Phosphogypsum

Phosphogypsum is a solid waste byproduct from processing phosphate ore to make phosphoric acid that is later used in fertilizer. The phosphate ore and the resulting phosphogypsum contain radium, which decays to form radon gas. Both radium and radon are radioactive and can cause cancer. EPA’s regulations require that phosphogypsum be managed in engineered stacks to limit public exposure from emissions of radon. Phosphogypsum can be removed from these engineered stacks under limited approved uses. Additionally, the EPA may approve a request for a specific use of phosphogypsum if it is determined that the proposed other use is at least as protective of public health as placement in a stack.

On this page:

• EPA Regulation of Phosphogypsum
• Other Uses of Phosphogypsum
• Applications for Other Uses of Phosphogypsum
• Frequently Asked Questions

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EPA Regulation of Phosphogypsum

The radium contained within phosphogypsum is of concern because it decays to form radon, a radioactive gas that can cause lung cancer. Radon occurs naturally in soils and the atmosphere in trace amounts that are generally not a health concern. However, exposure to radon at higher levels and over prolonged periods of time can pose a serious hazard to human health by increasing the risk of developing lung cancer. Radon contained in the outside air can enter structures and reach levels that pose a health hazard over time.

The Clean Air Act regulations at 40 CFR Part 61, Subpart R require that phosphogypsum be managed in engineered stacks, in order to limit public exposure from emissions of radon. Owners and operators of the engineered phosphogypsum stacks must measure and report radon emissions from inactive stacks and take measures to keep radon emissions within the regulatory limits.

Learn more:

• Clean Air Act Regulations
  • Subpart R: National Emission Standards for Radon Emissions From Phosphogypsum Stacks
  • Subpart R: Resources
• Phosphogypsum Stacks
  • TENORM: Fertilizer and Fertilizer Production Wastes

Other Uses of Phosphogypsum

EPA's regulations allow the removal of phosphogypsum from stacks, under certain conditions and restrictions, for two uses: outdoor agricultural purposes and indoor research and development. Any other use of phosphogypsum requires prior approval from EPA. Requests for other uses of phosphogypsum must be submitted in a formal process. The regulations allow EPA to approve a request for a specific use of phosphogypsum if it is determined that the proposed use is at least as protective of public health as placement of phosphogypsum in a stack.

EPA evaluates potential risks from each requested other use of phosphogypsum on an case-by-case basis. Each proposed use is reviewed based on how the phosphogypsum would be used, in what amounts, and after determining if there are any possible health risks to workers and the public, including risks from handling and transportation. Under EPA’s regulatory process, these factors must be addressed in a risk assessment for the particular use.

EPA will only approve other uses of phosphogypsum that are at least as protective of public health as placement in a stack. The possible approval of an individual project does not imply approval of any other request. EPA’s full review process, including risk assessment, must take place for each request for other use of phosphogypsum, and approvals are granted on a case-by-case basis.

Frequently Asked Question:  How do I request approval of other use of phosphogypsum?

Approval of Requests:  Public Notification Process

If EPA determines that a request for other use of phosphogypsum can be approved because it meets the EPA's regulations in 40 CFR Part 61, EPA will:

• Issue a notice of pending approval.
• Make the request and EPA's supporting technical analysis publicly available.
• Seek input on the proposed decision during a public comment period.

EPA will review the public comments to determine if they:

• Raise human health or environmental impacts not previously considered in the risk analysis.
• Have the potential to revise the finding that the proposed other use is at least as protective as leaving the phosphogypsum in the stack.

If EPA’s review of public comments finds cause to change the pending approval, EPA will advise the requestor(s) about the issues and give them an opportunity to amend their analysis or proposed use or take other steps to address the concerns.

If EPA determines that the application can be approved, EPA will make the “response to comments” document available on this website, issue the approval, and notify the public.

Disapproval of Requested Use

If EPA determines that the requested use does not meet regulatory requirements and cannot be approved, EPA will notify the requestor of the disapproval and the reasons for it.  The application package and EPA's assessment and declination document will be posted to our website.

Applications for Other Uses of Phosphogypsum

Applications Under Review

There are no applications currently under review.

Approved Applications

Mosaic Fertilizer, LLC, Road Construction Pilot Project, New Wales, Florida

On December 23, 2024, EPA approved a request from Mosaic Fertilizer, LLC for use of phosphogypsum in a road construction project located on its private property in New Wales, Florida. EPA approved the application  after determining that the proposed use of phosphogypsum is as protective of human health as placement in a stack.

The project will incorporate phosphogypsum into road base, which would then be paved over with asphalt.  The test road is on private property owned by the Mosaic Company. Access to the property is controlled. Members of the public are not expected to come into contact with the phosphogypsum in the test road.

