The type of wood is not really a factor because everything other than the carbon structure should be burned off through pyrolysis. I would only be concerned with chemical contamination because heavy metals will remain. If you handle charcoal briquettes, you will likely need soap to clean your hands. If you handle biochar, your hands will just wipe clean because all sticky volatile compounds have been burned off. Biochar can be eaten and will help pull toxins out of your body. I will have some available for my livestock to eat free choice. They instinctively will eat it as needed. I remember seeing a video on living web farms you tube channel where the guy makes char out of roadkill. When he pulls it out, it looks just like it did going in, but it is black and easily breaks. He takes a bite of it to show you can eat it. 😂

I guess the type of feedstock matters for the pore structure of the final product. I would use any wood because the wood has plenty of pores for soil life to use and greatly increases the surface area. This larger surface area allows more contamination to be adsorbed (not absorbed). There are other benefits as well. This is a deep rabbit hole to go down let me know if you want suggestions for podcasts or videos on the subject. Here is a picture under a microscope