How Radon Causes Lung Cancer

radon periodical table letters with circles around it.
Radon Gas is the Most Potent Carcinogen in your Home

You cannot see radon gas and you cannot smell it or taste it. Did you know it may be a problem in your home? As the only gas in the decay chains of radioactive heavy metals, radon and its floating radioactive products can easily get into human body by inhalation. Whenever you breathe in air containing radon, it increases your risk of getting lung cancer. The National Academy of Sciences and the Environment Protection Agency estimates that in the U.S., radon in the home causes 21,100 lung cancer deaths each year.

Radiation is called the "complete carcinogen" because, unlike chemical carcinogens, it alone can initiate, promote and propagate cancer. The primary site of radioactive exposure to most people is their home. The average person receives a higher radiation dose from radon at home than from all other natural or man-made sources combined.

Radon is very potent and a proven "Class A" carcinogen. Safety limits on toxins or carcinogens in food or water are set at levels thousand times less lethal than what is the risk from radon in an average American home.

"Radon in homes causes more deaths than fires, drownings and airplane crashes combined." says the EPA.

The Lung Cancer Crisis

After smoking radon is the second leading cause of lung cancer and among non-smokers, radon is the number one cause of lung cancer deaths.

Lung cancer is the leading cancer killer of all Americans, claiming 160,000 lives every year, more than breast cancer, prostate cancer, and colorectal cancer combined. Over 171,000 new lung cancers are diagnosed in the U.S. each year.

The leading three causes of cancer deaths
Men Women
Lung cancer 33% Lung cancer 24%
Prostate cancer 12% Breast cancer 18%
Colorectal cancer 10% Colorectal cancer 11%

Lung cancer is the deadliest of all cancers. It has a 5-year survival rate of only 10 to 14 percent. By the time people develop symptoms (shortness of breath, coughing, bloody sputum), the cancer has grown to the size of an orange or has spread to other organs. While the death rates for many types of cancer have been declining during the last 60 years, the age-adjusted incidence and mortality rates for lung cancer have been rising.

There is a lung cancer crisis, particularly among women. Lung cancer deaths have increased by 20% among men during the past two decades but by 150% among women, and in the 1990's alone, lung cancer deaths of white females have increased 60%.

Children Are More Susceptible to Radon

Children are known to be more radiosensitive than adults. Analysis of Hiroshima victims showed a higher incidence of lung cancer among those who were exposed to the radiation blast as children. A single x-ray to the abdomen of a pregnant woman in the first six weeks of pregnancy leads to a 50 percent increase in cancer and leukemia risks to the child. The gamma rays emitted by radon progeny are far more energetic than x-rays but the emitted alpha and beta particles are even more harmful.

Radiation risk to embryos is higher than to children, which in turn is higher than to adults. Children are more susceptible to radon-induced cancer due to their rapidly dividing cells and higher breathing rates. It is compounded by their heavier exposure to radon by spending more time inside the house and/or in the basement.

Recent research in Europe confirms that radon is much more harmful to children than to adults. Lung cancer incidence as a result of radon exposure is estimated to be about ten times higher for people exposed at the age of about 15 than at about 50.

However, the onset of lung cancer takes decades. EPA has not found convincing epidemiologic evidence of increased risks to children (except to the smallest ones) and its radon guidelines for homeowners are thus based solely on the lung cancer risks to adults.

Radioactive Lining of the Lungs

After radon gas is inhaled, it readily dissolves in the blood and circulates through the body, organs, and tissues, until it is again exhaled through the lungs or skin. Equilibrium is established between the ambient and the internal radon concentrations. Since the radioactive half time of Radon-222 is 3.8 days, most radon atoms harmlessly leave the body before they can disintegrate.

The problem is not radon, but rather the radioactive particles it produces. As radon atoms undergo radioactive decay, they disintegrate into radiation and radon progeny ("daughters") - solid heavy metal particles of lead, polonium, and bismuth. These minute, electrically charged and chemically active particles float in the air, and when breathed in, some (less than 1%) get trapped permanently in the airways. About 600,000 radioactive particles get trapped in the lungs every hour.

The deposition in the lungs depends on whether the particles are attached to airborne dust or smoke, or unattached. Unattached daughters lodge deeper in the lung, which explains the severity and the type of radon-induced deep-lung cancers in non-smokers.

