Reuters
Appleswith"ProducedinJapan"stickersareseenataJapanesesupermarketinHongKongMarch21,2011.TheWorldHealthOrganizationsaidonMondaythatthedetectionofradiationinfoodafteranearthquakedamagedaJapanesenuclearplantwasamoreseriousproblemthanithadfirstexpected.TheHongKongGovernmentonMondayhasgivenassurancesthattheterritory'sfoodandwatersupplieshavenotbeencontaminatedwithradiationfromJapan,accordingtolocalmedia.
Countriesaroundtheworldhaveeitherbannedorsteppeduptestsonimportsfromquake-strickenJapanafterradioactivesubstanceswerefoundinitsfoodandwaterfollowingblastsatanuclearplant.
Exposuretolargeamountsofradioactivitycancausenausea,vomiting,hairloss,diarrhea,hemorrhage,destructionoftheintestinallining,centralnervoussystemdamage,anddeath.ItalsocausesDNAdamageandraisestheriskofcancer,particularlyinyoungchildrenandfetuses.
Belowarethethreeradioactivesubstanceshealthexpertsaremostconcernedabout,thedetectedlevelsinJapan,andwhattheymeanforhumanhealth:
IODINE-131
LeafygreenvegetablesinJapanwerefoundthisweektocontainupto22,000becquerelsofiodine-131foreverykilogram.
SuchalevelexceedsthelimitsetbytheEuropeanUnionby11times.Becquerelisameasureofradioactivity.
Eatingakilogram(slightlymorethantwopounds)ofsuchvegetableswouldgivehalftheamountofradiationtypicallyreceivedbytheaveragepersonfromthenaturalenvironmentinayear.
Eatingthisamounteverydayfor45dayswillaccumulate50millisieverts,theannualradiationlimitsetforanuclearplantworker.Millisievertquantifiestheamountofradiationabsorbedbyhumantissues.
Exposureto100millisievertsayearincreasestheriskofcancer.ThatisequivalenttoaboutthreewholebodyCTscans.
Ifinhaledorswallowed,iodine-131concentratesinthethyroidglandandincreasestheriskofthyroidcancer.Children,fetusesandyoungadultsareespeciallyvulnerable.
Theriskofthyroidcancercanbeloweredbytakingpotassiumiodidepills,whichhelpspreventtheuptakeoftheradioactiveiodine.
However,iodine-131disintegratesrelativelyquicklyanditsradioactivityishalvedevery8days.Thismeansitlosesallitsharmfulnessin80days.
CESIUM-134andCESIUM-137
VegetablesinJapanhavealsobeentaintedwithupto14,000becquerelsofcesiumforeverykilogram.
ThatexceedstheEUlimitbyover11times.
EatingakilogramofsuchtaintedvegetableseverydayforamonthwouldaccumulateradiationequivalenttoafullbodyCTscan-or20millisieverts.
Externalexposuretolargeamountsofradioactivecesiumcancauseburns,acuteradiationsicknessanddeath.Itcanalsoincreasetheriskofcancer.Ingestingorinhalingcesiumallowsittobedistributedinsofttissues,especiallymuscletissue,increasingcancerrisk.Itcanalsocausespasms,involuntarymuscularcontractionsandinfertility.
Unlikeiodine,uptakeofradioactivecesiumcannotbepreventedoncethepersonisexposed.
Thissubstanceisofmoreconcernthaniodine-131becauseitisveryhardyandtakesfarlongertodisintegrate.
Cesium-137hasahalflifeof30years,meaningittakesthatlongtoreduceitsradioactivitybyhalf.Itwilltakeatleast240yearsforthiscontaminanttoexhaustallitsradioactivity.
Cesium-134hasahalflifeof2years,whichmeansitwilltakeabout20yearsforittobecomeharmless.
Belowaretheeffectsofshort-term,high-levelexposuretoradiation,aspublishedbytheU.S.EnvironmentalProtectionAgency.Unlikecancer,theseeffectsfromacuteradiationexposureusuallyappearquickly,causingwhatisknownasradiationsickness,whichincludessymptomslikenausea,hairlossandskinburns.Ifthedoseisfatal,deathusuallyoccurswithintwomonths.
-Exposureto50-100millisieverts:changesinbloodchemistry.
-500:nausea,withinhours.
-700:vomiting
-750:hairloss,within2-3weeks
-900:diarrhea
-1,000:hemorrhage
-4,000:possibledeathwithin2months,ifnotreatment
-10,000:destructionofintestinallining,internalbleedinganddeathwithin1-2weeks
-20,000:damagetothecentralnervoussystemandlossofconsciousnesswithinminutes,anddeathwithinhoursordays.
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