of course they can (unless you have some that are made from paper xD ).

If you wear them in chlorinated pools, they won't last forever, though. They will get discoloured pretty quickly too.
But honestly I wouldn't advise opening your mouth underwater in public pools, ever.
Use them in clean lakes or the ocean if you can.

I use mine only in my own pool, and they're part of my mersona because I'm a sea serpent.