenclosedspacessuchasaircraftcabinsandsimulated estimated that in 2002 indoor air pollutionwas responsible for 1.5 officesbyexposingpeople,hair,orsoiledclothing.6,14–20Thesestudies milliondeathsand2.7%oftheglobalburdenofdisease.1Therefore, haveconsistentlyshownthatthepresenceofhumanoccupantsand betterunderstandingoftheairqualityandreactionsthatcanoccur soiledclotheswilldecreaseO3concentrationssubstantiallywithinthe within indoor environments isvery important.A major oxidant that enclosedspace,whilstvolatilespecieswillincreaseinthegasphase. hasbeenmeasuredinindoorenvironmentsisO3withconcentrations Thesevolatileproducts,especiallythedicarbonyls,havethepotential 2 21,22 inside buildings and houses ranging between ~5 and 150 ppb. O3 toberespiratoryirritants. Thecompositionandconcentrationof canbeinhaledbypeopleaswellasreactingwithindoorfurnishings, secondaryorganicaerosol(SOA),animportantfractionofindoorpar- cleaningproducts,andtheskinoilsoftheoccupantswithinthebuild- ticulatematter,wouldalsobeimpactedbychangesinO3concentra- ing.3–6Humanskinoilscontainmanyunsaturatedspeciesthatarere- tionsandvolatileorganiccompounds(VOCs).15,23–25 activetowardO3includingsqualene,fattyacids,waxesters,sterols, Squaleneozonolysisproductshavealsobeenobservedtoaccumu- glycerols,phospholipidsaswellasantioxidants(ascorbate,uricacid, lateinskinoilthathasbeenexposedtoozone.26Theselowervolatility 7–10 glutathione,andα-tocopherol),andcoenzymeQ. products may be skin irritants and could also be absorbed into the Indoor Air 2016; 1–13 wileyonlinelibrary.com/journal/ina © 2016 John Wiley & Sons A/S. | 1 Published by John Wiley & Sons Ltd LAKEY Ket Ll | 2 bloodstreamovertime.21,27,28Severalmodelsoftheskinexist,focus- ingondermalabsorptionfromthegasphase.29,30Forexample,Gong Practical implications et al. predicted the absorption rate of six different phthalate esters • Reactions of ozone with skin lipids in indoor environ- into the blood when skin was exposed to these gas-phase species mentsimpactindoorairqualitybydecreasingozonecon- 29 forvaryingamountsoftime. However,currentlytoourknowledge, centrations and increasing concentrations of squalene theseskinmodelshavenotcombinedphysicalprocesses(adsorption, ozonolysisproductsinthegasphase.Theseproductsin- desorption,anddiffusion)withchemistry.Ouraimwastodevelopa cludemonocarbonylsanddicarbonyls,whicharelikelyto modeltoestimatetheconcentrationsofO andrespiratoryandskin 3 berespiratoryandskinirritants.Monocarbonylscandif- irritants formed upon exposure of people to O in different indoor 3 fuse through the skin and enter the blood, potentially environments. causing adverse health effects. We have developed a model to quantify skin ozonolysis products in different indoorenvironments. 2 | DESCRIPTION OF THE KM- SUB- SKIN MODEL The kinetic multilayer model of surface and bulk chemistry of the The stratum corneum is the outermost part of the skin and skin (KM-SUB-Skin) was developed based on the kinetic multilayer consists of 15-20 layers of dead flattened cellswith a thickness of 31 35 model for aerosol surface and bulk chemistry (KM-SUB). A sche- ~25μm. Theviableepidermisistheskinbelowthestratumcorneum 36 matic ofprocessesoccurring inKM-SUB-Skin isshowninFigure1. andconsistsoflivingcellswithathicknessof~100μm. Inthisstudy, Themodelincludesdifferentlayers:agasphase,anear-surfacegas bothpartsweredescribedwith20bulklayers.Themodeltreatsthe phase,asorptionlayer,askinoillayer,anumberofbulklayersinthe