Aerotoxic syndrome, an ongoing environmental forensics investigation

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TheInternationalNetworkofEnvironmentalForensicsBulletin2016–volume1
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Aerotoxicsyndrome,anongoingenvironmentalforensicsinvestigation

Jean‐ChristopheBalouet(EnvironnementInternational,Orrouy,France),
DavidMegson(UniversityofToronto,Canada)

Organophosphates(OPs)have
successfulpropertiesthatmeanstheyhave
beenwidelyusedasflameretardantsand
pesticides.However,theirneurotoxic
propertieshavealsobeenlong
acknowledgedandusedinmoresinister
applicationssuchasnervegases(1).
Hundredsofthousandsvictimshavebeen
affectedbyorganophosphatesoverthelast
150years.Thishasoccurredsinceitsearly
usesinthe1890sasatreatmentto
tuberculosis,inthefamousgingerJake
poisoningcausedbycounterfeitalcohol
duringUSprohibitiontimes,andthe1959
Moroccanpoisoning,andnottoignorethe
estimated200000annualfatalitiesinthe
3rdworld(2).Interestinthisgroupof
compoundsisgrowingonceagainaswetry
toestablishthecauseofAerotoxic
syndrome.
InitsGuidancenoteMS17,TheUKHealth&
SafetyExecutive(3)warnedthatOPsof
Occupationalinterest“allactbyblockingthe
normalfunctionoftheenzyme
acetylcholinesteraseatneuronal,autonomic
effectororganorneuromuscularjunctionsand
thusinterferewiththenormaltransmissionof
nerveimpulses.”ThesymptomslistedbyHSE
correspond,onebyone,tothosedescribedfor
OPpesticidesandnerveagentsbytheCentersfor
DiseaseControlandPrevention(1)andEddleston
etal.(2),andthesymptomsofAerotoxic
syndrome(4).
Duetotheirwidespreaduseaspesticides,
organophosphatesareroutinelydetectedin
environmentalsamples.However,aspecific
concernhasariseninrecentdecadesashundreds
ofaircraftcrewandpassengers,havedeveloped
symptomsconsistentwithexposuretoOPs.
Organophosphatesarenotjustusedaspesticides
oncropsinfieldsbutarealsousedinaircraftas
flameretardantsinengineoilandhydraulicfluids
andonmaterialsurfaces.
BesidetheoccupationalexposuretoOP
pesticidesandflameretardantsdepositedon
aircraftinteriorsurfaces,OPscontainedinaircraft
lubricatingandhydraulicfluidscanenterthe
cabinair.Duringaflighttheaircabinpressure
andtemperaturearemaintainedwithoutsideair
thatispassedthroughthejetengine.Cabinairis
recycledfor50%,whereastheflightdeckairis
comprisedofacontinuousstreamofbleedair(5).
Enginesealsinuseareknownas“wet‐seals”,an
inherentdesignfeature,wherebyathinfilmofoil
preventsrotatingsurfacestocomeinto
mechanicalcontactwitheachother.Pressure
differentialsoverthesealscauseaconstantloss
ofoilandvapoursintothecoreengine.These
entertheinletofthehighpressurecompressor
and,contaminatethebleedair,whichistaken
downstream.Oil‐leaks‐by‐designcanresultinodd
smellsinthecabinandinmoreextremecases
smokeeventsasdepictedinFigure1.

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
Figure1.Smokeobservedinanaircraftcabin
duringaflight
Thisengineeringfaulthasbeenknownsincefirst
bleedairsystemsweredesignedin1953,leading
totensofthousandsofpublishedscientific
articles,engineeringandadministrative
documentsaswellasoccurrencereports
worldwide(5).ThetermAerotoxicSyndrome(4)
wasfirstpublishedin1999byaninternational
scientificteamtodescribethesymptomsand
exposureconditionsreportedbyaircraftcrew
fromAustralia,US,Europe.ThetermAerotoxic
referredtoairandaircraftaswellasthetoxic
compoundsandtheirassociatedexposures(4).
Sincetheconcernswereraisedin1999,several
officialenquirieshavebeenconducted
worldwide.Thousandsincidentreportshavebeen
collectedaroundleadingtoalargerangeof
statistics,suchasO.84incidentalflightsperdayin
theUS(7),2flightreportsperdayinGermanyin
2006,1flightin400,orseveralincidentalflights
perdayintheworld(5).OtherstatisticsbyUS
FAAindicatethatonly4%ofthesmokeandfume
eventsarereportedtotheauthorities
FAAsays“weareconcernedthatifcertain
mechanicalfailuresoccur,thecabinenvironment
maycontaincontaminants”.Although,Boeing
statesthat“cabinairissafetobreathe”.Research
hasconsistentlyshownthatcabinairmeets
healthandsafetystandardsandthatcontaminant
levelsaregenerallylow(referenceswithin6).
Overthepast20years,dozensofofficial
incident/accidentreportshaveconfirmedsimilar
facts.However,aircraftcrewworldwidehave
beenmedicallyacknowledgedforOPexposure
andseverallegalcaseshavebeensettledby
aviationindustry.Theaspectsofcausationof
Aerotoxicsyndromehavebeenstudiedunder
Hill’scriteriaandBayes‘rule(8).Despiteallofthis
researchtheinternationalenvironmental
forensicsdebatehasremainedbasically
unchanged,astheaviationindustry,thevictims
andtheirexpertsstilldebatethemajorfollowing
aspects:
Exposure:industrysupportstheviewthat
incidentalexposureeventsduringflightsarerare,
howeverunderreportedtheyare;andthatOP
concentrationsinnormalflightsaretoolowto
causesymptoms.Theydoacknowledgethe
presenceofTCPatlowconcentrationsas
measuredonthemajorityoftestedaircraft.
However,itcouldbearguedthatofficial
measurementcampaignshavenotdealtwith
incidentalexposureonflightswhereleakshave
occurred,andhavebeenselectiveonsought
compounds,i.e;lookingforToCPwhichisthe
leastabundantandtoxicTCPinaircraftfluids,.
Thesamplingandanalyticalprotocolsarealso
debated.Shouldsamplingbeundertakenonfresh
oil,usedoil,bleedairvapourandhowcanyou
targetsamplinganincidentalfume/smoke
event?Alsotherearesignificantanalytical
challengeswiththeneedtoquantifyallTCP
isomersandscreenforthepresenceof,and
identify,anynewcompoundsgeneratedby
pyrolysis.
Symptoms:Conditionshavebeendescribedsuch
asOPIDN(OPInducedDelayedNeuropathy)or
COPIDN(ChronicOPInducedDelayed
Neuropathy)orasCOPIND(ChronicOP
NeuroPsychologicalDisorder)(9,10).However,
industryrepresentativesviewseveralofthe

