PCBs Polychlorinated biphenyls

Polychlorinated biphenyls (PCBs) are a group of man-made compounds that were widely used in the past, mainly in electrical equipment, but which were banned at the end of the 1970s in many countries because of environmental concerns.

Because these compounds are generally very stable, they remain present in the environment today.

What are the health risks associated with PCBs?

1. Sourcedocument:ScientificFactson
IPCS-WHO(2003)
Summary &Details:
GreenFacts(2006)
PCBs
Polychlorinatedbiphenyls
Context-Polychlorinatedbiphenyls
(PCBs)areagroupofman-made
WhatarePCBs?.....................................21.
WhathappenstoPCBsinthe
environment?........................................2
2.
TowhatextentarehumansexposedtoPCBs?
...........................................................3
3.
compoundsthatwerewidelyusedinthe
past,mainlyinelectricalequipment,but
WhathappenstoPCBswhentheyenterthe
body?..................................................3
4.whichwerebannedattheendofthe
1970sinmanycountriesbecauseof
environmentalconcerns. WhataretheeffectsofPCBsonlaboratory
animals?..............................................3
5.
Becausethesecompoundsaregenerally
verystable,theyremainpresentinthe
environmenttoday.
HowhasPCBexposureaffectedhuman
health?.................................................4
6.
WhataretherisksposedbyPCB
exposure?.............................................4
7.
Whatarethehealthrisksassociatedwith
PCBs?
Conclusions..........................................58.
ThisDigestisafaithfulsummaryoftheleadingscientificconsensusreport
producedin2003bytheInternationalProgrammeonChemicalSafety(IPCS)
oftheWorldHealthOrganization(WHO):
"Polychlorinatedbiphenyls:Humanhealthaspects.Conciseinternationalchemicalassessmentdocument55"
ThefullDigestisavailableat:http://www.greenfacts.org/en/pcbs/
ThisPDFDocumentistheLevel1ofaGreenFactsDigest.GreenFactsDigestsarepublishedinseveral
languagesasquestionsandanswers,inacopyrighteduser-friendlyThree-LevelStructureofincreasing
detail:
•EachquestionisansweredinLevel1withashortsummary.
•TheseanswersaredevelopedinmoredetailinLevel2.
•Level3consistsoftheSourcedocument,theinternationallyrecognisedscientificconsensus
reportwhichisfaithfullysummarisedinLevel2andfurtherinLevel1.
AllGreenFactsDigestsareavailableat:http://www.greenfacts.org/
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2. 1.WhatarePCBs?
Labellingtransformerscontaining
PCBs
Source:USfederalGovernment
Polychlorinatedbiphenyls,inshortPCBs,areagroupof
man-madechemicals.
1.1PCBshavebeenusedinmanydifferentproducts,including
electricalequipment,surfacecoatings,inks,adhesives,
flame-retardants,andpaints.PCBsmaybereleasedintothe
environment,forinstancewhenwastethatcontainsPCBsis
incineratedorstoredinlandfills.About10%ofthePCBs
producedsince1929stillremainintheenvironmenttoday.
Becauseofpossibleimpactsonhumanhealthandthe
environment,theuseandproductionofPCBsarenowbannedorseverelyrestrictedinmany
countries.
1.2AllPCBsareman-madeandhaveasimilarbasicstructure.Theyaremadeofcarbon,
hydrogenandchlorineatoms.Becausetheseatomscanbecombinedinmanydifferent
ways,atotalof209differentPCBmoleculescanbeformed.SomePCBsaremoreharmful
thanothers.
Generally,PCBsareverystablewhichexplainstheirpersistenceintheenvironment.At
hightemperatures,PCBscanburnandgeneratedangerousby-productssuchasdioxins.
PCBstendnottoevaporateortodissolveeasilyinwater.However,theyareverysoluble
infatandsimilarsubstances,whichexplainswhyPCBscanbuildupinanimalfatandalong
thefoodchain.
2.WhathappenstoPCBsintheenvironment?
PCBscanbuildupalong
thefoodchain.
