What's the viability of breeding plants to concentrate as much arsenic as possible, and then spending several growing seasons extracting it from fields, collecting the plants, and disposing of them?
Chinese brake fern (Pteris vittata) seems to be a candidate: https://www.newsweek.com/plant-arsenic-chemical-highly-toxic...
Plants as Useful Vectors to Reduce Environmental Toxic Arsenic Contenthttps://www.ncbi.nlm.nih.gov/pmc/articles/PMC3913097/
I do have to wonder if we would find ourselves inviting invasive species with such an exercise. But on the other hand, the goal is to "grow'em, burn'em, and carefully dispose of the ash" so maybe that concern is manageable.