水污染的性质(专业英语)

NatureofwaterpollutionWater,oneofman'smostpreciousresources,isgenerallytakenforgranteduntilitsuseisthreatenedbyreducedavailability（可用性）orquality.Waterpollutionisproducedprimarilybytheactivitiesofman,specificallyhismismanagementofwaterresources.Thepollutantsareanychemical,physical,orbiologicalsubstancesthataffectthenaturalconditionofwateroritsintendeduse.Becausewaterpollutionthreatenstheavailability,qualityandusefulnessofwater,itisofworldwidecriticalconcern.Theincreaseinthenumberandvarietyofusesforwaterthroughouttheworldhasproducedawiderangeofstandardsofwaterqualitythatmustbesatisfied.Thesedemandsinclude:①preservationofriversintheirnaturalstate;②potability（饮用）ofthewatersupply;©preservationandenhancementoffishandwildlife;④safetyforagriculturaluse;⑤safetyforrecreational（娱乐的）useincludingswimming;©accommodation（适应；供应）toagreatvarietyofindustrialpurpose;©freedomfromnuisance（有害的东西）;©generationofpowerforpublicutilities（公用事业）;⑨dilution（稀释）andtransportofwastes.Besidesthespecificchemical,biological,andphysicalrequirementsforthemultitudeofusesnotedabove，thereareconstraints（约束、限制）reflectingpublichealthrequirements，aesthetics（美学），economics，andshortandlong-termecologicalimpacts.Consequently,thereisnorigid（严格的）orspecificdefinitionofwaterpollution，sincetheintendeduseorusesofthewatermustbetakenintoconsiderationinanydefinitionofwhatconstitutespollutedwater.Onemethodofclassifyingthegaseous，liquidandsolidconstituentsofwaterthatconstitutepollutiondependsontheintendeduseofthewater.Thepollutantsarethengroupedasnotpermissible，asundesirableandobjectionable（不适合的），aspermissiblebutnotnecessarilydesirable，orasdesirable.Forexample，ifwateristobeusedimmediatelyforanimalconsumption，toxic（有毒的）compoundsarenotdesirable,whereas（然而）acertainamountofoxygenisnotobjectionable.Ontheotherhand,ifthewateristobeusedinapowerplantforsteamgeneration,toxicmaterialsmightbeallowableorevenperhapsdesirable,whereasoxygenthatcouldpossiblycorrode（侵蚀、损害）equipmentwouldbeobjectionable.Anothermethodofclassifyingpollutantsthatenterwaterasaresultofman'sdomestic,industrialorotheractivitiesistodistinguishbetweenconservativeandnon-conservativepollutants.Conservativepollutantsarethosethatarenotalteredbythebiologicalprocessesoccurringinnaturalwaters.Thesepollutantsareforthemostpartinorganicchemicals,whicharedilutedinreceivingwaterbutarenotappreciablychangedintotalquantity.Industrialwastescontainnumeroussuchpollutants,includingmetallicsaltsandothertoxic,corrosive,colored,andtaste-producingmaterials.Domesticpollutionandreturnflowfromirrigationmaycontainnumeroussuchpollutants,includingchlorides（氯化物）andnitrates（硝酸盐）.Non-conservativepollutants,ontheotherhand,arechangedinformofreducedinquantitybychemicalandphysicalprocessesinvolvedinbiologicalphenomenaoccurringinwater.Themostcommonsourceofnon-conservativepollutantsisdomesticsewage－highlyputrescibleorganicwastethatcanbeconvertedintoinorganicmaterialssuchasbicarbonates（重碳酸盐），，sulfates（硫酸盐）,andphosphates（磷酸盐）bythebacteriaandothermicroorganisminthewater.Ifthewaterisnottooheavilyladenwithwastes,itwillundergo“self-purification”.Thisprocessinvolvestheactionofaerobicbacteria,thatis,bacteriathatrequirefreeoxygentobreakdownwastes,anditproducesnooffensiveodors.If,however,thewaterisladenwithwastesbeyondacertainamount,theprocessofbiologicaldegradationbecomesanaerobic.Thatis,itproceedsbytheactionofbacteriathatdonotrequirefreeoxygen.Intheprocess,noxioushydrogensulphidegas（硫化氢），methane（甲烷）,andothergasesareproduced.Theaer