How I Screwed Up My Radon Test

OK, I’m stupid.

Here are the details. I dutifully followed the directions (mostly) on the Pro-Lab radon testing kit. I placed the two detector-vials on a flat surface in my basement, more than 2 feet above floor and 3 feet away from walls. After the prescribed 96-hour testing period, I capped the detectors, and then carefully put them in my desk drawer for later mailing to Pro-Lab. The latter action was my screw up. I should have immediately mailed them to Pro-Lab for reading. By sticking the detectors in my desk I demonstrated a fundamental misunderstanding of the nature of the thing I was testing for.

This is as good an entree as any to the properties of radon.

As every real estate agent has heard repeatedly, radon is a colorless, odorless, naturally-occurring gas. It is the heaviest of the noble gases, which are a group of elements that don’t easily react with other elements. Helium, neon, and argon are the better known noble gases that we encounter in our daily lives. Radon is also radioactive. It is this property in combination with its inertness as a noble gas that makes it such a troublemaker.

Naturally occurring uranium in the ground is the ultimate source of radon. Uranium-238, the most common isotope, is weakly radioactive. Over the course of time—a long time—it decays to lead-206. I say “a long time” because uranium-238’s half-life, or the time it takes half the radioactive atoms in a sample to decay, is 4.5 billion years. By the way the much rarer isotope, uranium-235, in a highly enriched form, was the explosive (fissile) material for the “Little Boy” atomic bomb dropped on Hiroshima.

As you can see on the chart above, the chain of radioactive decay from uranium-238 to lead-206, a process known as transmutation, is quite long. Radon sits in the middle, more or less. Under normal conditions the elements above radon in this chain are solids, and, as such, stays fixed in the soil. However, when radium-226 decays to radon-222 things change. Radon, as reported above, is a gas, and, more specifically, a noble gas, a gas that doesn’t chemically interact (or bond) easily. It’s a free spirit, so to speak, and migrates to the earth’s surface through pores in rock/soil and ground water. For reasons I will delve into later, radon tends to concentrate in the basement levels of buildings.

Radon is highly radioactive. Its half-life is 3.8 days. It decays by emitting an alpha particle to become polonium-218. Polonium-218 decays in similar fashion to lead-214 (radioactive). Lead-214 emits a beta particle to form bismuth-214, et cetera. Each of the successive progeny of radon emits either an alpha or beta particle as the decay chain continues towards lead-206. Both types of radiation pose health hazards.

If radon was the last stage before non-radioactive lead-206, it probably wouldn’t pose a serious environmental issue. Although we might inhale it, we would likely exhale it in the next breath. In any case the next element in the decay chain would be the non-radioactive lead-206. While lead is an environmental hazard, the concentration we’re talking about here is extremely small and wouldn’t by itself create much of a hazard (lead from old paint is a completely different story).

But radon isn’t the penultimate decay stage. The elements it transmutes into are chemically reactive solids as opposed to inert gases. Polonium-218, lead-214, bismuth-210, and the rest of the radioactive progeny, are likely to attach themselves to dust particles and tobacco smoke, which, in turn, become lodged in lung tissue, where radioactive emissions in the form of alpha and beta particles can do real damage.

Now back to my original act of gross stupidity...the purpose of the detector-vials that I left open for 96 hours in my basement was to collect a representative sample of radon, whose radioactivity then has to be measured by a lab. Problem is the radon within the capped detector-vials doesn’t stay “radon.” It decays into polonium, lead, bismuth, etc., each of which has its own characteristic half-life, so when the lab measures radioactivity a few days after the vials are capped and mailed, it actually measures the radioactivity of the mixture of elements created by radon’s decay, each of whose concentration is constantly changing. Obviously there’s a time relationship between radioactivity and the original radon concentration, but I suspect the longer you wait, the more sources of error creep into the reading. As it costs $30 to read my radon test, I will opt to repeat it rather than risk a bad reading because I delayed shipping the test vials to the lab.

Radon 101

With this post I start to explore the subject of radon. The focus of my line of inquiry is to improve understanding of the nature and hazard presented by radon gas in residential properties.

For anyone who sells real estate in central Pennsylvania radon is one of several common inspection issues. To a great extent the testing and subsequent remediation of radon in homes has become routine.

When I started selling real estate in 1995 the EPA had not yet published an “actionable level” for radon. Today the actionable level is 4 pCi/L (picocuries per liter), meaning the EPA recommends that you install a radon mitigation system for home radon levels at or above 4 pCi/L.

In 1995 we relied on a chart in the EPA radon pamphlet that estimated the increased risk of lung cancer based on the radon reading in the home and length of exposure, i.e., risk vs dosage. Buyers and sellers would negotiate over the actionable level. It wasn’t unusual to write a sales agreement specifying 10 pCi/L, 12 pCi/L, or even 20 pCi/L as the level above which the seller would install a radon system. In essence the parties were negotiating risk.

This seemed like a grown-up way to deal with this type of environmental hazard. Even at 20 pCi/L the actual risk of lung cancer is still small. For many homebuyers this incremental risk is acceptable in the context of all the other risks that we are exposed to in our daily lives. Unfortunately, as far as I am concerned, the risk vs dosage chart disappeared after the EPA published new guidelines that included its recommendation that 4 pCi/L was the actionable level. This took away a useful tool for evaluating risk. It made radon as a real estate issue cut & dry—above 4 pCi/L the seller installs a system. It almost certainly resulted in more radon systems being installed. And, not inconsequentially, it increased the cost of the typical real estate transaction.

The EPA has made the reduction of indoor radon a matter of public policy and effectively substituted its judgement of acceptable risk for the homeowner's.

Facts & figures…in Cumberland and Dauphin counties, where I live and work, the average radon levels are, respectively, 11.7 pCi/L and 13.9 pCi/L (apparently the geology of southcentral PA makes high radon likely). Over 60% of homes in these counties likely exceed 4 pCi/L radon level in the basement.

Radon testing and a radon system cost about $850 ($100 test + $750 system). In 2009 the median-priced house in my multi-list area was $162,000. Therefore radon remediation adds about ½% to the typical home purchase. This is not insignificant. Certainly it is not unreasonable to ask whether the benefit of reducing the radon concentration below 4 pCi/L is always worth this cost. What if the original reading is 4.5 pCi/L? What if the new owners don’t intend to spend much time in the basement?

There is a lot of documentation about radon available online—both consumer-oriented and academic. The EPA maintains an extensive web site, as does the Pennsylvania Department of Environmental Protection. While 4 pCi/L is the de facto standard for safe indoor air quality—it’s pre-printed on the Pennsylvania Association of Realtors (PAR) sales agreement—the EPA actually recommends homeowners ”consider” installing a radon system when the radon reading is between 2 and 4 pCi/L (what does “consider” mean here? ). By this strict standard 80% of homes in southcentral PA need a radon system. For reference the average outdoor reading is 0.4 pCi/L.

As it happens I don’t know the radon level in my own house. Several years ago I finished the basement. I spend a lot of time down there, so it’s a probably a good idea I find out (I don’t disagree with the EPA’s recommendation to test your house). To this purpose I bought a testing kit for about $7 at Home Depot. The test kit is manufactured by Pro-Lab. While I intend to discuss testing in a separate post, for the record this particular kit is a passive, short-term test using liquid scintillation technology. Tomorrow I will cap the two detectors that I placed in the basement and send them to Pro-Lab for reading.