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What is radon?
Radon is a naturally occurring radioactive gas. It is produced from the radio-active breakdown, or decay, of Radium which is formed through several intermediate steps from the decay of Uranium. Since Radium and Uranium are common elements in rock and soil, Radon is constantly being generated. Because it is not chemically attracted to other materials, it can move easily through even very small spaced such as those between particles of soil and rock. Radon 222, produced by the decay of Radium 226, is a type of Radon most commonly of concern in indoor environments.
Where does indoor radon come from?
The major source of indoor Radon is Radium in the soil and rock under and surrounding building. Radon moves through soil and rock and can enter a building through cracks or openings (sewer pipes and sump pump openings), cracks in concrete, wall and floor joints, and hollow concrete block walls. Lower air pressure inside buildings, caused for example, by wind, can help to pull Radon into a house. The amount of Radon reaching a building is dependent upon several factors, including the amount of Radium in the surrounding soil, or rock, and soil permeability. In some regions, water is supplied from underground aquifers, or wells, and contains dissolved Radon produced in rock near those supplies. The churning of water in washers, showers toilets and sinks releases much of the dissolved Radon. In some areas of the country, elevated levels of Radon have been observed in water from private wells. Radon can also diffuse from building materials containing large amounts of Radium, but such materials are not common.
Why is exposure to indoor radon gas potentially harmful?
Radon undergoes radioactive breakdown and produces Radon decay products that are also radioactive. Long term exposure to Radon decay products is associated with an increase in the risk of lung cancer. The decay products tend to adhere to dust particles or other surfaces, and if inhaled, can also adhere to the airways of the lung. Alpha particles emitted by two of the Radon decay products (polonium 214 and polonium 218) can strike cells of the lung and damage them. This damage may lead to the formation of cancerous cells. Radon, on the other hand, is almost chemically inert, and an inhaled Radon atom is very likely to be exhaled before it decays. Thus, the main risk from Radon is lung cancer associated with breathing in its short-lived decayed products. This is clearly an adequate basis for concern about indoor Radon exposure.
What are the measurement units for radon and radon decay products?
For Radon decay products the unit is a working level (WL). A WL is a measure of how much alpha particle energy will be eventually released in the air by the short-lived Radon decay products. It is roughly proportional to the concentration in air of the shortlived Radon decay products.
For Radon, the unit is pico curies per liter of air (PCi/L). A curie is a measure of the number of radioactive decays per unit of time. One pico curie is one trillionth of a curie. One pico curie per liter of i indoor Radon is usually assumed to result in 0.005 WL under typical conditions in a building.
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How harmful is radon?
Based on data from studies and on assumptions of the average concentrations of Radon decay products in homes, the United States Environmental Protection Agency estimates that exposure to indoor Radon decay products causes perhaps 5,000 to 15,000 lung cancer cases per year in the U.S. Insufficient data exists to define an average residential Radon level, but a reasonable assumption is about 1 pico curie per liter of air. In terms of an individual's risk, exposure over a lifetime at that level gives rise to about three chances in a thousand of developing lung cancer. For long term exposures at higher levels, an individual's risk is proportionally larger than the estimated risk of exposures at the assumed average level.
Why do radon level vary from one building to another?
Many different factors affect the Radon concentration in a building. They include building type, local geology and climate and occupant activities. Differences in these factors can cause the annual average indoor Radon concentrations to be as much as one hundred times greater in one building than another. These variations make it very difficult to predict areas of the country, or houses that will have elevated indoor Radon concentrations. Some of the more important factors affecting Radon concentrations are:
- Soil characteristics - the potential for indoor Radon increases with increasing permeability and Radium content of the soil. Clays and water laden soils for example, are likely to retard the flow of Radon
- Building type -- the type of structure and its design affect the amount of area in contact with the soil, the air exchange rate in the building and the number and size of entry points for Radon. Homes with well ventilated crawlspaces, for example, are likely to have less Radon than would other homes on the same site.
- Foundation condition - cracks and openings in foundation walls and floors can serve as entry points for Radon.
The EPA recommends remedial measures to be taken to lower exposure when Radon is found above .02 working levels, or 4 pico curies/liter of air. Recent samples taken in Colorado houses in the Front Range area have found Radon above acceptable levels. of 31% of those structures checked, the natural radiation in the state of Colorado was twice the amount found at sea level. Colorado can be expected to have a considerable share of high indoor Radon levels as a result of Radium and Uranium deposits.
This material has been prepared in the interest of providing you with valuable information so that you will be better informed and prepared to make the proper choices in coping with the hazards of Radon.
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