CONRAD WEIFFENBACH
We can expect questions from the public and radon professionals about the WHO recommendation for a 2.7 pCi/L (100 Bq/m3) radon reference level, so I’m working on an all-purpose answer.
That recommendation is in the Word Health Organization’s new Radon Handbook, which also says national radon reference levels should be within 100 – 300 Bq/m3. The US EPA has not changed our radon action level from 4.0 pCi/L (148 Bq/m3), and in Wisconsin we follow EPA. They provided support for the WHO radon efforts, are aware WHO is now recommending a reference level of 2.7 pCi/L, and know how that recommendation came about.
I can tell you that lowering our radon action level has been carefully considered in the past and rejected for a number of reasons. Questions about the risk below 4 pCi/L were not among those reasons. The risk was already assumed to be linear with radon exposure below 4 pCi/L, which is now further supported by the residential epidemiology results. In the EPA’s Technical Support Document for the 1992 Citizen’s Guide to Radon (160 pages, May 1992) the national cost /benefit ($ per lung cancer death prevented) was analyzed thoroughly for action levels of 2, 3, and 4 pCi/L. The analysis supported a 4 pCi/L action guideline better than 2 pCi/L. The cost of operating mitigation systems dominates the calculation, and I think some of the extrinsic factors included the ability to measure and mitigate effectively below 2 pCi/L. Nothing I know of has changed significantly for appropriate input assumptions since then.
In northern states like Wisconsin, for a typical house the year-average main-floor radon level is about 50% of the 2-day basement screening test (which is the closed-house measurement used in real-estate transfers.) In a typical house, a basement screening at 4.0 already represents a radon exposure of about 2 pCi/L for the residents – comparable to the 2.7 pCi/L reference level.
If we used basement screening tests with an action level of 2.7 pCi/L in Wisconsin, we’d presumably be finding the houses with main-floor year-averages above 1.3 pCi/L.
However, in Canada and the United Kingdom the action level is 5.4 pCi/L (200 Bq/m3), and applies in Canada for spaces occupied at least 4 hours per day (and “not unfinished basements”); while in the UK ”This Action Level refers to the annual average concentration in a home, so radon measurements are carried out with two detectors (in a bedroom and living room) over three months, to average out short-term fluctuations.”
In my opinion, there is already plenty of public skepticism about our radon program, and I respect it more than I do skepticism from scientists. I suspect that if we lowered the action level, the public response could be bad for radon businesses and for our public health enterprise.
What do you think? Please comment/respond below.
Sources:
a. WHO Radon Handbook, at www.who.int/ionizing_radiation/env/radon/en/index1.html
b. Technical Support Document to the 1992 Citizens Guide [EPA 400-R-92-011, May 1992] Copies can be ordered from EPA's National Center for Environmental Publications (NSCEP) www.epa.gov/nscep/)
c. www.epa.gov/radon/healthrisks.html
d. Canada: www.hc-sc.gc.ca/ewh-semt/radiation/radon/guidelines_lignes_directrice-eng.php
e. UK: www.hpa.org.uk/web/HPAweb&HPAwebStandard/HPAweb_C/1195733807197
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