Friday, March 4, 2011

The Truth about Radon

Every few months the media reports on a toxic and mysterious radioactive gas: Radon. I have personally done quite a bit of research on radon and think I might be able to offer an unbiased and scientific perspective...at least I'll try.

Chemical Description of Radon

As with most things radioactive the first questions asked are: what is it and where did it come from? How does it behave in the environment and what does this mean for me and others (aka: is it dangerous)? These are the questions I will answer for radon and in a following post will look specifically at Port Hope, Ontario, a town where radon is a major concern.

What is it and where does it come from?


Radon, chemical symbol Rn, is an odourless, colourless radioactive gas. In order to understand where radon comes from we have to discuss radioactive decay and uranium. The source of radon is the radioactive decay of uranium. Uranium is a radioactive metal that occurs naturally in almost all places on Earth. The major isotope of uranium is 238U. 238U comprises 99% of all uranium isotopes and has a half life of 4.47 billion years. One of the daughter products produced by the decay of uranium is radon.

Decay Chain of 238U (CNSC)

As the diagram above shows, the decay of 238U occurs over many years.  There are several steps to be taken before radon can be produced. There are two modes of decay shown in the diagram above: alpha and beta. Alpha decay is the radioactive decay process that occurs when a nucleus of a radioactive element ejects two neutrons and two protons (a helium nucleus). Alpha particles have a low penetration ability, but are very ionizing. This means that they cannot travel very far or through objects, but they have a high enough energy to be dangerous to living things very near them. Ingesting or inhaling alpha emitters is dangerous to people however, merely being in their presence is not very dangerous as alpha particles cannot penetrate skin. The other type of radiation emitted during the decay of uranium is beta. Beta decay involves the emission of an electron from around the atom and is more penetrating than alpha radiation. Gamma radiation is also emitted at several steps in the uranium decay process.

As these alpha particles and electrons are emitted, the decay progresses and eventually radon is produced.

How does radon behave?

The meaning of the question how does radon behave encompasses several other questions such as how it travels and interacts in the environment and where in the environment is it produced?

Radon is a noble gas. This means it is very un-reactive in the environment and does not interact readily with other compounds or elements that are present around it. This means that in the environment radon travels all on its own and does not attach itself to other elements as a way to get around. This does not hinder the ability of radon to transfer from air to water and back again, in fact, radon transfers very readily. As a gas radon is present in the atmosphere, in the gas trapped between soil grains, it can even be found dissolved in water. In fact, the transport of radon in water is a relatively new field in radiochemistry studies and it has been applied to tracing the movement of groundwater as well as the transport of radioactive waste over short distances and time spans. Up until now I have been taking it for granted that radon is in the environment, but I have not explained how it gets there in the first place. Sure, we have gone into the radiochemistry and basic physics side of how radon is produced from uranium, but this doesn't really explain how radon ends up in our water or air.

Uranium is present ubiquitously throughout the environment. It is in soil, it is in rocks, it is in the oceans, it is even in lakes, rivers, streams and groundwater. Of course, as we know, the decay of uranium produces radon and since there is uranium in pretty much everything radon can be produced from all of these places. The amount of radon produced is proportional to the amount of uranium present.

Is radon dangerous?


The short answer to this question is: yes, radon is indeed dangerous. The why, how are we exposed and what can we do about it are a bit longer. As I mentioned above radon is an alpha emitter, meaning that it is only dangerous when we are in very close proximity to it or it has been ingested or inhaled. Furthermore, once in our body the radon will continue to decay and produce other daughter products such as 214Pb and 214Bi, which are highly radioactive and very dangerous. The unfortunate thing is that as a gas it is very easy for us to inhale radon making it extremely dangerous. In fact, it is estimated that 10% of lung cancer is caused by radon inhalation, making it an extremely serious threat to human health.

Radon accumulates in confined spaces such as in our houses or other buildings, particularly in basements as radon is heavier than air. In the open air there is no threat from radon, however, Canadians and many other cultures spend a great deal of their time inside, especially during winter (it is  -20 with wind chill as I write this). This is a major concern as all of this time spent indoors can greatly increase radon exposure.

So how does radon get indoors in the first place and why does it accumulate there? Firstly, radon can enter our homes through two main pathways. It can come in as a gas through holes in our basements, sump pumps, windows... essentially any place where our homes are connected to soil or rock. It can also enter in our water, especially if we use groundwater. Once radon is dissolved in water it needs to interact with air in order to leave the water so a perfect place is our taps, and showers which cause air-water interaction and force any radon dissolved in the water to de-gas.  The source of radon for our homes has to do with the type of soil and bedrock where we live. If there is lots of uranium in the soil or bedrock our homes are built on then there will be lots of radon produced as well.

How radon enters our homes
In Canada the Health Canada limit for radon in air is 200Bq/m^3. Here is a map showing where radon exceeds this level in Canada. 

Radon in Canada

OK, well that is it for now. I hope this article, which turned out not as brief as I originally intended, has been a bit informative. Here are some links for more info on radon. Feel free to ask me any questions you might have about radon though, especially if you live in Ontario. There will be future posts relating to radioactivity as it is kind of an interest of mine...weird, I know.

Links:

Health Canada:
http://www.hc-sc.gc.ca/ewh-semt/radiation/radon/index-eng.php
Canadian Nuclear Safety Commission:
http://www.nuclearsafety.gc.ca/pubs_catalogue/uploads/February-2011-Radon-and-Health-INFO-0813_e.pdf

Matt







6 comments:

  1. Radon mugged my father and left him to bleed out in the gutter...thankfully helium came along to lift his spirits! HEYO! Noble gas humor!

    Seriously though, I now feel more aware of the potential health risks associated with Radon. Good read.

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  2. Sweet! Thanks Martin. Love the noble gas humour...at least you didn't go with the obvious methane joke.

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    1. Methane jokes? I don't get it?!

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    2. I know methane is not really noble at all. In fact, it may be the most ignoble of all the gases. It can sure cause offense when present.

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