Silver Iodide is a toxic substance, but the argument is that it is very dispersed in the process. The issue is that these things are not simple to study. If there is some increasing level of toxicity occurring within the body because of sporadic, repeated exposure, how long would a study have to go on for, what are the 'safe' limits (and so on)? The issue with a lot of these technologies is that if you are causing a problem that might not manifest until 20 years down the track, no one is really going to give a shit about it.
