Poisoning, radioactive iodine

Toxicants that are ingested generally are absorbed through the small intestine walls and are transported to the liver. The liver is the main site of toxicant metabolism and is where some poisonous substances are converted to less toxic forms more readily eliminated from the body whereas other substances are converted to toxic species. Toxic species are distributed around the body by the blood and lymph system, which can lead to systemic poisoning at sites remote from the entry of the substance into the body. Bone and adipose tissue (fat) are major sites of storage of toxicants. Bone accumulates heavy metals including lead and some radioactive materials, especially strontium-90, which biochemically behaves like calcium. Radioactive iodine accumulates in the thyroid and can cause thyroid cancer. Lipophilic toxicants, such as polychlorinated biphenyls (PCBs), that are poorly soluble in water tend to accumulate in adipose tissue. 

Long-lived radioactive isotopes such as cobalt-60 (>5year half-life) or cesium-137 (30-year half-life) can contaminate and render an area uninhabitable for many years. Biologically active isotopes (such as iodine-131) attack specific organs (such as the thyroid) or systems in the hiunan body, causing serious health effects such as cancer. Many radioactive isotopes are not only radiation hazards but are also heavy metals and poisons. 

The most important fission product poison is xenon-135. Xenon-135 is formed directly as a fission product and by decay of iodine-135. Xenon-135 is lost by radioactive decay and by neutron absorption to become xenon-136 which is called burnout. 

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