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Aerotoxicsyndrome,anongoingenvironmentalforensicsinvestigation
JeanChristopheBalouet(EnvironnementInternational,Orrouy,France),
DavidMegson(UniversityofToronto,Canada)
Organophosphates(OPs)have
successfulpropertiesthatmeanstheyhave
beenwidelyusedasflameretardantsand
pesticides.However,theirneurotoxic
propertieshavealsobeenlong
acknowledgedandusedinmoresinister
applicationssuchasnervegases(1).
Hundredsofthousandsvictimshavebeen
affectedbyorganophosphatesoverthelast
150years.Thishasoccurredsinceitsearly
usesinthe1890sasatreatmentto
tuberculosis,inthefamousgingerJake
poisoningcausedbycounterfeitalcohol
duringUSprohibitiontimes,andthe1959
Moroccanpoisoning,andnottoignorethe
estimated200000annualfatalitiesinthe
3rdworld(2).Interestinthisgroupof
compoundsisgrowingonceagainaswetry
toestablishthecauseofAerotoxic
syndrome.
InitsGuidancenoteMS17,TheUKHealth&
SafetyExecutive(3)warnedthatOPsof
Occupationalinterest“allactbyblockingthe
normalfunctionoftheenzyme
acetylcholinesteraseatneuronal,autonomic
effectororganorneuromuscularjunctionsand
thusinterferewiththenormaltransmissionof
nerveimpulses.”ThesymptomslistedbyHSE
correspond,onebyone,tothosedescribedfor
OPpesticidesandnerveagentsbytheCentersfor
DiseaseControlandPrevention(1)andEddleston
etal.(2),andthesymptomsofAerotoxic
syndrome(4).
Duetotheirwidespreaduseaspesticides,
organophosphatesareroutinelydetectedin
environmentalsamples.However,aspecific
concernhasariseninrecentdecadesashundreds
ofaircraftcrewandpassengers,havedeveloped
symptomsconsistentwithexposuretoOPs.
Organophosphatesarenotjustusedaspesticides
oncropsinfieldsbutarealsousedinaircraftas
flameretardantsinengineoilandhydraulicfluids
andonmaterialsurfaces.
BesidetheoccupationalexposuretoOP
pesticidesandflameretardantsdepositedon
aircraftinteriorsurfaces,OPscontainedinaircraft
lubricatingandhydraulicfluidscanenterthe
cabinair.Duringaflighttheaircabinpressure
andtemperaturearemaintainedwithoutsideair
thatispassedthroughthejetengine.Cabinairis
recycledfor50%,whereastheflightdeckairis
comprisedofacontinuousstreamofbleedair(5).
Enginesealsinuseareknownas“wetseals”,an
inherentdesignfeature,wherebyathinfilmofoil
preventsrotatingsurfacestocomeinto
mechanicalcontactwitheachother.Pressure
differentialsoverthesealscauseaconstantloss
ofoilandvapoursintothecoreengine.These
entertheinletofthehighpressurecompressor
and,contaminatethebleedair,whichistaken
downstream.Oilleaksbydesigncanresultinodd
smellsinthecabinandinmoreextremecases
smokeeventsasdepictedinFigure1.
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Figure1.Smokeobservedinanaircraftcabin
duringaflight
Thisengineeringfaulthasbeenknownsincefirst
bleedairsystemsweredesignedin1953,leading
totensofthousandsofpublishedscientific
articles,engineeringandadministrative
documentsaswellasoccurrencereports
worldwide(5).ThetermAerotoxicSyndrome(4)
wasfirstpublishedin1999byaninternational
scientificteamtodescribethesymptomsand
exposureconditionsreportedbyaircraftcrew
fromAustralia,US,Europe.ThetermAerotoxic
referredtoairandaircraftaswellasthetoxic
compoundsandtheirassociatedexposures(4).
Sincetheconcernswereraisedin1999,several
officialenquirieshavebeenconducted
worldwide.Thousandsincidentreportshavebeen
collectedaroundleadingtoalargerangeof
statistics,suchasO.84incidentalflightsperdayin
theUS(7),2flightreportsperdayinGermanyin
2006,1flightin400,orseveralincidentalflights
perdayintheworld(5).OtherstatisticsbyUS
FAAindicatethatonly4%ofthesmokeandfume
eventsarereportedtotheauthorities
FAAsays“weareconcernedthatifcertain
mechanicalfailuresoccur,thecabinenvironment
maycontaincontaminants”.Although,Boeing
statesthat“cabinairissafetobreathe”.Research
hasconsistentlyshownthatcabinairmeets
healthandsafetystandardsandthatcontaminant
levelsaregenerallylow(referenceswithin6).
Overthepast20years,dozensofofficial
incident/accidentreportshaveconfirmedsimilar
facts.However,aircraftcrewworldwidehave
beenmedicallyacknowledgedforOPexposure
andseverallegalcaseshavebeensettledby
aviationindustry.Theaspectsofcausationof
Aerotoxicsyndromehavebeenstudiedunder
Hill’scriteriaandBayes‘rule(8).Despiteallofthis
researchtheinternationalenvironmental
forensicsdebatehasremainedbasically
unchanged,astheaviationindustry,thevictims
andtheirexpertsstilldebatethemajorfollowing
aspects:
Exposure:industrysupportstheviewthat
incidentalexposureeventsduringflightsarerare,
howeverunderreportedtheyare;andthatOP
concentrationsinnormalflightsaretoolowto
causesymptoms.Theydoacknowledgethe
presenceofTCPatlowconcentrationsas
measuredonthemajorityoftestedaircraft.
