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Human Health and Enviro Notes Lecture 5

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University of Toronto St. George
School of Environment

Lecture 5 Heavy Metals  No specific definition; however some are defined by molecular weight or density; some are mixed in terms with trace elements  Metals found in nature: in soil  They can be extracted from the ground as an ore and once extracted from nature, they enter a cycle or incorporated in some products  However, 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 state  They can be widely dispersed, mostly by human activities.  When in the environment, they can enter the human body like other chemicals.  What makes them different is that they can accumulate in some certain tissues  Another major characteristic is that they are toxic in very low levels (ppb or ppm)  How 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 (e.g. 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 micronutrients.  Iron is important in the functioning of hemoglobin  Chromium is important in lowering blood sugar levels (used as a supplement) o Toxicity: Class B> Borderline> Class A  Mechanism of Toxicity: o Blocking essential functional groups such as proteins or enzymes, proteins can’t 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 ass.  Coping Mechanisms o Resistance: species develop mechanisms that do not uptake the metal (e.g. lead). This is evident in some plants. o Tolerance: the capacity of species to withstand high levels of metal  Internal detoxifying mechanisms (metabolize metal to a weaker state) (e.g. methylation of arsenic in marine biota)  Binding of certain elements to non sensitive sites  Some species can tolerate a variety of toxic materials. (e.g. phytoaccumlators can consume a wide variety of metals, thought of a good way to clean up toxic areas). o As human beings, we do not have a high enough GPA as plants do to have these useful mechanisms.  Bioavailability o The part of the total amount of an element that can be absorbed or take up into the body of any living organism is known as the bioavailability of that given element. o It depends on many things. The element is the main factor. The second is state and form of the element (e.g. gas or liquid? Cation or anion?) wish you paid attention in chemistry and Ms. Katyal eh? o Neutral species are more available (mostly as organics) o pH of the solution affects bioavailability. Most metals are more bioavailable under acidic conditions (pH is under 5.5). Molybdenum is more bioavailable under basic conditions (only one the professor knows meaning she doesn’t know much) o Temperature is another factor. The warmer the solution the more bioavailable the element. o Iron will form in species that are more suitable for oxidation  Routes of exposure o Inhalation (dust or PM, fume, gas) o Ingestion (soil, food, plants accumulate metal in roots and leafs)  Which part of the plant is more concentrated of metal? Consider wheat. In the roots. Then in the shoot, leave, and flower. Then finally the grain. Why? Since the metal is in the soil it is more in contact with the roots. The further it travels, the less contaminated it will become.  Would you eat carrots or corn on contaminated soil? Corn. Why? The edible part of the carrot is grown in the soil which was contaminated with the elements. What about the potato? Trick question. It is edible because the potato we eat is the storage of the plant and not the root.  What do we do with contaminated soil? What do we grow then? The professor would grow grain plants (lol sticking to her U.S.S.R. farming roots). o Through the skin o Mostly accumulate in liver, bones, kidney o Damage the brain, kidney, some carcinogens o Hard to diagnose (symptoms are weakness, headache, hypertension). These symptoms are not specific. They are found for many different aches, pains, and sicknesses.  Mercury o Most talked about and most toxic o It can exist in all three states at the same time and makes its environmental chemical knowledge complex. To learn about this the professor doesn’t know, you have to take an environmental chemical course. o It serves many purposes. o Mercury in the liquid state does not pose a significant threat to the human body until it evaporates o Inorganic and organic forms are very toxic o Its main threat is biomagnifications and bioaccumulation (especially in fish). o The average adult should not eat tuna fish no more than once or maximum twice per week because of this. NO MORE THAN THA
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