All Metal pollution is bad, but while they are tucked away in specific spots the actual symptoms may be less since the body has adapted to them. Sure Lead and Mercury break about 1700 enzymatic functions and make the body age faster but you aren’t aware of that due to adaptation.
In comes iodine, it mobilizes Lead and some Mercury. You now have two choices; get rid of it or let it settle in some other spot. But that settling either doesn't occur or is severely slowed down while Iodine is used…