Cesium-137 (Cs-137) is a significant byproduct of nuclear fission. This radioactive isotope is not found naturally but is created during nuclear reactions. Understanding its properties and how it interacts with the human body is essential for comprehending the health risk it presents.
Defining Cesium-137 and Its Radioactive Properties
Cesium-137 (Cs-137) is an artificial radioactive isotope produced when elements like uranium or plutonium undergo nuclear fission inside reactors or during atomic explosions. The unstable atomic structure of Cs-137 causes it to decay by emitting radiation over time. This decay process poses a threat to human health and the environment.
Cs-137 primarily decays through beta emission, where an electron is expelled from the nucleus. This transforms Cs-137 into Barium-137m (Ba-137m), a metastable isotope of Barium. Ba-137m rapidly emits high-energy gamma radiation to reach a stable state.
The gamma radiation released by Ba-137m is a penetrating form of ionizing radiation that can pass through the body, exposing internal organs and tissues. This external hazard is concerning when a person is near a concentrated source of Cs-137, such as mishandled industrial or medical equipment. The physical half-life of Cs-137 is approximately 30.17 years.
This long half-life means that once Cs-137 is released into the environment, it persists for centuries; it takes roughly 300 years for the radioactivity to diminish by 99.9%. The isotope’s longevity ensures it remains a long-term contaminant in the soil, water, and food chain. Cs-137 is considered one of the most problematic fission products due to its slow decay rate and lasting radiological impact following nuclear events.
How Cesium-137 Affects the Human Body
Cs-137 primarily enters the human body through ingestion of contaminated food or water, or inhalation of airborne particles. Once ingested, nearly all the cesium is absorbed into the bloodstream, making contaminated food the main source of internal exposure. The danger stems from its chemical similarity to the biologically important element potassium.
Cesium ions are mistaken for potassium ions by the body’s biological transport systems due to their similar size and charge. Potassium is an electrolyte distributed throughout the body’s soft tissues, especially muscle, where it is essential for nerve and muscle function. This chemical mimicry causes absorbed Cs-137 to be distributed similarly, concentrating in muscle and other soft tissues.
Once distributed, the isotope remains in the body, continually emitting radiation that exposes nearby cells and DNA. This internal exposure includes beta particles from Cs-137 and highly energetic gamma rays from its daughter product, Ba-137m. The continuous bombardment of ionizing radiation can damage cellular structures and genetic material, increasing the likelihood of developing cancer over time.
The health consequences depend heavily on the level of exposure. Chronic, low-level exposure, such as consuming contaminated food over many years, increases the long-term risk of cancer. Acute, high-level exposure, typically from being near an unshielded source, can cause immediate effects like burns, acute radiation sickness, and death. The body attempts to excrete cesium, similar to potassium, with a biological half-life of about 110 days in adults.
Environmental Presence and Reducing Exposure
The presence of Cs-137 in the environment today results primarily from historical nuclear activities. The main sources are fallout from atmospheric nuclear weapons testing in the 1950s and 1960s, and accidental releases from major nuclear reactor disasters, such as Chernobyl and Fukushima. While weapons testing dispersed Cs-137 globally, reactor accidents caused the highest concentrations in specific regions.
Once deposited, Cs-137 moves easily through the environment because its compounds are highly soluble in water. It binds strongly to certain types of soil, but plant uptake allows it to enter the food chain. Cs-137 concentration can be higher in certain organisms, such as wild mushrooms and some types of wild game, which act as bioindicators of contamination.
To reduce exposure risk, the public should check local food advisories, especially in areas affected by past nuclear incidents. Since plants absorb Cs-137 competitively with potassium, enriching soil with stable potassium can reduce the isotope’s uptake by crops. For acute internal contamination, medical intervention utilizes a compound called Prussian Blue (ferric hexacyanoferrate).
Prussian Blue works by binding to cesium ions in the gut, forming an insoluble compound that prevents the material from being absorbed into the bloodstream. This compound has a high affinity for cesium and acts as a selective sequestering agent, speeding up the excretion of Cs-137 through the feces. This countermeasure significantly decreases the biological half-life of cesium, reducing the duration of internal radiation exposure.