Tampa fertilizer giant Mosaic is seeking federal approval to use an estimated 337 tons of phosphogypsum, a mildly radioactive byproduct from the company’s phosphate manufacturing process, as a test ingredient in road construction. When processing phosphate rock to make fertilizer, the phosphorous is removed by dissolving the rock in an acidic solution. The waste that is left behind is called phosphogypsum. Most of the naturally-occurring uranium, thorium and radium found in phosphate rock ends up in this waste. Uranium and thorium decay to radium and radium decays to radon, a radioactive gas.

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Sources:

https://www.epa.gov/radtown/radioactive-material-fertilizer-production

https://www.orlandosentinel.com/2023/07/22/mosaic-wants-to-test-radioactive-road-with-337-tons-of-phosphogypsum-records-show/

https://flsenate.gov/Session/Bill/2023/1191/?Tab=Amendments