Lec 5 Heavy Metals.docx

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University of Toronto Scarborough
Environmental Science
Silvija Stefanovic

Lecture 5 Heavy Metals 1 Heavy Metals  Different definitions for heavy metals  Heavy toxic metals 1. They have a wide dispersion in all parts of the environment 2. They have a tendency to accumulate in selected tissues 3. Toxic in very low concentrations o Even the ones which are essential for human life, might be toxic Classification of Metals (not in textbook) Class A  Micronutrients which are essential for biological processes  Are low in toxic but we cant say they are NOT toxic Class B  Very toxic elements  Not essential for human body  Mercury, Lead  Most toxic chemicals known Borderline  Somewhere in between which are essential for psychosocial processes but are not needed in large amounts  Iron Mechanism of toxicity  These metals can prevent the receptors from carrying various groups  Some organic molecules have a different conformation which can be changed through metals, which disrupts some biological function Coping Mechanisms  All living things have a kind of mechanism to fight against these metals  Some living things can live in the presence of lead  If plants are able to tolerate high levels of metals, it does not enter out food chain  Tolerance o The metal binds to non-sensitive compound structures instead of sensitive compounds o Arsenic is toxic in its inorganic form but not very toxic in organic forms o Plants can tolerate not just one but many different metals Bioavailability  In simple words, not everything that we are inhaling or ingesting is causing toxic effects  We are taking more than the actual receptors are taking up  The amount of chemical that’s causing the harmful effects is bioavailability  Bioavailability is usually presented from a scale of 0-1  It is changing and depends on the conditions of the environment  If they are less bioavailable, they are less toxic  The PH of the solution is also a factor  Presence of acid conditions leads to more bioavailability and more toxicity  Redox potential means oxygen is reducing the toxicity of metals and the metals are present in oxidized forms (less toxic) Routs of exposure  Dust- particulate matter  Ingestion of food and plants  The highest concentration is in the root and then in the leafs  Some metals can easily penetrate through the skin e.g. Mercury o Can go through the latex gloves and can cause death within couple of hours  Very difficult to diagnose as there is no particular symptoms Mercury  Liquid mercury- pure mercury is extremely difficult to find it  It is not toxic but when it is spilled, millions of small points will spill around  The fumes of liquid mercury are very toxic especially when it is sprayed  Mercury is toxic in all forms- organic and inorganic  Mercury bioaccumulates and thus, accumulates in various kinds of fish  Pregnant women cannot eat tuna fish  During the 19 century, it was po
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