I haven’t used every etching mordant but here is a very good site:
NontoxicPrint.com This is a site by and for printmakers who have
developed the best modern safe techniques. It is really an on line
book! Silver is not really used for printing plates ($$$$) and has
one really special consideration- It won’t use a chloride containing
mordant!! Silver chlorides are insoluble and don’t work well. The
electro etching procedures described are very nice and easy to
control. You won’t find Islamic acid mentioned but it is a usable
material. Every thing is relatively safe within limits. you can get
lots of including toxicity with goggle searches.
I have collected a lot of on etching processes which I
will share with you.