Chapter 49 - Radiation Non-Ionizing.docxVIP专享VIP免费原创优质

Chapter49-Radiation:Non-IonizingELECTRICANDMAGNETICFIELDSANDHEALTHOUTCOMESBengtKnaveInrecentyearsinteresthasincreasedinthebiologicaleffectsandpossiblehealthoutcomesofweakelectricandmagneticfields.Studieshavebeenpresentedonmagneticfieldsandcancer,onreproductionandonneurobehaviouralreactions.Inwhatfollows,asummaryisgivenofwhatweknow,whatstillneedstobeinvestigatedand,particularly,whatpolicyisappropriate—whetheritshouldinvolvenorestrictionsofexposureatall,“prudentavoidance”orexpensiveinterventions.WhatweKnowCancerEpidemiologicalstudiesonchildhoodleukaemiaandresidentialexposurefrompowerlinesseemtoindicateaslightriskincrease,andexcessleukaemiaandbraintumourriskshavebeenreportedin“electrical”occupations.Recentstudieswithimprovedtechniquesforexposureassessmenthavegenerallystrengthenedtheevidenceofanassociation.Thereis,however,stillalackofclarityastoexposurecharacteristics—forexample,magneticfieldfrequencyandexposureintermittence;andnotmuchisknownaboutpossibleconfoundingoreffect-modifyingfactors.Furthermore,mostoftheoccupationalstudieshaveindicatedonespecialformofleukaemia,acutemyeloidleukaemia,whileothershavefoundhigherincidencesforanotherform,chroniclymphaticleukaemia.Thefewanimalcancerstudiesreportedhavenotgivenmuchhelpwithriskassessment,andinspiteofalargenumberofexperimentalcellstudies,noplausibleandunderstandablemechanismhasbeenpresentedbywhichacarcinogeniceffectcouldbeexplained.Reproduction,withspecialreferencetopregnancyoutcomesInepidemiologicalstudies,adversepregnancyoutcomesandchildhoodcancerhavebeenreportedaftermaternalaswellaspaternalexposuretomagneticfields,thepaternalexposureindicatingagenotoxiceffect.Effortstoreplicatepositiveresultsbyotherresearchteamshavenotbeensuccessful.Epidemiologicalstudiesonvisualdisplayunit(VDU)operators,whoareexposedtotheelectricandmagneticfieldsemittedbytheirscreens,havebeenmainlynegative,andanimalteratogenicstudieswithVDU-likefieldshavebeentoocontradictorytosupporttrustworthyconclusions.NeurobehaviouralreactionsProvocationstudiesonyoungvolunteersseemtoindicatesuchphysiologicalchangesasslowingofheartrateandelectroencephalogram(EEG)changesafterexposuretorelativelyweakelectricandmagneticfields.Therecentphenomenonofhypersensitivitytoelectricityseemstobemultifactorialinorigin,anditisnotclearwhetherthefieldsareinvolvedornot.Agreatvarietyofsymptomsanddiscomfortshasbeenreported,mainlyoftheskinandthenervoussystem.Mostofthepatientshavediffuseskincomplaintsintheface,suchasflush,rosiness,ruddiness,heat,warmth,prickingsensations,acheandtightness.Symptomsassociatedwiththenervoussystemarealsodescribed,suchasheadache,dizziness,fatigueandfaintness,tinglingandprickingsensationsintheextremities,shortnessofbreath,heartpalpitations,profusesweatings,depressionsandmemorydifficulties.Nocharacteristicorganicneurologicaldiseasesymptomshavebeenpresented.ExposureExposuretofieldsoccursthroughoutsociety:inthehome,atwork,inschoolsandbytheoperationofelectricallypoweredmeansoftransport.Whereverthereareelectricwires,electricmotorsandelectronicequipment,electricandmagneticfieldsarecreated.Averageworkdayfieldstrengthsof0.2to0.4µT(microtesla)appeartobethelevelabovewhichtherecouldbeanincreasedrisk,andsimilarlevelshavebeencalculatedforannualaveragesforsubjectslivingunderornearpowerlines.Manypeoplearesimilarlyexposedabovetheselevels,thoughforshorterperiods,intheirhomes(...