Answer
The hazards of radioactive materials are basically three:
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radiation burns and hair loss from intense radiation
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cancer from long term low level exposure to radiation or from intense, short-term exposure
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potential for genetic damage - demonstrated in test animals but not seen in humans such as survivors of the bombings of Hiroshima and Nagasaki.
Answer
Hazards
In practice there is no such thing as zero radioactivity. Not only is the entire world constantly bombarded by
cosmic rays, but every living creature on earth contains significant quantities of
carbon-14 and most (including humans) contain significant quantities of
potassium-40. These tiny levels of radiation are not any more harmful than sunlight, but just as excessive quantities of sunlight can be dangerous, so too can excessive levels of radiation.
Low level contamination
The hazards to people and the environment from radioactive contamination depend on the nature of the radioactive contaminant, the level of contamination, and the extent of the spread of contamination. Low levels of radioactive contamination pose little risk, but can still be detected by radiation instrumentation. In the case of low-level contamination by isotopes with a short half-life, the best course of action may be to simply allow the material to naturally
decay. Longer-lived isotopes should be cleaned up and properly disposed of, because even a very low level of radiation can be life-threatening when in long exposure to it. Therefore, whenever there's any radiation in an area, many people take extreme caution when approaching.
High level contamination
High levels of contamination may pose major risks to people and the environment. People can be exposed to potentially lethal radiation levels, both externally and internally, from the spread of contamination following an
accident (or a
deliberate initiation) involving large quantities of radioactive material. The
biological effects of external exposure to radioactive contamination are generally the same as those from an external radiation source not involving radioactive materials, such as
x-ray machines, and are dependent on the
absorbed dose.
Biological effects
The biological effects of internally deposited
radionuclides depend greatly on the activity and the biodistribution and removal rates of the radionuclide, which in turn depends on its chemical form. The biological effects may also depend on the chemical
toxicity of the deposited material, independent of its radioactivity. Some radionuclides may be generally distributed throughout the body and rapidly removed, as is the case with
tritiated water. Some radionuclides may target specific organs and have much lower removal rates. For instance, the
thyroid gland takes up a large percentage of any
iodine that enters the body. If large quantities of radioactive iodine are inhaled or ingested, the thyroid may be impaired or destroyed, while other tissues are affected to a lesser extent. Radioactive iodine is a common
fission product; it was a major component of the radiation released from the
Chernobyl disaster, leading to many cases of pediatric
thyroid cancer and
hypothyroidism. On the other hand, radioactive iodine is used in the diagnosis and treatment of many diseases of the thyroid precisely because of the thyroid's selective uptake of iodine.