Radon and Cumulative Health Risks
I found on Riskworld a news item of an analysis of 13 case-control studies of indoor radon exposure and lung cancer incidence from nine European countries, to be published in the British Medical Journal. Recall that a case control study is a retrospective comparison of exposures of persons with a disease (cases) versus persons without the disease (controls), and is one of the more robust study methods in epidemiology (some resources on epidemiology are here and here). The authors concluded that collectively, though not separately, these 13 studies show appreciable hazards from residential radon, particularly for smokers and recent ex-smokers.
The authors stratified smokers into a separate group (i.e. examined cancer incidence and radon exposure separately between smokers and non-smokers). After stratification of smokers, there was strong evidence of an association between indoor radon concentrations and lung cancer. The dose-response relation seemed to be linear, with no evidence of a threshold dose; evidence of a dose-response relationship is an important factor in toxicology and epidemiology in judging that an environmental hazard can produce adverse health effects. A linear dose-response relationship is considered to be a characteristic feature of radiation carcinogenesis (we’ll talk about hormesis some other time).
The absolute risk to smokers and recent ex-smokers was much greater than to lifelong non-smokers. In the absence of other causes of death, the absolute risks of lung cancer by age 75 years at usual radon concentrations of 0, 100, and 400 Bq/m3 (0, 2.7 and 10.8 pCi/L for we Americans) would be about 0.4%, 0.5%, and 0.7%, respectively, for lifelong non-smokers, and about 25 times greater (10%, 12%, and 16%) for cigarette smokers. Radon in the home accounts for about 9% of deaths from lung cancer and about 2% of all deaths from cancer in Europe. The authors note that the findings of this analysis were consistent with comparable studies in North America and China.
More information on radon can be found here, including U.S. Environmental Protection Agency’s (EPA) risk assessment on radon, and a neat radon hazard map of the U.S.
There are some interesting asides from this issue. First, when figuring out priorities for risk reduction, radon, or other volatile indoor air contaminants such as PCE, seem to be less “popular” than cleaning up volatile organic compounds (VOCs) as groundwater contaminants or outdoor toxic air pollutants. Indeed, one of the hottest issues in managing hazardous waste sites is indoor vapor intrusion of VOCs from soil or groundwater contamination. Vapor intrusion gains a lot of press, because it has protagonists, controversy and a narrative. It’s hard to find someone else to blame for indoor radon, and harder to blame ourselves for PCE exposure from bringing dry-cleaned clothes home. Although, what would be a good story is why efforts to commercialize “green” alternatives to PCE for dry-cleaning are so feeble.
Second, it shows how disconnected are the efforts to manage the various forms of environmental risks. There appears to be as yet no meaningful effort to measure and rank workplace exposure to carcinogens, indoor air contaminants such as radon, dietary carcinogens, global pollutants (POPs), hazardous waste contaminants, toxic air pollutants, etc., even though your body doesn’t particularly care where the chemical insult is coming from. All of these risks have their own constituencies jockeying for precedence and their own regulatory frameworks that are often inconsistent and conflicting. EPA’s and OSHA’s disparate risk management philosophies for carcinogens represent one glaring example of this problem. EPA has made a stab at developing a framework for performing cumulative risk assessments, which is a step in the right direction. However, it seems to largely sit on the shelf, with little or no movement to translate it into a usable regulatory framework, and no incentive to do so under the Bush administration.
3 Comments:
This was an excellent summary. Of course the radon risk is well-known and the source sometimes hard to mitigate, unlike your PCE example. I think I would take issue with your reasoning there, however, as I don't think most consumers are very aware of the PCE hazard from dry-cleaning (which is quite variable for the consumer). The Halogenated Solvents Industry Association (HSIA) has been very effective in keeping this solvent in commerical use despite the fact that there are good alternatives (as you link). I have been told by some drycleaners who use alternatives (like the best solvent of all, water) that they don't publicize it for fear the public will think it doesn't work as well. Also many drycleaning establishments are small mom and pop stores who themselves have little appreciation for the health consequences of PCE.
Because of its widespread use and improper disposal, PCE is one of the most prevalent contaminants in US groundwater, hence the concern with vapor intrusion in homes. In those cases it is likely to be the major source of PCE exposure (assuming no occupational exposure).
PCE (and TCE) should be rapidly phased out of commercial use. Safer processes are available to do the same things. The HSIA and its member companies have been successful in keeping the EPA from seriously taking on PCE. Our environmental watchdog is more of an environmental lapdog.
I suspect that most American's don't realize how effectively they are shut out of environmental decison-making (such as phasing out PCE and TCE use) by the combination of regulators and industry groups. As much as I have heard about public participation and the "triple bottom line", these actually have little day-to-day impact on regulatory decision-making.
I'm not a radon mitigation specialist, but what I'm told is that installation of mitigation systems on residences is fairly routine and reasonably priced, which is why I'm surprised they aren't more widely used. I've learned this because radon mitigation is also used to control vapor intrusion pathways for residences overlying TCE and PCE contamination in soil or groundwater.
VI a significant exposure source in localized areas (much of the work I do these days consists of VI investigations), however, microenvironment studies, such as the TEAM study have shown the importance of localized sources for personal exposure, such as dry-cleaned clothes and PCE. Of course, occupational PCE exposures are still more significant.
The point I closed with was the critical one - these exposures are cumulative, and need to be addressed in an integrated manner. A radon mitigation system would reduce risks from radon as well as volatile groundwater contaminants. A PCE risk reduction strategy needs to address groundwater contaminants as well as phasing out PCE uses. As yet, the regulatory framework does not treat these risks as cumulative.
Of course, a PCE phase-out would be a win for everyone, that is except for the HSIA members.
I accept your experience in these matters. I note that in Massachusetts efforts by the Toxic Use Reduction Institute (funded by the state) has led to the voluntary reduction of TCE use by industry of about 90%. PCE has not had a comparable reduction, unfortunately.
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