A Very Short History of Radiation Hormesis

The extremely tall people on Niue Island (averaging height 6'6") receive 10 times more radiation from the soil than the world average. [Eugaster, Subradiation experiments concerning the concept of the natural radiation background, Aerospace Medicine, 35, 524, 1964.]

Why, you might logically ask, was the hormesis phenomenon not discovered until some eighty years after Roentgen, Becquerel, and the Curies made their contributions to radiation science? Why was there not an earlier Professor Luckey? [Professor Luckey is credited with coining the term "Radiation Hormesis" from his 1981 book Hormesis with Ionizing Radiation.]

Actually there was of sorts, and he, oddly enough, was also a professor at the University of Missouri. In 1896, Professor W. Shrader inoculated guinea pigs with the diphtheria bacillus. [Shrader, W. Experiments with X-rays upon germs. Electrical Engineering, 22, 170, 1896.]

The group exposed to X-rays prior to inoculation survived; the unexposed cohort died within twenty-four hours. Shrader, in the same series of experiments, was apparently the first person to discover that "Roentgen Rays" could be used to kill germs.

During the early twentieth century, radiation was used for a variety of experimental therapies, but the doses were generally far above hormetic levels and may well have caused more harm than good. Patent medicines such as "Radithor" (more on this in chapter 24) were popular, with single doses having nearly a million times the daily radium intake allowed by current government regulators. Hundreds of thousands of vials of elixirs were consumed without any widespread harm occurring and with a sizable number of "miracle cures" being reported. Few controls, however, were employed to scientifically assess the actual worth of the treatments leaving one to believe that most of these "cures" may have been either the product of advertising hype or a placebo effect.

Medical research wasn't the big draw for world-class physicists. We might remember that in the early days of radiation experimentation important discoveries were being made almost daily, while health considerations - except, possibly, for the annoying, minor and superficial skin "beta burns" - were considered to be of no consequence. The doses of radiation these unprotected experimenters received are estimated to exceed by thousands of times the maximums under which today's nuclear industry workers are allowed to continue on the job.

Madame Curie, discoverer of both polonium and radium, offers a good example of the "non-standards" of the day. [In 1516, a silver lode was discovered in St. Joachim's Dale (Joachimsthal), which was - naturally - confiscated by the government of Count von Schlick. Coins minted from this mine were known as Joachimsthalers, which (for obvious reasons) came to be known as thalers - in English, dollars. It was from this mine that the Curies obtained pitchblende - an ore rich in uranium and its daughters, radium and polonium.]

It is anecdotal that whenever Marie Sklodowska [in case you were curious why she named her first discovery for Poland] Curie walked into a room, electroscopes immediately discharged. [Gold is so malleable that it can be pressed into leaves less than 1/10,000 of an inch thick. If you hang two pieces of leaf in an air-filled jar, with provision to charge both - you have an electroscope. Charging the leaves with the same polarity causes them to "push apart" and, because they are so light, the electrostatic "pushing" force exceeds the gravitational force that would cause them to "droop" into a vertical position. Such devices were used to assay the content of uranium ores - not from the non-penetrating alpha radiation of the uranium, but from the accumulated daughters of which the gamma ray emitting radium was a significant component. Air, when ionized, is a conductor that discharged the electroscope at a rate proportional to the amount of ionizing radiation present.]

It is almost certain that she had an enormous lung burden of radium - the element she was extracting from uranium ore - which took quite a bit of patience, since there are only about 0.003 grams of radium per ton of ore. Madam Curie died almost certainly from the effects of long-term and extremely high doses of radiation. Yet, at age sixty-six, she still exceeded by ten years the life expectancy of her day.

Later in the century, the subject of hormesis would have doubtlessly been trifling compared to other matters. From August 1939 - when a letter from Albert Einstein was delivered to Franklin Roosevelt recommending the development of an atomic bomb - until the end of World War II, the focus of virtually the entire nulcear physics community became the Manhattan project. (This venture, equivalent in size to the total automotive industry at that time, is described in fascinating detail in The Making of the Atomic Bomb [Richard Rhodes, Simon & Schuster, New York, 1986].)

