Saturday, May 23, 2009

Radioactive gas Radon may affect the people of Ranchi city in India.

Radon problem cannot be ruled out in the houses of Ranchi city in India.
Dr. Nitish Priyadarshi
Fig. House build on the rocks in Ranchi city.
Earth has many ways to kill us. We keep on the lookout, and rightly so, for volcanic eruptions, earthquakes, landslides, flooding, cosmic impacts, climate change and falling rocks on the highway. Should we still worry about radon?
You remember radon—that radioactive gas that comes up from the soil and collects in basements and ground floors, sometimes in well water. Radon is a prominent villain in many countries. Blamed for tens of thousands of deaths from lung cancer. Like asbestos, radon was looked at more kindly when it was new, and today it too is more feared than it deserves.
Radon Geology:
To the geologist, radon is interesting, not worrisome. For one thing, radon starts with uranium, which is worth knowing about for its energy content and its important role in the Earth's heat budget.

Uranium turns to lead via a long, slow cascade of nuclear decay, and radon sits at an important point in that process.

Not only does the radon nuclide decay quickly, with a half-life less than four days, but the next four nuclides in the cascade decay with a combined half-life less than an hour. In other words, radon packs a powerful dose of radioactivity, and because it is a gaseous element, it can drift out of the minerals where it forms into the air. Thus it's a good signal of uranium, even for buried deposits.

Humans have always been exposed throughout their period of existence to naturally occurring ionising radiation. Specifically, naturally occurring radionuclides are present in variable amounts in our environment. To assess radiological health hazards, naturally occurring radionuclides are being measured in soil, sand, marble, bricks etc throughout the world.

Terrestrial radiation comes from radioactive elements that were present at the time the earth was formed. They continue to decay and form additional radioactive materials.
Unusual soil composition has increased background radiation twenty-five fold or more in a few areas in the world. Locations with high background radiation in the soil, mainly from uranium, include the Rocky Mountains, Kerala India, coastal regions of Brazil, granite rock areas of France, and the northern Nile Delta.

Seeing the rock types and its mineral composition Radon problem cannot be ruled out in the houses of Ranchi city of Jharkhand State in India. This fact was justified by a published report of Research Reactor Institute, Kyoto University, Japan. According to the report Air-gamma dose rate was 0.30 μSv/h on the surface in the densely populated area in the city. In Ranchi the concentration of K-40 (potassium-40) and thorium is high. Concentration of Radium-226 was 75 Bq/Kg in the soils.

Very interesting thing in the Ranchi city is that name of one of its major road is RADIUM ROAD. Till today no body knows from where did this name came from. Name of this road exists from the British rule in India i.e. before 1947.

Seeing the presence of apatite, sphene and zircon in the Ranchi rocks, presence of Uranium cannot be ruled out. According to the report Uranium concentration is also high in Ranchi. All these concentrations are of natural origin. Radioactivity in the bricks made by the local soil may pose threat to the people living in the houses made by these bricks.

When Uranium is there, presence of Radon cannot be ruled out. It is radioactive gas that comes up from the soil and collects in basements and ground floors, sometimes in well water. Radon is a prominent villain in the United States, blamed for tens of thousands of deaths from lung cancer.
Even the granites of the Daltonganj area of Jharkhand state contain anomalous uranium values. Uranium mineralization has also been observed in the granitic rocks comprising the southern periphery of the Hutar basin of Daltonganj area. The Proterozoic granitoids, forming the provenance for the Hutar and Auranga subbasin, have been analyzed which revealed uranium content up to 520 ppm. ( Virnave, 1999).
The radon in home indoor air can come from two sources, the soil or water supply. The radon in water supply poses an inhalation risk and an ingestion risk. Research has shown that risk of lung cancer from breathing radon in air is much larger than the risk of stomach cancer from swallowing water with radon in it. Most of the risk from radon in water comes from radon released into the air when water is used for showering and other household purposes.
Radon in home water in not usually a problem when its source is surface water. A radon in water problem is more likely when its source is ground water, e.g., a private well or a public water supply system that uses ground water.
From last several years people of Ranchi are becoming more dependent on ground water for their daily uses. Indiscriminate deep borings are rampant in the granite rocks of Ranchi city. People are going more and more deeper for search for water.
People of Jharkhand state are unaware of danger from Radon gas.
Radon loves fractures because they set it free. Solid mineral grains are a pretty good trap for gases, but break the grains and the gas escapes. So just having rocks rich in uranium is not enough—they must be fractured, too.
Ranchi rocks are filled with fractures and joints. Ground waters are mined through these fractures and joints. So threat of Radon Poisoning looms large in Ranchi city.

