Caves are reasonably biologically inert once you get a bit deeper in simply due to the lack of sunlight. If you leave waste down there, it'll stay there for a l

Caves are reasonably biologically inert once you get a bit deeper in simply due to the lack of sunlight. If you leave waste down there, it'll stay there for a long time and have a relatively large impact on the fragile cave microbiota. It's polite and considered responsible to pack it out, though on more hardcore expeditions it's not always possible to take all your urine back with you. On the other hand, bolts don't tend to have any long term environmental impact apart from their presence and are already only placed when necessary anyway.