Source And Effects

Radon gas is produced by the decay of naturally occurring uranium found in almost all soils and rocks. Figure 5.28.1 shows the decay chain that transforms uranium into radon and its progeny. Radon is also found in soils contaminated with certain types of industrial waste, such as the by-products of uranium mining. Phosphate rock is a source of radon because deposits of phosphate often contain high levels of uranium, approximately 50 to 150 ppm.

A significant amount of radon is present in wells and soil in many parts of this country. Radon is commonly associated with granite bedrock and is also present in the natural gas and coal deposits in this rock. In its natural state, radon rises through airspace in the soil and enters a house through its basement, is released from agitated or boiled water, or escapes during natural gas use.

The most common pathways through which radon gas seeps in from the soil include cracks in concrete floors and walls, drain pipes, floor drains, sumps, and cracks or pores

FIG. 5.28.1 Radium decay chart. About halfway through its decay sequence, uranium becomes a gas, radon, which as it disintegrates gives off radioactive particles of polonium, bismuth, and lead. Also noted is the half-life of each material—the time required for half of its radioactivity to dissipate.

FIG. 5.28.1 Radium decay chart. About halfway through its decay sequence, uranium becomes a gas, radon, which as it disintegrates gives off radioactive particles of polonium, bismuth, and lead. Also noted is the half-life of each material—the time required for half of its radioactivity to dissipate.

in hollow block walls. Radon is drawn in by reduced air pressure, which results when the interior pressure drops below the pressure in the ground. This pressure drop is commonly caused by a warmer indoor climate; kitchen or attic exhaust fans; or consumption of interior air by furnaces, clothes dryers, or other appliances.

Radon is a colorless, odorless, almost chemically inert, radioactive gas. It is soluble in cold water, and its solubility decreases with increasing temperature. This characteristic of radon causes it to be released during water-related activities, such as taking showers, flushing toilets, and general cleaning.

Scientists and health officials express fears that the reduced infiltration of fresh air from the outside to increase energy efficiency is eliminating the escape route for radon and making a bad indoor pollution problem worse. Other factors to consider include the inflow rate of radon which depends on the strength of the radon source beneath the house and the permeability of the soil.

Since radon is naturally radioactive, it is unstable, giving off radiation as it decays. The radon decay products, radon progeny, or radon daughters, which are formed, cling to dust. If inhaled, the dust can become trapped in the lung's sensitive airways. As the decay products break down further, more radiation is released which can dam age lung tissue and lead to lung cancer after a period of ten to thirty years. Outside, radon dissipates quickly. However, in an enclosed space, such as a house, it can accumulate and cause lung cancer. Scientists believe that smoking increases any cancer risk from radon.

Figure 5.28.2 shows how the lung cancer risks of radon exposure compare to other causes of the disease. Scientists at the U.S. EPA estimate that if 100 individuals are exposed to a level of 4 picocuries per liter (pCi/l) over seventy years, between one and five of them will contract lung cancer. If these same individuals live in houses with levels of 200 pCi/l for only ten years, the number of anticipated lung cancer deaths would rise to between four and forty-two out of 100.

Working Levels (WL) and pCi/l

By definition, a curie is the decay rate of one gram of ra-dium—37 billion decays per sec. Radioactivity in the environment is usually measured in trillionth of a curie or a picocurie (pCi). With a concentration of 1 pCi/l of air, pCi/l WL

Comparable Exposure Levels

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