That is nice work Skip!

Ok so after some reading and a walk to the chem lab...

Phenol levels in pine wood I have no absolute information but I have had an opinion that it would be around 8-9 mg/m3. That is an opinion. We can smell the phenols in pine so lets say that aspen is somewhat lower that 8mg. Fair? that same can be said for oils in the wood you can feel pine oils where Aspen is noticeably less.

There are a huge amount of industrial uses of phenol and it is hard to find data on raw phenols in pine. The best info I can find is the limit value is about 35mg/m3 and that is raw. So lets say the safe limit is 10mg/m3 that is a guess! long tern exposure is less than that again. So my best guess raw pine would be at the very high end of safe. Kiln dried would be something lower than that but again it is a guess as to how much lower.

We can detect levels in pine so lets say at least 8mg/m3 we can smell.

Ammonia has very similar issues as phenols. The question is how long does urine take to become ammonia? I have not found that answer yet. Personally I check daily for urine and other things :-) so it is not likely to stay in the environment for long. it is more of an issue I would think the more snakes you have. So this is a yes and no. Yes it matters if there is a chance of urinates sitting for longer than 24 hours and no if it is shorter.

The other issue with paper substrates is the ammonia that is in the paper to start with and the trace dioxin. Carefresh has lots of info all conflicting and nothing based in evidence so it is impossible to make an informed opinion.

Phenols are demonized because of media hype. Why is dioxin ignored and PCDs demonized? Dioxin will kill you dead, pcbs might give you cancer.

What substrates are completely safe? I have no idea I am sure that with digging there is some issue with them all. Personally I use Cyprus coco husk mix (eco earth) I know how completely sad the cyprus issues are, I have been thinking of a switch to Aspen. Or just eco earth. Again I don't have answers only more questions. I can't find kiln dried pine chips that are free of bark and bit of junk. The bits I looked at was full of bark and aphids, ants and who knows what else. The pine chips where I am are kept outside in open piles. Clean kiln dried pine that is in sealed bags after it has been dried and doesn't smell super piney would likely be ok. I can't find any.

Interesting debate but to my mind there is no clear answer.