Octamethylcyclotetrasiloxane (Cyclotetrasiloxane, 2,2,4,4,6,6,8,8-octamethyl-)(D4); Draft Risk Evaluation Under the Toxic Substances Control Act (TSCA); Extension of the Comment Period

Issuing agencies

Abstract

In the Federal Register of September 17, 2025, Environmental Protection Agency (EPA) announced the availability of and sought public comment on a draft risk evaluation under the Toxic Substances Control Act (TSCA) for Octamethylcyclotetrasiloxane (Cyclotetrasiloxane, 2,2,4,4,6,6,8,8-octamethyl-) (D4) (CASRN 556-67-2). The purpose of risk evaluations under TSCA is to determine whether a chemical substance presents an unreasonable risk of injury to health or the environment under the conditions of use (COUs), including unreasonable risk to potentially exposed or susceptible subpopulations identified as relevant to the risk evaluation by EPA, and without consideration of costs or non-risk factors. EPA used the best available science to prepare this draft risk evaluation and to preliminarily determine, based on the weight of scientific evidence, that D4 poses unreasonable risk to health and the environment driven primarily by COUs analyzed in the draft risk evaluation. This document extends the comment period, which was scheduled to end on November 17, 2025, for 15 days.