I also am surprised you would say that Joegrane. Perhaps your understanding is set, but as Estee posted, to begin with, Silver isn't classed as a heavy metal, its classed by Physicists as, Noble aka inert, safe in Science understanding.
Silver doesn't cause Oxidative stress. Our bodies inability or inefficiency at removing free radicals created by the oxidating process, be they from our lymphatic systems actions or any number of oxidizers we can take, causes oxidative stress. CS being an example of one of the safest since its oxidation rating is moderate. (and BTW if oxidative stress is ever a concern, it's simple enough to take antioxidents to assist the bodies normal antioxidant systems)
Here's a paper detailing a study where a much larger than ever (could be) used in CS use, of metallic silver, dose was, non orally, administered to lab animals. The results do not bear out with your statement as to the use of CZ and it's being left in the brain.