What, oxygen?
Why not? Pure oxygen is toxic, so it must be a toxin. I've seen it argued here that mj must be toxic, because it's intoxicating, so I think we have the logical groundwork already laid.
He had the crawl space dug out under his house for headroom, topsoil brought in, grow lights, even water lines for irrigation.
Electricity wasn't an issue --- he only grew enough for his own use and therefore his lights compared to maybe one extra major appliance.
I don't know about toxicity, but the smell that permeated his whole house was unmistakeable. He wasn't fooling anyone with a nose.