Gabe Smith wrote:From what I can tell from the second picture, those 4"*4"posts that go into the ground are most likely pressure treated. If the boards are in contact with the ground in any way, and you do not see evidence of decomposition, they are likely pressure treated. Unless those are black locust, untreated wood will begin decaying pretty much within a year if it is contact with soil. If they are older than about 20 years, they will likely be the kind that was pressure treated with arsenic. The newer pressure treated is still toxic, but not quite as bad. If they are pressure treated, they probably leach into the soul only if they are the new style that actually rots eventually. I believe some sort of copper compound. I would say that any scraping or standing,even if the paint is latex paint, will inevitably find it's way into your soil. Personally, I would not bother with the hassle of testing, etc. I would remove them entirely.
You're right, I'm also now pretty positive that this wood is pressure treated. Right after I posted this, I looked more closely at the wood and saw all of the regular impression marks where the wood treatment is injected. I tried to remove my post since I made a decision at that point not to use the wood, but I couldn't figure out how to take down this posting. Perhaps this conversation will still be helpful to someone in the future.
I am aware of the higher toxicity of pressure treated wood from a couple of decades ago. Unfortunately, I don't know the age of the wood that is on our property, but we have dozens of retaining walls just like the one in the picture all over our backyard which is a steep terraced hill. I hadn't considered the potential of the pressure treated wall posts to leach into the soil, but it's a really good point. I would not be surprised if the garden beds were put in around the same time as the terraces and therefore using the same wood. This could have been over or around 20 years ago. In any case, I've decided I'll definitely remove the planter bed wood and dispose of it safely. I'm considering filling the holes that are left with some tree trunks and branches we have left from some downed trees to start some hugelkulture beds. I'm now curious if there's any fungi that could help take care of potential arsenic in the soil. Funny how one problem leads to so many more questions and exciting things to explore! Thanks for your response.