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Introduction
Sincemanlearnttoprocessmetaloresandusethemineverydaylife,theyhave
becomeever-present.Metalshaveservedasmaterialforproductionofmanyconsu-
mergoods.Mostofthemnotinbondbutatomicformdonotconstituteadirect
hazardtopeopleandthenaturalenvironment.Toxiceffects,connectedwiththe
presenceofmetalsinbiologicalsystems,spreadduetothepossibilityoftheirexi-
stenceasions.
Amongmetals,twogroupscanbedistinguished:agroupofessentialelements,
whichconstituteanimportantsystemofmicroelements,andagroupofnonessen-
tialmetals,whichdonotfulfilanybiologicalfunction,oftendisturbthebody’sme-
tabolismandproducetoxiceffects.Thesemetalcompoundsarethesubjectofmany
differentprocesseswhicharecalledxenobioticsmetabolism.Themainprocessesof
xenobioticsmetabolismareabsorption,distribution,biotransformationandexcre-
tion.
Beforeachemicalsubstancepenetratesintothecellsoftissuesandorgans,it
hastobeabsorbedintothebloodcirculationsystem.Xenobioticsgainintheblood
asaresultofacontactactionacrosstheskinandmucousmembranesthroughthe
respiratorytractorfromthedigestivesystem.Distributionmeansthedivisionof
thesubstanceamongseparatetissuesandorgans,aswellastheinterpenetration
throughtheinnerbarriers;italsoinvolvesbindingtheplasmaproteinsandthepro-
teinsoftheorgansandtheiraccumulationintissues.Broadlyspeaking,distribution
isalsorelatedtothebiotransformationprocessesofxenobiotics,mostoftenleading
totheirmetabolites’formation,whichthencanbeexcreted.
Organismsdonottakeupmetalsintheatomicform,butastheionic(charged)
speciesandalsowhenassociatedwithorganicandinorganicmolecules.Thetoxic
effectsoftheiractionaretheresultofmetalcompoundsstability.Theirdisintegra-
tionprovidesintracellularenvironmentwithmetalions.Thefateofmetalsinorga-
nismsdependsonthechemicalforminwhichtheyhavebeentakenupbythemfrom
theouterenvironment.
Xenobioticmetalscompetewithessentialmetalsforbindingtovariouscofactors
(suchastopaquinon),receptors,transcriptionfactors,transporters(suchasZIP
andZnT-family),andothermetalloproteins,andindoingsotheygainaccessto
variouscellularandsubcellularcompartmentsandinterfereinthefunctionsofthe
essentialmetals.Fornon-essentialmetals,highchemicalreactivityisoftencharac-
teristic,andforthatreasonmetalsalsointeractnonspecificallywithamultitudeof
othercellularligandsandinterferewithmanyothermetabolicprocesses.
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