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The topic
of this lecture
is Toxicology.
Toxicology 
is the science of poisons and
poisoning.
Poisoning can happen for many reasons, it
can be
accidental, when somebody eats something
that they shouldn't eat.
It can be environmental, when people are
poisoned by chemicals present in the
environment,
such as the many people around the world
who have to drink groundwater
contaminated with arsenic.
It can be occupational,
when workers who have to work with a
particular toxic substance
start to feel the effects because they are
not properly protected.
It can also be deliberate.
Poisoning for many, many centuries now,
has been used for both suicide and murder.
The
use of poisoning to commit murder goes
back
a very, very long way in human history.
And even up to say 100 years ago, it was
still relatively common.
Nowadays, it's much less common.
We see fewer cases of poisoning, and the
reason
is very simple. In the old days, anyone
could
go into a drug store or a pharmacy and
could buy, over the counter, the most
horribly poisonous chemicals.
Nowadays, these chemicals are very tightly
controlled, so it's much more
difficult to obtain these awful substances
nowadays than in the past.
Well, before we move on to the classic
poisons, there are other
substances which will cause damage to the
human body in other ways.
In particular, strong acids and strong
alkalis are corrosive.
And from the GHS symbol, you can see very
graphically, the effect that they have on
the human body.
The best known and most often abused
of these chemicals is concentrated
sulfuric acid,
also known under its old name of vitriol.
And even today, this stuff is quite
readily available because
of course, it's the acid that's used in
car batteries.
There have been many cases from around the
world of people using sulfuric acid to
attack.
There have been cases, for instance, in
Cambodia, in Bangladesh, in Pakistan.
Recently, there where cases of it being
thrown rather indiscriminately at markets
in Hong Kong.
And here's one case in Malaysia, where a
man came
home and attacked his wife and daughter
with sulfuric acid.
Possibly the most celebrated case is the
case of the Iranian lady, Ameneh
Bahrami, and you can see from the picture
here the drastic
effects that sulfuric acid can have on the
human body, and this
is what she looks like after
multiple operations and extensive medical
treatment.
What happened in her case, is that a young
man proposed to her,
she rejected him, and he got his revenge
by attacking her with sulfuric acid.
Other chemicals
can also be irritants.
For instance, many salts of the elements
lead or mercury
or arsenic, when they get into the gut,
irritate the gut,
and this causes nausea or diarrhoea.
And this is an automatic reaction of the
body to get rid of these substances.
So in the gut, these things can act as
irritants. Of course, these chemicals
after they're absorbed from the
gut into the body can then have other
effects, and
we'll talk about some of these later in
the lecture.
Now, let's look at poison themselves,
systemic poisons.
These things that we normally consider
poisons, they
will typically attack particular
biochemical systems within the body.
That is, they will interfere with the
molecular machinery that keeps us alive.
For instance, one of the most famous of
all poisons, is cyanide.
And what cyanide will do is that when it
gets into
the cells, it will interfere with the
action of the mitochondria.
And the mitochondria are those parts of
the cell
which are involved with processing energy
to keep us going.
So it's essentially like taking a hammer
to the cell's fusebox.
As we'll see on the next slide, carbon
monoxide, interferes with the work of
hemoglobin in our blood. And a poison such
as strychnine, which used to be
quite common, like many other poisons, it
shuts down the nervous system.
Morphine is a poison,
we will talk about that more in our
lecture on drugs.
Atropine, another poison, and like morphine
and strychnine, it's derived from a plant.
And atropine also affects the nervous
system, and
we'll talk about that later in this
lecture.
Strychnine, morphine, and atropine are
purely natural compounds.
But synthetic pesticides that are used by
farmers,
some of these are very, very toxic indeed.
And later in the lecture, we'll also look
at
some of the synthetic nerve agents that
have been used.
In the last part of the lecture, we'll
look at some
inorganic poisons, such as the elements
arsenic, antimony, mercury, and thallium.
Now, at the beginning of this slide, I
mentioned the very famous poison, cyanide.
And normally, cyanide is very difficult
to obtain.
But cyanide poisoning does still occur,
and
one of the reasons is this plant here.
This plant is cassava.
The root of the cassava plant is used as
staple food
by many, many millions of people around
the world, particularly in Africa.
And there's a problem.
Because when the root of the cassava
plant is
cut open, the plant will start to release
cyanide.
Now, normally what people do when they're
preparing cassava to eat, there's
a whole procedure they have to go through to
process the root
and after that procedure then it's quite
safe,
the cyanide has been eliminated.
But every year, there are a few cases of
cyanide poisoning due
to cassava, and simply because they
haven't prepared the root properly.
Now, let's look at one of the poisons that
I mentioned,
and that is carbon monoxide.
Carbon monoxide poisoning remains quite
common.
So, every year from around the world,
there are cases of carbon monoxide
poisoning.
Almost all of them are accidental,
a few of them are deliberate.
Now, carbon monoxide works as a poison by
blocking hemoglobin.
Hemoglobin is the protein in our blood
that
is responsible for transporting oxygen
from the lungs,
where it comes into our body, to the
cells, where it's consumed as part of our
metabolism.
Now, hemoglobin is a complex protein.
It contains four sub-units
and in each sub-unit, there's an iron atom,
and it's the iron atom that does the
work.
So when the hemoglobin arrives in the
blood vessels
near the lungs, it picks up an oxygen
molecule
which has come in with the air we breathe,
and that oxygen molecule coordinates to
the iron atom, sticks to the
iron atom, and then is transported through
the bloodstream to where it's needed.
Well, if iron can pick up a small molecule
like oxygen,
it can also pick up a small molecule like
carbon monoxide.
