INVESTIGATORY PROJECT IN BIOLOGY
In partial fulfillment of project in Biology By
………………………………
ULTRAVIOLET RAYS ________________________________ SUBMITTED
TO: DEPARTMENT OF BIOLOGY AL-FAROOK RESIDENTIAL SCHOOL
[Affiliated to CBSE, New Delhi] 2009-10 Al Farook
Residential School [Affiliated to CBSE, New Delhi] Farook college-673632
Laboratory
certificate
This is to certify that the project work titled Is a
bonafide record done by: Reg. No. ……………………………… In partial fulfillment of the
project in Biology during the year 2009-2010 Mrs. Mercy
Abraham
Mr. XYZ Department of Botany
Principal Mrs. XYZ Department of Zoology
Certified that the candidate was examined by us in the
project work/viva voce examination held at Al-farook residential school
on……………………….
Internal examiner
external examiner
INTRODUCTION
In the present 21st century world one does not need to say
about ultra violet rays, it is the most talked about topic in this era. From
the common man to academicians UV rays hold an important place. UV rays have
been discussed for long around the world especially after the discovery of the
hole in the ozone layer in 1990s.The hole meant the approaching death of our
mother earth. A host of studies have been undertaken by many people and
organizations such as the United Nations, GREENPEACE etc. Even when the world
speaks much about this great calamity that has befallen our mother earth, it
would surely be a great injustice on the part of the younger generation
especially the student fraternity to be in utter ignorance of this slow killer
as they are the future generations who should live on this earth. Thus taking
into considerations these points this project has been taken up not only to
know about UV rays but also how it affects the bio diversity of our planet.
Here this project deals with the above mentioned points. Also the project aims
to give a comprehensive picture on the impending disaster that would take place
if we be ignorant on this issue. ACKNOWLEDGEMENT Many people have taken great
pains to make this project a reality. First of all I convey my deep thanks to
Mrs.Pravitha, Dept. of Zoology without whose guidance this project would have
become nothing. Also I am deeply indebted to Mrs. Mercy Abraham, Dept of Botany
who too was instrumental in collecting the data required for this project. Last
but not the least I deeply acknowledge the help given to me by my classmates
whose valuable tips and suggestions helped me bring about such a project. I am
deeply indebted to them for also helping me collect the relevant information
from many sources and also providing many diagrams required to emphasise my
points.
CONTENTS
1 ULTRAVIOLET RAYS
1.1 Sources of UV
1.2 UV-A, UV-B &
UV-C
2 EFFECTS OF UV RADIATION ON NATURE AND
HUMANS
2.1 Damage to marine life
2.2 Degradation of polymers, pigments and dyes
2.3 HARMFUL EFFECTS ON HUMANS
2.3.1 Effects on Eye
2.3.2 Effects on Skin
2.3.3 Genetic effects
2.3.4
Effects on immune system
2.4 OZONE DEPLETION AND UV RADIATIONS
2.5 VULNERABILITIES DUE TO UV RADIATIONS
ULTRAVIOLET RAYS In 1801, the German physicist Johann Wilhelm
Ritter, found that there exist invisible rays beyond the violet end of the
visible spectrum of the Sun that darken silver chloride even more efficiently
than visible light. This spectra region between visible light and X-rays was
found to be more chemically active than visible light, and named as the
ultraviolet region. Ultraviolet (UV) light is electromagnetic radiation with a
wavelength shorter than that of visible light, but longer than x-rays, in the
range 10 nm to 400 nm, and energies from 3 eV to 124 eV . The name means
“beyond violet” (from Latin ultra, “beyond”), violet being the colour of the
shortest wavelengths of visible light. UV light has a shorter wavelength than
that of violet light The electromagnetic spectrum of ultraviolet light can be
subdivided in a number of ways. The draft ISO standard on determining solar
radiances (ISO-DIS-21348)[3] describes the following ranges: Name Abbreviation
Wavelength range in nanometers Energy per photon Ultraviolet A, long wave, or
black light UVA 400 nm–320 nm 3.10–3.94 eV Near NUV
400 nm–300 nm 3.10–4.13 eV Ultraviolet B or medium wave UVB
320 nm–280 nm 3.94–4.43 eV Middle MUV 300 nm–200 nm
4.13–6.20 eV Ultraviolet C, short wave, or germicidal UVC
280 nm–100 nm 4.43–12.4 eV Far FUV 200 nm–122 nm 6.20–10.2
eV Vacuum VUV 200 nm–10 nm 6.20–124 eV Extreme EUV
121 nm–10 nm 10.2–124 eV Natural sources of UV The Sun emits
ultraviolet radiation in the UVA, UVB, and UVC bands. The Earth’s ozone layer
blocks 98.7% of this UV radiation from penetrating through the atmosphere.