After granting pending approval of the request, EPA opened a 30-day public comment period on October 9, 2024 and extended it by 15 days to November 23, 2024.  

• The majority of comments were opposed to the use of phosphogypsum in public roads. Some comments were critical of the current state of phosphogypsum management and regulation. These comments were determined to be outside the scope of this action, which is limited to this small-scale pilot project on a private road.  

• Some commenters questioned whether use of phosphogypsum in road construction was permissible at all. The Clean Air Act regulations as amended in 1992 do not provide general permission to use phosphogypsum in road construction. Use of phosphogypsum in road construction is eligible to be considered as an “other use” subject to EPA approval of a complete request on a case-by-case basis. Unless EPA approves such requests in advance, “other uses” of phosphogypsum, including in road construction, remain prohibited. 

• Some comments expressed criticism of the risk assessment used to support the pilot project application. After consideration of these comments, EPA concluded that the risk assessments were valid. The current radiological risk assessment methodologies were sufficient to evaluate the project and showed that the proposed use of phosphogypsum in a road construction pilot project is as protective of human health as placement in a stack. The risk posed by this project to the public and workers is extremely low. 

After review of public comments, EPA concluded that Mosaic Fertilizer’s application met the criteria outlined in 40 CFR Part 61, Subpart R and issued final approval of the request. EPA's approval does not supersede any other federal, state or local requirements. Requestors must still abide by all applicable federal, state, and local restrictions, prohibitions, and regulations. 

View the December 23, 2024 Notice of Final Approval for Other Use of Phosphogypsum.

View EPA's Response to Public Comments:  Request for approval of use of phosphogypsum in a small-scale road pilot project on private land in Florida submitted by Mosaic Fertilizer, LLC: Response to Comments (pdf) (344.09 KB, December 11, 2024, EPA-HQ-OAR-2024-0446)

View the October 9, 2024 Notice of Pending Approval for Other Use of Phosphogypsum.

View the November 8, 2024 Notice of Pending Approval for Other Use of Phosphogypsum; Extension of Public Comment Period.

View public comments received in Docket No. EPA-HQ-OAR-2024-0446 on regulations.gov.

Related Documents

• Letter from EPA issuing final approval of the request from Mosaic Fertilizer, LLC (pdf) (180.33 KB)
• Letter from EPA issuing pending approval of the request from Mosaic Fertilizer, LLC (pdf) (205.82 KB)
• Review of the Small-Scale Road Pilot Project on Private Land in Florida Submitted by Mosaic Fertilizer, LLC (pdf) (729.28 KB)
• Revised Request from The Mosaic Company to Use Phosphogypsum in Road Construction Pilot (pdf) (238.56 KB) (August 2023)
  • Attachment: Letter from ARCADIS- Phosphogypsum – Road Pilot Study – Radiological Risk Review – Update (pdf) (388.57 KB, August 15, 2023)
  • Original March 2022 Request from The Mosaic Company to Use Phosphogypsum in Small-Scale Pilot Project on Private Land (pdf) (3.02 MB)
    • March 17, 2023 letter from EPA on completeness determination for original March 2022 Mosaic request (pdf) (435.91 KB)
• February 7, 2024 Response to EPA Questions from Mosaic (pdf) (1.78 MB, February 7, 2024)
  • Report Provided with February 7,2024 Response:
    Beneficial Use of Mosaic Phosphogypsum (pdf) (2.23 MB, February 7, 2024) , University of Florida, February 7, 2024
  • Report Provided with February 7, 2024 Response:
    Phosphogypsum for Secondary Road Construction (pdf) (3.88 MB, June 1998) , Publication Nos. 01-033-077 and 01-041-077, University of Miami, June 1998
  • Scientific Publications Provided with February 7, 2024 Response: 
    • Jiahui Men, Yiming Li, Peifeng Cheng, Zhanming Zhang, “Recycling phosphogypsum in road construction materials and associated environmental considerations: A review”, Heliyon, Volume 8, Issue 11, 2022, e11518.
    • Kate D. Weiksnar, Kyle A. Clavier, Nicole M. Robey, Timothy G. Townsend, ”Changes in trace metal concentrations throughout the phosphogypsum lifecycle”, Science of The Total Environment, Volume 851, Part 1, 2022, 158163.
    • Kate D. Weiksnar, Timothy G. Townsend, “Enhancing the chemical performance of phosphogypsum as a road base material by blending with common aggregates”, Resources, Conservation and Recycling, Volume 200, 2024,107300. 
    • Kate D. Weiksnar, Kyle A. Clavier, Steven J. Laux, Timothy G. Townsend, ”Influence of trace chemical constituents in phosphogypsum for road base applications: A review”, Resources, Conservation and Recycling, Volume 199, 2023.
    • Raja Zmemla, Mounir Benjdidia, Ikram Naifar, Chaouki Sadik, Boubaker Elleuch, Ali Sdiri. “A phosphogypsum-based road material with enhanced mechanical properties for sustainable environmental remediation”, Environ Prog Sustainable Energy, 2022, Volume 41, Issue 1, e13732.
• May 20, 2024 letter from EPA on completeness determination for revised Mosaic request (pdf) (379.11 KB)

