Radon: Scourge or Blessing for Mankind?

Government was tightening industrial radioactive emission standards to ridiculously low levels, while demanding that homeowners modify their homes to the point where radon doses to the average citizen were hundreds of times greater than the levels dictated to nuclear workers.

Radon is the heaviest of the "noble gases," so named because it - like its cousins neon, argon, krypton, and xenon - does not react with other elements to form compounds. It is radon's "nobility" that minimizes its effects on the body, since it is mostly a transient that is breathed in and then expelled without any chemical reaction taking place. When radon decays in the body, however, it spawns a series of short half-life progeny that are not only chemically reactive with tissue, but are - as we would suspect from their half-lives - also highly radioactive.

[When uranium decays (which isn't very often with a half-life of 4.5 billion years), the products of the decay go through four more stages (taking a couple of million years) until radium is formed. With a half-life of 1,600 years, radium 226 decays into radon gas with a half-life of 3.8 days. The daughters of radon are polonium 218, lead 214, bismuth 214, polonium 214 - and a couple of others. The aforementioned have very short half-lives and are therefore highly radioactive.]

Hazard to Miners?

For years, radon has been thought to be a hazard to miners, and a special confusing unit of activity - the Working Level (WL) - was derived to measure the danger. [One WL is the activity of air containing 100 pCi (3.7 Bq) of radon in equilibrium with its daughters (which, by the way, virtually never happens in the real world) per liter of air. For an approximation, a Working Level Month (WLM) is equivalent to a one-time whole body dose of about 300 mrem (0.3 cGy).]

Recently, however, as evidence of radiation hormesis has emerged, the jury is back out to deliberate a reconsideration of radon's guilt. It is now recognized that other carcinogens - in particular, the particulates suspended in the air of all mines and, more recently, the fumes from diesel engines - were present, but never considered. Radon was assumed to be the carcinogenic culprit, a theory that appears now to be based on flimsy circumstantial and anecdotal evidence.

A related re-evaluation of lung cancer in the Joachimsthal mining community [a famous mine in Czechoslovakia] noted that victims were invariably "pensioners," i.e. miners (not their unexposed, above-ground cohorts) who had made it to a retirement age, which was about ten years longer than their life expectancy. One might easily speculate that the cancer was caused by microscopic dust lodged in the lungs, and the miners' long lives a beneficial product of radon gas. [One of Europe's most famous health spas is Bad Gastein near Salzburg, Austria, which advertises "air with the highest radon content in Europe." The activity of its water is noted in Table 6, in this blog's entry on Monday, January 25, "Specific Activities."]

There has also been a piece of the puzzle right under our noses.

Radon gives its dose of mixed radiation primarily to the bronchial epithelium (fancy scientific words for "windpipe"), hence one would expect cancers caused by radon to be concentrated in this area. Au contraire! The miners' cancers are deep in the lungs [Nobel Laureate Rosalyn Yalow, Radiation and Society, Interdisciplinary Science Reviews, 16, 4, 1991], similar to the cancers caused by the South African amphibole-type asbestos [not to be confused with the common, domestic serpentine type of asbestos, which has not been shown to cause disease], used in ships because of its resistance to brine, acids, and oils.

It is difficult not to see the parallel between non-degradable asbestos fibers in the lungs and non-soluble silica particulates found in most mining environments.

Hormesis U.: A Review

Before leaving dear old Hormesis U., here is a short review to see if you've got a handle on the curriculum. You should know...

• Elements are identified by the number of protons in the nucleus (atomic number).
• Isotopes of elements have different numbers of neutrons (n + p = atomic weight).
• Atoms of some isotopes are stable, while others are radioactive and, over time, will disintegrate (decay) into other elements of a lower atomic number.
• Alpha and beta particles have a short range (a few inches and a few feet respectively).
• Gamma rays and X-rays can penetrate several inches of steel or feet of concrete.
• The half-life of a radioactive isotope is the time it takes half of the original amount to decay; after thirty half-lives the original amount is considered to be gone.
• The longer the half-life, the lower the activity of an isotope.
• A curie is 37 billion becquerels.
• A pCi is a picocurie and is equal to one-trillionth (10^-12) of a curie.
• Absorbed doses of radiation are measured in rads or grays; 100 rads equal 1 gray.
• Biological doses are measured in rems or sieverts; 100 rems equal 1 sievert.
• The absorbed dose and the biological dose are the same for gamma and X-rays. 
• A fatal acute dose is about 4 sieverts or 400 rems (50% fatalities in thirty days) when received in a relatively short time (a few days or less).
• Radiation sickness occurs at about 1 sievert or 100 rems (50% of those exposed over a short time). 
• Doses below 1 sievert or 100 rems (100,000 millirems) have no immediate biologic effects but are generally thought to increase the risk of cancer in the future.

Thanks for your attendance at Hormesis U. No doubt you'll find the rest of the information on radiation hormesis much more understandable now than when you were a mere freshman. Oh, and be sure to send in your contribution to the Alumni Fund.

