Stanton,
Dream on! BASC have had biodegradable wads sitting in a garden at HQ for years exposed to the elements and they are still there today !

Eley do have a wad that is water soluble but it still lingers around as a slimey mess for days after becoming into contact with moisture .
Interestingly enough only yesterday I was made aware that some plastics of the polyurethane type may well contain Lead as a constituent?
Sorry to say that as an avid shooting person I now feel abandoned , up the creek without a paddle.