If I had a link to see what they are, and to know if what you are referring to is the same thing I found when I looked up the term, then I could give a reply. But I don't really want to reply without knowing exactly what I would be replying on. If it's what I found when I did a search, I would say yes they can be used as a
growing medium. But I would want to make sure there was no unwanted chemicals in them (another reason I wanted a link). Though I don't know if it would be economical even so. That's about the best I can say without being able to see what it is were talking about.