Radon Does Not Even Have to Hit the Cell

The Los Alamos National Laboratory researchers discovered in 1997 that alpha particles emitted by radon do not have to hit the nucleus of a cell to damage the cell's DNA, which resides in the nucleus. Moreover, the alpha particles do not even have to hit the cell - a bombardment of the surrounding medium produces chemical radicals inside the cells, which cause DNA damage.

Does Radon Cause Other Diseases?

It is generally assumed that inhaled radon gas is quickly exhaled and has little time during its circulation through the body to deposit its radioactive products in human organs, tissues, or bones. However, the story may be more complicated. Some scientists believe that radon dissolved in the blood may cause additional diseases beside lung cancer. In addition to the gas, one-third of the inhaled radon decay particles also pass through the lungs into the blood stream and then, get trapped. 

As we breathe in through the skin, the air also carries radon gas. Some studies suggest that the radiation dose to the basal layers of the skin is high with a consequent risk of skin cancer.

Radon gas is soluble in lipids and accumulates in lipid tissue throughout the body with the highest concentration in the brain, bone marrow, and nervous system. But none of its heavy metal daughters are soluble in the lipids and consequently, remain trapped in the brain and bones, where they continue to emit gamma radiation and alpha particles. Several studies indicate that radon also causes leukemia ("cancer of the blood") and other types of cancers.

Researchers at the University of North Dakota discovered that the presence of radioactive radon daughters in the brains of non-smoking persons with Alzheimer’s and Parkinson’s disease was 10 times greater than it was in the brains of persons with no previous evidence of neurological disorders. Interestingly, the geographic distribution of Parkinson’s disease mortality is considerably higher in states with a greater radon potential.

Animals exposed to high concentrations of radon progeny display beside lung carcinoma emphysema, pulmonary fibrosis, and a shortened life span.

Nevertheless, the risk of other cancers or diseases is much lower than that of lung cancer. The National Academy of Sciences estimates that radon ingested with water causes about 20 stomach cancer deaths per year, which is 1,000 times fewer than from lung cancer. Since the radiation dose to other organs is much smaller than from radon decay products deposited in the bronchial epithelium, ICRP estimates the cancer risk to other organs at about 2% of the lung cancer risk.

Possible Genetic Damage

Ionizing radiation causes random damage to the chromosomes and DNA molecules contained in the nucleus of the cell, including genetic mutations that may affect future generations. Substances having a carcinogenic effect also have genetic and teratogenic effects. Damage to the DNA of reproductive cell, e.g. gamma irradiation of sperm, can lead to genetic deficiencies in the offspring, and if an embryonic cell is damaged, the normal development of the fetus can be disrupted.

In areas of high natural background radiation, an increased frequency of chromosome aberrations has been observed. "Any individual dose, however small, is able to produce gross malignancies and deformities if it is administered to a sufficiently large population."

When Can a Person Exposed to Radon Finally Relax?

Never, unless already well advanced in age. The most intense radiation from radon progeny occurs during the first hours, when polonium and bismuth quickly decay into radioactive Lead-210. But then follows a much slower decay through bismuth, polonium and lead radionuclides into stable Lead-206. The total half-life of these nuclides is over 22 years. If a person has been exposed to radon, 75 percent of the radon progeny in lungs will become "harmless" lead particles after 44 years.

When an alpha particle damages a cell to make it cancerous, the onset of lung cancer takes a minimum of 5 years but most often 15 to 25 years, and even longer. The decades-long decay of radon progeny and the slow onset of cancer make it almost impossible to measure the increase in death rates caused by radon in a mobile population. Therefore, most lung cancer studies are based on the thousands of miners exposed to radon or on extensive animal, cellular and radiological research.

Only few people exposed to radon will develop lung cancer. However, once exposed to radon, the lung cancer risk lasts for one's lifetime. Children and young people naturally have a higher risk of developing lung cancer during their lifetime.

Minimize the Radon Level in Your Home!

Many of the 21,000 lung cancer deaths caused by radon in the U.S. each year are preventable. The "action" and "consider action" limits of 4 or 2 pCi/L are merely cost/benefit guidelines - EPA has left the radon mitigation decision and responsibility up to the individual homeowner. EPA has warns the public: "Any radon exposure has some risk of causing lung cancer. The lower the radon level in your home, the lower your family's risk of lung cancer."

You should always try to reduce the radon level in your home to a practical minimum. The target of the U.S. Radon Abatement Act is the natural level outdoors (average 0.4 pCi/L). Whether you current level is 30 or 3 pCi/L, or if a mitigation system is already installed, reducing radon in your home by 90 or 50 percent will reduce the risk to your family by 90 or 50 percent.


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