Caesium metal is one of the most reactive elements and is highly explosive when it comes in contact with water. The hydrogen gas produced by the reaction is heated by the thermal energy released at the same time, causing ignition and a violent explosion. This can occur with other alkali metals, but caesium is so potent that this explosive reaction can even be triggered by cold water.[10] The autoignition temperature of caesium is also −116 °C, so it is highly pyrophoric, and ignites explosively in air to form caesium hydroxide and various oxides. Caesium hydroxide is a very strong base, and will rapidly corrode glass.[15]
The isotopes 134 and 137 are present in the biosphere in small amounts from human activities and which differs between locations. Radiocaesium does not accumulate in the body as effectively as many other fission products (such as radioiodine and radiostrontium). About 10% of absorbed radiocaesium washes out of the body relatively quickly in sweat and urine. The remaining 90% has a biological half-life between 50 and 150 days.[107] Radiocaesium follows potassium and tends to accumulate in plant tissues, including fruits and vegetables.[108][109][110] Plants absorb caesium differently, some do not absorb it much, and some take it large amounts, sometimes displaying great resistance to it. It is also well-documented that mushrooms from contaminated forests accumulate radiocaesium (caesium-137) in their fungal sporocarps.[111] Accumulation of caesium-137 in lakes has been a high concern after the Chernobyl disaster.[112][113] Experiments with dogs showed that a single dose of 3.8 millicuries (140 MBq, 4.1 μg of caesium-137) per kilogram is lethal within three weeks;[114] smaller amounts may cause infertility and cancer.[115] TheInternational Atomic Energy Agency and other sources have warned that radioactive materials, such as caesium-137, could be used in radiological dispersion devices, or "dirty bombs".[116]
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