Melissa, don't let the internet
terrorize you. Some of those hits refer to quartz sand as a carcinogen. Tt isn't. In fact, it is INERT and essentially is GLASS.
Now, any inert material that gets into your lungs and isn't expelled is likely to be a long-term irritant, but calling it a carcinogen is a huge stretch. Inhaling dusts of any kind is not good, regardless of their source. To single
out sand and try to make a causal connection, borders on terrorism.
Ditto for bentonite. Bentonite is essentially CLAY. In pet litters, it is dessicated and dried out and then when it is wetted again--it absorbs the moisture and swells back up. Again, it is INERT and that's a very good thing.
Sand and clay? That's essentially what we call DIRT. Animals
have evolved to live on it, eat on it, sleep on it.
Your cat is not a bird and should not be eating gravel, rocks, or feces. If it is--you've got another problem to deal with.
And if your cat was eating litter, or even yard dirt, it would not permanently swell his belly up. As Tao mentioned, he may need a lubricant but the INERT CLAY will be PASSED OUT in a reasonably short time, unless there is a bigger problem, like a mass formed or trapped that may need some encouragement to break up.
As far as hazardous ingredients go, INERT SAND AND CLAY are probably about as safe as you can get. Wood shavings are often commercially available, but they may also get trekked around the house. Do you know what resins are in the wood? Oil
from the blades? Other contaminants? Do you think a cat can eat and digest wood?
Life is dangerous. Make your choices, but don't let "some folks on the internet" terrorize you into making them. And do find out why your cat is eating kitty litter, that just isn't right. The 'lump' might not even be related--it might be a medical
issue, see a vet.