Be aware that there are now a number of chemicals used for treated lumber. The gold standard for 50 yrs +/- was CCA, but is no longer used for most applications - but it is still allowed for a few - including agricultural + industrial (read: pole barns + phone poles) and marine. Why? because nothing else works that well, and the big hoo-hah over the arsenic in CCA disappeared because, in the cold, sober light of actual science, there was no merit in the concerns. Negative PR caused the Borg to insist on a change from their suppliers.
Also - there are various treatment "levels" for any chemical, measured in lb/cu ft of chemical retained in the wood. Something like 0.15 lb/cu ft for non-ground contact (read: fence boards) all the way up to 6.0 lb/cu ft for seawater immersion (read: sea walls, dock posts, etc.). More chemical = more resistant to decay.
And - yes, I used to work in that industry. No longer, not shilling for them, just been in that rodeo. My info is a little dated, but should still be pretty much on target.