Radon is an invisible, radioactive atomic gas that results from the radioactive decay of radium, which may be found in rock formations beneath buildings or in certain building materials themselves. Radon is probably the most pervasive serious hazard for indoor air in the United States and Europe[i]. It is the second leading cause of lung cancer in the UnitedStates and the leading cause of lung cancer among people who have never smoked. Radon-induced lung cancer is responsible for an estimated average of 21,000 American deaths annually.[ii] Plant air purifiers remove radon from the air.
The element Radon (Rn) emanates naturally from the ground, and some building materials, all over the world,
The chart above shows you the mean concentrations of radon in the atmosphere. Those areas in orange red have the highest concentrations and strongly suggest where the highest concentrations of radon are found in the ground.
Radon is a colorless, odorless gas, a radioactive byproduct of radium which is part of the natural radioactive decay series starting with uranium-238. So prolific is uranium that if you were to dig up the top 6 feet of an acre of land you would find, on average, about 50 pounds of uranium according to the EPA.
Above is a chart showing the natural decay series from Uranium 238 to lead.
The decay of radon-222 with emission of an alpha particle is followed within about an hour by a series of four further decays, two of them accompanied by emission of alpha particles and the other two accompanied by other types of radiation. The short-lived atoms into which a radon atom decays are actually isotopes of polonium, lead, and bismuth, but they are referred to collectively as radon daughters, or, by those sensitive to questions of gender, as radon progeny. The radon daughter atoms float around in the air during their few minutes of existence, often becoming attached to dust particles which people breathe in.
The radon gas simply goes in and out of the lungs, doing little damage, but the radon daughters, being basically solid materials, and sometimes being electrically charged, can stick to the surfaces of our bronchial tubes. This puts them right where they can do the most harm, for the cells lining our bronchial tubes are among the cells of our body most sensitive to radiation-induced cancer. The alpha particles emitted in the decay of radon daughters, in spite of their poor penetrating power, can reach these very sensitive cells because they are deposited so close to them. To make matters very much worse, alpha particles are much more efficient than other types of radiation for inducing cancer. The very fact that they are not penetrating means that they dump a lot of their energy into each of the biological cells they pass through, and this large release of energy into a single cell is just what is needed to initiate a cancer. As a result an alpha particle is a hundred times more likely to cause cancer than other types of radiation, if it can reach the target cells. Our breathing processes allow the alpha particles from radon daughters to reach these cells.
With every breath you take in a confined space where radon is present radioactive progeny lodge in your lungs, bronchi, and trachea. The radiation disrupts and mutates cells and can, eventually, result in lung cancer.
Radon flows up from the soil into buildings. It is a dangerous vehicle for the dispersion of these shortlived radioactive decay products infiltrating into the home from cracks and seams in basement floors, walls, and drains, as well as through the pores of concrete foundations and wood floors.
The danger of radon exposure in dwellings was discovered in 1984 with the case of Stanley Watras, an employee at the Limerick nuclear power plant in Pennsylvania. Watras set off the radiation alarms on his way into work for two weeks straight while authorities searched for the source of the contamination. They were shocked to find that the source was astonishingly high levels of radon, around 100,000 Bq/m3 (2,700 pCi/L), in his house’s basement and it was not related to the nuclear plant. The risks associated with living in his house were estimated to be equivalent to smoking 135 packs of cigarettes every day
The EPA has set the level of concern of radon at 4 picoCuries per liter of air (4 pCi/L). This is a concentration of 70,000 atoms of radon in each liter of air (about 2 million radon atoms in every cubic foot of air). This is a very low concentration, roughly one radon atom in a billion-billion air atoms, We breathe about 20 liters of air into our lungs each minute. At 4 pCi/L we accumulate about 10,000 radioactive atoms in our lungs, trachea, and bronchi every minute.
Yet 4 pCi/L is not necessarily a safe level, for in one of the most comprehensive radon studies, performed in the United States, by Dr. R. William Field and colleagues, they found a 50% increased lung cancer risk even at protracted exposures at the EPA’s action level of 4 pCi/L
EPA representative emphasized that the current action level does not imply that levels below 4 pCi/L are safe; significant risk exists below the action level and, in fact, no safe exposure level has been identified. In 2009, the World Health Organization (WHO) revised its recommendation for a maximum acceptable radon concentration in a residential dwelling to 2.7pCi/L.442
EPA MAP OF RADON ZONES
Looking at the map above you can see how pervasive are the regions in the United States with homes having 4 pCi/L of radon, and how pervasive the regions having 2-4 p Ci/L are. Well over half the United States could well be located in areas where radon might be a danger to people’s lives.
According to one study 15-20% of homes have unacceptably high levels (presumably meaning > 4 pCi/l). And in another study Up to 6 percent of U.S. homes are estimated to have radon concentrations at or above the action level.439 . The reason an exact figure cannot be found is because radon testing is not mandatory. But one thing is certain, radon is a dangerous airborne pollutant and one that an air purifier should deal with. Source control is important as well and one should seal all cracks in the air barrier where radon could infiltrate the structure.
Plant air purifiers make ideal radon removers. That is because the entire filter bed is composed of materials — activated carbon and light weight expanded clay, known as Leca–which are both adsorbents and absorbents. Adsorption is the process by which charged particles of other substances combine with the charged particles on the outer surface of the adsorbent. At a certain PH the adsorbent carries a negative charge, while radiation carries a positive charge. the positively charged ions are attracted to the negatively charged surfaces of the activated carbon and clay molecule. An exchange reaction occurs in which the adsorbent’s ions are swapped for the ions of the positive charged substance and the two form an ionic bond. However once the radioactive substance has undergone the ionic change, it enters into the spaces within the activated carbon and Leca because these now act as an absorbent. This causes the ions that were formerly only sticking to the surface of the adsorbent’s outer structure, being now pulled inside. The result radon and the radon progeny are effectively removed from the air.
But this is not the end of the process, for were the radon and its progeny to simply remain in the activated carbon and leca they would eventually saturate it and the filter bed would have to be replaced.
Additionally there is a novel approach added, that of using plant systems for removing high concentrations of radon and its progeny from the filter bed. The rational for this design evolved from wastewater treatment studies and is based on moving large volumes of contaminated air. In the final step the plant roots and their associated microorganisms eventually convert these radionuclides into new plant tissue, which holds the contaminent in a far more concentrated form, than it was held in the filter bed, as much as 700 times more concentrated, with the end result that the filter bed never needs replacement. Meanwhile the radioactive substances continue their decay within the plant and eventually become lead.
Other air purifiers may have adsorbents and may be able to sequester radionuclides within the filter bed, but no other air purifier remove radon from the filter bed. With the end result that the filter beds of all other air purifiers either become saturated and have to be replaced, or merely spew radioactive toxins back into the air for inhabitants to breathe. Plant air purifiers do the job of purifying the air of radon contamination far more effectively than any other form of purification method now on the market today.
A last thing should be mention with reference to radon and that is that radon exposure only adds to the woes of those who either suffer from second hand smoke or smoke. In fact Approximately 80% of deaths attributed to radon occur among smokers or those breathing in second hand smoke. Therefore it is imperative that plant air purifiers be utilized in those homes where there is both radon and a smoker, as all within stand a much higher risk of disease.
[ii] 2008-2009 Annual Report, President’s Cancer Panel. “Environmental Cancer Risk—What we can do now” U.S. Department of Health and Human Services, N.I. H. & the National Cancer Institute