Cesium is a naturally-occurring element found in rocks, soil, and dust at low concentrations. Granites contain an average cesium concentration of about 1 part of cesium in a million parts of granite (ppm) and sedimentary rocks contain about 4 ppm. Natural cesium is present in the environment in only one stable form, as the isotope 133Cs. Pure cesium metal is silvery white in color and very soft, but pure cesium is not expected to be found in the environment. Pure cesium metal reacts violently with air and water, resulting in an explosion-like reaction. Cesium compounds do not react violently with air or water and are generally very soluble in water. The most important source of commercial cesium is a mineral known as pollucite, which usually contains about 5-32% cesium oxide (Cs2O). No known taste or odor is associated with cesium compounds. Cesium is not mined or produced in the United States and very little is imported from other countries. There are relatively few commercial uses for cesium metal and its compounds. Sometimes cesium is used as a getter for residual gas impurities in vacuum tubes and as a coating in tungsten filaments or cathodes of the tubes. Crystalline cesium iodide and cesium fluoride are used in scintillation counters, which convert energy from ionizing radiation into pulses of visible light for radiation detection and spectroscopy. Cesium is also used in highly accurate atomic clocks.
Radioactive forms of cesium are produced by the fission of uranium in fuel elements (fuel rods) during the normal operation of nuclear power plants, or when nuclear weapons are exploded. Radioactive forms of cesium are unstable and eventually change into other more stable elements through the process of radioactive decay. The two most important radioactive isotopes of cesium are 134Cs and 137Cs. Radioactive isotopes are constantly decaying or changing into different isotopes by giving off radiation. Each atom of 134Cs changes into either xenon 134 (134Xe) or barium 134 (134Ba), neither of which is radioactive, while each atom of 137Cs decays to barium 137 (137Ba), which is also not radioactive. As 134Cs and 137Cs decay, beta particles and gamma radiation are given off. The half-life is the time it takes for half of that cesium isotope to give off its radiation and change into a different element. The half-life of 134Cs is about 2 years and the half-life of 137Cs is about 30 years.
Quantities of radioactive cesium, as well as other radioactive elements, are measured in units of mass (grams) or radioactivity (curies or becquerels). Both the curie (Ci) and the becquerel (Bq) describe the rate of decay and tell us how much a radioactive material decays every second. The becquerel is a new international unit known as the SI unit, and the curie is an older, traditional unit; both are currently used. A becquerel is the amount of radioactive material in which 1 atom transforms every second. One curie is the amount of radioactive material in which 37 billion atoms transform every second; this is approximately equivalent to the radioactivity of 1 gram of radium.
Pathways for cesium in the environment
Naturally-occurring cesium occurs in the environment mostly from the erosion and weathering of rocks and minerals. The mining and milling of certain ores can also release cesium to the air, water, and soil. Radioactive cesium is released to the environment during the normal operation of nuclear power plants, explosion of nuclear weapons, and accidents involving nuclear power plants or nuclear powered satellites or submarines.
Nonradioactive (stable) cesium can be neither created nor destroyed under typical environmental conditions, but can react with other compounds found in the environment and change into different cesium compounds. Radioactive decay decreases the concentration of 134Cs and 137Cs. Both stable and radioactive cesium are the same element and behave in a similar manner chemically and in the body. Cesium compounds can travel long distances in the air before being brought back to the earth by rainfall and gravitational settling. In water and moist soils, most cesium compounds are very soluble. Cesium binds strongly to most soils and does not travel far below the surface of the soil.
Consequently, cesium is not readily available for uptake by vegetation through roots. However, radiocesium can enter plants upon falling onto the surface of leaves.
Exposure to cesium
You can be exposed to stable or radioactive cesium by breathing air, drinking water, or eating food containing cesium. The level of cesium in air and water is generally very low. The concentration of natural cesium in air is generally less than 1 nanogram (1 nanogram equals 1/1,000,000,000 of a gram) per cubic meter of air (ng/m3). The amount of cesium in drinking water is ordinarily about 1 microgram (1 microgram equals 1/1,000,000 of a gram) per liter of water (µg/L). On average, a person swallows about 10 µg of stable cesium per day in food and water, and breathes about 0.025 µg per day. Plants and animals contain cesium at concentrations of about 1-300 ng/g.
Radioactive cesium has been detected in surface water and in many types of food. This includes breast milk and pasteurized milk. The amount of radioactive cesium in food and milk is highly dependent upon several factors. The most important factor is whether or not there has been recent fallout from a nuclear explosion such as a weapons test or an accident that has occurred at a nuclear power plant. However, atmospheric testing of nuclear weapons was halted many years ago, and there have only been two major reactor accidents at nuclear plants where radiocesium was released in significant amounts. The two accidents occurred in Windscale, England in 1957 and Chernobyl, Russia in 1986. You should understand that cesium only contributed a small fraction of the total radioactivity released following these events. The radiological impacts in Europe from 137Cs and 134Cs released from the Chernobyl accident, however, were great. These included environmental dispersion of radiocesium and uptake in reindeer, caribou, and livestock. Furthermore, the consequences of external exposure to gamma radiation and beta particles are not unique to 137Cs and 134Cs, but are very similar for all gamma and beta emitting radionuclides. People who work in industries that process or use natural cesium or cesium compounds can be exposed to higher-than-normal levels of cesium. An estimated 16,461 workers (4,276 of these are female) are potentially exposed to natural cesium and cesium compounds in the United States. If you work in the nuclear power industry, you may also be exposed to higher-than-normal levels of radioactive cesium, but there are many precautionary measures taken at these facilities to minimize this exposure.
