School of Natural Resources and Environment
440 Church Street, 3012 Dana Building
Ann Arbor, MI 48109-1041
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DRAFT(9/13/2016)LiteratureReviewofProductEnvironmentalFootprints:
TOMATOES
Overview
TomatoesareubiquitousintheU.S.diet:intermsofper-capitaconsumption,theyarethefourthmost
popularfresh-marketvegetable,andtheU.S.issecondonlytoChinaintomatoproduction1.Butasany
backyardgardenerknows,notalltomatoesarecreatedequal,andthisholdstruefortheir
environmentalfootprintaswell.How,when,andwheretomatoesaregrown,processedanddistributed
allaffecttheoverallfootprint.
Thepurposeofthissummaryistohighlightwhatisknownabouttheenvironmentalimpactsoftomato
production,processing,distributionandconsumptionbasedonareviewofpublicallyavailablelifecycle
assessment(LCA)studies.Suchstudiescanidentifythosepartsofthevaluechainwith
disproportionatelyhighenvironmentalburdens,allowingimprovementeffortstofocuswheretheyare
likelytohavethemostbearing.TheseLCAstudiescanalsopointtopotentialtrade-offsbetween
environmentalindicatorsorabatementstrategies.Thissummarydoesnotprovideinformationthatis
specifictoOregontomatoproduction,butneverthelessmaybeusefultobothproducersandusersof
tomatoesandtomatoproductsinOregonaswellasotherlocations.
TomatoesareproducedintheU.S.fortwodistinctlydifferentmarkets:fresh-andprocessing.Freshmarkettomatovarietiesarejuicierand,incommercialproduction,oftenharvestedpriortobeingripein
ordertotolerateshippingandextendshelflife.Processingvarietiescontainhigherpercentagesof
solublesolids,arevineripened,andtypicallyhaveathickerskininordertowithstandmechanical
harvestingandbulktransport.Processingtomatoesareconvertedtotomatopastes,sauces,juicesand
cannedtomatoproducts.ThetotalU.S.productionoffresh-markettomatoesin2015was1.3billionkg,
with87millionkgofthisgrownunderprotectivestructures;13.4billionkgofprocessingtomatoeswere
alsoproduced.Californiaaccountsfor96%ofU.S.processingtomatooutput.Fresh-markettomatoesare
producedineverystateinthecountry,buttwo-thirdstothree-fourthsofcommercialscaleproduction
occursinCaliforniaandFlorida.Fresh-markettomatoessoldinOregonthatarenotproducedlocally
likelycomefromMexicointhewinterandCaliforniaduringtherestoftheyear,althoughhothouse
tomatoesfromBritishColumbiaarealsocommon.
AvailableLCAresearch
Tomatoeshavebeenwellstudiedinthelifecycleassessment(LCA)literature;weidentified17separate
publishedreports,allfrompeer-reviewedjournals.Whilewesoughtstudiesdatingbackto2005,all
identifiedtomatostudieswerepublishedbeginningin2011.Agivenstudywilloftenconsiderdifferent
productionpracticesorscenarios;59separatescenarioswereidentifiedacrossthe17reports.U.S.
basedstudiesarelimitedtooneconsideringprocessingtomatoesgrowninCaliforniaandonelookingat
openfieldproductioninFlorida.TheremainingstudiesconsiderproductioninItaly,Spain,France,
1
http://www.ers.usda.gov/topics/crops/vegetables-pulses/tomatoes.aspx
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Austria,Australia,UK,Switzerland,IranandMorocco.Themajorityofstudiesfocusongreenhousegas
emissions(GHGE)andenergyuse,withsomeconsiderationofwateruse.Ahandfulofstudiesconsidera
broaderspectrumofenvironmentalimpacts(eutrophication,acidification,humanandeco-toxicity)but
ingeneral,itisfarmoredifficulttodrawbroadlyapplicableconclusionsastheseimpactstendtocarry
highuncertaintyandaremuchmorelocalizedandspatiallydependent.Thus,conclusionsinthis
summaryfocusonGHGE.
