NATURAL based cat litter that is made with Corn or soy or wheat IS safe, but ONLY those types of litters. They are typically very expensive, but they are 100% safe. They do not give off silica dust because their made from grains, Clay based litters give off this, but people cant seem to figure out that there actually is a difference between sand litters and these grain based litters :rollseyes.
Litters like Words best cat litter, Swheat Scoops are made from corn and wheat, they are EDIBLE, and Flushable. and because... once again... their made from grains their dust IS safe, its no different then the dust from your hays or rabbits food, because whats in your rabbits food?
These litters are clumping and make scooping the bunnys box in the morning quite easy, but once again they are expensive. And if the litter you have in your house isnt one of these natural grain litters, dont use it plain and simple. Dont use other loose sandy cat litters , because not onlyare those litters dangerous for your rabbit, but their dangerous for you and your cat.