氡從何處來？
    室內氡的來源是多途徑的，但主要是：
    １、巖石（土壤）是室內氡積累的普遍而直接的來源，而且是主要的來源（當居室中各類建材的放射性符合國家標準時）。
    ２、構造帶。構造帶不是直接的氡來源，但它是地下氡匯集和遷移的通道，有時比巖石因素更重要。例如某地房屋建在裂隙不很發育的花崗巖上，在相同的其他建材條件下，室內的氡往往要比房屋建在放射性較低，而裂隙發育又相當厲害的砂巖上為低。
    ３、水源有時也是室內氡的重要來源，直接來自地下的、鈾礦區或油氣田區的水往往有較高的氡濃度。
    ４、在房屋基底經完好密封時，墻地磚的放射性就成了室內氡的主要來源。
    ５、煤氣通常稱液化氣或天然氣，往往有著相對高的氡濃度。

    氡對人體的主要傷害是什么？
    專家們把氡稱為“導致人類肺癌的第二大‘殺手’”，是除吸煙以外引起肺癌的第二大因素。世界衛生組織把氡列為使人致癌的19種物質之一。

    如何降低居室中的氡？
    １、不要購買建筑在富鈾區、伽瑪高值區、斷裂構造區的樓宇。要知道室內的氡含量是否超標，最有效的方法就是進行室內氡濃底的檢測，個人購買住房時，也應考慮這個因素。
    ２、在裝飾裝修時，要盡量按照國家標準選用放射性含量低的建筑和裝飾材料。
    ３、室內裝飾中，要注意填平、密封地板和墻上的所有裂縫，特別是地下室、一層和平房的住戶更要如此。
    ４、做好室內通風換氣，這是最簡便、最省錢的方法。門窗關閉的房屋內，氡的濃度往往比敞開門窗時高數倍到數十倍。專家曾做過試驗，一間氡濃度在151貝可/m3　房間，開窗１小時后，室內氡濃度可降為48貝可/m3。如果配備優質的室內空氣凈化器更好。
    ５、孩子與婦女比成年男性更易受氡侵害，應盡量減少或禁止在室內吸煙。

國外相關報道：

美國環保署：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.