However,itcouldbearguedthatofficial
measurementcampaignshavenotdealtwith
incidentalexposureonflightswhereleakshave
occurred,andhavebeenselectiveonsought
compounds,i.e;lookingforToCPwhichisthe
leastabundantandtoxicTCPinaircraftfluids,.
Thesamplingandanalyticalprotocolsarealso
debated.Shouldsamplingbeundertakenonfresh
oil,usedoil,bleedairvapourandhowcanyou
targetsamplinganincidentalfume/smoke
event?Alsotherearesignificantanalytical
challengeswiththeneedtoquantifyallTCP
isomersandscreenforthepresenceof,and
identify,anynewcompoundsgeneratedby
pyrolysis.
Symptoms:Conditionshavebeendescribedsuch
asOPIDN(OPInducedDelayedNeuropathy)or
COPIDN(ChronicOPInducedDelayed
Neuropathy)orasCOPIND(ChronicOP
NeuroPsychologicalDisorder)(9,10).However,
industryrepresentativesviewseveralofthe
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symptomsreportedbycrewmembersasnon
specific,suchassalivation,lacrymation,difficulty
breathing,tachychardyevolvingwithtimeto
bradycardy,coughing,dizziness,nausea,
diaorrheaandfatiguewhichcouldbeeasily
causedbyoralsowronglymisattributedtojetlag.
Themostworrisomesymptomsreportedbycrew
membersareneurotoxic,includingimpairedshort
termmemory,alteredcoordination,blurred
visionandspeech.Thesecausesignificant
immediateconcernsforflightsafetytoaircraft
crewandindeedpassengers.Therearealsolong
termconcerns;dopeopleexposedonboardan
aircraftdevelopneurologicalsymptomsinthe
future?
Toxicology:mostofthedebatecentreson
tricresylphosphate(TCP),whichispresentin
lubricatingoilsatapproximately35%.Industry
supportstheprincipleofanothresholdlevel,
indeedTheWorldHealthOrganisation(11)state
thatbecauseofconsiderablevariationamong
individualsinsensitivitytotriocresylphosphate
(ToCP),itisnotpossibletoestablishasafelevelof
exposure.However,CraigandBarth(12)have
morerecentlycalculatedanoeffectlevel;others
arguetheuseofalinearnothresholdlimit,
versusthehormesisprinciple(13)orNon
monotonicdoseresponse(14)bywhichthedose
responsemaynotbelinear.Allparties
acknowledgethatOPsareneurotoxicants,
howeveritismoredifficulttoestablishthe
toxicityofthejetoilvapourasnewcompounds
maybesynthesisedbypyrolysisandthesecould
playanimportantadditiveorsynergisticrole.
Thereisalsotheaddedcomplicationduetothe
largevariationinindividualsandtheirabilityto
metaboliseandeliminateOPs.Approximately4%
ofthehumanpopulationpoorlymetabolisesOPs
(8),andcrews/frequentflyersmayhavehad
alreadytheircholinesteraselevelsdepletedby
previousexposuresandthereforebemore
susceptible.TheeffectoftheAutoimmune
systemisfirstlookedatbyAbouDonia(9)in
responsetoalowdoseofOPscausingneuronal
celldeathinthebrain.Neurofilamentsofthese
decayingcellpassthedamagedBloodBrain–
BarrierintothebloodstreamandtriggeranIgG
mediatedTmemorycellresponse.The
amplificationfactoroftheimmunesystemis
severalordersofmagnitudegreaterthanthe
originaldoseeffectresponse.Consequential
irreversibledamagetotheperipheralnervous
systemandorganslikethehearthavebeen
observed(15).
Conclusions
Thereisanevergrowinglistofaircraftpersonnel
thatarereportingsymptomsconsistentwith
exposuretoOPs.Luckily,manyofthesecrew
membersrecoverandreturntotheirflightduties,
howevertoomanystaffhavelosttheirjobs,and
evenmoresadly,severalhavepassedaway.UK
CoronerPayne,recentlyissuedaregulationto
preventfurtherdeathsfollowingthedeathof
CaptainRichardWestgate,whichwaslinkedtoOP
poisoning.Twomorepostmortemcases(Bass,
Brady)havesincebeenidentifiedwithsimilar
findingsasapossiblecauseofdeath(Lymphocytic
Myocarditis).Still,theaircraftcrewand
passengersarepoorlyinformedastowhattoxic
chemicalstheyhavebeenpotentiallyexposedto.
Therefore,incaseswheresymptomsdodevelop
theyareoftennotabletogetpropermedical
care.
WhenmanylegalcasesassociatedwithAerotoxic
syndromehavebeensettledorhandledbyCourts
inthepast,dozensofcasesarestillon,facingthe
samedisputes,foralmost20years.Thisiswhere
environmentalforensicsisneededtoimproveour
environment,healthandwellbeing,forfactsnot
vestedopinions.
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Acknowledgements
TheauthorsthankDrMichelMulderx&Mathew
Robsonfortheirconstructivecommentsonthis
article.
References
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