Hi. It’s Mr. Andersen and this is AP environmental science video 32. It is on the health impacts
of pollution. Way back in the 1930s, the Chisso Chemical Corporation built a factory in Minamata
which is way southwest Japan. It was located between the Minamata River and the Minamata
Bay. And they were producing chemicals like acetyl aldehyde, which is not inherently dangerous.
It is used as a precursor to make things like vinegar. But they were using an enzyme that
contained mercury. And as the pumped the pollution back into the bay that methyl mercury got
into the food supply. And it moved its way up the food chain to the point where people
were eating fish that contained mercury in it. They started to develop a disease called
the Minamata Disease. They did not know what really caused it and then they eventually
traced it back to this factory. Over 2000 people developed Minamata Disease over that
time. And so anything that negatively impacts human health is a disease. It could be a chronic
disease that takes a long time to develop. Or it could be acute. It develops very quickly.
It can be caused by many different things. Disease could be caused by pathogens, like
viruses and bacteria. An example could be the ebola outbreak in Western Africa. That
would be an acute disease that comes on very quickly and is caused by an ebola virus. Human
health disease can also be caused by our risks. Smoking for example leads to lung cancer.
But it can also be impacted by pollution, in other words chemicals that get into the
environment become toxins and then they affect us in a negative way. We classify these in
five different groups. There are the neurotoxins which attack the brain and the nervous system.
We have carcinogens which will lead to cancer. We have teratogens which affect the embryo.
We have then endocrine disruptors which impact the endocrine system, the hormones in our
body. And then finally we have allergens which do not affect everyone. Now we use chemicals
in our body. So lots of time we have to figure out what is the safe dose of a chemical. And
so we use a test called the LD50. And I will walk you through that. The problem with a
lot of these chemical is they bioaccumulate. They are picked up by living systems and then
as they move up the food chain they biomagnify. And so we ban a lot of chemicals. The Stockholm
Convention was a convention to ban 12, they called them the dirty dozen, 12 endocrine
disruptors. And I think they have added another 9 since then. And so disease can be caused
by pathogens, but they can be acute. They come on very very quickly, like this outbreak
of ebola recently. But most of the diseases that impact humans, so this is a list of the
largest diseases in humanity, are going to come on very slowly. They are going to be
chronic diseases of the upper respiratory track. You see we have heart disease, stroke,
things like that that are killing most of the people on our planet. Health risks are
changing over time. So it used to be that the traditional risks were things like undernutrition,
bad air pollution inside, poor sanitation. But you can see over time we are shifting
towards more modern risks, smoking for example, obesity, inactivity, urban air quality. These
are becoming the risks of the modern world. And a lot of those risks are one that we take
on our own. So if we are looking at lung cancer deaths for example, most of those are formed
from smoking, not caused by air pollution. But this video is mostly about pollution.
It is about toxicology. It is about the harmful chemicals that can affect humans. And we break
those into five categories. The neurotoxins, so the methyl mercury in Minamata Disease
would be an example of that. Lead is a great example of a neurotoxin. So it is actually
damaging parts of the brain, especially the highlighted portions here in the prefrontal
cortex. So as this person right here is recycling batteries, that lead, they are being exposed
to lead, and that is going to be a neurotoxin. We also have carcinogens. These are chemicals
that can lead to cancer. A famous one would be asbestos which was used way back in the
1950s as an insulator. But now causes diseases like lung cancer and mesothelioma, which is
rare form of cancer caused by asbestos. We also have teratogens. These are going to be
chemicals that affect us before we are born. And so a famous example is thalidomide. It
was given to women and what it does is it decreases morning sickness. But what you got
were these awful birth defects, since it is a teratogen. Another example of that could
be alcohol. It causes fetal alcohol syndrome. We have endocrine disruptors. And so the way
that our cells communicate is through hormones. So it will dock with a receptor on our cell
and then there is a message that is sent into the cell. The way that endocrine disruptors
work is they either block that receptor, so the hormone cannot dock or they can imitate
the hormone itself. That is what DDT does. And the Stockholm convention was a number
of different countries that go together to ban the use these dirty dozen these 12 endocrine
disruptors. And then finally we have allergens. These are going to be chemicals that affect
each of us in a different way. And so this person is taking an allergy test where they
are exposed to all of these different chemicals and they are seeing where the response is.
And this can be deadly. If you think about a peanut allergy can lead to anaphylaxis.
And so you have to kind of know what chemicals you are susceptible to. Now almost all chemicals
on the planet can be a toxin if we get them in large enough amounts. And so what is the
safe amount of coffee for example that I can drink. Well we use a test called the lethal
dose or LD50 test. And a lot of this unfortunately is done on animals. What you do is you take
a new chemical and you apply larger doses to a set of mice for example. So the first
group is given very low amounts, low dosage. And then those at the end are given a high
dosage. And what you are looking at is mortality rate. So those that got a low dose, the percent
that died is almost nil. But those who got a high dose, 100% mortality. So to calculate
the LD50 what you do is you look for the point at which that graph crosses 50 percent mortality.
And so we could say it is at 3.8 milligrams per kilogram. You then divide that by 10 and
that is going to be your LD50 for mice. And so it would be 0.38 milligrams per kilogram.
That is going to be the safe dose. If we see where that is on the graph, it is going to
be way down here. Now the LD 50 then, to extrapolate that for humans, what we will do is we divide
it by 10 again, because there may be different susceptibility in humans and mice. And then
we will divide it by 10 again, just to be safe. And so the LD50 in humans would be 0.0038
milligrams per kilogram. Now the problem with a lot of these chemicals is they bioaccumulate.
So that methyl mercury that was pumped into Minamata Bay was picked up by phytoplankton.
In other words as they were taking in water they were taking in some of those chemicals.
They do not kill those phytoplankton. But those phytoplankton are eaten by zooplankton
which are eaten by small fish. And as we move up the food chain the chemicals do not go
away. They bioaccumulate. And so over time they get to larger and larger doses. And so
the EPA put a list out of what fish are safe to eat in an area where methyl mercury may
be found. And so they said at the lower parts of the food chain, krill and maybe oysters
for example it is safe to eat an unlimited amount of these. But as we move up to tuna
and sharks you should minimize the amount that you are eating because there are going
to be larger loads of mercury. Did you learn the following? Could you pause the video at
this point and fill in the blanks? Let me do that for you. Human health can be impacted
by diseases which are chronic. It take a long time or acute. It can be caused by pathogens,
like viruses for example ebola virus or risks like smoking. But pollution is chemicals that
are toxic to us. We break those into five categories, neurotoxins, carcinogens, teratogens,
endocrine disruptors, remember we used the Stockholm Convention as a treaty to try to
stop using the dirty dozen of these endocrine disruptors. We have allergens which affect
each of us differently. The dose response we use is the LD50 test. And then the thing
that we have to be wary of in environments is bioaccumulation, biomagnification. That
is health impacts of pollution. And I hope that was helpful.