98.7% of the ultraviolet radiation that reaches the Earth’s surface is UVA.
Other sources:
There are also several artificial methods to produce UV
rays such as from black light (Wood’s light), Ultraviolet fluorescent lamps,
Ultraviolet LEDs, Ultraviolet lasers, synchrotron radiation sources, Argon and
deuterium discharge lamps etc… UVA, UVB & UVC Among the different types of
UV, we consider the main subdivisions as UV A, UV B & UV C. UVA (320-400 nm):
Ultraviolet light, type A. These are rays of light from the sun which are not
visible but can cause damage to the skin. UVB (280-320 nm) Ultraviolet light,
type B.
These are rays of light from the sun which are not visible
but can cause damage to the skin. The amount of UV-B light received by a
location is strongly dependent on: Latitude and elevation of the location: At
high-latitude polar regions the sun is always low in the sky. Because the
sunlight passes through more atmosphere more of the UV-B is absorbed. For this
reason average UV-B exposure at the poles is over a thousand times lower than
at the equator. Cloud cover : the reduction in UV-B exposure depends the
cover’s thickness. Proximity to an industrial area: Due to the protection
offered by photochemical smog. Industrial processes produce ozone, one of the
more irritating components of smog, which absorbs UV-B. This is thought to be
one of the main reasons that significant ozone losses in the southern
hemisphere have not been mirrored in the northern hemisphere. UVC (100-280 nm):
UVC rays are the highest energy, most dangerous type of
ultraviolet light. Exposure to it can even lead to death. Little attention has
been given to UVC rays in the past since they are filtered out by the
atmosphere. However, their use in equipment such as pond sterilization units
may pose an exposure risk, if the lamp is switched on outside of its enclosed
pond sterilization unit.
EFFECTS OF UV RADIATION ON NATURE AS WELL AS
HUMANS
The effects of UV radiation on earth’s ecosystems are not
completely understood. Even isolating the effects of UVA versus UVB is somewhat
arbitrary. 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
over exposure 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. The sunlight reaching us
consists of only approximately 0.5% UV-B radiation, in terms of radiant energy.
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.
Damage to marine life: The penetration of increased amounts
of UV-B light has caused great concern over the health of marine plankton that
densely populate the top 2 meters of ocean water. The natural
protective-response of most chlorophyll containing cells to increased light-radiation
is to produce more light-absorbing pigments but this protective response is not
triggered by UV-B light.
Another possible response of plankton is to sink deeper
into the water but this reduces the amount of visible light they need for
photosynthesis, and thereby reduces their growth and reproduction rate. In
other words, the amount of food and oxygen produced by plankton could be
reduced by UV exposure without killing individual organisms. Degradation of
polymers, pigments and dyes: Many polymers used in consumer products are
degraded by UV light. The problem appears as discoloration or fading, cracking
and sometimes, total product disintegration if cracking has proceeded
sufficiently.
