11/27/2014 Whyuseleadinpaint?

http://www.rsc.org/chemistryworld/News/2007/August/21080701.asp 1/2

Why use lead in paint?

21August2007

Mattel,theworld'sbiggesttoymaker,hasrecalledmillionsoftoysthatwerecoatedwithleadpaint.Lead'spoisonouspropertieshavebeenknownforthousandsofyears,sowhywasleadeveraddedtopaint,andwhyisleadpaintstillbeingmade?Whatis'leadpaint'?Anypaintthatreliesonleadcompoundsforitscolour.Whitelead,orlead(II)carbonate(PbCO3),isatypicalexample,andwasoncewidelyusedtopaintwoodensurfacesinhomes.Otherleadcompounds,likevividyellowleadchromate(PbCrO4),wereusedascolouredpigments.Aswellasgivingthepaintitstint,leadpigmentsarehighlyopaque,sothatarelativelysmallamountofthecompoundcancoveralargearea.Whiteleadisveryinsolubleinwater,makingthepainthighlywaterresistantwithadurable,washablefinish.Leadcarbonatecanalsoneutralisetheacidicdecompositionproductsofsomeoftheoilsthatmakeupthepaint,sothecoatingstaystough,yetflexibleandcrackresistant,forlonger.Sowhat'stheproblem?Leadistoxic,andasyoungchildrentendtochewthings,theyareparticularlypronetoingestingit.Notgoodfortheirvulnerable,developingbrains.Itwasincreasinglyrecognisedinthefirsthalfofthe20thcenturythatchildrenwerebeingpoisoningwithleadpaint,anditsuseincotsandtoyshadbeenphasedoutintheWestbythe1950s.However,leadbaseddecorativehouseholdpaintswerestillusedforanothercoupleofdecadesbeforethistooendedduetohealthconcerns.Whyisleadtoxic?Leadcandisruptnumerouscrucialbodilyfunctions,andhencehasawidevarietyofsymptoms,fromvomitingtomadnesstodeath.It'sknowntobeapotentblockerofreceptorsofglutamate,aneurotransmittercrucialforlearning.Itisalsoabletodisplaceaseriesofothermetalsfromdoingtheirnormaljobinthebodymostsignificantly,calcium,ironandzinc.Aparticularproblemisthatleaddisplacesthezincfromtheenzymedeltaaminolaevulinatedehydratase,whichiscrucialforthebiosynthesisofheme,theironbindingpartofthehaemoglobinmoleculethatcarriesoxygenaroundtheblood.Thisresultsincellsaroundthebodybeingshortofoxygen,causingacascadeofassociatedproblems.Allleadpaintshavebeenbannedthen?Almost.Forthevastmajorityofuses,leadpigmentshavebeenreplacedwithtitaniumdioxide,whichissosafeit'salsousedinfoodcolouringsaswellasinsunscreen.IntheEU,leadpaintcannowonlybeusedfortherestorationandmaintenanceofworksofartandhistoricalbuildings.IntheUS,leadpaintcanbeusedinlimitedindustrialsettings,suchastocoatshipshulls.Howwasthetoxicpaintfound?Mattelidentifiedthetoxicpaintduringroutinesafetychecks.Leadinpainteitherinitsliquidform,orasadriedcoatingonaproductcanbedetectedbyanumberofanalyticaltechniques,saidAllanStewartoftestingandcertificationfirmIntertek'sMeasurementScienceGroupLabonTeesside,UK.Atomicabsorptionandxrayfluorescencespectroscopyarebothgeneralmethodsthatcanrevealthepresenceoflead,whileinductivelycoupledplasmamassspectrometrycandetectleadinlessthanpartperbillionquantities,headded.Sowhat'shappeninginChina?Chinaisgraduallycrackingdownontheuseoflead,banningleadedpetrolin2000,forexample.However,leadpaintischeaperthanthealternatives,whichseemstohavetemptedcertainChinesemanufacturerstouseitinpreferencetothenontoxic,andlegal,replacements.Inresponsetoa

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11/27/2014 Whyuseleadinpaint?

http://www.rsc.org/chemistryworld/News/2007/August/21080701.asp 2/2

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