Plutonium, By the Way.....

I had been working on a project about the development of nuclear power plants in this country and through a list-serve of scientists and engineers found a few who were willing to educate me on the early days of nuclear power. They’d spent most of their lives working either for the industry or for government regulatory agencies, and had a lot to say about the early days. This provided some pretty interesting reading. It was one of my last questions however, about worker health, which clearly revealed the bias of one respondent.

“By the way,” he wrote, “plutonium is not toxic when eaten. You can eat it with a spoon if you want to.” To his credit he did concede that if you happen to inhale plutonium, there is a long-term risk of cancer, “just like naturally occurring polonium in tobacco smoke.”

He’s right of course. You could eat plutonium if you wanted to. You could also eat dioxin or arsenic if you wanted. But why would you?

Plutonium, like some forms of strontium, uranium and the now famous polonium-210 is a radioactive metal or element, although plutonium and radioactive strontium differ from uranium in that they do not occur naturally in our environment (for the most part) but are by-products of our “tinkering” with natural elements. Human activities like uranium mining, nuclear weapons production and testing, and nuclear energy production, are the primary human activities which have lead to environmental releases of plutonium, radioactive strontium, and other radioactive elements.

What sets apart the radioactive elements from the non-radioactive elements is their lack of stability. They can disintegrate spontaneously, sometimes even changing into other elements over time. Uranium, for example, will eventually decay into lead (although it may take billions of years.)

Generally speaking, elements are defined by what is in their nucleus. The nucleus of any atom consists of protons (positive elements), neutrons (neutral elements) and electrons (negative elements). While the chemical properties of an element are primarily dependent on the number of protons in the nucleus, the radioactive properties generally depend on the number of neutrons, and the balance among the protons, neutrons and electrons. An element can have several different stable forms, or forms in which the number of protons remains the same (thereby imparting the chemical properties), yet the number of neutrons might vary. Water, for example consists of two hydrogen atoms and one oxygen atom. Most often, the hydrogen in water contains just one proton and one neutron in its nucleus. This form of hydrogen is stable and does not undergo radioactive decay. But some hydrogen atoms exist that have two or even three neutrons. Those with two are called deuterium and those with three are referred to as tritium. Both deuterium and tritium can combine with oxygen forming heavy water which, for the most part, behaves chemically just like normal water. Deuterium atoms are stable. Tritium atoms however are not stable and at some point in time they will disintegrate, eventually leading to the production of helium (although in a much shorter period of time than it takes uranium to decay to lead - something in the order of decades rather than billions of years).

When atomic disintegration occurs radiation is released and depending on the element, may occur as alpha particles, beta particles or gamma rays. Although each one of these radioactive emissions has their own characteristics (see box), all three types are known as ionizing radiation, a powerful form of radiation capable of stripping electrons from other atoms and molecules (causing them to become either unstable or reactive) and breaking chemical bonds. The displaced electrons become free energetic electrons, and in turn are capable of imparting their energy to electrons of other molecules, either exciting them or knocking them out, continuing the process of bond breaking, excitation, and ionization.

In the body, the making and breaking of the chemical bonds between atoms is a highly coordinated process, normal and essential to life, and the “unscheduled” breaking of chemical bonds can cause cell death, permanent cell damage, or damage to the cell’s DNA.

Human DNA is contained within the 46 chromosomes (making up 23 pairs) that carry our genetic code. Replication of these chromosomes during cell division is a critical process, requiring an immense number of complex biochemical interactions, which involve copying and construction of identical chromosomal pairs that are split off into the newly divided cell. Since integrity of the genetic material is essential to life, there are biochemical systems involved in maintaining chromosomes during division, including mechanisms by which errors may be repaired.

As discussed above, ionizing radiation results in highly energized electrons that are capable of breaking any chemical bond in the body. Likewise, the track of an energized electron is capable of breaking chromosomal bonds, thereby breaking off pieces of the chromosome. Once a break occurs, depending on conditions within the cell and location of the break, the broken pieces may rejoin the chromosome, leaving little or no evidence of damage; the broken piece may remain separate, becoming a chromosomal deletion; or the deleted piece may continue to copy itself, as will the chromosome that is now lacking a portion of genetic information. It is generally agreed that the critical genetic damage from ionizing radiation is most likely the result of chromosome breaks, although other types of genetic damage can occur as well.

If the genetic damage becomes permanant, or “fixed”, and begins to propagate within the cell, the change can lead to the development of cancer, or to mutations that may be either genetic (capable of being passed on to offspring) or teratogenic (impacting only the exposed fetus) in nature.

So, when an element like plutonium disintegrates, it releases alpha particles and though these particles don’t travel vary far, once inside the body (say, from ingestion or inhalation), they are capable of interacting with, and potentially harming any bodily tissue along their path.

In other words, wherever the plutonium ends up, be it in the stomach, or the liver, or the bones, where it’s most likely to travel once it leaves the stomach, it has the potential to emit alpha particles, and cause tissue damage for as long as it remains in the tissue, which in the case of plutonium can be decades.

There is a great deal of information on the health impacts of radiation available on the web. Here are a just few sites that may be of interest if you wish to learn more:

The Institute for Energy and Environmental Research: http://www.ieer.org/

The US EPA: http://www.epa.gov/radiation/topics.html

And, if you really want to read the details there is the National Research Council’s latest report on “Health Risks from Exposure to Low Levels of Ionizing Radiation,” which is available online (and for purchase) at http://www.nap.edu/books/030909156X/html/R1.html

BOX:

Radiation Type	Emission	Distance traveled in air	Health threat from external exposure (penetration)	Health hreat from internal exposure	Emitted by:
Alpha (a)	2 protons, 2 neutrons	Centimeters	Low	High	Plutonium-236; uranium-238, radium-226
Beta (b)	Electron	Meters	High	High	Strontium-90; tritium, Iodine 131; Cesium 137
Gamma (g)	Photon (electromagnetic radiation)	Thousands of meters	High	High	Cobalt-60; Cesium-137