Not since the original Psycho has there has been such intense concern about the dangers of showering. The Environmental Protection Agency is preparing to set limits on the presence of radon in household water to keep people from inhaling the radioactive gas as it evaporates from showers, washing machines, and dishwashers. This move could cost hundreds of millions of dollars annually in order to…well, actually, it's not clear if it would accomplish anything.
Welcome to the latest phase in the crusade against radon, an invisible, odorless, naturally occurring gas produced by the breakdown of the radioactive elements uranium and thorium, which are found in rocks and soil. Radon has stirred the anxieties of regulators and the public for much of the past two decades, especially because of accumulations of the gas in basements and other confined spaces. Millions of homeowners have had their houses tested for the substance, and many have installed vent pipes or taken other measures to reduce radon levels.
Not coincidentally, radon seeped into public awareness at much the same time that the nuclear power industry encountered serious opposition. By the mid-1980s, defenders of nuclear energy were asserting–quite correctly–that the public is exposed to much higher radiation levels from radon than from power plants. This argument did not have its intended effect. The industry "managed to get people afraid of radon rather than less concerned about nuclear power," says University of Maryland physicist Robert L. Park.
Radon is a known human carcinogen–that is, it is known to cause lung cancer among underground uranium miners who routinely inhale huge quantities of the stuff. Whether radon poses a danger to anyone else is unknown. Studies have failed to find any correlation between lung cancer and radon exposure in quantities encountered by the general public; to the contrary, lung cancer rates are relatively low in New England and the Rocky Mountain states–regions with notably high levels of radon. Some scientists have even speculated that, by stimulating the body's defense mechanisms, radon can help prevent lung cancer.
Nonetheless, the EPA and the federally funded National Academy of Sciences have produced some grim estimates about radon's impact on public health. (The EPA is required by law to consider NAS estimates in formulating its radon policies.) According to an NAS study released in February 1998, radon causes as many as 21,800 lung cancer deaths per year in the United States. This estimate, however, was not based on any actual cases of people getting cancer from radon in their homes; rather, it was produced by taking information on the group facing the highest risk from exposure to radon–uranium miners–and plugging it into a linear, no-threshold model of radiation's effects.
Such a model is "linear" because it assumes that radiation which is harmful to health at high concentrations must be proportionately harmful at lowest levels of exposure. It also assumes there is no level ("threshold") at which radiation is harmless. Those assumptions have been called into question, due in part to epidemiological data showing that groups exposed to low levels of radiation (such as Navy shipyard workers) have cancer rates no higher than the general public. A growing understanding of molecular biology helps explain such resilience: While radiation can damage DNA (and thus cause cancer), various enzymes are constantly working to repair DNA.
There is, then, plenty of reason to doubt that radon kills tens of thousands of people each year, or indeed that it kills anyone other than uranium miners (and even there, the statistics are complicated by the fact that many miners are smokers). Yet the EPA is embarking on a costly expansion of its war against radon, which is hard to justify even if radon is as dangerous as the agency contends.
Under the 1996 Safe Drinking Water Act, the EPA is authorized to establish a "maximum contaminant level" for waterborne radon, even though water–whether ingested directly or inhaled after evaporation–is a marginal source of radon.
This provision, backed by environmental groups such as the Natural Resources Defense Council, is reminiscent of the proverbial drunk who searches for his keys under a lamp rather than in the darkness where he lost them. Water–whether ingested directly or inhaled through evaporation–is a marginal source of radon; but it is a source that lends itself to control by regulations imposed on utilities. "The predominant risk from radon is from inhalation," says Dan W. Pedersen, a regulatory engineer at the American Water Works Association, an industry group that includes some 4,000 utilities. "The predominant source of radon for inhalation is actually air seeping from the ground into the house."
A 1994 EPA report estimated that waterborne radon causes 192 deaths per year, or almost 1 percent of radon's alleged death toll. In September 1998, the NAS placed the figure at 180, of which only 20 are stomach cancer cases attributed to drinking radon; the remainder result from inhaling evaporated water, particularly in showers and other areas where water is heated or agitated. (Ingesting radon is acknowledged to be less dangerous than inhaling it. Radon's radioactivity consists of alpha particles, which are generally unable to pass through the stomach's lining but may lodge in the lungs.)
Of course, the above estimates could be wrong. If the linear, no-threshold hypothesis is mistaken, then the death toll from waterborne radon might be zero (or even a negative number, if radon exposure actually prevents some fatalities).
But if waterborne radon does kill nearly 200 people a year, what should be done? Water purification plants can remove radon by spraying their water through the air before sending it to customers. Unfortunately, such aeration is an expensive and potentially risky process. Sprayed water is more likely to come into contact with airborne viruses and bacteria and then must be disinfected with chlorine. The water also must be pretreated to prevent impurities from oxidation that can damage pipes and equipment.
In its 1994 report, the EPA estimated that preventing 84 of the putative 192 annual cancer deaths caused by waterborne radon would cost $272 million per year. The American Water Works Association put the annual cost at $2.5 billion. The industry group says the EPA did not adequately account for the cost of additional water treatment.
Moreover, all these figures were based on a never-enacted 1991 EPA proposal to limit waterborne radon. Even though there is no limit on waterborne radon, the Safe Drinking Water Act may empower the EPA to set an even more-stringent standard than the one proposed in 1991. (The level will not be announced until mid-1999.) In any event, the costs will be borne mainly by smaller communities: Gas evaporates more slowly from wells than from rivers or reservoirs, and the high fixed cost of filtration makes water treatment an expensive process for utilities that serve a small number of customers.
Despite its name, the Safe Drinking Water Act is not only about water. Under a complicated provision, if the EPA sets its waterborne radon maximum below a certain level, then the states are allowed to propose "multimedia radon mitigation programs" that address air quality and household water; new regulations may be placed on airborne radon even if the gas didn't originate from evaporated water. This approach may seem sensible, since it's often cheaper to install ventilation systems than it is to treat water. But the result would give regulators more control over radon reduction measures that have until now been mostly voluntary. For instance, many homeowners conduct radon testing or remediation in accordance with EPA guidelines; increasingly, they may be taking such measures because of EPA rules.
This is where things stand in the war against radon: To combat minor or nonexistent health risks, the federal government will impose a set of costly, extensive, and possibly dangerous new regulations on the water you drink and the air you breathe. Taking a shower may never again be such a relaxing experience.
Kenneth Silber (firstname.lastname@example.org) writes about science, technology, and economics.