United States (again)

"Studies of populations chronically exposed to low-level radiation, such as those residing in regions of elevated natural radiation, have not shown consistent or conclusive evidence of an associated increase in the risk of cancer." [This statement conflicts with the conclusions of the report.] [From the Executive Summary, Carcinogenic Effects. Biological Effects of Ionizing Radiation Committee (BEIR) of the National Academy of Science, Report V, 1990, p. 5.

In a study of 900,000 U.S. residents with various levels of radium in water supplies, the BEIR was confounded by finding more bone cancer in Chicago - with only 1 mBq/l - than in the areas where the level exceeded 110 mBq/l. [From BEIR IV, Health Risks of Radon and Other Deposited Alpha Emitters, National Academy Press, Washington, D.C., 1988.]

A multivariant examination of forty-three urban populations of the United States showed a statistically significant negative correlation [more radiation, less cancer] between total cancer mortality and background levels of ionizing radiation. [Hickey, R.J., et al. Low level ionizing radiation and human mortality; multi-regional epidemiological studies. Health Physics, 40, 625, 1981.]

They Lived to Tell About It

The A-bomb survivors are living longer than the controls despite the 400 radiation-induced cancer deaths. - Professor John Cameron, University of Wisconsin School of Medicine

On the morning of August 6, 1945, Hiroshima, Japan, exploded into the first and largest high-level radiation test laboratory in the world. Three days later, because skies over the Kokura Arsenal on the north coast of Kyushu were overcast, Nagasaki became the second. Most victims died from the intense heat or the blast effect, but hundreds were to succumb later to effects of radiation - while thousands of survivors were instantaneously hit with trillions of neutrons and gamma rays.

In the early 1950s, studies of the effects of radiation were needed by the U.S. military and civilian defense authorities because of the threat of nuclear war with the Soviet Union. A joint U.S.-Japan program was initiated to analyze radiation effects on the populations.

Doses to survivors were estimated by their locations at the time of the blasts, with a "health handbook" being kept by each exposed person in which his medical history was meticulously recorded. Of great importance were the potential mutagenic effects (the original concern over "nuclear monsters"), since it was well known that radiation had a mutational effect on fruit flies and other lower organisms and, therefore, was expected to affect humans at high levels. No such consequences were ever found. In fact, not only were the offspring of survivors not negatively affected, but there were benefits that we might now attribute to a hormetic effect of the radiation.

But the primary concern was cancer. Earlier studies of 15,000 people in Great Britain, who had been exposed to upwards of 400 rems in treatment of spinal ailments, had shown a link between high levels of radiation and cancer in a significant percentage of the exposed. The Japanese study, among others, would further refine this relationship to be a 0.018% increase for every absorbed rem. (This is added to the approximately 20% risk of cancer for the average American.) For example a survivor who suffered radiation sickness from an initial pulse of 100 rems would have his or her chance of cancer increased from about 17% to 18.8%. (Remember, this is a dose equal to four times the average lifetime exposure for U.S. residents, occurring in a few seconds or minutes.)

Indeed, there were several hundred excess cancer deaths in Japan among those who received high doses of radiation. [RERF statistics estimate 339 excess cancer deaths (out of 4,687 total cancer deaths) through 1990. John Cameron estimates the projected total at 400.]

And because of the much greater number of persons receiving lesser amounts (typically equivalent to a lifetime of background radiation absorbed in a few seconds) it was feared, on the basis of the newly adopted Linear No-Threshold and collective dose theories, that these survivors were in for even more tragedy. Leukemia would be kicking in in about three to ten years after exposure, with the other cancers occurring within twenty or, at most, thirty years.

But a funny thing happened on the way to the graveyard: The bomb survivors were outliving their unexposed peers. As Dr. Sohei Kondo put it in his 1993 book entitled Health Effects of Low-Level Radiation, "The age-specific rates of death from all causes (observed deaths) [for exposed survivors] in people over sixty years of age were significantly lower than those for people without the health handbook (expected deaths) presumed to be unexposed." [Mentioned earlier in regard to his apoptosis research, Dr. Kondo is professor emeritus of biology, Osaka University and senior researcher, Atomic Energy Research Institute, also in Osaka.] [Kinki University Press, Osaka, 1993, and Medical Physics Publishing, Madison, Wisconsin, 1993. Any serious researcher must have this book. It is the definitive work on the Japanese atomic disaster.]

In short, the exposed had a significantly lower death rate than those who were fortunately out of town for the war-ending fireworks.

Figure 13 demonstrates the classic hormesis-curve shape for death rates of bomb survivors as a function of absorbed dose. [Notes for Figure 13: Death Rates of A-Bomb Survivors in Hiroshima and Nagasaki (1950-85) 1. "Relative Risk is the number of people who have died in a particular exposed cohort compared with (divided by) deaths in a similar group of the general population. 2. These data are for male survivors. 3. Only the acute dose resulting from the blast radiation is considered; external and internal doses by fission products, which would enhance the data, are not included. Source: Mine, M. Okumura, Y., Ichimara, M., Nakamura, T., and Kondo, S. Apparently beneficial effect of low to intermediate doses of A-bomb radiation on human life span. International Journal of Radiation Biology, 58:1035, 1990.]

Up to approximately 70 rems (or cSv), the death rate for exposed persons is lower than unexposed. [Mine et al. Apparently beneficial effect of low to intermediate doses of A-bomb radiation on human life span. International Journal of Radiation Biology, 58:1035, 1990.]

(Not shown on this graph, the relative risk for 325 rems is 1.28.) Note that these data were from forty years after Hiroshima and Nagasaki - concluding well past the established latency time for cancer onset from effects of radiation.

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.