Rat Litter Box?

[SunflowerPop]

I recently got a litter box for my new rats. I did as the directions said, and waited until they pooped in that corner and then moved the litter box in with the litter. The box is far away from their food and water, but it's still pretty large.
Should I be worried about them eating the litter? I think I saw one of the nibbling on some of it but I'm not sure if he was eating it or just checking it out since it's new.
I don't think he was eating it since I moved some of their poop into the box so they'll figure out what it's for but I'm still paranoid. The litter is made specifically for small animals like rats.

 

[jorats]

What litter are you using? Are you sure they are ingesting it or just nibbling and spitting out the litter? Also, could he have been nibbling his poo? Rats do engage in coprophagia. That's how some recycle their nutrients.