Radiation Protection

Subpart R: National Emission Standards for Radon Emissions From Phosphogypsum Stacks

Rule Summary

Subpart R protects the public and the environment from the hazards of radioactive materials found in phosphogypsum. Phosphogypsum is a radioactive waste product that results from processing phosphate ore to make phosphoric acid that is later used in fertilizer. Because the phosphate ore contains uranium and radium, phosphogypsum also contains these radionuclides. The radium is of particular concern because it decays to form radon, a cancer-causing, radioactive gas.

EPA requires that phosphogypsum be stored in above-ground stacks, which are designed to keep emissions of radon and other radionuclides in line with acceptable risk practices. EPA also requires owners and operators to monitor radon emissions from the inactive (completed) stacks. The owner/operators have to take measures to keep radon emissions within regulatory limits.

Additional Resources

Under certain conditions, phosphogypsum may be removed from stacks for outdoor agricultural purposes or indoor research and development. Any other use of phosphogypsum requires advance permission from EPA. See: Subpart R: Resources.


All facilities subject to any NESHAP must meet 40 CFR Part 61, Subpart A: General Provisions.