Introduction

Everyone is exposed to radon, but some populations described in the literature are at higher risk of exposure to increased radon levels. In addition, some populations are more at risk of adverse health effects from radon exposure.

Radon exposure is, after tobacco smoke, the leading environmental cause of lung cancer death (Copes 2007; EPA 2009a). Thus for nonsmokers, radon exposure is the leading cause of lung cancer death, period (EPA 2009b).

The risk of lung cancer from radon exposure is estimated at between 10 to 20 times greater for persons who smoke cigarettes as compared with those who have never smoked.

Radon Exposure Dose

Theory holds that everyone is at risk from radon exposure, and this health risk increases linearly with dose.

• Approximately 6 million homes in the United States have radon levels above 4 picocuries per liter (pCi/L), which is the remediation level EPA recommends.
• Miners in uranium, tin, silver, coal, and other types of underground mines may have increased radon exposure. Good ventilation can effectively reduce the incidence of lung cancer in miners.
• The risk of lung cancer from radon exposure is estimated between 10 to 20 times greater for persons who smoke cigarettes as compared with those who have never smoked. The added risk is unclear regarding medical exposure, which can exceed that from radon.

Environmental Causes of Lung Cancer Deaths

Lung cancer is a leading cause of cancer death worldwide (Wakelee 2007). In the United States, lung cancer remains the leading cause of cancer death in both men and women. Exposure to tobacco smoke is the leading cause of lung cancer, with active smoking causing most cases. But passive smoking also contributes to the lung cancer burden.

Radon exposure is the second-leading environmental cause of lung cancer death, after tobacco smoke (Copes 2007; EPA 2009a), and the leading cause of lung cancer death for nonsmokers (EPA 2009b).

• Radon exposure is responsible for about 21,000 lung cancer deaths per year in the United States (NCI 2004; EPA 2007; EPA 2009b).

Some estimates suggest that approximately 14% of the 300,000 annual lung cancer cases in the United States are attributable to radon (EPA 2009b).

• The World Health Organization (WHO) estimates that radon causes between 6% and 15% of lung cancers worldwide (WHO 2005). Everyone is exposed to environmental radon.

Estimated Risk of Developing Lung Cancer from Radon Exposure

In 1999, the National Research Council of the National Academy of Sciences published the Biological Effects of Ionizing Radiations VI report, Health Effects of Exposure to Radon (NAS 1999), which concludes that indoor radon is “the second leading cause of lung cancer after cigarette smoking” (NRC 1999; EPA 2003).

EPA estimates that exposure to high radon levels is the leading environmental cause of death in the United States (EPA 2003).

EPA estimates that at its recommended guideline of 4 pCi/L, the risk of developing lung cancer for a lifetime exposure to radon is

• 1% for nonsmokers,
• 3% for former smokers, and
• 5% for smokers.

These estimates can change based on factors that influence a population group’s risk. In determining the risk of radon in homes or offices with the same concentration, assessors must consider not only the average level of radon, but also the occupants and their lifestyles. For example, the highest radon levels are typically found in the lowest level of the house.

Many factors influence the risk of radon-related lung cancer due to exposure, such as

• Age during exposure,
• Duration of exposure,
• Concentration of radon as a function of age and duration,
• Cigarette smoking,
• Time spent and concentrations in different portions of the home, in transportation routes, and in the office, (e.g., where and how long persons sleep, work, and recreate).
• Source of water - if well water is the major radon source, upper floors can be affected more than lower floors (e.g., showers),
• Climate and time of year—in colder climates, radon levels are often higher in the winter and lower in the summer,
• Static-prone times of year—degree to which radon progeny attach to dust particles can increase during static-prone times (e.g., in April and October) and,
• Time elapsed since initiation of exposure.

EPA Radon Risk Evaluation

Figure 2 shows the risk of developing lung cancer over a lifetime of exposure to radon gas at different exposure levels. This figure provides risks for both, smokers and nonsmokers, as well as recommended solutions to reduce those levels of exposure and risk.

Figure 2. Radon risk evaluation chart for smokers and nonsmokers (Modified from EPA 2009)

Note: If you are a former smoker, your risk may be lower than a current smoker.

