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Lecture 5

EESA10H3 Lecture Notes - Lecture 5: Arsenic Pentoxide, Immunosuppression, Silt

Environmental Science
Course Code
Jovan Stefanovic

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Lecture 5 Heavy Metals
• Naturally occurring, extracted from the earth, in ore
• Wide environmental dispersion
• Tendency to accumulate in select tissues
• Toxic in even low concentrations
1. Class A:
• K, Na, Mg, Ca
• Macronutrients (essential for biological processes)
• Tend to form ionic bond
• Low toxicity
2. Class B:
• Hg, Pb, Ti
• Nonessential elements
• Tend to form covalent bond
• Very toxic (form soluble organometallics)
3. Borderline:
• Cr, Cu, As, Co, Ni, Zn, Mn, Fe
• Almost all micronutrients
Toxicity: Class B > Borderline > Class A
Mechanisms of Toxicity
1. Blocking essential functional groups such as proteins or enzymes, proteins can not carry
2. Displace other metals (class B, borderline)
3. Modifying the active conformation of biomolecules (class B)
Coping Mechanisms
Resistance species develop mechanisms not to uptake metal (example Pb)
Tolerance the capacity of a species to withstand high level of metals Internal detoxifying
• Binding to non sensitive compound structures
• Metabolic transformations to less toxic forms (methylation of As in marine biota)
Can develop multiple tolerance - Cu, Pb, Zn, Cd.
Bioavailability of Metals
• Species of the metal - free ions (charged ions Zn+2 are more bioavailable than Zno )
• Neutral species may be bioavailable, important in complexes
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