The box I cobbled together from old pallets, dirt is a mix of potting soil and local dirt spiced with chicken poo.
For the more observant viewers, you may notice that the closest 'V' is slimmer than the upper square -- the pallets were a little short. I plan to plant smaller vegetables in those areas.
The point is that modern pressure treated wood is treated with copper, so unless you think copper is going to be bad for the soil/plants, modern pressure treated wood is safe to use for garden beds.