Heavy Metals Notes

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Environmental Science
Jovan Stefanovic

Lecture 5 Heavy Metals and Human Health Heavy Metals - Naturally occurring extracted from the earth’s crust o Toxic  even at LOW concentrations  mostly are in the industrial section. o Wide environmental dispersion  Impacts the water, air, soil  enters the food chain  ultimately affects humans.  Biomagnification – increase accumulation as you go up in the food chain  Bioaccumulation – accumulation of one compound/chemical in a tissue o E.g. Arsenic – goes directly into nails and accumulates - Metals are classified according to toxicity and importance to the biological system: o Class B > Borderline > Class A o Class A  Essential for biological processes  Macronutrients – animals need these in their bodies  Very low toxicity  Form ionic bonds (attraction between positive and negative ions)  E.g. K, Na, Mg, Ca o Class B  Not important for biological processes  Very toxic in ANY form  E.g. Mercury is toxic in its organic and inorganic form  Form covalent bonds (two ions share electrons – very strong bond)  They are also organometallics  complexes between metals and organic compounds  In addition to this, they are also soluble when they enter the body  that’s why they are very toxic  Eg. Hg, Ti, Pb, Ag, Au o Borderline  Important for biological processes in very LOW concentrations (as opposed to macronutrients)  Micronutrients  Eg. Arsenic (As)  Belongs to the borderline group o It’s not essential and not even a metal but belongs here because of its toxicity.  Eg. Cr, Fe, Co, Ni, Cu, Zn, Mn - Mechanism of Toxicity o Metals can:  Block functional groups such as proteins and enzymes  so proteins cannot carry anything  Displace other metals  Non-essential ones can replace the essential metals in our bodymostly Class B’s and borderlines  Change/modify the conformation of biomolecules  Class B  Make them inactive - Coping Mechanisms o Resistance  Some species have mechanisms not to take toxic metals in their system.  E.g. Plants have a mechanism not to take in toxic chemicals o Tolerance – the capacity of organism to withstand high levels of metals  Internal detoxifying mechanisms  Bind to nonsensitive compound structures o Metals will bind to other less crucial chemicals instead to essential proteins in the body  so won’t affect the metabolism.  Metabolic transformations to less toxic form o Methylation of Arsenic (As) in marine biota  Arsenic is converted from a toxic inorganic form to a less toxic organic form  E.g. As III to As V  Can develop multiple tolerance o E.g. Cu, Pb, Zn, Cd - Bioavailability of Metals o Species of a metal  Free ions – some are more available than others  E.g. Charged Zn (Zn ) ions are more available than neutral Zn  pH affects bioavailability  Metals are more bioavailable and toxic in acidic solutions o E.g. in acidic soil, plants accumulate more Lead (Pb)  Redox potential (ability of the medium to oxidize or reduce a metal)  More oxygen = Increased oxidization = Less toxic metals  Less oxygen = decreased oxidization = more toxic metals - Routes of Exposure o Plants accumulate metals  Generally, roots accumulate more metals than leaves  Seeds have the less concentration of metals  Better to grow something from seeds  corn, wheat, seeds  Roots are not good for us  carrots, beans  Potato is more of a storage than a root o Inhalation (dust, particulate matter (PM), fumes, gas)  Can enter through the skin, inhalation, ingestion (through roots and leaves of plants)  Accumulate in bones, liver, tissues, kidney etc…  Damage bodily systems/organs  carcinogens  Very hard to diagnose  common s/s such as headaches, flu, weakness, HTN Mercury (Hg) - Toxic in any form (organic or inorganic) o E.g. batteries, dental amalgams (can release mercury at a high level), thermometers (not toxic until it evaporates) o Exception = liquid form  not a significant hazard until it evaporates  When spilled, it scatters into silver puddles that releases invisible vapor that is heavier than air  hazard especially to children and pregnant wo
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