TomatoLifeCycleDiagram(Fresh-marketandProcessing)
ProductionCategories
Forthepurposesofreviewingenvironmentalfootprints,itisusefultodividetomatoproduction
methodsintothefollowingfourcategories:
• Openfield,processing–Nearlyallprocessingtomatoesaregrowninopenfieldconditionsas
seasonalityandappearancearelessofaconcern.Theyareoftenmechanicallyharvestedand
undergovariousdegreesofprocessingtobecomepurée,sauce,paste,juice,etc.
• Openfield,fresh-market–Thiscategoryincludesin-groundproductionwithoutoverhead
protection.OpenfieldproductionisseasonalinnearlyalllocationsintheU.S.Fertilizationand
irrigationmethodscanvarywidely.Tomatoesgrownforfreshmarketaretypicallyhandharvested.
• Protected,fresh-market–Protectedproductionuseslow-orhigh-tech“greenhouse,”shadehouseortunnelstructuresthatprovideprotectionfromweatherandpests,butdonotinvolve
supplementalheatorlight.Productioncanbeintheground,insoillessmedia,orhydroponic.The
addedprotectionoffershigheryieldandmoreconsistentqualitythanopenfieldproduction.In
milderclimates,suchprotectionissufficienttopermitgrowingincoolerseasons.
• Greenhouse,freshmarket–Inthissummary,greenhousespecifiesenclosedstructureswith
supplementalheatingand/orlightingforoff-seasonproductionincoldclimateregions.These
systemstypicallyusesoillessmedia,hydroponicsorotherabove-groundgrowingapproaches.
TheymayalsoinvolveCO2enrichment(increasingthein-houseatmosphericconcentrationof
CO2)topromotehigheryields.
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KeyFindings
Fulllifecycleresults
Tosummarizetheresultsfromidentifiedstudies,wedividedthescenariosfoundintheliteratureinto
thefourproductioncategorieslistedabove,compiledreportedGHGEvaluesatmajorlifecyclestages,
andaveragedvaluesatlifecyclestages(Figure1).Thismeta-analysisisdonewithprudenceasstudies
varyinmethodologicalapproaches,boundaryconditionsandscenariospecifics.Still,general
characterizingtrendscanbeobserved.
Thefollowinglifecyclestages,representedinthediagramabove,havebeenincludedinFigure1:
• Agricultureincludesallimpactsuptofarmgate,includingtheproductionoffarminputs
(fertilizer,pesticides,greenhouses,tractorfuel)and(inmostcases)fieldemissionsofnitrous
oxide,apotentgreenhousegasthatcanformwhenagriculturalfieldsarefertilized.The
agriculturalstageisconsideredinmoredetailbelow.
• Processingisonlyexpectedtobeanimportantstageforprocessingtomatoesasfresh-market
tomatoesexperiencenoprocessing.Insightsarepresentedinthe“Processingtomatoes”section
below.
• Packagingshouldincludeallmaterialsusedtoencloseandprotectproductsfromfarmto
consumer.Smallamountsofpackagingareusedforfresh-markettomatoes,butthisstageisfar
moreimportantforprocessingtomatoes(see“Processingtomatoes”sectionbelow).
• Transport&logisticsincludesthemovementofproductfromfarmtoprocessortoretail.Despite
thefocusonfoodmilesinrecentyears,environmentalimpactstendtodependmoreon
transportmode(seafreight,rail,truck,airfreight)thanondistancetraveled.Still,distance
matters,andthestudiespresentedinFigure1assumeawiderangeoftraveldistances,makingit
challengingtodrawconclusionsontheimportanceoftransport.Afewgeneralobservations,
however,areworthnoting:1)astransporttimeislessimportantforalreadyprocessedtomato
products,moreefficienttransportmodes(seafreight,rail)canbeused,thusreducingthe
environmentalimpact,evenoverlongdistances;2)anadvantageofheatedgreenhouse
productioninoff-seasonscanbesimplifyingtransportlogisticsandreducingdistance.
• RetailstagesinfoodLCAstypicallyincludeaproduct’sshareoftheoverheadenergyuse(lighting,
heating,airconditioning,refrigeration)ingrocerystores.NoneofthetomatoLCAstudies
includedthisstage.Giventhattomatoesaretypicallynotrefrigeratedatretail,thecarbon
footprintofthisstageisexpectedtobeminimal.
