You can safely use lead slugs and buckshot in your Toz-34. Don't use magnums as the chambers are only good for 2 3/4" shells.
The use of steel shot can be debated.
This model was imported here only in 12 ga fixed Full/Imp.Modified chokes. I know that some owners are using steel shot in their Toz-34 without problems. I don't doubt the quality of the steel the Russians use in their firearms. However, fact is that the Toz-34 was designed in the sixties (before the advent of steel shot). This shotgun was not designed and never tested by the makers for use with steel shot.....
I use Kent's Impact (Tungsten Matrix) in my Toz. It patterns very well in my Russky and is deadly for waterfowl at long range.