Please take a look at the link below;
Now, as I have said, I am no expert on film development, or in anything else when it comes to photography for that matter. I speak as I find. In number 1, in the article, it quotes...."Silver attaches readily to surfaces"..
Now, as this is an article on silver recovery from darkroom fixers, and it also warns of the dangers of discharging used fixer in to the enviroment, I can only assume that there is a silver content in used fixer. At what point a fixer reaches a point where as it becomes a hazard does not concern me. The fact is that used fixer will have silver particles, or what ever word you wish to use, in it. As this silver is capable of attaching itself to surfaces, in this instance it would be the soft emulsion of my film, I have chosen that during my own development routine I do not wish to subject my film to such a risk, however small.
Yes, as this post proves there are many APUGers re-using fixer with no complaint, and they are very happy with their results, as I am with mine. So there is no reason for any of us to change our development routines.
EDIT...I thought I would just add PARTICLE/A MINUTE PORTION OF MATTER. and please, I am in no way trying to sound smart here (I always find that quite difficult!)