Heavy Metals and Human Health
• Naturally occurring, extracted from the earth in ore (ground, earth’s 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)
• 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)
• 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
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)
• 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
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 Corporation’s 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.
Mechanism of toxicity: blocking essential functional groups such as proteins or enzymes, proteins cannot carry anything, displace other metals (class b, borderline, modifying the active conformation of biomolecules (class b) Bioavailability of metals (cid:0) species of the metal - free ions (charged ions zn+2 are more bioavailable then zn) (cid:0) neutral species may be bioavailable, important in complexes (cid:0) ph of solution (cid:0) redox potential of solution. 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. First discovered in minamata city in japan in 1956. I t was caused by the release of methyl mercury in the industrial wastewater from the.