The wood is SYP with CA-C pressure treatment. I realize the toxicity is considered "safe" but the science does say the chemicals leach into the soil. Whether that is acceptable is based off a number someone came up with, and the science why that number was chosen is not so clear. For me, better just to stick with stone.
We tend to have more ACQ here but the Copper Azole is around as well. The CCA that they replaced had arsenic that was best avoided, but really only affected a small area of soil near to the treated wood. Still, I wouldn't personally use CCA near food plants.
The azole compounds in CA are used in agriculture, although that may not change your feelings about them:
https://en.wikipedia.org/wiki/TriazoleThe "quat" in ACQ is also used elsewhere but, again, may not be your personal choice:
https://en.wikipedia.org/wiki/Didecyldimethylammonium_chlorideThey are much better than CCA, although you need to choose the right screws/nails so the copper doesn't corrode them. For myself, I have used them in projects (deck, etc.) and think they are fine for ornamental garden beds. For anything food related, stone walls are probably better if you have concerns. YMMV.
If I needed to use ACQ for a garden bed, I might make a small gravel drainage layer along the wood and cover with landscape fabric. I don't think the water leaching would be particularly strong past 1/2" of gravel. If much of it leached from the wood, it wouldn't make a very good preservative!