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Lecture 5

EESA10 - Lecture 5.doc

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University of Toronto Scarborough
Environmental Science
Jovan Stefanovic

Lecture 5 Heavy Metals and Human HealthHeavy MetalsWe say that heavy metals are all elements that have metallic characteristics but they also have a very high atomic weightnumber one definition is based on atomic weightThe second definition says that it is based on the density of the elementdensity of elemental forms of these metalThey say that all elements that have density higher than 7gcm3 belong to this groupSome other scientists say that this is not truewe are going to base this definition on a specific gravityWe actually dont know or dont agree with what heavy metals are and not only thatSome elements known as metalloids not really truly metalsArsenic is it doesnt have full characteristics but we still consider arsenic as a heavy metalThere is another term that is very often used and seen in literature this is known as trace elementsIt is different than metalstrace elements can be any element found in environment of lower concentrationvery low sometimes hard to detectFor us here in our class and for most of the people heavy metals are toxiconly elements that are toxic based on their toxicityWhere can we find them They are coming from the groundpart of normal geological ground core of the planetWe humans extract them as ore and mine them as ore and then extract them from the ore in different forms sometimes in a pure form or sometimes as a salt and incorporate them as different kinds of productsAfter that when we mine them use them for some products that product will finish their life cycle and possibly can be reused or can be deposited if some depositions occur again under the groundThis closed circle of metalsbefore metal finished circle it is very widely spread everywhere in water environment food airMost of them are toxic especially in some certain concentrations because every metal is toxic in some concentration some of them in extremely low concentrationsThey affect different types of organs and accumulate in certain parts of our bodyselected tissuesClassification of metalsThere are 3 basic groupings of the metalsFirst is class Anot very toxic low toxicity ie K Na Mg Ca Al are essential elements for plants for us they contribute to many physiological processes in our body and they are needed in significant amounts that is why we call them macronutrients and are essentialThese elements tend to form ionic bond are usually positively chargedOther class is class Bis very toxic ie Hg Ti Pb Ag Au these elements are not essential we dont need them for any process in our body they just can interfere with the processes in our body and cause some adverse effectsThey have high electron negativity opposite from class A tendency to acquire electrons form a covalent bond form pairs of electronsThird class are metals that we call borderline somewhere in between these twoAll of them are micronutrientsthey are necessary for many physiological processes in our body including plants ie Cr Cu As Co Ni Zn Mn FeToxicity class B is the most toxic then borderline then class A is least toxic
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