^* Lifetime risk of lung cancer deaths from EPA Assessment of Risks from Radon in Homes (EPA 402-R-03-003).

Note: If you are a former smoker, your risk may be higher.

^* Lifetime risk of lung cancer deaths from EPA Assessment of Risks from Radon in Homes (EPA 402-R-03-003).

Public’s Assessment of Radon Exposure Risk

The public often underestimates the potential risk of cancer due to radon. This could discourage assessment and abatement measures in the home, as given that the general population does not see the problem.

In fact, several studies have noted optimistic biases in the public's assessment of radon exposure’s potential health risks. For the most part, the general public thinks radon exposure does not pose a risk.

Home Dwellers and Indoor Radon Exposure Risk

An extensive body of literature now addresses the risks of exposure to indoor radon (NRCC 1999; Darby 2005; Krewski et al 2005). Populations with the highest nonoccupational exposure risk to increased radon gas levels include home dwellers, particularly when they dwell in homes that

• Have high concentrations of radon gas trapped indoors, (i.e., released into the air from soil, water, natural gas use, and building materials) and,
• Are built with or atop tailings from mines and mills.

Children and Radon Exposure Risk

Due to lung shape and size differences, children have higher estimated radiation doses than do adults. Children also have breathing rates faster than those of adults.

• Risk of lung cancer in children resulting from exposure to radon may be almost twice as high as the risk to adults exposed to the same amount of radon.
• If children are also exposed to tobacco smoke, the risk of getting lung cancer increases at least 20 times.

Miners and Radon Exposure Risk

Among underground miners, radon was the first environmental respiratory carcinogen linked to increased lung cancer risk. Many epidemiologic studies of those who mine uranium and other ores have established exposure to radon daughters as a lung cancer cause (NRCC 1999). Other recognized or suspected carcinogens in mine air include silica dust, cigarette smoke, arsenic, and diesel exhaust particles.

Miners’ long-term exposure effects to radon are well known. Investigation is ongoing to determine the potential of other mine air contaminants as study confounders. For example, at one mine accounting for arsenic reduced the calculated radon risk rate by a factor of three (Nourgalieva et al. 2003).

Accounting for silica would be expected to reduce further the computed risk of radon exposure, although this is yet to be attempted.

• As early as the 16th century, Paracelsus and Agricola described a wasting disease in miners. In an 1879 investigation of miners in Schneeberg, Germany, Herting and Hesse identified this same condition as lung cancer (ATSDR 2008).
• Since the 1970s, indoor radon daughters have been widely recognized as a potential problem in Europe and in Scandinavian countries.

Due to the high airborne levels of radon and its progeny, the most frequent occupational exposures to radon typically result from employment in underground uranium and other hard- rock mining (NIOSH 2006).

Although persons engaged in uranium mining are believed to receive the greatest exposures, the number employed in uranium mining in the United States has greatly decreased.

Additionally, continuous improvements in engineering controls have greatly increased ventilation, thus reducing radon exposure in underground mines (NIOSH 1987). Enhanced ventilation systems have also reduced exposure to other actual and potential carcinogens.

Other Types of Workers and Radon Exposure Risk

A list of common occupations with potential for high radon and progeny exposure include employees of

• Excavators,
• Fish hatcheries,
• Health mines and spas,
• Hospitals,
• Natural caverns (in releases from exposed walls),
• Natural gas and oil piping facilities,
• Nuclear waste repositories (in releases from tunnel walls),
• Oil refineries,
• Phosphate fertilizer plants,
• Fossil fuel power plants (in release to air after fuel is burned),
• Sites radioactively contaminated with radium (because most radioactively contaminated sites are not contaminated with radium, radon is not an issue at these sites),
• Utility and subway tunnels (in releases from walls), and
• Water treatment plants (in releases during aeration). (EPA 2003; Field 1999; Fisher et al. 1996)

In some areas of the country, higher exposure can also occur to farmers, radon mitigation professionals, and scientists studying radon or other radionuclides, although exposure to local radon sources can occur in any occupation (Field 1999).

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