Withdrawn or Disapproved Applications

Withdrawal of Approval to Use Phosphogypsum in Government Road Projects

On June 30, 2021, the EPA withdrew previously granted conditional approval to use phosphogypsum in government road construction projects.  On October 14, 2020, EPA approved The Fertilizer Institute’s request to use phosphogypsum in government road construction projects subject to certain terms and conditions.  Under Clean Air Act (CAA) regulations, EPA may approve a request for a specific use of phosphogypsum if it is determined that the proposed use is at least as protective of public health as placement in a stack. Upon review, EPA found that The Fertilizer Institute’s request did not provide all the information required for a complete request under these regulations. The EPA withdrew the approval for this reason. The decision was effective as of June 30, 2021. 

• View Federal Register Notice "Withdrawal of Approval for Use of Phosphogypsum in Road Construction" (86 FR 35795).
• View Docket No. EPA-HQ-OAR-2020-0442 on www.regulations.gov.
• View the 2021 withdrawal, the 2020 approval letter, and supporting document

Voluntary Withdrawal of Petition to test Phosphogypsum at the Brevard County Solid Waste Landfill

On December 22, 2004, EPA issued a pending approval to a request from the Florida Institute of Phosphate Research to test the use of phosphogypsum as a daily cover at the Brevard County Solid Waste Landfill.  However, the Florida Institute of Phosphate Research formally withdrew its the petition while EPA was still evaluating whether to issue a final approval.

FREQUENTLY ASKED QUESTIONS

How is phosphogypsum managed? 

Phosphogypsum is typically managed in large, engineered stacks. Because the radionuclides within phosphogypsum are a source of radon gas and direct gamma radiation, the EPA regulates phosphogypsum as a source category of radionuclides under the Clean Air Act. Phosphogypsum stacks additionally contain low-pH process water and heavy metals as a result of the wet acid fertilizer production process. The regulations at 40 CFR 61 Subpart R require phosphogypsum to be managed in stacks to limit public exposure from emissions of radon. (Stacking was the predominant method of phosphogypsum management before the regulation was promulgated.) The phosphogypsum is placed on the stack in a liquid slurry. As the stack dewaters, the liquid effluent is captured, treated, tested, and discharged in accordance with regulations and permit conditions under the Clean Water Act. Newer stacks contain a liner to help prevent the effluent from being released directly into the soil and groundwater;  older stacks may not. When a stack becomes inactive, an engineered cover is typically placed over the phosphogypsum to prevent further water infiltration. The regulations at 40 CFR Part 61, Subpart R require that the stack be tested to demonstrate that it meets the radon flux regulatory limit of 20 picocuries (0.74 becquerel) per square meter per second.

How do I request approval of other use of phosphogypsum?

Requests for approval of other uses of phosphogypsum must be submitted in a formal process outlined in the regulations at 40 CFR Part 61, Subpart R. EPA may only consider complete applications. The information required in the application is relevant to assessing the risk of any requested use. A complete application is required for every individual proposed use of phosphogypsum.

For more information on requesting other use of phosphogypsum, see:

• Workbook: Applying to EPA for Approval of Other Uses of Phosphogypsum: Preparing and Submitting a Complete Petition Under 40 CFR 61.206 (pdf) (437.64 KB)
  The purpose of this document is to provide information on how to prepare a complete petition to the U.S. EPA for the distribution and use of phosphogypsum for "other purposes" that is consistent with the requirements of our regulations for radon emissions from phosphogypsum stacks.
• Some Guidance on Applying for Approval for Other Uses of Phosphogypsum (pdf) (27.73 KB)
  This document provides "some guidance" in recognition that we will continue to add more guidance in response to your questions about how to apply for approval of other uses for phosphogypsum.

Do approvals for other uses of phosphogypsum expire? 

An approval is valid as long as the legal requirements and conditions of the approval are met. Records must be maintained for five years, or longer if required by EPA as a condition of the approval. Changes to the approved use are not allowed. A change in the approved use is considered a new request subject to the review and approval process.

Do state laws affect EPA’s regulation of phosphogypsum?

State laws on phosphogypsum management and use do not override or affect the Clean Air Act regulations at 40 CFR Part 61, Subpart R. Any request for a specific use of phosphogypsum must be submitted to EPA for review and consideration. EPA’s approval is legally required before the material can be used. EPA's approval does not supersede any other federal, state or local requirements. Requestors must still abide by all applicable federal, state, and local restrictions, prohibitions, and regulations.