The rate of attack increases with exposure time and
sunlight intensity. It is known as UV degradation, and is one form of polymer
degradation. Sensitive polymers include thermoplastics, such as polypropylene
and polyethylene as well as speciality fibres like aramids.
UV damaged polypropylene rope (left) and new rope (right)
There are several other considerations: Ultraviolet levels are over 1,000 times
higher at the equator than at the polar regions so it is presumed that marine
life at the equator is much better adapted to the higher enviromental UV light
than organisms in the polar regions. The current concern of marine biologists
is mostly over the more sensitive antarctic phytoplankton which normally would
recieve very low doses of UV. Only one large-scale field survey of Anarctic
phytoplankton has been carried out so far [Smith et.al _Science_1992] ;
they found a 6-12% drop in phytoplankton productivity once
their ship entered the area of the spring-time ozone hole. Since the hole only
lasts from 10-12weeks this translates into a 2-4%loss overall, a measurable but
not yet catastrophic loss. Both plants and phytoplankton vary widely in their
sensitivity to UV-B. When over 200 agricultural plants were tested, more than
half showed sensitivity to UV-B light.
Other plants showed neglible effects or even a small
increase in vigor. Even within a species there were marked differences; for
example one variety of soybean showed a 16% decrease in growth while another
variety of the same soybean showed no effect [R.Parson]. An increase in UV-B
could cause a shift in population rather than a large die-off of plants An
increase in UV-B will cause increased amounts of Ozone to be produced at lower
levels in the atmosphere. While some have hailed the protection offered by this
‘pollution-sheild’ many plants have shown themselves to be very sensitive to
photochemical smog.
HARMFUL EFFECTS ON HUMANS
Being the one which commonly affects our health, we usually
discuss the harmful effects of UV-B. The consequences of increased exposure of
the human body to UV-B radiation will in the first instance be characterized by
the physical properties of this type of radiation.
UV-B radiation does not penetrate far into the body; most
of it is absorbed in the superficial tissue layers of 0.1 mm depth.
This limits the primary effects to the skin and the eyes.
There are, however, also systemic effects; these start with a primary reaction
in the superficial layers, but have consequences throughout the body. It is the
main cause of sunburn and tanning and it has influences on the immune system.
UV-B radiation is also the main cause of snowblindness and an important factor
in the induction of cataracts.
UV-B radiation contributes significantly to the aging of
the skin and eyes, and it is the UV-B range that is the most effective in
causing skin cancer. Genetic damage: Ultraviolet photons harm the DNA molecules
of living organisms in different ways. DNA absorbs UV-B light and the absorbed
energy can break bonds in the DNA. Most of the DNA breakages are repaired by
proteins present in the cells nucleus.
These may mend the damage, or part of the damage. The
repair systems may, however, themselves be damaged by increased UV-B exposure.
But unrepaired genetic damage of the DNA can lead to skin cancers. In one
common damage event, adjacent thymine bases bond with each other, instead of
across the “ladder”. This makes a bulge, and the distorted DNA molecule does
not function properly.
Effects on Skin:
“ Ultraviolet (UV)
irradiation present in sunlight is an environmental human carcinogen. The toxic
effects of UV from natural sunlight and therapeutic artificial lamps are a
major concern for human health. The major acute effects of UV irradiation on
normal human skin comprise sunburn inflammation erythema, tanning, and local or
systemic immunosuppression. ” — Matsumura and Ananthaswamy , (2004) i.
Sunburn: 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.
ii. Sun tan: As a defense against UV radiation, the amount of the brown
pigment melanin in the skin increases when exposed to moderate (depending on
skin type) levels of radiation; this is commonly known as a sun tan. The
purpose of melanin is to absorb UV radiation and dissipate the energy as
harmless heat, blocking the UV from damaging skin tissue. UVA gives a quick tan
that lasts for days by oxidizing melanin that was already present and triggers
the release of the melanin from melanocytes. UVB yields a tan that takes
roughly 2 days to develop because it stimulates the body to produce more
melanin. The photochemical properties of melanin make it an excellent
photoprotectant.
iii. Photodermatoses: Photodermatoses
are skin diseases where the skin lesions are caused by light. Such lesions may
be itching papules, whealing of the skin, fierce reddening and peeling, etc.
