> Don't forget, we used creosote on fences for donkeys years before anyone thought anything of it.
The problem with creosote is that some animals can deal with certain chemicals and flush them from their body systems, and some can't. Cresols and phenols are especially toxic to cats, being one of the species that can't. the chemicals then build up in the liver and over time can cause issues and/or shorten their lives. (The same with other chemicals that are OK for dogs and humans, but deadly to cats, such as aspirin).
Cats which get creosote, cresols, or phenols - that includes pine disinfectants - on their coats or paws and then lick them off can get acute poisoning.
It's something that has only relatively recently been known... well, I say relatively, but the dangers to cats from these compounds has been well known for over 30 years, I would guess it's taken time to seep through to the public consciousness.
By the way, Tea Tree oil is extremely high in phenolic compounds - its active antibacterial agent - so I would never use it around cats.