Dangers from nuclear detonations are such things as radioiodine.
This stuff can fuck up your thyroid and literally kill it. Luckily it has a short half life.
Normal iodine can fill your thyroid and stop it being able to absorb the radioactive iodine in the area after a nuclear detonation.
You have to saturate your thyroid with iodine. Doing this for extended periods will also destroy your thyroid. Going too far and taking 100x the amount required to saturate your thyroid is also not healthy.
Iodine can be used to purify ALL water. It will kill all bugs and bacteria. Four drops of liquid Betadine will purify 1L of water in an hour or two.
Iodine is also necessary for nerve growth. Iodine deficiencies lead to such things are improper neuronal development and functioning and mental retardation.