Certainly the scientists were aware of potential dangers from radiation - especially the highly penetrating neutrons from "atomic piles" - but these risks were minimal, compared with the reality of thousands of deaths from the war every day. Concerns about low-level radiation - either harmful or beneficial - weren't even on the radar scope.

Interestingly, the only health physics experiment I've ever come across that occurred during the Manhattan project was indicative of radiation hormesis:

"In 1943, a group of [radiation scientists] on the Manhattan District Project were worried about the unknown toxicity of uranium. They grew a colony of rats in an atmosphere laden with sufficient uranium dust to kill them fast (the Manhattan Project didn't have time for fancy radiobiologists). As a control, a similar colony breathed clean air. After several months, nothing happened, but eventually the rats lived out their natural lifespans, with one surprise: the first health physics experiment demonstrated that rats who breathed uranium dust lived longer and were happier (i.e., had a better reproductive history) than normal rats. Not a tumor in the bunch." [From a letter by Marshall Brucer, M.D. to Time magazine (from the files of Petr Beckmann).]

During this period there are reports of relatively minor medical experimentation to determine the effect of ionizing radiation on the healing of wounds. The exposure levels, however, were high (1 Gy or 100 rem) - suggesting its use as a bactericide. The availability of antibiotics in 1942, and the post-Hiroshima bombing concerns over high-level dangers, caused a loss of interest in research of this nature by the end of World War II.

After the war, the Japanese cities of Hiroshima and Nagasaki became laboratories for research on the effects of radiation on humans. But the focal point was on the high-dose subjects - in particular on their excess cancers and the possible mutational effects on children. When low-dose victims showed beneficial health effects, the data were ignored as being anomalies (a fancy scientific words for "it doesn't fit in with what we're expecting").

Luckey addresses this subject:

"Statistical analysis of observed data was missing in many reports of experiments involving low doses of ionizing radiation. Most of the reports simply indicated that an unexpected phenomenon had been observed, but the researchers failed to pursue it systematically... Any unexpected result was rejected by the 95% rule: One experiment in each twenty was accepted as a variant. Closer inspection showed this was a consistent result; it usually occurred in the group exposed to the least radiation, the only one in the hormetic range. Hormetic data were ignored because they did not fit the models of the zero thesis." [Radiation Hormesis, p. 45.]

When someone really writes a history of radiation hormesis, the first "official" recognition of the phenomenon will go to the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) in a 1994 report "Adaptive Responses to Radiation in Cells and Organisms":

"Manifestations of the adaptation described in mammals after exposure to low doses of radiation include accelerated growth rate in the young, increase in reproductive ability, extended life-span, stimulatory effects on the immune system, and a lower than expected incidence of spontaneous tumors."

You might want to read that again.

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.

100 Picocuries - That's a Lot! (Or is it?)

Since most Americans have no idea what danger might lurk in a glass of water with 200 picocuries per liter, we are at the mercy of those who might use this lack of knowledge to their political advantage.

Imagine sitting in a chair three feet away from a gram of an unknown radioactive metal, about the size of a penny, on the floor in front of you. Should you be concerned? I know I would be - at least until I knew more about what it was. Obviously we would be interested in what type of radiation was being emitted. It if were alpha or beta particles, there would be no problem as the 3 feet of air would stop any significant amount. But what if it were gamma rays? Then we would want to know just how "active" the source was - with the activity of a radioactive source being measured in the number of atoms that disintegrate every second.

Let's suppose our one gram of material is radium, specifically 226Ra. Would you care to guess the number of disintegrations per second? A mere 37,000,000,000 (37 billion)! This, by the way, is the number of disintegrations defined as 1 curie, or 1 Ci, since the curie is defined as the activity of one gram of radium. You needn't run away, but you might not want to hang around. If it were one gram of cesium 134, a quick exit would be advisable. [Cesium 134 is a gamma and beta emitter that has about fifteen times the activity of the Goian cesium 137, which is only a beta emitter.]

