Miners in uranium and other types of underground mines are at risk of increased radon exposure.
As early as the 16th century, Paracelsus and Agricola described a wasting disease of miners. In 1879, this condition was identified as lung cancer by Herting and Hesse in their investigation of miners from Schneeberg, Germany. Radon itself was discovered some 20 years later by Rutherford. Subsequently, an increase in the incidence of lung cancer among miners was linked to radon daughter exposure in mines. Underground uranium mines found throughout the world, including the western United States and Canada, pose the greatest risk because of their high concentration of radon daughters in combination with silica dust, diesel fumes, and, typically, cigarette smoke. Iron ore, potash, tin, fluorspar, gold, zinc, and
lead mines also have significant levels of radon, often because of radium in the surrounding rock. In the past, it was not uncommon to use the tailings from these mines as fill on which to build homes, schools, and other structures.
Indoor radon daughters have been widely recognized as a potential problem in Europe and the Scandinavian countries since the 1970s. Public awareness in the United States was heightened in December 1984, when "Worker A" at the Limerick nuclear plant in Pennsylvania began setting off radiation alarms when he entered the plant. The cause was traced to levels of excessive radon daughters in his home-500 times the level at which the U.S. Environmental Protection Agency (EPA) recommends remediation (i.e., 4 picocuries per liter [pCi/L]). Radon daughters attach to dust particles in the air that are attracted to items such as clothing, especially when the air is cold and dry.
In 1987, the federal government allotted $10 million to the states to determine the extent of radon contamination in homes and schools, and subsequently amended the Toxic Substances Control Act to assist the states "in responding to the threat to human health posed by exposure to radon." In 1988, EPA and the Office of the Surgeon General jointly recommended that all US homes below the third floor be tested for radon. In 1990, Congress appropriated $8.7 million for grants to states to develop and enhance programs to reduce radon risk in homes and schools. It has become standard practice in some states to measure radon levels in homes at the time of real estate transactions. Radon testing is required for all government buildings.
Approximately 6 million homes in the United States have radon concentrations above 4 pCi/L.
The amount of radon emanating from the earth and concentrating inside homes varies considerably by region and locality, and is greatly affected by the residential structure as well as soil and atmospheric conditions. Nearly every state in the United States has dwellings with measured radon levels above acceptable limits. EPA estimates that 6% of American homes (approximately 6 million) have concentrations of radon above 4 pCi/L. In Clinton, New Jersey, near a geologic formation (the Reading Prong) that is high in radium, all 105 homes tested were above the recommended guidelines; the levels in 40 homes exceeded 200 pCi/L. In the "Worker A" home, levels of 2,700 pCi/L were found in the basement.
Areas of the country that are likely to have homes with elevated radon levels are those with significant deposits of granite, uranium, shale, and phosphate, which are all high in radium content and, therefore, potential sources of radon gas. Some homes in these areas, however, might not have elevated levels of radon. Because of the many determinants of indoor radon levels, local geology alone is an inadequate predictor of risk.
The only way to determine indoor radon concentration is by testing. A home 100 feet away from the "Worker A" home did not have measured radon concentrations that required remediation, yet both houses were on the same geologic formation. Other factors that predispose homes to elevated levels of radon include soil porosity, foundation type, location, building materials used, entry points for soil gas, building ventilation rates, and source of water supply. Further research is being conducted on ways to predict which homes are most likely to have significant levels of radon.
Exposure to excessive radon levels increases the already elevated risk of lung cancer for smokers. The primary adverse health effect of exposure to radon is lung cancer.
Several studies have shown that smokers exposed to radon are at greater risk for lung cancer than are similarly exposed nonsmokers. It is generally believed that exposure to radon and cigarette smoking are synergistic; that is, that the combined effect exceeds the sum of their independent effects. The risk of lung cancer from radon exposure is estimated to be 10 times greater for persons who smoke cigarettes in comparison with those who have never smoked. According to the National Academy of Sciences Committee on the Biological Effects of Ionizing Radiation (BEIR VI), a breakdown of the contribution of smoking and radon exposure to lung cancer deaths in the United States illustrates that of every 100 persons who died of lung cancer, approximately 93 were current or former smokers, whereas 7 had never smoked.
Data on the effects of radiation in children are limited, and even less is known about the effects of radon exposure in this age group. Cancer development in Japanese atomic bomb survivors suggests an increased susceptibility to radiation in children compared to that in adults. Children also have different lung architecture, resulting in a somewhat larger dose of radiation to the respiratory tract, and children have longer latency periods in which to develop cancer. However, no conclusive data exist on whether children are at greater risk than adults from radon.
Who else in the home of the patient discussed in the case study could be at risk for lung cancer as a result of elevated radon levels?
2.
Would your patient's neighbors be equally at risk of exposure to radon? Explain.
3.
How are the risks of radon exposure increased for your patient's daughter, who is a smoker? How does the daughter's smoking affect the risk for other members of the family?