• Consumptionstagescanincludepersonalvehicletransportfromretailtohome,refrigerationin
home,andpotentiallycooking.Theonetomatostudythatincludedconsumptionwasbasedin
Australiaandinterviewed50shopperstogiveanindicationofdistancetravelledtothe
supermarket,aswellashowoftentomatoesarestoredintherefrigerator.Whileobviouslya
smallsampleforastagewithhighvariability,theresultofthisstudy(seeninopenfield,freshmarketandgreenhouse,fresh-marketcategoriesinFigure1)suggeststhattheseconsumption
stageimpactscanbenotable.ThisisinagreementwithotherfoodLCAstudies.
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•
Wastemanagementtypicallyincludestheend-of-lifeimpactsofdisposingproductsortheir
associatedpackaging.Noneofthestudiesconsideredhereexplicitlyreportedvaluesforwaste
management.Thisdoesnotnecessarilymeanthatsuchimpactswerenotconsideredinthe
study,butthattheywerenotreportedseparatelyfromotherstages.
Asterisks
(*) means
data were
not
available
for stage
Figure1.Lifecyclegreenhousegasemissionresultsfromallstudiesreviewed,dividedintoproductioncategories
anddisplayedacrosslifecyclestages.Circlesrepresentindividualstudyresults,offeringasenseofthedataspread
orcluster.Horizontalblackbarsrepresentaveragesforeachstage,andgreyblocksare95%confidenceintervals
aroundtheaverages.The“ReportedTotal”columnshowstotalsfromagivenstudy,althoughitisimportantto
recognizethatnotallstudiesincludethefulllifecyclestagesrepresentedhere.Stagesmarkedwithanasterisk(*)
arethoseforwhichsomeenvironmentalimpactsareexpectedtooccur,butnodatawereavailableinthe
identifiedstudies.Redbarsindicatethesumoftheaveragesfromeachlifecyclestage,foreachproduction
category.
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Nextweexploreafewlifecyclestagesinmoredetail:agriculturalproduction,packagingand
transportation.
AgriculturalProduction:Greenhouses(usually)meanmoreGHGE
Focusingonlyontheagriculturalproductionoftomatoes,thereisadistinctdifferenceinGHGEperkgof
tomatoesbetweenheatedgreenhouseproductionandotherproductioncategories(Figure2).
Manufacturingofthegreenhouseinfrastructurecancontributemildlytothis,butitislargelydueto
supplementalheatingrequiredtooperatesuchgreenhousesout-of-seasonincoldclimates.Greenhouse
heatingaverages64%oftheagriculturalstage(high=77%,low=37%)acrossthesixheatedgreenhouse
scenariosthatreportsufficientdetailtodisaggregatecontributions.Oftengreenhousesareheatedwith
naturalgasorotherfossilfuels,bututilizationofwasteheatorintegrationwithcombinedheatand
powersystemscanleadtoimprovementsinenvironmentalperformance.Productionyieldsstrongly
influenceenvironmentalimpactsperkgofproductforallproductionsystems,butespeciallyforheated
greenhouses,asitisthevolumeofthespacethatmustbeheated,andbiggeryieldmeansmorekgper
unitvolume.
Figure2.Agriculturalstage(cradletofarmgate)greenhousegasemissionsaveragedacrossidentifiedliteratureforfour
distinctproductioncategories.Thenumberofreportedvaluesincludedineachaverageare21,8,11and19foropenfield
processing,openfieldfresh-market,protectedfresh-marketandheatedgreenhousefresh-market,respectively.Errorbars
represent95%confidenceintervals.Notethatthevaluefor“openfield,processing”appearslowerherethaninFigure1
asithasbeencorrectedheretobasisofakgofwhole(farmgate)tomato,whereastheagriculturestagevalueinFigure1
reflectsthequantityoffarmgatetomatoesneededperkgofprocessedproduct.
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Thedominantcontributionstotheagriculturalstageforprotected,freshmarketproductionare(on
average)fromagrochemicals–primarilyfertilizerproduction–andsubsequentfieldemissions2(37%),
andthegreenhouseinfrastructure(22%).UsingastudyfromFlorida(Jonesetal.2012)asa
representativeexampleofopenfield,fresh-markettomatoproduction,pesticideproductioncontributes
39%ofagriculturalrelatedGHGs,followedbya17%contributionfromfertilizerproductionand17%
fromfieldemissions,andanadditional7%fromfieldmachineryemissions.IrrigationintheFloridastudy
isbetween3and27%ofagriculturalproduction,dependingontheirrigationmethod.
