I guess just heat and humidity. They're only about a year old. They were kept in the original script bottle in a dresser drawer. Do they become toxic when they degrade?
I honestly have no idea, hopefully someone comes along who can help you out! Age Vs quality/the state of them I'd say they probably would have lost their potency though
I once received crumbly old looking Valium when I was young and I took it with no ill effects. Sadly I was too young to realize that may not have been just "normal aging" but I didn't notice a change however I was also too young to really know benzos. I would think from a "will it kill you" stand point you will be completely fine. But I cant comment on anything else.