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Environmental Science
Course Code
Jovan Stefanovic

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Lecture 5: Metals and Human Health Heavy Metals Define: Based on atomic weight, based on density (all elements having density higher than 7gm/cm ).3 Trace elements are elements found in a lower concentration. Very low sometimes hard to detect. • Naturally occurring, extracted from the earth (ground) in ore in different forms. • Used for different applications • Wide environmental dispersion (water, food, air etc) • Tendency to accumulate in select tissues • Toxic in even low concentrations Classification of metals 1. Class A: K, Na, Mg, Ca, Al Macronutrients (essential for biological/physiological processes) Usually cations. Tend to form ionic bond. Opposite forces are attracted to each other. (Na can react with Cl form table salt) _ Low electro negativity (tendency to lose rather than acquire electrons) _ Low toxicity 2. Class B: _ Hg, Ti, Pb, Ag, Au _ Nonessential elements (not needed by the body and can interfere in the body) _ Tend to form covalent bond _ High electro negativity (tendency to acquire rather than lose electrons) _ Very toxic (form soluble organometallics) 3. Borderline: _ Cr, Cu, As, Co, Ni, Zn, Mn, Fe Contribute in many important physiological processes. _ Micronutrients Toxicity: Class B > Borderline > Class A Mechanism of toxicity 1. Blocking essential functional groups such as proteins or enzymes, proteins can’t carry anything 2. Displace other metals (class B, borderline) 3. Modifying the active conformation of biomolecules (twisting of molecules) (class B): like what you see in the mirror. Really harmful for humans. Coping Mechanisms _ Resistance – species develop mechanisms not to uptake metal (example Pb) www.notesolution.com _ Tolerance – the capacity of species to withstand high level of metals. There are two types of chemicals: threshold and non-threshold chemicals. _ Internal detoxifying mechanisms _ Binding to nonsensitive compound structures (not very toxic) _ Metabolic transformations to less toxic forms (methilation of As in marine biota) _ Can develop multiple tolerance to chemicals - Cu, Pb, Zn, Cd. Bioavailability of metals Not every form of chemical is bioavailable _ Species of the metal (ionic form, neutral, organic/inorganic etc) - free ions (charged ions Zn+2 are more bioavailable than Zn) Usually charged electrons are more bioavailable. As vs Hg As is less toxic in organic form then in inorganic form. Hg is toxic is any form. Hg changes forms quickly too. _ Neutral species may be bioavailable, important in complexes _ pH of solution (in acidic conditions, most of the metals are more toxic and bioavailable. In basic conditions, they are less toxic and less bioavailable) _ Temperature (higher temperatures: more toxicity) _ Redox potential of solution (amount of O i2 water and soil. If amount of O is2low, most of the heavy metals are more toxic) Routes of exposure to chemicals: _ Inhalation (dust or PM, fume, gas) _ Ingestion (soil, food, plants accumulate metals in roots and leafs) (Concentration in roots then stems and then leafs and then for some plants some grains.) In potatoes: they store starch and they are not a root so they are better than most plants. _ Through the skin _ Mostly accumulate in liver, bones, kidney _ Damage the brain, kidney, some carcinogens _ Hard to diagnose (symptoms are weakness, headache, hypertension): no specific symptoms. Mercury (Hg) _ Metallic form - in batteries, dental amalgams, thermometers is toxic. _ In industry in different forms _ Liquid in pure form, not significant hazard _ When volatile very toxic _ Organic and Inorganic forms, both toxic _ Bioaccumulation (tuna fish) Canned tuna is safe to eat than fresh tuna. _ Tremor of the hands, excitability, memory loss, insomnia, sometimes delirium. _ Sensitivity of fetal and infant nervous system to low levels of Hg (mental retardation,
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