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UV rays
Center for Global Environmental Research, National Institute for Environmental
Studies Japan
Johann W. Ritter was a German physicist born on December the 16th, 1776 in
Samitz bel Haynau Silesia, now Poland.
Johann W. Ritter
He devoted his efforts to studying electricity and electrochemistry. However his
main discovery was the ultraviolet region of the spectrum. In 1801 he conducted
experiments with silver chloride and a prism. He projected a beam of sunlight
through the prism, which split the beam into the colors of the spectrum. He them
put chloride in each color to see the outcome. The red caused a small change
while the deep violet darkened the chloride. Ritter placed chloride in the
lightless area just beyond the violet and it darkened as it were in a smoky
fire. The was evidence of another wave form just barely higher than the violet
of visible light. It is now known as ultraviolet or UV light. It wasn't until
the twentieth century, however, that any photographic records in either of these
spectra were made
NASA Graphic
Solar Ultraviolet or
UV rays make up part of the electromagnetic or photonic spectrum of light and
radiant energy. Part of this spectrum is broken down into wavelengths and is
measured by nanometers or nm, for short. The electromagnetic spectrum within the
wavelength region ranges from the vacuum ultraviolet to the far infrared. We
cannot see ultraviolet light and it is shorter in wavelength than visible light.
Ultraviolet radiation (UV) comes
naturally from the sun. There are also some manmade lamps and tools (welding
tools, for instance) that can produce UV radiation. For most of us, however, the
sun is the primary source of UV. UV is divided into at least three different
categories based on wavelength:
UVA wavelengths(320-400
nm) are only slightly affected by ozone levels. Most UVA radiation is able to
reach the earth's surface and can contribute to tanning, skin aging, eye
damage, and immune suppresion.
UVB wavelengths(280-320
nm) are strongly affected by ozone levels. Decreases in stratospheric ozone
mean that more UVB radiation can reach the earth's surface, causing sunburns,
snow blindness, immune suppression, and a variety of skin problems including
skin cancer and premature aging.
UVC wavelengths
(100-280 nm) are very strongly affected by ozone levels, so that the levels
of UVC radiation reaching the earth's surface are relatively small.
The effects of UV radiation on
earth's ecosystems are not completely understood. Even isolating the effects of
UVA versus UVB is somewhat arbitrary. All UV radiation can be damaging. This
knowledge has prompted many manufacturers of sun screen and sunglasses to offer
products that protect against both UVA and UVB wavelengths.
While humans can choose various
courses of protection, for instance avoiding noon-time sun, plants and animals
are not so fortunate. Studies have shown that increased UV radiation can cause
significant damage, particularly to small animals and plants. Phytoplankton,
fish eggs, and young plants with developing leaves are particularly susceptible
to damage from overexposure to UV.
Solar UV radiation levels are
highest during the middle of the day. In total, almost half the daytime total UV
radiation is received during the few hours around noontime. Clouds, as well as
ozone, have a tremendous affect on UV radiation levels. However, cloudy skies
generally do not offer significant protection from UV. Thin or scattered clouds
can have minor impacts on UV and even, for a short time, increase UV above what
it would be on a blue sky day by further scattering the radiation and increasing
the levels that reach the surface.
Here are the
different types of radiation in the EM spectrum, in order from lowest energy to
highest:
NASA Graphic
To determine UV ray levels an instrument capable of measuring these
"invisible" rays must be used.
Effects of UV
Radiation on You
UV Rays enter the human body
Positive
effects
Ultraviolet rays have their place
in our ecosystem, (and it isn’t merely to provide manufacturers an opportunity
to sell their sunscreens). UV rays, for example, are necessary for our body to
produce vitamin D, a substance that helps strengthen bones and safeguards
against diseases such as Rickets. Some scientists have shown that Vitamin D
lowers the risk of getting some kinds of internal cancer, like colon cancer.
UV light is also used as a
therapy for psoriasis, a condition in which the skin sheds its cells too
quickly, resulting in itchy, scaly patches on various parts of the body. When
exposed to ultraviolet rays, the growth of the skin cells is slowed, relieving
the symptoms.
UV rays are also used in various
commercial functions, such as disinfecting fish tanks and sterilizing medical
equipment. Animal life makes their own use of these wavelengths too—certain
animals can actually see ultraviolet light, and use it to their advantage. Bees
use the reflection of UV off of flower petals to guide their pollen collecting.
Negative
effects
Though ultraviolet rays do have a
purpose, one must not use this information as a validation for their sunbathing
habits. The dangers of UV exposure are real, and public ignorance concerning
these matters could lead to increased health problems in the future.
