U.S. Environmental Protection Agency (EPA) announced on November 13, 2025, that it is delaying the deadline for comments on the draft risk evaluation for octamethylcyclotetrasiloxane (D4) by 15 days. In September 2025, EPA released the draft risk evaluation for D4 under the Toxic Substances Control Act (TSCA) for public comment and independent peer review. EPA granted the manufacturer request for the risk evaluation for D4 in October 2020.

A colorless, volatile, oily liquid, D4 is primarily used to make silicone chemicals. Commercial uses for D$ include adhesives and sealants, automotive care products, paints and coatings, and other plastic and rubber products. It is also used as an ingredient in consumer products such as cosmetics, medical devices, and food contact materials.

Under the TSCA, the purpose of a risk evaluation is to determine whether a chemical substance presents an unreasonable risk of injury to human health or the environment. For D4, EPA used the best available science to preliminarily determine, based on the weight of scientific evidence, that D4 poses unreasonable risk to human health and the environment driven primarily by certain conditions of use analyzed in the draft risk evaluation.

Comments are now due December 2, 2025. Additionally, the EPA will hold a virtual public meeting 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 has also announced the postponement of a virtual public preparatory meeting until December 1, 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 are currently available.