EPA Releases Draft TSCA Risk Evaluation for D4 for Public Comment and Peer Review
Released September 17, 2025
Today, the U.S. Environmental Protection Agency (EPA) released its draft risk evaluation for octamethylcyclotetrasiloxane (D4) under the Toxic Substances Control Act (TSCA). EPA has preliminarily determined that D4 presents unreasonable risk of injury to human health and the environment under certain conditions of use (COUs).
D4 Draft Risk Evaluation
EPA is preliminarily determining that D4 presents unreasonable risk of injury to human health driven by risk to workers from 23 COUs and risk to consumers from one COU. Workers who manufacture D4, use D4 in the processing of products including adhesives and sealants, or use paints and coatings containing D4 in industrial and commercial applications, and consumers who use certain paints and coatings containing D4 are at a higher risk of exposure. The agency is also preliminarily determining that D4 presents an unreasonable risk to the environment from seven COUs. EPA did not preliminarily identify a risk of injury to human health or the environment from the other 37 COUs for D4. For COUs with unreasonable risk to workers, these preliminary risk determinations do not reflect the use of personal protective equipment (PPE); however, as the draft risk evaluation shows, the use of PPE may reduce exposures and mitigate risk. EPA did not preliminarily identify unreasonable risk of injury to human health for the general population from any COU. EPA is not yet making preliminary determinations regarding the contribution to the unreasonable risk to the environment from 18 COUs and to human health from two COUs. EPA is seeking comment on all aspects of the draft risk evaluation, including for the COUs where EPA is not making a preliminary determination.
EPA has integrated recently published information on bioaccumulation and biomagnification metrics into this draft risk evaluation as this field is an area of active research with D4. Although these values indicated that D4 is bioaccumulative, laboratory and field studies suggest that D4 has low potential for biomagnification, meaning it is more likely for D4 concentrations to decrease as it moves up the food chain through dietary exposure. Furthermore, recent research on D4 uptake in fishes has found that while uptake of D4 will occur via both dietary and environmental exposure routes, D4 that is ingested can be metabolized thus limiting uptake and reducing significant accumulation from dietary sources.
Read the draft risk evaluation for D4.
Next Steps
EPA will accept public comments on the draft risk evaluation for D4 via docket EPA-HQ-OPPT-2018-0443 on www.regulations.gov for 60 days until November 17, 2025.
EPA will hold a virtual public meeting to be held on December 2-5, 2025, for the agency’s Science Advisory Committee on Chemicals (SACC) to discuss the draft risk evaluation and technical support documents for D4. EPA will also hold a preparatory virtual public meeting on November 18, 2025, for the SACC and the public to consider and ask questions regarding the scope and clarity of the draft charge questions. Registration instructions for the virtual preparatory and peer review meetings will be announced on the SACC website approximately one month prior to each meeting.
The draft charge questions are available on the SACC website and, upon publication of a Federal Register notice, will be available in the peer review docket for public comment. If you would like the SACC to consider comments on the draft risk evaluation, technical support documents, and charge questions during the preparatory and peer review meetings, written comments should be submitted by November 4, 2025, to the peer review docket EPA-HQ-OPPT-2025-1610 on www.regulations.gov.
To present oral comments during the preparatory meeting, registration should be completed by 12:00 p.m. ET on November 11, 2025, and a written version of oral comments should be submitted by 12:00 p.m. ET on November 14, 2025, to the Designated Federal Official (DFO). For attendees not making oral comments, registration will remain open through the end of the preparatory meeting on November 18, 2025.
To present oral comments during the peer review meeting, registration should be completed by 12:00 p.m. ET on November 25, 2025, and a written version of oral comments should be submitted by 12:00 p.m. ET on November 28, 2025, to the DFO. For attendees not making oral comments, registration will remain open through the end of this meeting on December 5, 2025.
For additional information about the peer review, please see the Federal Register notice or contact the DFO, Dr. Alaa Kamel at kamel.alaa@epa.gov.
After the agency has considered public comments and recommendations from an independent, expert peer review, EPA will issue a final risk evaluation that includes its determination as to whether D4 represents an unreasonable risk of injury to human health or the environment.