Waste 'n' Time

Uh, oh. I'm afraid I've kind of painted myself into a corner here by minimizing the "problem" of nuclear wastes. If I give it short shrift, it will appear that I'm avoiding the subject. On the other hand, while the matter of nuclear wastes is somewhat afield from our general topic, there is a connection that might be of interest.

The only danger even attributed to nuclear wastes is that of causing cancer in future generations that are too stupid not to bit into a glassified chunk of power-plant waste. As we shall see, there is a threshold below which - even for those future glass munchers - there is no fear of increased cancer risk. But even if there weren't such a threshold, there are a number of issues regarding nuclear wastes that have been ignored in the media's misreporting of the subject that you should know about.

• More than 95% of the long half-life "waste" in nuclear fuel is not waste at all, but uranium and plutonium that may be reprocessed into fresh fuel assemblies. Most other industrialized nations do just this, as our government promised the utilities, but the Carter administration reneged on the agreement. (More about this later.)
• Among the "wastes" that anti-nuclear activists are eager to bury are valuable medical radionuclides that are produced at high cost in specialty reactors. As in the case of the reprocessable fuel, the baby is being thrown out with the bath water.
• The most sensible way to eliminate the unusable wastes from reprocessed fuel (which about to about 1% of their volume) is to dilute it a few millionfold and pour it down the drain, or to dump it into ocean abysses where there is no biological activity. Man's puny efforts at creating radionuclide wastes are dwarfed by the enormous amounts existing in nature. There are, for example, 36 billion curies of rubidium 87 and 380 billion curies of potassium 40 in the oceans, almost all of which will still be there when the few million curies of man's wastes have long since decayed to undetectable amounts. 

Why then, you may ask, are there hundreds or thousands of government- (read "taxpayer-") supported scientists busy writing reports on Yucca Mountain? I suggest there may be three reasons: (1) they don't know - or, more than likely, don't care - that low-level radiation is not harmful; (2) it beats having to get a real job; or (3) grants to study the mating habits of the Zambian sweat bee have already been taken.

The Concept of Half-Life

When an atom of a radioactive isotope decays, two things happen. First, energy is given off from the conversion of mass to energy according to Einstein's famous formula, E = mc2. (The newly formed atom and any emitted particles are always lighter than the original atom - and it is this difference in mass that is converted to energy.) Simultaneously the original element is transmuted to an element with a lower atomic number. The secondary element is called the daughter (or progeny) of the first; it can be either a stable isotope or can itself be radioactive and go through a radioactive decay. Eventually, however, the original element decays to a stable form, and no more energy is given off.

One can deduce from this that a radioactive element has a finite amount of energy to emit. Either it emits this energy very rapidly - in which case the radiation is intense and short-lived - or slowly, which would logically result in a relatively low radiation output. You can't have it both ways - a serious problem in nuclear medicine, as some of the intensely emitting therapeutic isotopes cannot be stored for more than a day.

Half-life is the time in which half the initial number of radioactive atoms decay.

If you stop to think about this phenomena, it's difficult not to have some kind of religious experience. Just think: In a tiny piece of (for example) uranium, one atom may have an internal "clock" that commands it to disintegrate in a second, while an adjacent atom in the same small sample will not decay for 13,500,000,000 years. How do they know then to "do their thing?" It's a problem that science may never solve.

Iodine 131 (used in thyroid diagnosis and ablation) has a half-life of about eight days. Thus if we started with a gram of 131I, after eight days and fifty-seven minutes we would have only a half-gram with the other half having been transmuted to stable tellurium. In another eight days we would have only one-fourth. After eighty days - ten half-lives - there is less than 1/1000 of the original specimen; beyond thirty half-lives, the isotope is considered to have disappeared. With its relatively short half-life, 131I is an intensely radioactive isotope.

Let's look for a moment at one of the most ubiquitous radioactive isotopes around: 238U, the primary uranium isotope making up 99.3% of the element's existence on Earth. [There are approximately 5,000 pounds of uranium in a volume of average soil one square mile by one foot deep.] It has a half-life of 4.5 billion years - approximately the same time estimated for Earth's age. Uranium takes 207,000,000,000 times as long to decay as 131I - with an inverse (longer time, less radiation) emission rate in approximately that proportion. Obviously it is a weak sister when it comes to being radioactive - which is fortunate for us or it would all be gone.

So, just in case I haven't made this clear, let me emphasize the following:

Short half-life = intense emitter, but gone after a short time

Long half-life = low activity and inherently not dangerous

Those who oppose nuclear technology want us to believe "Long half-life = dangerous," but it's just not true.

Understanding the concept of half-life and its relationship to intensity makes one realize that Barry Commoner - when he invokes references to a "nuclear priesthood watching over wastes for thousands of years" - is either terribly ignorant himself or is hoping that we are.