Disinfectant#2:Chlorine:IsChlorineStillattheHeadoftheClass??
Similartoquaternaryammoniumsolutions,mostpeopleareveryfamiliarwiththeantimicrobial
qualitiesofchlorinebasedsolutions.Chlorinecompoundswererecognizedfortheirdeodorizingand
disinfectingpropertiesin19thcenturyandtheirwideusebegansoonthereafter.Today,chlorine’s
antimicrobialcapabilitiesaremostcommonlyharnessedforuseinwatertreatmentorsurface
disinfection.
ThisishowwewouldrateChlorinedisinfectantsbasedonthekeydecisionmakingcriteria:(seebelow)
ChlorineAcidDisinfectantReportCard
Subject
Grade
Speedof
Disinfection
A
to
C
Spectrumof
Kill
A
to
C
D
Cleaning
Effectiveness
SafetyProfile
Environmental
Profile
Cost
Effectiveness
B
to
D
A to B
A
Comments
Mostbestpracticeguidelinesrecommend10minutecontacttimesbe
utilizedwithbleachbasedsolutions.
Higherconcentrations(>1000ppm)canelicitmorerapidkillagainst
bacteriaandviruses
Similartothespeedofdisinfection,performanceinthiscriteriaistied
tothein-useconcentration.
5000ppmisrecognizedassporicidal;1000ppmaseffectiveagainst
non-envelopedviruses;<1000ppmsolelyforuseasalowlevel
disinfectant
Chlorinesolutionshavenoinherentdetergencycapabilities;best
practiceguidelinesunanimouslysupportthepracticeofcleaning
surfaceswithadetergentpriortousingbleachasadisinfectant
Thisisanotherparameterlargelyaffectedbythein-useconcentration
ofthesolution.
>1000ppmsolutionsaregenerallyirritatingtoeyesandskin
(respiratoryirritationalsobecomesagreaterconcernathigher
concentrations);<1000ppmsolutionsrequirelessprecaution
Althoughchlorinecompoundsarenotpersistentintheenvironment
upondisposal,becausetheytendtobesohighlyreactivetherisklies
moreinthepotentialcross-reactionswithotherchemicalsthatmaybe
presentinwaste-water
Bleachisacommoditythatisreadilyavailableinconcentrated
formats,howeverthedilutedsolutionsmustbereplacedregularly
whichmayresultinwastedproduct
Chlorinesolutions,eveninverylowlevels,canshowhighantimicrobialactivity.Themicrobicidalaction
isattributedtohypochlorousacid,oftenreferredtomoregenerallyas“freeavailablechlorine”.The
antimicrobialactivityofchlorineisverydependentonthepHofthesolutionasthisdeterminesthe
concentrationofdissociated(available)hypochlorousacidinsolution.Anexampleofthe“pHeffect”
canbeillustratedbyastudythatfound25PPMchlorinetokill99%ofbacterialsporeswithin2.5
minuteswhenthesolutionisatapHof6,however,thecontacttimerequiredtoachievethesamelevel
ofkillwitha25PPMsolutionatapHof12.86was465minutes.OnecaveatthatImustmakeistonote
thataproductrequiresa99.9999%killinordertoachieveEPAorHealthCanadasporicidalclaimsso
don’tbefooledintothinkinga25ppmconcentrationofchlorineissporicidal!
Asignificantdisadvantageofchlorinesolutions,particularlyhypochlorites(bleach)isthattheiroverall
performanceistiedsocloselytothestabilityofthehypochlorousacid.Thestabilityofhypochlorous
acidinthesolutionsignificantlydependsonchlorineconcentration(thelowertheconcentration,the
lowertheefficacy,butthehigherthestability),presenceofcatalystsorreducingagents(catalysts
reducethestability),pHofthesolution(higheralkalinityincreasesstability,butdecreasesefficacy),
temperatureofthesolution(lowertemperatureincreasesstability),presenceoforganicmaterial
(organicmaterialreducesbothstabilityandefficacy).Inshort,thereisamultitudeoffactorsthatneed
tobetakenintoaccounttoensuretheeffectivenessofachlorinesolutionforuseasadisinfectant.
Forthoseofyouwithkeeneyes,youwillhaveidentifiedthecompetinginterestsinverselyaffectedby
pH.Ononehand,thedisinfectantcapabilitiesofhypochloritesolutionsaremuchbetteratlowerpH
values,howeverattheselowervaluesthesolutionsarealsoveryunstable.Therefore,most
commerciallyavailableproductsareonlyavailableashigherpHsolutionstoensurestabilitybut
compromisewitheithercontacttimesthataretoolong(10minutes)toberealisticallyachievedor
concentrationsat5000ppmorhigherthatwhileimprovinguponspeedalsoincreaseoccupational
healthandsafetyrisks.
Aswehavedwelleduponinpreviousblogs,anotherveryimportantconsiderationisaproduct’sability
tocleanandaidintheabilitytoliftandremovalsoilsfromasurface.Chlorineisableachingagentand
whileexcellentathelpingtowhitenandbrighten,Chlorinedoesnothaveanydetergencyproperties.It
isunabletoreducethesurfacetensionbetweensoilsandasurfaceandasaresultchlorine’scleaning
abilityorefficiencyisequivalenttowater.Certainly,therearesomeready-to-useformulationsthat
incorporatebothchlorineandsurfactantswhichwillimprovecleaningperformance,butin
concentratedformulationsofchlorinetheadditionofsurfactantswilldegradeboththechlorineand
thesurfactantresultinginaproductthatcanneitherkillnorclean.
Similartoefficacy,theconcentrationofchlorineisdirectlyrelatedtothechemical’stoxicity.Chlorineis
astrongoxidizingagentthatishighlyreactivenotonlywithotherchemicals,butwithcellcomponents
suchasDNA,proteins,lipidsandcarbohydrates.Whileingestionofchlorinesolutionscanbelethal,
theextentoftoxicityisdirectlyrelatedtotheconcentration.Toxicitystudiesofexposureofchlorine
toskinandeyesexposurehavefoundthatconcentrations<1000ppmtobenonskinsensitizingand
causeonlyslightirritationtoskinandeyes,atconcentrations>1000ppmtheirritationincreases
significantlyastheconcentrationincreases.
BoththeconcentrationpHchlorinehasadirectaffectonrespiratoryirritationandtoxicity.Studieson
theratesofasthmainchildrenandcompetitiveswimmershavefoundalinkbetweentheexposuresto
chlorinefromindoorswimmingpoolstoincreasedratesinasthma.Concentrationsofbleach>5000ppm
especiallyifusedinenclosedspaceswithlittleventilationhavebeenfoundtobeirritatingtotheuser.
AtpHof5orhigher,thedevelopmentofchlorinegasisnegligible;howeveracidifiedsolutionswitha
pHlessthan5willreleasechlorinegasandcanbetoxicifinhaled.
Lastly,oneadvantagetochlorineisthatitreadilydegradesandisnotpersistentintheenvironmentasit
degradestooxygenandchloride.Thislimitsthechancepathogenswilldevelopchemicalresistance,
howeverdoesnotinanywaymakeitenvironmentallybenign.Chlorineaswehavestatedishighly
reactive.Itcancreatetoxicbi-productswhenmixedwithchemicalsandifreleaseddirectlyintowater
isverylethaltoaquaticlife.
Withthesekeypointsfreshinyourmind,howwouldyougradechlorineasadisinfectantchemistry?
Rememberthatchlorine,particularlyhypochlorites,isutilizedwithinaspectrumofvarious
concentrations.