Emergent threat to environment and human health Environmental pollution is one of the most talked about topics and alarming issues in the ecologically threatened world of today. Pollution of different environmental components is leading to terrific environmental degradation that ultimately results in the deterioration of ecological balance. Radioactive substance is a highly toxic material, a fatal environmental pollutant. The magnitude of its mischievous effects is in a range that might be said figuratively to represent a 'quantum jump'.
Naturally occurring radioactive elements normally exist in the rocks, water and air and in all living organisms as background radiation. For million of years, background radiation remained at a relatively constant level. Recently, however, the radiation that we are normally exposed to has increased and can be expected to increase further cosmic radiation from the outer space reaching the earth's surface and terrestrial radiation from natural radio-isotopes present in the earth's crust. Cosmic ray bombardment of the atmosphere continuously produces a few radio-active materials of short half-life. The following table indicates the half-life and radiation of the important radioactive elements-
Radiations also originate from the anthropogenic activities involving the use of radioactive materials. Radioactive materials are used for the production of nuclear weapons, nuclear fuel and for the production of electric power. One of the most harmful uses of radioactive material is in the nuclear weapons, especially in atom bombs. The present world has already experienced the nature of destruction as well as impact of radioactivity on man and environment during the World War II when atom bombs were dropped over Hiroshima and Nagasaki, the two Japanese towns. During the last forty years there have been a number of nuclear weapons testings either in sea or underground, resulting in the increase of the level of radiation on the environment. A study revealed that the radioactive materials which cause such explosions are fission products as Strontium-90, Caesium-137, Iodine-131 and unused explosives. These radioactive elements either settle down in the soil or water or remain suspended in the atmosphere, thus becoming a major cause of radioactive pollution.
Radiation is also produced when nuclear fuels are used to generate electricity. Besides, the disposal of radioactive or nuclear waste is a great problem and a cause of environmental pollution. It includes remaining metal products at the site of mines, fission products and activation products. These are of three categories, viz. low level, intermediate level and high level. Among these, high level products remain in the environment for several hundred years. Similarly, leakage in the nuclear reactors often became the cause not only of environmental pollution but also of the death of hundreds of people as happened at Chernobyl Atomic Reactor in erstwhile USSR in 1986. There are various forms of radiation. Different forms of radiation have different effects. X-rays are more energetic and are, therefore, biologically injurious because of their destructive action on cells and tissues.
Because these highly energetic forms of radiation tend to split substances, including living matter, into ions they are called ionizing radiation the other forms include electromagnetic radiation and particulate radiation. Ultraviolet radiation is highly injurious to the tissues of some organisms. It is well recognised that sun-burn is caused largely by the ultraviolet content of the sun's radiation and that excessive exposure can cause serious injury to both the superficial and deep layers of the skin.
The fate of a radioactive contaminant is also dependent on ecological conditions. Radioactive pollution causes deposition of the contaminants on ground and surface waters. The water consumed by plants thus acts as a medium for radioactivity. This contamination is passed on the vegetation and animals through the nourishment from soil and water.
This pollution also causes harm to the active particles present in the air and has a direct impact on man's respiratory system while indirect contamination occurs by consumption through the food chain. Radioactive pollution can cause numerous fatal diseases like cancer, mutations in man. Besides, it may also cause abnormal birth, skin diseases. Chronic exposure to radiations leads to leukemia in an individual and even affects an unborn child in the womb. The radiations from medical X-rays, colour TV, luminous dials of clocks and watches, X-ray fluoroscopes are also contributing to the risks.
As leakage of radioactivity from reactors is not only a health hazard but a cause of death and other disorders to thousands of people, similarly, nuclear testing in seawaters not only creates disorder in the oceanic ecosystem but becomes a cause of the destruction of marine life.
Although radioactivity has numerous harmful effects, visible light and infrared heat rays and certain kinds of radiation are generally beneficial. Moreover, nuclear power and other uses of radioactive elements have become an integral part of modern development. Many of the environmentally conscious countries in the world depend on nuclear power significantly for their electricity generation. At present, 17 percent of the world's electricity is generated through nuclear sources. To make it environmentally safer, there is still a need for monitoring and prevention measures.
Monitoring of radiation is very necessary for the control of radiation. The sample of air, water and soil have to be collected regularly and their analysis, both manual and instrumental, should be done, not only to know the actual level of radiation active pollution, but also for its control. All measures should so aim that the level of radioactive pollution should not exceed the maximum permissible limit. Industrial wastes having radioactive elements should only be discharged after proper treatment. But it's a matter of regret that industrial wastes both solid and liquid having radioactive elements and other toxic materials are dumped into the water bodies in and around the big cities including the capital city of Dhaka without taking environmental issues under consideration. The rivers of Turag, Balu, Buriganga, and Sitalakkhya are the glaring examples of it.
The high activity wastes should not be discharged. Now, a few techniques have been developed through which these wastes can be used if treated property. The disposal of the wastes into sea is not a safe method but if nothing is possible, these wastes should be sealed in concrete filled steel drums and discharged into depths of 1000 fathoms or more.
However, the emission of radioactive pollutants should be controlled for the greater environmental interest. Besides, there is a need to control radiation hazard for workers and officials working in reactors or other places having danger of radioactivity. To serve the purpose of radioactive pollution control, the following measures can be highly considered. In uranium mines, wet drilling can be employed. Closed-cycle systems with gaseous coolants of very high purity may be used in the case of nuclear reactors to prevent extraneous activation. What is more: personnel at power stations must be trained in radiation control and radiation hazard control measures.
The UN and other international agencies of the world are in favour of total ban on nuclear weapons but very little progress has been made in this field. On the contrary, a competition is going on silently among different nations in terms of making advancement in nuclear power including atom bombs and other nuclear weapons to ensure husbandary in the world political order. Let us hope that the time will soon come when the planet earth, one and only habitat for living organisms, will be free from the danger of environmental pollution.
