What is Radon and where does it come from?
Radon-222 is a radioactive gas released during the natural decay of thorium and uranium, which are common, naturally occurring elements found in varying amounts in rock and soil. Odorless, invisible, and without taste, radon cannot be detected with the human senses. Radon-222 decays into radioactive elements, two of which -- polonium-218 and polonium-214 -- emit alpha particles, which are highly effective in damaging lung tissues. These alpha-emitting radon decay products have been implicated in a causal relationship with lung cancer in humans.
Radon gas can enter a home from the soil through cracks in concrete floors and walls, floor drains, sump pumps, construction joints, and tiny cracks or pores in hollow-block walls. Radon levels are generally highest in basements and ground floor rooms that are in contact with the soil. Factors such as the design, construction, and ventilation of the home affect the pathways and sources that can draw radon indoors. Another source of radon indoors may be air released by well water during showering and other household activities. Compared to radon entering the home through soil, radon entering the home through water will in most cases be a small source of risk.
Outdoors, where it is diluted to low concentrations in the air, radon poses significantly less risk than indoors. In the indoor air environment, however, radon can accumulate to significant levels. The magnitude of radon concentration indoors depends primarily on a building's construction and the amount of radon in the underlying soil. The soil composition under and around a house affects radon levels and the ease with which radon migrates toward a house. Normal pressure differences between the house and the soil can create a slight vacuum in the home that can draw radon gas from the soil into the building.
What is the danger?
If inhaled, radon decay products (polonium-218 and polonium-214, solid form), unattached or attached to the surface of aerosols, dusts, and smoke particles, become deeply lodged or trapped in the lungs, where they can radiate and penetrate the cells of mucous membranes, bronchi, and other pulmonary tissues. The ionizing radiation energy affecting the bronchial epithelial cells is believed to initiate the process of carcinogenesis. Although radon-related lung cancers are mainly seen in the upper airways, radon increases the incidence of all histological types of lung cancer, including small cell carcinoma, adenocarcinoma, and squamous cell carcinoma. Lung cancer due to inhalation of radon decay products constitutes the only known risk associated with radon. In studies done on miners, variables such as age, duration of exposure, time since initiation of exposure and especially the use of tobacco have been found to influence individual risk. In fact, the use of tobacco multiplies the risk of radon-induced lung cancer enormously.
The EPA and the U. S. Surgeon General recommend testing all homes below the third floor for radon. Data gathered by the EPA national radon survey indicate that elevated radon levels are present in about six million (6,000,000) homes throughout the United States. In every state there are homes with dangerously high radon levels. Because the radon concentration inside a home is due to factors relating to its structure and geographic location, each individual home must be tested to determine its radon level. Two adjacent houses may have radically different radon levels. And any kind of home can have elevated levels -- new or old, drafty or well-sealed, and basement or non-basement.
The Health Threat With A Simple Solution - Radon Testing Methods
The quickest way to test for radon is with a short-term "do-it-yourself" radon test kit, available by mail order and in many retail outlets or by hiring an EPA qualified or state-certified radon tester. Common short-term test devices are charcoal canisters, alpha track detectors, liquid scintillation detectors, electret ion chambers, and continuous monitors. A short-term testing device remains in the home for two (2) to ninety (90) days, depending on the type of device. Because radon levels tend to vary from day-to-day and season-to-season, a long-term test is more likely than a short-term test to measure the home's year-round average radon level. If results are needed quickly, however, a short-term test followed by a second short-term test may be used to determine the severity of the radon problem.
Long-term test devices, comparable in cost to devices for short-term testing, remain in the home for more than three (3) months. A long-term test is more likely to indicate the home's year-round average radon level than a short-term test. Alpha track detectors and electret ion detectors are the most common long-term test devices.
In some cases, such as real estate transactions, "qualified" or state-certified contractors conduct the radon test. The EPA's pamphlet Home Buyer's and Seller's Guide to Radon, which addresses issues during real estate transactions, is also available from state radon offices.
Charcoal canister and liquid scintillation detectors contain small quantities of activated charcoal. Radon and its decay products are absorbed onto the charcoal and are measured by counting with a sodium iodide detector or a liquid scintillation counter.
Alpha track detectors contain a small sheet of plastic that is exposed for a period of one (1) to three (3) months. Alpha particles etch the plastic as they strike it. These marks are then chemically treated and counted in the laboratory to determine the radon concentration.
Electret ion detectors contain an electrostatically charged Teflon disk. Ions generated by the decay of radon strike and reduce the surface voltage of the disk. By measuring the voltage reduction, the radon concentration can be calculated.
Continuous monitors are active devices which need power to function. They require operation by trained testers and work by continuously measuring and recording the amount of radon in the home.
During a short-term test, doors and windows are closed twelve (12) hours prior to testing and throughout the testing period. (A short-term test lasting two (2) or three (3) days should not be conducted during unusually severe storms or periods of unusually high winds.) The test kit is placed in the lowest lived-in level of the home, at least twenty (20) inches above the floor, in a room that is used regularly, but not in the kitchen or bathroom where high humidity or the operation of an exhaust fan could affect the validity of the test. At the end of the test period, the kit is mailed to a laboratory for analysis; results are mailed back in a few weeks. The test process is similar for a continuous radon measurement device except the results are returned within the hour if not immediately.
No radon level is considered "safe". The risk of developing lung cancer is directly proportional to the levels and duration of exposure to radon: the higher the radon concentration, the higher the lung cancer risk. The 4 pCi/L "Action Level" is based on current mitigation technology. Today, mitigation technology can almost always reduce high radon concentration levels to below 4 pCi/l and to 2 pCi/L or below 70-80 percent of the time. The average radon level in homes is about 1.25 pCi/L. Although Congress passed legislation in 1988 establishing a national goal that indoor radon levels not exceed ambient outdoor radon levels (0.2-0.7 pCi/L), this goal is not yet technologically achievable.