Cesium-137 (Cs-137) is a radioactive isotope that does not occur naturally, instead forming as a common byproduct of nuclear fission. This includes its production in nuclear reactors and its release during nuclear weapons testing or severe nuclear accidents. The primary concern regarding this substance is its relatively long physical half-life, which is approximately 30.17 years. Cs-137 decays by emitting both beta particles and gamma rays, which are forms of ionizing radiation that pose a threat if the material is taken inside the body.
How Cesium-137 Enters the Body
Internal contamination with Cesium-137 occurs when the radioactive material enters the body through specific pathways. The most common routes of entry are ingestion and inhalation. Ingestion happens through the consumption of contaminated food or drinking water, especially after an environmental release where the radionuclide has entered the food chain.
Inhalation involves breathing in airborne particles, such as dust or fallout, that contain Cs-137, which can occur during or immediately following a nuclear event. Once deposited, Cs-137’s high water solubility allows it to move easily through soil and be taken up by plants. This subsequently contaminates animals and the broader food supply, making environmental sources a long-term concern.
Though less common, absorption through damaged skin or wounds can also introduce the isotope into the bloodstream. The primary health risk stems from the material’s ability to be readily absorbed from the lungs or the gastrointestinal tract. This absorption makes Cs-137 an internal hazard that exposes soft tissues to continuous radiation.
Distribution and Retention Inside the Body
Once absorbed, Cesium-137 is distributed rapidly throughout the body because its chemical behavior mimics that of potassium. Both cesium and potassium are alkali metals, and the body’s cells use potassium for essential functions like maintaining electrical charges and fluid balance. Biological systems cannot easily distinguish the radioactive cesium from stable potassium.
This mimicry leads to the widespread distribution of Cs-137 into all soft tissues and bodily fluids. Because muscle tissue makes up a large portion of the body mass, Cesium-137 tends to concentrate heavily in the muscles. While the physical half-life of Cs-137 is about 30 years, its residence time inside the body is much shorter due to excretion.
The biological half-life is the time it takes for half of the absorbed amount to be naturally eliminated from the body. For adults, this period is typically between 70 to 150 days, with the Cs-137 being primarily excreted through urine and feces. This relatively short biological half-life means the body naturally clears most of the contaminant within several months, mitigating the overall internal radiation dose.
Health Consequences of Internal Radiation Exposure
The health risks from internal Cesium-137 exposure arise from the ionizing radiation emitted while the isotope is distributed within the soft tissues. Cesium-137 emits beta particles directly, and its short-lived decay product, Barium-137m, emits penetrating gamma rays. Beta particles travel a very short distance, delivering a localized, high-energy dose to the surrounding tissue.
Gamma rays are highly penetrating and can travel throughout the body, contributing to a uniform, whole-body radiation dose. Both types of radiation disrupt the molecular structure of cells by causing ionization, which can lead to DNA damage and cell death. The resulting biological effect is proportional to the total absorbed radiation dose and the duration the material remains in the body.
In cases of chronic, low-level internal exposure, the primary long-term consequence is an increased risk of cancer. Cumulative DNA damage from continuous internal radiation raises the likelihood of cells becoming malignant. This elevated risk is associated with tissues where Cs-137 concentrates, such as muscle, and the prolonged exposure to gamma radiation throughout the body.
Conversely, extremely high internal doses can lead to acute health effects, presenting as symptoms typical of Acute Radiation Syndrome (ARS). These immediate symptoms often include nausea, vomiting, and diarrhea, which are common manifestations of cellular damage. The hematopoietic system, responsible for blood cell production in the bone marrow, is particularly sensitive to high radiation doses.
Severe internal exposure can cause profound bone marrow depression, compromising the body’s ability to fight infection and clot blood. Doses in the range of 50 rad (0.5 Gy) may cause observable, subclinical changes in blood factors. Higher internal doses can progress to severe symptoms, tissue necrosis, and ultimately death if damage to critical organ systems is extensive.
Medical Treatment for Internal Contamination
For confirmed internal contamination with Cesium-137, the primary medical goal is to accelerate the elimination of the radioactive material from the body. This is achieved by reducing the effective biological half-life of the isotope, thereby minimizing the total accumulated radiation dose. The approved treatment is the oral administration of Prussian Blue, formally known as Ferric hexacyanoferrate.
Prussian Blue works inside the digestive tract by acting as an ion-exchange agent. It binds chemically to the Cesium-137, forming a stable compound that the body cannot absorb through the intestinal lining. This binding prevents the reabsorption of Cs-137, effectively interrupting the natural recycling of the isotope within the body.
By trapping Cs-137 in the gut, Prussian Blue significantly increases its excretion through the feces. This enhanced fecal clearance reduces the time the radionuclide spends in soft tissues, drastically lowering the patient’s long-term radiation exposure. Supportive care is provided, and bioassays monitor the amount of Cs-137 cleared to guide the duration of therapy.