The more sensitive patients cannot even stand one minute of outdoor daylight.
In several of these diseases the UV-B radiation in sunlight is the predominant
causative agent. Loss of adaptation of the skin to light appears to be a
predominant factor in these diseases.
iv. Premature Ageing of Skin : Another effect of ultraviolet rays on the
skin is photo ageing. 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. Even careful tanning kills skin cells,
damages DNA and causes permanent changes in skin connective tissue which leads
to wrinkle formation in later life. UVA, UVB and UVC can all damage
collagen fibers and thereby accelerate aging of the skin. Both UVA and UVB
destroy vitamin A in skin which may cause further damage. v. Skin Cancer: 9 0%
of the skin carcinomas are attributed to UV-B exposure [Wayne] and the chemical
mechanism by which it causes skin cancer has been identified [Tevini].
The above named carcinomas are relatively easy to treat, if
detected in time, and are rarely fatal. There are various types of skin cancer.
One main class is formed by the cutaneous melanomas, the cancers of the pigment
cells. There appears to be a correlation between brief, high intensity
exposures to UV and eventual appearance (as long as 10-20yrs) of melanoma. The
other main types are basal cell carcinomas and squamous cell carcinomas,
cancers of the epithelial cells. These carcinomas of the skin are sometimes,
collectively, called “non-melanoma skin cancers”. For the present example we
will deal with these non-melanoma skin cancers. In white caucasians, the
incidence of these cancers ranks high among the various types of cancer; in
some populations it is in fact the highest of all. The incidence is lower in
more pigmented populations, typically by a factor of 10 or even 100. The
mortality rate is low in comparison with that for other types of cancer:
approximately 1% in areas with good medical care.
he non-melanoma skin cancers are clearly correlated to
sunlight. They occur mostly in light-skinned people, and then predominantly on
skin areas most exposed to sunlight, such as the face.
In people of
comparable genetic background, the incidences are higher in the sunnier
geographical areas. Early experiments showed that white rats exposed to sunlight
developed skin cancers, but similar rats exposed to sunlight filtered through
window glass did not. As the window glass absorbed mainly UV-B radiation, this
result indicated that the carcinogenic effect was to a large extent due to the
UV-B radiation in sunlight.
In technical terms, carcinogenic effectiveness was defined
as the reciprocal value of the daily dose of radiation at a certain wavelength
required for the induction of tumors of 1 mm diameter in 50% of a group of mice
in 300 days. The tumors in these mice were predominantly squamous cell
carcinomas. UVB light can cause direct DNA damage. The radiation excites DNA
molecules in skin cells, causing aberrant covalent bonds to form between
adjacent cytosine bases, producing a dimer. When DNA polymerase comes along to
replicate this strand of DNA, it reads the dimer as “AA” and not the original
“CC”.
This causes the DNA replication mechanism to add a “TT” on
the growing strand. This is a mutation, which can result in cancerous growths
and is known as a “classical C-T mutation”. The mutations that are caused by
the direct DNA damage carry a UV signature mutation that is commonly seen in
skin cancers. Effects on Eye: High intensities of UVB light are hazardous to
the eyes, and exposure can cause welder’s flash (photokeratitis or arc eye) and
may lead to cataracts, pterygium, and pinguecula formation.
Another Possible eye damage that can result from high doses
of UV light is particularly to the cornea which is a good absorber of UV light.
