Cesium-137 (Cs-137)

Cs-137 is a fission product of uranium and plutonium, produced in nuclear reactors and weapons [1]. The 1986 Chernobyl explosion released 85 petabecquerels of Cs-137 across Europe and the Northern Hemisphere; the 2011 Fukushima accident released approximately 10 petabecquerels [2]. Nuclear weapons testing deposited global Cs-137 fallout from 1945-1980. Cs-137 is also used in medical brachytherapy devices, industrial gauges, and radiological laboratories — 'orphaned' sources (lost, stolen, or abandoned industrial Cs-137 devices) have caused radiation accidents when found by unsuspecting people [1]. The half-life of Cs-137 is 30.2 years, meaning areas contaminated by Chernobyl will not reach background levels until roughly 2086 [2].

Near nuclear accident sites, Cs-137 contaminates soil and vegetation and enters the food chain through leafy vegetables, mushrooms, berries, and grazing animals [1]. Fish in contaminated lakes and rivers accumulate Cs-137. For the general population distant from accident sites, dietary Cs-137 from residual global fallout is very small [2]. External gamma irradiation from contaminated soil is a pathway for people living in or visiting contaminated zones [1]. Contact with orphaned Cs-137 industrial sources is a rare but serious acute exposure scenario [2].

Cs-137 emits high-energy gamma radiation that penetrates the entire body, irradiating all tissues [1]. Unlike bone-seekers (radium, strontium), Cs-137 distributes throughout soft tissues, with muscle having the highest concentration (Cs mimics potassium in cellular transport) [2]. Internal Cs-137 from ingestion irradiates the whole body from within. The radiological risk is primarily cancer (thyroid cancer — from radioiodine co-released in accidents — leukemia, and solid tumors) [1]. For children evacuated from Chernobyl, thyroid cancer rates increased dramatically from I-131 exposure; solid tumor increases were attributed partly to Cs-137 [2].

Populations living in or near the Chernobyl exclusion zone (Ukraine, Belarus, Russia) had the highest exposures from the 1986 accident [1]. Children and pregnant women are most radiation-sensitive due to higher cellular division rates [2]. Workers involved in nuclear accident cleanup (Chernobyl 'liquidators') had documented elevated exposures and cancer rates [1].

1. Follow official guidance on food consumption and residence restrictions in any radiologically contaminated zone [1]. 2. Potassium iodide (KI) tablets protect only the thyroid from radioiodine (I-131), not from Cs-137 — follow official distribution guidance during nuclear emergencies [2]. 3. For orphaned source encounters: if you find an unknown device with radiation warning symbols, do not touch it; call emergency services [1]. 4. Prussian blue (potassium ferric hexacyanoferrate) is the FDA-approved treatment for internal Cs-137 contamination — reduces Cs-137 biological half-life from 110 to ~30 days [2].