Processingtomatoes:Packagingmatters
Acrossthe21processingtomatoentriesconsidered,agriculturalproductionaverages32%ofthetotal
lifecycleGHGE,processingaverages23%,whereaspackagingisanaverage36%ofthetotal.Thus,while,
agriculturalproductionandprocessingrepresentsignificantcontributionstoGHGE,packaging’slarge
impactsarenotablebecausereductionscanreadilybeachieved.
OnestudylookingatItaliangrownandprocessedtomatoesconsideredvaryingdegreesofprocessing
(peeled,chopped,puréed)andpackagingformats(DelBorghietal.2014).Onaweightbasisofpackaged
product,thisstudyfoundverylittledifferencebetweenprocessingmethods,butpapercarton-based
containershadconsiderablylowerGHGEthanglassorsteelcontainers,andimpactsdecreasedwith
largerformatpackaging.Whensteelcanswereused,packagingrepresented50%ormoreoftheoverall
lifecycleGHGE;withglass,packagingis40-45%ofthetotallifecycle;withcarton-basedcontainers,
packagingisaround5%ofthetotal.
AnotherstudyconsiderstheenvironmentalfootprintofprocessedtomatoesgrowninCalifornia(Brodt
etal.2013).Accordingtothisstudy,1kgoftomatopasterequires4.6timestheamountofraw
tomatoesas1kgofdicedtomatoesbecauseoftheconcentrationthatoccurs.Thus,onabasisoffinal
productweight,theagriculturalandprocessingstagesfortomatopastehave4.5-5.5timestheimpactin
GHGEandenergydemandasdodicedtomatoes,buttheimpactsfromconsumerpackagingareabout
thesame.Infact,packagingdicedtomatoesintypical14.5oz.steelcansrepresentsmorethanhalfof
thetotallifecycleenergydemandandGHGE(whenexcludingtransport).However,thetypicalserving
sizeismuchsmallerfortomatopaste,33gcomparedto122gfordicedtomatoes.Onaservingsize
basis,agriculturalproductionandprocessingarecomparablebetweenpasteanddiced,butimpactsof
consumerpackagingaswellastransportperservingare3.5timesgreaterfordiced.Thissuggeststhat,if
theservingsizedifferencesarerepresentativeandtherearen’tnotabledifferencesinconsumer-level
preparation(cooking,forexample),thensomesavingsperservingcanberealizedbyusingpasteover
diced,merelybecauseofreducedpackagingvolumeandtransportweight.
2
Fieldemissions:Nitrousoxide(N2O),agreenhousegas265timesaspowerfulasCO2,canbereleasedfromnitrifyingand
denitrifyingactivitiesinthesoilwhennitrogenfertilizersareaddedtoagriculturalsoils.
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Figure3showsthedistributionacrosslifecyclestagesofanumberofenvironmentalimpactsforthe
productionanddeliverytoretailofItaliantomatopurée(ManfrediandVignali2014).Formost
environmentalimpacts,packagingisthesinglelargestcontributor.Thisstudyconsideredafew
achievablescenariosaimedatreducingimpacts:a15%reductioninnaturalgasconsumption(through
energyoptimizationofprocessingequipment);replacingallgridelectricityusedinthesystem
(productionthroughdistribution)withphotovoltaicelectricity;reducingtheaveragedistancefrom
processortoretailerfrom550kmto400km;andreducingthejarglassweightby20%.Allofthese
scenarioshadminimaleffectsofa2-3%reductionincradle-to-distributionimpactsonthefirsteight
categoriesinFigure3(waterfootprintwasnotincluded)exceptreducingglassweight,whichresultedin
7-12%reductionsinallcategoriesbuteutrophicationpotential,wherethereductionwasaround3%.
Again,thisemphasizestheimportanceofpackagingintheoveralllifecycleofprocessedtomato
products.
