BiomagnificationThroughaFoodChain
Purpose:
Theconceptsofbioaccumulationandbiomagnification(orbiologicalmagnification)areoftenconfused. Theformeristheincreaseintheconcentrationofafat-solubletoxinwithinthe tissuesoforganisms;thelatterdescribestheincreaseinthattoxinasyoumoveupthroughafoodchain.Whereaswater-solubletoxinswillsimplybeexcreted,fat-solubletoxinsremainwithinthetissuesandorgansofanorganismsothatwhenthatorganismiseaten,theconsumeringeststhetoxinaswell. Tertiaryconsumers,suchasBaldEaglesandotherbirds-of-prey,areespeciallyvulnerabletotheeffectsofbiomagnification. ThisactivitywilldemonstratetheconceptsofbioaccumulationandbiomagnificationusingtheclassicexampleofDDT.
Objective:
To examine the concepts of bioaccumulation and biomagnification of a chemical in a food chain
Background:
ShortlyafterWWII,anewsuper-pesticidewasputintowide-spread useacrosstheUnitedStates.Dichloro-diphenyl-trichloroethane (DDT),thefirstsyntheticpesticide,hadbeenusedwithmassivesuccessduringWorldWarIItocombatmalariaandotherdiseasescarriedbyinsects.Inthebaby-boomperiodrightafterthewarthisnewtechnologywascalledupontohelpkeepAmerica'sagriculturehealthyandprosperousandAmericanfamilies'housesidyllicabodesfreeofinsects. Nooneknewthattheywereactuallyunleashingoneofthemostpersistenttoxicchemicalscommerciallyavailable. NotuntilRachelCarson's1962bookSilentSpringdidpeoplestarttoquestionthischemicalandtheunforeseennegativeeffectsiiwas havingontheenvironment
Carson'sbookoutlinedhowDDTstayedwithinafoodchain,buildingintoxicityasitwaspassedinthetissuesfromonetrophiclevellothenext Thisphenomenon,knownasbiomagnification, seemedtoaffectlargerbirdsmorethansmalleronesandnotbysimplykilling them,butbyalteringhowtheymetabolizedcalcium.Becausetheycouldnotprocesscalciumproperly,thesebirdscouldnotbuildshellsstrongenoughtolastthroughincubation. Thus,bythelate1960'spopulationsofOsprey,BrownPelicans,andBaldEagleswerecriticallylowandsomespecies,suchasthePeregrineFalcon,wereextinctincertainregions. FortunatelythedevastatingeffectsofDDTwererecognizedrelativelyearlyonandin1972thisorganochloridepesticidewasbannedforcommercialuseintheUnitedStates. HoweverinotherpartsoftheworldDDTwasstillwidelyused.
In2001,theStockholmConventiononPersistentOrganicPollutants(POPs)was introducedattheConferenceofPlenipotentiariesntotryandeliminateand/orcontroltheuseofDDTandotherPOPsaroundtheworld.Ultimatelysignedbyover150 countries,theConventionlimitstheuseofDDTtothepreventionofmalariainselectcountries.
Theconventionalsoplaceslimitationsonotherlong-lived,fat-soluabletoxins,nicknamed"TheDirtyDozen",suchasdioxin,aldrin,chlordane,andPCB's.WhilethesePOPsarestillusedinmanycountriesandthereforestillposeariskgloballyduetotheireaseoftransportboththroughtheairandinwater,effortsarebeingmadetoeliminatethemandtheirenvironmentalthreat.
Vocabulary:
- Bioaccumulation – theprocessbywhichafat-solubletoxinbuildsupwithinthetissuesofanorganism
- Biomagnification – theincreaseofafat-solubletoxinateachsuccessive levelofafoodchain
- Phytoplankton – microscopicplantsthatliveinbodiesofwater,e.g.singlecelledalgaelikediatoms
- PersistentOrganicPollutants (POPs) –enduringchemicalsthataccumulateinthetissuesoforganisms,arepassedupafoodchainandposeahealthrisktohumansandtheenvironment
- TheDirtyDozen – thetwelvetoxicchemicalsinitiallynamedbytheStockholmConventiontobetargetedforreduction/eradication;9ofthe12arepesticides
- Zooplankton – microscopicanimalsthatliveinbodiesofwater,e.g.copepods
Materials:
100 slips of paper –“phytoplankton”
20smallcups – "zooplankton"
5mediumcups – "minnow"
2largecups-"eel#1" and "eel#2"
1bowl–"osprey"
Procedure:
1.Thepileofpaper slipsrepresentsthephytoplanktonpopulationinalake. Theprinted“M”oneach sliprepresentstheamountofDDT(inppm)thealgaeingestedfrompesticiderunofffromanearbyagriculturalarea. Thereare100 slipsinthepile. Eachboxbelowrepresentsonephytoplankton.Marktheamountoftoxineachphytoplanktonhasingested.Ifthereisafull“M”on the slipthenthatphytoplanktonhasingested1 ppmofDDT,so writea“1”inoneoftheboxesbelow. Ifthereisno“M”ontheslipthenthatphytoplanktondidnotingestanyDDTsowritea“0”inoneof theboxesbelow.
Ifthereisapartial“M”ontheslipthenestimatehowmuchofthe“M”thereis.Forexample,ifthereisonlyonehumpofthe“M”thenthatwouldequal½ of aunitofDDTingestedbythatphytoplanktonsoyouwouldfillinoneoftheboxesbelowwith “½.”
