I'm not sure, but from a cursory bit of searching the mining of phosphorous may include radioactive trace elements which might be removed or concentrated at var

I'm not sure, but from a cursory bit of searching the mining of phosphorous may include radioactive trace elements which might be removed or concentrated at various steps of the production of fertilizer. I found e.g., https://www.sciencedirect.com/science/article/pii/S1687850714000053 https://www.sciencedirect.com/science/article/pii/S168785071... and https://www.osti.gov/biblio/459030-issues-natural-radioactivity-phosphates https://www.osti.gov/biblio/459030-issues-natural-radioactiv...