Hi Paul, Its says on product description that it is ' Perfect for all reptiles, amphibians and invertebrates up to 1 pound!'
To me that means that it is appropriate and therefore considered safe (surely something that is perfect is safe?). My interpretation sorry.
I think the grit is actually the polystyrene (?) and coating that just comes off, and that it may continue to do that - I washed it and fine bits still come off. I will wash it again though.