Environmental Issues Test - 83

The meltdown of the reactor core is the primary reason for the reactor mishap. The core is made up of the radioactive material. The core is subjected to the extremely high temperature and in the absence of the water, it melts. Its melting also breaks down the steel container and the radioactive waves leak from the reactor. The coolants are used to prevent this meltdown. Hence, the correct answer is 'Meltdown of reactor core'.

The exposure to the UV radiations have an ionizing and distorting effect to the body of the humans. It causes damage to the eyes by destroying the essentials of the eye-lens. The sunburn occurs due to high intensity. Skin cancer is caused due to distortion of the DNA by the formation of the pyrimidine dimers, such that the DNA cannot be replicated properly.

The concentration of the organic waste and its subsequent decomposition determines the BOD of the water. If the organic concentration is high, there will be high BOD because more dissolved oxygen will be used to breakdown the organic mass by the bacteria. So, high BOD marks high pollution. Distilled water has no content of the organic substances as it has been treated and filtered. Unpolluted water pond will not have polluted source of organic mass but the existing organisms die and their dead bodies contribute to a little raised BOD. Highly polluted water will show a very high value of BOD as it will take a lot of dissolved oxygen to breakdown the organic mass in water body. So, distilled water is least polluted, followed by unpolluted pond water and then highly polluted pond water.

Chernobyl accident occurred on 25-26 April 1986 in Ukraine. It was a nuclear accident that occurred due to explosion in the core nuclear rods during the emergency shutdown of the reactor after a failed test. There were faults in the designs of the reactor and the arrangement of the core was leaky. It resulted in official 31 deaths and massive relocation of the residents. 

Lead is released from the vehicular emissions and it persists in the environment. It causes severe neurological degradation. Cobalt is responsible for the cardiomyopathy in which the heart becomes big and floppy. Nausea, headache, lung disorders are other effects of the cobalt poisoning. Uranium is a radioactive element. The radioactive radiations emitted by it are highly ionizing. It is known to cause bone and liver cancer.

•  The UV region covers the wavelength range 100-400 nm and is divided into three bands: UVA (315-400 nm) UVB (280-315 nm)
• The most common form of UV radiation is sunlight, which produces three main types of UV rays: UVA, UVB, UVC.
• At certain wavelengths, UV is mutagenic to bacteria, viruses and other microorganisms. Particularly at wavelengths around 260–270 nm, UV breaks molecular bonds within microorganismal DNA, producing thymine dimers that can kill or disable the organisms.
• UVB, the chief cause of skin reddening and sunburn, tends to damage the skin's more superficial epidermal layers. It plays a key role in the development of skin cancer and a contributory role in tanning and photoaging.

Cataracts and blindness are among the most common eye diseases associated with further ozone layer depletion and increased UV-B at the Earth's surface.  A 1% decrease in stratospheric ozone may result in 100,000 to 150,000 additional cases of blindness due to eye cataracts worldwide. The ozone layer is responsible for absorbing harmful ultraviolet rays, and preventing them from entering the Earth's atmosphere.

A river with an inflow of domestic sewage rich in organic waste will reduce the dissolved oxygen (DO). The organic waste will increase biological oxygen demand of the river thus depleting the O2 content and may result in the death of fish due to lack of oxygen.