This waste is usually radioactive from the uranium found with raw phosphate, and acidic from the concentrated sulphuric acid used in the process. Another highly toxic byproduct of the process is fluorine, one of the most toxic, corrosive oxidizers known to man; deadly to all living tissue.
Chemical fertilizer is the catalyst that powers the modern industrial agricultural revolution, but estimates are that the supply of phosphate will be exhausted in 50 years or so. Also, petroleum based fertilizers deplete the nutrients from the soil, and the bodies of the people eating the harvest of that soil. Finally, the fertilizers erode from the point of application and work down through the water systems, creating dead zones in streams, lakes and oceans.