Iodine in air can combine with water particles and precipitate into water or soils. Iodine in soils will combine with organic matter and remain in the same place for a long time. Plants that grow on these soils may absorb iodine. Cattle and other animals will absorb iodine when they eat these plants.
Iodine in surface water will vaporize and re-enter the air as a result. Humans also add iodine gas to the air, by burning coal or fuel oil for energy. But the amount of iodine that enters the air through human activity is fairly small compared to the amount that vaporizes from the oceans.
Iodine may be radioactive. The radioactive isotopes are formed naturally during chemical reactions in the atmosphere. Most radioactive isotopes of iodine have very short half-lives and will reshape into stable iodine compounds quickly. However, there is one radioactive form of iodine that has a half-live of millions of years and that is seriously harmful to the environment. This isotope enters the air from nuclear power plants, where it is formed during uranium and plutonium processing. Accidents in nuclear power plants have caused the release of large amounts of radioactive iodine into air.
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