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symptomsreportedbycrewmembersasnon‐
specific,suchassalivation,lacrymation,difficulty
breathing,tachychardyevolvingwithtimeto
bradycardy,coughing,dizziness,nausea,
diaorrheaandfatiguewhichcouldbeeasily
causedbyoralsowronglymisattributedtojetlag.
Themostworrisomesymptomsreportedbycrew
membersareneurotoxic,includingimpairedshort
termmemory,alteredcoordination,blurred
visionandspeech.Thesecausesignificant
immediateconcernsforflightsafetytoaircraft
crewandindeedpassengers.Therearealsolong
termconcerns;dopeopleexposedonboardan
aircraftdevelopneurologicalsymptomsinthe
future?
Toxicology:mostofthedebatecentreson
tricresylphosphate(TCP),whichispresentin
lubricatingoilsatapproximately3‐5%.Industry
supportstheprincipleofano‐thresholdlevel,
indeedTheWorldHealthOrganisation(11)state
thatbecauseofconsiderablevariationamong
individualsinsensitivitytotri‐o‐cresylphosphate
(ToCP),itisnotpossibletoestablishasafelevelof
exposure.However,CraigandBarth(12)have
morerecentlycalculatedano‐effectlevel;others
arguetheuseofalinearno‐thresholdlimit,
versusthehormesisprinciple(13)orNon‐
monotonicdose‐response(14)bywhichthedose
responsemaynotbelinear.Allparties
acknowledgethatOPsareneurotoxicants,
howeveritismoredifficulttoestablishthe
toxicityofthejetoilvapourasnewcompounds
maybesynthesisedbypyrolysisandthesecould
playanimportantadditiveorsynergisticrole.
Thereisalsotheaddedcomplicationduetothe
largevariationinindividualsandtheirabilityto
metaboliseandeliminateOPs.Approximately4%
ofthehumanpopulationpoorlymetabolisesOPs
(8),andcrews/frequentflyersmayhavehad
alreadytheircholinesteraselevelsdepletedby
previousexposuresandthereforebemore
susceptible.TheeffectoftheAuto‐immune
systemisfirstlookedatbyAbouDonia(9)in
responsetoalowdoseofOPscausingneuronal
celldeathinthebrain.Neurofilamentsofthese
decayingcellpassthedamagedBlood‐Brain–
BarrierintothebloodstreamandtriggeranIgG
mediatedT‐memorycellresponse.The
amplificationfactoroftheimmunesystemis
severalordersofmagnitudegreaterthanthe
originaldose‐effectresponse.Consequential
irreversibledamagetotheperipheralnervous
systemandorganslikethehearthavebeen
observed(15).
Conclusions
Thereisanevergrowinglistofaircraftpersonnel
thatarereportingsymptomsconsistentwith
exposuretoOPs.Luckily,manyofthesecrew
membersrecoverandreturntotheirflightduties,
howevertoomanystaffhavelosttheirjobs,and
evenmoresadly,severalhavepassedaway.UK
CoronerPayne,recentlyissuedaregulationto
preventfurtherdeathsfollowingthedeathof
CaptainRichardWestgate,whichwaslinkedtoOP
poisoning.Twomorepost‐mortemcases(Bass,
Brady)havesincebeenidentifiedwithsimilar
findingsasapossiblecauseofdeath(Lymphocytic
Myocarditis).Still,theaircraftcrewand
passengersarepoorlyinformedastowhattoxic
chemicalstheyhavebeenpotentiallyexposedto.
Therefore,incaseswheresymptomsdodevelop
theyareoftennotabletogetpropermedical
care.
WhenmanylegalcasesassociatedwithAerotoxic
syndromehavebeensettledorhandledbyCourts
inthepast,dozensofcasesarestillon,facingthe
samedisputes,foralmost20years.Thisiswhere
environmentalforensicsisneededtoimproveour
environment,healthandwellbeing,forfactsnot
vestedopinions.

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Acknowledgements
TheauthorsthankDrMichelMulderx&Mathew
Robsonfortheirconstructivecommentsonthis
article.
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