Figure3.DistributionofenvironmentalimpactsacrosslifecyclestagesfortheproductionanddeliverytoretailofItalian
tomatopurée.AdaptedfromManfrediandVignali2014.
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Productionvs.transport:Sowhataboutfoodmiles?
Heatedgreenhousesallowoff-seasonlocalproductionincoldclimates.Buthowdoestheenvironmental
impactofheatingcomparewithlongdistancetransportfromwarmerregions?Studiescomparinglocal,
out-of-seasonproductionoffreshtomatoesinNorthernEuropewithimportsfromsouthernproduction
regionsofferpotentialparallelstoaNorthAmericansituation.Allofthefollowingexamplesshowthatit
isenvironmentallypreferable,intermsofGHGE,toshiptomatoeslongdistancesthantoheatalocal
greenhouse.
OnestudyconsidersfouroptionsfortomatoesconsumedinVienna,Austria:in-season,freshtomatoes
grownorganicallyunderprotection;out-of-seasonproductioninaheatedAustriangreenhouse;out-ofseason,freshtomatoesgrowninprotectedcultureinSpainandshippedtoAustria,andItaliancanned
tomatoes(Theurletal.2014).Thein-season,localtomatoescontributedthelowestGHGEperkgof
tomatoes.Out-of-season,freshtomatoesshippedfromSpain(growninprotectedstructures)have
lowerGHGEthancannedtomatoesfromItaly(growninopenfield)orlocal,freshtomatoesproducedin
heatedgreenhouses.Inallcases,themanufacturingofgreenhouse/hoophousestructurescontributes
lessthan10%tooverallGHGE,socontributionsfrombuildingthestructuresareminor.Inthecaseof
cannedtomatoesfromItaly,theprocessingandpackagingcontributemorethanthreetimestheGHGE
asdoesthelongdistancetransport(1600km)toVienna.
AseparatestudyfoundthatproductionoffreshtomatoesinheatedglasshousesintheUKrequiredfour
timestheenergyandresultedinthreetimestheGHGEperkgdeliveredtoaregionaldistributioncenter
intheUKthanprotectedcultureproductioninSpainthatisshipped2300kmviatruck(Webbetal.
2013).ThisisdespitetomatoyieldintheUKgreenhousesbeing2-3timesthatinSpain.Thetransport
energyinshippingtomatoesfromSpaintotheUKwasaboutonethirdofthetotalfortheSpanishcase.
AnotherstudycomparedtomatoproductionunderprotectedcultureinMoroccoandtransportedto
Francewithlocal(French)off-seasonproductioninheatedgreenhouses,andfoundasimilartrend
(Payenetal.2015).Local,off-seasonproductionhasgreaterimpactnotonlyonclimatechange,butalso
non-renewableenergyconsumptionandmarineeutrophication.However,thisstudyalsoevaluated
wateruseimpact–waterdeprivation–andwateruseforgrowingtomatoesinMoroccohadnearlyfour
timestheimpactasout-ofseasonproductioninFrance(seeFigure4).Thisresultsuggeststhatwhileit
appearsthatlong-distancetransportispreferabletoheatingagreenhouse,theremaybetrade-offs
dependingonthedistantproductionneeds.
ResearchGaps
WhilegeneralanalogiescanbedrawnfromEuropeanstudies,moreNorthAmericanstudiesareneeded
totrulyunderstandtheimpactsoftomatoproductionanddistributionoptionsavailableintheU.S.
AnalysisoftomatoproductioninMexico,especially,wouldbeavaluableaddition.
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4
impactsnormalizedtoFrenchproduc3onvalues
3.5
3
off-seasoninheatedgreenhouse(France)
transport,MoroccotoFrance
unheatedgreenhouses(Morocco)
2.5
2
1.5
1
0.5
0
climatechange
non-renewable
energy
consump<on
marine
eutrophica<on
freshwater
eutrophica<on
terrestrial
waterdepriva<on
acidifica<on
Figure4.Comparisonofoff-seasonproductioninheatedgreenhousesinFrancewithprotectedculturein
Morocco(andtransportedtoFrance)acrossvariousenvironmentalimpactcategories.Notetherelative
impactsofproduction(blue)andtransport(red)fortheMoroccogrowntomatoes.Valueshavebeen
normalizedineachimpactcategorysuchthatFrenchproduction=1.AdaptedfromPayenetal.2015.
