On 17 September, 2025, the U.S. Environmental Protection Agency (EPA) published the draft risk evaluation for octamethylcyclotetrasiloxane (D4) under the Toxic Substances Control Act (TSCA) and initiated a 60-day public-comment period and independent peer-review process. EPA’s preliminary conclusion is that, under certain conditions of use (COUs), D4 presents an “unreasonable risk” to workers’ health and the environment, warranting further controls.
Risk Findings
- Human health (personal protective equipment not assumed)
• Workers: 24 COUs pose unreasonable risk via inhalation and dermal exposure. Key scenarios include domestic manufacture, import, use as a reaction intermediate, monomer, processing aid, and manufacture/use in adhesives, sealants, coatings, paints and solvents.
• Occupational non-users (ONUs): 1 COU presents unreasonable risk via inhalation—industrial solvents such as cleaning/degreasing in aircraft maintenance.
• Consumers: 1 COU presents unreasonable risk via inhalation and dermal contact—consumer paints and coatings (indoor/outdoor use).
• General population: No unreasonable risk identified under any COU. - Environmental risk
• Aquatic ecosystems: 7 COUs pose unreasonable risk to surface-water and benthic organisms through D4 releases to surface water and subsequent sediment deposition.
Next Steps
- Public comment: Submit via https://www.regulations.gov/ (Docket EPA-HQ-OPPT-2018-0443) through 17 November 2025.
- Peer-review meetings (virtual):
• Preparatory session: 18 November 2025
• Formal review: 2–5 December 2025
Registration and written comments due 11 and 25 November respectively; details on EPA’s Science Advisory Committee on Chemicals (SACC) website. - Final evaluation: EPA will issue the final D4 risk evaluation after incorporating public comments and peer-review findings, then decide whether to impose bans, restrictions, labeling or other controls.
