[Pfhreak]

Biochar, the solid product of pyrolized biomass, is considered a beneficial soil amendment (it's basically elemental carbon -- like what you'd get in a charcoal filter). It's probably not a good idea to breathe it though.

I'm not sure about bio-oil specifically, as it contains much more of the tar-like compounds. It's likely it contains benzene and other compounds. I found this in a cursory google search: https://www.nrel.gov/docs/fy07osti/37779.pdf

[Nasrudith]

Notably the dose makes the poison as well. If just "helps plants grow" was enough to be an environmental good then fertilizer run off would be a good thing.