If you want to see what the damage can look like, I'll show you. I only recently put two and two together and realized that the persistently dead spot on my lawn was where I sawed the lumber I made the treated wood arbor out of last year. It's the same spot I sawed the lumber I made my kids' treated wood tree house. That's the spot where the sawdust went. What a dummy
!
I'm probably going to incite the wrath of HG on this, but I think if you're not seeing dead grass around the posts, you're not getting enough leaching to be concerned about. The lumber I used most recently was soaking wet. with the chemical treatment. In fact, even the place where I laid the lumber down in the yard as a staging area died this year. I have an 8 foot long, 1 foot wide dead spot. Had I used the kiln dried lumber ($$$), I'm pretty sure the 8 foot long spot would not have happened. It might be that the other dead spot would not have occurred, either. Anyway, I'm treating with compost and corn meal to replenish and feed the microbes. It's working well, but then again, I'm growing grass, not blackberries.
If you are really concerned and have plants or grass growing at the base of the fence posts now, send a soil sample and plant samples to the
Texas Plant and Soil Test Lab. Tell them what you have going on, what you want to do, and ask what to do about it. They're the only soil testing lab I would trust. Their prices are only slightly higher than other soil test labs, but they do a lot more testing routinely that would greatly increase the cost at the other labs.