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.
Even a pallet from Walmart, motor oil or pool chemical spill on it, no way of knowing.
There is some places that do one time pallet use and wouldn’t be at risk, but I don’t think the majority of people are sourcing those.