Skin
One of the most common effects of
UV exposure is "erythema", also known as sunburn. Sunburn occurs when skin cells
are damaged by the absorption of energy from UV rays. To compensate for this
injury, the skin sends extra blood to the damaged skin in an attempt to repair
it—thus accounting for the redness that is associated with sunburn. The amount
of time it takes for a sunburn to occur is dependent mostly on the relative
amounts of UV rays that are hitting the skin, and on a person’s skin type.
People with naturally dark skin already have inherently high levels of melanin,
and so are able to spend a longer amount of time in the sun before burning, if
they burn at all. Fair-skinned people don’t have it quite so easy—burning can
occur within a relatively short amount of time.
Another effect of ultraviolet
rays on the skin is photoaging. Recent studies have shown that many of the
symptoms commonly associated with mere aging (i.e. wrinkles, loosening of the
skin) may instead be related to UV exposure—so though your tan may look good
now, you could be paying your dues in wrinkles later.
The UV Index
In order to inform the public
about the intensity of UV radiation the UV Index was invented and is now
published in newspapers and on TV. The definition of the UV Index is the same
throughout the world, so it's a great way to learn about the UV hazards at your
travel destinations. The Index is a simple number. 1-3 means low exposure; 4-6
means medium; 7-9 means high; and more than 10 means extreme exposure. The time
you can stay outside in the sun at a given UV Index depends also on on your skin
type. For example, if you have fair skin (Skin type I) and the UV Index is
seven, it takes less than 20 minutes until your skins starts to redden. If you
have a dark skin color the same UV level may need more than 40 minutes to cause
an effect.
Skin Cancer
A common misconception among the
public is that if the damage isn’t visible, no damage has been done. The only
way to dispute this is to observe the long term effects of a stimulus. One of
these effects has been identified to be skin cancer. The American Cancer Society
has predicted that in the year 2001, approximately one million new cases of
non-melanoma type skin cancers will be diagnosed, along with an additional
51,400 melanoma cases. It is also predicted that in this same year, 7,800 people
will die from melanoma, and 2,000 people will die from other skin cancers (i.e.
squamous and basal cell carcinoma). What is the significance of this? Skin
cancer rates have been on the rise in the United States since the 1970’s, with
melanoma incidences increasing at a rate of 6% a year until 1981. Since then,
the melanoma incidence rate has increased steadily at a 3% increase a year.
(Statistics taken from The American Cancer Society Statistics Page at
www.cancer.org) These increasing rates mean that the threat of cancer has become
a personal issue to the average American. Luckily, it is believed that the
causes of the majority of skin cancers have been identified—ultraviolet
radiation.
Basal and
squamous cell carcinoma
There are three basic types of
skin cancer: melanoma, basal cell carcinoma, and squamous cell carcinoma. Basal
and squamous cell carcinoma make up the most common and less dangerous forms,
called non-melanoma cancers. It is believed that ultraviolet rays (specifically
UV-B) are one of the chief causes in these two cancers. In order to understand
why, it is helpful to know that cancers occur when mutated or damaged cells in
the body begin to divide and invade other areas, forcing out the healthy cells
and tissues. In the case of skin cancer, the ultraviolet rays from the sun are
usually the instigator. Researchers whose work is specifically geared towards
squamous and basal cancers have isolated the gene suspected of being mutated,
namely the p53 gene. Under normal circumstances, this gene works against
cancerous tumors, inhibiting the division of cells that have been mutated or
damaged. If the cell cannot be repaired, the p53 gene induces the cell to
destroy itself, or commit “cellular suicide”, so that its mistakes cannot be
passed on to another cell during division. If the p53 gene is mutated, however,
(for example through UV-B rays) then it will prohibit a damaged cell from
committing suicide, thus leaving it available to divide as normal. The damaged
cells then begin to replace the healthy cells, and the condition known as cancer
is developed. These types of cancers, though common, are not usually fatal, as
they rarely metastasize (extend to other parts of the body).
Malignant
melanoma
The causes of malignant melanoma
are much less defined. Some suspect that there is a relationship between UV
exposure and melanoma rates, but there are varying theories.
Some scientists have developed a
theory that UV-A radiation is much more effective in causing melanoma than
assumed previously. If this were the case, then many sunscreens currently
available offer only very little protection against melanoma, as they mostly
block UV-B, and not UV-A. This would be a possible explanation for the observed
trend in melanoma cases, where incidences are more prevalent among the
fair-skinned population who use sunscreen than among the darker skinned, or even
among the fair-skinned who don’t use sunscreen. An explanation for this lies in
the nature of sunscreen—it blocks the UV-B rays that cause sunburn, thus
allowing those of fair skin to stay outside for longer amounts of time and still
feel "safe". Instead, they are exposing themselves to greater quantities of UV-A
rays, which could be increasing their risk of melanoma. The danger to sunscreen
could also be two-fold—not only does it persuade people to stay in the sun
longer, but habitual sunscreen users tend to lack tans, which is the body’s
natural protection against both UV-A and UV-B. This allows even more UV-A to
penetrate the skin. The moral to this story? Don't rely exclusively on
sunscreens as your UV protection. Block also UV-A radiation by wearing hats and
appropriate clothing.