The curie, a United States (USA) unit, is still in common use but is gradually being replaced by the International Standard (SI) becquerel or Bq, which is defined as one disintegration per second. Obviously, then, 1 curie is equal to 37 billion Bq - not exactly the easiest conversion constant to work with, especially when you have to go the other way: 1 Bq = 2.7 x 10^-11 Ci = 27 pCi.

A few elements of interest and their specific activities - that is, their activity per gram - are given in Table 5.

Table 5 – Specific Activities of Selected Elements
Element	Curies	Becquerels	Half-Life
Thorium 232	0.000000166	4,316	14.05 billion years
Uranium 238	0.000000333	12,300	4.47 billion years
Potassium 40	0.00000722	267,200	1.27 billion years
Radium 226	1	37 billion	1,620 years
Strontium 90	139	5,143 billion	28.8 years
Cesium 134	1,290	47,900 billion	2.06 years
Iodine 131	124,000	4,588 trillion	8.04 days
Tellurium 133	113,000,000	4,200,000 trillion	12.4 minutes

Note that the half-life of the low activity 238U is very long - 4.5 billion years, while one-half the very active 131I isotope is gone in 8.04 days. We would expect this, since there are a finite number of atoms in a gram of any substance, and if the rate of decay (i.e., the activity) is high, it will take less time for the substance to lose its radioactivity. This is verified by the very low relative activity of the primordial radionuclides such as thorium, uranium and potassium, which have extremely long half-lives since these were presumably created at the same time as the Earth - estimated by most cosmologists as some 4.6 billion years ago. The shorter half-life isotopes - say a mere few million years or so - are long gone, although some are being replaced by decay products of the low activity elements.

Units of Measurement

There's just no way to avoid the next subject, because, unless you get at least semi-comfortable with certain units of measurement, most of the book is not going to make much sense. We'll start by looking at a little shorthand "trick" used by lazy scientists and engineers.

One curie of radioactivity is a sizable amount. Many times a much smaller unit is needed especially when referring to amounts contained in milk, water supplies and other common products. We could write this unit as 0.000000000001 curie, or 1 x 10^-12 curie or spell it out as one-trillionth of a cure. But that's time consuming and a heck of a lot of trouble when you're writing it fifty times a day. The shorthand version for a trillionth of a curie is generally written as 1 pCi - or even 1 pC - with the "p" standing for pico and pCi referred to as a picocurie.

Similarly, 1 becquerel is a very tiny amount of activity amounting to one radioactive disintegration per second, while we often are interested in millions or billions of decays for a single gram of a radioactive isotope. So instead of a million Bq or 10^6Bq, it is written as MBq, with the M standing for mega.

Table 4 shows prefixes and their corresponding powers of ten. Since I find that use of so many prefixes makes comparisons difficult, I'll be limiting them to as few as possible. However, others will occur in quotations and in literature you might run across.

Table 4 - International Standard (SI) Prefixes
Quintillion = 10^18 = exa = E
Quadrillion = 10^15 = peta = P
Trillion = 10^12 = tera = T
Billion = 10^9 = giga = G
Million = 10^6 = mega = M
Thousand = 10^3 = kilo = k
Hundred = 10^2 = hecto = h
Ten = 10^1 = deka = da
Tenth = 10^-1 = deci = d
Hundredth = 10^-2 = centi = c
Thousandth = 10^-3 = milli = m
Millionth = 10^-6 = micro = Greek letter mu
Billionth = 10^-9 = nano = n
Trillionth = 10^-12 = pico = p
Quadrillionth = 10^-15 = femto = f
Quintillionth = 10^-18 = atto = a

Well, we now know that radiation is caused by an atom suddenly going to pieces, but so far there is no clue as to why these particles are dangerous - if indeed they really are. So let's move on to some quantitative information about the effect of these atomic disintegrations.