Source:WisconsinDept.ofNatural
Resources[seehttp://dnr.wi.gov/
org/water/wm/foxriver/whatarepcbs.
html]
2.1Inriversandlakes,PCBsattachtosedimentswherethey
canremainburiedforalongtimebeforebeingeventually
releasedintowaterandair.PCBsintheaircanreachthe
groundwithfallingrainandsnow,orsimplywhensuspended
particlessettlewithgravity.
2.2PCBscanbuildupinanimalsovertimeandalongthe
foodchain.PCBsarefoundinthefattytissuesofanimals
livinginwateroronland,particularlythoseatthetopofthe
foodchain.ThushumanscanalsoaccumulatePCBsfromthe
foodtheyeat.Someanimalspecies,includinginsectsand
otherinvertebrates,birds,fish,andmammals,canbreak
downortransformcertainPCBswithintheirbodies.
2.3Inair,PCBsarebrokendownbytheindirecteffectof
sunlight.DependingonthespecifictypeofPCB,ittakesfrom
afewdaystoseveralmonthsforhalftheamountinitially
presenttobedegraded.Inwater,breakdownofPCBsisslower,andcanoccurunderthe
actionofsunlightormicroorganisms.Theseorganismsplayanimportantroleinthe
breakdownofPCBsinsoilsandsediment.
2.4Outdoors,PCBlevelsinairwerefoundtobelowerinruralandremoteareasthanin
urbanandindustrialareas.Inindoorair,concentrationsofPCBsaretypicallyatleastten
timeshigherthaninoutdoorair.
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3. PCBlevelsinseawatertendtobehighestinwatersnearindustrialareas.Sincethe1970s,
whenrestrictionswereimposedontheproductionofPCBs,concentrationsinnewdeposits
ofriversedimentsandinfishhaveshownagradualdecrease.
3.TowhatextentarehumansexposedtoPCBs?
Humansareexposedthrough
contaminatedmeat,fish,andpoultry
HumansareexposedtoPCBsviafood,airanddrinkingwater.
3.1Overall,humansaremainlyexposedthroughconsumption
ofcontaminatedfoods,particularlymeat,fish,andpoultry.
ThedietaryintakeofPCBsforadultsrosetoahighinthe
late1970s,butthendecreasedtoalowerlevelbythe1990s.
3.2InfantscanbeexposedtoPCBscontainedinhumanbreastmilk.Asinfoods,average
levelsinbreastmilkhavedecreasedsincethe1970s.
3.3ThegeneralpopulationisexposedtolowlevelsofPCBspresentintheairtheybreathe
particularlyindoors,butalsooutdoors.However,inPCBdisposalfacilities,PCBconcentrations
inaircanbesignificantlyhigherleadingtoagreaterexposureinworkers.
3.4ThegeneralpopulationcansometimesbeexposedtolowlevelsofPCBsindrinking
water,thoughconcentrationsareoftentoolowtobemeasured.
4.WhathappenstoPCBswhentheyenterthebody?
HumanscanabsorbPCBsbyeatingordrinkingcontaminatedfood,and,toalesserextent
bybreathingcontaminatedairorthroughtheskin.
Onceabsorbed,PCBsmoveintocellmembranesandintothebloodvesselsandthelymphatic
system.ThehighestconcentrationsofPCBsareusuallyfoundintheliver,fattytissue,brain,
andskin.Theyarealsopresentintheblood.Inmothers,PCBshavebeenfoundtopass
intoumbilicalcordblood,theplacentaandbreastmilk.
Inbothhumansandanimals,PCBscanalsobetransformedintosubstancesthataccumulate
inspecifictissuesandbodyfluids.Theymayalsobetransformedintoothersubstances
allowingthemtobeexcretedthroughurineandfeces.
5.WhataretheeffectsofPCBsonlaboratoryanimals?
seealsoourDioxins
study[see
http://www.greenfacts.org/
en/dioxins/index.htm]
5.1Inanimals,exposuretoonelargedoseofPCBscancause
diarrhea,breathingdifficulties,dehydration,decreasedresponseto
pain,andcoma.PCBswerefoundtomainlydamagethelungs,the
stomach,andthepancreas.LowerdosesofPCBsadministeredover
aperiodoftimecaninterferewithliverandthyroidfunction,and
may,inthelongterm,leadtolivercancer.
5.2Effectsonfertility,reproductiveorgans,andfemalehormonal
activityhavealsobeenseenintestanimalsexposedforalongtimetohighdosesofPCBs
throughtheirfood.