AsisoftentruewithfoodLCAstudies,downstreamstagesofretailandconsumptionhavenotbeen
includedinmostoftheexistingliterature.Thesestagescanhavenotablecontributions,buttheyare
challengingtomodelassituationsandbehaviorsarehighlyvariable.
Alsoabsentisconsiderationofretail-andconsumer-levelfoodwaste.Foodwasterepresentsanotable
inefficiencyinourfoodsystemthatmustbeaddressed;theenvironmentalburdenofproducingfood
thatiswastedisthesameasfoodthatiseaten.Abetterunderstandingoftheroleoftomatowaste
couldbeparticularlyrelevantinmakingchoicesbetweenfreshandprocessedtomatoes:freshtomatoes
areexpectedtohavesignificantlymoreretail-levelandconsumer-levelwasteduetospoilage,andthis
maybesignificantenoughtobalanceouttheincreasedimpactsofprocessingandpackaging.Likewise,
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duetothehighcosmeticstandardsforfresh-markettomatoes,cullingratescanbesignificant.Some
retailersareaddressingthisbyselling“ugly”produceatslightlydiscountedprices.
AmorethoroughinclusionofenvironmentalimpactcategoriesbeyondGHGEwouldofferamore
completepictureoftomatoproductionandconsumption.Ofparticularinterestmaybewateruse
impactsandhumanandeco-toxicity,especiallystudiesthatfocusontheimpactsandtrade-offsof
pesticideuse.
Oneinterestingquestionthatisnotcompletelyansweredwiththeexistingliteratureisthe“freshvs.
processed”and/or“tomatosaucevs.tomatopaste”questionwhentheend-consumeditemisatomato
saucebasedfood.Tofullyanswerthisquestion,at-home(orinindustrialkitchen)cooking,wasteand
storagelogistics,andsensitivitytotransportationmodesanddistancesallshouldbeaccounted.
Conclusions
TomatoesareacommoncomponentoftheU.S.diet,makingconsiderationoftheenvironmentalimpact
oftheirproduction,processing,packaging,distributionandconsumptionavaluablecasestudy.Results
fromthelifecycleassessmentliteraturesuggestafewgenerallyapplicableconclusions:
• Heatinggreenhousesforout-of-seasontomatoproductionaddsasignificantcontributionto
greenhousegasemissionsandotherenvironmentalimpacts,andthiscontributiontypically
outweighstheimpactsoflongdistancetransportfromwarmerproductionregions.
• Agrichemicals–bothfertilizerandpesticideproduction–andfertilizer-relatedfieldemissionsare
importantcontributorstothegreenhousegasemissionsofopen-fieldandprotectedtomato
production.Insufficientdataareavailabletodeterminewhetherorganicproductionreduces
greenhousegasemissionsperkgoftomatoproduced.
• Packagingisanimportantcomponentofthelifecycleimpactsofprocessedtomatoproducts,
andeffortstoreducepackagingimpacts(lighterglassjars,papercartoncontainers,etc.)can
significantlyinfluencetheoveralllifecycleperformance.
• Growingfresh-markettomatoesunder(unheated)protectedstructuresappearstooffer
considerablebenefitintermsofyieldandqualitywithoutaddinganotableenvironmentalimpact
burden.
• Trade-offsbetweendifferentenvironmentalburdenscanbeanimportantconsiderationwhen
comparingdifferentsystems.
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TermsandDefinitions
(Notethatinthefinalversion,thesetermsanddefinitionswilllikelyresideinan“overview”or
“preamble”documentthatwillserveasanintroductiontoLCAandthisprojectforallsummarysheets.
Wehaveincludeddefinitionshereforyourreferenceinreview.Ifyou’veencounteredothertermsthat
shouldbedefinedhere,pleasecomment!)
LifeCycleAssessment(LCA)isaninternationallyacceptedandstandardizedmethodologythatdefinesasystematicsetof
proceduresfor“compilationandevaluationoftheinputs,outputsandthepotentialenvironmentalimpactsofaproduct
systemthroughoutitslifecycle”.Acradle-to-gravesystemboundaryconsidersthelifecyclestagesofaproductfromraw
materialextractionthroughtothedisposalattheendoflifeoftheproduct.Acradle-to-gatesystemboundaryconsidersthe
lifecyclefromrawmaterialextractionthroughanintermediatelifecyclestage(e.g.:tomatoproduction).
