Biochar of dyed wood chips

I ended up using a bunch of the cheap dyed decorative wood chips last year. I hated them, for many reasons, and I'm removing them.
What do they dye those things with?
I'm debating burying as a semi hugel type thing or biocharring them, just how toxic are they?

My only other option would be to load them all up and take them to the dump, which is more work than I want to do.

You don't have to worry about it. Red color comes from iron oxide, the same for red clay soil. Black color is from something cheap and carbon based so it will burn away if you make char.

That's really useful information, May. How did you figure that out?
Thanks,
John S
PDX OR