大学英语四级美文欣赏：灰尘背后的那些事儿思维导图

Butthere'sahigherickfactortodustthanyoumightthink.Andthere'sasciencetohowitgetsaround—asciencethatDavidLaytonandPalomaBeamer,professorsofenvironmentalpolicyattheUniversityofArizona,areexploring.

LaytonandBeamer,whoselateststudyhasbeenacceptedforfallpublicationinthejournalEnvironmentalScience&Technology,knewalotabouttheirsubjectevenbeforetheysettowork.Historically,everyonefromchemiststohomemakershastriedtofigureoutjustwhatdustismadeof,andtheArizonaresearchersdrewtheirpreliminarydatamostlyfromtwostudiesofhouseholddustconductedintheNetherlandsandtheU.S.TheAmericansurveyinparticularwasabigone,coveringsixMidwesternstates.LaytonandBeameralsoincludedalocalizedstudyinSacramento,Calif.,thatfocusedparticularlyonleadcontamination.Whatallthosesurveysshowedwasdecidedlyunappetizing.

Thespecificdustmixinanyhouseholddiffersaccordingtoclimate,ageofthehouseandthenumberofpeoplewholiveinit—nottomentiontheoccupants'cooking,cleaningandsmokinghabits.Butnearlyeverywhere,dustconsistsofsomecombinationofshedbitsofhumanskin,animalfur,decomposinginsects,fooddebris,lintandorganicfibersfromclothes,beddingandotherfabrics,tracked-insoil,soot,particulatematterfromsmokingandcooking,and,disturbingly,lead,arsenicandevenDDT.

"Therearemore[components],"Beamersays."Dustisahodgepodgeofallsortsofthings.Itwouldprobablybeimpossibletomakealistofallthepossibleitems."

Butdust'singredientlabelisnotthewholestory,sinceallofthoseflecksandbitsbehavedifferentlyandpresentdifferentlevelsofhealthrisk.Toinvestigatethosefactorsmoreclosely,LaytonandBeamerdevelopedacomputeralgorithmthatlookedatthesize,sourceandtoxicityofdustparticlesaswellashoweasilytheyenterthehouse,iftheyeverexitand,ifso,bywhatroute.Thatinformation,byextension,canprovideatleastaroughsenseofthedustloadinyourownhome.

Asageneralrule,themajorityofhouseholddust—about60%—comesfromoutside,throughwindows,doors,ventsand,significantly,onthesolesofyourshoes.Smallerdustparticles—from28to49microns,orthousandthsofamillimeter—tendtostayonyourshoes.Therestisshakenoffinside.Ahighershareofthedustthatfloatsintheairgetsdeposited,butagain,there'salotthatdetermineshowmuchanyonehomewillget.

"HereinArizona,"saysBeamer,"whereweleaveourwindowsopenmostoftheyearandhaveanaridclimate,wewouldprobablyhaveahigherratio."Industrialcentersorsootycitieshaveplentyofdusttoo,thoughfordifferentreasons.

There'snotmuchtofretaboutinsimpleparticlesofdirtororganicmaterialssuchaspollen(thoughtheycantriggerallergies),butlead,arsenicandDDTcanbeamoreseriousmatter.Aboutone-thirdofthearsenicintheatmospherecomesfromnaturalsources—volcanoesprincipally.Therestcomesfrommining,smelting,burningfossilfuelsandotherindustrialprocesses.Eveninrelativelylowconcentrations,arsenicisnotwithoutrisk,especiallytosmallchildrenwhoplayonthefloorandroutinelytransferthingsfromtheirhandstotheirmouths.Thesameistrueforlead,whichcomeslessfromwallpaint—thesourcemostpeoplewouldexpect—thanfromautoexhaust,smeltingandsoildeposits."Leadloadingonfloorsisakeydeterminantofblood-leadlevelsinchildren,"LaytonandBeamerwroteintheirpaper.

ThefactthatDDTisstillinhousedustisasurprisetomostpeople,sincethepesticidewasbannedintheU.S.in1972.Butahouseisalittlelikealivingorganism:onceitabsorbsacontaminant,itmayneverpurgeitcompletely."Dustinourhomes,"saysBeamer,"especiallydeepdustinourcarpetsandfurniture,isaconglomerateofsubstancesoverthelifeofthehomeandcanprovideahistoricalrecordofchemicalsthathaveenteredit."

Themessthatoriginateswithinthehomeisaloteasiertomeasureandcontrol.Themorepeoplewholivethere,themoreskinthat'sgoingtobeshed,themorepets,themoreanimalfur.And,asMomalwayswarned,themoreyouwalkaroundthehousewhileeating,themorefooddebrisyou'lldroponthefloor—whichalsoattractsmoreinsectsthatwilldie,decomposeandaddtheirownspecialzesttoyourdust.Cookingsmokeandtobaccosmoke,whicharethemostobviouscontributorswhenthey'rebeingproduced,actuallymakeonlyasmallcontributiontowhatwindsuponfloorsandsurfaces.Thetinysizeoftheparticlesmakesthemlikeliertoriseandadheretoothersurfacesorsimplyremainintheairthantosettle.

Itgoeswithoutsayingthatyourhomewillneverbedust-free,buttherearewaystoreduceyourowndustloading—andit'simportantthatyoutry.Dustmites,whichfeedonshedskin,produceallergensthatareknowntriggersforpeoplesufferingfromasthma.Samegoesforcockroachdust,especiallyincities.Nooneneedsmuchconvincingaboutthewisdomofgettingridofarsenic,andthegoodnewsisthatabout80%ofitcanberemovedsimplybycleaningfloordustregularly.

Noneofthismeansthatdustposesaclearandpresentdangerorthatyouneedtotakeanyextraordinarymeasures.Justcleanregularly,don'tsmoke,eatatthetable—andtrynottofreakout.Dustbunniesarestillonlybunnies;youmayjustwantfewerofthem.

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