The potential hazard of radiation exposures to radon gas and its daughter products from natural background is a world wide problem. The `Environmental Protection Agency’ (EPA) and the `National Council on Radiation Protection and Measurement’ (NCRP) both based in America, the `International Commission on Radiation Protection’ (ICRP) and other groups are concerned with radiation protection matters and all have issued guidelines. These guidelines and recommended actions are in general agreement, although they differ in detail.
Many articles have been published in the scientific literature dealing with the issue of human risk from radon exposures, and many of these appear in publications by the National Academy of Sciences (NAS), NCRP, EPA, Department of Energy (DOE), as well as in the radiation related journals, primarily the Health Physics Journal, and its Newsletter, and Radiation Research. There are different perspectives on the significance of environmental radon, and the referenced documents illustrate the range of opinion regarding this issue.
Several key points are now noted:
The risk of environmental radon levels is not higher now than in the past, when residential exposures were not considered to be a significant health hazard. It has now been raised from a nominal natural background contributor to human exposures to the prime contributor based on a new way of calculating dose, and not on increased exposures in the home due to tighter more energy efficient houses, or new information on radiation dose and/or biologic risk (See Domistry)
The great majority of the radiation dose is not from radon itself, but from the short-lived alpha particle-emitting radon daughters, most notably Po-218 (radioactive T1/2=3 minutes), and Po-214 (radioactive T1/2=0.164 milliseconds), along with beta particles from Bi-214 (T1/2=19.7 minutes). [T1/2 is physical half-life]. (See The Radon Decay Chain)
Measurement of radon in homes is simple and relatively inexpensive and may be accomplished by various means. NRPB who provides free measurements of homes remains the method of choice by the average homeowner. (See Measurement of Radon levels)
There is no way to avoid radiation exposures completely, much of which comes from the natural environment as well as from radioactivity in our own bodies. (See Radioactive concentrations>)
Radon gas can penetrate houses from many sources in many fashions. It is not possible to radonproof a home, but it is possible to reduce its level. The most important contributor to indoor radon is the soil from which radon can be drawn through large and small subsurface gaps in the house foundation. Houses that are in direct contact with the ground will have higher radon levels than houses with an air space under the dwelling. Radon levels in the upper floors of a multi-story building are lower than on the ground floor. If one lives in a high radon area, it is prudent to determine the level in the home and to take appropriate action if the level is found to be high, i.e. greater than 200 Bq m-3 (See Sources of Radon in Buildings)
Evidence for a health effect from radon exposure is based upon data gathered from epidemiologic studies of miners, and animal studies. Extensive radiobiologic data predict a linear dose response curve in the low dose region due to poor biological repair mechanisms for the high density of ionising events that alpha particles create. If this is the mechanism that underlies lung cancer induction, there is reason to believe that there will be some degree of increased lung cancer risk even from low level environmental radon exposures. However, no compelling evidence for increased lung cancer risk has yet been demonstrated from “acceptable” levels (<200 Bq M-3), increased lung cancer risk is primarily in cigarette smokers, and abatement of that risk can best be accomplished by changes in smoking status. (See Dosimetry section 2.7)
Protection of radon in the home can be accomplished by a variety of means. The level to which protection should be directed is under dispute, to the extent that some groups suggest the level should be maintained at less than or equal to 20 Bq M-3 (the average outdoor level).