Peer Review of the Draft Risk Evaluation for Octamethylcyclotetrasiloxane (D4)

Octamethylcyclotetrasiloxane (D4) is undergoing risk evaluation under the Toxic Substances Control Act. EPA is planning a virtual public meeting for the Science Advisory Committee on Chemicals (SACC) to review the draft risk evaluation for D4 in December 2025.

D4 is a colorless, oily liquid with an annual total U.S. production volume between 750 million and 1 billion pounds. The primary uses for D4 are to make other silicone chemicals with commercial uses including, but not limited to, adhesives and sealants, automotive care products, paints and coatings, and other plastic and rubber products. 

On September 10, 2025, EPA called for nominations of scientific and technical experts to be considered as ad hoc reviewers assisting the SACC with this peer review. Nominations should include the candidate’s name, affiliation, contact information, and must be submitted by September 25, 2025, to the OCSPP Peer Review mailbox at OCSPP-PeerReview@epa.gov. These nominations will help the agency select approximately seven to eight ad hoc reviewers to assist the SACC with their review.

Nominees should be scientists with sufficient professional qualifications, including training and experience, to provide expert comments on the scientific issues for this review. Individuals nominated for this peer review meeting should have expertise in one or more of the following areas: 

• Identification of hazards relevant to human health risk assessment. 
• Evaluation and use of the D4 physiologically based pharmacokinetic (PBPK) model. 
• Handling of uncertainties associated with exposure and release assessments. 
• Characterization of bioaccumulation, bioconcentration, biomagnification, and potential trophic transfer. 
• Human fish consumption for the general population and potentially exposed or susceptible subpopulations. 
• Identification of hazards relevant to ecological risk assessment.

The peer review will take place at a virtual public meeting in December 2025. EPA will announce the dates for this meeting in the coming weeks.

For additional information, contact the Designated Federal Official, Dr. Alaa Kamel at kamel.alaa@epa.gov.