Radon gas was "discovered" as an important environmental issue in the mid-1980s, when levels 1,000 times the average of about 1.5 picocuries/liter (pCi/l) were found in homes in the eastern United States. Radon is present in all homes, and even in outdoor air, because it is a gaseous decay product of radium naturally present in the soil. Since even an average indoor exposure to radon's own decay products-isotopes of polonium, bismuth, and lead-was estimated to cause a 0.1 to 1% risk of lung cancer, depending on whether one smoked, these high levels sounded an immediate alarm.
By the mid-1980s, scientists had already proven that indoor radon levels 10 to 100 times the average-an unacceptable amount-occurred in homes in various locations throughout the U.S. They also knew why levels could vary so greatly from one home to another and what could be done to lower levels that were deemed excessive. This knowledge had been gained during a broad effort by the research community beginning in the late 1970s and led to a large degree by the LBL radon group. Treating the problem as one of building science, LBL scientists spearheaded efforts to understand the physical processes accounting for radon entry and to analyze systematically the U.S. data from monitored homes.
The Indoor Environment Program's Efforts
These are still major interests of the Indoor Environment Program's Radon Group. Other IEP groups are studying airborne chemicals, emissions from combustion appliances, control techniques, and the energy performance of buildings. The program's basic approach is to investigate the behavior of indoor pollutants and associated air and energy flows. This has led to the recognition that the small pressure differences across the building shell that drive the overall infiltration of outdoor air to the interior could be drawing radon-bearing air from the soil, through the substructure, and into the occupied space.
The radon group's investigation of this process and of measures to reduce radon entry continues. One major effort has involved placing a pair of "small structures," essentially small basements, in the ground at a site in the Santa Cruz mountains and equipping them with an array of sensors for measuring pressure, radon concentration, and temperature in the surrounding soil. The purpose is to investigate, in long- or short-term controlled experiments, the dependence of radon entry rates on these parameters for various artificially imposed pressure differences between the structures' interiors and the outdoor air. In an-other effort, the group has expanded its development of computer models that simulate the transport of air carrying radon from the soil into homes. Increasingly, they use these models to evaluate the effectiveness of proposed control methods, particularly "subslab ventilation" techniques, which alter the pressure field and associated air flows between the soil and the building interior.
A third research area involves analyzing various types of radon field data gathered across the country, data that provide the basis for both understanding risks to humans from radon exposure and designing effective control strategies. A 1984 analysis yielded a tentative frequency distribution of indoor concentrations in U.S. homes averaging about 1.5 pCi/l and an estimate that about 7% of single-family houses have concentrations above 4 pCi/l, the action guideline set by the Environmental Protection Agency in 1986. This tentative distribution introduced some reality to the debate over radon and was confirmed in the early 1990s by a multimillion-dollar EPA survey.
Since 1986, researchers familiar with the concentrations and behavior of radon, those at LBL among them, have criticized the EPA's representation of the radon issue and its strategy for control. One focus of criticism has been the EPA's use of short-term monitoring data, often taken in basements, to indicate that 20 or 30% of homes exceeded the EPA guideline. In point of fact, only the long-term average exposure is relevant to risk, and primary living space is where most of the exposure occurs. The EPA has also tended to exaggerate risks, most recently exposing itself to criticism for asserting that children in schools were at greater risk from radon exposure than the adults.
A fundamental issue is whether the nation's control strategy ought to reduce radon levels everywhere or, instead or first, mount a concentrated effort to identify the homes with particularly high levels. For example, 50,000 to 100,000 homes are estimated to have annual average concentrations in primary living space of 20 pCi/l or more. This level causes an annual radiation exposure roughly equal to the occupational exposure limit (established for underground uranium miners, the group that provides most of the data for estimating the risk from radon exposure). Twenty years' occupancy of such a house would yield an added risk of lung cancer of about 1%, even among nonsmokers. This level of risk is very high compared with the risks estimated for other kinds of environmental exposures regulated by the EPA.
However, the average level of radon in homes is also estimated to cause risks at the 0.1% level for nonsmokers, larger than other known environmental risks, including radon outdoors. The result is that the EPA's regulatory effort has focused on near-average indoor exposures, engendering a conflict over the orientation of control strategies. The conflict is unlikely to be resolved without more careful evaluation of inherent risks in the indoor environment.
In 1992, I published an article called "A National Strategy for Indoor Radon" in Issues in Science and Technology (Fall 1992, pp. 33-40), explaining what had happened since the mid-1980s and proposing an alternative course. The article recommended a commitment to several near-term steps:
It also proposed several longer-term initiatives, including:
To some extent, the EPA has been trying to remedy the failings of its outreach program (in its public information efforts, for example). However, plenty of evidence suggests that this remedial effort is superficial: it still relies on short-term measurements. Its current proposal of a model building standard is not based on sound science and has not been tested adequately. Finally, the manner in which the agency has been representing data from schools is a repeat of how it exaggerated data from homes. It emphasizes the percentage of schools with one or more school rooms exceeding 4 pCi/l in short-term measurements rather than the fact that levels are generally lower in schools than in homes. In any case, because less time is spent at school, 4 pCi/l contributes very little to a child's annual or lifetime exposure. Much remains to be done to achieve a sensible and effective national radon strategy.
Next issue: developing a methodology for identifying high-radon areas.
Indoor Environment Program
(510) 486-6377; (510) 486-6658 fax
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