Biology Project on Ultraviolet Rays
INVESTIGATORY PROJECT IN BIOLOGY
In partial fulfillment of project in
DEPARTMENT OF BIOLOGY
AL-FAROOK RESIDENTIAL SCHOOL
[Affiliated to CBSE, New Delhi]
Al Farook Residential School
[Affiliated to CBSE, New Delhi]
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
Mrs. Mercy Abraham Mr. K.Kunhoyi
Department of Botany Principal
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
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.
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.
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
1. 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) 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.
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.
The 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:
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.
- 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