followingmasstransportandchemicalreactionsexplicitly:adsorption stratumcorneumandintheviableepidermis,andalayerofbloodves- anddesorptionfromthesurfaceoftheskinoil,bulkdiffusioninthe sels.Theskinisassumedtobeuniformlycoveredby~0.45-μ m-thick skinoil,stratumcorneum,viableepidermis,andintothebloodvessels, 32 skinoil. Itshouldalsobenotedthatthereissomevariabilityinthe chemicalreactionsbetweenO3andsqualene,O3andotherreactive skinoilthicknessofapersonandskinoilconcentrationsindifferent speciesandreactionsofproductswithintheskinoil,stratumcorneum, 32–34 regionsofthebody. Thiswouldaffecttheconcentrationsofboth andviableepidermisaswellasgas-phasereactionsbetweenO3 and ozoneandthesqualeneozonolysisproducts,astherewouldbemore volatileproducts.Productionofsqualenebyoilglandsandintercellular squalenemoleculesforozonetoreactwith.Sensitivitytestsshowed lipidswasalsotreated.37Detailsofthedifferentialequationsincluded thatavariabilityofskinoilthicknesswouldnotaffectthepredicted inthemodeldescribingtheevolutionofspecieswithinthegasphase concentrationsintheskinandfluxesintothebloodsignificantly(see anddifferentlayersoftheskinduetomasstransport,production,and SupportingInformation). lossaresummarizedintheSupportingInformation. FIGURE 1 InteractionsofO3withtheskin.ReactionsofO3withskinlipidsincludingsqualene.Reactionproductsincludegas-phase volatileorganiccompoundssuchas4-OPAand6-MHOaswellassemi-­ orlow-volatileproducts,whichmaydiffusethroughthestratum corneumandtheviableepidermistotheblood.TherightpanelshowstheschematicoftheKM-SUB-Skinmodeldevelopedinthisstudy.Mass transportfluxesandchemicalreactionsareshownasgreenandredarrows,respectively.SqandPsymbolizesqualeneandozonolysisproducts, respectively.Notethatwealsoincludeotherspeciesandreactionswithinthemodel(seetextformoredetails).Thesubscriptsg,gs,oil,sc1,scn, ve1,andvenrepresentthegasphase,near-surfacegasphase,oillayer,firstlayerofthestratumcorneum,lastlayerofthestratumcorneum,first layeroftheviableepidermis,andlastlayeroftheviableepidermis,respectively. LAKEY K et L l TABLE 1 Squaleneozonolysischemistry,partitioncoefficients,anddiffusioncoefficientsofsqualeneozonolysisproducts.Seetextformoredetailsabouthowvalueswereobtained Vapor pressure Volatile/ Partition Diffusion coefficient in the Diffusion coefficient in the Structure Name Ozonolysis products at 298K (Pa) Non- volatilea coefficient stratum corneum (cm2 s−1) viable epidermis (cm2 s−1) Squalene Acetone,6-MHO,Geranylacetone, 1.52×10−4 Non-volatile N/A 7.3×10−18 3.4×10−13 TOT,TOP,TTT Acetone NOREACTION 3.09×104 Volatile 34 4.6×10−11 3.9×10−6 6-MHO 4-OPA,Acetone 238 Volatile 6.3×105 9.7×10−11 8.6×10−7 Geranyl 4-OPA,4-MON,Acetone,6-MHO 3.35 Volatile 7.1×106 1.3×10−10 9.7×10−8 acetone TOT Acetone,6-MHO,Geranylacetone, 2.26×10−5 Non-volatile N/A 1.9×10−15 1.3×10−11 4-OPA,4-MON,TTT,TOP, ProductA,ProductC,ProductD TOP Acetone,6-MHO,Geranylacetone, 1.39×10−3 Non-volatile N/A 1.5×10−13 2.7×10−10 4-OPA,4-MOD,TTT,ProductB, ProductC TTT Acetone,6-MHO,Geranylacetone, 5.37×10−2 Non-volatile N/A 1.5×10−11 5.4×10−9 4-MOD,1,4-butanedial,ProductA 4-OPA NOREACTION 454 Volatile 4.8×104 5.9×10−12 3.0×10−6 4-MON 4-OPA 3.19 Volatile 1.3×107 2.1×10−11 1.0×10−6 4-MOD 4-OPA,1,4-butanedial 4.72 Volatile 6.5×106 3.1×10−11 1.0×10−6 1,4-butanedial NOREACTION 697 Volatile 3.0×103 9.8×10−12 3.2×10−6 (Continues) | 3 LAKEY Ket Ll | 4 Table1summarizesthechemicalstructuresofthesqualeneozo- ) −1 nolysisproductsandliststheskin-airpartitioncoefficientsaswellas