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Lecture 6

Week 6 Lecture

Environmental Science
Course Code
Jovan Stefanovic

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Heavy Metals and Human Health
Heavy Metals
Naturally occurring, extracted from the earth in ore (ground, earths crust)
oDuring the processing, metals can be released into the environment
Wide environmental dispersion (environmental impacts = soil, water, air)
oThey may be consumed by living organisms
oThrough the food, through the air, through the water
Tendency to accumulate in select tissues
oWhen it enters the human organism, usually it stays in specific tissues (nails,
Toxic in even low concentrations
oMetals are extremely toxic (i.e. lead, mercury, arsenic = top 3)
Classification of metals
1. Class A:
K, Na, Mg, Ca
Macronutrients (essential for biological processes) = needed in big amounts
Tend to form ionic bond
Low toxicity
2. Class B:
Hg, Ti, Pb, Ag, Au
Nonessential elements
Tend to form covalent bond
Very toxic (form soluble organometallics)
3. Borderline:
Cr, Cu, As, Co, Ni, Zn, Mn, Fe
Class B > Borderline > Class A
Mechanism of toxicity
1. Blocking essential functional groups such as proteins or enzymes, proteins cannot 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 species to withstand high level of metals
o Internal detoxifying mechanisms
Binding to nonsensitive compound structures
Metabolic transformations to less toxic forms (methilation of As in
marine biota)
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Can develop multiple tolerance - Cu, Pb, Zn, Cd.
Bioavailability of metals
Species of the metal - free ions (charged ions Zn+2 are more bioavailable then Zn)
Neutral species may be bioavailable, important in complexes
pH of solution
Redox potential of solution
Routes of exposure
Inhalation (dust or particulate matter/PM, fume, gas)
Ingestion (soil, food, plants accumulate metals in roots and leafs)
Through the skin
Mostly accumulate in liver, bones, kidney
Damage the brain, kidney, some carcinogens
Hard to diagnose (symptoms are weakness, headache, hypertension)
Mercury (Hg)
Metallic form - in batteries, dental amalgams, thermometers
In industry in different forms
Liquid in pure form, not significant hazard
When volatile, fumes are very toxic
Organic and Inorganic forms, both toxic
Bioaccumulation (tuna fish and other kinds of fish)
Tremor of the hands, excitability, memory loss, insomnia, sometimes delirium.
Sensitivity of foetal and infant nervous system to low levels of Hg (mental
retardation, language, memory and neural problems if mother are exposed during
the pregnancy)
When spilled, mercury scatters into silver puddles and beads that give off an invisible vapor
that is heavier than air. Breathing this vapor is a health hazard especially for young
children and the fetus carried by pregnant women.
There are still no credible scientific proofs that mercury exposure from dental amalgam
fillings cause serious human diseases in a community.
Case study: Minamata disease
The Chisso factory and its wastewater routes
First discovered in Minamata city in Japan in 1956.
It was caused by the release of methyl mercury in the industrial wastewater from the
Chisso Corporations chemical factory, which continued from 1932 to 1968.
This highly toxic chemical bioacumulated in shellfish and fish in Minamata Bay and the
Shiranui Sea, which when eaten by the local population resulted in mercury poisoning.
Cat, dog, pig and human deaths continued over more than 30 years.
The government and company did little to prevent the pollution.
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