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4. TheoffspringofanimalsfedPCBsduringpregnancyandduringbreast-feedingmayalsobe
affectedandmanyhaveshownlearningandbehavioraldifficulties.Intheyoung,
developmentoftheimmunesystemandcertainorganssuchastheliver,thyroidandkidney
havealsobeenaffectedbyexposuretoPCBs.
5.3ObservedeffectsofPCBsontheimmunesystemincludedalesserproductionof
antibodies,anincreasedsusceptibilitytodisease,anddecreasedweightofthethymus
gland.AdultanimalsappeartobelesssensitivethanthefetustotheeffectsofPCBs.
5.4PCBswithdifferentchemicalsstructuresbehaveindifferentways.CertainPCBsbehave
likedioxinsandmaycauseanincreasedriskofcancer.Otherscanaffectthedevelopment
ofthenervoussystemathighexposures.
6.HowhasPCBexposureaffectedhumanhealth?
PCBexposuremay
affecthuman
reproduction
©MicroApplications
ItisdifficulttodeterminetowhatextentPCBexposureaffectshuman
health,becausedifferentpeopleareexposedtodifferentamountsand
mixturesofPCBs,andbecausetheymayalsobeexposedtoother
toxicsubstanceatthesametime.
6.1Manystudiessuggestthatthereisalinkbetweenexposureto
PCBsandincreasedriskofcancersofthedigestivesystem,theliver,
andoftheskin.Furthermore,highlevelsofPCBsinthebloodmaybe
linkedtoacancerofthelymphaticsystem.
6.2PCBexposuremayaffecthumanreproductionandmaybelinked
toreducedfertilityinwomenandalowermobile-spermcountinmen.
Exposureduringpregnancyandbreastfeedingmaybelinkedtoslowedinfantgrowthand
development.
6.3PCBexposuremayalsobelinkedtoneurologicalhealtheffects,(suchasnumbnessand
headaches),morefrequentinfections,andchangesoftheskin,particularlyrashesand
chloracne.
7.WhataretherisksposedbyPCBexposure?
CurrentunderstandingabouttheeffectsofPCBexposureonhumanhealthismainlybased
onfindingsfromanimalstudiesusingmixturesofPCBs.
7.1StudiesrevealedatwhatdailydoseofPCBsasensitivespeciesofmonkeysstarted
showingsignsofnegativehealtheffects(ontheimmuneandnervoussystem).
7.2BasedontheseexperimentalfindingsatolerabledailyintakeofPCBshasbeen
establishedforhumans.
7.3IntheUSAforinstance,itisestimatedthatpeopleareexposedto1000timesless
PCBsthantheminimumintakecausingadverseeffectsinanimals,andfourtimeslessthan
thetolerabledailyintake.
7.4EstablishingaTolerableDailyIntakebasedonstudiesonanimalsentailsuncertainties.
Ontheonehand,monkeysmaybemoresensitivetoPCBsthanhumans.Inthiscasethe
predictedtolerableintakewouldbetooprudent.Ontheotherhand,specificPCBstowhich
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5. humansareexposedmaybemoreorlesstoxicthanthePCBmixturesusedforthestudies
onmonkeys.
8.Conclusions
Manycountrieshaveseverely
restrictedorbannedtheproduction
ofPCBs
Source:www.seton.com
PCBsareagroupofman-madechemicalsthathavebeen
usedinavarietyofmanufacturedgoodssince1929.PCBs
cantendtopersistintheenvironmentandaccumulateinthe
foodchain.Manycountrieshavebannedorseverelyrestricted
theproductionofPCBs.
HumansmaybeexposedtoPCBsbyconsumingcontaminated
food,andalsobydrinkingcontaminatedwaterandbreathing
contaminatedair.MothersexposedtoPCBsmaytransmit
themtotheirchild.ThespeedatwhichPCBsaretransformedinthebodyandtheextent
towhichtheyareeitherstoredorexcretedvaryaccordingtothetypeofPCB.
Dependingonthedose,thetypeofPCBs,andotherfactors,exposuretoPCBscanaffect
fertility,childdevelopment,theimmunesystem,andpossiblyincreasetheriskofcertain
cancers.
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