What are the effects of iodine on someone who has had their Thyroid killed or removed?

I know you are not suppose to have anything with iodine in it, crustaceans, etc. after the removal of a thyroid. I am interested in what actually happens if someone ingests iodine or has it used as a topical cleaner for a wound. How toxic is it? Since iodine is in a lot of our foods, is it only in excess that someone will be effected? Can you have an iodine build up over time that would create problems? or is the excess eventually a waste product and naturally removed from the body? Are there any signs or symptoms that would show if someone had ingested or had a reaction to iodine?