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specific defenitions

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Lecture 5Heavy MetalsNo specific definition however some are defined by molecular weight or density some are mixed in terms with trace elementsMetals found in nature in soilThey can be extracted from the ground as an ore and once extracted from nature they enter a cycle or incorporated in some productsHowever when the life of that product is over they may end up in a landfill or some other place in the environment but never as an ore or in their previous stateThey can be widely dispersed mostly by human activitiesWhen in the environment they can enter the human body like other chemicalsWhat makes them different is that they can accumulate in some certain tissuesAnother major characteristic is that they are toxic in very low levels ppb or ppmHow do we classify them o They are divided into three major groups there are overlap of some elements o CLASS A CLASS B Borderline o CLASS A macronutrients necessary for our physiological function in big amounts and surround us in significantly big amounts in food and water What distinguishes is that they have tendency to form ionic bonds They are of very low toxicity o CLASS B very toxic eg mercury lead silver and gold They are not essential for the body They can change states easily and also can exist as an organic form or an inorganic form What distinguishes them from Class A is that they have a tendency to form covalent bonds o Borderline They are necessary and are Chromium Copper Arsenic Cobalt Nickel Zinc Manganese and Iron They are considered micronutrientsIron is important in the functioning of hemoglobinChromium is important in lowering blood sugar levels used as a supplement o Toxicity Class B Borderline Class AMechanism of Toxicity o Blocking essential functional groups such as proteins or enzymes proteins cant carry anything If a metal is combining with the protein it may block essential functional groups and the protein may become dysfunctional o Displace other metals class B borderline For example Mercury can replace some of the borderline elements in their functions and can disrupt the normal function o Modifying the active conformation of biomolecules twisting of molecules class B It may change the chemical arrangement of the molecule The functioning of Class B is usually responsible for this form of pain in the assCoping Mechanisms o Resistance species develop mechanisms that do not uptake the metal eg lead This is evident in some plants o Tolerance the capacity of species to withstand high levels of metalInternal detoxifying mechanisms metabolize metal to a weaker state eg methylation of arsenic in marine biotaBinding of certain elements to non sensitive sites
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