Free tier, this brief uses 1 of 2 remaining for the month.Resets May 1
¶EPA is conducting a Draft Risk Evaluation of octamethylcyclotetrasiloxane (D4) under TSCA, and this docket draws comments from industry trade associations, individual manufacturers, academic and health-advocacy groups, and occupational health bodies. The dominant industry position is conditional: commenters generally acknowledge worker exposure concerns but argue that a broad D4 phase-out or ban would severely disrupt silicone-dependent supply chains in automotive, semiconductor, marine, and medical sectors, and request either exemptions, concentration limits, or extended comment periods. Health and reproductive-science commenters, led by the UCSF Program on Reproductive Health and the Environment, urge EPA to strengthen the hazard characterization and expand the scope of potentially exposed or susceptible subpopulations (PESS). A distinctive concern raised by individual submitters is that women with silicone breast implants and their children represent an overlooked PESS not captured by current consumer or occupational exposure models.
Octamethylcyclotetrasiloxane (Cyclotetrasiloxane, 2,2,4,4,6,6,8,8-octamethyl-) (D4); Draft Risk Evaluation Under the Toxic Substances Control Act (TSCA); Notice of Availability and Request for Comment
EPA is announcing availability of and requesting public comment on a draft risk evaluation for octamethylcyclotetrasiloxane (D4, CASRN 556-67-2) under TSCA section 6. The evaluation was initiated in response to a 2020 manufacturer request by the American Chemistry Council's Silicones Environmental, Health, and Safety Center. EPA preliminarily determines, 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, including occupational exposures and environmental releases. The comment period closes November 17, 2025, after which EPA will consider public and Science Advisory Committee on Chemicals (SACC) input before issuing a final risk evaluation.
Manufacturers and trade groups argue that D4 is functionally irreplaceable in silicone products (sealants, rubber, semiconductors, automotive parts) and request exemptions for cured silicone, concentration caps (e.g., 0.1% free D4), or narrowed regulatory scope rather than a broad ban.
"Allow continued use of D4 in silicone-based sealants and adhesives for marine/boat building but limit the concentration of free D4 (residual, unreacted monomer) in finished products to no more than 0.1% by weight."
Representative quote, cluster 01
Several manufacturers and industry groups state they cannot complete reformulation testing or supplier consultations before the comment deadline closes, and formally request more time.
"We request additional time to the public comment period for us to complete the evaluation of the performance of the reformulated products to ensure their adhesion, durability and UV resilience."
Representative quote, cluster 02
Academic scientists and health professionals, primarily from UCSF PRHE, argue that EPA should strengthen its characterization of D4 as a reproductive toxicant and persistent bioaccumulative substance, and push for broader PESS identification including pregnant workers and infants.
"Please see the attached comments from the University of California, San Francisco Program on Reproductive Health and the Environment, academics, scientists, health professionals, and clinicians."
Representative quote, cluster 03
Commenters from PIP Action Campaign and individual submitters argue that women with silicone breast implants and their children represent a chronic internal-exposure pathway ignored by EPA's models, and request explicit PESS designation, implant-recipient exposure modeling, and FDA coordination under TSCA Section 9.
"I respectfully request that the U.S. Environmental Protection Agency identify women with silicone breast implants...and their children (in utero and during breast feeding) as a Potentially Exposed or Susceptible Subpopulation (PESS) in the final Risk Evaluation for D4."
Representative quote, cluster 04
AIHA argues that EPA's inhalation threshold for unreasonable risk diverges substantially from AIHA's published WEEL of 10 ppm TWA, both derived from the same WIL Research 2001 study, and calls on EPA to explain and reconcile the difference and apply its own proposed risk-factor criteria under 40 CFR 702.39(f)(3).
"The inhalation exposure concentration that EPA derived as a threshold for determining unreasonable risk of injury to human health is far different from the WEEL. AIHA believes the risk evaluation would benefit from a description of why that difference exists."
Representative quote, cluster 05
EDF submits comments on the draft scope of the risk evaluation, likely addressing the adequacy of conditions-of-use coverage, exposure pathways, and environmental fate considerations for D4.
"Please find attached comments submitted by Environmental Defense Fund on the Draft Scope of the Risk Evaluation for Octamethylcyclotetra-Siloxane (D4)."
Representative quote, cluster 06
The Semiconductor Industry Association submits comments on D4's role in semiconductor manufacturing and the potential supply chain disruption from restriction or phase-out.
"Please find attached the comments of the Semiconductor Industry Association (SIA)."
Representative quote, cluster 07
Key tensions
Worker health protection
↕ vs.
supply chain continuity for silicone-dependent industries