ProductCarbonFootprints(CF)areasubsetofLCAthatfocusonlyontheclimatechangeortheglobalwarmingpotential
impactcategory.Aproductcarbonfootprint,reportedinCO2-equivalents,isameasureofgreenhousegas(GHG)emissions
(carbondioxide,methane,nitrousoxide,fluorinatedgases)overaproduct’slifecycle.SomeGHGshaveastrongerwarming
effectthancarbondioxide,suchasmethanewitha100-yearGlobalWarmingPotentialof28kgCO2-equivalents(30forfossil
methane)andnitrousoxideat265kgCO2-equivalents,accordingtotheIntergovernmentalPanelonClimateChange(IPCC)
th
5 AssessmentReport(Table8.7).
Carbondioxideequivalent(CO2e):Theuniversalunitofmeasurementtoindicatetheglobalwarmingpotential(GWP)of
eachgreenhousegas,expressedintermsoftheGWPofoneunitofcarbondioxide.Itisusedtoevaluatereleasing(or
avoidingreleasing)differentgreenhousegasesagainstacommonbase.
Eutrophicationoriginatesmainlyfromnitrogenandphosphorusinsewageoutlets,manuresandfertilizers.Nutrientsthatrun
off,leachorotherwiseenterwaterwaysacceleratethegrowthofalgaeandothervegetationinwater.Degradationofthis
excessorganicmaterialconsumesoxygen,resultinginoxygendeficiencyandfishkills(deadzones).Eutrophicationpotential
quantifiesnutrientenrichmentbythereleaseofsubstancesinwaterorintothesoil,andiscommonlyexpressedinPO4
equivalents.
Acidificationoriginatesfromtheemissionsofsulfurdioxideandoxidesofnitrogen,whichreactwithwatervaporinthe
atmosphereandformacidsthatprecipitatetotheearth’ssurface(acidrain).Acidificationpotentialmeasuresthe
contributionofanemissionsubstancetoacidification,typicallyexpressedinSO2equivalents.
Wateruse:Waterresourcesarealsoessentialforagriculturalproduction,andirrigationwithsurfaceandgroundwater
(termed“bluewater”inwaterusejargon)makesagriculturepossibleinmorearidregions.Geographicallocationinfluences
theamountofbluewaterrequiredtoproduceagivencrop.Theimpactofthatwateruseonthelocalenvironmentandother
potentialusers,however,alsovarieswithlocation:usingwaterinwaterstressedregionsismoreimpactfulthanusingwater
inregionswithamplesupply.Generalizationofwaterusefromoneproductionregiontoanotherisdifficultandunadvisable.
WateruseinLCAisoftenreportedsimplyasaninventory(liters),butconsensusisbuildingastohowbesttoincorporatethe
impactofwateruseinanLCAframework.
Humantoxicitypotential,eco-toxicitypotential:Atoxicologicaleffectisanadversechangeinthestructureorfunctionofa
speciesasaresultofexposuretoachemical.Characterizationfactorsforvariouschemicalsaredevelopedbasedon
multimediachemicalfatemodels,exposurecorrelations,andchemicalriskscreenings.Toxicitypotentialsarecharacterized
byhighuncertaintiesduetothecomplexfate,exposureandtoxicologicalmodelingrequired.
95%Confidenceintervalisastatisticalparameterthatactsasagoodestimateoftheuncertaintyofasampleofdata.Inthe
caseofestimatingaproduct’scarbonfootprint,wedon’tactuallyknowthe“true”meanvalue.Whenaveragingestimates
fromanumberofstudies,thereisobviouslyuncertainty;notonlydoLCAmethodsintroduceuncertainty,butthereis
expectedvariabilitydependingonthespecificsofthemodeledsystem(soil,climate,electricitygridmix,etc).A95%
confidenceintervalmeansthatif100samplesweretakenandaconfidenceintervalwerecomputedforeachsampling,we
wouldexpect95outof100oftheintervalstocontainthe“true”meanvalue.
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