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Lecture 5

Lecture 5 Study Guide

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Department
Environmental Science
Course Code
EESA10H3
Professor
Jovan Stefanovic

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Human Health and the Environment
Lecture 5: Heavy Metals and Human Health
Heavy Metals
We say that heavy metals are all elements that have metallic characteristics but they
also have a very high atomic weight number one definition is based on atomic weight
The second definition says that it is based on the density of the element density of
elemental forms of these metal
They say that all elements that have density higher than 7g/cm3 belong to this group
Some other scientists say that this is not true we are going to base this definition on a
specific gravity
We actually dont know or dont agree with what heavy metals are and not only that
Some elements known as metalloids (not really truly metals)
Arsenic is it doesnt have full characteristics but we still consider arsenic as a heavy
metal
There is another term that is very often used and seen in literature; this is known as
trace elements
It is different than metals trace elements can be any element found in environment of
lower concentration (very low sometimes hard to detect)
For us here in our class and for most of the people heavy metals are toxic only
elements that are toxic based on their toxicity
Where can we find them? They are coming from the ground part of normal geological
ground core of the planet
We 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 products
After 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 ground
This closed circle of metals before metal finished circle it is very widely spread
everywhere in water, environment, food, air
Most of them are toxic especially in some certain concentrations because every metal is
toxic in some concentration (some of them in extremely low concentrations)
They affect different types of organs and accumulate in certain parts of our body
selected tissues
Classification of metals
There are 3 basic groupings of the metals
First is class A not very toxic, low toxicity (i.e. 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 essential
These elements tend to form ionic bond; are usually positively charged
Life SupportEESA10H3 S
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Other class is class B is very toxic (i.e. 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 effects
They have high electron negativity (opposite from class A), tendency to acquire
electrons, form a covalent bond (form pairs of electrons)
Third class are metals that we call borderline (somewhere in between these two)
All of them are micronutrients they are necessary for many physiological processes in
our body including plants (i.e. Cr, Cu, As, Co, Ni, Zn, Mn, Fe)
Toxicity: class B is the most toxic, then borderline, then class A is least toxic
Mechanism of toxicity
1) Metal is attached to protein that means that protein can carry anything because the
essential functional groups that need to attach hormone or something else are already
satisfied with the metal
Protein can carry anything means that proteins function is blocked
2) Especially for class B and borderline is that instead of some necessary metal
important for our physiological processes some other toxic metals from class B or
borderline is attached
3) Changing molecule some organic compound such as biomolecule twisting that
molecule changing the conformation of molecule means that new molecule will be like
what you see in the mirror (different conformation)
Coping Mechanisms
Class B metals are really harmful for humans how do we cope with this? Not just
humans, plants, other organisms cope with this
First is resistance, simply do not uptake the metal (humans do not have this function,
mechanism)
Some of the plants have a great mechanism to resist and even to uptake the metals (i.e.
Pb, will grow acceptably well on some soils)
What we do have is tolerance to some chemicals
There are two groups of chemicals being threshold and non-threshold chemicals
Threshold means that in a very low concentration we can tolerate them without
experiencing any adverse affects
Non-threshold means that just in very low concentration already we are going to
experience some adverse affects
How else can this happen? Can happen by metabolizing some of these chemicals, that is
also a possibility can metabolize part of the metals and get less toxic forms (i.e.
methilation of As in marine biota, it means forming organic forms of arsenic are less
toxic that inorganic forms)
Some other example is binding to non sensitive compound structures somewhere
where it is not that toxic
We and plants can develop and resist tolerance not only to one metal but more than one
metal we call this multiple tolerance (i.e. Cu, Pb, Zn, Cd)
Bioavailability of metals
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Bioavailability is everything that is available to us
If you look at the environment and you see how many lead you have all around you not
everything is available for you that you can uptake or absorb
Not every form of the metal is bioavailable some are more available and others are less
available
It depends on species, not plant or animal species species of metal (means form is it
ionic form, or stable neutral form, or is it organic or inorganic form)
Huge differences depend on form, element as well because different elements from
different forms
For example Zn is a charged electron such as Zn+2 are more bioavailable than just
neutral elemental thing
Usually the charged electrons are more bioavailable
But it doesnt meant that neutral species are bioavailable but also may be available
somehow especially when they form complexes
They can form complexes with any kind of organic metal and as organic they can be
bioavailable
Compare two elements arsenic and mercury arsenic is less toxic in organic form than
in inorganic form
On the other hand mercury is opposite it is toxic in any form
Mercury changes form very quickly, every form is very toxic even inorganic form
Ph of solution, water, soil, stomach can affect everything in acidic conditions (below 7)
more 4, 4.5, 5
Most of the metals are more toxic and more bioavailable
When we say bioavailable means more toxic
In Ph above 7 and neutral they are less bioavailable and less toxic
How does temperature affect the bioavailability? If you look at sea water and find some
concentration of mercury (Hg) what do you think whether itll be more bioavailable in
the coast of the Caribbean or here in Canada?
In warm waters is more available that is how the temperature affects the
bioavailability (also seasonal)
Redox potential of solution the actual amount of oxygen in water, soil, solution, and so
on
If the amount of oxygen is low most of the heavy metals are toxic
Heavy metals are in more toxic form in contaminated water because there is not enough
oxygen in the water (potentially more toxic forms for us)
Routes of exposure
Three major routes we see not only for metals but for all chemicals are inhalation (dust
or PM, fume, gas), ingestion (soil, food, plants accumulate metals in roots and leafs), and
through the skin
If we eat plants it can be a source of metals in our body
The higher concentration is going to be in the roots, then stem, and then leaves means
that if we have contaminated soil it is not good to eat plants
Life SupportEESA10H3 S
www.notesolution.com

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Description
Human Health and the Environment Lecture 5: Heavy Metals and Human Health Heavy Metals We say that heavy metals are all elements that have metallic characteristics but they also have a very high atomic weight number one definition is based on atomic weight The second definition says that it is based on the density of the element density of elemental forms of these metal They say that all elements that have density higher than 7gcm3 belong to this group Some other scientists say that this is not true we are going to base this definition on a specific gravity We actually dont know or dont agree with what heavy metals are and not only that Some elements known as metalloids (not really truly metals) Arsenic is it doesnt have full characteristics but we still consider arsenic as a heavy metal There is another term that is very often used and seen in literature; this is known as trace elements It is different than metals trace elements can be any element found in environment of lower concentration (very low sometimes hard to detect) For us here in our class and for most of the people heavy metals are toxic only elements that are toxic based on their toxicity Where can we find them? They are coming from the ground part of normal geological ground core of the planet We 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 products After 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 ground This closed circle of metals before metal finished circle it is very widely spread everywhere in water, environment, food, air Most of them are toxic especially in some certain concentrations because every metal is toxic in some concentration (some of them in extremely low concentrations) They affect different types of organs and accumulate in certain parts of our body selected tissues Classification of metals There are 3 basic groupings of the metals First is class A not very toxic, low toxicity (i.e. 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 essential These elements tend to form ionic bond; are usually positively charged Life Support EESA10H3 S www.notesolution.com
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