High doses of UV light can causes a temporary clouding of the cornea, called
‘snow-blindness’, and chronic doses has been tenitively linked to the formation
of cataracts. Higher incidences of cataracts are found at high elevations,Tibet
and Bolivia; and higher incidences are seen at lower latitudes(approaching the
equator).UV light is absorbed by molecules known as chromophores, which are
present in the eye cells and tissues. Chromophores absorb light energy from the
various wavelengths at different rates – a pattern known as absorption
spectrum. If too much UV light is absorbed, eye structures such as the cornea,
the lens and the retina can be damaged.
Effects on immune system:
Prolonged exposure
can cause damage to the human immune system. Cells or tissue components which
are altered by the radiation may be recognized as foreign by the immune system
and removed. Certain functions of the immune system are, however, suppressed by
exposure to UV-B radiation. When skin is exposed to more UV-B radiation than it
is accustomed to, it has the ability to adapt. OZONE DEPLETION AND UV
RADIATIONS Ozone depletion results in an increase of UV-B radiation, but the
shorter the wavelength, the stronger the increase, even within the UV-B range.
A 1%decrease in the ozone layer will cause a estimated 2%increase in UV-B
irradiation; it is estimated that this will lead to a 4%increase in basal
carcinomas and 6%increase in squamous-cell carcinomas.[Graedel & Crutzen].
Many scientists today believe that this life-protecting stratospheric ozone layer
is being reduced by the chlorofluorocarbon gases released into the atmosphere
by different sources on the earth. Many environment groups are vehemently
protesting against the use of these gases, and their use in many places in the
world has been banned. Pollution on the earth has already caused a hole in the
ozone layer above the Antarctic.
VULNIRABILITIES DUE TO UV RADIATIONS A diagram produced by
WHO based on ‘global burden of diseases from solar ultraviolet radiation’ in
the year 2006: An article pointing out the increasing Solar UV & Ozone
Depletion.
CONCLUSION
Thus we can conclude that UV rays have a disastrous impact
on our planet. It will lead to many dangers which would affect not only us but
also the entire living community on this earth. UV rays could lead to many
unforeseen disasters which could also signal the end of life on this beautiful
planet. All the dangers attributed to UV rays reaching our earth reside only on
man.
Man by his reckless actions have dug graves not only for
himself but also for the earth too. It’s his only responsibility to restore the
earth back to its healthy mode. Thus a concerted effort is needed on the side
of mankind to quickly address this danger.
Steps have to be
taken from individual to the international level to protect our earth. From
abandoning plastics to decreasing the dependence on automobiles man has to be
careful to ensure that he does not push earth to its death.
We also need to ensure that we do not create UV rays by
machines and that their usage is strongly restricted only to the academic
field. Also we need to create awareness among ourselves on the need
of the hour to protect life.
It’s a pity that we try to blame domestic animals for
increasing the levels of methane in the atmosphere. What we need to understand
is that their methane levels are nothing compared to our creation of a hole on
the ozone layer. Their actions are too small to be even compared to our sins.
As future generations the student community also needs to be aware in this
topic, a primary reason for me selecting this project.
We too should take care not to harm our earth in any way.
Always we should remember that we have not inherited the earth from our fathers
but have leased it from our future generations. This alone will make us
responsible and be steadfast in our Endeavour to combat the penetration of UV
rays.
BIBLIOGRAPHY
R.Parson, FAQ
111 ,UV and biological effects of UV FDA
Consumer Magazine and publications: FDA#87-8272, #81-8149
and #92-1146 M.Tevini, UV-B Radiation and
Ozone Depletion: Effects on humans, animals, plants,
microorganisms and materials Lewis Pub. Boca Raton, 1993. R.P.Wayne, Chemistry
of the Atmospheres 2nd ed. Oxford 1991 R.Smith ,
“Ozone depletion:
Ultraviolet radiation and phytoplankton biolgy in antarctic waters” ‘ Science ,
255, 952. (1992) Brien Sparling, UV Radiation SunSmart publications, UV Rays
Jan C. van der Leun and Frank R. de Gruijl, Influences of Ozone Depletion on
Human and Animal Health
No comments:
Post a Comment