Pathways for cesium in the body
Stable and radioactive cesium can enter your body from the food you eat or the water you drink, from the air you breathe, or from contact with your skin. When you eat, drink, breathe, or touch things containing cesium compounds that can easily be dissolved in water, cesium enters your blood and is carried to all parts of your body. Cesium is like potassium; it enters cells and helps to maintain a balance of electrical charges between the inside and the outside of cells so that cells can perform tasks that depend on those electrical charges. Cells like muscle cells and nerve cells require changing electrical charges in order to function properly and allow you to think and move.
Once cesium enters your body, your kidneys begin to remove it from the blood; some cesium is quickly released from your body in the urine. A small portion is also released in the feces. Some of the cesium that your body absorbs can remain in your body for weeks or months, but is slowly eliminated from your body through the urine and feces.
Health effects of cesium
To protect the public from the harmful effects of toxic chemicals and to find ways to treat people who have been harmed, scientists use many tests.
One way to see if a chemical will hurt people is to learn how the chemical is absorbed, used, and released by the body. In the case of a radioactive chemical, it is also important to gather information concerning the radiation dose and dose rate to the body. You should know that one way to learn whether a chemical will harm people is to determine how the body absorbs, uses, and releases the chemical. For some chemicals, animal testing may be necessary. Animal testing may also help identify such health effects as cancer or birth defects. Without laboratory animals, scientists would lose a basic method for getting information needed to make wise decisions that protect public health. Scientists have the responsibility to treat research animals with care and compassion. Scientists must comply with strict animal care guidelines because laws today protect the welfare of research animals.
Additionally, there are vigorous national and international efforts to develop alternatives to animal testing. The efforts focus on both in vitro and in silico approaches and methods. For example, the National Toxicology Program (NTP) at the National Institute of Environmental Health Sciences (NIEHS) created the NTP Interagency Center for the Evaluation of Alternative Toxicological Methods (NICEATM) in 1998. The role of NICEATM is to serve the needs of high quality, credible science by facilitating development and validation—and regulatory and public acceptance—of innovative, revised test methods that reduce, refine, and replace the use of animals in testing while strengthening protection of human health, animal health and welfare, and the environment. In Europe, similar efforts at developing alternatives to animal based testing are taking place under the aegis of the European Centre for the Validation of Alternative Methods (ECVAM).
You are not likely to experience any health effects that could be related to stable cesium itself. Animals given very large doses of cesium compounds have shown changes in behavior, such as increased activity or decreased activity, but it is highly unlikely that you would breathe, eat, or drink amounts of stable cesium large enough to cause similar effects. If you were to breathe, eat, drink, touch, or come close to large amounts of radioactive cesium, cells in your body could become damaged from the radiation that might penetrate your entire body, much like x-rays, even if you did not touch the radioactive cesium. You would probably experience similar effects if you were exposed to any other substance with similar radioactivity. You might also experience acute radiation syndrome, which includes such effects as nausea, vomiting, diarrhea, bleeding, coma, and even death. A number of people in Brazil, who handled radioactive cesium that was scavenged from a medical machine used for radiation therapy, became sick from exposure to the radiation; a few of them died. But people exposed to radioactive cesium that has been widely dispersed in air, water, soil, or foods following nuclear bombings or accidents have not been exposed to amounts large enough to cause the same effects.
Health effects in children
This section discusses potential health effects from exposures during the period from conception to maturity at 18 years of age in humans.
Children can be affected by cesium in the same ways as adults. Stable cesium is not likely to affect the health of children, but large amounts of gamma radiation, from sources such as radioactive cesium, could damage cells and might also cause cancer. Short exposure to extremely large amounts of radiation might cause nausea, vomiting, diarrhea, bleeding, coma, and even death. In addition, if babies were to be exposed to enough radiation while in their mother's womb during the time when their nervous system is rapidly developing, they could experience changes in their brains that could result in changes in behavior or decreased mental abilities. However, it is unlikely that children or babies would be exposed to enough gamma radiation from a radioactive cesium source to do such damage to their bodies.
Reducing risk of exposure to cesium
If your doctor finds that you have been exposed to significant amounts of cesium, ask whether your children might also be exposed. Your doctor might need to ask your state health department to investigate.
Since cesium is naturally found in the environment, we cannot avoid being exposed to it. However, the relatively low concentrations of stable cesium do not warrant any immediate steps to reduce exposure. You are unlikely to be exposed to high levels of radioactive cesium unless there is a fuel meltdown and accidental release at a nuclear power plant or a nuclear weapon has been detonated. In such cases, follow the advice of public health officials who will publish guidelines for reducing exposure to radioactive material when necessary.
Medical tests for exposure to cesium
Everyone has small amounts of cesium in their body. Laboratories use special techniques to measure the amount of cesium in body fluids such as blood and urine, as well as in feces or other human samples. This can give an indication of whether a person has been exposed to levels of cesium that are higher than those normally found in food, water, or air. Special radiation detectors can be used to detect if a person has absorbed radioactive cesium. It is difficult to determine if a person has been exposed only to external radiation from radioactive cesium. Health professionals examining people who have health problems similar to those resulting from radiation exposure would need to rely on additional information, such as the testing of blood samples for cell counts and chromosomal damage, in order to establish if such people had been affected by being near a source of radioactivity.
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.