So if you breathe in some carbon monoxide,
some of
your hemoglobin molecules, will pick up
CO instead of O2.
That means that that hemoglobin
molecule
is not available for transporting oxygen.
Now, at any given time, a certain amount
of your
hemoglobin is in this form, with CO bound
to it.
The CO binds strongly so the oxygen
cannot compete.
Now, the reason we always have a certain
amount of hemoglobin carrying carbon
monoxide in our blood is because there's
always carbon monoxide in the air.
Whenever hydrocarbon fuels are burned,
a small amount of CO will be produced.
So when someone drives a car, a little
bit of CO is emitted.
And therefore, we're going to breathe it
in.
The amount of CO in ordinary air is too
small to do us any harm.
It's only when the amount of CO in the
air gets above a certain level
that we can get poisoning.
Now, blood of course is red, it's red
because of the hemoglobin.
But the colour of the hemoglobin depends
on
the small molecule that's bound to the
iron.
So of course, blood is red because when
oxygen
is bound to hemoglobin, it's a very bright
red colour.
When carbon monoxide is bound to
hemoglobin, it's a slightly
different colour, it's a pinkish colour.
So in fact, one
of the signs that someone is
suffering from
carbon monoxide poisoning, is that they
will look a bit pink.
Now, let's look specifically at the
chemistry of carbon monoxide poisoning.
So, let's consider the burning of butane
gas,
and butane is commonly used around the
world as a gas for cooking.
So, butane is the molecule C4H10.
If you burn butane in the presence of
plenty of air
then for each butane molecule, six and a
half oxygen molecules are going to be
consumed,
and you will get four carbon dioxide
molecules and five water molecules.
This is not a problem.
But suppose that same gas is burned in a
limited amount of air.
Suppose we don't have six and a half
oxygens,
suppose we have one oxygen left.
We only have five and a half oxygens.
In that case, for each butane molecule,
you'll get two molecules of carbon
dioxide, five molecules of water, but two
molecules of the toxic carbon monoxide.
So, if you burn hydrocarbon fuels where
there's
a restricted amount of air, and there's
improper
ventilation, then the concentration of
carbon monoxide in
that place can easily build up to toxic
levels.
And this happens for instance, if you have
a room with a gas heater
and the flue of the gas heater was not
properly maintained.
Carbon monoxide will easily build up to
lethal levels.
Another way carbon monoxide can build up
is in a car.
Suppose you've been driving your car for a
long time,
maybe you're a taxi driver.
You've been driving your car all day
and you're tired,
you want to take a nap.
So you pull over,
you park somewhere.
It's hot,
so you leave the engine running, because
you like the air conditioning.
So you close your eyes,
you go to sleep.
Now, perhaps this is an old vehicle,
the exhaust pipe is a bit leaky.
So that means carbon monoxide, as well as
the
other exhaust gases, can leak out of the
exhaust system.
Maybe the cab of the car is a bit leaky as
well, which means
that carbon monoxide from the exhaust can
seep into the cabin of the car.
And there have been cases of people
takings naps in cars,
engine running, and never waking up due
to carbon monoxide poisoning.
Here's another example of carbon monoxide
poisoning
and this is a tragedy that killed five
people a few years ago.
And this is a group of teenagers who
checked
into this motel in Miami to have a party.
But this is a rather unusual motel in
that the rooms are up above, and below
the
room, there's a parking garage, and then
there's a
stairway leading from the garage up to the
room.
So what these guys did, was to park their
car in the garage
and they decided to leave the car engine
running.
And apparently, this is because it was a
rather old car, and they were worried
that if they turned the engine off, they
might not be able to start it anymore.
Well, they were eventually found some time
later.
They were all in the room, and they were
all dead.
And what had happened was that carbon
monoxide produced by the car engine had
seeped up the stairs, into the room, and
had tragically killed all of them.
Carbon monoxide's cousin is carbon
dioxide, a molecule that a lot
of people have been talking about these
last few years.
Now, carbon dioxide is much less toxic
than carbon monoxide.
It does not bind to hemoglobin in blood,
so
it can't do the same trick as carbon
monoxide.
The principal danger with carbon dioxide
is the danger of asphyxiation.
And that is, if you're in a place where so
much carbon dioxide can be
released that it simply replaces the air
in that environment
and then there's no oxygen around for
people to breath.
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The most tragic and dramatic incident of
this in
recent years was at a place called Lake
Nyos.
Now, Lake Nyos is an old volcanic crater.
It's in Cameroon in West Africa,
and it's an old volcanic crater that has
filled
up with rain water and it's become a
lake.
But the ground under the lake is still
geologically active, and it's giving off
carbon dioxide.
So, carbon dioxide from underground is
slowly seeping into the lake.
Now, the lower layer of the lake
is cold water.
It's building up carbon dioxide, and in
fact has become super-saturated in carbon
dioxide.
The carbon dioxide can't escape because
on top of the lower layer,
there's the top layer of warmer water
acting as a kind of lid.
And that's warmed because of course it's
warmed by the sun.
And this situation is unstable.
But, for the carbon dioxide in the lower
layer to be
released, there has to be some event that
disturbs the lake.
And it's believed that what happened, is
that at
one side of the lake, there was a
landslide.
Okay, rocks crashed down into the lake.
That stirred up the lake, and then, rather
like a Coca Cola
bottle that's been shaken, and then the
lid has been taken off,
the CO2 from the super-saturated lower
layer
was released. Because CO2 is denser than
air,
the carbon dioxide coming out of the lake
flowed over the ground, spread down the
valley,
and approximately 1,700 people were
asphyxiated by that carbon dioxide.
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