MadSci Network: Medicine |
Hello Arisa,
You have asked a very interesting question. Your ideas linking ozone
depletion to increased skin cancer rates are important for evaluation.
First I will explain the difference between producing pollution and
suffering from pollution. Then I will describe the pattern of ozone
destruction. Finally, I'll give you an idea about why skin cancer rates
are higher in Australia than New York that is independent of ozone
destruction. Along the way I'll throw in some extra information just for
fun!
Pollution Moves
Unfortunately, the people who make pollution aren't usually the ones that
suffer from it. In general, pollution does not stay still. Pollution can
be moved easily by water and air. For example, pollutants are often dumped
into river water. The polluted water then floats downstream to another
city where the people are affected by it. Canada is a country with many
beautiful lakes. The life in some of the Canadian lakes has been killed
off by acid rain. But the pollution that caused the acid rain did not come
from Canada, it came from factories in the United States.
Because pollution moves around, international treaties are made to prevent
one country's pollution from hurting another country's people. For
example, the United States now has a
Clean Air Act
to help prevent air pollution from spreading to Canada.
About Ozone Destruction
UV light causes mutations in DNA, which can lead to the formation of skin
cancers. The ozone layer helps keep UV light from getting down to the
ground. Some kinds of pollution (in particular, CFCs) get up into the
atmosphere and destroy ozone. But the ozone-destroying pollution doesn't
go straight up. Instead the pollution is carried by wind currents to above
the North and South Poles. Far more ends up over the South Pole than the
North Pole. Because Australia is much closer to the South Pole than New
York is, ozone depletion may be worse over Australia than it is over New
York. This would cause rates of skin cancer to go up in Australia, while
skin cancer rates in New York would remain the same.
The ozone layer has been a frequent topic written about by the MAD
Scientists. I encourage you to read through some of these other essays:
Karla Wilson has posted a description of the hole in the ozone layer which
includes a
great map.
Linda Engebretson wrote an interesting essay about why the
ozone holes are where they are.
John Christie wrote an easy to understand essay about
changes in the ozone layer.
Skin Cancer in Australia
Places near the equator receive more of all kinds of light than areas away
from the equator. Australia is nearer to the equator than New York is, so
Australia has always received more UV light than New York.
If you'd like to read more about how UV light causes skin cancer, please
read two great MAD Scientist essays already written:
James Cotton's essay describes the specifics of how UV light mutates DNA.
Scott Dietert's essay describes skin cancer and explains the link between
ozone loss and increased skin cancer.
Many inhabitants of both Australia and New York are descendants of
Europeans. Europeans tend to have very light skin. Light skin is very bad
at blocking out large amounts of UV light. When Europeans moved Westward
to New York, they did not move much closer to the equator, so they did not
increase their exposure to UV light. When Europeans moved Southward to
Australia however, they moved much closer to the equator. Their pale skin
is not as good at protecting them from UV light as the darker native
Australian skin is.
Although pollution may be making skin cancer worse in Australians by
destroying atmospheric ozone, skin cancer would be much more common there
anyway.
Exposure to different levels of UV light at different places on Earth has
lead to the evolution of different skin colors in different people. Darker
skin protects much better against UV light than light skin. That's why
native people from near the equator usually have darker skin than natives
farther from the equator.
Why do humans who evolved far from the equator have lighter skin? Although
UV light can cause cancer, it is also used for a good purpose in the human
body. We use UV energy to make vitamin D from cholesterol! So the lighter
skin allows the smaller amount of UV light available in the North to enter
the body to be used to make this important vitamin!
Thank you for your interesting question. If there's anything else you're
curious about, please ask more questions!
John Carlson,
MAD Scientist
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