Cesium (Cs) is a naturally occurring element, a soft, silvery-white alkali metal that can even be liquid near room temperature. It exists primarily as the non-radioactive isotope cesium-133 in nature, found in rocks, soil, and dust in small amounts. While natural cesium is stable, radioactive Cesium-137 (Cs-137) introduces a different concern. This artificial radionuclide has drawn public attention due to its persistence and potential environmental impacts. Cs-137 is a byproduct of nuclear fission, and its presence in the environment is a direct consequence of human activities.
Understanding Radioactive Cesium
Cesium-137 is a radioactive isotope of cesium, distinct from the stable, naturally occurring cesium-133. It forms as a common fission product during the nuclear fission of uranium-235 and other fissionable isotopes in nuclear reactors and weapons. Cs-137 is an artificial isotope, not found in nature. It has a half-life of approximately 30.17 years, meaning it takes over three decades for half of its radioactivity to decay.
During its decay, Cesium-137 primarily emits beta particles and gamma rays. It undergoes beta decay, producing gamma radiation that can penetrate the human body, posing both an internal and external hazard. Its artificial origin, long half-life, and emission of both beta particles and penetrating gamma radiation make Cesium-137 an environmental and health concern.
Sources of Environmental Release
The presence of Cesium-137 in the environment largely stems from historical events and major nuclear incidents. Atmospheric nuclear weapons testing during the mid-20th century dispersed significant quantities of Cs-137 globally as radioactive fallout. Trace amounts of Cs-137 from past weapons tests can still be found in soil and other environmental compartments worldwide. Over 70% of the Earth’s surface is covered by water, leading to the accumulation of Cs-137 in oceans and seas from these tests.
Nuclear power plant accidents represent another major source of environmental Cs-137 release. The Chernobyl disaster in 1986, for instance, released an estimated 80,000 terabecquerels of Cesium-137 into the atmosphere. This accident caused widespread contamination across Europe, with Cs-137 becoming the primary long-term radiological hazard due to its half-life. Following the Fukushima Daiichi nuclear accident in 2011, Cs-137 was also released, with atmospheric estimates ranging from 7 to 20 petabecquerels.
Approximately 40-80% of atmospheric Cs-137 from the Fukushima release deposited into the ocean, alongside direct leaks of contaminated water. Cesium’s low boiling point allows it to travel long distances in the air during accidents or explosions. Other potential sources include reprocessing of nuclear fuel, medical waste, and industrial applications, though these typically involve smaller, more localized releases.
Biological and Ecological Impacts
Radioactive cesium is a concern for living organisms and ecosystems due to its chemical similarity to potassium, an essential element for biological processes. Organisms, including plants, animals, and humans, can absorb Cs-137 through normal metabolic pathways. Once absorbed, cesium distributes throughout the body, particularly concentrating in soft tissues like muscle. This internal exposure means the emitted beta particles and gamma radiation can directly damage cells and tissues.
The uptake of Cesium-137 by plants from contaminated soil allows it to enter the food chain. Herbivores consume contaminated plants, and carnivores then consume herbivores, leading to a process known as bioaccumulation, where the concentration of Cs-137 can increase at higher trophic levels. This pathway can lead to contamination of agricultural products, such as milk and meat, as well as wild game and mushrooms.
Internal exposure to Cesium-137 increases the risk of various health effects in humans and animals. The ionizing radiation it emits can damage DNA, leading to an increased risk of cancer, including thyroid cancer and leukemia. High doses can also cause acute radiation sickness, burns, and death. In ecosystems, contamination can disrupt ecological balance, affecting wildlife populations and their reproductive success.
Detection and Remediation
Detecting and measuring radioactive cesium in the environment, food, and organisms is important for assessing risk and implementing management strategies. Gamma spectroscopy is a primary method to identify and quantify Cs-137 in various samples, relying on detecting the specific energy “fingerprint” of gamma photons emitted during its decay. This technique is sensitive, allowing for the detection of low levels of radioactivity in environmental samples like water and soil. Real-time autoradiography can also detect radioactive cesium microparticles in environmental samples.
For assessing internal contamination in humans, whole-body counters are used. These specialized instruments measure gamma rays emitted from radionuclides within the human body, providing a direct measure of the internal Cs-137 burden. The data from these measurements help estimate the radiation dose received and track changes in exposure over time, which is particularly useful in populations potentially exposed to Cs-137 fallout.
Mitigation strategies for contaminated areas often involve agricultural countermeasures. Since cesium chemically resembles potassium, applying potassium-rich fertilizers to soil can reduce the uptake of radioactive cesium by plants, including crops like rice and buckwheat. This helps control the transfer of radiocesium into the food chain. Other agricultural techniques include deep plowing, which can dilute the concentration of radiocesium in the topsoil where crops grow, and mixing topsoil with manure or other potassium-containing materials.
Environmental cleanup techniques include physical removal of contaminated topsoil, which reduces the inventory of radionuclides available for uptake. However, this generates large volumes of radioactive waste. Chemical methods, such as washing agents or subcritical water treatments, aim to remove radioactive cesium from soil particles. For acute internal exposure in humans, Prussian blue, a compound known as ferric hexacyanoferrate(II), can be administered orally. This medication binds with cesium in the digestive tract, reducing its absorption and accelerating its elimination from the body, thereby decreasing the overall radiation dose.