Even the houses build on the rocks filled with cracks and fractures are under threat of Radon poisoning inside the house. Most of the radon indoors is contributed by the ground underneath buildings.
The amount of radon entering buildings from the ground is influenced by the following four factors.
a) Radon concentrations in soil gas: This depends on the concentration of the immediate precursor of Rn-222, Ra-226, in rocks and soils. Elevated levels of radium are found in some granites, limestone's and sandstone's and other geologies.
b) Permeability of the ground: This depends on the nature of the rock and soil under the building Disturbed ground can have greatly increased permeability. Usually the radon comes from the ground within a few metres of the building, but if the ground is particularly permeable or fissured it may come from a greater distance.
c) Entry routes into homes: Concrete floors often have cracks around the edges and gaps around services entries such as mains water supply, electricity or sewage pipes. If homes have suspended timber floors the gaps between the floorboards are the major route of entry. Pathways for soil gas to enter houses are often concealed, and vary between apparently identical houses.
d) Under-pressure of homes: Atmospheric pressure is usually lower indoors than outdoors owning to the warm indoor air rising; this creates a gentle suction at ground level in the building through the so-called `stack effect'. Wind blowing across chimneys and windows can also create an under-pressure (the `Bernoulli effect'). The result is that the building draws in outside air, typically at the rate of one air change per hour. Most of this inflow comes through doors and windows, but perhaps 1% or so comes from the ground. In an average house, this amounts to a couple of cubic metres of soil gas entering the house each hour. The radon concentration in a building depends on the rate of entry of the radon and the rate at which it is removed by ventilation. Increasing the ventilation rate will not always decrease the radon concentrations, however, because ventilation rate and under-pressure are related, and some ways of increasing ventilation, such as the use of extract fans or opening upstairs windows, can also increase the under-pressure.

Recently high concentrations of radioactive gas radon have been detected in Bengalooru’s groundwater, which means a higher risk of stomach cancer for those who drink it.A team from the Bangalore University and the Baba Atomic Research Centre in Mumbai collected 78 samples of water from bore wells, shallow wells, surface water and the supplied drinking water in Bengalooru. More than half the samples contained radon in concentrations up to a thousand times the permissible limit of 11.1 Becquerel per litre.

In the case of Bengalooru (old name Bangalore) it is the large reserves of granite that is causing the problem. Being highly soluble, radon easily dissolves in groundwater. The rate at which radon is released from rocks depends on the porosity of the rocks and the intensity of water flow.
Radon is a cancer-causing natural radioactive gas that we can’t see, smell or taste. Its presence in the home can pose a danger to family's health. Radon is the leading cause of lung cancer among non-smokers. Radon is the second leading cause of lung cancer in America and claims about 20,000 lives annually.
Any home can have a radon problem. This means new and old homes, well-sealed and drafty homes, and homes with or without basements. In fact, people and their family are most likely to get greatest radiation exposure at home. That is where they spend most of their time. Jharkhand government should come forward to analyze the amount of Radon present in groundwater and in the air inside the house.
Virnave, S.N. Nuclear Geology and Atomic Mineral Resources. Bharati Bhawan, Patna. 169.
Post a Comment