There is also significant danger from the ingestion of cage litter. Impaction of crops and digestive tracts are relatively common problems encountered by veterinarians as are both low grade and clinical bacterial infections. There are advantages and disadvantages to most choices of what we choose to put in a cage bottom. Sand can be eaten and is not digestible. Its heavy and degree of cleanliness varies greatly with the source though it can be very inexpensive and is not prone to flying around with flapping wings.
Cat litter has similar qualities.
Additionally some litter is treated to reduce odor and dust adding yet more chemicals and opportunities for problems. Pine shavings are more natural, but easily blown out of the cage by flapping wings. They are also hard to clean without complete replacement. Chances of ingestion are small as chewing wood without problems is a trait of most pet birds, but still remotely possible. Plastic and waxed paper are easy to replace though relatively expensive and completely non-digestable.