According to Bob :

It appears that you have a misconception about treated wood.
Treated wood does Not prevent it from rotting.
Its purpose is to prevent termite and other bug infestation - has
noting to do with preservative.

Actually both. The formulations are designed to be toxic to
both insects and rot fungi/molds. CCA had copper (first C) to kill
fungi (copper is specific to invertibrates and plants), and arsenic
(the A) to kill or at least discourage insects. The second C
(chromium) keeps it together, and isn't terribly nice either.
--
Chris Lewis,

Age and Treachery will Triumph over Youth and Skill
It's not just anyone who gets a Starship Cruiser class named after them.