2.Zooplanktoninthelake(populationsize20)eacheat5algae.Move5slips intoeachofthezooplanktoncups.RecordtheamountofDDTeachzooplanktonhasingestedusingtheinstructionsfromstep1.Writetheseamountsontotheindividualcopepodpicturesbelow:
3.Minnows(populationsizeof5)inthelakeeacheat4zooplankton,ingestingthetoxinthatisstoredinthezooplankton. Movethecorrect number of slipsfromthezooplanktoncupsintotheminnowcups. RecordtheamountofDDTingestedbyeachofthesmallfishontothefishbelowusingtheinstructionsfromstep1tocalculatethetotalamountforeachfish.
4.Twoeelsthencomealongfordinner. Oneeeleats2minnowsandtheothereeleats3minnows.Movethecorrectnumberof slips from theminnowcupsintotheeelcups.WritetheamountofDDTingestedbyeacheelontothepicturesbelow.Usetheinstructionsfromstep1tocalculatethetotalamountofDDTforeach.
5.Finally,anospreyfliesbyandeatsbotheels.Movethecorrectnumberofslips from the eelcupsinto theospreybowl. CalculateandthenwritethetotalamountofDDTingestedbytheospreyontothepicturebelow:
DataCollection:
1.DataTable.
a.Fill in the population of organisms at each level of the food chain.
b.Usingthenumbersyouhavewrittenontotheimagesabove,calculatetheaverageamountofDDTingestedateachlevel of the food chain. Showallyourworkbelow. Writethefinalaveragesinto the data table.
Population of Organisms / DDT Ingested (ppm)Phytoplankton
Zooplankton
Minnows
Eels
Osprey
DataAnalysis:
1.Showyourcalculations for the average DDT at each level in the food chain:
2.Drawapyramidofnumbers representing the populations andapyramidshowingtherelativeconcentrationsofDDTateachlevel of the food chainusingthevaluesfromthedatatable.
3.SummaryofDataTrends.
a.ComparetheamountofDDTfoundintheospreywiththeamountoftoxinfoundinonephytoplankton.Bespecific. Discussnumericalevidence.
b.Compareandcontrastwhatyourpyramidstellyou.Discusssimilaritiesanddifferencesbetweenthepyramids,aboveandbeyondtheobvious. Dothe variousshapesmakesense,givenwhatyouknowaboutfoodchainsingeneralandbiomagnifications?Whyorwhynot?
Conclusion:
1.Summarizewhatyouhavelearnedthroughdoingthislab.
2.Doyouthinkthepurposeofthelabwasachieved?Whyorwhynot?
3.Arethereanybiasesorassumptionsbehindthecollectionofdataortheexperimentaldesign?Ifso,didtheyhowdidtheyimpacttheoutcomeoftheexperiment?
4.Arethereanyothersourcesoferrorthatimpactedthefinalcalculations?Ifso,whataretheyandwhatcouldbedonetonegatetheireffect?
Youwillneedtodosomeoutside researchtoanswertheselasttwo questions
5.IstheamountofDDTateachlevelinthismodelisaccuratecomparedtothe"realworld"?
6.Wouldtheamountcalculatedfortheospreyinthissituationbedetrimentaltoarealosprey?
SuggestionsforFurtherInvestigation:
1.Researchoneoftheother"DirtyDozen"pollutants,preferablyonethathasahistoryinyourarea.Findoutwhatthechemicalwas/isusedfor,atypicalfoodchainthatitimpacts,whatthetoxiceffectsonthatfoodchainareandhowitsuseisbeingcontrolled(i.e.isitbannedoutrightoraretherecertainusesitis stillallowedfor?).
2.Theothermainsubstancesthattendtobiomagnifyareheavymetals.Researchaheavymetalthathasahistoryofbioaccumulationinhumans.Findoutwhatthemetalwas/is used for,howhumanstypicallyingesttheheavymetal,whatthetoxiceffectsareandhow,orif,itsuseisbeingcontrolled.
3.Researchthefollowingpesticides:alachlor,metalachlor,cyanazine,atrazine,methoxychlor,pyrethrin.Createatablethatcomparestheirtoxicitylevels.Includeeffectsonhumans,half-lifeintheenvironment,persistencelevel,mobilitylevel,impactongroundwater,andeffectsonaquaticlife. Includeanoverallrankingofmosttoxictoleasttoxic.
4.Flame-retardantchemicalshavebeenusedforyearsincommonhouseholdproductssuchaselectronics,polyurethanefoamfurniturecushionsandchildren'sflame-resistantclothing. Recentlyattentionhasbeenfocusedonthetoxicityandbioaccumulativepropertiesofthisgroupofchemicals,thepolybrominateddiphenylethers(PBDEs),namelydecabromodiphenyl ether(decaBDE),pentaBDE,andoctaBDE. PBDEshavebeen foundinconcerninglevelsinhumanblood,fat,breastmilk,andin thebrain. Whiletheirexacteffectsarenotaccuratelyknown,theyarebelievedtocausedamagetotheliver,thyroidandslowneurologicaldevelopmentininfants. HumanstypicallyinhalePBDEsfromtheirenvironmentbutalsoingesttheminthefoodtheyeat,namelyfishandpoultrywhichhavebeenexposedtothechemicalsthroughnon-pointpollutionfromlandfills. Giventhisbackgroundinformation,designanexperimentwhichwouldhelpdemonstratethatPBDEsarebioaccumulativeinhumans.
Based on: Biomagnification Through a Food Chain from Lab Manual for Environmental Science by Edward Wells, Brooks/Cole Publishing, 2009