Use cannabis plans to extract the pollution from the soil, then extract and concentrate the pollution from the biomass, then find a way to safely store it or break it down safely.
It depends. Some plants will break certain elements down into less toxic components. In the best case, the components are non-toxic and you can do whatever you want with it.
Nothing can breakdown lead and other toxic metals unless you have a neutron source.
I usually turn my old lead into gold. I've almost perfected the technique.
Blaze it
No! a) these aren't the THC types so you won't get high and b) the hemp is a collector, so the nasty stuff would be in the tree.
This material is for industrial hemp, making rope and fabric and things.