ENVR 200 Lecture Notes - Molybdenum, More Than That, Headache

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26 Nov 2012
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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
o As human beings, we do not have a high enough GPA as plants do to have these useful
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
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.
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
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 THAT.
o Canned tuna fish has more mercury than fresh tuna due to possible processing.
o The average child should eat not eat tuna fish no more than once or maximum twice per
week and pregnant shouldn’t touch tuna fish at all.
o It can cause tremor of the hands, memory loss (insomnia) and delirium, mental
o Children and fetuses are very sensitive to mercury exposure.
What are the wood preservatives?
o Chemicals that protect wood from rooting due to insects and microbial agents and on
that way prolong age in service of wood products.
o Contains chromium oxides, copper oxides and arsenic oxides. These oxides are soluble
in water and make the solution acidic and are used for wood treatment.
Vacuum-Pressure impregnation treatment of wood
o CCA in incorporated into the wood under high-pressure and the remaining CCA is
recycled for future use.
o People working in these environments must use protective gear.
o Wood is removed from the retort and left to rest from 3 weeks to a month to achieve a
fixation process the chromium, copper, and arsenic require some time to react with
the organic components/chemicals of the wood resulting is different compounds.
Production of CCA treated (before 2003)
o 100% of residential lumber
o 70% of all wood products
o Important industry in N. America (annual gross sales in USA of around 3.91 x 109)
o It is a very good preservative and contributes to sustainable forest management (cutting
less wood or cutting wood which is used less).
o CCA can prolong the life of the wood for 20-50 years and is useful in marine (salty water)
o It is odourless, UV resistant and cheap to produce.
Environmental Concerns
o When it is raining or snowing, part of the Chromium, Copper and Arsenic incorporated
in this wood will leach out of the wood. Why? These metals are not complete fixed in
the wood because of the process and the type of wood and etc. The incomplete fixated
chemicals leach out.
o When these elements leach out they will usually make contact with the soil first.
Part of the soil may be ingested or inhaled.
Eating plants will enter the human body and humans may get
Soil organisms (e.g. insects) may get affected
In addition, ground water may be contaminated due to leaching.
Aquatic systems may be contaminated due to leaching.
Leaching is higher in salty and warmer waters.
The CCA may get rubbed onto hands because of contacts with picnic tables,
playgrounds, gazebos, decks and etc. The CCA may be ingested by accident
o Risk of children getting cancer from arsenic ingestion from CCA treated woods.
However, the problem with this risk assessment is that it depends on how much time a