Plutonium is a silvery-white radioactive metal that exists as a solid under normal conditions. It is produced when uranium absorbs an atomic particle. Small amounts of plutonium occur naturally, but large amounts have been produced by man in nuclear reactors. Plutonium can be found in the environment in several forms called isotopes. The most common plutonium isotopes are plutonium-238 and plutonium-239. Because plutonium is a radioactive element, it constantly changes or "decays." In this decay process, energy is released and a new product is formed. The energy released is called radiation.
When plutonium decays, it divides into two parts—a small part that we call "alpha" radiation and the remainder, different from original plutonium, called the daughter. The daughter is also radioactive, and it, too, continues to decay until a nonradioactive daughter is formed. During these decay processes, alpha, beta, and gamma radiation are released. Alpha particles can travel only very short distances and cannot go through the thickness of your skin. Beta particles can travel farther and can penetrate a few millimeters into your tissues. Gamma radiation travels the farthest and can go all the way through your body. It takes about 90 years for one-half of a quantity of plutonium-238 to break down to its daughter and about 24,000 years for this to happen to plutonium-239.
Plutonium-238 is used to provide on board power for electronic systems in satellites. Plutonium-239 is used primarily in nuclear weapons. Most plutonium is found combined with other substances, for example, plutonium dioxide (plutonium with oxygen) or plutonium nitrate (with nitrogen and oxygen).
Plutonium has been released to the environment primarily by atmospheric testing of nuclear weapons and by accidents at weapons production and utilization facilities. In addition, accidents involve weapons transport satellite reentry, and nuclear reactors have also released smaller amounts of plutonium into the atmosphere. When plutonium was released to the atmosphere, it returned to the earth's surface as fallout. Average fallout levels in soils in the United States are about 2 millicuries (mCi)/square kilometer (about 0.4 square miles) for plutonium-230 and 0.05 mi/square kilometer for plutonium-238. A millicurie is a unit used to measure the amount of radioactivity; 1 mCi of plutonium-239 weighs 0.016 gm, while 1 mCi of plutonium-238 weighs 0.00006 gm.
Measurements in air have been made at a few locations. For example, air levels of plutonium-239 in New York in the 1970s were reported to be 0.00003 picocuries (pCi) per cubic meter of air. One pCi is one billionth of a mCi. Persons who work at nuclear plants using plutonium have a greater chance of being exposed than individuals in the general population. However, you could be exposed to plutonium if there was an accidental release of plutonium during use, transport, or disposal. Because plutonium does not release very much gamma radiation harmful health effects are not likely to occur from being near plutonium unless you breathe or swallow it.
Pathways in the body
You are most likely to be exposed to plutonium by breathing it in. Once breathed in, the amount that stays in the lungs depends on several things, particularly the particle size and form of the plutonium compound breathed in. The forms that dissolve easily may be absorbed (pass through the lungs into other parts of the body) or some may remain in the lung. The forms that dissolve less easily are often coughed up and then swallowed. However, some of these may also remain in the lung. Plutonium taken in with food or water is poorly absorbed from the stomach, so most of it leaves the body in feces. Absorption of plutonium through undamaged skin is very limited, but is may enter the body through wounds.
Some of the plutonium absorbed into the body leaves the body in urine. The rate of plutonium removal from the tissues of the body is very slow, however, occurring over years. Most of the plutonium that stays in the body is found in the lungs, liver, and skeleton.
Plutonium may remain in the lungs or move to the bones, liver, or other body organs. It generally stays in the body for decades and continues to expose the surrounding tissues to radiation. This may eventually increase your chance of developing cancer, but it would be several years before such cancer effects became apparent. The experimental evidence is inconclusive, and studies of some human populations who have been exposed to low levels of plutonium have not definitely shown an increase in cancer. However, plutonium has been shown to cause both cancers and other damage in laboratory animals, and might affect the ability to resist disease (immune system). We do not know if plutonium causes birth defects or affects the ability to have children. However, radioactivity from other radioactive compounds can produce these effects. If plutonium can reach these sensitive target tissues, radioactivity from plutonium may produce these effects.
Plutonium is odorless and tasteless so you cannot tell if you are being exposed to plutonium. If you breathe in plutonium, some of it will be retained in your body. When discussing harmful health effects, the amount of plutonium that caused these effects is usually given as the amount of plutonium retained or deposited in the body rather than as the amount that was in the air.
There is no information from studies in humans or animals to identify the specific levels of exposures to plutonium in air, food, or water that have resulted in harmful effects. However, it is generally assumed that any amount of absorbed radiation, no matter how small, may cause some damage. When expressed as the amount of radioactivity deposited in the body per kilogram of body weight (kg bw) as a result of breathing in plutonium, studies in dogs report that 100,000 pCi plutonium/kg bw caused serious lung damage within a few months, 1,700 pCi/kg bw caused harm to the immune system, and 1,400 pCi/kg bw caused bone cancer after 4 years. In each of these cases the dogs were exposed to the plutonium in air for one day.
There are tests available that can reliably measure the amount of plutonium in a urine sample even at very low levels. These measurements can be used to estimate the total amount of plutonium that is carried by the body. However, these measurements cannot be used to directly determine the levels to which the person was exposed or to predict the potential for health effects. In addition, there are tests to measure plutonium in soft tissues (such as body organs), feces, bones, and milk. These tests are not routinely available in your doctor's office because special laboratory equipment is required.
Disclaimer: This article is taken wholly from, or contains information that was originally published by, the Agency for Toxic Substances and Disease Registry. Topic editors and authors for the Encyclopedia of Earth may have edited its content or added new information. The use of information from the Agency for Toxic Substances and Disease Registry should not be construed as support for or endorsement by that organization for any new information added by EoE personnel, or for any editing of the original content.