Sensational assertions have been made that plutonium is the most hazardous substance known to mankind. But is that right? In fact, it is the greatest myth perpetuated about radiation. Plutonium is an a emitter, no different from radon or radium or any other radiation that undergoes a decay. However, plutonium is not nearly as radioactive as an equivalent mass of radon because it has a much longer half-life (24,100 years vs. 3.8 days) and radioactivity is inversely related to half-life. We are all exposed to varying levels of radon in our homes, and some homes have high enough levels to perhaps require mitigation when it is greater than 150 becquerels (radioactive decays per second) per cubic meter (see Chapter 8). Plutonium is primarily a hazard if it is attached to microscopic particles and is trapped in the lungs. Certainly it is true that plutonium could cause lung cancer if it were in a high enough concentration. This is exceedingly unlikely, though, even after the Chernobyl nuclear accident. So the claim of Caldicott that the plutonium released after Chernobyl could have killed everyone on earth is simply not credible. This does not mean that we should not respect the risks of exposure to radiation. It just means “watch out for publicity seeking sensationalists!”

The other route for plutonium exposure is from consumption through food or water, which could possibly be a hazard from nuclear waste disposal (see Chapter 9). As it turns out, though, plutonium is not readily absorbed by the gas­trointestinal tract. Only about 0.05% of plutonium is absorbed by the GI tract (37). Of the plutonium that is absorbed, it acts similarly to a toxic metal deposited about equally between the liver and the skeleton.

We actually do know something about the health risks of plutonium from workers at Los Alamos National Laboratory who worked on developing the atomic bomb and received higher accidental exposures than any other group of people. These people formed a group known as the UPPU (you pee plutonium) Club consisting of 26 members! George Voelz, who was later the director of the Los Alamos Health Division, was interviewed in 1995 about the group. According to him, of the original 26 members with high doses of plutonium measured in their urine in 1945, only 7 had died. “One was a lung cancer death, and two died of other causes but had lung cancer at the time of death. All three were heavy smokers. In fact 17 of the original 26 were smokers at the time. . . . There were three other deaths due to heart disease and one due to a car accident. According to the national mortality rate, one would have expected 16 deaths in this group by this time, so the mortality rate for the group is about 50% lower than the national average” (38). So much for the myth that plutonium is the most toxic substance on earth!

SUMMARY

The fundamental mechanisms of how radiation causes damage are well under­stood. X-rays and у rays interact through the photoelectric effect, the Compton effect, and pair production to knock electrons out of atoms and accelerate them. These electrons, as well as other charged particles such as protons and a particles, cause further ionizations of atoms in their path. Ionization of atoms can break chemical bonds, leading to damage to cells. The most critical target for damage is DNA.

Radiation causes damage to DNA in the form of single and double strand breaks, base damage, and DNA-protein crosslinks that depend on the dose given. And yet, most of this damage does not either kill the cell or cause mutations that lead to cancer because of a variety of DNA repair systems to repair the damage and the large excess of non-coding DNA. The most important form of DNA dam­age is the formation of double strand breaks, which can lead to chromosomal aberrations such as deletions and reciprocal translocations. These types of dam­age do not generally kill the cell, but they can lead to the initiation of a cancer by activating cellular oncogenes or deleting tumor suppressor genes in a cell. This initiating event is by no means a guarantee that an actual cancer will form. That depends on a number of further genetic changes in a cell, such as activation of more oncogenes, inactivation of additional tumor suppressor genes, mutations in DNA repair genes, and induction of genetic instability, all of which are improb­able events. These many necessary molecular changes are the reason there is a latency period of many years from the time of exposure of radiation until a cancer forms—if it forms at all, and in most cases it does not.

Furthermore, we know a great deal about the probability that cancer will develop after a given dose of radiation based on various human exposures to radi­ation, particularly the Japanese bomb survivors. Indeed, we probably know more about the carcinogenic effects of radiation than of any other physical or chemical agent. Based on this information, we can confidently predict the risk of getting cancer from a particular dose of radiation.

So it is a myth that exposure to radiation will inevitably cause cancer, though this myth is widely propagated by anti-nuclear activists and is probably what most people believe. What really matters is the dose that you are exposed to. And we are all exposed to radiation as an unavoidable consequence of living on earth. The next chapter will explore the doses of radiation that we are exposed to from natural sources and from medical procedures.