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Pahlsson1989;Al-Hiyalyetal.1993;Broadleyetal.2007;Hassan&Aarts
2011).ThereareafewdocumentedcriticalZnconcentrationsfortissuesof
thebroad-leavedtreespecies.Thus,forexample,260ppmZnindryneedles
matterwasfoundtobecriticalintheSitkaspruce(Piceasitchensis),whereas
nosuchdatawasfoundforminimumtoxicityinScotspine(Balsberg-
Pahlsson1989;Dmuchowski&Bytnerowicz1995).Duetohighsusceptibi-
litytoaccumulationofthiselement,pineneedleshaveaparticularrele-
vancefordeterminingthelevelofzincintheenvironment(Nieminen&
Helmisaari1996;Giertychetal.1999;Migaszewskietal.2001).Suchhigh
levelofZncausesadecreaseinphotosynthesisandchlorosis,resultingin
bleachingandwrinklingofleaves,thusslowergrowth.However,sometree
speciessuchasBetulapubescensandB.pendulacanproducevarietiesresis-
tanttotheexcessofzincinthesoil(Brown&Wilkins1985).
Similarlytozinc,copperisamicronutrientwhichallplantsneedto
functionproperly.Itoccursinsoilcombiningwithorganicmatter,clay
mineralsandinotherformssuchassulphates,sulphidesandcarbonates
(Kabata-Pendias2004).CopperistakenupbyplantsintheformofCu2+
ionsorintheformofcopperchelates.Asaco-factorformanyenzymesand
anelectrontransporterinavarietyofbiochemicalreactions,Cuaffects
physiologicalandmetabolicprocessesinplants.Cuisimportanttoseed
production,diseaseresistanceandwaterrelationsinaplant(Helmisaariet
al.1995).Thetoxicitythresholdlevelsareconsideredbetween15and25
ppmCuindryweight.Theexcessofcoppercausesplantpoisoning,harm-
fulaccumulationinchloroplasts,interferenceintheprocessofrespiration
andsynthesisofchlorophyll,andasizeableamountofenzymes.Symptoms
ofCuexcess,initiallyconstitutesdarkgreencolourandthenchlorosis.This
elementishighlyboundtoplasmaproteinsandisoftenretainedinthe
rootsofplantswhichtendtobeshort,thickanddevoidofroothairs
(Prasad&Hagemeyer2004).LikeinthecaseofZn,theexcessofCuin-
creasesabbreviationsandabnormalitiesatroottipmitosis.Thenumberof
cellsundergoingmitosisisdecreasedandthemitoticactivityisdisturbed.
Athighersoillevels,Cucanbeextremelytoxic,althoughseveralplantspe-
ciesareabletoevolveresistantgenotypes(Xiongetal.2008).
CadmiumisanothertypeofHMaccumulatedinsoilsinthevicinityof
non-ferrousmetalsmelters.IntheMŚLsoils,Cdisthesecondheavymetal,
afterzinc,inrespectofconcentrationinsoil.Asanon-essentialmicronutri-
ent,itisconsideredtoxiceveninsmalldoses.Itspresencecausesveryseri-
ousconsequencesinvolvinggrowthretardationanddisorders,i.e.inphoto-
synthesisandtranspirationrate,decreasedabilitytoretrieveCO2,changes
inthepermeabilityofcellmembranesandthestructureofDNA,andmany
more(DiToppi&Gabbrielli1999;Banerjee&Flores-Rozas2005).Cadmium
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