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1、Unit2SpecialEnglishinEnvironmentalChemistryChapter1IntroductionsofEnvironmentalChemistryTheoriesPassage1ContaminantTransportandTransformationintheEnvironment(1)Becauseofthepotentialhazardthatexposuretohazardouscompoundsposestohumansandtheenvironment,thelevelsoftoxicandcarcinogenicsubst
2、ancesintheenvironmenthavebecomeimportantcriteriaforevaluatingenvironmentalquality.Theamountofamaterialwhichenterstheenvironment,though,isnotalwaysindicativeoftheamountthatwillbefoundthere.Theconcentrationofacontaminantatanypointintheenvironmentdependsonthequantityaddedandtheprocessesth
3、atinfluenceitsfate.Thiscanincludebothtransportandtransformationmechanisms.Transportprocessestendtomovematerialsfromonepointtoinvolveinter-mediaexchangesbetweenatmospheric,aquatic,andsoilenvironments,aswellasmovementwithineachofthesemedia.Transportmaybeduetoadvective,dispersive,ordiffus
4、ionprocesses.Associatedwithtransportprocessesarepartitioningprocesses,whichdictatehowmuchofthematerialwillbeinthegas,liquid,andsolidphases.Partitioningisdependentonthecompound'ssolubility,density,polarity,ionicstate,andvaporpressure.Anotherformofpartitioningisbioaccumulation,inwhichcom
5、poundsaretakenupbylivingorganismsandconcentratedintheirtissues.Transformationprocesseswithineachmediachemicallyalterthecontaminantstonewcompoundsthatmayhavelower,equal,orgreatertoxicity.Transformationsmaybeduetochemical,photochemical,orbiologicalprocesses.Theratesatwhichchemicalsaretra
6、nsformedarecriticaltoanunderstandingoftheseriousnessofaparticularpollutionincident.Forexample,asmallspillofsodiumacetatemayhaveminimalenvironmentalimpactbecauseitisrapidlybiodegradedbybacteriainsoilandwater,whereasasmallspillofcreosotemayhavemuchgreaterimplicationsbecauseofitsgreaterpe
7、rsistenceintheenvironment.Manybookshavebeendedicatedtothetopicofcontaminantfateandtransportintheenvironment(Clark,1997;Hemond,1994;Knox,1993;LaGrega,Buckingham,andEvans,1994;Schnoor,1997;Thibodeaux,1996).Inthefollowingsections,wewillonlysuperficiallydescribetheseprocessessothattherea