How to identify
Melanoma?
One of the best ways to protect
against the dangers of melanoma is to catch it before it’s too late. Melanoma
has a high cure rate if it is caught early on. A simple way to determine if a
growth of a mole is dangerous is to check the ABC’s:
A—Asymmetry. Does one half of the
mole look like the other?
B—Border Irregularity. Are the
edges smooth and regular, or are they crooked?
C—Color. Is the color uneven?
D—Diameter. Is it larger than one
cm?
Moles that develop later in life
should also be a source of concern. Most benign moles have been present since
childhood. However, it is possible for childhood moles to become malignant.
Because of this, changes in the appearance of any mole should be noted.
Australian Skin Cancer
Australians
suffer the highest rates of skin cancer in the world. Each year, around 1,200
Australians die from what is an almost totally preventable disease. Everyone can
develop skin cancer; however, some people may be at higher risk than others, due
to a range of factors.
Australia exposed to more UV
Ultraviolet (UV) radiation levels in Australia are higher than in Europe, even
during summer. Being located close to the ozone hole over the Antarctic means
much higher, more severe levels of UV radiation get through to ground level.
During summer, the earth's orbit brings Australia closer to the sun than Europe
during its summer, resulting in an additional seven per cent solar UV intensity.
This, coupled with our clearer atmospheric conditions, means Australians
are exposed to up to 15 per cent more UV than Europeans.
First launched by a cartoon seagull
singing ‘Slip! Slop! Slap!’ on TV screens in 1980,
SunSmart adopted its name and mission in
1988. An initiative of The Cancer Council Victoria and supported by the
Victorian Health Promotion Foundation, SunSmart was developed to combat
spiralling skin cancer incidence and mortality rates.
Since then, attitudes towards tanning and
sun protection have changed dramatically. Australians have realised the pitfalls
of their sun-loving, outdoor lifestyle and are taking preventative measures to
reduce their risk of sun damage and skin cancer. Research by The Cancer Council
Victoria shows SunSmart’s messages have reached a majority of Australians and
had a stong impact on their behaviour.
Consequently, skin cancer deaths have
slowed and for females, have even started to decline. More Australians are
detecting skin cancers early, increasing their chances of surviving the disease.
Ultraviolet rays can be reflected
towards the eyes by certain substances, such as sand and snow. When this
happens, the amount of UV rays the eyes are exposed to is increased. This fact
is the basis of the condition photokeratitis, also known as snow blindness.
Photokeratitis is a sunburn of the cornea, and usually recedes within one to two
days. It occurs when the eyes are exposed to large quantities of UV light in a
short amount of time. The reflection of UV rays off of snow and sand are enough
to incur this injury.
It is more difficult to isolate
the exact amount of damage that UV imposes on the eye over a long period of
time, as the body has its own built-in defense against harmful rays. If you were
to try to look up at the sun, you would find that you would not be able to do so
for any length of time. Your eyes would naturally start to close. This effect is
also noticed on especially bright days, displayed in the form of squinting. What
is known, however, is that cumulative exposure to UV rays is one of the causes
of opacity of the eye's lens, called cataract, a condition that displays itself
primarily in elderly people, and results in blurred and fuzzy vision.
Effects on the
Environment
Even though some species respond
positively, extensive tests in several countries have shown that hundreds of
species of plants and animals display negative effects from an increase in UV
radiation.
Effects on phytoplankton
phytoplankton images
Ultraviolet radiation can harm
phytoplankton in the oceans. This is of great concern as this type of plankton
is the first link of the marine food chain. Variations in its population could
potentially cause greater disturbances in the balance of other life forms like
fish or whales. Specifically the effects of UV on phytoplankton inhabiting the
Antarctic waters are extensively investigated by scientists as UV-B exposure in
these waters has greatly increased during the last decades due to the seasonal
ozone hole
Effects on plants
Another issue that may seem more relevant
to the human population is the effect of UV on plants and food crops. Greater
exposure of plant life to UV-B can result in a decrease in production rates,
meaning less food available world-wide.
Throughout the world efforts are being
made to increase the level of UV resistance in staple crops, such as rice, where
some species are extremely sensitive to UV radiation, and other species of rice
can withstand a great increase. With this knowledge, scientists can find the
most effective and economical species to use in rice farming, thereby increasing
the UV resistance of much of the world's food supply.
Credit:NOAA,NASA, EPA, National
Science Foundation Polar Programs UV Monitoring Network Maintained by
Biospherical Instruments Inc.,Center for Global Environmental Research, National
Institute for Environmental Studies Japan, American Cancer Society's 2007 Facts
& Figures
