氡从何处来？
    室内氡的来源是多途径的，但主要是：
    １、岩石（土壤）是室内氡积累的普遍而直接的来源，而且是主要的来源（当居室中各类建材的放射性符合国家标准时）。
    ２、构造带。构造带不是直接的氡来源，但它是地下氡汇集和迁移的通道，有时比岩石因素更重要。例如某地房屋建在裂隙不很发育的花岗岩上，在相同的其他建材条件下，室内的氡往往要比房屋建在放射性较低，而裂隙发育又相当厉害的砂岩上为低。
    ３、水源有时也是室内氡的重要来源，直接来自地下的、铀矿区或油气田区的水往往有较高的氡浓度。
    ４、在房屋基底经完好密封时，墙地砖的放射性就成了室内氡的主要来源。
    ５、煤气通常称液化气或天然气，往往有着相对高的氡浓度。

    氡对人体的主要伤害是什么？
    专家们把氡称为“导致人类肺癌的第二大‘杀手’”，是除吸烟以外引起肺癌的第二大因素。世界卫生组织把氡列为使人致癌的19种物质之一。

    如何降低居室中的氡？
    １、不要购买建筑在富铀区、伽玛高值区、断裂构造区的楼宇。要知道室内的氡含量是否超标，最有效的方法就是进行室内氡浓底的检测，个人购买住房时，也应考虑这个因素。
    ２、在装饰装修时，要尽量按照国家标准选用放射性含量低的建筑和装饰材料。
    ３、室内装饰中，要注意填平、密封地板和墙上的所有裂缝，特别是地下室、一层和平房的住户更要如此。
    ４、做好室内通风换气，这是最简便、最省钱的方法。门窗关闭的房屋内，氡的浓度往往比敞开门窗时高数倍到数十倍。专家曾做过试验，一间氡浓度在151贝可/m3　房间，开窗１小时后，室内氡浓度可降为48贝可/m3。如果配备优质的室内空气净化器更好。
    ５、孩子与妇女比成年男性更易受氡侵害，应尽量减少或禁止在室内吸烟。

国外相关报道：

美国环保署：http://www.epa.gov/radon/healthrisks.html

Exposure to Radon Causes Lung Cancer In Non-smokers and Smokers Alike

Lung cancer kills thousands of Americans every year. The untimely deaths of Peter Jennings and Dana Reeve have raised public awareness about lung cancer, especially among people who have never smoked. Smoking, radon, and secondhand smoke are the leading causes of lung cancer.  Although lung cancer can be treated, the survival rate is one of the lowest for those with cancer.  From the time of diagnosis, between 11 and 15 percent of those afflicted will live beyond five years, depending upon demographic factors.  In many cases lung cancer can be prevented; this is especially true for radon.

Smoking is the leading cause of lung cancer.  Smoking causes an estimated 160,000* deaths in the U.S. every year (American Cancer Society, 2004).  And the rate among women is rising.  On January 11, 1964, Dr. Luther L. Terry, then U.S. Surgeon General, issued the first warning on the link between smoking and lung cancer.  Lung cancer now surpasses breast cancer as the number one cause of death among women.  A smoker who is also exposed to radon has a much higher risk of lung cancer.

Radon is the number one cause of lung cancer among non-smokers, according to EPA estimates.  Overall, radon is the second leading cause of lung cancer.  Radon is responsible for about 21,000 lung cancer deaths every year.  About 2,900 of these deaths occur among people who have never smoked.  On January 13, 2005, Dr. Richard H. Carmona, the U.S. Surgeon General, issued a national health advisory on radon.  Visit www.cheec.uiowa.edu/misc/radon.html⁷  for more on a study by Dr. William Field on radon-related lung cancer in women.

Secondhand smoke is the third leading cause of lung cancer and responsible for an estimated 3,000 lung cancer deaths every year.  About 1,000 of these are people that never smoked, and about 2,000 are former smokers.  Smoking affects non-smokers by exposing them to secondhand smoke.  Exposure to secondhand smoke can have serious consequences for children’s health, including asthma attacks, affecting the respiratory tract (bronchitis, pneumonia), and may cause ear infections.

Learning more about lung cancer.  The following sources provide a wide range of good information about lung cancer, prevention, and treatment.

Why is radon the public health risk that it is? 

EPA estimates that about 20,000 lung cancer deaths each year in the U.S. are radon-related.  Exposure to radon is the second leading cause of lung cancer after smoking.  Radon is an odorless, tasteless and invisible gas produced by the decay of naturally occurring uranium in soil and water.  Radon is a form of ionizing radiation and a proven carcinogen.  Lung cancer is the only known effect on human health from exposure to radon in air.  Thus far, there is no evidence that children are at greater risk of lung cancer than are adults.

Radon in air is ubiquitous. Radon is found in outdoor air and in the indoor air of buildings of all kinds.  EPA recommends homes be fixed if the radon level is 4 pCi/L (pico Curies per Liter) or more. Because there is no known safe level of exposure to radon, EPA also recommends that Americans consider fixing their home for radon levels between 2 pCi/L and 4 pCi/L. The average radon concentration in the indoor air of America’s homes is about 1.3 pCi/L. It is upon this level that EPA based its estimate of 20,000 radon-related lung cancers a year upon. It is for this simple reason that EPA recommends that Americans consider fixing their homes when the radon level is between 2 pCi/L and 4 pCi/L. The average concentration of radon in outdoor air is .4 pCi/L or 1/10^th of EPA’s 4 pCi/L action level.

For smokers the risk of lung cancer is significant due to the synergistic effects of radon and smoking. For this population about 62 people in a 1,000 will die of lung-cancer, compared to 7.3 people in a 1,000 for never smokers. Put another way, a person who never smoked (never smoker) who is exposed to 1.3 pCi/L has a 2 in 1,000 chance of lung cancer; while a smoker has a 20 in 1,000 chance of dying from lung cancer. Figure A compares the risks between smokers and never smokers; smokers are at a much higher risk than never smokers, e.g., at 8 pCi/L the risk to smokers is six times the risk to never smokers.

The radon health risk is underscored by the fact that in 1988 Congress added Title III on Indoor Radon Abatement to the Toxic Substances Control Act. It codified and funded EPA’s then fledgling radon program. Also that year, the Office of the U.S. Surgeon General issued a warning about radon urging Americans to test their homes and to reduce the radon level when necessary (U.S. Surgeon General).

Unfortunately, many Americans presume that because the action level is 4 pCi/L, a radon level of less than 4 pCi/L is ‘safe’. This perception is altogether too common in the residential real estate market. In managing any risk, we should be concerned with the greatest risk. For most Americans, their greatest exposure to radon is in their homes; especially in rooms that are below grade (e.g., basements), rooms that are in contact with the ground and those rooms immediately above them.